CN107715271B

CN107715271B - Humidification of respiratory gases

Info

Publication number: CN107715271B
Application number: CN201711113667.2A
Authority: CN
Inventors: 伊恩·马尔科姆·史密斯; 安德鲁·罗德里希·巴特; 纳坦·约翰·罗; 亚历山大·威尔
Original assignee: Resmed Pty Ltd
Current assignee: Resmed Pty Ltd
Priority date: 2008-03-06
Filing date: 2009-03-06
Publication date: 2023-10-24
Anticipated expiration: 2029-03-06
Also published as: CN107715271A; CN101537221A; CN113425974A

Abstract

A humidifier for a respiratory device for delivering a humidified flow of breathable gas to a patient, comprising: a humidifier chamber configured to store supply water for humidifying the flow of breathable gas and including a first heating element configured to heat the supply water; a humidity sensor for detecting the humidity of ambient air and generating a signal indicative of the ambient humidity; a first temperature sensor for detecting the temperature of ambient air and generating a signal indicative of the ambient temperature; a controller configured to control the first heating element to provide a predetermined absolute humidity, a predetermined temperature, and/or a predetermined relative humidity to the flow of breathable gas; and a second temperature sensor for detecting a temperature of the first heating element, wherein the controller is configured to control the duty cycle of the first heating element such that the controller is configured to apply a 100% duty cycle to the first heating element when the first heating element temperature is below the threshold temperature and to apply a fixed duty cycle to the first heating element when the first heating element temperature is above the threshold temperature.

Description

Humidification of respiratory gases

The present application is a divisional application of patent application No. 2014105431009, application No. 2009, 3 months and 6 days, and the application name "humidification of respiratory gas", and the patent application No. 2014105431009 is a divisional application of patent application No. 200910138707.8, application No. 2009, 3 months and 6 days, and the application name "humidification of respiratory gas".

Cross Reference to Related Applications

The present application claims priority from the following U.S. patent applications, application 61/034,318 on the date of application 3, month 6, 2008, application 61/042,112 on the date of application 4, month 3, 2008, and application 084,366 on the date of application 29, month 7, 2008, each of which is incorporated herein by reference in its entirety.

Technical Field

The present application relates to systems and methods for controlling the humidity of breathable gas for use in ventilation systems of various forms of respiratory devices, including invasive or non-invasive ventilation, continuous Positive Airway Pressure (CPAP), bi-level therapy and treatment of Sleep Disordered Breathing (SDB) conditions, such as Obstructive Sleep Apnea (OSA), and various other respiratory disorders and diseases.

Background

Respiratory devices typically have the ability to vary the humidity of the breathable gas in order to reduce patient airway dryness and patient discomfort and related complications due to airway dryness. The use of a humidifier placed between the flow generator and the patient mask may produce humidified gases that minimize drying of the nasal mucosa and increase patient airway comfort. In cooler environments, it is often more comfortable to apply warm air to the facial area within and around the mask than to apply cool air.

There are many types of humidifiers, although the most convenient form is one that is integral with or configured to be attached to the associated breathing apparatus. While passive humidifiers may provide some relief, heated humidifiers are often required to provide sufficient humidity and temperature to the air so that the patient will feel comfortable. Humidifiers typically include a water tub having a capacity of hundreds of milliliters, a heating element for heating water in the water tub, a controller to enable variation in humidity level, a gas inlet to receive gas from a gas flow generator, and a gas outlet adapted to be connected to a patient conduit that delivers humidified gas to a patient mask.

Typically, the heating element is integrated with a heating plate, which is located below and in thermal contact with the water tub.

The humidified air may cool down along the path from the humidifier to the patient's conduit, causing a "rain-out" phenomenon, or condensation to form on the inner walls of the conduit. To overcome the above problems, a known solution is to additionally heat the gas supplied to the patient by a heating wire circuit inserted into a patient conduit that supplies humidified gas from a humidifier to the patient mask. Such a system is set forth on page 97 in a respiratory care device of the molar ratio (Mosby's Respiratory Care Equipment) (seventh edition). Alternatively, the heating wire circuit may be positioned on a wall of the patient catheter. Such a system is described in U.S. Pat. No. 6,918,389.

In a hospital environment, the ambient temperature within the hospital is controlled by an air conditioner to be typically maintained at, for example, about 23 ℃. The temperature required for the humidified gas provided by the breathing apparatus can be controlled within fixed temperature parameters. The controlled temperature parameters ensure that the humidified gases are maintained at a temperature above their dew point to prevent condensation within the breathing conduit.

Humidifiers are also often used in home care environments for treatment of, for example, respiratory and sleep apnea disorders. Humidification systems for use with home CPAP devices suffer from a number of limitations due to cost constraints and the need to make the system compact and lightweight, with comfortable hoses and masks, and the need for low complexity in facing untrained users. In systems used in clinic or in hospitals, this limitation is not generally a problem, and temperature and humidity sensors may be placed in the airway and adjacent the patient's nose to provide direct feedback to the control system, thus ensuring good results. The cost, size, weight and discomfort of the above-described systems are not yet suitable for domestic use. The home user can therefore rely only on experience obtained through experimentation and error to obtain acceptable results.

In a home care environment, the range of ambient and gas temperatures may far exceed that of a hospital environment. In home care, the ambient temperature may be as low as 10 ℃ at night, while the daytime temperature may exceed 20 ℃. Such temperature variations cause the above-described commonly used control techniques to suffer from disadvantages. With humidifiers of the type described above, condensation (or rain wash) on the breathing conduit will occur, at least to some extent. The degree of condensation depends greatly on the ambient temperature, the greater the difference between ambient temperature and gas temperature, the greater the degree of condensation. The formation of large amounts of water within the breathing tube causes considerable inconvenience to the patient and may accelerate the cooling of the gas to eventually clog the tubing, create a water flow sound in the tube, or water may be sprayed into the patient. Furthermore, patients may also feel uncomfortable when the temperature of the breathing gas being delivered varies greatly from the ambient temperature. Excessive condensation can also result in inefficient use of the water within the humidifier chamber of the humidifier.

Monitoring ambient temperature and air flow has emerged as inputs to control algorithms that predict corrective heating inputs to track the user's initial settings in an attempt to address these problems associated with the home respiratory system. However, this approach still relies on the user determining an appropriate setting for each use case.

Disclosure of Invention

One solution is a respiratory device that addresses patient complaints regarding insufficient warmth of breathable gas delivered to a patient interface, nasal dryness, and/or excessive condensation within an air delivery hose, etc.

Another aspect is a respiratory device that allows a patient to select the temperature and/or relative humidity and/or absolute humidity of breathable gas delivered to a patient interface. In an alternative and/or additional approach, the absolute humidity of the humidifier outlet is controlled to adjust to a predetermined relative humidity delivered to the patient.

Yet another aspect is a respiratory device that provides a humidified flow of air at a predetermined temperature and/or humidity to a patient interface while accounting for changes in ambient temperature and/or humidity.

Yet another aspect is a respiratory device that provides a humidified flow of breathable gas at a predetermined temperature and/or humidity to a patient interface while accounting for varying the flow of the humidified flow of breathable gas.

Yet another aspect relates to a respiratory device that includes a flow generator and a humidifier that are connectable together to allow communication and/or indication of connection and/or removal between the flow generator and the humidifier.

Yet another aspect relates to a respiratory device that includes a humidifier and a heated air delivery tube, hose, or conduit. The duty cycle of the heating element of the humidifier and the duty cycle of the heating tube may be controlled such that the duty cycle synthesized from the above two duty cycles does not exceed 100%, and/or such that the heating element and the heating tube of the humidifier do not receive power at the same time. In an alternative and/or additional approach, the heating element and/or heating tube of the humidifier regulates the temperature rather than applying a fixed duty cycle. In another alternative and/or additional arrangement, the temperature of the humidified flow of breathable gas within the air delivery tube is measured downstream of the humidifier to adjust to a predetermined relative humidity delivered to the patient.

Another aspect relates to a flow generator that detects the connection of a conduit, such as a heating tube, and/or the size of the connecting tube, and/or the separation of the conduit from a humidifier.

Yet another aspect relates to an airflow generator that includes constants, such as control parameters, stored in a table, for example, that can be inserted three-linearly to control a humidifier and/or a heating tube.

A further aspect relates to a respiratory device and controller thereof, the device including a humidifier and a non-heating tube connectable to the humidifier.

Yet another aspect relates to a humidifier controller that converts a voltage measured on, for example, a thermistor, to a temperature.

A further aspect relates to a respiratory device that includes a flow generator and a humidifier that are connectable and can transmit data and/or instructions over a serial communication link.

According to one exemplary embodiment, a humidifier for a respiratory device for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store a supply of water to humidify the flow of breathable gas, the humidifier chamber including a first heating element configured to heat the supply of water; a relative humidity sensor that detects ambient air relative humidity and generates a signal indicative of ambient relative humidity; a first temperature sensor that detects an ambient air temperature and generates a signal indicative of the ambient temperature; and a controller configured to determine an absolute humidity of the ambient air from signals generated by the relative humidity sensor and the first temperature sensor to control the first heating element to provide a predetermined absolute humidity to the flow of breathable gas.

According to another exemplary embodiment, a humidifier for a respiratory device for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store supply water for humidifying the flow of breathable gas, the humidifier chamber including a first heating element configured to heat the supply water; an absolute humidity sensor that detects an absolute humidity of the humidified airflow and generates a signal indicative of the absolute humidity; and a controller configured to receive the signal generated by the absolute humidity sensor and to control the first heating element to provide a predetermined absolute humidity to the flow of breathable gas.

