EP4673197A1

EP4673197A1 - Method and system for characterising flow paths

Info

Publication number: EP4673197A1
Application number: EP24763348.0A
Authority: EP
Inventors: Cameron Leslie MATTHEWS; Thomas Heinrich Barnes; Rachel GLAVES; Matthew Jon Payton
Original assignee: Fisher and Paykel Healthcare Ltd
Current assignee: Fisher and Paykel Healthcare Ltd
Priority date: 2023-03-01
Filing date: 2024-03-01
Publication date: 2026-01-07
Also published as: AU2024228803A1; CN120857954A; WO2024180517A1

Abstract

Embodiments of the invention are directed to methods of characterising flow paths within a patient's respiratory airways. A method of characterising flow paths comprises receiving a first input relating to a flow of gases provided to the patient, receiving a second input relating to a flow of gases at the mouth or nose of the patient, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and/or the second input.

Description

METHOD AND SYSTEM FOR CHARACTERISING FLOW PATHS

Technical Field

[0001] The present invention relates to a method and system for characterising flow paths within a patient's respiratory airways. In particular, embodiments of the invention may relate to methods and systems for characterising flow paths within a patient's respiratory airways in oxygen therapy, although the scope of the invention may not necessarily be limited thereto.

Background of Invention

[0002] When providing respiratory support, for example in medical procedures where it is beneficial to provide oxygenation to a patient, it is often desirable for a clinician to know various respiratory parameters, such as flow paths of a provided gas within the patient's respiratory airways, airway patency, whether an input flow rate of gases provided by the respiratory support meets an inspiratory demand of the patient, a proportion of expired CO2, tidal volume and the like. Such parameters are not always readily available and may not be easily measurable during such medical procedures.

[0003] A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Summary of Invention

[0004] According to a first aspect of the invention, there is provided a method of characterising flow paths within a patient's respiratory airways, the method comprising receiving a first input relating to a flow of gases provided to the patient, and receiving a second input relating to a flow of gases at the mouth or nose of the patient, characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and/or the second input. [0005] In particular, the method includes characterising one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input and the second input, or the second input as described in further detail below.

[0006] The flow of gases at the mouth or nose of the patient may be leaving or entering the patient through the mouth or nose. The flow of gases leaving or entering the patient may include at least a proportion of the flow of gases provided to the patient, gases inhaled/exhaled by the patient, or a combination of both.

[0007] Knowledge of flow path characterisation may be beneficial in a number of ways. For example, knowledge of the flow pathways within a patient's respiratory airways may enable determination of certain aspects of the patients' physiological state and whether a particular therapy, or form of respiratory support, will be effective. It is therefore desirable to provide a method and/or system for characterising flow paths within a patient's respiratory airways to thereby facilitate critical decision making by clinicians. For example, information regarding flow paths within the patient's respiratory airways may enable a clinician to make a critical decision on whether to change a type of therapy provided to the patient so as to provide a better therapeutic effect at the patient. Moreover, the information may enable the clinician to make such critical decision in a more timely manner.

[0008] The first input may be indicative of an input flow rate of gases provided to the patient, and the second input is indicative of a measured flow rate of gases at the mouth or nose of the patient.

[0009] Characterising one or more flow paths of delivered gases within the respiratory airways of the patient may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed (e.g. soft palate open) condition, determining a nasal passage obstructed (e.g. soft palate closed) condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose. [0010] The method may further include determining one or more respiratory parameters of the patient.

[0011] The one or more respiratory parameters may include any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0012] In accordance with a first embodiment of the first aspect, the step of characterising may include characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0013] In accordance with a first embodiment of the first aspect, the first input may be indicative of an input flow rate of gases provided via a sealing patient interface to one nostril of the patient. The second input may be indicative of a measured flow rate of gases at the other nostril of the patient. The step of characterising one or more flow paths may include determining whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

[0014] In accordance with a first embodiment of the first aspect, the first input may be indicative of an input flow rate of gases provided via a sealing patient interface, wherein the sealing patient interface includes a flow delivery portion for providing the input flow of gases to the nose of the patient. The second input may be indicative of a measured flow rate of gases passing through an exhaust(outlet) of the sealing patient interface.

[0015] In accordance with a first embodiment of the first aspect, the step of characterising one or more flow paths includes determining a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle.

[0016] In accordance with a first embodiment of the first aspect, the method may further include determining a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a sealing patient interface to one nostril of the patient, and

Q_m(t) is the second input indicative of a measured flow rate of gases at the other nostril of the patient.

[0017] In accordance with another embodiment of the first aspect, the method may further include determining a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a sealing patient interface, and

Q_m(t) is the second input indicative of a measured flow rate of gases at the sealing interface (e.g. at an exhaust or outlet of the sealing interface).

[0018] In some embodiments, Q_m(t) is a positive value when the measured flow of gases at the patient leaving the patient, and a negative value when the measure flow of gases is entering the patient. Typically, Q (t) is a positive value indicative of a magnitude of the flow rate of gases provided to the patient.

[0019] In accordance with a first embodiment of the first aspect, the step of characterising one or more flow paths may include determining either one or both of a mouth open condition, and a nasal passage obstructed (e.g. soft palate closed) condition if the first input substantially equals the second input consistently over a full respiratory cycle.

[0020] In accordance with a first embodiment of the first aspect, the step of characterising one or more flow paths may further include determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle. [0021] The method in accordance with a first embodiment of the first aspect may further include receiving a third input indicative of a measured fraction of CO2 at the nose of the patient, and determining an expired fraction of CO2 (F_E co₂) based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a sealing patient interface to one nostril of the patient,

Q_m(t) is the second input indicative of a measured flow rate of gases at the other nostril of the patient, and

Fm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient.

[0022] The method in accordance with another embodiment of the first aspect may further include receiving a third input indicative of a measured fraction of CO2 at the nose of the patient, and determining an expired fraction of CO2 (F_E co₂) based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a sealing patient interface,

Q_m(t) is the second input indicative of a measured flow rate of gases at the sealing interface (e.g. at the exhaust or outlet of the sealing interface), and

Fm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the at the sealing interface (e.g. at the exhaust or outlet of the sealing interface).

[0023] The method in accordance with a first embodiment of the first aspect may include determining any one or more of a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

[0024] The method in accordance with a first embodiment of the first aspect may include determining any one or more of a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

[0025] The method in accordance with a first embodiment of the first aspect may include determining any one or more of a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

[0026] In accordance with a second embodiment of the first aspect of the invention, the step of characterising includes characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the second input.

[0027] In accordance with the second embodiment of the first aspect of the invention, the first input may be indicative of an input flow rate of gases provided via a non-sealing patient interface to the nares of the patient, and the second input may be indicative of a measure flow rate of gases at the mouth of the patient. The step of characterising one or more flow paths may include determining that the mouth of the patient is open.

[0028] The method in accordance with the second embodiment of the first aspect may include determining either one or both of a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases exceeds inspiratory demand if the second input is consistently greater than zero over a full respiratory cycle.

[0029] The method in accordance with the second embodiment of the first aspect may include determining either one or both of a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases does not meet inspiratory demand if the second input reduces below zero at any point in time during a respiratory cycle, and an integral of the second input over the respiratory cycle is greater than a threshold integral value. The threshold integral value may be substantially zero.

[0030] The method in accordance with the second embodiment of the first aspect may include determining a nasal passage obstructed (e.g. soft palate closed) condition if the second input reduces below zero at any point in time during a respiratory cycle, and an integral of the second input over the respiratory cycle is substantially zero.

[0031] The method in accordance with the second embodiment of the first aspect may further include receiving a third input indicative of a measured fraction of CO2 at the mouth of the patient, and determining an expired fraction of CO2 (F_E co₂) based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface to the nares of the patient, and

Fm_mouth_co2 (t) is the third input indicative of a measured fraction of CO2 at the mouth of the patient.

[0032] The method in accordance with the second embodiment of the first aspect may further include receiving a third input indicative of a measured fraction of CO2 at the mouth of the patient, and receiving a fourth input indicative of a measured fraction of O2 at the mouth of the patient, and receiving a fifth input indicative of a measured fraction of O2 in the input flow of gases, wherein the method further includes determining an expired fraction of O2 (F_{E 0} ), and then subsequently an expired fraction of CO2 (F_E co₂) based on wherein Fm_mouth_co2 (t) is the third input indicative of a measured fraction of CO2 at the mouth of the patient,

Fm_mouth_o2 (t) is the fourth input indicative of a measured fraction of O2 at the mouth of the patient, and

F₀(t) is the fifth input indicative of a measured fraction of O2 in the input flow of gases provided via a non-sealing patient interface to the nares of the patient.

[0033] The method in accordance with the second embodiment of the first aspect may include determining a numerical value (Zc(t)) indicative of a proportion of delivered gases passing through the mouth based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface to the nares of the patient,

Q_m(t) is the second input indicative of a measure flow rate of gases at the mouth of the patient,

Fm_mouth_co2 (t) is the third input indicative of a measured fraction of CO2 at the mouth of the patient, and

FE_CO2 (t) is an expired fraction of CO2.

[0034] The second input may include receiving one or more discrete values relating to a flow of gases at the mouth or nose of the patient at any time during a respiratory cycle.

[0035] Receiving the first input may include receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

[0036] The method may further include generating an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient. [0037] The method may further include displaying the output on a graphical user interface. The step of displaying may further include displaying the output textually, numerically and/or graphically.

[0038] The method may further include providing a flow of gases to the patient via the patient's nares. Providing the flow of gases to the patient may include providing a flow of gases to the patient via a sealing patient interface through a single nostril of the patient.

[0039] Providing the flow of gases to the patient may include providing a flow of gases to the patient via a non-sealing patient interface.

[0040] The method may further include sensing the flow of gases provided to the patient to provide the first input.

[0041] The method may further include sensing the flow of gases at the mouth or nose of the patient to provide the second input.

[0042] Providing the flow of gases to the patient may include providing a flow of gases to the patient via a sealing patient interface through the patient's nose. The method may further include sensing the flow of gases passing through an exhaust (outlet) of the sealing patient interface to provide the second input.

[0043] Sensing the flow of gases provided to the patient may include sensing a flow rate of the flow of gases provided to the patient. Sensing the flow of gases at the patient may include sensing a flow rate of the flow of gases at the patient. The flow of gases at the patient may be entering or leaving the patient.

[0044] The method may further include any one or more of sensing a proportion of CO2 in the flow of gases leaving the patient through the mouth or nose of the patient, and sensing a proportion of O2 in the flow of gases at the patient through the mouth or nose of the patient.

[0045] According to a further embodiment of the first aspect of the invention, there is provided a non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform a method of characterising flow paths within a patient's respiratory airways as described herein in accordance with the first aspect of the invention.

[0046] According to another embodiment of the first aspect of the invention, there is provided a respiratory support system controller for characterising flow paths within a patient's respiratory airways, the controller being configured to perform a method of characterising flow paths within a patient's respiratory airways as described herein in accordance with the first aspect of the invention.

[0047] According to yet another embodiment of the first aspect of the invention, there is provided a respiratory support system comprising a controller as described herein.

[0048] The respiratory support system may include a sealing patient interface for delivering the flow of gases provided to the patient.

[0049] The sealing patient interface may be configured to seal against a first nostril of the patient to deliver the flow of gases to the patient. The sealing patient interface may be configured to seal against a second nostril of the patient to measure the flow of gases at the patient's nares. The sealing patient interface may include a nasal interface configured to seal against the second nostril of the patient to measure the flow of gases leaving the patient's nares, and wherein the nasal interface is open to atmosphere such the flow of gases leaving the patient's nares enters the atmosphere via the nasal interface. The nasal interface may be configured to measure a flow of gases entering the patient's nares, for example via the atmosphere.

[0050] The sealing patient interface may include one or more output sensors for measuring the flow of gases at the patient's nares. The one or more output sensors may include a differential pressure sensor.

[0051] The sealing patient interface may include a flow delivery portion configured to seal against a first nostril of the patient to deliver the flow of gases to the patient, and a flow measurement portion configured to seal against a second nostril of the patient to measure the flow of gases at the second nostril of patient. [0052] The flow measurement portion may be open to atmosphere such that the flow of gases leaving the second nostril enters the atmosphere via the flow measurement portion. The flow measurement portion may be configured to measure a flow of gases entering the patient's nares, for example via the atmosphere.

[0053] The respiratory support system may further include a differential pressure sensor integrated with the flow measurement portion of the sealing patient interface.

[0054] In some embodiments, the respiratory support system may further include a nonsealing patient interface for delivering the flow of gases provided to the patient. The nonsealing patient interface may be configured to deliver the flow of gases to the patient via the patient's nares.

[0055] In some embodiments, the respiratory support system may further include a mouthpiece assembly configured to measure the flow of gases at the patient's mouth. The mouthpiece assembly may include one or more output flow sensors for measuring the flow of gases at the patient's mouth. The one or more output flow sensors may include a differential pressure sensor.

[0056] The respiratory support system may further include one or more input flow sensors for measuring the flow of gases provided to the patient. The input flow sensors may be configured to measure a flow rate of the flow of gases provided to the patient.

[0057] The respiratory support system may further include any one or more of a flow generator for generating the flow of gases provided to the patient, and a humidifier for humidifying the flow of gases provided to the patient.

[0058] In accordance with a second aspect of the invention, there is provided a method of characterising flow paths within a patient's respiratory airways, the method comprising receiving a first input relating to a gas proportion of one or more gas species in a flow of gases at the patient through the mouth and/or nose of the patient, generating an output to allow characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input. [0059] The characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed (e.g. soft palate open) condition, and determining a nasal passage obstructed (e.g. soft palate closed) condition.

[0060] The method may further include determination of one or more respiratory parameters of the patient based on the first input. The one or more respiratory parameters include any one or more of: input flow rate of gases delivered to the patient exceeding inspiratory demand, and input flow rate of gases delivered to the patient not meeting inspiratory demand.

[0061] In one embodiment, the first input may be indicative of a proportion of O2 in a flow of gases at the patient through the mouth and/or nose of the patient.

[0062] In another embodiment, the first input may be indicative of a proportion of CO2 in a flow of gases leaving the patient through the mouth and/or nose of the patient.

[0063] In one embodiment, the first input may be indicative of a proportion of O2 in a flow of gases at the patient through the mouth and/or nose of the patient, and the method may further include receiving a second input indicative of a proportion of CO2 in the flow of gases leaving the patient through the mouth and/or nose of the patient.

[0064] The method may include characterising flow paths within a patient's respiratory airways based on one or both of the first input and the second input.

[0065] In accordance with a first embodiment of the second aspect of the invention, the first input may be indicative of a proportion of CO2 in a flow of gases leaving the patient through the mouth of the patient.

[0066] The method in accordance with this first embodiment of the second aspect may further include determining whether the mouth of the patient is open or closed based on a comparison of the first input and a proportion of CO2 in ambient air. [0067] The method in accordance with this first embodiment of the second aspect may include determining a mouth closed condition if the first input does not exceed a proportion of CO2 in ambient air during a full respiratory cycle.

[0068] The method in accordance with the first embodiment of the second aspect may include determining a mouth open condition if the first input is greater than a proportion of CO2 in ambient air at any point during a respiratory cycle.

[0069] In accordance with a second embodiment of the second aspect of the invention, the first input may be indicative of a proportion of O2 in a flow of gases at the patient through the mouth of the patient.

[0070] The method in accordance with the second embodiment of the second aspect may further include generating a waveform based on the first input with respect to time, and determining whether the mouth of the patient is open or closed based the generated waveform.

[0071] The method in accordance with the second embodiment of the second aspect may include determining a mouth closed condition if no dips are detected in the waveform during a full respiratory cycle.

[0072] The method in accordance with the second embodiment of the second aspect may include determining a mouth open condition if at least one dip is detected in the waveform during a full respiratory cycle.

[0073] The method in accordance with the second embodiment of the second aspect may include determining either one or both of a nasal passage not obstructed (e.g. soft palate open) condition, and that an input flow rate of gases delivered to the patient does not meet inspiratory demand, if two dips are detected in the waveform during the full respiratory cycle.

[0074] The method in accordance with the second embodiment of the second aspect, may include determining either one or both of a nasal passage not obstructed (e.g. soft palate open) condition, and that an input flow rate of gases delivered to the patient exceeds inspiratory demand, if the first input is substantially equal to a proportion O2 in a flow of gases delivered to the patient at any point during a full respiratory cycle.

[0075] The method in accordance with the second embodiment of the second aspect may include determining a nasal passage obstructed (e.g. soft palate closed) condition, if the first input does not substantially equal a proportion O2 in a flow of gases delivered to the patient during a full respiratory cycle.

[0076] The method in accordance with the second embodiment of the second aspect may include determining a nasal passage obstructed (e.g. soft palate closed) condition, if the first input is consistently less than a proportion O2 in a flow of gases delivered to the patient during a full respiratory cycle.

[0077] In accordance with a third embodiment of the second aspect of the invention, the first input may be indicative of a proportion of O2 in a flow of gases at the mouth of the patient, and the second input is indicative of a proportion of CO2 in the flow of gases leaving the patient through the mouth of the patient.

[0078] The method in accordance with a third embodiment of the second aspect may include determining whether the mouth of the patient is open or closed based on a comparison of the second input and a proportion of CO2 in ambient air.

[0079] The method in accordance with a third embodiment of the second aspect may include determining a mouth closed condition if the second input does not exceed the proportion of CO2 in ambient air over a full respiratory cycle.

[0080] The method in accordance with a third embodiment of the second aspect may include determining a mouth open condition if the second input is greater than the proportion of CO2 in ambient air at any point in time during a respiratory cycle.

[0081] The method in accordance with a third embodiment of the second aspect may include determining a nasal passage obstructed (e.g. soft palate closed) condition if the first input consistently below a proportion of O2 in a flow of gases provided to the patient over the full respiratory cycle. [0082] The method in accordance with a third embodiment of the second aspect may include determining a nasal passage not obstructed (e.g. soft palate open) condition if the first input is substantially equal to a proportion of O2 in a flow of gases provided to the patient at any point in time during the respiratory cycle.

[0083] The method in accordance with a third embodiment of the second aspect may include determining that the input flow rate of gases does not meet inspiratory demand if the first input is substantially equal to a proportion of O2 in ambient air at any point in time during an inspiratory phase of the respiratory cycle.

[0084] The method in accordance with a third embodiment of the second aspect may further include generating a waveform based on the first input with respect to time, and determining that the input flow rate of gases does not meet inspiratory demand if at least two dips are detected in the waveform during a full respiratory cycle.

[0085] The method in accordance with a third embodiment of the second aspect may further include determining that the input flow rate of gases exceeds inspiratory demand if the first input is consistently above a proportion of O2 in ambient air during an inspiratory phase of the respiratory cycle.

[0086] In accordance with a fourth embodiment of the second aspect of the invention, the first input is indicative of a proportion of O2 in a flow of gases at the nose of the patient.

[0087] The method in accordance with a fourth embodiment of the second aspect may further include generating a waveform based on the first input with respect to time, and determining whether the mouth of the patient is open or closed based on the waveform.

[0088] The method in accordance with a fourth embodiment of the second aspect may further include determining a mouth open condition if no dips are detected in the waveform during a full respiratory cycle.

[0089] The method in accordance with a fourth embodiment of the second aspect may include determining a mouth closed condition if at least one dip is detected in the waveform during a full respiratory cycle. [0090] The method in accordance with a fourth embodiment of the second aspect may further include determining either one or both of a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases delivered to the patient exceeds inspiratory demand if a single dip is detected in the waveform during the full respiratory cycle.

[0091] The method in accordance with a fourth embodiment of the second aspect may further include determining either one or both of a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases delivered to the patient does not meet inspiratory demand if two dips are detected in the waveform during the full respiratory cycle.

[0092] In accordance with a fifth embodiment of the second aspect of the invention, the first input is indicative of a proportion of CO2 in a flow of gases leaving the patient through the nose of the patient.

[0093] The method in accordance with a fifth embodiment of the second aspect may include determining a mouth open condition if the first input substantially equals a proportion of CO2 in ambient air during a full respiratory cycle.

[0094] The method in accordance with a fifth embodiment of the second aspect may include determining either one or both of a mouth open condition if the first input does not exceed a proportion of CO2 in ambient air during a full respiratory cycle.

[0095] The method in accordance with a fifth embodiment of the second aspect may include determining either one or both of a mouth closed condition, and a nasal passage not obstructed (e.g. soft palate open) condition if the first input is greater than a proportion of CO2 in ambient air at any point during a full respiratory cycle.

[0096] In accordance with a sixth embodiment of the second aspect of the invention, the first input may be indicative of a proportion of O2 in a flow of gases at the nose of the patient, and the second input is indicative of a proportion of CO2 in the flow of gases leaving the patient through the nose of the patient. [0097] The method in accordance with a sixth embodiment of the second aspect may include determining whether the mouth of the patient is open or closed based on a comparison of the second input and a proportion of CO2 in ambient air.

[0098] The method in accordance with a sixth embodiment of the second aspect may include determining a mouth open condition if the second input does not exceed the proportion of CO2 in ambient air over a full respiratory cycle.

[0099] The method in accordance with a sixth embodiment of the second aspect may include determining either one or both of a mouth closed condition, and a nasal passage not obstructed (e.g. soft palate open) condition if the second input is greater than the proportion of CO2 in ambient air at any point in time during a respiratory cycle.

[0100] The method in accordance with a sixth embodiment of the second aspect may further include generating a waveform based on the first input with respect to time, and determining that the input flow rate of gases delivered to the patient does not meet inspiratory demand if two dips are detected in the waveform during the full respiratory cycle.

[0101] The method in accordance with a sixth embodiment of the second aspect may further include generating a waveform based on the first input with respect to time, and determining that the input flow rate of gases delivered to the patient exceeds inspiratory demand if two dips are not detected in the waveform during the full respiratory cycle.

[0102] Receiving the first input may include receiving one or more discrete values of the first input at any time during a respiratory cycle. Receiving the second input may include receiving one or more discrete values of the second input at any time during a respiratory cycle.

[0103] The method in accordance with a sixth embodiment of the second aspect may further include generating an output based on the characterisation of flow paths within a patient's respiratory airways.

