NL2027207B1

NL2027207B1 - Ventilation system for ventilating a subject

Info

Publication number: NL2027207B1
Application number: NL2027207A
Authority: NL
Inventors: Christiaan Bijleveld Pieter; Kaashoek Irene; Van Dijk Geert
Original assignee: Demcon Macawi Respiratory Systems B V
Priority date: 2020-12-23
Filing date: 2020-12-23
Publication date: 2022-04-05

Abstract

Ventilation system for ventilating a subject on the basis of at least one respiratory parameter that is indicative for the subject’s respiratory mechanics, wherein the ventilation system comprises: 5 - a blower module comprising a gas inlet, a gas outlet, an impeller rotatably mounted between said gas inlet and gas outlet and a driving mechanism for driving the impeller; - a controller for controlling said driving mechanism of said blower module, wherein said controller is arranged for controlling a rotational speed of the impeller for providing a ﬂow of breathable gas at the gas outlet having a base pressure and wherein the controller is further 10 arranged for varying the rotational speed of the impeller for superimposing a forced oscillating pressure variation onto said base pressure, - wherein the controller comprises at least one input that is arranged for receiving the at least one respiratory parameter, wherein said at least one respiratory parameter is indicative for the subject’s respiratory response to the forced oscillating pressure variation, and wherein the 15 controller is arranged for adjusting said base pressure on the basis of the received respiratory parameter.

Description

Ventilation system for ventilating a subject The invention relates to a ventilation system for respiratory support. The invention further comprises to a method of controlling a pressure and/or flow using a ventilation system.

Ventilation systems for respiratory support are typically designed to deliver a flow of gas at a certain pressure to a subject, for instance a patient requiring respiratory support. In some situations the systems are used to only assist the subject in breathing more easily, whereas in other situations the ventilation system is driving the supply of fresh air to the subject’s lungs.

A commonly used method for ventilating a subject is a proportional pressure assist method, wherein the ventilation system provides breathable gas at a time-varying pressure to the subject. Proportional pressure assist was designed to decrease the work of breathing and improve subject- ventilator synchrony by adjusting the airway pressure in proportion to the subject's effort. Unlike other modes in which the physician presets a specific tidal volume or pressure, proportional assist ventilation (PAV) lets the subject determine the inspired volume and the flow rate. The support given is a proportion of the subject's effort and is normally set between 30 and 80 % dependent on the amount of assist needed by the patient. This support is always changing according to subject's effort and lung dynamics. If the subject's effort and/or demand are increased, the ventilator support is increased, and vice versa, to always give a set proportion of the breath. The method aims at keeping the subject's work of breathing constant regardless of his or her changing effort or demand. This however, requires an accurate assessment of the subject's effort and lung dynamics, which is often estimated by the operator of the ventilation system. Thereby, assist levels close to 100% would put the subject at risk of over-assistance in case of errors in the estimation of the subject's effort and lung dynamics, as this could result in over-estimation of the pressure needed. The goal of the invention is thus to provide for an improved ventilation system that allows for more accurately setting the assist levels for providing respiratory support using the proportional pressure assist method. In a first aspect, the invention relates to a ventilation system for ventilating a subject on the basis of at least one respiratory parameter that is indicative for the subject’s respiratory mechanics, wherein the ventilation system comprises:

- a blower module comprising a gas inlet, a gas outlet, an impeller rotatable mounted between said gas inlet and gas outlet and a driving mechanism for driving the impeller; - a controller for controlling said driving mechanism of said blower module, wherein said controller is arranged for controlling a rotational speed of the impeller for providing a flow of breathable gas at the gas outlet having a base pressure and wherein the controller is further arranged for varying the rotational speed of the impeller for superimposing a forced oscillating pressure variation onto said base pressure, - wherein the controller comprises at least one input that is arranged for receiving the at least one respiratory parameter, wherein said at least one respiratory parameter is indicative for the IO swobject’s respiratory response to the forced oscillating pressure variation, and wherein the controller is arranged for adjusting said base pressure on the basis of the received respiratory parameter. Superimposing a forced oscillating pressure variation onto said base pressure, for instance during a predetermined period of time, allows to accurately estimate the respiratory dynamics of the subject, as is also explained in more details in the paragraphs below. This thus enables a non-invasive method that aims to evaluate the respiratory system resistance and elastance during ventilation of the subject with a base pressure. The method is based on the superposition of (sinusoidal) oscillating pressure variations around the base pressure of the flow of breathable gas that is supplied to the subject. By, for instance, determining the subject’s respiratory response to the pressure variations by monitoring pressure and/or flow variations in the flow of exhaled gas of a subject, a resistance and/or elastance of the respiratory system can be estimated. The system according to the invention uses the impeller of the blower module for generating both the flow of breathable gas at a base (or first) pressure for the subject as well as for superimposing the forced oscillating pressure variation around said base pressure. Thereby, no additional oscillator is required that increases the compressible volume (i.e. dead volume) of the system and a higher overall efficiency of the system is obtained. As the compressible volume of at least the ventilation system is not increased, it is also easier to generate and control the forced oscillating pressure variation that is superimposed onto the base pressure. As the forced oscillating pressure variation (as delivered to a subject’s respiratory system, e.g. lungs) can be controlled more accurately, the respiratory dynamics of the subject can also be determined more accurately through such a system.