According to another exemplary embodiment, a humidifier for a respiratory device for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store supply water for humidifying the flow of breathable gas, the humidifier chamber including a first heating element configured to heat the supply water; a relative humidity sensor that detects the relative humidity of ambient air and generates a signal indicative of the ambient relative humidity; a first temperature sensor that detects an ambient air temperature and generates a signal indicative of the ambient temperature; and a controller configured to determine an absolute humidity of the ambient air from signals generated by the relative humidity sensor and the first temperature sensor and to control the first heating element to provide a predetermined absolute humidity, a predetermined temperature, and/or a predetermined relative humidity to the flow of breathable gas.

According to another exemplary embodiment, a humidifier for a respiratory device for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store supply water for humidifying the flow of breathable gas, the humidifier chamber including a first heating element configured to heat the supply water; an absolute humidity sensor that detects an absolute humidity of ambient air and generates a signal indicative of the absolute humidity of the ambient air; a first temperature sensor that detects an ambient air temperature and generates a signal indicative of the ambient temperature; and a controller configured to control the first heating element to provide a predetermined absolute humidity, a predetermined temperature, and/or a predetermined relative humidity to the flow of breathable gas.

According to yet another exemplary embodiment, a respiratory device for providing a humidified flow of breathable gas to a patient includes a flow generator and a humidifier as described above that generate a flow of breathable gas.

According to yet another exemplary embodiment, a method of humidifying a flow of breathable gas provided to a patient, the method comprises determining an absolute humidity of ambient air used to form the flow of breathable gas; and controlling a temperature of the supply water for humidifying the flow of breathable gas to provide a predetermined absolute humidity corresponding to the predetermined temperature and the predetermined relative humidity of the flow of gas delivered to the patient.

According to another exemplary embodiment, a humidifier for a respiratory apparatus for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store supply water to humidify the flow of breathable gas. The humidifier further includes an inlet configured to receive the flow of breathable gas, a first heating element configured to heat the supply water, and an outlet configured to deliver a humidified flow of breathable gas to the conduit. A controller configured to control the power supplied to the heating element to provide a predetermined absolute humidity to the humidified flow of breathable gas. The controller continuously adjusts the power supplied to the first heating element to continuously provide a predetermined absolute humidity in response to changes in the ambient conditions and/or the flow of breathable gas.

According to another exemplary embodiment, a method of humidifying a flow of breathable gas provided to a patient, the method includes determining an absolute humidity of ambient air used to form the flow of breathable gas; and controlling a temperature of the supply water for humidifying the flow of breathable gas to provide a predetermined absolute humidity to the humidified flow. Controlling the temperature of the supply water includes adjusting the temperature of the supply water to continuously provide the predetermined absolute humidity in response to changes in the ambient air temperature, the relative humidity of the ambient air, the absolute humidity of the ambient air, and/or the breathable gas flow.

According to yet another exemplary embodiment, a method of humidifying a flow of breathable gas provided to a patient, the method comprises detecting a temperature of the humidified flow at one end of a transfer hose configured to be connected to a patient interface; generating a signal indicative of the temperature of the humidified gas flow at the end of the transfer hose; and controlling the transmission hose heating element in response to the signal.

According to yet another exemplary embodiment, a humidifier of a respiratory device for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store supply water for humidifying the flow of breathable gas, the humidifier chamber including a first heating element configured to heat the supply water; an absolute humidity sensor that detects an absolute humidity of ambient air and generates a signal indicative of the absolute humidity; and a controller configured to receive the signal generated by the absolute humidity sensor and to control the first heating element to provide a predetermined absolute humidity to the flow of breathable gas. The predetermined absolute humidity corresponds to the predetermined temperature and the predetermined relative humidity.

Drawings

Exemplary embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a flow generator and a humidifier according to an example embodiment;

FIG. 2 schematically illustrates the airflow generator of FIG. 1;

fig. 3 schematically illustrates the humidifier of fig. 1;

FIG. 4 schematically illustrates an air delivery hose and a patient interface according to an exemplary embodiment;

FIG. 5 schematically illustrates the air transfer hose of FIG. 4 at an opposite end of the air transfer hose, and an electronic connection connectable thereto;

FIG. 6 schematically illustrates a breathing apparatus, according to an example embodiment;

fig. 7 schematically illustrates the relationship between the absolute humidity of the ambient air and the temperature of the ambient air in the case of water vapor saturation;

FIG. 8 schematically illustrates a relationship between water temperature within a humidifier tub and ambient air temperature without a change in ambient absolute humidity, according to one example;

fig. 9 schematically illustrates the relationship between the temperature of water within the humidifier tub and the temperature of the flow of gas delivered to the patient interface and the ambient temperature without a change in the absolute humidity of the environment, according to one comparative example;

FIG. 10 schematically illustrates changes in water temperature in response to changes in temperature of a transmission gas, according to another example;

FIG. 11 schematically illustrates changes in water temperature in response to changes in ambient humidity without changes in ambient temperature, according to another example;

FIG. 12 schematically illustrates changes in water temperature in response to changes in average gas flow through a humidifier, according to one example;

fig. 13 schematically illustrates a humidifier according to another example embodiment;

FIG. 14 schematically illustrates an exemplary setting of a compensation humidifier by controlling a heating element of the humidifier in response to changes in ambient environment and/or average flow during use of the breathing apparatus, according to one exemplary embodiment;

FIG. 15 schematically illustrates control of a respiratory device according to an exemplary embodiment;

FIG. 16 schematically illustrates control of a respiratory device according to another exemplary embodiment;

FIG. 17 schematically illustrates control of a respiratory device according to another exemplary embodiment; and

fig. 18 schematically illustrates control of a breathing apparatus according to another example embodiment.

Detailed Description

Humidification theory

Humidity represents the water vapor content of the air. Humidity is typically measured in two ways: absolute Humidity (AH) and phaseFor Humidity (RH). Absolute humidity is the actual content of water recorded per volume weight. Absolute humidity is typically measured in grams per cubic meter (g/cm) ³ ) Or milligrams per liter (mg/L).

Relative humidity is the percentage of the actual water vapor content in a gas relative to the capacity to carry water at any given temperature. The ability of air to carry water vapor increases with increasing air temperature. For air with a stable absolute humidity, the relative humidity will decrease as the air temperature increases. Conversely, for water saturated air (i.e., 100% RH), if the temperature drops, too much water will condense from the air.

The air breathed by the person is heated and humidified by the airway to a temperature of 37 ℃ and 100% rh. At this temperature, the absolute humidity was approximately 44mg/L.

Humidification for CPAP

ISO8185 requires a medical humidifier that can provide a minimum of 10mg/LAH and a minimum of 33mg/L when the patient's upper airway is bypassed. These minimum requirements are calculated by inputting dry air. These minimum requirements are also only suitable for short-term use. These minimum requirements are often insufficient to minimize symptoms of nasal and upper airway dryness. Under normal operating conditions, the patient or clinician should be able to set the temperature of the air transmitted from the environment to the patient interface to approximately 37 ℃. If the breathing apparatus is not provided with an alarm system or indicator, the temperature of the air delivered to the patient interface should not exceed 41 ℃ under normal and single default conditions (single faultcondition) according to parts 51.61-51.8 of ISO 8185.

For CPAP, an upper limit level of 44mg/L may not be appropriate because the patient's upper airway is not bypassed. On the other hand, the lower level of 10mg/L may be too low for CPAP, especially for patients with oral leaks.

Although no study was made to determine the minimum level of humidity required for CPAP, wiest et alSleepVolume 24, phase 4, pages 435-440, 2001) found that the average absolute humidity of 10mg/L was too low for north american and european patients when CPAP therapy was not used with a humidifier system. This study has tested two typesHumidifiers, both of which provide an absolute humidity of at least 23 mg/L. Wiest et al concluded that levels of 10mg/L AH required to exceed ISO8185 for CPAP, but could be lower than 23mg/L AH used in the study. Applicants have determined that an absolute humidity of about 20-30mg/L provides adequate patient comfort.

Humidifier and airflow generator

Referring to fig. 1, a breathing apparatus 1 may include a flow generator 2 and a humidifier 4 configured to be connectable to each other. Such a flow generator and humidifier combination is disclosed, for example, in WO 2004/112873 A1, the entire contents of which are incorporated herein by reference. The humidifier may also be a humidifier as disclosed in U.S. patent 6,935,337, the entire contents of which are incorporated herein by reference.

The airflow generator 2 may include an ON/OFF switch 6 and a display 8, such as an LCD, to display the operational status of the airflow generator and other parameters as will be described in detail below. The airflow generator 2 may also include a button 14 for controlling the operation of the airflow generator 2, for example to select various programs stored in a memory of a controller configured to control the operation of the airflow generator. The push button 14 may also be used to set various parameters, such as the flow rate of the flow generator 2.

Humidifier 4 may include a control knob 10 for controlling the power to a heating element (not shown) and setting the temperature at the patient interface, as will be explained in detail below. Alternatively, control of the humidifier 4 may be combined with the flow generator 2. Humidifier 4 may also include an outlet 12, with outlet 12 configured to be connected to an air delivery hose or conduit for delivering a humidified flow of breathable gas to a patient via a patient interface.

Referring to fig. 2, the airflow generator 2 may be formed of, for example, a rigid plastic material molded into two parts, a top case 16 and a bottom case 18. The top and bottom shells 16, 18 define an engagement surface 20 of the flow generator 2, the engagement surface 20 being configured to engage the humidifier 4 when the humidifier 4 is connected to the flow generator 2. The engagement surface 20 includes a pair of slots 22 configured to engage corresponding tabs (not shown) provided on the humidifier 4 by which the flow generator 2 and humidifier 4 are connected together. An electrical connector 24 may be provided for providing electrical power to the humidifier 4 when the flow generator 2 is connected to the humidifier 4. The flow generator 2 may further comprise an outlet 26 configured to deliver a flow of breathable gas to the humidifier 4 when the flow generator 2 is connected to the humidifier 4.