[0104] The method in any one of the embodiments described herein may further include displaying the output on a graphical interface. The step of displaying further includes displaying the output textually, numerically and/or graphically. [0105] According to a further embodiment of the second aspect of the invention, there is provided a non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform a method of characterising flow paths within a patient's respiratory airways as described herein with reference to the second aspect.

[0106] According to another embodiment of the second aspect of the invention, there is provided a respiratory support system controller for characterising flow paths within a patient's respiratory airways, the controller being configured to perform a method of characterising flow paths within a patient's respiratory airways as described herein with reference to the second aspect.

[0107] According to yet another embodiment of the second aspect of the invention, there is provided a respiratory support system comprising the controller in the preceding paragraph.

[0108] The respiratory support system may further include a non-sealing patient interface for delivering a flow of gases to the patient. The non-sealing patient interface may be configured to deliver the flow of gases to the patient via the patient's nares.

[0109] The respiratory support system may further include one or more sensors for detecting the gas proportion of one or more gas species in the flow of gases at the mouth and/or nose of the patient.

[0110] The one or more sensors may include a CO2 sensor for sensing a proportion of CO2 in the flow of gases leaving the patient through the mouth of the patient.

[0111] The one or more sensors may include a CO2 sensor for sensing a proportion of CO2 in the flow of gases leaving the patient through the nose of the patient.

[0112] The one or more sensors may include a O2 sensor for sensing a proportion of O2 in the flow of gases at the mouth of the patient.

[0113] The one or more sensors may include a O2 sensor for sensing a proportion of O2 in the flow of gases at the nose of the patient. [0114] The one or more of the sensors may be coupled with the non-sealing patient interface. The non-sealing patient interface may include a nasal cannula.

[0115] The respiratory support system may further include one or more input flow sensors for measuring a flow of gases provided to the patient.

[0116] The respiratory support system may further include any one or more of a flow generator for generating a flow of gases provided to the patient, and a humidifier for humidifying the flow of gases provided to the patient.

[0117] The respiratory support system may further include a sealing patient interface for delivering a flow of gases to the patient's nose.

[0118] The respiratory support system may further include one or more sensors for detecting the gas proportion of one or more gas species in the flow of gases leaving the patient through an exhaust of the non-sealing patient interface.

[0119] According to a third aspect of the invention, there is provided a computer method of characterising flow paths within respiratory airways, the method comprising receiving a first input relating to a flow of gases provided to a gas delivery patient interface, and receiving, from one or more sensor units, a second input relating to a flow of gases at or proximate the gas delivery patient interface, characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways based on the first input and/or the second input.

[0120] In accordance with embodiments of the third aspect, the first input may be indicative of an input flow rate of gases provided to the gas delivery patient interface. The second input may be indicative of a measured flow rate of gases at or proximate the gas delivery patient interface.

[0121] In accordance with embodiments of the third aspect, the second input may be indicative of a measured flow rate of gases passing through an exhaust of the gas delivery patient interface. [0122] In accordance with embodiments of the third aspect, characterising one or more flow paths of delivered gases within the respiratory airways may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed condition, determining a nasal passage obstructed condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0123] In accordance with embodiments of the third aspect, the computer method may further include determining one or more respiratory parameters. The one or more respiratory parameters may include any one or more of: input flow rate of gases exceeding inspiratory demand, input flow rate of gases not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0124] According to a fourth aspect of the invention, there is provided a system of characterising flow paths within respiratory airways, the system comprising an input module operatively configured to receive a first input relating to a flow of gases provided to a gas delivery patient interface, and a second input relating to a flow of gases at or proximate the gas delivery patient interface, a processor being operatively configured to characterise one or more flow paths of delivered gases within the respiratory airways based on the first input and/or the second sensor input.

[0125] In accordance with embodiments of the fourth aspect, the first input may be indicative of an input flow rate of gases provided to the gas delivery patient interface. The second input may be indicative of a measured flow rate of gases at or proximate the gas delivery patient interface. [0126] In accordance with embodiments of the fourth aspect, the second input may be indicative of a measured flow rate of gases passing through an exhaust of the gas delivery patient interface.

[0127] In accordance with embodiments of the fourth aspect, characterising one or more flow paths of delivered gases within the respiratory airways may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed condition, determining a nasal passage obstructed condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0128] In accordance with embodiments of the fourth aspect, the system may further include determining one or more respiratory parameters.

[0129] In accordance with embodiments of the fourth aspect, the one or more respiratory parameters may include any one or more of: input flow rate of gases exceeding inspiratory demand, input flow rate of gases not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0130] According to a fifth aspect of the invention, there is provided a computer method of characterising flow paths within a patient's respiratory airways, the method comprising receiving a first input indicative of an input flow rate of gases provided a gas delivery patient interface, and receiving a second input indicative of a pressure in the patient's respiratory airways, characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and/or the second input. [0131] In accordance with embodiments of the fifth aspect, the computer method may further include characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a comparison between the second input and a predetermined threshold pressure value.

[0132] In accordance with embodiments of the fifth aspect, the predetermined threshold pressure value may be based on the first input. A different predetermined threshold pressure value may correspond to a different input flow rate for the first input.

[0133] In accordance with embodiments of the fifth aspect, the computer method may further include receiving a varying first input in which the input flow rate of gases is increasing or decreasing at a constant rate from a predetermined minimum value to a predetermined maximum value, determining a pressure gradient based on a change in the value of the second input corresponding to the variation in the first input when the input flow rate of gases is varied between the predetermined minimum value to the predetermined maximum value, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a comparison between the pressure gradient and a predetermined threshold gradient.

[0134] In accordance with embodiments of the fifth aspect, the predetermined threshold gradient may be a value between a mouth open pressure gradient based on a change in the value of the second input corresponding to the variation in the first input when the input flow rate of gases is varied between the predetermined minimum value to the predetermined maximum value during a mouth open condition, and a mouth closed pressure gradient based on a change in the value of the second input corresponding to the variation in the first input when the input flow rate of gases is varied between the predetermined minimum value to the predetermined maximum value during a mouth closed condition. [0135] In accordance with embodiments of the fifth aspect, the computer method may further include determining a pressure differential between a two reference values for pressure in the patient's respiratory airways, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a comparison between the pressure differential and a predetermined threshold pressure differential value.

[0136] In accordance with embodiments of the fifth aspect, the two reference values may include a maximum pressure in the patient's respiratory airways (Pmax) and a minimum pressure in the patient's respiratory airways (Pmin).

[0137] In accordance with embodiments of the fifth aspect, the predetermined threshold differential value may be a value between a mouth open pressure differential based on a difference between P_max and P_min during a mouth open condition, and a mouth closed pressure differential based on a difference between P_maxand P_min during a mouth closed condition.

[0138] In accordance with embodiments of the fifth aspect, characterising one or more flow paths of delivered gases may include determining any one or more of a mouth open condition, a mouth closed condition, and a nasal passage obstructed condition.

[0139] According to a sixth aspect of the invention, there is provided a computer method of characterising flow paths within a patient's respiratory airways, the method comprising receiving one or more inputs indicative of any one or more of a respiratory rate, a ratio of inspiratory time to total breathing time, and a pressure in the patient's respiratory airways, and characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways of the patient based on the one or more inputs. [0140] In accordance with embodiments of the sixth aspect, characterising may include characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a notable increase or decrease in the one or more inputs.

[0141] In accordance with embodiments of the fifth aspect, characterising one or more flow paths of delivered gases may include determining any one or more of a mouth open condition, and a mouth closed condition.

[0142] According to a further aspect of the invention, there is provided a non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform the method according to any one or more of the methods as described herein.

[0143] In order that the invention may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings.

[0144] It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

Brief Description of Drawings

[0145] Figure 1 is a schematic diagram illustrating a respiratory support system in accordance with one embodiment of the invention.

[0146] Figures 2A illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient exceeds the inspiratory demand of the patient.

[0147] Figure 2B illustrates flow paths within a patient's respiratory airways during an expiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient. [0148] Figure 2C illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient does not meet the inspiratory demand of the patient.

[0149] Figures 3A illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition of the patient.

[0150] Figures 3B illustrates flow paths within a patient's respiratory airways during an expiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition of the patient.

[0151] Figures 4A illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient exceeds the inspiratory demand of the patient.

[0152] Figure 4B illustrates flow paths within a patient's respiratory airways during an expiratory phase of the patient's respiratory cycle during a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient.

[0153] Figure 4C illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient does not meet the inspiratory demand of the patient.

[0154] Figure 5 is a high-level flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to some embodiments of the invention. [0155] Figure 6A is a flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to one embodiment of the method of Figure

5.

[0156] Figure 6B is a flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to another embodiment of the method of Figure 5.

[0157] Figures 7A and 7B illustrate one example patient interface associated with the method of characterising flow paths as summarised in Figure 6A.

[0158] Figures 7C and 7D illustrate another example patient interface associated with the method of characterising flow paths as summarised in Figure 6B.

[0159] Figure 7E illustrates the patient interface of Figures 7C and 7D mounted to a patient's face.

[0160] Figure 8A is a detailed flow diagram illustrating methods of characterising flow paths within a patient's respiratory airways as shown in Figures 6A and 6B.

[0161] Figure 8B is a detailed flow diagram illustrating methods of characterising flow paths within a patient's respiratory airways as shown in Figures 6A and 6B.

[0162] Figures 9A to 9E are graphs illustrating a comparison between example waveforms of an input flow rate of gases provided to the patient and a measured flow rate of gases at the patient corresponding to different flow path characterisations as determined using the method shown in Figure 8.

[0163] Figure 10A is a flow diagram detailing steps for determining one or more other respiratory parameter associated with the patient in accordance with the method shown in Figure 8A.

[0164] Figure 10B is a flow diagram detailing steps for determining one or more other respiratory parameter associated with the patient in accordance with the method shown in Figure 8B. [0165] Figure 11 is a flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to another embodiment of the invention.

[0166] Figures 12A and 12B illustrate a patient interface associated with the method of characterising flow paths as summarised in Figure 11.

[0167] Figure 13A is a detailed flow diagram of the method of characterising flow paths within a patient's respiratory airways as shown in Figure 11.

[0168] Figure 13B is a detailed flow diagram of another method of characterising flow paths within a patient's respiratory airways as shown in Figure 11.

[0169] Figure 14A is a graph illustrating an example waveform of an input flow rate of gases provided to the patient corresponding to a particular flow path characterisation as determined using the method shown in Figure 13.

[0170] Figures 14B to 14E are graphs illustrating example waveforms of an input flow rate of gases provided to the patient and a measured flow rate of gases at the patient corresponding to different flow path characterisations determined using the method shown in Figure 13.

[0171] Figure 15 is a flow diagram detailing steps for determining one or more other respiratory parameter associated with the patient in accordance with the method shown in Figure 13.

[0172] Figure 16 is a high-level flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to other embodiments of the invention.

[0173] Figures 17A to 17C are detailed flow diagrams of methods of characterising flow paths within a patient's respiratory airways in accordance with the general method illustrated Figure 16.

[0174] Figures 17D and 17E are detailed flow diagrams of further methods of characterising flow paths within a patient's respiratory airways in accordance with the general method illustrated Figure 16. [0175] Figures 18A to 18C are detailed flow diagrams of further methods of characterising flow paths within a patient's respiratory airways in accordance with the general method illustrated Figure 16.

[0176] Figures 18D to 18E are detailed flow diagrams of further methods of characterising flow paths within a patient's respiratory airways in accordance with the general method illustrated Figure 16.

[0177] Figures 19A to 19D are graphs illustrating example waveforms of proportions of O2 and CO2 measured at the patient corresponding to the different flow path characterisations determined via the methods shown in Figures 17A to 17D.

[0178] Figures 20A to 20D are graphs illustrating example waveforms of proportions of O2 and CO2 measured at the patient corresponding to the different flow path characterisations determined via the methods shown in Figures 18A to 18C.

[0179] Figure 21A is a flow diagram of a method of characterising flow paths within a patient's respiratory airways based on pressure values.

[0180] Figure 21B is an example look-up table to facilitate determination of a threshold pressure value by a controller executing the method of Figure 21A.

[0181] Figure 21C is an example line graph illustrating patient pressure values for varying input flow rates during mouth open and mouth closed conditions.

[0182] Figure 22A is a flow diagram of another method of characterising flow paths within a patient's respiratory airways based on pressure gradients.

[0183] Figure 22B is a table illustrating the determination of an appropriate threshold gradient value based on pressure gradient values for mouth open and mouth closed conditions.

[0184] Figure 23A is a flow diagram of another method of characterising flow paths within a patient's respiratory airways based on differential pressure values. [0185] Figure 23B is a table illustrating the determination of an appropriate threshold differential pressure value based on differential pressure values for mouth open and mouth closed conditions.

[0186] Figure 23C is an example line graph illustrating fluctuations in patient pressure values for mouth open, mouth closed and nasal passage obstructed (e.g. soft palate closed) conditions.

[0187] Figure 24 are example line graphs illustrating changes in patient pressure, respiratory rate, and a ratio of inspiratory time to total breathing time between mouth closed and mouth open conditions.

[0188] Figures 25A to 28B are flow diagrams illustrating methods of characterising flow paths within a patient's respiratory airways based on the respiratory parameters shown in Figure 24.

Detailed Description

Overview

[0189] Embodiments of the invention provide various methods and systems for characterising flow paths within a patient's respiratory airways, for example during a medical procedure such as a medical procedure involving the provision of respiratory support e.g. oxygen therapy.

[0190] A patient's respiratory airways may refer to the patient's upper and/or lower airways, which may include any one or more of the patient's nose, mouth, sinuses, pharynx, and larynx, the trachea (windpipe), bronchial tubes, and lungs. Characterising flow paths within a patient's respiratory airways may include any qualitative and/or quantitative determinations in relation to the flow of one or more gases within the patient's respiratory airways. Examples of qualitative determinations may include determination of categorical variables (e.g. binary data) which indicate any one or more of a mouth open or closed condition, and a nasal passage not obstructed (e.g. soft palate open)/closed condition. An example of a quantitative determination may include the determination of a numerical value (e.g. 'k') indicative of a proportion of delivered gases passing through the patient's mouth or nose. More specific examples of flow path characterisations will be discussed in further detail below with reference to Figures 2A to 4C.

[0191] Medical procedures should be considered broadly and can comprise any aspect of providing a medical procedure, comprising operative procedures, pre and post -operative procedures, any time prior to, during or after sedation or anaesthesia (sedation and anaesthesia more generally referred to herein as "anaesthetic procedures"), including administering sedatives and/or anaesthetics, during oxygenation and pre-oxygenation phases or procedures, or at any other time without limitation. Medical procedure can also encompass providing respiratory support such as high flow respiratory support. In the context of this specification, medical procedure can also encompass monitoring a patient, whether or not a particular procedure is being provided to the patient. The embodiments described are not just restricted to use in medical procedures. It could be used in ICU, or any other situation where respiratory support is provided.

[0192] To provide the respiratory support, one or more gases is provided to the patient. The one or more gases may be provided to the patient at a predetermined input flow rate. The input flow rate of gases delivered to the patient may be provided at any suitable flow rate in accordance with patient requirements. In some embodiments, high flow respiratory support may be provided to a patient in which gases delivered to the patient is provided at a high flow rate.

[0193] In this specification, "high flow" means, without limitation, any gas flow with a flow rate that is higher than usual/normal, such as higher than the normal inspiration flow rate of a healthy patient. It can be provided by an open or non-sealing respiratory system in which substantial leak may occur at the entrance of the patient's airways due to an open or non-sealing patient interface, for example a nasal cannula having non-sealing nasal prongs. In some embodiments, "high flow" respiratory support may be provided via a sealing patient interface. One such example of a sealing patient interface is described below with reference to Figures 7C and 7D. Typically, high flow respiratory support is provided with humidification to improve patient comfort, compliance and safety. Alternatively, or additionally, it can be higher than some other threshold flow rate that is relevant to the context - for example, where providing a gas flow to a patient at a flow rate to meet inspiratory demand, that flow rate might be deemed "high flow" as it is higher than a nominal flow rate that might have otherwise been provided. "High flow" is therefore context dependent, and what constitutes "high flow" depends on many factors such as the health state of the patient, type of procedure/therapy/support being provided, the nature of the patient (big, small, adult child) and the like. Those skilled in the art would understand from context what constitutes "high flow". It is a magnitude of flow rate that is over and above a flow rate that might otherwise be provided.

[0194] Without limitation, some indicative values of high flow can be as follows.

[0195] In some configurations, delivery of gases to a patient is provided at a flow rate of greater than or equal to about 5 or 10 litres per minute (5 or 10 LPM or L/min).

[0196] In some configurations, delivery of gases to a patient at a flow rate of about 5 or 10 LPM to about 150 LPM, or about 15 LPM to about 95 LPM, or about 20 LPM to about 90 LPM, or about 25 LPM to about 85 LPM, or about 30 LPM to about 80 LPM, or about 35 LPM to about 75 LPM, or about 40 LPM to about 70 LPM, or about 45 LPM to about 65 LPM, or about 50 LPM to about 60 LPM. For example, according to those various embodiments and configurations described herein, a flow rate of gases supplied or provided to an interface via a system or from a flow source, may comprise, but is not limited to, flows of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 LPM, or more, and useful ranges may be selected to be any of these values (for example, about 20 LPM to about 90 LPM, about 40 LPM to about 70 LPM, about 40 LPM to about 80 LPM, about 50 LPM to about 80 LPM, about 60 LPM to about 80 LPM, about 70 LPM to about 100 LPM, about 70 LPM to about 80 LPM).

[0197] In "high flow", the gas delivered will be chosen depending on for example the intended form of respiratory support. Gases delivered may comprise a percentage of oxygen. In some configurations, the percentage of oxygen in the gases delivered may be about 15% to about 100%, about 20% to about 100%, or about 21% to about 100%, or about 30% to about 100%, or about 40% to about 100%, or about 50% to about 100%, or about 60% to about 100%, or about 70% to about 100%, or about 80% to about 100%, or about 90% to about 100%, or about 100%, or 100%. [0198] Flow rates for "high flow" for premature/infants/paediatrics (with body mass in the range of about 1 to about 30 kg) can be different. The flow rate can be set to 0.4-0.8 L/min/kg with a minimum of about 0.5 L/min and a maximum of about 70 L/min. For patients under 2 kg maximum flow is set to 8 L/min.

[0199] In some embodiments, the flow rate of gases (input gases) provided to a patient during respiratory support can be time-varying (e.g. oscillating). This time-varying flow rate can help with therapy.

[0200] As an example, the time-varying flow rates can step between a first flow rate and second flow rate, one or both of which can fall in the range of about 0LPM to 70LPM. For example, the time-varying flow rate may be in the range of: about 0% to about 200% of an average flow rate, about 0% to 100% of the average flow rate, about 100% to 200% of the average flow rate, or about 50% to 150% of the average flow rate, and/or is in the range of about 0-140LPM, about 0-70LPM, about 70-140LPM, about 40-100LPM, or about 20-60LPM

[0201] In the above ranges, the average flow rate may refer to the effective average flow rate of input gases provided to the patient when a time-varying flow rate is used.

[0202] It will be understood that the above example ranges are not limiting flow rates.

[0203] Advantageously, High flow has been found effective in meeting or exceeding the patient's normal real inspiratory flow, to increase oxygenation of the patient and/or reduce effort in breathing. Additionally, high flow may generate a flushing effect in the nasopharynx such that the anatomical dead space of the upper airways is flushed by the high incoming gas flows. This creates a reservoir of fresh gas available of each and every breath, while minimising re-breathing of carbon dioxide, nitrogen, etc. [0204] Embodiments of methods and systems described herein may also determine one or more other respiratory parameters associated with the patient. Similarly, these other respiratory parameters may include qualitative and/or quantitative determinations. For example, the one or more other respiratory parameters may include any one or more of determinations of whether an input flow rate of gases provided to the patient meets the inspiratory demand of the patient, an expired proportion of CO2, an expired proportion of O2, tidal volume, and the like.

[0205] Generally, when considering whether a flow of gases provided to the patient at a predetermined flow rate is considered to meet or exceed the patient's inspiratory demand, a comparison is made between the delivered flow rate of gases passing through the pharynx and into the patient's lungs with an inspiratory demand of the patient.

[0206] In this specification, reference to "proportion" in the context of a gas species refers to any relative measure of a constituent gas component in a total gas comprising two or more constituent gas components. For example, proportion could cover: volume fraction, fraction, volume concentration, concentration, molarity, mass fraction, and partial pressure.

[0207] The proportion measured may be the parameter that is measured by the sensor being used, be it concentration, fraction, partial pressure or otherwise. The proportion determined may be the parameter desired by a user and/or processed by a component of a respiratory support system or associated with a respiratory support system.

[0208] In this specification, any reference to "concentration" can also be termed "fraction" and can be indicated as percentage by volume of the gas of interest versus the volume of constituent gases overall in the gas flow in question, be it exhaled gas flow, apparatus flow or any other flow. However, the parameter could be a different measure and the gas could be different - these are just examples. Respiratory Support System

[0209] Figure 1 shows a respiratory support system 10 for providing a therapeutic gas flow therapy or other form of respiratory support to a patient. In some embodiments, the system 10 is configured to deliver a constant flow rate of gases to the patient 16. In other embodiments, the system 10 may be configured for delivering a time-varying flow rate of gases to the patient 16. The system 10 may include any suitable arrangement of integrated units or separate modular components to provide the necessary system functionality. For example, components described herein as shown in each of the boxes 11, 50 may be provided as single integrated unit, or as separate modular components. The system 10 may be used for any suitable purpose including preoxygenation during an anaesthetic procedure, during an anaesthetic procedure, high flow respiratory support, ventilation, whilst treating patients in respiratory distress, treating patients with obstructive sleep apnoea or in any other application where monitoring of an aspect of patient breathing is desired.

[0210] The system 10 comprises a flow source 50 for providing an input flow rate of gases 31 such as oxygen, or a mix of oxygen and one or more other gases. Alternatively, the system 10 can have a connection for coupling to an external flow source (not shown). As such, the flow source might be considered to form part of the system 10 or be separate to it, depending on context. In embodiments having an external flow source, the system 10 may include one or more connection ports for connection to the external flow source. Moreover, one or more parts of a flow source may form part of the system 10, and one or more other parts of the flow source may be external to the system 10.