The base pressure may relate to a normal breathing pattern of a subject, whereby the delivered pressure (i.e. the first pressure) consecutively varies, at for instance an (average) natural breathing frequency of the subject, between a lower mean pressure (e.g. positive end-expiratory pressure, or PEEP, of the subject), during the expiration phase of the subject and a higher mean pressure (e.g. peak inspiratory pressure, or PIP, of the subject) during the inhalation phase of the subject.

Furthermore, by arranging the controller such that is can vary the rotational speed of the impeller for superimposing the forced oscillating pressure variation around said base pressure, forced oscillating pressure variation is generated directly by the impeller that is controlled to rotate at varying speeds, such that there is no need for, for instance, dynamically operable valves that are arranged up- or downstream of the impeller for generating pressure oscillations. As these types of valves would operate on the basis of creating an oscillation additional resistance in the flow path of the breathable gas, they would in fact dissipate energy and thus reduce the overall efficiency of the system.

In order to minimize the compressible volume of the ventilation system and to thereby improve the dynamic pressure bandwidth of the overall (pneumatic) system when ventilating a subject, it is preferred that the ventilation system comprises only a single blower module and that the blower module comprises only a single impeller. The dynamic pressure bandwidth refers to a frequency range wherein the overall system is able to accurately deliver the required pressure oscillations to the subject.

It is preferred that the controller comprises a speed converter unit that is arranged for generating an impeller speed control signal for controlling the rotational speed of the impeller, wherein said impeller speed control signal is determined on the basis of the base pressure and the forced oscillating pressure variation. The generated base pressure, and the forced oscillating pressure variation around said first pressure, is generated by rotating the impeller while varying the rotational speed for superimposing the forced oscillating pressure variation. A speed converter unit is therefore preferably arranged for determining, in dependence of the requested base pressure, a base rotational speed of the impeller such that the rotating impeller can supply the flow of gas at the requested pressure. Furthermore, it is preferably arranged for determining, in dependence of the requested forced oscillating pressure variation around said first pressure, the speed variations of the impeller that are needed for superimposing said forced oscillating pressure variation. The speed converter unit thus allows for driving the impeller at the desired (varying) speed to supply the flow of gas having the right (varying) pressures.

Preferably, the controller is arranged for controlling the forced oscillating pressure variation by only varying the rotational speed of the impeller. Hereby, no additional oscillator is required that would otherwise increases the compressible volume of the system and thereby reduce its overall efficiency. As the compressible volume of at least the ventilation system is not increased, it is also easier to generate and control the forced oscillations that are superimposed onto the base pressure. The controller is, in a preferred embodiment of the ventilation system, arranged to form the forced oscillating pressure variation from one or more (simultaneous) periodic oscillating pressures each having a respective frequency, a respective pressure amplitude and, preferably, a respective phase shift and wherein the controller is arranged for receiving said respective frequencies , respective pressure amplitudes and, preferably, respective phase shifts for superimposing the forced oscillating pressure variation onto said base pressure. By composing the oscillating pressure variation from one or more periodic oscillating pressures each having a respective frequency, a respective pressure amplitude and, preferably, a respective phase shift, e.g. a multi-sine signal, it is possible to obtain the respiratory response at multiple frequencies at the same time, such that the respiratory dynamics of the subject can also be determined faster, when compared to a sine-sweep signal wherein the frequencies are not simultaneously, but sequentially superimposed on the base frequency. It furthermore allows to increase the number of frequencies for which the respiratory response is obtained in the same time span, i.e. while not (significantly) increasing the length (i.e. time) of the forced oscillating pressure variation signal.

Itis then further preferred that the forced oscillating pressure variation comprises a superposition of a plurality of periodic oscillating pressures, wherein each of the plurality of periodic oscillating pressures is a sinusoidal signal having a respective frequency that is different from the frequency of the others of the plurality of periodic oscillating pressures. Hereby, such a multi-sine signal can be obtained, which is preferably a random phase multisine (RPM).

Preferably, the respective frequencies are in the range of 0.01 Hz to 25 Hz, more preferably from

0.1 Hz to 20 Hz. Hereby, the respiratory dynamics of the subject can be determined in the relevant bandwidth for determining the PEEP and PIP setting of the proportional pressure assist method. Pressure amplitudes of the forced oscillating pressures around the base pressure are preferably in the range of 0.1 hPa - 25 hPa, more preferably 0.5 hPa - 20 hPa, even more preferably 1 hPa - 15 hPa, most preferably around 10 hPa. Pressures amplitudes of the forced oscillating pressures in these ranges have been shown to lead to respiratory response that can be accurately measured. It is noted, however, that lower amplitudes typically excite a mostly linear response of the respiratory system, thereby making it easier to identify the linear (or linearized) lung dynamics.