As shown in fig. 3, humidifier 4 may include a hinged cover 28. Humidifier 4 may also include a tub as disclosed in U.S. patent application publication 2008/0302361 A1, the entire contents of which are incorporated herein by reference. Humidifier 4 may also include a heating element controllable by control knob 10. Such heating elements are disclosed, for example, in WO 2008/148154 A1, the entire contents of which are incorporated herein by reference. The humidifier may also be heated as disclosed in WO 2004/112873 A1.

While the flow generator and humidifier have been disclosed as separate devices that can be connected as a unitary device, it should be appreciated that the flow generator and humidifier can be provided as separate elements that cannot be connected together to present a unitary appearance, as disclosed in U.S. patent 6,338,473, the entire contents of which are incorporated herein by reference.

Air transmission hose

Referring to fig. 4, an air delivery conduit or hose 30 is connected to a patient interface 32, such as a mask, for delivering a humidified flow of breathable gas from the humidifier outlet to the patient. It should be appreciated that patient interface 32 may be a nasal mask, full face mask, nasal cannula, nasal pillow, or nasal prongs, or a combination of a cushion and nasal prongs or nasal pillows configured to surround the patient's mouth.

The air delivery hose 30 may be a heating tube, as disclosed in U.S. patent application publication 2008/0105257 A1, the entire contents of which are incorporated herein by reference. The air delivery hose 30 may be formed of a tube 30a made of, for example, a thermoplastic elastomer (TPE) and a spiral rib 30b made of, for example, very low density polyethylene. The wires 30c, 30d, 30e may be supported by the spiral rib 30b so as to be in contact with the outer surface of the tube 30 a. Wires 30c, 30d, 30e may be used to heat tube 30a and send signals to or receive signals from controllers in flow generator 2 and/or humidifier 4. It should be appreciated that the air transfer hose 30 may include two wires, and that signals may be multiplexed through the two wires. It should also be appreciated that the air delivery hose 30 may include a heating element, for example in the form of a heating strip or wire, as disclosed in WO2009/015410 A1, the entire contents of which are incorporated herein by reference.

The air delivery hose 30 includes a connector or cuff (cuff) 34 configured to connect the air delivery hose 30 to the patient interface 32. Patient interface envelope 34 may include a temperature sensor, such as a thermistor as disclosed in U.S. patent application publication 2008/0105257 A1, the entire contents of which are incorporated herein by reference, for detecting the temperature of the humidified flow of breathable gas delivered to patient interface 32.

Referring to fig. 5, the air delivery hose 30 includes a connector or cuff 36 configured to connect to the outlet 12 of the humidifier. The humidifier jacket 36 includes an end 36a configured to be connected to the outlet 12, and a grip portion 36b to provide a better grip for the connection and disconnection of the air delivery hose 30 to the outlet 12.

The humidifier jacket 36 may be connected to a controller of the humidifier 4 by an electrical connection 38. The electrical connection 38 provides electrical power to the wires 30c, 30d, 30e of the air delivery hose 30 to heat the air delivery hose 30 along its length from the humidifier 4 to the patient interface 32.

Respiratory system

Referring to fig. 6, a respiratory system according to an exemplary embodiment of the present invention may include an airflow generator 2, a humidifier 4, and an air delivery hose 30. The patient interface 32 may be connected to the air delivery hose 30.

The airflow generator 2 may include a controller 40. The airflow generator controller 40 may include, for example, a programmable logic controller or an Application Specific Integrated Circuit (ASIC). The flow generator 2 may further include a flow sensor 42 to detect the volume (e.g., liters/minute) of the flow of breathable gas generated by the flow generator 2 and delivered to the inlet of the humidifier 4. It should be appreciated that the flow may be estimated from the motor speed of the airflow generator rather than being provided directly by the flow sensor.

Humidifier 4 may include a controller 44. Humidifier controller 44 may be, for example, a programmable logic controller or an ASIC. It should be appreciated that where the flow generator and humidifier may be connected together to form a unitary device, the flow generator controller and humidifier controller may be a single controller configured to control both devices. Alternatively, the controller 40 of the flow generator may include all the functions of the controller 44, and when the humidifier is connected, the functions relating to humidification may be obtained from the controller 40.

Humidifier 4 further includes a heating element 46 configured to heat the supply water stored within humidifier 4. The heating element 46 may be, for example, a plate disposed below the humidifier tub. It should also be appreciated that the heating element 46 may comprise a heating element as disclosed in WO 2009/015410 A1, the entire contents of which are incorporated herein by reference. A temperature sensor 48 may be provided to detect the temperature of the water heated by the heating element 46. It should be appreciated that the water temperature may be determined by detecting or measuring the temperature of the heating element 46, such as by directly detecting the temperature of the heating element using a temperature sensor.

Humidifier 4 may further include a temperature sensor 50 for detecting the temperature of the ambient air and a relative humidity sensor 52 for detecting the relative humidity of the ambient air. The humidifier may optionally also include an ambient pressure sensor 53. It should be appreciated that the sensors 50, 52, 53 need not be provided on the humidifier, but may be provided separately, for example, from a location that includes the sensors and is connectable to the humidifier 4. It should also be appreciated that the sensors 50, 52, 53 may be provided to the flow generator 2 rather than the humidifier 4, or that ambient temperature, relative humidity, and ambient pressure may be provided to the flow generator 2 from a location rather than the humidifier 4. It should further be appreciated that the flow sensor 42 may be provided to the humidifier 4 instead of the flow generator 2, or that the flow sensor 42 may be provided to the humidifier 4 in addition to the flow generator 2. It should be further appreciated that the ambient temperature, relative humidity and pressure sensors 50, 52, 53 may be replaced by absolute humidity sensors configured to detect the absolute humidity of the humidified airflow, for example at the humidifier outlet, and generate a signal indicative of the absolute humidity.

The air delivery hose 30 includes a temperature sensor 54, such as a thermistor, within the patient interface envelope 34. It should be appreciated that temperature sensor 54 may be disposed within patient interface 32 rather than within cuff 34. The temperature detected by the temperature sensor 54 may be transmitted as a signal through the air delivery hose 30 to the humidifier controller 44.

The system of fig. 6 may be configured to allow the patient to select and set the temperature of the humidified flow of breathable gas delivered to patient interface 32. For example, the system may be configured to allow a user to set the temperature of the humidified gas flow at the patient interface 32 using the control knob 10 on the humidifier 4 or the control button 14 of the gas flow generator 2. For example, the system may be configured to allow the patient or clinician to select a temperature of the humidified gas flow of the patient interface ranging from about 10 ℃ to about 37 ℃, such as about 26 ℃ to about 28 ℃. The system may be configured to prevent the patient or clinician from selecting and/or setting a temperature value below ambient temperature. The ambient temperature may be displayed on the display 8 of the flow generator or information may be displayed when the selected temperature is below ambient temperature that alerts the patient or clinician that the temperature is not valid. Alternatively, the system may allow for selection of an automatic or default temperature setting, such as 27 ℃.

The system of fig. 6 may also be configured to provide an absolute humidity to patient interface 32 of between about 10-44mg/L, for example. The relative humidity of the patient interface gas flow may be controlled to be less than 100% RH, such as about 70-90% RH, for example about 80% RH as a default value. Maintaining the relative humidity of the air flow in the air delivery hose 30 below 100% RH helps prevent rain out (rain out) phenomena within the air delivery hose between the humidifier 4 and the patient interface 32. The system may also be configured to provide an automatic or default relative humidity, such as 80%, at the patient interface 32. The system may also be configured to allow the patient or clinician to set the relative humidity of the airflow of patient interface 32. Although the relative humidity of the air flow of patient interface 32 may be detected directly by a humidity sensor disposed within the patient interface, because the humidity sensor is easily misread or because of condensation failure, a more reliable method may be to detect the relative humidity and temperature of the ambient air or incoming air flow and calculate the absolute humidity.

The system of fig. 6 can compensate over a wide range of ambient temperature and humidity variations. The temperature of the airflow at patient interface 32 may be directly detected, for example, by temperature sensor 54. The relative humidity of the patient interface airflow may be calculated from the following data: 1) Moisture content of ambient air (from its ambient temperature and relative humidity); 2) The temperature of the water within the humidifier tub (e.g., as detected by temperature sensor 48); and/or 3) flow through the humidifier tub (e.g., as detected by flow sensor 42 of the flow generator). It should be appreciated that relative humidity may also be detected directly, for example, by a relative humidity sensor in the end of tube 30 or patient interface 32.

The temperature of the air flow at patient interface 32 may be controlled by controlling the power supplied to air delivery hose 30, such as by controlling the current to the wires of hose 30. The relative humidity of the air flow at patient interface 32 may be controlled by the temperature of the water within the humidifier tub, with ambient temperature, ambient relative humidity, and flow as input parameters.