[0211] For example, the flow source may include an in-wall oxygen supply, a tank of oxygen 50A, one or more tanks of other gases and/or a high flow respiratory support apparatus having a blower/flow generator 50B. Figure 1 shows a flow source 50 having a flow generator 50B. By way of a non-limiting illustrative example, the flow generator 50B includes an optional air inlet 50C and optional connection to an Ch source (such as tank or O2 generator) 50A via a shut off valve and/or regulator and/or other gas flow control 50D. The flow source could be one or a combination of a flow generator, O2 source, air source as described. [0212] The flow source 50 may provide a (high) flow of gases that can be delivered to a patient 16 via a delivery conduit, and patient interface 51. As described in further detail below with respect to the different embodiments, the patient interface 51 may be an unsealed (also termed "non-sealing") interface, a sealed interface, or an interface having a combination of sealing and non-sealing components. The gas flow provided by the flow source 50 may have a continuous flow rate. In particular, the gas flow provided by the flow source 50 may have a continuous flow rate independent of the patient's breathing. Moreover, the continuous flow rate of the gas flow provided by the flow source 50 may be time-varying or generally constant.

[0213] The flow source could provide a flow rate of between, e.g. about 0.5 L/min and about 375 L/min, or any range within that range, or even ranges with higher or lower limits.

[0214] A humidifier 52 can optionally be provided between the flow source 50 and the patient 16 to provide humidification of the delivered gases 31. The humidifier 52 may be integrated with the flow source 10 to form an integrated unit 59. Alternatively, the humidifier 52 may be a modular component provided separately, and coupled to the flow source 50. In some embodiments, the humidifier 52 may be a standalone humidifier with a chamber and base, whereby the humidifier 52 is coupled to the flow source 50 via conduits or other suitable connectors. One or more sensors 53A, 53B, 53C, 53D such as flow rate, oxygen fraction or other gas fraction, full or partial pressure, humidity, temperature or other sensors can be placed throughout the apparatus and/or at, on or near the patient 16. Alternatively, or additionally, sensors from which such parameters can be derived could be used. In addition, or alternatively, the sensors 53A-53D can be one or more physiological sensors for sensing patient physiological parameters such as, heart rate, oxygen saturation (e.g. pulse oximeter sensor 54E), partial pressure of oxygen in the blood, respiratory rate, partial pressure of O2 and/or CO2 in the blood. Alternatively, or additionally, sensors from which such parameters can be derived could be used. Other patient sensors could comprise EEG sensors, torso bands to detect breathing, and any other suitable sensors. In some configurations the humidifier 52 may be optional, or it may be preferred due to the advantages of humidified gases helping to maintain the condition of the airways. Humidification is typically used with high flow gas flows to increase patient comfort, compliance, support and and/or safety. One or more of the sensors may form part of the system 10, or be external thereto, with the system 10 receiving inputs from any one or more of the external sensors.

[0215] In some embodiments as discussed in further detail below, flow sensors may be used to measure a flow of gases at the patient's 16 nose and/or mouth. Some exemplary embodiments are described in further detail below with reference to Figures 7A, 7B and 12A, 12B.

[0216] Moreover, one or more sensors 14 for measuring a gas parameter (of a target gas) of the patient composite gas outflow may be provided. That is, depending on the target gas (e.g., oxygen, carbon dioxide, nitrogen, helium and/or an anaesthetic agent such as sevoflurane), one or more sensors may be provided to sense that gas in the composite gas outflow. Each sensor may be a mainstream, a side stream sensor, or any other suitable sensor, and can be placed proximate (in, on, near) the nose and/or mouth of the patient 16. Other positions are possible. By way of a non-limiting example, the system 10 may provide one or more sensors 14 to measure one or both of a fraction of CO2 and a fraction of O2 in the composite gas outflow at the patient's nose or mouth.

[0217] The composite gas outflow of the patient is a leaked gas flow combined with an exhaled (or expired) gas flow of the patient 16. Leak gas flow may comprise any excess gas flow from the delivered respiratory support that is not inhaled and/or has not entered the lower airways of the patient by the patient and escapes to ambient via the mouth and/or nose.

[0218] In various embodiments, one or more flow sensors and/or one or more sensors 14 for measuring a gas parameter (of a target gas) of the patient composite gas outflow may be releasably or permanently mounted to or proximate the patient interface 51, the patient's nose and/or mouth such that the sensing elements of the one or more flow sensors and/or one or more sensors 14 are in direct fluid communication with the sensed gases at the patient. In some embodiments, one or more flow sensors and/or one or more sensors 14 may be releasably or permanently mounted elsewhere in the respiratory support system 10, for example, upstream of the patient interface 51. Typically, when the sensor(s) are mounted elsewhere in the system 10, the sensing elements of the sensor(s) may be coupled with one or more gas conduits, sampling tubes and/or sampling probes to facilitate fluid communication with sensed gases at the patient 16. Elaborating further, the one or more gas conduits, sampling tubes and/or sampling probes may be positioned proximate the patient's mouth and/or nose so as to provide fluid communication between the sensed gases at the patient and the sensing element of the one or more flow sensors and/or one or more sensors 14.The output from the sensors can be transmitted to a controller 19 to facilitate control of one or more functions provided by the system 10, including among other things, to vary the flow of gases provided to the patient 16. In some embodiments, the controller 19 executes software instructions stored therein to characterise flow paths within the patient's 16 respiratory airways based on any one or more input parameters received from one or more the sensors described herein. Furthermore, the controller 19 may be configured to execute software instructions stored therein to determine one or more other respiratory parameters associated with the patient 16. This will be described in further detail below.

[0219] Alternatively, or additionally, the controller 19 may be configured to receive input from a user. The controller 19 is coupled to the flow source 50, humidifier 52 and sensors 53A to 53D, 14. The controller 19 may be configured to operate the flow source 50 to provide the delivered flow of gases to the patient 16. It can also operate a gas flow modulator(s) (including the flow source) to control the flow, pressure, volume and/or other parameters of gases provided by the flow source 50 based on feedback from one or more sensors (e.g. 53A to 53D, 14), or optionally without feedback (e.g. using default settings). The controller 19 can also control any other suitable parameters of the flow source 50 to meet oxygenation requirements and/or CO2 removal. The controller 19 can also control the humidifier 52 based on feed-back from the sensors 53A-53D, 14. Based on input from the sensors, the controller 19 can determine oxygenation requirements and provide information to prompt a medical professional to control the components of the respiratory support system 10 so as to provide the desired respiratory support (e.g. flow rate, O2 fraction, humidity, etc.) and/or control parameters of the flow source 50, gas flow modulator(s) and/or humidifier 52 as required. Alternatively, the controller 19 could be provided as a monitoring apparatus for providing information to a medical professional and/or communicating control parameters of the respiratory support system 10 to prompt decision making by the medical profession to determine a desired respiratory support. Based on information provided by the controller 19, the medical professional can then control the respiratory support system 10 to provide the desired respiratory support. As such, in some embodiments, the controller 19 may not always determine oxygenation requirements and control parameters of the system 10.

[0220] The controller 19 may also be configured to operate the system 10 so that the flow of gases provided to the patient 16 has a time-varying flow rate that provides respiratory support. The controller 19 may control operations of the flow generator 50B or any other suitable gas modulator to provide the time-varying flow rate in the flow of gases provided to the patient 16. A gas modulator can be used to modulate (that is, varying, modify, adjust or otherwise control parameters of the gas flow). Each gas flow modulator can be provided in the flow source (and the flow source itself can be a gas flow modulator), after the flow source and before the humidifier, after the humidifier, and/or in any other suitable place in the system 10 to modulate the gas flow as required. The controller 19 can also operate the gas flow modulator(s) (including the flow source) to control the flow, pressure, volume and/or other parameters of gas provided by the flow source based on feedback from sensors, or optionally without feedback (e.g. using default settings). The controller 19 can also control any other suitable parameters of the flow source to meet oxygenation requirements.

[0221] In embodiments requiring a varying gas proportion in the flow of gases provided to the patient 16, the controller 19 may be additionally or alternatively configured to operate the system 10 so that the gas flow has a time-varying gas proportion (such as O2 fraction or other gas fraction and/or O2 partial pressure or other gas partial pressure) that provides therapy/respiratory support. In some example embodiments, the controller 19 may control a proportional valve coupled to an O2 source 50A. The controller 19 can then measure the composite gas outflow and or determine (e.g. obtain an estimate of) the gas parameter using any of the following techniques. In one embodiment, there are two proportional valves that operate 180 degrees out of phase. As one opens, the other closes. One controls O2 fraction in the delivered gas flow, and the other controls air fraction in the delivered gas flow, but together keeping the total gas flow rate constant. In another alternative, a single proportional valve is used with an impeller where the proportional valve controls an O2 fraction and the impeller controls the flow rate. In some embodiments, the single proportional valve may be used before or after the impeller. Where the single proportional valve is used before the impeller, the proportional valve controls the O2 fraction into the inlet of the impeller along with the ambient air. In some embodiments, more than one proportional valve may be used with an impeller and may be positioned anywhere in the system with respect to the impeller. The controller 19 can control the proportional valve(s) to operate as required to achieve the time-varying gas proportion.

[0222] In some embodiments, the controller 19 may be a specialist controller operatively configured to receive input from the one or more sensors 53A to 53D, 14, and/or one or more flow sensors (e.g. see Figures 7A, 7B, 12A, 12B) to characterise flow paths within a patient's respiratory airways as described herein. One or more separate controllers (not shown) may be provided in the respiratory support system 10 for interfacing and controlling with the flow source 50 and/or humidifier 52.

[0223] An input/output user interface 54 (such as a display and/or input device) is provided. The input device is for receiving information from a user (e.g. clinician or patient) that can be used for example for determining oxygenation requirements, anaesthetic gas agent, detection (e.g. breath detection, detection with respect to inspiratory or expiratory phases of the patient's breathing, detection in relation to a state of the patient), flow rates, gas fractions, partial pressures and/or any other parameter that might be controlled by the system 10.

[0224] In some embodiments, the user interface 54 may include a graphical user interface for displaying visual output to provide a visual indication of the characterisation of the one or more flow paths of delivered gases within the respiratory airways of the patient 16. The graphical user interface may further display output to provide visual indications of the one or more determined respiratory parameters associated with the patient 16. The output may be displayed on the graphical user interface textually, numerically and/or graphically. In some embodiments, the user interface 54 may be configured to generate audio output (e.g. in the form of audio messages) to provide an indication of the characterisation of the one or more flow paths of delivered gases within the respiratory airways of the patient 16, and/or one or more determined respiratory parameters associated with the patient 16. The visual and/or audio output may be generated based on real-time or near real-time sensor data continuously during a medical procedure. In some embodiments, the visual and/or audio output may be updated continuously or periodically, for example during or after each respiratory cycle here.

Flow Paths in Respiratory Airways

[0225] The characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient can be conducted in a number of different ways. In some embodiments, the flow paths within the patient's 16 respiratory airways can be characterised by determining whether the patient's mouth is open or closed. In some embodiments, it may be additionally determined whether the patient's nasal passage is obstructed or not obstructed. Typically, the nasal passage refers to the passage between the nasal and oral cavity of the patient. In one example, the nasal passage may not be obstructed if the soft palate is open. Similarly, the nasal passage may be obstructed if the soft palate is closed. As such, a determination that the nasal passage is not obstructed may suggest that the soft palate is open, and a determination that the nasal passage is obstructed may suggest that the soft palate is closed. It may often be observed that a nasal passage obstructed (e.g. soft palate closed) or not obstructed condition in a patient may be temporary. In other examples, the patient's anatomical structure or underlying patient condition may give rise to a nasal passage obstruction that persists. Throughout the specification, the condition of the soft palate in either an open or closed position may be described as examples of not obstructed or obstructed conditions of the nasal passage, for example as described below with reference to Figures 2A to 4C. In practice, the controller 19 may determine whether the nasal passage is obstructed or not obstructed and this may infer whether the soft palate is closed or open respectively.

[0226] As described in further detail below, characterising one or more flow paths of delivered gases within the respiratory airways of the patient may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed (e.g. soft palate open) condition, determining a nasal passage obstructed (e.g. soft palate closed) condition, determining a numerical value (e.g. 'k') indicative of a proportion of delivered gases passing through the mouth or nose. [0227] In various embodiments of methods for characterising flow paths and/or determining respiratory parameters as described herein, any one or more of the flow path characterisations and respiratory parameters may be determined at various steps of the methods. Where the determination of more than one of the flow path characterisations and/or respiratory parameters are possible, the controller 19 may determine any one or more, or all of the possible flow path characterisations and respiratory parameters, and provide an output presenting the any one or more, or all of the possible determinations. Similarly, any one or more steps of any method described herein can be combined with any one or more steps of any other method to determine a combination of flow path characterisations and/or respiratory parameters, where appropriate.

[0228] As shown in Figure 2A, a flow of gases 100 is provided to the patient 16 via the patient's nares 106 by a respiratory support system 10 at a constant or time-varying flow rate, for example during high flow respiratory support. The flow of gases 100 may have a fixed concentration of O2 or a varying concentration of O2. Figure 2A illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 and soft palate 104 are both open, a flow of gases leaving the patient may pass through both the mouth 102 and nose 106 of the patient during the inspiratory phase. The flow of gases leaving the patient is a portion of the delivered gases 100.

[0229] Typically, the flow rate of the input flow of gases 100 (referred to herein as Qi) is a known value of the gas flow generator 50B. In some embodiments, the flow rate Qi may be measured (e.g. via a flow sensor) in or at the patient interface 51, in or at the patient's respiratory airways, or at any suitable location in the respiratory support system 10 upstream of the patient interface 51.

[0230] Figure 2B illustrates flow path conditions during an expiratory phase of the patient's 16 respiratory cycle. During the expiratory phase, a flow of gases leaving the patient may pass through both the mouth 102 and nose 106 of the patient 16. A portion of the delivered gases 100 may leave the patient 16 via the patient's mouth 102 and/or nose 106. Moreover, gases exhaled 108 by the patient 16 may leave the patient 16 via the patient's mouth 102 due to a lower resistance pathway (when compared to the resistance of the pathway out of the nose).

[0231] In this scenario illustrated in Figures 2A and 2B, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition. It may also be determined that in this scenario, the input flow rate of gases 100 provided to the patient 16 exceeds the inspiratory demand of the patient 16 in Figure 2A.

[0232] In the mouth open condition, where the mouth 102 of the patient 16 is open, this refers to the mouth 102 being open to an extent such that a substantial flow of gases can pass through the mouth 102. In the nasal passage not obstructed (e.g. soft palate open) condition, where the soft palate 104 of the patient is open, this refers to the soft palate 104 being open to an extent such that a substantial flow of gases can pass the soft palate 104.

[0233] Conversely, in a mouth closed condition, where the mouth 102 of the patient 16 is closed, this refers to the mouth being closed to an extent such that a substantial flow of gases cannot pass through the mouth 102, to or from atmosphere. In a soft palate 104 closed condition, where the soft palate 104 of the patient is closed, this refers to the soft palate 104 being closed to an extent such that a substantial flow of gases cannot pass the soft palate 104.

[0234] A different scenario will now be described with reference to Figure 2C. As shown in Figure 2C, a flow of gases 100 is provided to the patient 16 via the patient's nares 106. Figure 2C illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 and soft palate 104 are both open, the patient entrains ambient air through the mouth 102. In some cases, a portion of the delivered gases 100 may leave the patient via the patient's nose 106. In this scenario, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition. In addition, it can be determined that the input flow rate of gases 100 provided to the patient 16 does not meet the inspiratory demand of the patient 16.

[0235] A further scenario will now be described with reference to Figures 3A and 3B. A flow of gases 100 is provided to the patient 16 via the patient's nares 106. Like numerals refer to like features previously described. Figure 3A illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, none (or a negligible amount) of the delivered gases 100 passes through the pharynx and into the patient's lungs as the patient's 16 soft palate 104 is closed and all (or almost all) of the delivered gases 100 leaves the patient 16 through the nose 106. The patient's mouth 102 is open. As such, the patient entrains ambient air 110 through the mouth 102 during the inspiratory phase.

[0236] Figure 3B illustrates an expiratory phase of the patient's respiratory cycle. During the expiratory phase, none (or a negligible amount) of the delivered gases 100 passes through the pharynx and into the patient's lungs, or enters the oral cavity, as the patient's 16 soft palate 104 is closed and all (or almost all) of the delivered gases 100 leaves the patient 16 through the nose 106. The patient's mouth 102 is open. As such, the patient's exhales gases 108 pass through the mouth 102 during the expiratory phase.

[0237] In this scenario as illustrated in Figures 3A and 3B, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition.

[0238] Yet another scenario will now be described with reference to Figures 4A and 4B. A flow of gases 100 is provided to the patient 16 via the patient's nares 106. Like numerals refer to like features previously described. Figure 4A illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 is closed and the soft palate 104 is open, a flow of gases leaving the patient passes through the nose 106 of the patient during the inspiratory phase. No (or a negligible amount of) gases pass through the mouth 102 of the patient. Moreover, a portion of the delivered gases 100 may leave the patient 16 via the patient's nose 106 during inspiration. [0239] Figure 4B illustrates flow path conditions during an expiratory phase of the patient's 16 respiratory cycle. During the expiratory phase, a flow of gases leaving the patient passes through the nose 106 of the patient 16. No (or a negligible amount of) gases pass through the mouth 102 of the patient as the patient's mouth 102 is closed. A portion of the delivered gases 100 may leave the patient 16 via the patient's nose 106. Moreover, gases exhaled 108 by the patient 16 leave the patient 16 via the patient's nose 106.

[0240] In this scenario illustrated in Figures 4A and 4B, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition. In relation to the scenario illustrated in Figure 4A, it may also be determined that, the input flow rate of gases 100 provided to the patient 16 exceeds the inspiratory demand of the patient 16.

[0241] A different scenario will now be described with reference to Figure 4C. As shown in Figure 4C, a flow of gases 100 is provided to the patient 16 via the patient's nares 106. Like numerals refer to like features previously described. Figure 4C illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 is closed and the soft palate 104 is open, the patient entrains ambient air through the nose 106 only. No gases pass through the mouth 102 of the patient 16 as it is closed.

Moreover, there is no flow of gases leaving the patient during the inspiratory phase. In this scenario, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition. In addition, it can be determined that the input flow rate of gases 100 provided to the patient 16 does not meet the inspiratory demand of the patient 16.

[0242] In some embodiments, a numerical value (e.g. k) indicative of a proportion of delivered gases passing through the mouth 102 or nose 106 of the patient 16 may also be determined. This will be described in further detail below with reference to Figures 8 to 15.

[0243] In all embodiments of the invention as described herein, it is assumed that the patient 16 is breathing (e.g., the patient 16 is not apnoeic). Characterising Flow Paths

[0244] Methods and systems of characterising flow paths within the patient's 16 respiratory airways in accordance with embodiments of the invention will now be described below. In some embodiments, one or more other respiratory parameters can also be determined.

[0245] As summarised in the flow diagram 200 of Figure 5, methods of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, may include the general steps of by providing 202 a flow of gases to the patient via a patient interface 51 of the respiratory support system 10, and measuring 204 a flow of gases at the patient's mouth or nose using one or more sensors (the one or more sensors may be provided by or proximate the patient interface 51), and characterising 206 one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 either based on the one or more sensor measurements, or a comparison between the flow of gases provided to the patient 16 via the patient interface 51 and the one or more sensor measurements.

[0246] Accordingly, the execution of methods characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, by controller 19 according to these embodiments may include the steps of receiving a first input relating to a flow of gases provided to the patient 202 (e.g., from a flow rate sensor 53A to 53D), receiving a second input relating to a flow of gases at the mouth 102 or nose 106 of the patient 16 (e.g., from a flow rate sensor [e.g. see Figures 1, 7A, 7B, 7C, 7D and 12A, 12B] provided proximate the mouth 102 or nose 106 of the patient 16) 204, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input and/or the second input 206.

[0247] In particular, the method includes characterising one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input and the second input, or the second input as described in further detail below. [0248] In step 208, the controller 19 may optionally generate output to provide indications of the characterisation, for example audibly via audio messages or visually via a graphical user interface associated with the controller 19. Displaying the visual indications may include displaying the visual indications textually, numerically and/or graphically.

[0249] The first input relating to a flow of gases provided to the patient may be received from one or more sensors 53A to 53D provided in the respiratory support system 10. In some embodiments, the first input may be a flow rate of the flow of gases provided to the patient 16. In some embodiments, the controller 19 may include a sensing module to sense the flow of gases provided to the patient 16. In some embodiments, the sensing module may be separate to the controller 19. In some embodiments, respiratory support system 10 may include a manual flow meter to provide the respiratory support separately to the controller 19. The supplied flow rate on the manual flow meter may be transmitted to the controller 19 to provide an indication of a flow rate of gases provided to the patient.

Flow Sensing at Nares

[0250] As illustrated in the flow diagram of Figure 6A, a method 301 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, according to one embodiment of the method 200 includes the general steps of by providing 302 a flow of gases to the patient 16 nares via a sealing patient interface (e.g. patient interface 400 as described below with reference to Figures 7A and 7B), and measuring 304 a flow of gases at the patient's nose (e.g. from one of the patient's nostrils as described below with reference to Figures 7A and 7B), comparing 306 the flow of gases delivered to the patient 16 with the flow of gases at the patient 16, and characterising 308 one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 based on the comparison.

[0251] As illustrated in the flow diagram of Figure 6B, another method 303 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, according to another embodiment of the method 200 includes the general steps of by providing 344 a flow of gases to the patient 16 nares via a sealing patient interface (e.g. patient interface 420 as described below with reference to Figures 7C and 7D), and measuring 346 a flow of gases passing through the exhaust (outlet) 424 (into or exiting the patient interface 420), comparing 348 the flow of gases 100 delivered to the patient 16 via the nasal pillows (prongs) 422 of the patient interface 420 with the flow of gases 426 passing though the exhaust 424, and characterising 350 one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 based on the comparison.