In a preferred embodiment, the at least one respiratory parameter is a frequency response function, an impedance fonction, an elastance function, an inertial function and/or a resistance function of the respiratory system. The subject's effort and lung dynamics are well represented by the respective a frequency response function, an impedance function, an elastance function, an inertial 5 function and/or a resistance function of the respiratory system. This enables to fine tune the settings for a proportional pressure assist method. Preferably, the ventilation system comprises at least one detector for measuring a flow rate and/or pressure of the flow of inhaled and/or exhaled gas from the subject for determining the subject’s respiratory response to the forced oscillating pressure variation. This enables to measure an input signal delivered to, and/or output signal originating from, the respiratory system by performing measurements of the flow rate and/or pressure from the flow of, respectively, the inhaled or exhaled gas, such that a transfer function of the respiratory system can be obtained by determining a (complex) ratio between the output signal and input signal. The ventilation system preferably comprises at least one detector for measuring a flow rate and/or measuring a pressure of the flow of breathable gas. In addition, a more accurate control of the generated pressures is enabled in a further preferred embodiment of the ventilation device, wherein the controller comprises a feedback control loop for controlling the impeller speed on the basis of the measured flow rate and/or the detected pressure provided by the blower.

The gas outlet of the blower module is, in a preferred embodiment, coupled to a conduit for guiding the flow of breathable gas from the gas outlet to a subject, or at least to a subject interface module that is arranged to form a flow path from the conduit to the respiratory system of the subject, and wherein the conduit is further arranged for guiding a flow of exhaled gas from the subject, or at least from the subject interface module, to an exhalation outlet. This allows, for instance, to arrange the at least one detector, as described above, in simple manner to measure the flow rate and/or pressure of the flow of inhaled and/or exhaled gas by a single detector that is arranged in the conduit. It is then preferred that the at least one detector is arranged in the conduit. Preferably, a single detector only is arranged for determining the flow rate and/or pressure of the flow of inhaled and/or exhaled gas and for determining the flow rate and/or pressure of the flow of breathable gas. Hereby, a more simplified and compact ventilation system can be obtained. It is preferred that the subject’s respiratory response, as described in the preceding paragraphs, is determined by taking measurements, for instance pressure and/or flow rate measurements, from a flow of the inhaled and/or exhaled air.

This allows for estimating the lung dynamics of a subject, for instance in the form of transfer response functions as described in the preceding paragraphs.

In a preferred embodiment, the ventilation system further comprising a respiratory mechanics processing unit that is arranged for determining the at least one respiratory parameter that is indicative for the subject’s respiratory mechanics, wherein the at least one respiratory parameter is determined on the basis of a subject’s respiratory response to the forced oscillating pressure variation, wherein said respiratory mechanics processing unit is arranged for providing the controller with said at least one respiratory parameter.

Although it is possible, that the determination of the at least one respiratory parameter is performed by an external processing unit, that is not an integral part of the ventilation system, but a separate system that allows for inputting the relevant data obtained from the ventilation system, either manually or automatically through a data connection, it is preferred if the respiratory mechanics processing unit is an integral part of the ventilation system.

This allows, for instance, providing for a closed feedback control loop of the respiratory response due to the forced oscillatory pressure variations that are superimposed onto the base pressure for determining, and/or setting, of the base pressure provided by the ventilation system, as is explained in more detail in the following paragraphs.

It is then preferred that the respiratory mechanics processing unit is arranged for determining a real-time natural breathing frequency from subject's respiratory response over a predetermined period and wherein the respiratory mechanics processing unit is arranged for determining an averaged natural breathing frequency by taking an average of the determined real-time natural breathing frequency of the subject over the predetermined period.

This allows to also provided for a base pressure signal that has an improved matching with the normal breathing pattern of a subject, whereby the delivered pressure consecutively varies, at the natural (i.e. average) breathing frequency of the subject, between a lower mean during the expiration phase of the subject and a higher mean pressure during the inhalation phase of the subject.

In order to achieve this in an efficient manner, the controller is preferably arranged for controlling the rotational speed of the impeller to provide, as said base pressure, an oscillating base pressure pattern at the averaged natural breathing frequency at the gas outlet.

Additionally, by matching the oscillating base pressure pattern with the averaged natural breathing frequency of the subject, a breathing lock-in of the subject can be achieved, whereby the natural breathing will synchronize with the provided oscillating base pressure pattern of the subject.

This allows, as is described in more detail in the subsequent paragraphs, for obtaining a more accurate estimate of the subject’s respiratory dynamics, i.e. lung dynamics.

In a preferred embodiment, the respiratory mechanics processing unit is arranged for determining the respective frequencies of the one or more periodic oscillating pressures such that said respective frequencies are spectrally spaced apart, or at least different, from the averaged natural breathing frequency and, preferably, its higher harmonics. For obtaining accurate transfer functions on the basis of input signals (for instance in the form of the forced oscillatory pressure variations) and the output signals (for instance in the form of the measured flow rate and/or pressure of the exhaled air of the subject), it is preferred that there are minimal external distarbances. As the natural breathing of the subject itself is such an external disturbance, which also has a significant impact on the respiratory response (i.e. the output signal), it is preferred if this disturbance can be filtered out, or separated from the input/output signals. By selecting the one or more periodic oscillating pressures to be different from the averaged natural breathing frequency and, preferably, its higher harmonics, this allows for filtering, separating, or for otherwise reducing the impact of the disturbance on the measured (or otherwise obtained) respiratory response of the subject, such that a more accurate estimate of the subject’s respiratory dynamics, i.e. lung dynamics, is obtainable. It is then preferred that the respective frequencies of the one or more periodic oscillating pressures are spectrally spaced apart, or at least different, from the averaged natural breathing frequency by atleast 5%, preferably at least 10%, more preferably at least 20% of the averaged natural breathing frequency. By spacing the frequencies of the one or more periodic oscillating pressures sufficiently far from the averaged natural breathing frequency, it allows for a more effective and improved filtering and/or separating of the disturbances due to the subject’s natural breathing from the measured respiratory response.