Humidity control

Referring to fig. 7, the saturated absolute humidity of ambient air may be calculated from the humidity characteristics of water vapor. See, e.g., Y. Qian Jier, maxwell-HillHeat transfer(Heat TransferY.Cengel, mcGraw-Hill), 1998 (pages 958-59, table A9). Or may be used, for example, as part of a new application, see,industrial water and steam thermodynamic property calculation formula IAPWS issued in 1997(Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam)International Association of Water and Water vapor Properties (The International Association for the Properties of Water and Steam), 9 months 1997, germany, el lan Gen (Erlangen). As shown in FIG. 7, absolute humidity is expressed in mg/L, i.e., the mass of water vapor per unit volume of air, with the conditions being ambient temperature and standard (sea level) pressure, or ATPS. The absolute humidity AHa of the ambient air may be defined by any equation or look-up table corresponding to the humidity characteristics of the water vapor. For example, the following quadratic equation:

AHa＝RHa·(K ₁ -K ₂ ·Ta+K ₃ ·Ta ² ) (1),

Where RHA is the relative humidity of the ambient air, ta is the temperature of the ambient air, K ₁ 、K ₂ And K ₃ Is a coefficient. For example coefficient K ₁ 、K ₂ 、K ₃ The data may be determined empirically, such as by curve fitting. For example K ₁ Can be equal to 7.264, K ₂ Can be equal to 0.09276, K ₃ May be equal to 0.02931.

The target temperature Tm of the airflow at the mask and the target relative humidity RHm at the mask also define the absolute humidity AHm at the mask, as defined by the following equation:

AHm＝RHm·(K ₁ -K ₂ ·Tm+K ₃ ·Tm ² ) (2),

wherein, for example, K ₁ ＝7.264，K ₂ = 0.09276, and K ₃ ＝0.02931。

The difference Δah between the ambient absolute humidity AHa determined by equation (1) and the absolute humidity AHm at the mask determined by equation (2) is equal to the absolute humidity added to the flow of air by the humidifier 4. Of course, if AHm < AHa, humidification is not required. Given the flow rate F (L/min) through the humidifier tub, a derived equation describing the humidifier response may be used to determine the evaporation rate E of water. For example, in one embodiment, the evaporation rate may be determined from the change in flow and absolute humidity by the following equation:

E(g/hr)＝ΔAH(mg/L)·F(L/min)·(60min/hr)·0.001g/mg (3)。

as an example, for CPAP treatment using the system of FIG. 6, 10cm H is supplied ₂ O pressure to treat OSA patients. At 10cm H ₂ At O, the flow F is approximately 35L/min, which is equal to the mask ventilation flow at the predetermined pressure. In the case where the ambient temperature Ta is 20 ℃ and the ambient relative humidity RHa is 50%, the absolute humidity AHa of the air entering the humidifier is equal to 0.5·17.3=10.4 mg/L according to equation (1). Assuming that the patient selects a mask temperature Tm of 25 ℃ and the relative humidity is selected or automatedSet to 90%, the absolute humidity at the mask AHm is equal to 0.9·23.3=20.9 mg/L according to equation (2). The absolute humidity Δah to which the humidifier is added is equal to 20.9-10.4=10.5 mg/L. The evaporation rate E of the humidifier was thus determined to be e= (10.5 mg/L) · (35L/min) · (60 min/hr) · (0.001 g/mg) =22 g/hr) according to equation (3).

The rate of evaporation of water is related to its vapor pressure, which is driven by the temperature of the liquid water. In general, the saturated steam pressure is almost doubled every 10℃increase in water temperature. See, e.g., Y. Qian Jier, maxwell-HillHeat transfer1998 (pages 958-59, table A9). Or may be used, for example, as part of a new application, see,industrial water and steam thermodynamic property calculation formula published in 1997 IAPWSInternational Association of Water and Water vapor Properties, month 9 1997, germany, el lan Gen. In addition, the ambient air water content, i.e. the vapor pressure of the water already present in the ambient air, as determined by the ambient air temperature and the ambient air relative humidity, reduces the evaporation rate. The atmospheric pressure of ambient air also affects the evaporation rate, but not so much as the water temperature increases and the ambient air water content affects the evaporation rate. The lower the atmospheric pressure, the faster the water vapor evaporates, e.g., the higher the altitude the faster the water vapor evaporates.

The water temperature in the humidifier tub may be closed-loop controlled. Alternatively, the temperature of the heating element under water may also be closed loop controlled. Other parameters may be used for the set point of the closed loop control. For example, the evaporation rate E is limited by the saturation of the water vapor in the humidifier tub. The saturation of the water vapor in the tub is dependent on the temperature of the air flowing from the flow generator to the humidifier. The flow generator may increase the temperature of the air flowing into the humidifier, for example, by heat generated from the flow generator motor.

The theoretical relationship between evaporation rate and water temperature also assumes that the water vapor in the humidifier tub is effectively removed from the tub. However, the airflow pattern through the tub may bypass some of the water vapor generating containers. In addition, the agitating action of the air flow can uniformly transfer heat through the water in the tub.

The theoretical relationship also assumes that the evaporation rate is largely unaffected by the air temperature in the drum until saturation is reached. In practice, for example, reducing the ambient air temperature to cool the water surface may reduce the evaporation rate. There is a temperature gradient from the heating tub through the water and the inner wall of the tub to the outside of the humidifier. These temperature gradients may lead to inconsistencies between the detected temperature and the temperature of the actual water surface. Even without the use of a temperature sensor, the temperature gradient may cause inconsistencies in the water temperature and the water surface temperature. The evaporation rate is related to the temperature of the water surface.

Example 1-control of mask temperature to adjust for ambient temperature changes

In this example, the system of fig. 6 is configured to deliver saturated air to the mask at 30 ℃. The patient or clinician may use the control button 14 of the flow generator 2 and/or the control knob 10 of the humidifier 4 to set the temperature. For example, during a sleeping period in the bedroom of the patient when the patient is sleeping, the absolute humidity of the ambient air is 10mg/L, which does not change with the temperature change of the ambient air. As shown in table 1, the water temperature in the humidifier tub was adjusted to obtain 100% rh of air at the patient interface.

TABLE 1

As shown in fig. 8, the result of the closed loop control is that the water temperature in the tub must be controlled at about the same set point regardless of the ambient temperature of the indoor air. Thus, if the temperature at the mask is adjusted, the system need not respond to changes in the temperature of the ambient air.

Comparative example 1-adjustment of ambient temperature changes without control of mask temperature

In this comparative example, the temperature of the air delivered to the patient interface is not under the feedback control loop. Instead, the system is controlled such that the water temperature in the humidifier tub is controlled to track the ambient air temperature, as shown in table 2 and fig. 9.

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TABLE 2

In this comparative example, although the relative humidity of the air delivered to the patient interface is 100% RH for all temperatures, the absolute humidity of the air delivered to the patient interface varies greatly, for example from 12.5mg/L to 30.7mg/L. The temperature of the air flow delivered to the patient interface also varies according to the ambient air temperature. The patient is unable to raise the temperature of the airflow delivered to the patient interface.

Example 2-adjustment of set temperature variation at patient interface

Referring to tables 3 and 10, in this example, the system of FIG. 6 is controlled to deliver saturated air and the temperature of the patient interface is changed.

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TABLE 3 Table 3

The ambient air was assumed to be 22.5℃and the absolute humidity was 10mg/L and the relative humidity was 50%. It is assumed that the ambient air conditions have not changed. The water temperature in the humidifier tub was adjusted to achieve 100% rh at the patient interface, as shown in table 3. As the desired temperature at the patient interface increases, the water temperature within the humidifier tub also increases to maintain the saturation of the air being delivered. As shown in fig. 10, the relationship between the temperature of the water within the humidifier tub and the temperature of the air delivered is approximately linear, e.g., the water temperature increases by approximately 1.55 ℃ for each 1 ℃ increase in the temperature of the air delivered to the patient interface. The temperature at the mask can be controlled automatically and independently by controlling the power applied to the heating tube.

In this example, the temperature of the air delivered to the patient interface may be selected by the patient or clinician using, for example, the control buttons 14 of the flow generator 2. The patient may select a mode of operation that allows for adjustment of the air temperature at the patient interface. The heating element of the humidifier is then automatically controlled to increase the water temperature within the humidifier tub as the desired air temperature at the patient interface increases, and correspondingly decrease the water temperature as the desired air temperature decreases.

Example 3-Conditioning of environmental humidity changes

The system of fig. 6 may also be configured to adjust for changes in ambient humidity. For example, signals from the sensors 50, 52 may be provided to the controllers 40 and/or 44 to periodically or continuously calculate the absolute humidity of the ambient air. As shown in table 4 and fig. 11, the temperature of the ambient air remains relatively constant, e.g., 22.5 ℃, but the absolute humidity varies throughout the patient's sleep cycle.

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TABLE 4 Table 4

The water temperature in the humidifier tub is adjusted to achieve 100% rh at the patient interface. The temperature at the patient interface is kept constant, for example 30 ℃. The water temperature within the humidifier tub decreases as the absolute and relative humidity of the ambient air increases. The system allows the temperature of the saturated air delivered to the patient interface to remain relatively constant in this manner of control, as shown in table 4.

Example 4-modulation of air flow variation

Referring to tables 5 and 12, the ambient temperature and relative humidity and the temperature of the air delivered to the patient interface are constant.

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TABLE 5

The flow through the humidifier may be, for example, by Raschedd (ResMed)The control algorithm. The flow may also be adjusted, for example, in response to an air leak at the patient interface. As shown in table 5 and fig. 12, the water temperature within the humidifier tub increases with increasing air flow to maintain saturation at the patient interface.

The respiratory system may be controlled according to each of examples 1-4 or a combination thereof. The data provided in tables 1 and 3-5 and figures 8 and 10-12 may be stored in, for example, the memory of controllers 40 and/or 44. The controllers 40, 44 may be programmed to access data in the stored information. The controller 40, 44 may also be programmed to insert and/or extrapolate data in the stored information. The set points of the heating elements that provide the appropriate evaporation rates for each combination of ambient temperature and humidity, flow rate, and predetermined output humidity may be empirically determined so that the design is expressed and then introduced into the controller, for example stored as a table in memory or as a set of equations.