[0252] Accordingly, the execution of the method 301 or 303 for characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, by controller 19 according to this embodiment may include the general steps of receiving a first input relating to a flow of gases 100 provided 302, 344 to the patient 16 (based on a known value of the flow generator 50 or measurement from one or more flow sensors mounted to or adjacent the patient interface 51 or elsewhere in the system 10), receiving a second input relating to a flow of gases at the nose 106 of the patient 16 (based on measurement from sensors provided with the patient interface (e.g. 400, 420) or mounted to or adjacent the patient interface 51 or elsewhere in the system 10), and characterising 306, 350 one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input and the second input (e.g. by comparing 306, 350 the first input with the second input).

[0253] The first input may be a flow rate of the flow of gases provided to the patient 16. The second input may be a flow rate of the flow of gases at the nose 106 of the patient 16. In relation to the second input, the flow of gases at the patient may be leaving or entering the patient at different respiratory phases (e.g. inspiration/expiration phase) of each respiratory cycle.

[0254] Typically, the second input is a sensor input relating a flow of gases at the nose 106 of the patient as provided by one or more sensor units positioned within or proximate either one or both of the patient's nares, integral to or separately from the patient interface, or elsewhere in the system 10 as previously discussed.

[0255] In one embodiment, the one or more sensor units for determining the second input may be integrated with or mounted to the patient interface. An example of such a patient interface 420 is described below with reference to Figures 7C and 7D, in which the patient interface 420 includes one or more outlet openings (exhaust) 424 to allow a flow of gases leaving the patient 16 therethrough. As such, one or more sensors for determining the second input may be provided by the patient interface as illustrated by example patient interface 420.

[0256] The method 300 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, by controller 19 will be described in further detail below with reference to Figures 8 to 10.

[0257] An example patient interface 400 configured to provide the flow of gases 100 to the patient 16 and measure a flow of gases leaving or entering the patient 16 via the patient's nose 106 is illustrated in Figures 7A and 7B.

[0258] In particular, the patient interface 400 is a sealing patient interface. The sealing patient interface 400 includes a flow delivery portion 402 (or flow delivery nasal interface) configured to seal against a first nostril of the patient 16 to deliver the flow of gases 100 to the patient 16 as shown in Figure 7A.

[0259] The sealing patient interface 400 further includes a flow measurement portion 404 (or flow measurement nasal interface) configured to seal against a second nostril of the patient to measure the flow of gases at the second nostril of patient (e.g. a flow of gases leaving/entering the patient via the second nostril) as shown in Figure 7B. The flow measurement nasal interface 404 is open to atmosphere such that a flow of gases leaving the patient's nares enters the atmosphere via the nasal interface 404. Similarly, a flow of gases from the atmosphere may enter the patient's nares via the measurement nasal interface 404.

[0260] In the embodiment shown in Figure 7B, the flow measurement nasal interface 404 includes an integrated mass flow sensor (also known as a differential pressure sensor) 412, which measures the flow rate, based on a differential pressure. In particular, a restriction 410 is provided in a gas flow passage of the flow measurement nasal interface 404. Pressure measurements may be taken upstream 406 of the restriction 410 and downstream 408 of the restriction 410. A pressure differential across the restriction 410 may be used to determine a volumetric flow rate of gases at the second nostril of the patient 16. As the flow measurement nasal interface 404 is open to atmosphere, a pressure downstream of the restriction 410 may be assumed to be atmospheric pressure. Accordingly, in other embodiments, to determine the pressure differential, a single pressure measurement 406 upstream of the restriction 410 may be required.

[0261] As each of the flow delivery nasal interface 402 and the flow measurement nasal interface 404 is configured to seal against each respective nostril of the patient 16, it is assumed that all gas flow leaving the patient's nose passes through the flow measurement nasal interface 404.

[0262] In other embodiments, other suitable type of flow rate sensors may be used in the flow measurement nasal interface 404 to determine the flow rate of gases leaving/entering the patient via the second nostril. For example, thermal mass flow sensors may be used instead of a differential pressure sensor 412.

[0263] Another example patient interface 420 configured to provide the flow of gases 100 to the patient 16 and measure a flow of gases leaving or entering the patient 16 via the patient's nose 106 is illustrated in Figures 7C to 7E.

[0264] In particular, the patient interface 420 is also a sealing patient interface. The sealing patient interface 420 includes an inlet portion 421 for connection with the respiratory support system 10. A flow of gases 100 from the respiratory support system 10 enters the patient interface 420 via the inlet portion 421.

[0265] As more clearly shown in Figure 7D, the sealing patient interface 420 includes a flow delivery portions 422 (or flow delivery nasal interface) having a pair of nasal pillows for sealing engagement with both of the patient's nostrils. All or a portion 101 of the input flow of gases 100 may be delivered to the patient via the nasal pillows 422 of the patient interface 420. As explained below, some of the input flow of gases 100 may be redirected through outlet openings in the exhaust 424.

[0266] As more clearly illustrated in Figure 7C, the sealing patient interface 420 further includes an exhaust 424 defining one or more outlet openings to allow a flow of gases to exit the sealing patient interface 420. The flow of gases 426 leaving the sealing patient interface 420 through exhaust 424 may include gases redirected from the input flow of gases 100 and/or gases expired from the patient's nose. As the nasal pillows 422 are configured to seal against each respective nostril of the patient 16, it is assumed that all gas flow leaving the patient's nose passes through exhaust 424 of the patient interface 420.

[0267] In some scenarios, for example when the patient's inspiratory demand is not met, the patient may entrain gases from the atmosphere. In these scenarios, the entrained gases may enter the sealing patient interface 420 via exhaust 424 before entering the patient's nose via the flow delivery portions 422.

[0268] The sealing patient interface 420 may include one or more sensor units 14 integrated therein (or otherwise provided therewith) to measure any one or more input parameters including a flow rate of the delivered gases 100 (Qi), a flow rate of gases leaving the patient interface 420 via the exhaust 424 (Q_m), a fraction of oxygen (O2) in the delivered gases 100 (Finos), a fraction of oxygen (O2) in the flow of gases passing through (e.g. in/out) the exhaust 424 (Fmoz), and a fraction of carbon dioxide (CO2) in the flow of gases passing through (e.g. in/out) the exhaust 424 (Fmcoz), a respiratory rate, a ratio of inspiratory time to total breathing time, and a pressure in the patient's respiratory airways. In some embodiments, one or more sensor units may be mounted externally to the sealing patient interface 420 or elsewhere in the respiratory support system 10 to measure one or more of these input parameters. In some embodiments, a pressure sensor (hidden) may be provided by the patient interface 420 to measure a pressure in the patient's airways.

[0269] As illustrated in Figure 7E, a pressure measurement manifold 427 in fluid communication with the patient's airways may be provided to facilitate measurement of a pressure at the patient's airways by a pressure sensor. Typically, the pressure sensor is attached to the pressure measurement manifold 427 such that the pressure sensor is in fluid communication with manifold 427. The pressure sensor may be positioned at any suitable location in the respiratory support system 10.

[0270] It will be appreciated that any suitable patient interface can be provided. In other example embodiments, the patient interface may include one nasal pillow rather than two nasal pillows or prongs. In another example, the sealing patient interface may include a mask which covers the patient's nose. [0271] Figure 8A illustrates a method 300 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters in accordance with the method summaries 301, 303 as previously described with reference to Figures 6A and 6B, as executed by the controller 19. Figure 8A illustrates method steps 310 to 332 for characterising flow paths and optionally determining one or more other respiratory parameters based on measurements for first input Qj(t) and the second input (Q_m(t)) at least over a full respiratory cycle of the patient 16.

[0272] When the patient interface 400 (Figures 7A &7B) is used, the controller 19 is operatively configured to receive a first input (Q (t)) indicative of an input flow rate of gases 100 provided via the flow delivery nasal interface 402 of the sealing patient interface 400 to a first nostril of the patient 16, and a second input (Q_m(t)) indicative of a measured flow rate of gases at a second nostril of the patient 16 received via the flow measurement nasal interface 404.

[0273] When the patient interface 420 (Figures 7C & 7D) is used, the controller 19 is operatively configured to receive a first input (Q (t)) indicative of an input flow rate of gases 100 provided to the patient interface 420 , and a second input (Q_m(t)) indicative of a measured flow rate of gases passing through the exhaust 424 may be received via sensor units embedded in, or external to, the patient interface 420.

[0274] The controller 19 is operatively configured to characterise one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 based on a comparison of the first input (Q (t)) and the second input (Q_m(t)).

[0275] At step 310, the controller 19 receives the first input Q (t), and the second input (Q_m(t)) at least over a full respiratory cycle of the patient 16.

[0276] At query step 312, the controller 19 determines whether the second input (Q_m(t)) is greater than the first input (Qj(t)) at any point over the full respiratory cycle. If not, the method 300 proceeds to step 314. If so, the method proceeds to step 326.

[0277] At step 314, the controller 19 determines a mouth open condition associated with the patient 16. [0278] Once the controller 19 determine a mouth open condition, the controller 19 can determine a numerical value indicative of a proportion of delivered gases passing through the mouth or nose. The controller can determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based on equation [1] below. wherein

Qj(t) is the first input indicative of an input flow rate of gases 100 provided to a sealing patient interface (e.g. 400, 420), and

Q_m(t) is the second input indicative of a measured flow rate of gases at the sealing patient interface (e.g. 400, 420) (e.g. sensor measurement of flow rate of gases passing through the flow measurement portion 404 of patient interface 400, or sensor measurement of flow rate of gases passing through exhaust 424 of patient interface 420).

[0279] The calculation of k is also described with respect to further details of the method 300 as set out in Figure 10A.

[0280] At query step 316, the controller 19 determines if the first input Qj(t) substantially equals the second input Q_m(t) consistently over the full respiratory cycle. If so, the method 300 proceeds to step 318. If not, the method 300 proceeds to step 319.

[0281] At step 318, the method determines a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition associated with the patient 16. The graph in Figure 9E illustrates a comparison between the first input Q (t) and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open, and soft palate is closed.

[0282] At step 319, the method 300 determines a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition associated with the patient 16. The graphs in Figures 9A and 9B provide example traces illustrating the flow path characterisation as determined in this step.

[0283] As shown in Figure 9A, the second input Q_m(t) is consistently less than the first input over a full respiratory cycle. As illustrated in Figure 9B, the second input Q_m(t) is also consistently less than the first input Qj(t) over the full respiratory cycle. Figure 9A may illustrate an example waveform for the second input second input Q_m(t) for one patient when the first input Q (t) is about 70 (l/min), and Figure 9B may illustrate an example waveform for the second input second input Q_m(t) for another patient when the first input Qj(t) is about 10 (l/min). In both Figures 9A and 9B, the example waveforms illustrate the flow path determination of step 319 in which the patient's mouth is open and soft palate is open.

[0284] At step 326, the controller 19 determines a mouth closed condition (if the second input Qm(t) is greater than the first input Qj(t) at any point over the full respiratory cycle as determined in query step 312).

[0285] Once the controller 19 determines that the patient's mouth is closed, one or more other respiratory parameters may be determined. For example, the controller 19 may determine an expired fraction of CO2 (F_E co₂) of the exhaled gas flow associated with the patient 16. The controller 19 may receive a third input F_m_nose_co2 (t) indicative of a measured fraction of CO2 at the nose of the patient. The respiratory support system 10 may provide a gas sampling sensor 14 proximate the patient's nose to measure the third input F_m_nose_co2 (t). In particular, the controller 19 may determine an expired fraction of CO2 (F_E co₂) based on equation [2] below: wherein

Qj(t) is the first input indicative of an input flow rate of gases 100 provided via a sealing patient interface (e.g. 400, 420),

Q_m(t) is the second input indicative of a measured flow rate of gases at the sealing patient interface (e.g. 400, 420) (e.g. sensor measurement of flow rate of gases passing through the flow measurement portion 404 of patient interface 400, or sensor measurement of flow rate of gases passing through exhaust 424 of patient interface 420), and

Fm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 in the composite gas outflow at the sealing patient interface (e.g. 400, 420) (e.g. sensor measurement of a fraction of CO2 in the flow of gases passing through the flow measurement portion 404 of patient interface 400, or sensor measurement of flow rate of gases passing through exhaust 424 of patient interface 420). The third input may be obtained from sensor measurements of one or more sensor units provided by, mounted to or proximate the patient interface, or provided elsewhere in the system 10.

[0286] The composite gas outflow of the patient is the leak gas flow combined with the exhaled (or expired) gas flow of the patient 16. In the F_E ^determination of equation [2], the exhaled gas flow, leak gas flow and thus, the composite gas outflow are entirely passing out of the nose of the patient 16, as the mouth is closed.

[0287] At query step 328, the controller 19 determines if the second input Q_m(t) is consistently greater than zero during the respiratory cycle. If so, the method 300 proceeds to step 330. If not, the method 300 proceeds to step 332.

[0288] At step 330, the controller 19 determines a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases exceeds inspiratory demand. The graph in Figure 9C illustrates a comparison between the first input Q (t) and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, the soft palate is open, and the input flow rate of gases exceeds inspiratory demand. As illustrated in Figure 9C the second input Q_m(t) exceeds the first input Q (t) during the expiration phase of the respiratory cycle and the second input Q_m(t) is consistently greater than zero during the respiratory cycle.

[0289] At step 332, the controller 19 determines a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases does not meet inspiratory demand. The graph in Figure 9D illustrates a comparison between the first input Q (t) and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, the soft palate is open, and the input flow rate of gases does not meet inspiratory demand. As illustrated in Figure 9D the second input Q_m(t) exceeds the first input Qj(t) during the expiration phase of the respiratory cycle and the second input Q_m(t) drops below zero during the inspiration phase of the respiratory cycle. [0290] After method steps 314, 326, 318, 319, 330 and 332, the method 300 may return to step 310 to measure the first input second input Qj(t) and second input Q_m(t) for the next respiratory cycle so as to provide continuous patient monitoring.

[0291] In some of the embodiments, it may be desirable for the controller 19 to determine the respiratory phase of the patient (e.g. whether the patient is in an inspiration, an expiration phase of a respiratory cycle or a transition between the inspiration phase and expiration phase (e.g. during which the patient flow is zero)). The respiratory phase can be determined using any suitable manner. For example, using a sensor to measure a proportion of a gas species such as CO2 at the patient's mouth or nose. In these embodiments, a measured proportion of CO2 at the patient that is greater than the proportion of CO2 in ambient air may indicate that the patient is in an expiration phase). In other non-limiting examples, an ECG or respiratory torso band could be used. In some embodiments, the controller 19 may determine the respiratory phase (e.g. inspiration, expiration or transition between inspiration and expiration) based on input from one or more of the above sensors. In another embodiment, the controller 19 may receive direct input (e.g. from another processor) indicative of a determined respiration phase.

[0292] In some embodiments, in relation to the calculation of an expired fraction of CO2 (F_E CO₂) ^as described herein, the controller 19 may determine when the patient is in an expiration phase of a respiratory cycle before calculating the expired fraction of CO2 (F_E co₂)- In some embodiments, the controller 19 may calculate a value for the expired fraction of CO2 (F_E CO₂) ^at any time, or continuously throughout one or more respiratory cycles of the patient 16. A value for the expired fraction of CO2 (F_E co₂) during an inspiratory phase may be substantially zero.

[0293] Figure 8B illustrates a method 360 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters in accordance with the method summaries 301, 303, as executed by the controller 19. Figure 8B illustrates method steps 310 to 332 for characterising flow paths and optionally determining one or more other respiratory parameters based on one or more sample (discrete) measurements for first input Q (t) and the second input (Q_m(t)). The sample measurements for first input Q (t) and the second input (Q_m(t)) may be taken at any point in time during a respiratory cycle of the patient 16. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0294] At step 362, the controller 19 receives one or more sample measurements for the first input Q (t), and the second input (Q_m(t)) at any point(s) in time during a respiratory cycle of the patient 16. Values for first input Q (t), and the second input (Q_m(t)) may be sampled concurrently such that for a given sampling time interval, a sampled value for the first input Qj(t) has a corresponding sampled value for the second input (Q_m(t)) .

[0295] At query step 364, the controller 19 determines whether the second input (Q_m(t)) is greater than the first input (Q (t)). If not, the method 360 proceeds to step 368. If so, the method 360 proceeds to step 366.

[0296] At step 366, the controller 19 determines a mouth closed condition associated with the patient 16. The controller 19 may further determine that the patient is in an expiratory phase of a respiratory cycle, and/or that the nasal passage of the patient 16 is not obstructed. As illustrated in Figures 9C and 9D, the second input Q_m(t) exceeds the first input Qj(t) during the expiration phase of the respiratory cycle, when the patient's mouth is closed, and the nasal passage is not obstructed.

[0297] At query step 368, the controller 19 determines if the sampled value for the first input Qj(t) substantially equals the corresponding sampled value for the second input Q_m(t). If so, the method 360 proceeds to query step 370. If not, the method 368 proceeds to step 376.

[0298] At query step 370, the controller 19 may calculate a gradient of two or more sampled values for the second input Q_m(t). Typically, the two or more sampled values are sampled at a frequency that is greater than a breathing frequency of the patient. In other words, the two or more sampled values are generally taken within the same respiratory cycle. If the gradient is non- zero, the method 360 proceeds to step 372. If the gradient is substantially zero, the method 360 proceeds to step 374.

[0299] At step 372, the controller 19 may determine a breath paused condition. The controller 19 may further determine a mouth closed condition. As illustrated in Figures 9C and 9D, the second input Q_m(t) intersects with the first input Q (t) momentarily when the patient is between the expiration phase and the inspiratory phase of the respiratory cycle, when the patient's mouth is closed. At this intersection, the gradient of Q_m(t) is non-zero. It may be considered that the patient's breath is momentarily paused between the expiration phase and the inspiratory phase of the respiratory cycle.

[0300] At step 374, the controller 19 may determine a nasal passage obstructed (e.g. soft palate closed) condition. As illustrated in Figure 9E, the second input Q_m(t) consistently equals first input Q (t), when the patient's nasal passage obstructed (e.g. soft palate closed). The value for the second input Q_m(t) also remains constant through the respiratory cycle. As such, the gradient of Q_m(t) is substantially zero when the patient's nasal passage obstructed (e.g. soft palate closed).

[0301] At query step 376, the controller 19 determines whether the sampled value for the second input Q_m(t) is greater than 0. If so, the method 360 proceeds to query step 378. If not, the method 360 proceeds to step 382.

[0302] At query step 378, the controller 19 determines whether the patient is expiring. This may be determined according to any known suitable manner, for example as described herein. If the controller 19 determines that the patient is expiring, the method 360 proceeds to step 380. If the controller 19 determines that the patient is not expiring, the method 360 proceeds to step 384.

[0303] At step 380, the controller 19 may determine a mouth open condition. In addition, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition. As illustrated in Figures 9A and 9B, first input Q (t) exceeds the second input Q_m(t), and the second input Q_m(t) is greater than zero during the expiration phase of the respiratory cycle, when the patient's mouth is open, and the nasal passage is not obstructed.

[0304] At step 384, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition. As illustrated in Figures 9A, 9B, 9C and 9D, during an inspiratory phase, at least some values for the second input Q_m(t) are greater than zero and less than the corresponding values for the first input Q (t). As such, further measurements of the first input Qj(t) and the second input Q_m(t) over at least an entire respiratory cycle would be required to make any further characterisations at this step, for example as described above with reference to method 300.

[0305] At step 382, the controller 19 may determine a mouth closed condition. The controller 19 may further determine an inspiratory phase condition indicating that the patient is inspiring. Moreover, the controller 19 may determine that an inspiratory demand of the patient is not met. As illustrated in Figure 9D, for a least some values of the second input Qm(t) during the inspiratory phase, the second input Q_m(t) is less than zero and less than corresponding values for the first input Qj(t), when the patient's mouth is closed and the inspiratory demand of the patient is not met.

[0306] After method steps 366, 372, 374, 380, 384 and 382, the method 360 may return to step 362 to take one or more subsequent sample measurements for the first input Q (t) and second input Q_m(t) so as to provide continuous patient monitoring.

[0307] Now reverting to the method 300, the controller 19 may be operatively configured to determine one or more other respiratory parameters. The determination of one or more other respiratory parameters will now be described in further detail below with reference to Figure 10A. Figure 10A illustrates method steps 310 to 342 determining one or more other respiratory parameters based on measurements for first input Q (t) and the second input (Q_m(t)) at least over a full respiratory cycle of the patient 16.

[0308] Steps 310, 312, 314 and 326 of method 300 as shown in Figure 10A are the same as those previously described with reference to Figure 8A.

[0309] At step 315, the controller 19 determines whether the patient is in an expiratory phase. The determination of the patient's respiratory phase may be based on known sensing techniques, for example as described herein. If the controller 19 determines that the patient is in an expiratory phase, the method 300 proceeds to step 334. If not, the method 300 returns to step 310.

[0310] In steps 334 and 336, the controller 19 determines that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is greater than zero (k>0). The controller may further calculate the specific numerical value (k) based on equation [1] above. [0311] At step 326, the method determines a mouth closed condition and the controller 19 can determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth to be zero ( k=0 when mouth is closed).

[0312] Once the controller 19 has determined a mouth closed condition associated with the patient 16 in accordance with query step 326, the controller 19 may perform calculations to determine a tidal volume associated with the patient in accordance with steps 338, 340 and 342 as described below.

[0313] At query step 338, the controller 19 determines whether the patient 16 is currently in an expiration phase of a respiratory cycle. If so, the method 300 proceeds to step 340. If not, the method 300 proceeds to step 342. The controller 19 may determine whether the patient 16 is in an expiration phase of a respiratory cycle in any suitable matter, for example as previously described. In some embodiments, the controller 19 may be operatively configured to receive sensor input from measuring a proportion of CO2 at the patient's mouth or nose, an ECG, or respiratory torso band and determine a respiratory phase (e.g. inspiration, expiration or transition between inspiration and expiration) based on the sensor input. In another embodiment, the controller 19 may receive information directly indicative of a determined respiratory phase from another processor. Other known methods for determining a respiratory phase may be used.

[0314] At step 340, the controller 19 has determined that the patient 16 is in an expiration phase of a respiratory cycle. The controller 19 may then determine a tidal volume (VT) associated with the patient 16 based on an expiratory flow rate of gases at the patient 16 Qp_exp(t) in accordance with equation [3] below: whereinS

Qp_exp(t) is a flow rate of gases at the patient during an expiration phase of a respiratory cycle.

[0315] The integral in equation [3] is calculated across the expiration phase to determine the tidal volume.