Preferably, the respiratory mechanics processing unit is arranged for determining, as the at least one respiratory parameter, a frequency response function, an impedance function, an elastance function, an inertial function and/or a resistance function of the respiratory system. The impedance function is a frequency dependent, complexed sum of the elastance, inertial and resistance functions of the respiratory system. The at least one respiratory parameter may also be a compliance function, which is the inverse of the elastance function. Any of these functions represent the respiratory dynamics, i.e. lung dynamics, of the subject in a sufficiently detailed manner to allow for adjusting the base pressure.

Ina preferred embodiment, the respiratory mechanics processing unit is arranged for computing a spectral input function from at least said forced oscillating pressure variation and for computing a spectral output function from at least said measured subject’s respiratory response and wherein the respiratory mechanics processing unit is arranged for determining the at least one respiratory parameter on the basis of a complex ratio of the spectral input function and the spectral output function. This allows for obtaining a frequency response function, an impedance function, an elastance function, an inertial function and/or a resistance function of the respiratory system.

It is preferred that the respiratory mechanics processing unit is arranged for determining, on the basis of the determined at least one respiratory parameter, a subject specific pressure amplitude, pressure pattern and/or flow rate of the flow of breathable gas, and wherein the controller is further arranged for controlling the rotational speed of the impeller for providing said subject specific pressure amplitude, pressure pattern and/or flow rate of the flow of breathable gas. As the pressure of the delivered inspiratory flow depends on, for instance, the patient’s impedance function, clastance function, inertial function and/or resistance function of the respiratory system and flow demand, the patient’s PIP may also depend on the impedance function, elastance function, inertial function and/or resistance function of the respiratory system and flow demand. More specifically, an increase in resistance or a decrease in compliance may increase the work of breathing. Additionally, if the patient’s flow demand increases, the work of breathing may also increase. Thus, the ventilation system may provide more ventilation support (i.e., an inspiratory flow at a higher pressure) to the patient to overcome the increased work of breathing, which may increase the patient's PIP. Similarly, if the patient's resistance decreases, compliance increases, and/or flow demand decrease, the ventilator may decrease the ventilation support by decreasing the base pressure (i.e., an inspiratory flow at a lower pressure), which may decrease the PIP of the patient. In this manner, the amount of support delivered to the patient may increase as the patient’s effort (i.e., flow demand) increases and decrease as the patient's effort decreases.

In a preferred embodiment, the blower module further comprises a housing comprising the gas inlet, the gas outlet and a compression chamber, wherein said impeller is rotatably mounted in the housing between the gas inlet and the compression chamber. Hereby, a compact blower module is obtained, wherein the compressible volume {or volume) can be reduced, such that the overall compressible, or dead, volume of the ventilation system is reduced and the bandwidth of the system is improved. It is preferred that said impeller comprises a conical shaped frontal surface that is substantially axisymmetric with respect to a central axis, wherein a plurality of fin-shaped member extend from the frontal surface in at least a direction parallel to the central axis and wherein the impeller is arranged to rotate around said central axis. Hereby, an efficient and compact impeller is used in the blower module. Said impeller is preferably made from materials having a density of 3.0 g/cm’ or less such as aluminum of plastics, more preferably from materials having a density of 1.2 g/cm) or less, such as (engineering and/or high performance plastics) plastics which may be reinforced. Said impeller is preferably monolithic, such that a lightweight impeller may be obtained by using high strength plastic material that can be injection molded into an impeller with minimal thicknesses. The impeller is therefore preferable a thin-walled injection molded part. These measures reduce the IO amount of unnecessary material and/or weight of the impeller, such that the mass inertia of the impeller around the central axis is also reduced. By lowering mass inertia of the impeller, the bandwidth of the blower module (i.e. the frequency with which the rotational speed can be varied) is increased. This contributes in enabling the ventilation system to generate the forced oscillating pressure variation having a rate of change of more than 15 Hz, preferably more than 20 Hz, more preferably more than 25 Hz, by varying the rotational speed of the impeller. In a preferred embodiment, the driving mechanism comprises an electric motor, wherein the impeller is connected to an output shaft of the electric motor and wherein the controller is arranged for supplying electric power to the electric motor and the rotational speed of the electric motor is controlled by varying a current, voltage and/or frequency of the electric power supplied. The controller is preferably arranged for controlling the electric motor speed by means of high- frequency sinusoidal modulation on top of the normal speed pattern of the motor. Hereby, the rotational speed variation for generating the superimposed forced oscillations can be imposed around a base rotational speed of the impeller for generating the base pressure.