While the relative humidity of the air delivered to the patient interface is described as 100% in each of examples 1-4, it should be appreciated that the relative humidity of the air delivered to the patient interface may be about 50% -100%, such as about 70% -90%, or as another example about 80%, or other value selected by the patient or clinician.

Humidifier control

Humidifier 4 may provide a user selectable setting that will provide for automatic delivery of a predetermined moisture content at mask 32. An example value for the moisture content of the air being transported is determined taking into account the situation that leads to undesired condensation in the pipe 30. For a user with normal upper respiratory tract, the desired physiological result is to condition the air to approximately normal nasal inhalation. For example, ambient air may be 20℃and 25% RH (4 mg/L AH). The air may be heated and humidified to a condition equal to about 20 c and 80% rh (14 mg/L AH). Therefore a moisture content of 14mg/L corresponding to an absolute humidity of 80% RH at 20℃can be chosen as an example value. The humidifier will be set to have an output of 14 mg/L. A difference of 10mg/L will be added by the humidifier. It should be appreciated that while this value may be selected as an example value and the humidifier may be configured to include user settings that automatically provide this value, the example value may be determined or modified based on clinical recommendations, the humidifier may be configured or reconfigured to include user settings that automatically provide clinically determined moisture content. For example, the patient or clinician may select an absolute humidity in the range of about 10mg/L to 25mg/L, such as 20mg/L, which generally corresponds to a relative humidity of between 70% -80% at a temperature of about 27-28 ℃.

In the case of a breathing apparatus provided with a heating tube, the actual temperature of the air delivered in the CPAP system may be higher than room temperature, typically about 29 ℃. Thus, the RH value at the nose will be 50% lower than the same absolute humidity value. In the case of a breathing apparatus without a heating tube, the humidified air in the tube is cooled to one to two degrees above the surrounding environment. Without the heating tube, air would be delivered at approximately 22℃and 70% RH (14 mg/L AH).

At an optimal setting, such as 10mg/L, condensation in the breathing tube will not occur unless the room temperature drops sufficiently to cause the temperature of the delivered air to drop below its dew point (which is about 16 ℃ for 29 ℃ air typically delivered to a mask having a CPAP apparatus operating in a 22 ℃ environment). The continued decrease in room temperature results in a decrease in the temperature of the delivered air, followed by an automatic decrease in the temperature of the heater to reduce the delivered moisture content below an optimal level, thereby avoiding condensation, but still reaching the optimal level as close as possible.

Referring to fig. 13, a humidifier 4 according to another exemplary embodiment of the invention includes a control knob 10, the control knob 10 including a setting indicator 10a. The humidifier 4 includes an indicator 11 that indicates a plurality of set values. The indicator 11a may represent an automatic setting that provides a default moisture content. For example, as shown in fig. 13, the automatic setting indicator 11a may include, for example, t. It should be appreciated that any other indicator may be used, for example, indicator 11a may include the word "best" or "automatic". The remaining indicators 11 may include numbers, such as 1-4 and 6-9, that allow the user to increase and decrease the humidity transmitted. The indicator may also be configured to display a value of relative humidity or absolute humidity and temperature, such as percentage RH. To select the default setting, the user aligns the setting indicator 10a of the control knob 10 with the automatic setting indicator 11a. To adjust the humidity setting, the user aligns the setting indicator 10a with any other indicator 11, or any position between any other indicators 11. For example, to decrease the humidity setting, the user may align the setting indicator 10a with any of the numbers 1-4, or any setting therebetween. Likewise, to increase the humidity setting, the user may align the setting indicator 10a with any of the numbers 6-9, or any setting therebetween. It should also be appreciated that the controller may not be a knob, for example, the controller may include a display such as an LCD to display the settings, and one or more buttons to allow selection of the settings or change of the displayed settings.

As shown in fig. 14, when an automatic default moisture content is selected, i.e., the setting indicator 10a is aimed at the indicator 11a, the humidifier 4 may be controlled such that the heating element 46 of the humidifier 4 is continuously adjusted to maintain the moisture content of the flow of breathable gas at a predetermined default level, such as 14mg/L. As discussed in more detail below, the heating element 46 is continually adjusted to maintain the moisture content of the air stream as close as possible to a default level while still preventing condensation or rain-out (rain-out) within the tube 30.

During sleep of the user, the heating element 46 is controlled to maintain a default moisture content, such as 14mg/L, in response to changes in indoor conditions, such as ambient temperature, ambient relative humidity, and/or ambient pressure, and/or in response to changes in airflow. For example, at the beginning of a patient's sleep phase (state 1), the indoor conditions may be a first temperature, a first relative humidity, and a first pressure. The flow generator may generate a first flow Q1 of air during a sleep onset phase of the patient. When the patient selects the automatic setting by aligning the setting indicator 10a with the indicator 11a, the heating element 46 of the humidifier 4 is controlled to provide a default moisture content, for example 14mg/L.

Although state 1 is described above as corresponding to a period of time during which the patient begins to sleep, it should be appreciated that state 1 may correspond to a time from the start of the respiratory system, such as a warm-up time that accounts for the effects of the temperature of the transmission air being above ambient temperature.

During the patient sleep process, the indoor state, including ambient temperature, ambient relative humidity, and/or pressure may change to the second state (state 2). The airflow Q2 generated by the airflow generator may also vary during the patient's sleep process. The heating element 46 of the humidifier 4 is controlled such that the water content of the air flow is a default value, e.g. 14mg/L, in state 2, regardless of the change in indoor conditions.

Likewise, if the patient selects a different setting at start-up (state 1), for example by aligning the setting indicator 10a with indicator "9" (increasing the water content from a default value) or indicator "1" (decreasing the water content from a default value), the heating element 46 is controlled so that the water content delivered to the mask in state 2 is the same as the water content delivered to the mask in state 1. The entire range of water content settings centered around the default setting is continuously and automatically readjusted in response to the monitored values of ambient temperature, ambient relative humidity, ambient pressure and the delivered air flow, such that the selected setting is always adjusted to deliver the selected water content.

First embodiment of humidity control

Referring to fig. 15, a control system for a respiratory device and method thereof are illustrated. At S1, a temperature Tm of the air flow delivered to the mask is determined. At S2, the relative humidity RHm of the air flow delivered to the mask is determined. It will be appreciated that the user may set the temperature Tm and the relative humidity RHm by, for example, using a button 14 on the airflow generator 2. Alternatively, the user may select the moisture content, i.e., the absolute humidity of the air flow delivered to the mask, by adjusting the control knob 10 of the humidifier. For example, the user may align the setting indicator 10a with the default setting indicator 11a. The default moisture content may be a nominal moisture content, such as 14mg/L, or a clinically determined moisture content. The user may also select other non-default moisture content values by aligning the setting indicator 10a with another indicator 11. In the case of a humidifier integrally connected with the flow generator, the breathing apparatus may be configured to allow a user to select the water content using the push button 14 on the flow generator 2 or the control knob 10 of the humidifier 4. In the event that the user selects a moisture content, the temperature Tm and relative humidity RHm transmitted to the mask correspond to the selected moisture content setting.

The heating element of the air delivery tube 30 is controlled to provide a predetermined temperature Tm to the air flow delivered to the mask. Temperature sensor 54 at the end of air delivery hose 30 the actual temperature of the air flow at the end of the air delivery hose 30 is detected. The difference Δtm between the predetermined temperature Tm and the detected temperature is determined by the controller 40 and/or 44 in S11, and the controller 40 and/or 44 adjusts the power supplied to the heating element of the air delivery tube 30 until the difference between the predetermined temperature and the detected temperature is substantially zero.

At S3, the temperature detected by the sensor 54 and the predetermined relative humidity RHm transmitted to the mask are input to equation (2) to provide the absolute humidity AHm, i.e., the moisture content, to the mask. At S5, the ambient temperature Ta from sensor 50 and the ambient relative humidity RHa from sensor 5 are input to equation (1) to provide the ambient absolute humidity AHa at S6. At S7, the difference Δah between the absolute humidity AHm transmitted to the mask and the ambient absolute humidity AHa is determined. The difference Δah is the absolute humidity that the humidifier 4 must add to the airflow to deliver the selected water content.

At S8, the flow F detected or estimated by the flow sensor 42 and the difference Δah are input to equation (3) for determining the evaporation rate E required for the supply water of the humidifier. At S9, the water temperature required to produce the evaporation rate E or the equivalent temperature of the humidifier heating element 46 is determined, for example, by closed loop control as discussed above.

At S10, a difference Δt between the water temperature detected by the sensor 48 and the required water temperature determined at S9 is calculated. The controller 40 and/or 44 controls the heating element 46 of the humidifier 4 until the difference between the desired water temperature and the detected water temperature is substantially zero. Alternatively, the heating element 46 is controlled until the difference between the desired heating element temperature and the detected heating element temperature is substantially zero.

Second embodiment of humidity control

Referring to fig. 16, a control system of a breathing apparatus and a method thereof according to another exemplary embodiment are illustrated. During use of the respiratory system, the flow may be measured, for example, byThe effect of the control algorithm is changed, which may provide a relatively slow flow change, or may provide a relatively fast flow change due to leaks in the perimeter of the mask cushion or the perimeter of the mouth when the nasal mask is in use. If the flow rate changes quickly, the control of the heating tube or hose and/or humidifier may not be sufficiently quick to prevent condensation within the tube, as the humidifier takes a relatively long time to change the temperature of the supply water, resulting in a slower response.