[0316] At step 342, the controller 19 has determined that the patient 16 is in an inspiration phase of a respiratory cycle. The controller 19 may then determine a tidal volume (VT) associated with the patient 16 based on an inspiratory flow rate of gases at the patient 16 Qpjns(t) in accordance with equation [4] below: wherein

Qpjns(t) is a flow rate of gases at the patient during an inspiration phase of a respiratory cycle.

[0317] The integral in equation [4] is calculated across the inspiration phase to determine the tidal volume.

[0318] After method steps 336, 340, 342, the method 300 may return to step 310 to measure the first input second input Q (t) and second input Q_m(t) for the next respiratory cycle so as to provide continuous patient monitoring.

[0319] Now reverting to the method 360, the controller 19 may be operatively configured to determine one or more other respiratory parameters. The determination of one or more other respiratory parameters will now be described in further detail below with reference to Figure 10B. Figure 10B illustrates method steps 362 to 398 determining one or more other respiratory parameters based on one or more sample measurements for first input Qj(t) and the second input (Q_m(t)) . The sample measurements for first input Qj(t) and the second input (Q_m(t)) may be taken at any point in time during a respiratory cycle of the patient 16. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0320] Steps 362, 364, 368, 376 and 378 of method 360 as shown in Figure 10B are the same as those previously described with reference to Figure 8B.

[0321] At step 362, the controller 19 receives one or more sample measurements for the first input Q (t), and the second input (Q_m(t)) at any point(s) in time during a respiratory cycle of the patient 16.

[0322] At query step 364, the controller 19 determines whether the second input (Q_m(t)) is greater than the first input (Q (t)). If so, the method 360 proceeds to step 386. If not, the method 360 proceeds to step 368.

[0323] At step 386, the controller 19 determines a mouth closed condition associated with the patient 16. The controller 19 may further determine that the patient is in an expiratory phase of a respiratory cycle. The controller 19 may further determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is zero (K=0).

[0324] At step 388, the controller 19 may determine a value for respiratory parameter patient flow (Qpatient) based on the equation Q_patient(t) = Q_m(t)-Qi(t), wherein patient flow Qpatient is a flow rate of gases specifically attributable to the patient. For example, when the patient's mouth is closed (K=0), if an input flow rate Q (t) delivered by a sealing interface is 70LPM, and measured flow rate Q_m(t) is 90LPM, and the patient is exhaling, Q_patient(t) may be determined as 90LPM-70LPM = +20LPM. A positive Q._patient(t) may indicate that the patient is exhaling. [0325] At query step 368, the controller 19 determines if the sampled value for the first input Qj(t) substantially equals the corresponding sampled value for the second input Q_m(t). If so, the method 360 proceeds to query step 390. If not, the method 368 proceeds to step 376.

[0326] At step 390, the controller 19 may determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is zero (K=0).

[0327] At query step 376, the controller 19 determines whether the sampled value for the second input Q_m(t) is greater than 0. If so, the method 360 proceeds to query step 392. If not, the method 360 proceeds to step 396.

[0328] At step 392, the controller 19 may determine a mouth open condition associated with the patient 16. The controller 19 may further determine a nasal passage not obstructed (e.g. soft palate open) condition.

[0329] At query step 378, the controller 19 determines whether the patient is expiring. This may be determined according to any known suitable manner, for example as described herein. If the controller 19 determines that the patient is expiring, the method 360 proceeds to step 394. If the controller 19 determines that the patient is not expiring, the method 360 does not make any determinations at this stage and returns to step 362.

[0330] At step 394, the controller 19 may determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is greater than zero (K>0) . In addition, the controller 19 may calculate the specific numerical value (k) based on equation [1] above.

[0331] At step 396, the controller 19 may determine a mouth closed condition. In addition, the controller 19 may determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is zero (K=0) .

[0332] At step 398, the controller 19 may determine patient flow (Qpatient) based on the equation Q_patient(t) = Q_m(t)-Qi(t), in a similar manner to step 388. For example, when the patient's mouth is closed (K=0), if an input flow rate Qj(t) delivered by a sealing interface is 70LPM, and measured flow rate Q_m(t) is 55LPM, and the patient is inhaling, Q_patient(t) may be determined as 55LPM-70LPIVI = -15LPM. A negative value for Q_patient(t) may indicate that the patient is inhaling.

[0333] After method steps 388, 390, 394, 396 and 398, the method 360 may return to step 362 to take one or more subsequent sample measurements for the first input Q (t) and second input Q_m(t) so as to provide continuous patient monitoring.

Flow Sensing at Mouth

[0334] As summarised in the flow diagram of Figure 11, a method 500 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, according to another embodiment of the invention includes the general steps of providing 502 a flow of gases to the patient 16 nares via a nonsealing patient interface (e.g. via a non-sealing nasal cannula), and measuring 504 a flow of gases leaving/entering the patient through the patient's mouth, and characterising 506 one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 based on the measured flow of gases leaving/entering the patient through the patient's mouth.

[0335] Accordingly, the execution of the method 500 for characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, by controller 19 according to this embodiment may include the general steps of receiving 502 a first input relating to a flow of gases provided to the patient 16, receiving 504 a second input relating to a flow of gases at the patient's mouth, and characterising 506 one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the second input.

[0336] In some embodiments, the method 500 may characterise one or more flow paths of delivered gases within the respiratory airways of the patient 16, and/or determine one or more other respiratory parameters based on the first input and the second input. [0337] The method 500 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, by controller 19 will be described in further detail below with reference to Figures 13 to 15.

[0338] A patient interface in the form of a mouthpiece assembly 600 is illustrated in Figures 12A and 12B. The mouthpiece assembly 600 includes a mass flow sensor for measuring the flow rate of gases at the patient's mouth to provide the second input for the controller 19. The mouthpiece assembly 600 is configured for sealing engagement with the patient's mouth so that all gases leaving/entering the patient through the patient's mouth passes through the mouthpiece assembly 600. The mass flow sensor integrated with the mouthpiece assembly 600 measures a volumetric flow rate of gases in accordance with the same operating principal as previously described with reference to the flow measurement nasal interface 404 as previously described and illustrated in Figure 7B. Similarly to the flow measurement nasal interface 404, a pressure differential across the restriction 602 in a gas flow passage of the mouthpiece assembly 600 can be used to determine a volumetric flow rate of gases at the mouth of the patient 16. The volumetric flow rate of gases may enter or leave the patient 16 via the mouth.

[0339] In other embodiments, another suitable type of flow rate sensor, such as a thermal mass flow sensor, may be used to determine the flow rate of gases at the patient.

[0340] In this embodiment, the system 10 may provide a non-sealing patient interface such as a non-sealing nasal cannula (not shown) to delivering the flow of gases provided to the patient 16 via the patient's nares 106. In other examples, the system 10 may provide a sealing patient interface, such as the sealing interface 420 as described herein with reference to Figures 7C and 7D.

[0341] The method 500 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 13A. Figure 13A illustrates method steps 510 to 520 for characterising flow paths based on measurements for the second input (Q_m(t)) at least over a full respiratory cycle of the patient 16. [0342] The controller 19 is operatively configured to receive a first input (Qi(t)) indicative of an input flow rate of gases 100 provided via a non-sealing patient interface such as a nonsealing nasal cannula to the patient's nares. The first input (Qj(t)) may be a time-varying flow rate and a constant concentration of O2. Alternatively, the first input (Q (t)) may have a constant flow rate and a time-varying concentration of O2. Alternatively, the first input (Q (t)) may have a constant or time-varying flow rate, and a constant or time-varying concentration of O2.

[0343] The controller 19 is also operatively configured to receive a second input (Q_m(t)) indicative of a measured flow rate of gases at the mouth of the patient 16 provided via the mouthpiece assembly 600. The controller 19 is operatively configured to characterise one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input (Qi(t)) and/or the second input (Q_m(t)). When using a mouthpiece assembly 600 such as the one shown in Figures 12A to 12B, it can be reasonably determined that the mouth of the patient is open. Accordingly, the controller 19 may be automatically configured to determine a mouth open condition associated with the patient 16 when a mouthpiece assembly 600 is used to provide the second input (Q_m(t)).

[0344] At step 510, the controller 19 receives the second input (Q_m(t)). The second input Q_m(t) is measured at least over a full respiratory cycle of the patient 16.

[0345] At query step 512, the controller 19 determines whether the second input (Q_m(t)) is consistently greater than zero over the full respiratory cycle. If so, the method 500 proceeds to step 514. If not, the method proceeds to step 516.

[0346] At step 514, the controller 19 further determines a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases exceeds inspiratory demand, in addition to the mouth open condition previously determined.

[0347] The graph in Figure 14B illustrates a comparison between a first input Qj(t) having a constant flow rate, and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open, the soft palate is open, and the input flow rate of gases exceeds inspiratory demand. As illustrated in Figure 14B, the second input Q_m(t) is consistently greater than zero over a full respiratory cycle. [0348] The graph in Figure 14D illustrates a comparison between a first input Qj(t) having a time-varying flow rate, and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open, the soft palate is open, and the input flow rate of gases exceeds inspiratory demand. As illustrated in Figure 14D, the second input Q_m(t) is also consistently greater than zero over a full respiratory cycle.

[0349] At query step 516, the controller 19 determines whether an integral of the second input Q_m(t) over the respiratory cycle is greater than a threshold integral value. If so, the method 500 proceeds to step 518. If not, the method 500 proceeds to step 520. The threshold integral value may be substantially zero. The integral of the second input Q_m(t) over the respiratory cycle may be calculated as follows: J Qm J Qm(+ve) ~ f I ?m( -ve) I

[0350] wherein

JQm(+ve) is the integral of the second input Q_m(t) over the respiratory cycle when Q_m(t) is a positive value,

JQm(-ve) is the integral of the second input Q_m(t) over the respiratory cycle when Q_m(t) is a negative value.

[0351] At step 518, the controller 19 determines a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases does not meet inspiratory demand, in addition to the mouth open condition previously determined.

[0352] The graph in Figure 14C illustrates a comparison between a first input Qj(t) having a constant flow rate, and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open, the soft palate is open, and the input flow rate of gases does not meet inspiratory demand. As illustrated in Figure 14C, the second input Q_m(t) reduces below zero during the inspiration phase of the respiratory cycle, and an integral of the second input Q_m(t) over the respiratory cycle would be greater than the threshold integral value (e.g. substantially zero).

[0353] The graph in Figure 14E illustrates a comparison between a first input Qj(t) having a time-varying flow rate, and the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open, the soft palate is open, and the input flow rate of gases does not meet inspiratory demand. As illustrated in Figure 14E, the second input Q_m(t) also reduces below zero during the inspiration phase of the respiratory cycle, and an integral of the second input Q_m(t) over the respiratory cycle would also be greater than the threshold integral value (e.g. substantially zero).

[0354] At step 514 or step 518, the controller 19 determines that the second input (Q_m(t)) is consistently greater than zero over the full respiratory cycle (as illustrated in Figures 14B, andl4D), or that the second input (Q_m(t)) is not consistently greater than zero over the full respiratory cycle and the integral of the second input Q_m(t) over the respiratory cycle is greater than the threshold integral value (e.g. substantially zero) (as illustrated in Figures 14C and 14E). In these situations, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition in addition to the mouth open condition previously determined. The controller 19 may then optionally generate output to provide an indication of the determined mouth opened condition and nasal passage not obstructed (e.g. soft palate open) condition.

[0355] At step 520, the controller 19 determines a nasal passage obstructed (e.g. soft palate closed) condition in addition to the mouth open condition previously determined.

[0356] The graph in Figure 14A illustrates a waveform of the second input Q_m(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open and the soft palate is closed. As illustrated in Figure 14A, the second input Q_m(t) reduces below zero during the inspiration phase of a respiratory cycle, and an integral of the second input over the respiratory cycle would be substantially zero.

[0357] After method steps 514, 518, 520, the method 500 may return to step 510 to measure the second input Q_m(t) for the next respiratory cycle so as to provide continuous patient monitoring.

[0358] Another method 530 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 13B. Figure 13B illustrates method steps 532 to 538 for characterising flow paths based on one or more sample measurements of the second input (Qm(t)), for example via mouthpiece assembly 600. The sample measurements for the second input (Qm(t)) may be taken at any point in time during a respiratory cycle of the patient 16. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0359] At step 532, the controller 19 receives one or more sample measurements for the second input (Q_m(t)) as measured at the mouth, for example using mouthpiece assembly 600.

[0360] At query step 534, the controller 19 determines whether the received value for the second input (Q_m(t)) is greater or equal to zero. If so, the method 530 proceeds to step 536. If not, the method 530 may return to step 532.

[0361] At query step 536, the controller 19 determines whether the patient is in an expiratory phase, for example using known detection methods. If so, the method 530 may return to step 532. If not, the method 530 proceeds to step 538.

[0362] At step 538, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition. As illustrated in Figures 14B to 14E, during an inspiratory phase, at least some of the values for the second input (Q_m(t)) is greater or equal to zero, when the nasal passage of the patient is not obstructed. Additional measurements for the second input (Q_m(t)) may be required, for example over at least one respiratory cycle, for the controller 19 to make further determinations.

[0363] A method 700 of determining one or more other respiratory parameters associated with the patient 700 as executed by the controller 19 will now be described in further detail below with reference to Figure 15. The method 700 may employ the same respiratory support system 10 setup as method 500 previously described.

[0364] In accordance with method 700, the controller 19 is operatively configured to receive a first input (Q (t)) indicative of an input flow rate of gases 100 provided via a nonsealing patient interface such as a non-sealing nasal cannula to the patient's nares. The first input (Qj(t)) may be a time-varying flow rate and a constant concentration of O2.

Alternatively, the first input (Q (t)) may have a constant flow rate and a time-varying concentration of O2. [0365] The controller 19 is also operatively configured to receive a second input (Q_m(t)) indicative of a measured flow rate of gases at the mouth of the patient 16 provided via the mouthpiece assembly 600. Accordingly, the controller 19 may be automatically configured to determine a mouth open condition associated with the patient 16 when a mouthpiece assembly 600 is used to provide the second input (Q_m(t)).

[0366] In addition, the controller 19 may be further operatively configured to receive third input (F_m_mouth_co2 (t)) indicative of a measured fraction of CO2 at the mouth of the patient during expiration, and a fourth input (F_m_mouth_o2 (t)) indicative of a measured fraction of O2 at the mouth of the patient during expiration. The third input (F_m_mouth_co2 (t)) may be provided by one or more sensor units located in, on or proximate the mouthpiece assembly 600. Alternatively, one or more gas conduits, sampling lines or sampling probs may be provided and positioned in fluid communication with a flow of gases at the mouth of the patient 16 and coupled with one or more sensor units located elsewhere in the respiratory support system 10. The one or more gas conduits, sampling lines or sampling probs may be integral with, mounted to or mounted adjacent the mouthpiece assembly 600.

[0367] The controller 19 may be further operatively configured to receive a fifth input (F₀(t)) indicative of a measured fraction of O2 in the input flow of gases provided via a nonsealing patient interface to the nares of the patient.

[0368] At step 702, the controller 19 receives the first input (Q (t)) and the second input (Q_m(t)). The first input Q (t) and the second input Q_m(t) are measured at least over a full respiratory cycle of the patient 16. The first input Q (t) may be a known value from the flow source 50 and/or measured via one or more flow sensors in the respiratory support system 10. The second input Q_m(t) may be measured using mouthpiece assembly 600 or any other suitable sensor unit(s) mounted to or adjacent the patient's mouth, or elsewhere in the respiratory support system 10.

[0369] At step 704, the controller 19 determines a mouth open condition associated with the patient 16 as a mouthpiece assembly 600 is used to provide the second input (Q_m(t)). [0370] At query step 706, the controller 19 determines whether a patient is currently in an expiration phase of the respiratory cycle by using any of the aforementioned methods, as an example. If so, the method 700 proceeds to step 708. If not, the method 700 proceeds to query step 707.

[0371] At step 708, the controller 19 has determined that the patient is currently in an expiration phase of the respiratory cycle. If the first input Q (t) is a time-varying flow rate and the fifth input F₀(t) is a constant O2 concentration, the controller 19 may determine an expired fraction of CO2 (F_{E C02}) based on equation [5] below wherein

Qj(t, t+At) is the first input indicative of an input flow rate of gases provided via a non-sealing patient interface to the nares of the patient, Qj(t, t+At) has a time-varying flow rate and a constant O2 concentration, and

Fm_mouth_co2 (t, t+At) is the third input indicative of a measured fraction of CO2 at the mouth of the patient.

[0372] For two samples taken at times (t) and (t+At), At, the time between samples, is sufficiently short such that it can be assumed that during the patient's expiratory phase, Fm_mouth_co2, Qm(t), and the proportion of the gas flow exiting the mouth (k) is approximately constant.

[0373] If the first input Q (t) is a constant flow rate and the fifth input F₀(t) is a timevarying O2 concentration, the controller 19 may determine an expired fraction of O2 (F_{E 0} ) based on equation [6] below, and subsequently an expired fraction of CO2 (F_E co₂) based on equation [7] below: wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface to the nares of the patient, Qj(t) has a constant flow rate and a timevarying constant O2 concentration, and

Fm_mouth_co2 (t) is the third input indicative of a measured fraction of CO2 at the mouth of the patient,

Fm_mouth_o2 (t, t+At) is the fourth input indicative of a measured fraction of O2 at the mouth of the patient, and

F₀(t, t+At) is the fifth input indicative of a measured fraction of O2 in the input flow of gases provided via a non-sealing patient interface to the nares of the patient.

[0374] At step 712, using the expired fraction of CO2 (F_{E C02}) as calculated in equation [5] or [7] above, the controller 19 may determine an expiratory flow rate of gases from the patient (Q_p_exp(t)) based on equation [7] below

[0375] The controller 19 may determine a tidal volume (VT) associated with the patient 16 based on an expiration flow rate of gases at the patient Q_{p e}xp(t) as calculated in equation [8] above using with equation [9] below:

V_T = f Qp_expC dt [9]

Wherein the integral of equation [9] is calculated across the expiration phase to determine the tidal volume.

[0376] At step 714, using the expired fraction of CO2 (F_{E co} ) as calculated in equation

[5] or [7] above, the controller 19 may further determine a numerical value (Xc(t)) indicative of a proportion of delivered gases passing through the mouth based on equation [10] below: wherein

FE_CO2 (t) is an expired fraction of CO2 as calculated in equation [5] or [7] above.

[0377] Alternatively, the numerical value Xc(t) may be calculated using equation [11] below:

[0378] At query step 707, the controller 19 determines whether the second input (Q_m(t)) is greater than zero (Q_m(t) > 0). If so, the method 300 proceeds to step 710. If not, the method 300 proceeds to step 709.

[0379] At step 709, the controller 19 determines that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is substantially zero (K=0).

[0380] In step 710, the controller 19 may have determined that the patient is currently in a transition between an inspiration phase and an expiration phase of the respiratory cycle (e.g. when patient flow is zero), and proceed to calculate a relevant numerical value Xc(t). The controller 19 may calculate the numerical value Xc(t) when patient flow is zero using equation [12] below:

[0381] Generally, the numerical value Xc(t) may indicate a degree of restriction present in any one or more of the flow paths in the patient's airways. This may provide useful information to a clinician to thereby facilitate critical decision making by the clinician, for example to make changes to improve therapy provided to the patient.

[0382] In some embodiments, the numerical value k(t), for example, as determined in equations [1], [10], [11], and [12] may be used to calculate tidal volume of the patient. Various methods of using the numerical value k(t) to calculate tidal volume is discussed in PCT application no. PCT/IB2022/057947 entitled "Method and/or Apparatus for Determining Respiratory Parameters", the entire disclosure of which is incorporated herein by reference.

[0383] As previously described with reference to step 708 of method 700, the controller 19 may determine FE_CO2 (t) the expired fraction of CO2 based on equations [5] and [7] above. Further detail regarding the determination of FE_CO2 (t) is described in PCT application no. PCT/IB2021/052062 entitled "Improvements Relating to Gas Monitoring", US application 62/989081 (from which PCT/IB2021/052062 claims priority), both of which are incorporated herein by reference in their entirety. A summary of the derivation of the equations [5] and [7] will now be described.

[0384] In some embodiments, FE_CO2 (t) may be determined based on an instantaneous measured proportion of expired CO2 at the patient immediately after stopping the flow of gases 100 delivered to the patient at the end of an expiration phase of the patient's respiratory cycle. Determination of the expiration phase may be done by using any one or more of the aforementioned methods. The measured FE_CO2 (t) at this instantaneous moment can be assumed to be accurate and can be used for subsequent respiratory cycles.

[0385] In some embodiments, the flow of gases 100 delivered to the patient may be stopped end of expiration periodically, at selective regular or irregular intervals throughout respiratory support, such that the controller 19 can make repeated and ongoing determinations of FE_CO2 (t) so as to provide continuous patient monitoring. Subsequently determined values for FE_CO2 (t) may supersede previously determined values. In some embodiments, consecutively determined values for FE_CO2 (t) may be compared to identify outliers, which may be disregarded. A measured FE_CO2 (t) can be assumed to be accurate for between 1-10 subsequent respiratory cycles before the FE_CO2 (t) determination is repeated. For this embodiment, the delivered flow of gases may have a constant flow rate and a constant concentration of O2 to provide the required respiratory support. [0386] After method steps 710 and 714, the method 700 may return to step 702 to measure the first input second input Q (t) and second input Q_m(t) for the next respiratory cycle so as to provide continuous patient monitoring.

Finding FE using time-varying flow rate

[0387] FE could be a measure of CO2 fraction (FE COZ) or O2 fraction (FE OZ (t)).

[0388] When the first input Q (t) indicative of an input flow rate of gases provided via a non-sealing patient interface to the nares of the patient has a time-varying flow rate and a constant O2 concentration, FE can be determined using one of the following equations.

[0389] For determining (general case) exhaled gas fraction Fsthe following is used:

[0390] For determining exhaled CO2 fraction Fsthe following is used, which is derived from the above:

[0391] FEcan be re-designated FE COZ where it is CO2 that is being determined.