In a second aspect, the invention relates to a method of obtaining at least one respiratory parameter, wherein the method comprises the steps of: - providing a ventilation system according to any of the preceding embodiments; - controlling a rotational speed of the impeller for providing a flow of breathable gas having a base pressure at the gas outlet and varying the rotational speed of the impeller for superimposing a forced oscillating pressure variation onto said base pressure; - determining, on the basis of a determined respiratory response of the subject, at least one respiratory parameter that is indicative for the subject’s respiratory mechanics. Hereby, the above described at least one respiratory parameter can be obtained efficiently using the above described ventilation system.

It is then preferred that the step of determining the at least one respiratory parameter comprises: - determining a subject’s respiratory response on the basis of at least a measured flow rate and/or pressure of a flow of exhaled gas; - determining said at least one respiratory parameter on the basis of the determined respiratory response and the superimposed forced oscillating pressure variation. Hereby, the above described at least one respiratory parameter can be obtained efficiently using the above described ventilation system that is able to at least measure the flow rate and/or pressure of the flow of exhaled gas.

The present invention is further illustrated by the following figures, which show preferred embodiments of the ventilation system, and are not intended to limit the scope of the invention in any way, wherein: - Figure 1 schematically shows a functional diagram of an embodiment of a ventilation system according to the invention.

IS - Figure 2 schematically shows an embodiment of a control diagram for a ventilation system according to the invention.

- Figure 3 schematically shows a flow chart of an identification method for determining the dynamics of the respiratory system that may be employed by the embodiment of the ventilation system according to the invention.

- Figure 4 schematically shows an example of the signals employed by the identification method for determining the dynamics of the respiratory system.

- Figure 5 schematically shows a perspective view of an embodiment of the ventilation system according the invention. - Figure 6 schematically shows a first exploded view of the centrifugal blower.

- Figure 7 schematically shows a second exploded view of the centrifugal blower.

- Figure 8 schematically shows a cross-sectional view of the centrifugal blower along a first plane.

- Figure 9 schematically shows a cross-sectional view of the centrifugal blower along a second plane that is substantially orthogonal to the first plane.

Figure 1 schematically shows a functional diagram, comprising an overview of the pneumatics of the different subsystems and their interconnections, of an embodiment of a ventilation system 100 according to the invention.

The ventilation system 100 can comprises five main subsystems, a blower module 110, an oxygen- source subsystem 120, a patient gas conduit subsystem 130, an expiration valve driver subsystem

150, a patient sensory subsystem 140 and a central control unit 160 for controlling the ventilation system 100 by controlling the different subsystems. The blower module 110 comprises a single centrifugal blower 113 comprising a rotating impeller that sucks in air through an ambient air inlet 111 and a filter and muffle unit 112 that is arranged in between the centrifugal blower 113 and the ambient air inlet 111. The blower module controller 116 is arranged for controlling the rotational speed of the centrifugal blower 113 for providing a flow of gas at the gas outlet at a first pressure, as the delivered pressure is directly dependent on the rotational speed of the impeller. The blower module controller 116 can receive its input from the central control unit 160, as is explained later. The blower module controller 116 can also be integrated in the central control unit 160, such that it directly controls the blower module 110.

The delivered flow (i.e. the obtained rate of flow) is dependent on the pressure generated by the blower 113 and the resistance downstream of the blower 113 of the pneumatic circuit of the ventilation system 100. Directly downstream of the centrifugal blower 113, a flow sensor 114 can be arranged that measures the rate of flow delivered by the centrifugal blower 113 at the outlet 115. The determined rate of flow allows controlling the centrifugal blower 113 to deliver a predefined flow when a flow controlled control approach is used.

Furthermore, the determined rate of flow can be used for determining the amount of oxygen that is to be mixed with the flow of ambient air in the mixing chamber 131 of the patient gas conduit subsystem 130. The oxygen is provided to the system 100 by the oxygen-source subsystem 120, wherein the oxygen is supplied from, for instance, an external source through an oxygen inlet 121. The oxygen-source subsystem 120 can further comprise an oxygen pressure sensor 122, a controllable oxygen valve 123 for controlling the flow of oxygen, which can be measured by oxygen flow sensor 124, to the mixing chamber 131. The controllable oxygen valve 123 can, for instance, be controlled by the central control unit 160 on the basis of the measurements taken by oxygen pressure sensor 122 and/or oxygen flow sensor 124, preferably in combination with a predefined set point for the oxygen concentration of the flow of breathable gas leaving the mixing chamber 131. The oxygen-source subsystem 120 can thus form a fast reacting mass flow controller to enable real time blending of oxygen into the flow delivered by the blower 113 in the mixing chamber 131.

The patient gas conduit subsystem 130, which comprises the mixing chamber 131, can further comprise a number of sensors for determining temperature 132, output-flow rate 133 and/or output-pressure 134 of the flow of breathable gas that is provided through the first outlet 101 of the ventilation system 100. Such that it can determine the total flow and pressure that is delivered to the patient 300. The expiration valve driver subsystem 150 is arranged for controlling the expiration valve 151 of the ventilation system. The patient sensory subsystem 140 in combination with patient flow and pressure sensor 202 determines the pressure of the flow of exhaled gas that comes from the patient, through a patient interface system 200. The patient interface system 200 is arranged as an interface between the ventilation system and the respiratory system of the patient 300 and can comprise a patient flow and pressure sensor 202. The patient interface system 200 can comprise a (so-called) IO two hose system 210 wherein the gas is passed to the patient 300 through a first hose 211 and at the end of a second hose 212 of this hose system 210 the gas flow is controlled by the expiration valve 151 which can be controlled by the expiration valve driver subsystem 150, which can be controlled by the central control unit 160.