As shown in fig. 16, at S12, a change or difference Δf in flow detected by the flow sensor 42 or estimated from, for example, blower speed is determined. The difference Δf may be determined by comparing the detected or estimated flows at periodic intervals. At S13, the difference ΔF is equal to the predetermined difference ΔF _ptd Comparison. If the difference DeltaF between the periodical flows exceeds a predetermined amount DeltaF _ptd The process proceeds to S14 and adjusts the temperature Tm of the gas delivered to the patient interface, such as by controlling the heating tube 30 using the controllers 40 and/or 44. If the difference DeltaF does not exceed the predetermined amount DeltaF _ptd The process proceeds as described above with respect to the first embodiment, and the required evaporation rate is calculated at S8 from the absolute humidity difference Δah and the detected or estimated flow rate.

If the difference Δf is a negative value, i.e., the flow rate change is decreasing, the temperature Tm increases in S14. The temperature Tm may be increased in S14 to a temperature Tm sufficient to maintain the air delivered to the patient interface above the saturation point. The decrease in flow also results in a decrease in water temperature or temperature of the heating element in S9, a difference Δt is calculated in S10, and the heating element is controlled by the controller 40 and/or 44 to decrease the temperature set point of the humidifier. As the temperature of the humidifier supply water decreases, the absolute humidity AHm has an overshoot margin without reaching the saturation point.

In S11, the difference Δtm between the temperature detected by the temperature sensor 54 and the adjusted temperature Tm is determined, and the heating pipe 30 is controlled until the difference Δtm is substantially zero. After a predetermined period of time, the adjusted temperature Tm is gradually reduced in S12 until the temperature of the supply water within the humidifier is reduced to a new set point of the humidifier.

If the flow rate difference DeltaF determined in S11 is a positive value, i.e., the change in flow rate is increasing, the flow rate difference is greater than the predetermined difference DeltaF _ptd The adjustment in S14 may be to decrease the temperature Tm in order to keep the absolute humidity AHm close to saturation. However, the patient may find it uncomfortable to lower the temperature Tm. In this case, the controller 40 and/or 44 may be configured to ignore the flow difference Δf indicative of the flow increase.

The humidifier and respiratory apparatus discussed herein with respect to the exemplary embodiments provide an automatic or default setting to a user inexperienced or new to heating the humidifier that is designed to provide a default moisture content (nominally 14 mg/L) to the delivered air under any given use condition. During the patient's sleep, automatic compensation will be initiated to reduce the default moisture content target value to avoid condensation within the air tube, if desired.

Proper operation the humidifier according to the exemplary embodiments disclosed herein does not require any user knowledge or intervention to properly set and operate the device. This is helpful to those users who find it difficult to establish proper humidifier settings. During sleep of the patient, proper operation is automatically maintained in response to changes in factors affecting the moisture content of the delivery air and possibly condensation, including ambient absolute humidity, ambient temperature, relative humidity and pressure, and the delivery air flow.

If desired, additional settings may be provided to the user to fine tune the automatic or default settings, depending on their preference. The full scale range available for setting is continuously readjusted to keep the centered value calibrated at the default water content to prevent condensation within the air delivery hose as described above. This means that, unlike prior art humidifiers, the default setting and the available full scale range of settings are always calibrated according to the actual environmental conditions. The climate difference, such as a cold and humid climate, of one zone does not jeopardize the available humidification performance or the available settings of another zone as is the case in devices with fixed heater settings.

For example, the user may determine a setting that is lower than a default or automatic setting, such as "3" marked by indicator 11, or a setting that is higher than a default or automatic setting, such as "7" marked by indicator 11, that provides the most comfortable flow of humidified air. The user can thus select the desired setting and the absolute humidity of the airflow delivered to the patient interface will be the most comfortable, which is determined by the patient irrespective of the ambient conditions and/or flow rate.

Third embodiment of humidifier control

Referring to fig. 17, a control system and process of a respiratory device according to another exemplary embodiment is illustrated. For the system and process of the exemplary embodiment of FIG. 17, the operations of S1-S8 and S11 are similar to the corresponding steps of the exemplary embodiment of FIG. 15 described above.

After calculating the evaporation rate required to deliver a predetermined humidity at a predetermined temperature in S8, a heating element temperature threshold is determined in S15, a fixed duty cycle is applied when the temperature is above the threshold, and the duty cycle to drive the humidifier is determined in S16. After determining the temperature threshold of the heating element in S15, it is determined in S17 whether the temperature of the heating element is above the threshold. If the temperature of the heating element is above the threshold (S17: yes), a fixed duty cycle is applied to the heating element in S21. If the temperature of the heating element is not above the threshold (S17: NO), a 100% duty cycle is applied to the heating element in S18.

In S19 it is determined whether the heating element temperature detected by the heating element temperature sensor 48 is higher than the safe operating temperature. If the detected heating element temperature is below the safe operating temperature (S19: NO), the heating element temperature is checked again in S17 to determine if the heating element temperature is above a threshold. If the detected heating element temperature is higher than the safe operating temperature (S19: yes), the duty cycle of the heating element is set to 0% in S20, i.e., the heating element is turned off.

The humidifier may be configured to operate using different types of containers or tanks containing the supply water. One such humidifier is disclosed, for example, in U.S. application 61/097,765, having a filing date of 2008, 9, 17, the entire contents of which are incorporated herein by reference. There are two types of humidifier tub that may be used, one is a "reusable" tub having, for example, a stainless steel base, and one is a "disposable" tub having, for example, an aluminum base. The heat exchange characteristics of the two substrates are different. When the heating element is conditioned to ambient temperature, the two barrels may provide different humidity outputs. However, it is desirable that the humidity output be predictable regardless of which cartridge is secured to the device. This is also preferred when there is a tool to detect what type of cartridge is secured to the humidifier.

The humidity output is related to the duty cycle at which power is provided to the heating element, rather than the temperature at which the heating element is maintained, as described above with reference to fig. 17. This is because at a constant duty cycle, power is delivered to the heating element at a constant rate, the main consumption of power in the system being through evaporation of water in the tub. In fact, the "disposable" and "reusable" barrels have the same evaporation rate when operated at the same duty cycle.

As also described with reference to fig. 17, the exemplary embodiment applies a constant duty cycle of power to the heating element rather than varying the duty cycle to adjust the temperature of the platen. The heating element is a resistive load R, for example 9.6 ohms, which is turned on and off for a constant potential V, for example 24V, with a timing defined by the duty cycle. This is equivalent to p=v ² The electrical power defined by/R, for example 60W at 100% duty cycle, drives the heating element.

The duty cycle-the characteristics of the pass-through device, whose performance takes into account three variables, can be determined in the same manner as the temperature set-point of the heating element is determined in the embodiment shown in fig. 15 and 16: ambient absolute humidity, gas temperature delivered to the patient, and gas delivery flow rate.

Two drawbacks of constant duty cycle operation are also overcome by this exemplary embodiment. The first disadvantage is that the body of water in the humidifier requires a longer time to warm from a cold, original state. The above-mentioned drawbacks are overcome by estimating the temperature threshold in S15 and driving the heating element at 100% duty cycle in S18 until it reaches the temperature threshold, and then switching to a constant or fixed duty cycle level required for the desired evaporation rate in S21.

A second disadvantage is that once the water in the humidifier tub is empty, for example when the water therein has evaporated entirely, the heating element may reach extremely high temperatures. By applying the operation of the maximum safe temperature in S19, if the maximum safe temperature is exceeded, the heating element is deactivated by setting the duty ratio to 0% in S20, so that the above-described disadvantage is overcome.

The exemplary embodiment of fig. 17 may also be used to control a humidifier without a heating tube. In this case, the patient directly controls the temperature of the heating element via the user interface (e.g., knob or dial 10 and/or control button 14) and can adjust it for comfort so that the patient using the reusable cartridge can tend to set a slightly higher temperature than the patient using the disposable cartridge. Without controlling the duty cycle of the power supplied to the heating element, a humidifier using a reusable cartridge will be less humid than a humidifier using a disposable cartridge, and provide less comfort to the patient to facilitate humidification.

The exemplary embodiment of fig. 17 also provides equivalent humidification therapy to all patients and maintains ease of operation thereof.

Fourth embodiment of humidifier control

In addition to controlling the duty cycle of the heating element 46 of the humidifier, the controller 40 and/or 44 may also be configured to control the duty cycle of the heating element of the air delivery hose or tube 30. This allows the humidifier to reduce the overall capacity of its power supply. The humidifier heating element and the heater tube may share an electrical load such that they are never actuated simultaneously when the humidifier heating element or heater tube may draw its full current, e.g., 2.5A instantaneous current at 24V. The controllers 40 and/or 44 calculate a duty cycle to assign to each of the humidifier and the heater tube such that the resultant duty cycle does not exceed 100%. The controllers 40 and/or 44 also synchronize the heating cycles of the humidifier and heater tubes so that they do not overlap. The controller 40 and/or 44 may be configured to periodically turn each heating element on and off according to the duty cycle provided by the airflow generator such that only one device is turned on at a time. Such power management control is disclosed, for example, in U.S. application 61/095,714, having a filing date of 9/10/2008, the entire contents of which are incorporated herein by reference.

According to this exemplary embodiment, the input values include: 1) The temperature set point of the heating pipe is set, for example, by a user interface or climate control algorithm; 2) The temperature detected by the heating tube is converted, for example, by a potential difference of the thermistor; 3) The type of heating tube (e.g., 15mm or 19 mm); 4) The temperature set point of the humidifier is set, for example, through a user interface or climate control algorithm; and 5) the temperature detected by the humidifier, for example converted by a potential difference of a thermistor.