Finding FE using time-varying O2 fraction

[0392] When the first input Q (t) indicative of an input flow rate of gases provided via a non-sealing patient interface to the nares of the patient has a constant flow rate and a timevarying constant O2 concentration, the following equation can be used to determine the exhaled O2 fraction FE:

[0393] FEcan be re-designated FE_O2 where it is 02 that is being determined. Gas Species Sensing

[0394] As summarised in the flow diagram of Figure 16, a method 800 of characterising flow paths within the patient's 16 respiratory airways according to yet another embodiment of the invention includes the general steps of measuring 802 a gas proportion of one or more gas species in a flow of gases at the mouth and/or nose of the patient, and generating an output to allow characterisation 804 of one or more flow paths of delivered gases within the respiratory airways of the patient based on the measured gas proportion(s).

[0395] Accordingly, the execution of the method 800 for characterising flow paths within the patient's 16 respiratory airways and determining one or more other respiratory parameters by controller 19 according to this embodiment may include the general steps of receiving a first input F_m relating to a gas proportion of one or more gas species in a flow of gases leaving or entering the patient through the mouth and/or nose of the patient, generating an output to allow characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input F_m.

[0396] Various methods of characterising flow paths within the patient's 16 respiratory airways by controller 19 in accordance with this embodiment will be described in further detail below with reference to Figures 17A to 18C.

[0397] In one embodiment, the system 10 may provide a non-sealing patient interface such as a non-sealing nasal cannula (not shown) to deliver the flow of gases provided to the patient 16 via the patient's nares 106. In another embodiment, the system 10 may provide a sealing patient interface such as the patient interface 420 as illustrated in Figures 7C and 7D.

[0398] The first input F_m may be determined by one or more sensor units provided by, mounted to or adjacent the sealing or non-sealing patient interface. Alternatively, or in combination, one or more sensor units for determining the first input F_m may be provided elsewhere in the system 10. In some embodiments, when the first input F_m relates to a gas proportion of one or more gas species in a flow of gases leaving or entering the patient through the patient's nose and a sealing patient interface such as the patient interface 420 is provided, one or more sensor units may be provided in or adjacent the patent interface 420 to sense a flow of gases passing in or out of the exhaust 424 of the patient interface 420. In some embodiments, the one or more sensor units may be embedded in patient interface 420. In some embodiments, the one or more sensor units may be externally mounted and positioned in the flow path of gases passing in or out of the exhaust 424.

CO2 Sensing at the Mouth

Full Respiratory Cycle Measurement

[0399] A method 810 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 17A.

[0400] In accordance with method 810, the controller 19 is operatively configured to receive a first input (Fmcoz) indicative of a fraction of CO2 in a flow of gases at the patient's mouth.

[0401] At step 812, the controller 19 receives the first input (Fmcoz) over at least a full respiratory cycle of the patient 16.

[0402] At query step 814, the controller 19 determines whether the first input (Fmcoz) exceeds a fraction of CO2 in ambient air during a full respiratory cycle. If not, the method 810 proceeds to step 816. If so, the method 814 proceeds to step 818.

[0403] At step 816, the controller 19 determines a mouth closed condition associated with the patient. The graph in Figure 19A illustrates a waveform of the first input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is closed. As illustrated in Figure 19A, the first input (Fmcoz) does not substantially exceed a fraction of CO2 in ambient air (about 0.04%) during the full respiratory cycle.

[0404] At step 818, the controller determines a mouth open condition associated with the patient. The graph in each of the Figures 19B, 19C, 19D are example traces illustrating this flow path characterisation. Each respective Figure 19B, 19C, 19D illustrates a waveform of the first input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open. As illustrated in each of the Figures 19B, 19C, 19D, the first input (Fmcoz) is greater than a fraction of CO2 in ambient air at least during an expiration phase of the respiratory cycle.

[0405] After method steps 816, 818, the method 810 may return to step 812 to measure the first input (Fmcoz) for the next respiratory cycle so as to provide continuous patient monitoring.

Discrete Value Sampling for Instantaneous Determination

[0406] Another method 811 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 17D. The method 811 characterises the flow paths based on one more sampled measurements for first input (Fmcoz) at any time during a respiratory cycle. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0407] In accordance with method 811, the controller 19 is operatively configured to receive a first input (Fmcoz) indicative of a fraction of CO2 in a flow of gases at the patient's mouth.

[0408] At step 813, the controller 19 receives one or more sampled measurements for the first input (Fmcoz) at any time during a respiratory cycle of the patient 16.

[0409] At query step 815, the controller 19 determines whether the first input (Fmcoz) is greater than 0.04% (i.e. the fraction of CO2 in ambient air). If not, the method 811 proceeds to step 817. If so, the method 811 proceeds to step 821.

[0410] At step 817, the controller 19 determines whether an expiration phase is present in the patient's breathing (i.e. whether the patient is expiring). This may be determined according to any known suitable manner, for example as described herein. If so, the method 811 proceeds to step 819. If not, the method 811 may return to step 813.

[0411] At step 819, the controller 19 determines a mouth closed condition associated with the patient. As illustrated in Figure 19A, during an expiration phase, the value for the first input (Fmcoz) is substantially equal to 0.04% (fraction of CO2 in ambient air) (i.e. not greater than 0.04%) when the patient's mouth is closed.

[0412] At step 831, the controller 19 determines a mouth open condition. The controller 19 may further determine that an expiration phase is present in the patient's breathing. As illustrated in Figures 19B, 19C and 19D, during an expiration phase, the value for the first input (Fmcoz) is greater than zero, when the patient's mouth is open and when the patient is exhaling.

[0413] After steps 819 and 831, the method 811 may return to step 813 for continuous monitoring.

O2 Sensing at the Mouth

Full Respiratory Cycle Measurement

[0414] Another method 820 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 17B.

[0415] In accordance with method 820, the controller 19 is operatively configured to receive a first input (Fmoz) indicative of a proportion of O2 in a flow of gases at the mouth of the patient. Moreover, in this embodiment, a fraction O2 in a flow of gases delivered to the patient (Finos) may be about 100%. In other embodiments, the fraction O2 in a flow of gases delivered to the patient (Finos) may be less than 100%. Ideally, the fraction O2 in a flow of gases delivered to the patient (Finos) may be greater than the fraction of O2 in ambient air (21%).

[0416] At step 822, the controller 19 receives the first input (Fmoz) over at least a full respiratory cycle of the patient 16, and may generate a waveform based on the first input (F_mo2) with respect to time.

[0417] At query step 824, the controller 19 determines whether at least one dip is detected in the waveform of the first input (F_mo2) during the full respiratory cycle. If so, the method 820 proceeds to step 826. If not, the method 820 proceeds to step 840. [0418] At step 826, the controller 19 determine a mouth open condition associated with the patient.

[0419] At step 840, the controller 19 determines a mouth closed condition associated with the patient. The graph in Figure 19A illustrates a waveform of the first input (Fmoz) over a full respiratory cycle of the patient 16 when the patient's mouth is closed. As illustrated in Figure 19A, no dips are present in the waveform of the first input (Fmoz) during the full respiratory cycle.

[0420] At query step 828, the controller 19 determines whether at least two dips are detected in the waveform of the first input (F_mo2) during the full respiratory. If so, the method 820 proceeds to step 830. If not, the method 820 proceeds to query step 832.

[0421] At step 830, the controller determines a nasal passage not obstructed (e.g. soft palate open) condition, and that an input flow rate of gases delivered to the patient does not meet inspiratory demand, in addition to the mouth open condition previously determined in step 826. The graph in Figure 19D illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, soft palate is open, and the input flow rate of gases delivered to the patient does not meet inspiratory demand. As illustrated in Figure 19D, two dips are present in the waveform of the first input (F_mo2) during the full respiratory cycle. Each dip corresponds to either an expiration or inspiration phase of the respiratory cycle.

[0422] At query step 832, the controller 19 determines whether the first input (F_mo2) is substantially equal to a proportion O2 in a flow of gases delivered to the patient (Ft_no2) at any point during a full respiratory cycle. If so, the method 820 proceeds to step 834. If not, the method 820 proceeds to step 836.

[0423] At step 834, the controller 19 determines a nasal passage not obstructed (e.g. soft palate open) condition, and that an input flow rate of gases delivered to the patient exceeds inspiratory demand, in addition to the mouth open condition previously determined in step 826. The graph in Figure 19C illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is open, soft palate is open, and the input flow rate of gases delivered to the patient exceeds inspiratory demand. As illustrated in Figure 19C, the first input (Fmoz) is substantially equal to Fi_no2, a fraction O2 in a flow of gases delivered to the patient (e.g. 100%) during an inspiration phase of the full respiratory cycle.

[0424] At step 836, the controller determines a nasal passage obstructed (e.g. soft palate closed) condition in addition to the mouth open condition previously determined in step 826. The graph in Figure 19B illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is open and soft palate is closed. As illustrated in Figure 19B, the first input (F_mo2) does not substantially equal Fi_no2, a fraction of O2 in a flow of gases delivered to the patient (e.g. 100%) at any point during the full respiratory cycle. Moreover, the first input (F_mo2) consistently less than a fraction of O2 in a flow of gases delivered to the patient (e.g. 100%) during the full respiratory cycle.

[0425] After method steps 826, 840, 834, 836, the method 810 may return to step 822 to measure the first input (F_mo2) for the next respiratory cycle so as to provide continuous patient monitoring.

Discrete Value Sampling for Instantaneous Determination

[0426] Another method 821 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 17E. The method 821 characterises the flow paths based on one more sampled measurements for first input (F_mo2) at any time during a respiratory cycle. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0427] In accordance with method 821, the controller 19 is operatively configured to receive a first input (F_mo2) indicative of a proportion of O2 in a flow of gases at the mouth of the patient. Moreover, in this embodiment, a fraction O2 in a flow of gases delivered to the patient (Fj_no2) may be about 100%. In other embodiments, the fraction O2 in a flow of gases delivered to the patient may be less than 100%. Ideally, the fraction O2 in a flow of gases delivered to the patient may be greater than the fraction of O2 in ambient air (21%). [0428] At step 823, the controller 19 receives one or more sampled values for the first input (Fmoz) at any time during a respiratory cycle of the patient 16.

[0429] At query step 825, the controller 19 determines whether the at least one sampled value for the first input (Fmoz) is substantially equal to a fraction O2 in a flow of gases delivered to the patient (Finoz), which may be 100%. If so, the method 821 may return to step 823. If not, the method 821 may proceed to query step 827.

[0430] At query step 827, the controller 19 determines whether the at least one sampled value for the first input (Fmoz) is substantially equal to 21% (the fraction O2 in ambient air). If so, the method 821 may return to step 823. If not, the method 821 may proceed to step 829.

[0431] At step 829, the controller 19 may determine a mouth open condition. In addition, the controller 19 may determine that an expiration phase is present in the patient's breathing. After step 829, the method 821 may return to step 823 for continuous monitoring.

O2 and CO2 Sensing at the Mouth

[0432] Yet another method 850 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 17C.

[0433] In accordance with method 850, the controller 19 is operatively configured to receive a first input (F_mo2) indicative of a proportion of O2 in a flow of gases at the mouth of the patient, and a second input (F_mco2) is indicative of a proportion of CO2 in the flow of gases leaving the patient through the mouth of the patient. In the present embodiment, a fraction O2 in a flow of gases delivered to the patient may be about 100%. In other embodiments, the fraction O2 in a flow of gases delivered to the patient may be less than 100%. Ideally, the fraction O2 in a flow of gases delivered to the patient may be greater than the fraction of O2 in ambient air (21%).

[0434] At step 852, the controller 19 receives the first input (F_mo2) and the second input (F_mco2) at least over a full respiratory cycle of the patient 16. [0435] At query step 854, the controller 19 determines whether the second input (Fmcoz) exceeds the fraction of CO2 in ambient air at any point in time during the full respiratory cycle. If so, the method 850 proceeds to step 858. If not, the method 850 proceeds to step 856.

[0436] At step 856, the controller 19 determines a mouth closed condition associated with the patient. Referring back to Figure 19A, the graph illustrates a waveform of the second input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is closed. As illustrated in Figure 19A, the second input (Fmcoz) does not exceed a fraction of CO2 in ambient air (about 0.04%) during the full respiratory cycle.

[0437] At step 858, the controller 19 determines a mouth open condition associated with the patient. The graph in each of the Figures 19B, 19C, 19D provide example traces illustrating this flow path characterisation. Each respective Figure 19B, 19C, 19D illustrates a waveform of the second input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open. As illustrated in each of the Figures 19B, 19C, 19D, the second input (Fmcoz) is greater than a fraction of CO2 in ambient air at least during an expiration phase of the respiratory cycle.

[0438] At query step 860, the controller 19 determines whether the first input (F_mo2) is substantially equal to the fraction of O2 in a flow of gases provided to the patient (Finos) (e.g. 100%) at any point in time during the respiratory cycle. If so, the method 850 proceeds to step 864. If not, the method 850 proceeds to step 862.

[0439] At step 862, the controller 19 determines a nasal passage obstructed (e.g. soft palate closed) condition in addition to the mouth open condition previously determined in step 858. The graph in Figure 19B illustrates a waveform of the first input (Fmoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open and soft palate is closed. As illustrated in Figure 19B, the first input (Fmoz) does not substantially equal a fraction of O2 in a flow of gases delivered to the patient (Fj_no2) (e.g. 100%) at any point during the full respiratory cycle. Moreover, the first input (F_mo2) consistently below a fraction of O2 in a flow of gases delivered to the patient (Fj_no2) (e.g. 100%) during the full respiratory cycle. Fi_no2 is not shown in Figures 19A to 19D. Typically, the value for Fi_no2 may be known based on operating parameters of the flow source 50. For example, Finoz may be set at 100%, or any other suitable percentage at the flow source 50.

[0440] At step 864, the controller 19 determines a nasal passage not obstructed (e.g. soft palate open) condition in addition to the mouth open condition previously determined in step 858. The graph in each of the Figures 19C and 19D provide example traces illustrating this flow path characterisation. Each respective Figure 19C and 19D illustrates a waveform of the first input (Fmoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open and soft palate is open. As illustrated in each of the Figures 19C and 19D, the first input (F_mo2) substantially equals a fraction of O2 in a flow of gases provided to the patient (e.g. 100%) at certain points in time during the respiratory cycle.

[0441] At query step 866, the controller 19 determines whether the first input (F_mo2) is substantially equal to a fraction of O2 in ambient air (e.g. 21%) at any point in time during an inspiratory phase of the respiratory cycle. If so, the method 850 proceeds to step 870. If not, the method 850 proceeds to step 868.

[0442] In an alternative embodiment, at query step 866, the controller 19 may generate a waveform based on the first input (F_mo2) with respect to time, and determines whether at least two dips are detected in the waveform of the first input (F_mo2) during a full respiratory cycle. If so, the method 850 proceeds to step 870. If not, the method 850 proceeds to step 868.

[0443] At step 868, the controller determines that the input flow rate of gases exceeds inspiratory demand in addition to the mouth open and nasal passage not obstructed (e.g. soft palate open) conditions previously determined in steps 858 and 864. The graph Figure 19C illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is open, soft palate is open and the input flow rate of gases exceeds inspiratory demand. As illustrated in Figure 19C, the first input (F_mo2) is consistently above a fraction of O2 in ambient air (21%) during an inspiratory phase of the respiratory cycle. Moreover, only a single dip can be detected in the waveform of the first input (F_mo2) during a full respiratory cycle. [0444] At step 870, the controller 19 determines that the input flow rate of gases does not meet inspiratory demand in addition to the mouth open and nasal passage not obstructed (e.g. soft palate open) conditions previously determined in steps 858 and 864. The graph Figure 19D illustrates a waveform of the first input (Fmoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open, soft palate is open and the input flow rate of gases does not meet inspiratory demand. As illustrated in Figure 19D, the first input (Fmoz) substantially equals a fraction of O2 in ambient air (21%) during an inspiratory phase of the respiratory cycle. Moreover, at least two dips are detected in the waveform of the first input (Fmoz) during a full respiratory cycle.

[0445] After method steps 856, 858, 862, 864, 870, 868, the method 850 may return to step 852 to measure the first input (F_mo2) and the second input (F_mco2) for the next respiratory cycle so as to provide continuous patient monitoring.

O2 Sensing at the Nose

Full Respiratory Cycle Measurement

[0446] A further method 880 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 18A.

[0447] In accordance with method 880, the controller 19 is operatively configured to receive a first input (F_mo2) indicative of a proportion of O2 in a flow of gases leaving or entering the patient through the nose of the patient.

[0448] At step 882, the controller 19 receives the first input (F_mo2) at least over a full respiratory cycle of the patient 16, and may generate a waveform based on the first input (F_mo2) with respect to time.

[0449] At query step 884, the controller 19 determines whether at least one dip is detected in the waveform of the first input (F_mo2) during a full respiratory cycle. If so, the method 880 proceeds to step 885. If not, the method 880 proceeds to step 892. [0450] At step 892, the controller 19 determines a mouth open condition associated with the patient. The graph in each of the Figures 20A and 20B provide example traces illustrating this flow path characterisation. Each respective Figure 20A and 20B illustrates a waveform of the first input (Fmoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open. As illustrated in each of the Figures 20A and 20B, no dips are detected in the waveform of the first input (Fmoz) during a full respiratory cycle.

[0451] At step 885, the controller 19 determines a mouth closed condition associated with the patient. The graph in each of the Figures 20C and 20D provide example traces illustrating this flow path characterisation. Each respective Figure 20C and 20D illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is closed. As illustrated in each of the Figures 20C and 20D, at least one dip can be detected in the waveform of the first input (F_mo2) during a full respiratory cycle.

[0452] At query step 886, the controller 886 determined whether two dips can be detected in the waveform of the first input (F_mo2) during the full respiratory cycle. If so, the method 880 proceeds to step 888. If not, the method 880 proceeds to step 890.

[0453] At step 888, the controller 19 determines a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases delivered to the patient does not meet inspiratory demand, in addition to the mouth closed condition previously determined in step 885. The graph Figure 20D illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, soft palate is open and the input flow rate of gases delivered to the patient does not meet inspiratory demand. As illustrated in Figure 20D, two dips can be detected in the waveform of the first input (F_mo2) during a full respiratory cycle.

[0454] At step 890, the controller 19 determines a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases delivered to the patient exceeds inspiratory demand, in addition to the mouth closed condition previously determined in step 885. The graph Figure 20C illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, soft palate is open and the input flow rate of gases delivered to the patient exceeds inspiratory demand As illustrated in Figure 20D, a single dip can be detected in the waveform of the first input (Fmoz) during a full respiratory cycle.

[0455] After method steps 885, 892, 890, 888, the method 880 may return to step 882 to measure the first input (Fmoz) for the next respiratory cycle so as to provide continuous patient monitoring.

Discrete Value Sampling for Instantaneous Determination

[0456] A further method 881 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 18D.

[0457] In accordance with method 881, the controller 19 is operatively configured to receive a first input (Fmoz) indicative of a proportion of O2 in a flow of gases leaving or entering the patient through the nose of the patient. Method 881 characterises flow paths based on one or more sampled measurements of first input (F_mo2). The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0458] At step 883, the controller 19 receives one or more sampled values of the first input (F_mo2) at any time during the respiratory cycle of the patient 16.

[0459] At query step 885, the controller 19 determines whether the sampled value of the first input (F_mo2) is substantially equal to a fraction O2 in a flow of gases delivered to the patient (Ft_no2), which may be about 100%. If so, the method 881 may return to step 883. If not, the method 881 proceeds to query step 887.

[0460] At query step 887, the controller 19 determines whether the sampled value of the first input (F_mo2) is substantially equal to 21% (the fraction of O2 in ambient air). If so, the method 881 proceeds to step 889. If not, the method proceeds to step 891.

[0461] At step 889, the controller 19 may determine a mouth closed condition. The controller 19 may further determine an expiration phase is present in the patient's breathing, and/or that the flow of gases 100 delivered to the patient does not meet inspiratory demand. In addition, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition.

[0462] At step 891, the controller may determine a mouth closed condition. The controller 19 may further determine an inspiration phase is present in the patient's breathing. In addition, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition.

[0463] After steps 889 and 891, the method 881 may return to step 883 for continuous monitoring.

CO2 Sensing at the Nose

Full Respiratory Cycle Measurement

[0464] A further method 900 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 18B.

[0465] In accordance with method 900, the controller 19 is operatively configured to receive a first input (Fmcoz) indicative of a proportion of CO2 in a flow of gases leaving the patient through the nose of the patient.

[0466] At step 902, the controller 19 receives the first input (Fmcoz) at least over a full respiratory cycle of the patient 16.

[0467] At query step 904, the controller 19 determines whether the first input (Fmcoz) is greater than a fraction of CO2 in ambient air (0.04%) at any point during a full respiratory cycle. If so, the method 900 proceeds to step 908. If not, the method 900 proceeds to step 906.

[0468] At step 906, the controller 19 determines a mouth open condition. The graph in each of the Figures 20A and 20B provide example traces illustrating this flow path characterisation. Each respective Figure 20A and 20B illustrates a waveform of the first input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open. As illustrated in each of the Figures 20A and 20B, the first input (Fmcoz) substantially equals a proportion of CO2 in ambient air (0.04%) consistently throughout the full respiratory cycle.

[0469] At step 908, the controller determines a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition. The graph in each of the Figures 20C and 20D provide example traces illustrating with this flow path characterisation. Each respective Figure 20C and 20D illustrates a waveform of the first input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is closed and soft palate is open. As illustrated in each of the Figures 20C and 20D, the first input (Fmcoz) is greater than a fraction of CO2 in ambient air (0.04%) during an expiration phase of the respiratory cycle.

[0470] After method steps 906, 908, the method 900 may return to step 902 to measure the first input (Fmcoz) for the next respiratory cycle so as to provide continuous patient monitoring.

Discrete Value Sampling for Instantaneous Determination

[0471] A further method 901 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 18E.

[0472] In accordance with method 901, the controller 19 is operatively configured to receive a first input (Fmcoz) indicative of a proportion of CO2 in a flow of gases leaving the patient through the nose of the patient. The method 901 characterises the flow paths based on one or more sampled values for the first input (Fmcoz). The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0473] At step 903, the controller 19 receives one or more sampled values for the first input (Fmcoz) measured at any time during a respiratory cycle of the patient 16.