In particular, the controller 116 is arranged for controlling a rotational speed of the impeller for providing a flow of gas at the gas outlet 115 at the target mean pressure that is received by the controller 116. The target mean (or first) pressure Tmp may relate to a normal breathing pattern of a patient 300, whereby the delivered pressure (i.e. the first pressure) consecutively varies, at for instance an (average) natural breathing frequency of the patient 300, between a lower mean pressure during the expiration phase of the patient and an upper mean pressure during the inhalation phase of the patient 300.

The blower 113 and controller 116 are arranged for generating a forced oscillating pressure variations up to frequency of more than 15 Hz, preferably more than 20 Hz, more preferably more than 25 Hz, by varying the rotational speed of the centrifugal blower 113. By composing the oscillating pressure variation from one or more periodic oscillating pressures (e.g. a predefined number of random phased sinusoidal signals) each having a respective frequency , a respective pressure amplitude and, preferably, a respective phase shift, e.g. a multi-sine signal, it is possible to obtain the respiratory response at multiple frequencies at the same time.

The central control unit 160 comprises a respiratory mechanics processing unit 161 that is arranged for composing a signal that is used for generating oscillating pressure variation by the blower module 110. It is noted that the respiratory mechanics processing unit 161 may also be a separate unit that is connected to the central control unit 160. The respiratory mechanics processing unit 161 is arranged to receive, from for instance the central controller 160, the sensor input of the respective flow and pressure sensors of the ventilation system 100.

On the basis of the pressure of the flow of exhaled gas that comes from the patient, which can be determined by the patient sensory subsystem 140 in combination with patient flow and pressure sensor 202, the respiratory mechanics processing unit 161 may determine a real-time natural breathing frequency from subject’s 300 respiratory response over a predetermined period. The respiratory mechanics processing unit 161 may be arranged for determining an averaged natural breathing frequency by takmg an average of the determined real-time natural breathing frequency of the subject over the predetermined period.

IO The respiratory mechanics processing unit 161 may then determine the respective frequencies of the one or more periodic oscillating pressures such that said respective frequencies are spectrally spaced apart, or at least different, from the averaged natural breathing frequency and, preferably, its higher harmonics. The blower 113 is then controlled by the blower module controller 116 to superimpose the respective one or more periodic oscillating pressures onto the base pressure by varying the rotational speed of the impeller 1133.

The respiratory mechanics processing unit 161 is also arranged for determining the at least one respiratory parameter, being a frequency response function, an impedance function, an elastance function, an inertial function and/or a resistance function of the respiratory system, that is indicative for the subject’s respiratory mechanics. This includes measuring, using the patient sensory subsystem 140 in combination with patient flow and pressure sensor 202, the subject's respiratory response to the forced oscillating pressure variation. By computing a spectral input function from at least said forced oscillating pressure variation and by computing a spectral output function from at least said measured subject’s respiratory response, the respiratory mechanics processing unit 161 is able to determine the respective respiratory parameter on the basis of a complex ratio of the spectral input function and the spectral output function.

The respective respiratory parameter is then received by the central control unit 160 that can, in dependence of the respective respiratory parameter, adjust the base pressure that the ventilation system 100 provides to the subject 300. The control approach is shown in more detail in figure 2. Figure 2 schematically shows an embodiment of a control diagram of the central control unit 160 and the blower module controller 116. In particular, the controller 116 is arranged for controlling a rotational speed of the impeller for providing a flow of gas at the gas outlet 115. The controller 116 comprises the speed converter unit 1162 that is arranged for converting an input pressure signal to the rotor speed signal Rss, comprising the average rotational speed of the blower 113 and the superimposed rotational speed variations due to the superimposed forced oscillating pressure, The rotor speed signal Rss is used by the motor controller 1163, which is also comprised in blower module controller 116, for driving the electric motor 1133 of the centrifugal blower 113. The central control unit 160 is seen to comprise respiratory mechanics processing unit 161, a breathable gas controller 162 that links, through the FOT control module 163, to the respiratory mechanics processing unit 161 that can compute the (estimates of) the elastance E; and resistance Raw of the respiratory system of a subject 300. The elastance E, and airway resistance R,, are subsequently used by the Proportional Pressure Assist (PPS) module 164 to determine the contributions of the Proportional Pressure Assist PPS, that is summed to the targed pressure signal Tps, originating from the breathable gas controller 162, the total pressure signal TotP.

This contribution can be determined on the basis the (measured) momentanious lung volume V‚ mom multiplied by the elastance E; and the measured flow that is pulled in by the subject Vy, (which are for instance measured by using the patient sensory subsystem 140 in combination with patient flow and pressure sensor 202) multiplied by the resistance R,,,, multiplied by a preset percentage of assistance.