The output values of the exemplary embodiment include: 1) Heating power applied to the humidifier, for example, duty cycle from 0% to 100%; and 2) heating power applied to the heating tube, for example, a duty cycle of from 0% to 100%.

Control also includes the use of constants for the heating tube, including: 1) A scale factor Pf; 2) A finishing factor If; and 3) a derivative factor Df. Likewise, control also includes use of constants for the humidifier, including: 1) A scale factor Pf; 2) A finishing factor If; and 3) a derivative factor Df.

The internal variables include: 1) Detected humidifier temperature, told, associated with the previous reading; 2) A cumulative sum of humidifier temperature differences, sumTd; 3) Detected heating tube temperature, told, associated with the previous reading; and 4) a running total of the heating tube temperature differences, sumTd.

The controllers 40 and/or 44 may include simplified proportional-integral control functions:

1. calculate temperature difference Td = the temperature reading minus the previous reading Told.

2. If the measured temperature approaches the set point (|td| less than 1/Pf),

a. then Td is multiplied by the integer If and the result is added to the cumulative sum of the temperature differences sumTd,

b. otherwise reset sumTd to zero.

3. Duty cycle=pf+if+sumtd is calculated.

4. The trim duty cycle is between 0 and 1.

The duty cycle of each of the humidifier and heating tube is then compared.

1. If the sum of the duty cycles of the humidifier and the heating tube exceeds 1.0, one or both duty cycles are reduced. For example, the heating tube duty cycle is reduced to 0.5, and then the humidifier duty cycle is reduced to the necessary extent.

2. The two duty cycles are multiplied by 100 for output to the humidifier controller as an integer value from 0 to 100 (indicating 100%).

Fifth embodiment of humidifier control

According to another exemplary embodiment, the controllers 40 and/or 44 may be configured to control the humidifier heating element and the heating tube using input values including: 1) The air flow rate detected by the air flow generator, for example, an average flow rate exceeding one minute; 2) Ambient relative humidity, e.g., as determined or detected by a humidifier; 3) Ambient temperature, e.g., detected by a humidifier; 4) If a heating tube is connected, the temperature detected by the heating tube is expressed, for example, in degrees celsius; 5) Heating tube settings from the user interface, for example in degrees celsius, or automatic settings; 6) Humidifier settings from the user interface, such as an automatic setting or a setting that is "wetter" or "drier" than a standard automatic setting; 7) Time stamp.

The output values of the control may include: 1) A temperature set point for the humidifier; and 2) a temperature set point for the heating tube.

The constants for control may include: 1) A conversion coefficient from relative humidity to absolute humidity comprising a) three coefficients applied to a quadratic equation; and 2) a table that determines a temperature set point from the desired humidifier humidity output.

The table may be a matrix of points from which the set points may be inserted three-wire, including: a) An axis for average air flow, for example corresponding to 10 to 70L/min at 12L/min intervals, which provides six points; b) An axis for a desired absolute humidity output, e.g., 0 to 40mg/L at 8mg/L intervals, which provides six points; and c) an axis for absolute humidity of the environment, for example corresponding to 0 to 35mg/L at 5mg/L intervals, which provides eight points.

The overall matrix size provides 6x6x8 = 288 data points. Each data point is a temperature from 5 to 95 ℃ in 0.1 ℃ increments. The matrix may be, for example, as shown in table 6 below.

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TABLE 6

The internal variables may include: 1) Absolute humidity of the environment; 2) Absolute humidity at the target of the mask; 3) Absolute humidity added by the humidifier; and 4) the measured prior flow.

To generate a temperature set point for the humidifier, the controllers 40 and/or 44:

1. according to the formula: absolute humidity = relative humidity (ratio of 1) x (a+ b x temperature+ c x temperature x temperature), the ambient absolute humidity is calculated using the ambient relative humidity and temperature, where the constant coefficients a = 7.264, b = 0.0928, c = 0.0293 are given.

2. The target absolute humidity is calculated from the temperature detected by the heating pipe. If the heating tube is not available, it can be replaced with ambient temperature. The function is the same as the quadratic equation used in step 1, but now the relative humidity is set via the user interface.

3. The absolute humidity to be added by the humidifier is calculated by subtracting the ambient absolute humidity from the target.

4. A temperature set point for the humidifier is calculated based on the absolute humidity, flow and ambient temperature added. The calculation is a tri-linear interpolation of table 6.

To generate a temperature set point for the heating tube:

1. the default temperature set point corresponds to a setting on the user interface.

2. If the flow drops suddenly, the temperature set point may be adjusted slightly (e.g., a few degrees celsius) above the set point for a limited time (e.g., 15 minutes).

Design considerations for airflow generators

The user interface of the flow generator may indicate that the humidifier is detected or removed, for example, within one second, when the humidifier is mounted to or dismounted from the flow generator. The user interface of the flow generator may indicate that the heating tube is detected or removed, for example, within one second, when the heating tube is mounted to or detached from the humidifier.

As described above, the flow generator controller may control the humidifier and the heating tube. The flow generator controller may use constants stored within the humidifier controller, including, for example, six control parameters, each having a value between 0 and 1 with an accuracy of 0.01 and a matrix with 6x6x8=288 data points. Each data point may be a temperature from 5 to 95 ℃ with an accuracy of 0.1 ℃.

During treatment, the flow generator may poll (poll) the humidifier to read the humidifier heating element and heating tube temperatures, for example, at least once every 10 seconds. During treatment, the flow generator may poll (poll) the humidifier to read ambient temperature and relative humidity, for example, at least once every 60 seconds.

The temperature can be transferred as a value from 5 to 95 ℃ with an accuracy of 0.1 ℃. The relative humidity may be transferred as an integer value from 0 to 100. Values outside this range should be limited to this range.

The flow generator may calculate the duty cycle applied by the humidifier, which is an integer value between 0 and 100 (where 100 represents 100% duty cycle). The flow generator may also calculate the duty cycle applied to the heating tube, which is an integer value between 0 and 100 (where 100 represents 100% duty cycle). The flow generator can ensure that the sum of the duty cycles for the humidifier and the heating tube does not exceed 100 (representing 100%).

During treatment, the demand from the flow generator to set the humidifier duty cycle may be transmitted, for example, at least 1 time every 3 seconds, and the demand from the flow generator to set the heating tube duty cycle may be transmitted, for example, at least 1 time every 1 second.

Humidifier design considerations

When both the heating tube and the humidifier require heating, the controller 40 and/or 44 may ensure that power is distributed such that both do not draw power at the same time. For this purpose, the heating pipe and the humidifier may be controlled by the same controller.

A suitable communication protocol may be developed to enable communication between the airflow generator and the humidifier, power supply, and any other device that may be added. The communication protocol may detect communication errors using, for example, a 16-bit CRC. The communication between the flow generator and the humidifier may be half duplex to minimize the pin count of the wiring connector.

The humidifier may transmit the following information to the FG on command: 1) Humidifier status (normal or error); 2) Reading of relative humidity; 3) Obtaining a temperature of the relative humidity reading; 4) The temperature of the heating element in the humidifier; 5) The humidifier heats the duty cycle.

The humidifier may respond to the following instructions from the flow generator: 1) A humidifier status is required; 2) A humidity reading is required; 3) A temperature requiring a humidity reading; 4) The temperature of the heating element within the humidifier is required; 5) The heating duty cycle in the humidifier is set.

The humidifier may stop heating the humidifier tub unless a need to set the heating duty cycle is received at least every 10 seconds.

Heating pipe design considerations

The humidifier may transmit the following information to the flow generator on command: 1) A heating tube state comprising a) the presence or absence of a heating tube, b) the diameter of the heating tube (15 mm or 19 mm), and c) normal or incorrect; 2) The temperature in the heating tube; and 3) a humidifier heating duty cycle.

The humidifier may respond to the following instructions from the flow generator: 1) A heating pipe state is required; 2) The temperature in the heating tube is required; 3) A heating power level within the humidifier is set.

The humidifier may stop heating the heating tube unless, for example, a demand to set the heating duty cycle is received at least every 1 second.

Temperature conversion

The controller 40 and/or 44 may utilize a look-up table to convert the measured potential on the thermistor to a temperature, for example in degrees celsius. Three tables are required: 1) And 2) temperature conversion tables (each having about 360 data points for a range of 5 to 40 ℃ with an accuracy of 0.1 ℃) for each type of heating tube (e.g., 15mm and 19 mm); and 3) a temperature conversion table for the humidifier (with about 960 data points for an accuracy of 0.1 ℃ for a range of 5 to 95 ℃). Each may be a look-up table that is represented by being equally spaced on the thermistor potential axis.

Climate control constant delivered to airflow generator

The humidifier may carry a table, such as table 6, as a constant and deliver it to the flow generator before climate control begins. Such that upgrades to the humidifier may be accomplished within the humidifier without the need to upgrade the flow generator software.

Indicating lamp

The humidifier may directly control a blue and a amber LED based on instructions from the flow generator, for example using instructions via a serial communication link. The humidifier may control the indicator light according to instructions received from the flow generator, each of which may include the following information: 1) Color-blue or brown; 2) Brightness-bright, dim, or off; and 3) fade-yes or no.

If the fade is: 1) The brightness should smoothly transition over three seconds, however; or 2) no, the brightness should be switched to a new level. The two indicator lights of the humidifier can be changed gradually at the same time, for example for a uniform gradual change, the flow generator can send two instructions simultaneously-one instruction for gradually turning off one indicator light and the other instruction for gradually turning on the other indicator light.