[0474] At query step 905, the controller 19 determines whether the at least one sampled value for the first input (Fmcoz) is greater than a fraction of CO2 in ambient air (0.04%). If so, the method 901 proceeds to step 911. If not, the method 901 proceeds to step 907. [0475] At query step 907, the controller 19 determines whether the patient is in an expiration phase of a respiratory cycle. This may be determined according to any known suitable manner, for example as described herein. If so, the method 901 proceeds to step

909. If not, the method 901 may return to step 901.

[0476] At step 909, the controller 19 determines a mouth open condition. The controller 19 may also determine that the patient is exhaling from the mouth.

[0477] At step 911, the controller 19 determines a mouth closed condition. In addition, the controller 19 may determine that the patient is in an expiration phase. Moreover, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition.

[0478] The method 901 may return to step 903 after steps 909 and 911 for continuous monitoring.

O2 and CO 2 Sensing at the Nose

[0479] A further method 910 of characterising flow paths within the patient's 16 respiratory airways as executed by the controller 19 will now be described in further detail below with reference to Figure 18C.

[0480] In accordance with method 910, the controller 19 is operatively configured to receive a first input (Fmoz) indicative of a proportion of O2 in a flow of gases leaving or entering the patient through the nose of the patient, and a second input (Fmcoz) indicative of a proportion of CO2 in the flow of gases leaving the patient through the nose of the patient.

[0481] At step 912, the controller 19 receives the first input (Fmoz) and second input (F_mco2) at least over a full respiratory cycle of the patient 16. The controller 19 may also generate a waveform based on the first input (F_mo2) with respect to time.

[0482] At query step 914, the controller 19 determines whether the second input (F_mco2) is greater than the fraction of CO2 in ambient air (0.04%) at any point in time during a respiratory cycle. If so, the method 900 proceeds to step 918. If not, the method 910 proceeds to step 916. [0483] At step 916, the controller 19 determines a mouth open condition associated with the patient. The graph in each of the Figures 20A and 20B provide example traces illustrating this flow path characterisation. Each respective Figure 20A and 20B illustrates a waveform of the second input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is open. As illustrated in each of the Figures 20A and 20B, the second input (Fmcoz) substantially equals (and does not exceed) the fraction of CO2 in ambient air (0.04%) consistently throughout the full respiratory cycle.

[0484] At step 918, the controller 19 determines a mouth closed condition, and a nasal passage not obstructed (e.g. soft palate open) condition associated with the patient. The graph in each of the Figures 20C and 20D provide example traces illustrating this flow path characterisation. Each respective Figure 20C and 20D illustrates a waveform of the second input (Fmcoz) over a full respiratory cycle of the patient 16 when the patient's mouth is closed and soft palate is open. As illustrated in each of the Figures 20C and 20D, the second input (Fmcoz) is greater than a fraction of CO2 in ambient air (0.04%) during an expiration phase of the respiratory cycle.

[0485] At query step 920, the controller 19 determines whether two dips are detected in the waveform of the first input (Fmoz) during the full respiratory cycle. If so, the method 910 proceeds to step 922. If not, the method 910 proceeds to step 924.

[0486] At step 922, the controller 19 determines that the input flow rate of gases delivered to the patient does not meet inspiratory demand, in addition to the mouth closed condition and nasal passage not obstructed (e.g. soft palate open) condition previously determined in step 918. The graph Figure 20D illustrates a waveform of the first input (Fmoz) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, soft palate is open and the input flow rate of gases delivered to the patient does not meet inspiratory demand. As illustrated in Figure 20D, two dips can be detected in the waveform of the first input (F_mo2) during a full respiratory cycle.

[0487] At step 924, the controller 19 determines that the input flow rate of gases delivered to the patient exceeds inspiratory demand, in addition to the mouth closed condition and nasal passage not obstructed (e.g. soft palate open) condition as previously determined in step 918. The graph Figure 20C illustrates a waveform of the first input (F_mo2) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, soft palate is open, and the input flow rate of gases delivered to the patient exceeds inspiratory demand. As illustrated in Figure 20D, a single dip can be detected in the waveform of the first input (Fmoz) during a full respiratory cycle.

[0488] After method steps 916, 918, 924, 922, the method 910 may return to step 912 to measure the first input (Fmcoz) and the second input (Fmcoz) for the next respiratory cycle so as to provide continuous patient monitoring.

Patient pressure monitoring

[0489] In some embodiments, the controller 19 may characterise the flow paths within a patient's respiratory airways based on an input indicative of a pressure value within the respiratory airways of the patient (referred to herein as patient pressure Ppatient). The input may be a sensor input provided by a pressure sensor mounted in or near the patient's respiratory airways. In one embodiment, the pressure sensor may be coupled to a conduit extending into the nasopharynx to measure patient pressure directly in the respiratory airways. In other examples, one or more pressure sensors may be mounted at any suitable location in the respiratory support system 10. For example, the one or more pressure sensors may be mounted to or proximate the patient interface (which may be sealing or non-sealing), at an inlet of the patient interface, in a gas conduit (e.g. inspiratory limb) coupled to the patient interface, at an outlet of the humidification chamber 52, and/or at the flow source 50 (e.g. at an outlet of the flow generator 50B).

[0490] As such, pressure value indicative of a pressure in the patient's respiratory airways may be measured directly from the patient's respiratory airways, and/or calculated based on one or more of the pressure values obtained from pressure sensors mounted throughout the respiratory support system 10.

[0491] As mentioned, in some embodiments, patient pressure Ppatient may be measured or estimated based on measurements from sensor(s) provided in or proximate the patient interface. In alternative embodiments, patient pressure Ppatient may be calculated based on measured and/or known pressure values elsewhere in the respiratory support system 10 upstream of the patient interface. [0492] Typically, the pressure values in the respiratory support system 10 are higher during a mouth closed condition, when compared to a mouth open condition. As such, by monitoring pressure changes at predetermined locations in the respiratory system 10 (so as to provide an indication of pressure changes at the patient 16) and/or directly at the patient 16, the controller 19 may characterise flow paths within the patient's respiratory airways. As illustrated in Figure 21C, in one example scenario, measured airway pressure at a patient 16 (Ppatient) increases with increasing input flow rate Qi of gases 100 delivered to the patient. Moreover, the measured pressure at the patient 16 (Ppatient) is generally higher across a range of input flow rates Qi when the patient's mouth is closed, when compared with when the patient's mouth is open.

[0493] In accordance with one embodiment, a method of characterising flow paths within a patient's respiratory airways, as executed by the controller 19 may include receiving a first input relating to a flow of gases 100 provided to the patient 16, and receiving a second input indicative of a pressure (Ppatient) in the patient's respiratory airways, characterising one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input and/or the second input.

[0494] Example methods 1000, 1010, 1030, of characterising flow paths within a patient's respiratory airways based on pressure monitoring will be described below with reference to Figures 21A to 23C. It will be appreciated that the specific pressure values provided in these embodiments are examples to illustrate the workings of each method more effectively. In practice, specific pressure values are typically based on the specific respiratory support system 10 used and the resistance to flow (RTF) associated with various points in the corresponding respiratory support system 10.

[0495] A method 1000 of characterising flow paths within a patient's respiratory airways based on pressure monitoring will now be described with reference to Figure 21A.

[0496] At step 1002, a flow rate Qi for a flow of gases 100 delivered to the patient 16 via a patient interface (also referred to herein as input flow rate Qi) may be set to a predetermined value at the flow generator 50B. The predetermined flow rate for the flow of gases 100 delivered to the patient may be transmitted to the controller 19 so as to provide a value for the first input. The controller 19 may therefore receive the first input Qi from the flow generator 50B. Alternatively, the controller 19 may receive the first input Qi from a flow sensor positioned an any suitable location in the respiratory support system 10.

[0497] As mentioned previously, a pressure value from one or more pressure sensors positioned at any suitable location in the respiratory support system 10 and/or at the patient 16 may be transmitted to the controller 19 to determine a pressure Ppatient at the patient 16. In embodiments where the patent pressure Ppatient is not measured directly, an estimation for patient pressure Ppatient may be calculated based on other measured and/or known pressure values in the respiratory support system 10 based on known relationships between Ppatient and the other pressure values in the respiratory support system 10.

[0498] At query step 1004, the controller 19 compares the received patient pressure value Ppatient (second input) with a predetermined threshold pressure value Pthreshoid corresponding to the input flow rate Qi. (E.g. Pthreshoid is a function of Qi.). Typically, the controller determines a mean patient pressure value (P_Patient_mean) of pressure in the patient's respiratory airways over at least one respiratory cycle and compares P patient_mean With Pthreshoid in this step. In other embodiments, a different patient pressure value may be used for comparison with Pthreshoid. For example, a PEEP or an averaged PEEP pressure value may be used for comparison with Pthreshoid. In some embodiments, a predetermined look-up table providing a range of corresponding threshold pressure values Pthreshoid for corresponding range of input flow rates Qi may be stored in the controller 19 memory. An example look-up table is illustrated in Figure 21B. As shown in Figure 21B, when the input flow rate Qi is 20L/min, an average patient pressure Ppatient is 1.75cmH2O when the patient's mouth is open, and 3 cmHzO when the patient's mouth is closed. Based on these two average patient pressure values, the threshold pressure value Pthreshoid may be set at 2.375 cmHzO in the look up table. Similarly, a threshold pressure value Pthreshoid of 3cmH2O, 3.625cmH2O, 4.25cmH2O and 5.5cmH2O may be set for corresponding input flow rates Qi of 30L/min, 40L/min, 50L/min, 70L/min.

[0499] Based on the comparison, if the second input ( Ppatient) is greater than the predetermined threshold Pthreshoid for the corresponding input flow rate Qi based on the look- up table, the method 1000 proceeds to step 1006. If not, the method 1000 proceeds to step

1008.

[0500] At step 1006, the controller 19 determines a mouth closed condition.

[0501] At step 1008, the controller 19 determines a mouth open condition.

[0502] After steps 1006, 1008 the method 1000 may return to step 1002 for continuous monitoring.

[0503] Another method 1010 of characterising flow paths within a patient's respiratory airways based on pressure monitoring will now be described with reference to Figure 22A.

[0504] At step 1012, an initial input flow rate Qi(initiai) (first input) and patient pressure Ppatient (second input) may be obtained in a similar manner as described previously with reference to method 1000.

[0505] At step 1014, the input flow rate Qi (first input) may be incrementally adjusted, for example increased from the initial value Qi(initiai) to a maximum flow rate Qi(max), or decreased from the initial value Qi(initiai) to a minimum flow rate Qi(min).

[0506] At step 1016, a plurality of pressure measurements for patient pressure Ppatient may be taken across the range of input flow rates between i(initiai) and i(max) or Qi(initiai) and Qi(min) to correspond with each input flow rate Qi increment within the range. In one embodiment, the controller 19 may determine a mean pressure or mean breath pause pressure P_patient_mean (a Iso referred to herein as the mean patient pressure P patient_mean ) of the values of patient pressure Ppatient corresponding to each input flow rate Qi. In other embodiments, another representative pressure value may be determined per respiratory cycle for each input flow rate Qi.

[0507] At step 1018, the controller 19 determines a rate of change in the mean patient pressure P_patient_mean against the input flow rate Qi. This rate of change may be referred to herein as a gradient AP_patient_mean/AQi. As illustrated in Figure 21C, the gradient AP patient_mean /AQi is lower when the patient's mouth is open when compared with the gradient AP_patient_mean/AQi when the patient's mouth is closed. [0508] At query step 1020, the controller 19 determines whether the gradient

AP patient_mean /AQi is greater than a threshold gradient value. The threshold gradient value may be a predetermined value based on experimental data for a specific respiratory support system 10. In one example as illustrated in Figure 22B, the gradient AP_patient_mean/AQi is 0.025 when the patient's mouth is open, and 0.1 when the patient's mouth is closed. For this example, the threshold gradient may be set at 0.0625. However, it will be understood that a different threshold value between the 0.1 and 0.025 may be used. If the controller 19 determines that the gradient AP_patient_mean/AQi is greater than the threshold gradient, the method 1010 proceeds to step 1022. If not, the method 1010 proceeds to step 1024.

[0509] At step 1022, the controller 19 determines a mouth closed condition.

[0510] At step 1024, the controller 19 determines a mouth open condition.

[0511] After steps 1022, 1024 the method 1010 returns to step 1012 for continuous patient monitoring.

[0512] A further method 1030 of characterising flow paths within a patient's respiratory airways based on pressure monitoring will now be described with reference to Figure 23A.

[0513] At step 1032, the input flow rate Qi (first input) is set to a predetermined value, for examplelOL/min. The input flow rate Qi may be set at the flow generator 50B.

[0514] At step 1034, the controller 19 continuously receives or calculates pressure values indicative of the range of patient pressure P_pressure over at least one respiratory cycle.

[0515] At step 1036, the controller 19 determines a minimum patient pressure value (Pmin) and a maximum patient pressure (Pmax) based on the range of patient pressure values received in step 1034.

[0516] At step 1038, the controller 19 determines a difference between the values for Pmax and Pmin (AP). Figure 23C illustrates changes between the values for Pmax and Pmin (AP) across a patient's respiratory cycles. Line 1052 illustrates changes in patent pressure Ppressure over time when the patient's mouth is closed. Line 1054 illustrates changes in patent pressure Ppressure over time when the patient's mouth is open. [0517] At query step 1040, the controller 19 determines whether the difference between the values for P_max and P_min (AP) (also referred to herein as a pressure differential AP) is greater than a threshold pressure differential value. In one example as illustrated in Figure 23B, AP is O.ScmFhO when the patient's mouth is open, and 2.3 cmFhO when the patient's mouth is closed. In this example, a threshold pressure differential value may be set at lcmPhO. If the controller 19 determines that the difference between the values for P_max and P_min (AP) is greater than a threshold pressure differential value, the method 1030 proceeds to step 1042. If not, the method 1030 proceeds to query step 1044.

[0518] It will be appreciated that the pressure differential AP may be determined using any suitable pressure reference values for P_patient. For example, instead of using Pmax and Pmin as the pressure reference values, a mean patient pressure value indicative of a mean pressure value in the patient's respiratory airways per respiratory cycle P_patient_mean may be used in conjunction with either Pmax or Pmin to determine the pressure differential AP. That is AP may be the difference between Pmax and P_patient_mean, or Pmin and P _Patient_mean-

[0519] At step 1042, the controller 1046 determines a mouth closed condition.

[0520] At query step 1044, the controller 19 determines whether the difference between the values for Pmax and Pmin (AP) is substantially zero. If so, the method 1030 proceeds to step 1046. If not, the method 1030 proceeds to step 1050.

[0521] At step 1046, the controller 19 determines a nasal passage blocked condition. Referring back to Figure 23C, broken line 1056 illustrates patent pressure P_pressure over time when the patient's nasal passage is blocked. In the particular example shown, Ppressure is roughly 2.2 cmFhO when the patient's nasal passage is blocked.

[0522] At step 1050, the controller 19 determines a mouth open condition.

[0523] After steps 1046 and 1050, the method 1030 may return to step 1032 for continuous patient monitoring. Monitoring of other respiratory related parameters

[0524] In some embodiments, the controller 19 may characterise the flow paths within a patient's respiratory airways based on one or more respiratory parameters including a respiratory rate (Rresp), a ratio of inspiratory time to total breathing time (Ti:T_tot), and a pressure in the patient's respiratory airways (Ppatient). The respiratory parameters (Rresp), (Ti :T_tot), and (Ppatient) may be monitored according to any of the methods as described herein and/or other methods known to a person skilled in the art.

[0525] As such, embodiments provide a computer method of characterising flow paths within a patient's respiratory airways. The method comprising receiving one or more inputs indicative of any one or more of a respiratory rate (Rresp), a ratio of inspiratory time to total breathing time (Ti :T_tot), and a pressure in the patient's respiratory airways (Ppatient), characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the one or more inputs.

[0526] Typically, the patient pressure Ppatient may be a representative or reference patient pressure. For example, the patient pressure Ppatient may relate to a mean pressure in the patient's respiratory airways over at least one respiratory cycle (e.g. P patient_mean), Or a Positive End-Expiratory Pressure (PEEP).

[0527] As illustrated in Figure 24, it may be observed that:

• the pressure in the patient's respiratory airways (Ppatient) is generally higher when the patient's mouth is closed when compared to when the patient's mouth is open,

• the respiratory rate Rresp is generally lower when the patient's mouth is closed when compared to when the patient's mouth is open, and

• the ratio of inspiratory time to total breathing time (Ti :T_tot) is generally lower when the patient's mouth is closed when compared to when the patient's mouth is open.

[0528] In some embodiments, each of these above respiratory parameters P patient, Rresp, Ti:Ttot may be monitored individually and independently to characterise flow paths within the patient's respiratory airways. However, the monitoring of two or more of the respiratory parameters Ppatient, Rresp, Ti:T_tot concurrently may provide a higher level of confidence in the accuracy of the characterisation.

[0529] The controller 19 may obtain values for the respiratory parameters P patient, Rresp, TiiTtot in any suitable manner. For example, patient pressure Ppatient may be obtained in accordance with the various methods as described herein, or according to other known methods. Values for respiratory parameters Rresp, Ti:T_tot may be obtained based on waveforms for patient pressure Ppatient, or in any other suitable manner known to a person skilled in the art.

[0530] Some example methods of characterising flow paths as executed by controller 19 are described below with reference to Figures 25A to 25J.

[0531] A method 2000 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (TiiTtot), and (Ppatient) is illustrated in Figure 25A.

[0532] At step 2002, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0533] At query step 2004, the controller 19 determines whether a notable increase in Ppatient can be observed. If so, the method 2000 proceeds to query step 2006. If not, the method 2000 returns to step 2002 for continuous monitoring.

[0534] At query step 2006, the controller 19 determines whether a notable decrease in both respiratory parameters Rresp, Ti:T_tot can be observed. If so, the method proceeds to step 2008. If not, the method 2000 returns to step 2002 for continuous monitoring.

[0535] At step 2008, the controller 19 determines a mouth closed condition. After step 2008, the method 2000 returns to step 2002 for continuous monitoring. Respiratory parameter monitoring example 2

[0536] Another method 2010 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (Ti:T_tot), and (Ppatient) is illustrated in Figure 25B.

[0537] At step 2012, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0538] At query step 2014, the controller 19 determines whether a notable increase in Ppatient can be observed. If so, the method 2010 proceeds to query step 2016. If not, the method 2010 returns to step 2012 for continuous monitoring.

[0539] At query step 2016, the controller 19 determines whether a notable decrease in both respiratory parameters Rresp, Ti:T_tot can be observed. If so, the method proceeds to step 2018. If not, the method 2010 returns to step 2012 for continuous monitoring.

[0540] At step 2018, the controller 19 determines a mouth open condition. After step 2018, the method 2010 returns to step 2012 for continuous monitoring.

Respiratory parameter monitoring example 3

[0541] Another method 2020 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (TiiTtot), and (Ppatient) is illustrated in Figure 26A.

[0542] At step 2022, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0543] At query step 2024, the controller 19 determines whether a notable decrease in a first one of Rresp or Ti :T_tot can be observed. If so, the method 2020 proceeds to query step 2026. If not, the method 2020 returns to step 2022 for continuous monitoring. [0544] At query step 2026, the controller 19 determines whether a notable increase in Ppatient can be observed, and whether a notable decrease in a second (the other) one of Rresp or Ti:T_tot can be observed. If so, the method proceeds to step 2028. If not, the method 2010 returns to step 2022 for continuous monitoring.

[0545] At step 2028, the controller 19 determines a mouth closed condition. After step 2028, the method 2020 returns to step 2022 for continuous monitoring.

[0546] Another method 2030 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (Ti:T_tot), and (Ppatient) is illustrated in Figure 26B.

[0547] At step 2032, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0548] At query step 2034, the controller 19 determines whether a notable increase in a first one of Rresp or Ti :T_tot can be observed. If so, the method 2030 proceeds to query step 2036. If not, the method 2030 returns to step 2032 for continuous monitoring.

[0549] At query step 2036, the controller 19 determines whether a notable decrease in Ppatient can be observed, and whether a notable increase in a second (the other) one of Rresp or Ti:Ttot can be observed. If so, the method proceeds to step 2038. If not, the method 2030 returns to step 2032 for continuous monitoring.

[0550] At step 2038, the controller 19 determines a mouth open condition. After step 2038, the method 2030 returns to step 2032 for continuous monitoring.

[0551] Another method 2040 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (Ti:Ttot), and (Ppatient) is illustrated in Figure 27A. [0552] At step 2042, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0553] At query step 2044, the controller 19 determines whether a notable decrease in Rresp can be observed. If so, the method 2040 proceeds to query step 2046. If not, the method 2040 returns to step 2042 for continuous monitoring.

[0554] At query step 2046, the controller 19 determines whether a notable increase in Ppatient and a notable decrease in Ti :T_tot can be observed. If so, the method proceeds to step 2048. If not, the method 2030 returns to step 2042 for continuous monitoring.

[0555] At step 2048, the controller 19 determines a mouth closed condition. After step 2048, the method 2040 returns to step 2042 for continuous monitoring.

[0556] Another method 2050 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (TiiTtot), and (Ppatient) is illustrated in Figure 27B.

[0557] At step 2052, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0558] At query step 2054, the controller 19 determines whether a notable increase in Rresp can be observed. If so, the method 2050 proceeds to query step 2056. If not, the method 2050 returns to step 2052 for continuous monitoring.

[0559] At query step 2056, the controller 19 determines whether a notable decrease in

Ppatient and a notable increase in Ti:T_tot can be observed. If so, the method 2050 proceeds to step 2058. If not, the method 2050 returns to step 2052 for continuous monitoring. [0560] At step 2058, the controller 19 determines a mouth open condition. After step 2058, the method 2050 returns to step 2052 for continuous monitoring.

[0561] Another method 2060 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (Ti:T_tot), and (Ppatient) is illustrated in Figure 28A.

[0562] At step 2062, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle.

[0563] At query step 2064, the controller 19 determines whether a notable decrease in TiiTtot can be observed. If so, the method 2060 proceeds to query step 2066. If not, the method 2060 returns to step 2062 for continuous monitoring.

[0564] At query step 2066, the controller 19 determines whether a notable increase in Ppatient and a notable decrease in Rresp can be observed. If so, the method 2060 proceeds to step 2068. If not, the method 2060 returns to step 2062 for continuous monitoring.

[0565] At step 2068, the controller 19 determines a mouth closed condition. After step 2068, the method 2060 returns to step 2062 for continuous monitoring.