PPS. = Yogssist (RawVaw + E‚V: mom) A feedback loop, taking into account the measured airway pressure of the subjects P‚w. may be used for obtaining the control signal Cs that is fed to the speed converter unit 1162. Hence, it is seen that an increase in the measured elastance Ej and airway resistance R,,, results in an increased Proportional Pressure Assist contribution PPS, and vice versa.

Figure 3 schematically shows a flow chart of an identification method 400 for determining the dynamics of the respiratory system that may be employed by the embodiment of the ventilation system 100. The method 400 is, preferably, implemented into the respiratory mechanics processing unit 161 as a computer implemented method.

The first step 401 comprises determining an averaged natural breathing frequency fsp, which can be determined by taking an average of the determined real-time natural breathing frequency of the subject over the predetermined period.

The real-time natural breathing frequency can be determined from (pressure and/or flow) measurements taken from the flow of exhaled gas from the subject 300. The forced oscillation pressure variation (i.e. the excitation, or input, signal) fo is determined in the second step 402, by defining fo = fsp/n, wherein n = k/m.

Herein “K” and “m” are both positive integers and “k” is not equal to “m” or a multiple of “m”. This allows constructing a forced oscillation signal having a multiple different frequencies which are not equal to the averaged natural breathing frequency fsp, or any of its multiples (i.e. higher harmonics). The multiple different frequencies preferably have been assigned a random phase, thereby generating a random- phase-multi-sine signal for the forced oscillation pressure variation.

In the third step 403, the oscillating (i.e. time-varying) pressure signal, comprising the oscillation frequencies fo and averaged natural breathing frequency Ísp, is generated by varying the rotational speed of the single impeller 1133 of the single blower module 113. By, in the fourth step 404, measuring the flow rate and pressure from the exhaled air of the subject 300 as described above, the output signals representing the respiratory response of the subject 300 are obtained. Further filtering and or model-fitting of the measured signal representing the respiratory response Qe of the subject 300 in an optional fifth step 405, a clean data set representing the respiratory response Qe can be obtained. From the data obtained, the (complex) impedance Zrs (n, fo) of the respiratory system of the subject 300 can be obtained for the different frequencies of the oscillation pressure signal. The elastance £; and airway resistance R,, can subsequently be obtained from the (complex) impedance Zrs (n, fo). Figure 4 schematically shows an example of the signals, which can be measured in the fourth step 404, employed by the identification method for determining the dynamics of the respiratory system. The target pressure signal 4041, comprising the oscillating pressure signal that is superimposed onto the base pressure, is generated by varying the rotational speed of the single impeller 1133 of the single blower module 113, thereby resulting in the actual generated pressure signal 4042 at the outlet of the blower module 115, or an outlet of the ventilation system 100. The airway pressure 4043 and subject flow 4044 are subsequently obtained by measuring the pressure and flow of the breathable gas. A negative flow, as seen in the subject flow 4043, relates to the exhalation of gas, whereas a positive flow relates to the inhalation of gas. Any changes in these output signals 4043, 4044 with respect to the input signal 4042 are thus caused by the dynamics of the respiratory system of the subject 300, that can subsequently be determined, as is described above. Figure 5 schematically shows a perspective view of an embodiment of the ventilation system 100 according the invention, wherein the blower module 110 is mounted centrally within the ventilation system 100. An example of a centrifugal blower 113 of the blower module 110 is best seen in figure 6 -9.

The centrifugal blower 113 can comprise a motor 1131 that is arranged for driving a rotatable shaft

1132. An impeller 1133 can be connected to the rotatable shaft 1132 that is driven by the motor

1131. The motor 1131 can be an electric motor, for example a brushless direct current (BLDC) electric motor or any other type of suitable motor, with a high dynamic bandwidth. The centrifugal blower 113 can further comprise a housing that preferably comprises two housing parts 1134 and

1135. During assembly these two housing parts 1134 and 1135 are joined together, for example using screws 1136, to form the housing. The rotatable shaft 1132 extends through a hole 1137 in first housing part 1134 and is fixed to the impeller 1133. The impeller 1133 is located inside of the housing, in between the first and second housing parts 1134, 1135. Generally, the housing 1134, 1135 is arranged as a stator, whereas the rotatable shaft 1132 and the impeller 1133 are arranged as rotors. The rotation of the shaft 1132 and the impeller 1133 defines the axis of rotation al.

The (assembled) housing parts 1134, 1135 comprise a centrally arranged gas inlet 1141 that is formed as a, preferably circular, opening in the second housing part 1135. The central gas inlet 1141 can be arranged coaxial to the axis of rotation al. The assembled housing parts 1134, 1135 further defines a compression chamber 1143. The compression chamber 1143 is substantially annular and arranged around the impeller 1133, preferably substantially coaxial to the axis of rotation al. The compression chamber 1143 has an annular gas inlet 1144 surrounding the impeller

3.

The impeller 1133 is arranged in a gas passage that is defined by the assembled housing parts 1134, 1135 and extends from the central gas inlet 1141 to the annular gas inlet 1144. The impeller 1133 is arranged for driving a gas mixture from the gas inlet 1141 through the gas passage and through the annular gas inlet 1144 into the annular compression chamber 1143 and, finally, through a gas outlet 1142. The impeller 1133 causes a circular motion of the gas mixture inside the compression chamber 1143, generally in the direction of the arrow I (in figure 6). The compression chamber 1143, or the diffuser, comprises a substantially helicoidal surface 1145, wherein the helicoidal surface is arranged coaxial to the axis of rotation al. The compression chamber 1143 aids in converting the high speeds with which the gas leaves the impeller 1133 into a gas flowing at a lower speed, but at an increase pressure.