Humidifier control sixth embodiment

A patient sleeping with a humidifier set to deliver less than saturated moisture inside the tube may experience in three situations in-tube condensation: 1) The ambient temperature drops so that the air cools within the tube below its dew point; 2) The ambient humidity increases so that the air leaving the humidifier increases in humidity and then cools down within the tube below its dew point; and 3) flow drops, such as when the automatic setting reduces the treatment pressure, the humidifier adds more humidity to the air, which then cools down in the tube below its dew point.

Current proposals for treating problems with condensation or rain water flushing in the tube provided to the patient include extending the tube under the bedding to reduce cooling in the tube and/or setting the humidifier at a lower heating set point. These methods result in less moisture being received by the patient throughout the night in order to be farther from the dew point after taking into account the night's changes.

As described above, the exemplary embodiments provide for performing climate control to deliver air of a predetermined temperature and humidity to the mask end of the tube. However, the climate control described with reference to the previous exemplary embodiments requires a temperature sensor within the tube to monitor the temperature of the air within the tube. Heating tubes with temperature sensing add cost and thus it would be advantageous to provide relief from condensation to the patient in systems with conventional, i.e., non-heating tubes.

Referring to fig. 18, according to another exemplary embodiment, climate control is provided in a tube that is not heated and does not measure the temperature of the transmitted air, but the temperature of the air is estimated from the readings of an ambient temperature sensor in S22. The estimation is based on the reported characteristics of the temperature difference between the ambient temperature and the temperature of the air being transported, in case of different situations of ambient temperature, air flow and heating sources in the device, such as power supply, motor, electronic or humidifier heating elements.

As described above, comparative example 1 (table 2) shows the response to the change in the ambient temperature without the change in the ambient absolute humidity and without the control of the mask temperature Tm, which was the case with the exemplary embodiments described above with reference to fig. 15 and 16. According to this exemplary embodiment, in which the transmitted air temperature Tm is not measured but estimated, an equivalent table for adjusting the water temperature to change the ambient humidity is shown in table 7 below, which is a selection of three different ambient air temperatures.

TABLE 7

A feature of this exemplary embodiment is that the temperature of the air being transmitted is estimated so that the device does not detect whether the duct is isolated from the ambient temperature, for example by a cloth bed cover or bedding. Insulation can increase the temperature of the air being transported by reducing cooling within the duct. In order to reduce the likelihood of condensation, it may be assumed that the duct is not insulated, so that the air transported is cooler and closer to its dew point than if insulation were provided.

It should be appreciated that the system of this exemplary embodiment will suitably respond to simultaneous changes in ambient temperature and ambient humidity and air flow. The system of this exemplary embodiment provides protection against condensation on the pipeline throughout the night, regardless of changes in ambient temperature, humidity and flow. The system of this exemplary embodiment also provides fully automatic control of the humidifier. With a predetermined relative humidity default value for the gas delivered, the patient no longer needs to adjust the humidifier. The system of this exemplary embodiment also provides a humidity setting via the user interface that can be converted to a predetermined relative humidity of the transport gas.

Unlike other exemplary embodiments that include heating tubes, this exemplary embodiment does not transmit warmer air or higher humidity carried by warmer air. This exemplary embodiment also does not allow the patient to select the temperature of the air being delivered. This exemplary embodiment also does not increase the humidity transmitted if the pipe is insulated. This can be overcome by changing the humidity setting through the user interface.

The humidifier control according to this exemplary embodiment allows the breathing apparatus to be provided with standard tubing rather than heated tubing, thus reducing system costs.

The above-described exemplary embodiments may also be implemented entirely in software or hardware (e.g., ASIC), such that the humidifier may be configured to operate as any of these three exemplary embodiments without increasing the capital cost of the device.

The humidifier according to the exemplary embodiments disclosed herein improves user compliance due to increased comfort, reduced likelihood of throat dryness/pain, and/or increased ease of use by providing an automatic optimized humidification setting.

The problem of prior art humidifiers tracking only indoor ambient temperature and flow is also addressed by humidifiers according to exemplary embodiments disclosed herein, which can track improper humidity output due to human error/confusion in formulating initial settings. Users of such humidifiers do not know what settings are closest to the optimal humidification level for any given situation, particularly when they experience significant changes from their normal environment/climate, for example, while traveling.

Humidifiers and breathing apparatuses according to the exemplary embodiments disclosed herein measure ambient relative humidity and pressure (altitude compensation), as well as ambient temperature, in order to improve the accuracy of the transmitted humidity level relative to prior art systems that do not detect ambient humidity and pressure. The availability of low cost humidity and pressure sensors in recent years now makes it feasible and practical to monitor such additional parameters even on CPAP devices.

A humidifier and respiratory apparatus according to the exemplary embodiments disclosed herein will respond to detected sustained oral leakage, but unlike prior art systems, will modify the humidity output to optimize the humidity density, rather than merely setting a less than optimal setting on a radical basis.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Furthermore, the various embodiments described above may also be implemented in combination with other embodiments, for example, some aspects of one embodiment may be combined with some aspects of another embodiment to implement yet another embodiment. Further, each individual feature or component of any given assembly may constitute an additional embodiment. Further, each individual component of any given assembly, one or more portions of a single component of any given assembly, and various combinations of components from one or more embodiments may include one or more ornamental design features. In addition, while the present invention has particular application to patients with OSA, it will be appreciated that patients with other diseases (e.g., congestive heart disease, diabetes, morbid obesity, stroke, bariatric surgery, etc.) may benefit from the above teachings. Furthermore, the teachings above have applicability to both patients and non-patients for non-medical applications.

In this specification, the word "comprising" is to be understood as its meaning "open", i.e. "comprising", and not limited to its meaning "closed", i.e. "consisting of only … …". The corresponding meanings apply to the corresponding words "comprise", "include" and "include" when they occur.

It should be further understood that the reference herein to any prior art, unless indicated to the contrary, is not an admission that such prior art is well known to those skilled in the art in connection with the present invention.

Claims

1. A respiratory apparatus for providing a humidified flow of breathable gas to a patient, the respiratory apparatus comprising:

a flow generator configured to supply a flow of breathable gas;

a humidifier configured to humidify the flow of breathable gas, the humidifier comprising a water storage chamber and a heater configured to heat water in the water storage chamber;

an air delivery hose having a heating element, the air delivery hose configured to receive a humidified flow of the breathable gas from the humidifier;

at least one temperature sensor configured to detect a temperature associated with the humidifier, and at least one temperature sensor configured to detect a temperature of the breathable gas at the air delivery hose; and

A controller in communication with both the flow generator and the humidifier, the controller configured to synchronize a humidifier heater duty cycle with an air transfer hose heating element duty cycle such that a resultant duty cycle of the humidifier and the air transfer hose heating element does not exceed 100%, and heating periods of the humidifier and the air transfer hose heating element do not overlap,

wherein the controller is further configured such that when the sum of the duty cycles exceeds 100%, the air delivery hose heating element duty cycle is reduced to a predetermined value and then the humidifier heater duty cycle is reduced to the necessary extent such that the sum of the duty cycles is 100% or less.

2. The respiratory device of claim 1, wherein the controller is configured to detect the humidifier when the humidifier is connected to the flow generator and to detect whether the humidifier is removed from the flow generator.

3. The respiratory device of claim 1, wherein the controller is configured to detect the air delivery hose when the air delivery hose is connected to the humidifier, and to detect whether the air delivery hose is removed from the humidifier.

4. The respiratory device of claim 1, wherein the flow generator is configured to determine the temperature of the humidifier heater and/or the temperature of the air delivery hose at a first predetermined interval, wherein the first predetermined interval is at least 10 seconds.

5. The respiratory device of claim 4, wherein the airflow generator is configured to determine the ambient temperature and the ambient relative humidity at a second predetermined interval, wherein the second predetermined interval is at least 60 seconds.

6. The respiratory device of claim 1, wherein the flow generator is configured to transmit a demand to set a duty cycle of the humidifier at a third predetermined interval, wherein the third predetermined interval is at least 3 seconds.

7. The respiratory device of claim 6, wherein the airflow generator is configured to transmit a demand to set a duty cycle of the air delivery hose at a fourth predetermined interval, wherein the fourth predetermined interval is at least 1 second.

8. The respiratory device of claim 1, wherein the controller is configured to detect the communication error with a 16-bit CRC using a communication protocol.

9. The respiratory device of claim 1, wherein communication between the flow generator and the humidifier is half duplex.

10. The respiratory device of claim 1, wherein the controller is configured to receive data from the humidifier related to at least one of a humidifier status, a relative humidity of the gases in the humidifier, a temperature of the humidified gases in the humidifier, a temperature of a humidifier heater, and a humidifier heater duty cycle.

11. The respiratory device of claim 10, wherein the humidifier status indicates whether the humidifier is operating with or without an error.

12. The respiratory device of claim 1, wherein the controller is configured to receive data related to at least one of an air delivery hose status, an air delivery hose diameter, an operating status of the air delivery hose, an air temperature in the air delivery hose, and the air delivery hose heating element duty cycle.

13. The respiratory device of claim 12, wherein the operational status of the air delivery hose indicates whether the air delivery hose heating element is operating with or without error.

14. The respiratory device of claim 1, wherein the humidifier is configured to terminate the supply of power to the humidifier heater when an interval between demands from the controller to set a humidifier heater duty cycle exceeds 10 seconds.

15. The respiratory device of claim 14, wherein the humidifier is configured to terminate the supply of power to the air delivery hose heating element when an interval between demands from the controller to set an air delivery hose heating element duty cycle exceeds 1 second.