[0566] Another method 2070 of characterising flow paths within a patient's respiratory airways, as executed by the controller 19, based on monitoring of respiratory parameters (Rresp), (TiiTtot), and (Ppatient) is illustrated in Figure 28B.

[0567] At step 2072, the controller 19 receives inputs (such as sensor inputs) indicative of respiratory parameters Rresp, Ti:T_tot, and Ppatient. In some embodiments, the controller 19 may continuously sample respiratory parameters Rresp, Ti:T_tot, and Ppatient over at least a full respiratory cycle. [0568] At query step 2074, the controller 19 determines whether a notable decrease in Ti:T_tot can be observed. If so, the method 2070 proceeds to query step 2076. If not, the method 2070 returns to step 2072 for continuous monitoring.

[0569] At query step 2076, the controller 19 determines whether a notable increase in Ppatient and a notable increase in R_resp can be observed. If so, the method 2070 proceeds to step 2078. If not, the method 2070 returns to step 2072 for continuous monitoring.

[0570] At step 2078, the controller 19 determines a mouth open condition. After step 2078, the method 2070 returns to step 2072 for continuous monitoring.

Output generation

[0571] The controller 19 may optionally generate an output to provide one or more indications of one or more flow path characterisations at any time during the execution of any one of the methods of characterising flow paths 300, 303, 360, 500, 530 700, 800, 811, 820, 821, 850, 880, 881, 900, 901, 910, 1000, 1010, 1030, 2000, 2010, 2020, 2030, 2040, 2050. 2060, 2070, 2090 as described herein. It would be understood that at any stage of any one of the methods 300, 303, 360, 500, 530 700, 800, 811, 820, 821, 850, 880, 881, 900, 901, 910, 1000, 1010, 1030, 2000, 2010, 2020, 2030, 2040, 2050. 2060, 2070, 2090 where a flow path characterisation made (e.g. nasal passage obstructed or not obstructed (e.g. soft palate closed/open), and/or a mouth open condition or a mouth closed condition), and/or where one or more other respiratory parameters are determined (e.g. input flow rate exceeds inspiratory demand), one or more outputs may be generated by the controller 19 to provide corresponding indication(s) to a clinician. As it will be appreciated, in any one of the flow path characterisation methods described herein, the controller 19 may make the determinations of any one or more, or all characterisations/calculations possible based on the received input(s), and similarly omit determinations of any one or more characterisations/calculations, for example based on application requirements. For example, where a determination of both a nasal passage obstructed or not obstructed (e.g. soft palate closed/open) condition, and a mouth open or closed condition is possible, the controller 19 may determine the nasal passage obstructed or not obstructed (e.g. soft palate closed/open) condition and omit the determination of a mouth open or closed condition, and vice versa. [0572] Moreover, controller 19 may terminate execution of any one of the methods 300, 303, 360, 500, 530700, 800, 811, 820, 821, 850, 880, 881, 900, 901, 910, 1000, 1010, 1030, 2000, 2010, 2020, 2030, 2040, 2050. 2060, 2070, 2090 at any stage after a required characterisation has been made depending on the specific use case scenario, and optionally return to the start of the corresponding method 300, 303, 360, 500, 530700, 800, 811, 820, 821, 850, 880, 881, 900, 901, 910, 1000, 1010, 1030, 2000, 2010, 2020, 2030, 2040, 2050. 2060, 2070, 2090 for re-execution of the corresponding method for the following respiratory cycle so as to provide continuous patient monitoring over any suitable time period. For example, in method 300, the controller 19 may terminate execution of the method 300 at step 314 after determining a mouth open condition, or at step 326 after determining a mouth closed condition and optionally return to step 310 for continuous monitoring of the next breathing cycle. In one embodiment, the methods 300, 303, 360, 500, 530700, 800, 811, 820, 821, 850, 880, 881, 900, 901, 910, 1000, 1010, 1030, 2000, 2010, 2020, 2030, 2040, 2050. 2060, 2070, 2090 may be executed continuously for each consecutive respiratory cycle. In another embodiment, the methods 300, 303, 360, 500, 530700, 800, 811, 820, 821, 850, 880, 881, 900, 901, 910, 1000, 1010, 1030, 2000, 2010, 2020, 2030, 2040, 2050. 2060, 2070, 2090 may be executed at regular or irregular intervals during a desired monitoring period, for consecutive or non-consecutive respiratory cycles of the patient 16.

[0573] The output may be generated in any suitable format, or a combination of different formats. For example, the controller 19 may generate the output audibly via audio messages or visually via a graphical user interface associated with the controller 19. Displaying the visual indications may include displaying the visual indications textually, numerically and/or graphically.

[0574] Advantageously, information pertaining to the characterisation of flow paths in a patient's respiratory airways can assist the clinician and patient in several ways. For example:

• Information relating to flow paths in the patient's respiratory airways may allow determination of tidal volume, minute volume and other respiratory parameters associated with the patient for patient monitoring, thereby enabling clinicians to make better clinical decisions. • Information relating to flow paths in the patient's respiratory airways may allow the clinician to better understand whether a particular therapy is effective for a patient, by enabling more effective determination of whether the patient has nasal obstruction, or soft palate closure. When appropriate, clinicians can indicate alternative therapy based on the flow path information. For example, in the event that it has been determined that the patient has nasal obstruction, or soft palate closure, the clinician may select orally administering therapy rather than nasally administering therapy.

• Automatic detection and notification of a mouth open/closed condition associated with the patient may benefit patient groups requiring additional airway pressure support. In particular, when the patient's mouth is open, the pressure benefit from nasal high flow respiratory support reduces, and when the patient's mouth is closed the patient pressure during high flow respiratory support is increased. When notified of a mouth closed condition, the clinician may take action to ensure that the mouth stays closed. When notified of a mouth open condition, the clinician may take action to close the mouth of the patient, if an increase in pressure is desired for the patient. Automatic detection is beneficial because it does not require continuous visual monitoring of the patient and allows the clinician to perform other tasks.

• Automatic detection and notification of a mouth closed condition associated with the patient may also be beneficial for determination of the appropriate sampling location for the capnography and other gas species monitoring. For example, when notified of a mouth closed condition, a clinician may instead choose to sample at the nose for capnography if they are not already doing so.

• Embodiments of the invention described herein may provide better approximation of the fraction of O2 that the patient is receiving during inspiration. This enables the clinician to better understand how much O2 from the gases delivered to the patient is reaching the patient due to physiology of that patient. Consequently, the clinician can have a better understanding of the oxygenation of the patient, and effectiveness of respiratory support. For example, this may be provided by knowledge of the nasal passage not obstructed (e.g. soft palate open)/closed condition as if the patients mouth is open but their soft palate is closed then the patient Is likely receiving less than the fraction of O2 of the high flow respiratory support, which the clinician may not be able to conclude from visual observation of the patient.

Interpretation

[0575] This specification, including the claims, is intended to be interpreted as follows:

[0576] Embodiments or examples described in the specification are intended to be illustrative of the invention, without limiting the scope thereof. The invention is capable of being practised with various modifications and additions as will readily occur to those skilled in the art. Accordingly, it is to be understood that the scope of the invention is not to be limited to the exact construction and operation described or illustrated, but only by the following claims.

[0577] Moreover, any feature or element described within one embodiment may be combined with any feature or element as described with respect to any other embodiment detailed within this specification, as deemed suitable and appropriate by those skilled in the art.

[0578] The mere disclosure of a method step or product element in the specification should not be construed as being essential to the invention claimed herein, except where it is either expressly stated to be so or expressly recited in a claim.

[0579] The terms in the claims have the broadest scope of meaning they would have been given by a person of ordinary skill in the art as of the relevant date.

[0580] The terms "a" and "an" mean "one or more", unless expressly specified otherwise.

[0581] Neither the title nor the abstract of the present application is to be taken as limiting in any way as the scope of the claimed invention. [0582] Where the preamble of a claim recites a purpose, benefit or possible use of the claimed invention, it does not limit the claimed invention to having only that purpose, benefit or possible use.

[0583] It should be noted that terms of degree such as "generally", "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of the modified term if this deviation would not negate the meaning of the term it modifies.

[0584] In the specification, including the claims, the term "comprise", and variants of that term such as "comprises" or "comprising", are used to mean "including but not limited to", unless expressly specified otherwise, or unless in the context or usage an exclusive interpretation of the term is required.

[0585] Furthermore, the recitation of any numerical ranges by endpoints herein includes all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term "about" which means a variation up to a certain amount of the number to which reference is being made if the end result is not significantly changed.

[0586] As used herein, the wording "and/or" is intended to represent an inclusive-or. That is, "X and/or Y" is intended to mean X or Y or both, for example. As a further example, "X, Y, and/or Z" is intended to mean X or Y or Z or any combination thereof.

[0587] Throughout the specification, like reference numerals refer to like features described herein. As such, any instance where features or components are indicated with the same references implies a direct correlation to the similar or identical features or components as previously described in the specification.

[0588] The disclosure of any document referred to herein is incorporated by reference into this patent application as part of the present disclosure, but only for purposes of written description and enablement and should in no way be used to limit, define, or otherwise construe any term of the present application where the present application, without such incorporation by reference, would not have failed to provide an ascertainable meaning. Any incorporation by reference does not, in and of itself, constitute any endorsement or ratification of any statement, opinion or argument contained in any incorporated document.

Claims

The claims defining the invention are as follows

1. A method of characterising flow paths within a patient's respiratory airways, the method comprising receiving a first input relating to a flow of gases provided to the patient, and receiving a second input relating to a flow of gases at the mouth or nose of the patient, characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and/or the second input.

2. The method of claim 1, wherein the first input is indicative of an input flow rate of gases provided to the patient, and the second input is indicative of a measured flow rate of gases at the mouth or nose of the patient.

3. The method according any one of the preceding claims, wherein characterising one or more flow paths of delivered gases within the respiratory airways of the patient includes any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed condition, determining a nasal passage obstructed condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

4. The method according to any one of the preceding claims, further including determining one or more respiratory parameters of the patient.

5. The method according to claim 4, wherein the one or more respiratory parameters includes any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

6. The method according to any one of the preceding claims, wherein the step of characterising includes characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

7. The method according to any one of the preceding claims, wherein the first input is indicative of an input flow rate of gases provided via a sealing patient interface to one nostril of the patient, and the second input is indicative of a measured flow rate of gases at the other nostril of the patient, and wherein the step of characterising one or more flow paths includes determining whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

8. The method according to any one of the claims 1 to 6, wherein the first input is indicative of an input flow rate of gases provided via a sealing patient interface, wherein the sealing patient interface includes a flow delivery portion for providing the input flow of gases to the nose of the patient, and the second input is indicative of a measured flow rate of gases passing through an exhaust of the sealing patient interface, and and wherein the step of characterising one or more flow paths includes determining whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

9. The method according to claim 7 or 8, wherein the step of characterising one or more flow paths includes determining a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle. Ill

10. The method of claim 9, further including determining a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based on

Q ( fc(t) = 1 -

Qi(t) wherein

11. The method according to any one of claims 7 to 10, wherein the step of characterising one or more flow paths includes determining either one or both of a mouth open condition, and a nasal passage obstructed condition if the first input substantially equals the second input consistently over a full respiratory cycle.

12. The method according to claim 7 or 8, wherein the step of characterising one or more flow paths further includes determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.

13. The method of claim 12, further including receiving a third input indicative of a measured fraction of CO2 at the nose of the patient, and determining an expired fraction of CO2 (F_E co₂) based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a sealing patient interface to one nostril of the patient, Q_m(t) is the second input indicative of a measured flow rate of gases at the other nostril of the patient, and

14. The method according to claim 12 or 13, including determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

15. The method according to claim 12 or 13, including determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

16. The method according to claim 12 or 13, including determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

17. The method according to any one of claims 1 to 5, wherein the step of characterising includes characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the second input.

18. The method according to any one of claims 1 to 5, wherein the first input is indicative of an input flow rate of gases provided via a nonsealing patient interface to the nares of the patient, and the second input is indicative of a measure flow rate of gases at the mouth of the patient, and wherein the step of characterising one or more flow paths includes determining that the mouth of the patient is open.

19. The method according of claim 17 or 18, including determining either one or both of a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand, if the second input is consistently greater than zero over a full respiratory cycle.

20. The method according to any one of claims 17 or 18, including determining either one or both of a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand, if the second input reduces below zero at any point in time during a respiratory cycle, and an integral of the second input over the respiratory cycle is greater than a threshold integral value.

21. The method according to any one of claim 17 to 20, including determining a nasal passage obstructed condition, if the second input reduces below zero at any point in time during a respiratory cycle, and an integral of the second input over the respiratory cycle is substantially zero.

22. The method of claim 20, wherein the threshold integral value is substantially zero.

23. The method according to any one of claims 18 to 22, further including receiving a third input indicative of a measured fraction of CO2 at the mouth of the patient, and determining an expired fraction of CO2 (F_E co₂) based on FE_CO₂ ( wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a non-sealing patient interface to the nares of the patient, and

24. The method according to any one of claims 18 to 22, further including receiving a third input indicative of a measured fraction of CO2 at the mouth of the patient, and receiving a fourth input indicative of a measured fraction of O2 at the mouth of the patient, receiving a fifth input indicative of a measured fraction of O2 in the input flow of gases wherein the method further includes determining an expired fraction of O2

(F_E o₂), ^{a r|}d then subsequently an expired fraction of CO2 (F_E co₂) based on wherein

F_m mouth 02 (t) is the fourth input indicative of a measured fraction of O2 at the mouth of the patient, and F₀(t) is the fifth input indicative of a measured fraction of O2 in the input flow of gases provided via a non-sealing patient interface to the nares of the patient.

25. The method of claim 23 or 24, further including determining a numerical value (Zc(t)) indicative of a proportion of delivered gases passing through the mouth based on wherein

Qj(t) is the first input indicative of an input flow rate of gases provided via a non-sealing patient interface to the nares of the patient,

FE_CO2 (t) is an expired fraction of CO2.

26. The method according to any one of claims 1 to 8, or 17 to 18, wherein receiving the second input includes receiving one or more discrete values relating to a flow of gases at the mouth or nose of the patient at any time during a respiratory cycle.

27. The method according to any one of claims 1 to 8, or 17 to 18, wherein receiving the first input includes receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

28. The method according to any one of the preceding claims, further including generating an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient.

29. The method according to claim 28, further including displaying the output on a graphical user interface.

30. The method according to claim 29, wherein the step of displaying further includes displaying the output textually, numerically and/or graphically.

31. The method according to any one of the preceding claims, further including providing a flow of gases to the patient via the patient's nares.

32. The method according to claim 31, wherein providing the flow of gases to the patient includes providing a flow of gases to the patient via a sealing patient interface through a single nostril of the patient.

33. The method according to claim 31, wherein providing the flow of gases to the patient includes providing a flow of gases to the patient via a non-sealing patient interface.

34. The method according to any one of the preceding claims, further including sensing the flow of gases provided to the patient to provide the first input.

35. The method according to any one of the preceding claims, further including sensing the flow of gases at the mouth or nose of the patient to provide the second input.

36. The method according to any one of the claims 31, wherein providing the flow of gases to the patient includes providing a flow of gases to the patient via a sealing patient interface through the patient's nose.

37. The method according to claim 36, further including sensing the flow of gases passing through an exhaust of the sealing patient interface to provide the second input.

38. The method of claim 34, wherein sensing the flow of gases provided to the patient includes sensing a flow rate of the flow of gases provided to the patient.

39. The method of claim 38, wherein sensing the flow of gases at the patient includes sensing a flow rate of the flow of gases at the patient.

40. The method according to any one of the preceding claims, further including any one or more of sensing a proportion of CO2 in the flow of gases leaving the patient through the mouth or nose of the patient, and sensing a proportion of O2 in the flow of gases at the mouth or nose of the patient.

41. A non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform the method according to any one of claims 1 to 30.

42. A respiratory support system controller for characterising flow paths within a patient's respiratory airways, the controller being configured to perform the method according to any one of claims 1 to 30.

43. A respiratory support system comprising a controller according to claim 42.

44. The respiratory support system of claim 43, further including a sealing patient interface for delivering the flow of gases provided to the patient.

45. The respiratory support system of claim 44, wherein the sealing patient interface is configured to seal against a first nostril of the patient to deliver the flow of gases to the patient.

46. The respiratory support system of claim 43 or 44, wherein the sealing patient interface is configured to seal against a second nostril of the patient to measure the flow of gases at the patient's nares.

47. The respiratory support system of claim 46, wherein the sealing patient interface includes a nasal interface configured to seal against the second nostril of the patient to measure the flow of gases leaving the patient's nares, and wherein the nasal interface is open to atmosphere such the flow of gases leaving the patient's nares enters the atmosphere via the nasal interface.

48. The respiratory support system of any one of claims 44 to 47, wherein the sealing patient interface includes one or more output sensors for measuring the flow of gases leaving the patient's nares.

49. The respiratory support system of claim 48, wherein the one or more output sensors includes a differential pressure sensor.

50. The respiratory support system of claim 44, wherein the sealing patient interface includes a flow delivery portion configured to seal against a first nostril of the patient to deliver the flow of gases to the patient, and a flow measurement portion configured to seal against a second nostril of the patient to measure the flow of gases leaving the second nostril of patient.

51. The respiratory support system of claim 50, wherein the flow measurement portion is open to atmosphere such that the flow of gases leaving the second nostril enters the atmosphere via the flow measurement portion.

52. The respiratory support system of claim 50, further including a differential pressure sensor integrated with the flow measurement portion of the sealing patient interface.

53. The respiratory support system of claim 43, further including a non-sealing patient interface for delivering the flow of gases provided to the patient.

54. The respiratory support system of claim 53, wherein the non-sealing patient interface is configured to deliver the flow of gases to the patient via the patient's nares.

55. The respiratory support system of claim 53 or 54, further including a mouthpiece assembly configured to measure the flow of gases leaving the patient's mouth.

56. The respiratory support system of claim 55, wherein the mouthpiece assembly includes one or more output flow sensors for measuring the flow of gases leaving the patient's mouth.

57. The respiratory support system of claim 56, wherein the one or more sensors includes a differential pressure sensor.

58. The respiratory support system of any one of claims 43 to 57, further including one or more input flow sensors for measuring the flow of gases provided to the patient.

59. The respiratory support system of claim 58, wherein the input flow sensors are configured to measure a flow rate of the flow of gases provided to the patient.

60. The respiratory support system of any one of claims 43 to 59, further including any one or more of a flow generator for generating the flow of gases provided to the patient, and a humidifier for humidifying the flow of gases provided to the patient.

61. A computer method of characterising flow paths within respiratory airways, the method comprising receiving a first input relating to a flow of gases provided to a gas delivery patient interface, and receiving, from one or more sensor units, a second input relating to a flow of gases at or proximate the gas delivery patient interface, characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways based on the first input and/or the second input.

62. The method of claim 61, wherein the first input is indicative of an input flow rate of gases provided to the gas delivery patient interface, and the second input is indicative of a measured flow rate of gases at or proximate the gas delivery patient interface.

63. The method of claim 62, wherein the second input is indicative of a measured flow rate of gases passing through an exhaust of the gas delivery patient interface.

64. The method according to any one claims 61 to 63, wherein characterising one or more flow paths of delivered gases within the respiratory airways includes any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed condition, determining a nasal passage obstructed condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

65. The method according to any one of claims 61 to 64, further including determining one or more respiratory parameters.

66. The method according to claim 65, wherein the one or more respiratory parameters includes any one or more of: input flow rate of gases exceeding inspiratory demand, input flow rate of gases not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

67. A computer method of characterising flow paths within a patient's respiratory airways, the method comprising receiving a first input indicative of an input flow rate of gases provided a gas delivery patient interface, and receiving a second input indicative of a pressure in the patient's respiratory airways, characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and/or the second input.

68. The computer method of claim 67, further including characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a comparison between the second input and a predetermined threshold pressure value.

69. The computer method of claim 68, wherein the predetermined threshold pressure value is based on the first input, and a different predetermined threshold pressure value corresponds to a different input flow rate for the first input.

70. The computer method of claim 67, further including receiving a varying first input in which the input flow rate of gases is increasing or decreasing at a constant rate from a predetermined minimum value to a predetermined maximum value, determining a pressure gradient based on a change in the value of the second input corresponding to the variation in the first input when the input flow rate of gases is varied between the predetermined minimum value to the predetermined maximum value, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a comparison between the pressure gradient and a predetermined threshold gradient.

71. The computer method of claim 70, wherein the predetermined threshold gradient is a value between a mouth open pressure gradient based on a change in the value of the second input corresponding to the variation in the first input when the input flow rate of gases is varied between the predetermined minimum value to the predetermined maximum value during a mouth open condition, and a mouth closed pressure gradient based on a change in the value of the second input corresponding to the variation in the first input when the input flow rate of gases is varied between the predetermined minimum value to the predetermined maximum value during a mouth closed condition.

72. The computer method of claim 67, further including determining a pressure differential between a two reference values for pressure in the patient's respiratory airways, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a comparison between the pressure differential and a predetermined threshold pressure differential value.

73. The computer method of 72, wherein the two reference values include a maximum pressure in the patient's respiratory airways (Pmax) and a minimum pressure in the patient's respiratory airways (Pmin).

74. The computer method of claim 73, wherein the predetermined threshold differential value is a value between a mouth open pressure differential based on a difference between P_max and P_min during a mouth open condition, and a mouth closed pressure differential based on a difference between P_max and P_min during a mouth closed condition.

75. A computer method of any one of claims 67 to 74, wherein characterising one or more flow paths of delivered gases includes determining any one or more of a mouth open condition, a mouth closed condition, and a nasal passage obstructed condition.

76. A computer method of characterising flow paths within a patient's respiratory airways, the method comprising receiving one or more inputs indicative of any one or more of a respiratory rate, a ratio of inspiratory time to total breathing time, and a pressure in the patient's respiratory airways, and characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways of the patient based on the one or more inputs.

77. The computer method of 76, wherein characterising includes characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on a notable increase or decrease in the one or more inputs.

78. The computer method of 76 or 77, wherein characterising one or more flow paths of delivered gases includes determining any one or more of a mouth open condition, and a mouth closed condition.

79. A non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform the method according to any one of claims 67 to 78.