The high bandwidth of the blower module 113, that allows for superimposing the dynamic pressure oscillations {of up to, preferably, 25 Hz) onto the target mean pressure Tmp is enabled by the use of a lightweight rotor 1132 with a compact impeller 1133, that is for instance obtained by using high strength plastic materials that are injection moulded for forming an impeller 1133 with minimal thicknesses. It is seen in figures 6 — 9 that the impeller 1133 is a thin-walled structure that has a low total volume. Hereby, the mass moment of inertia (around the axis of rotation al) is reduced, such that less force is required for causing the speed variations that create the superimposed pressure oscillations. The bandwidth of such a centrifugal blower 113 is further limited by any resonance frequencies that might occur in the drive system comprising the motor, 1131, rotor 1132 and impeller 1133. By reducing the overall mass moment of inertia, the rotor 1132 and motor 1131 also require less stiffening (and thus the use of more and/or more expensive materials) to still have a sufficient bandwidth.

It is noted that the present invention is not limited to the embodiment shown, but extends also to other embodiments falling within the scope of the appended claims.

Claims

Claims I. Respirator for ventilating a subject based on at least one respiratory parameter indicative of the breathing mechanics of the subject, the respirator comprising: a bladder module comprising a gas inlet, a gas outlet, an impeller rotatably mounted between the gas inlet and gas outlet and a driving mechanism for driving the impeller; - a controller for controlling the drive mechanism of the bladder module, the controller being adapted to control a rotational speed of the impeller to provide a flow of breathing gas at the gas outlet with a base pressure and the controller being further adapted to adjust the rotational speed varying the impeller to superimpose a forced oscillating pressure variation on the base pressure, the controller comprising at least one input adapted to receive the at least one respiratory parameter, the at least one respiratory parameter being indicative of the respiratory response of the subject to the forced oscillating pressure variation, and wherein the controller is adapted to adjust the base pressure based on the received respiratory parameter.

The ventilator of claim 1, wherein the ventilator comprises only a single bladder module and the bladder module comprises only a single impeller.

The ventilator of claim 1 or 2, wherein the controller comprises a speed converter unit adapted to generate a fan speed control signal for controlling the rotational speed of the fan, the fan speed control signal being determined from the base pressure and the forced oscillating pressure variation.

Respirator according to at least one of the preceding claims, wherein the controller is adapted to control the forced oscillating pressure variations by merely varying the rotational speed of the impeller.

A respirator according to at least one of the preceding claims, wherein the controller is arranged to form the forced oscillating pressure variation from one or more periodic oscillating pressures each having a respective frequency and a respective pressure amplitude and the controller is arranged to receive of the respective frequencies and respective pressure amplitudes for superimposing the forced oscillating pressure variation on the base pressure.

The respirator of claim 5, wherein the forced oscillating pressure variation comprises a superposition of a plurality of periodic oscillating pressures, each of the plurality of periodic oscillating pressures being a sinusoidal signal having a respective frequency different from the frequency of the others of the plurality of periodic pressures oscillating pressures.

Respiratory device according to claim 5 or 6, wherein the respective frequencies are in the range from 0.01 Hz to 25 Hz, preferably from 0.1 Hz to 20 Hz.

A ventilator according to at least one of the preceding claims, wherein the at least one respiratory parameter is a frequency response function, an impedance function, an elasticity function, an inertia function and/or a resistance function of the respiratory system.

A ventilator according to at least one of the preceding claims, wherein the ventilator comprises at least one detector for measuring a flow rate and/or pressure of the flow of inhaled and/or exhaled gas from the subject to determine the respiratory response of the subject. the subject on the forced oscillating pressure variation.

A respiration device according to at least one of the preceding claims, wherein the respiration device comprises at least one detector for measuring a flow rate and/or measuring a pressure of the flow of the respiration gas.

A respirator according to at least one of the preceding claims, wherein the gas outlet of the bladder module is coupled to a conduit for directing the flow of breathing gas from the gas outlet to a subject, or at least to a subject interface module configured to have a flow path from the conduit to the subject's respiratory system, and wherein the conduit is further configured to direct a flow of exhaled gas from subject, or at least from the subject interface module, to a vital respiratory outlet.

12. Respiratory device according to claim 11 and 9 or 10, wherein the at least one detector is arranged in the conduit.

Respiratory device according to at least one of claims 9 to 12, wherein only a single detector is arranged for determining the flow rate and/or the pressure of the flow of inhaled and/or exhaled gas and for determining the flow rate and /or pressure of the breathing gas flow.

A respirator according to at least one of the preceding claims, wherein the subject's respiratory response is determined by taking measurements from the inhaled and/or exhaled air.

The ventilator of at least one of the preceding claims, further comprising a respiratory mechanics processor configured to determine the at least one respiratory parameter indicative of the subject's respiratory mechanics, the at least one respiratory parameter being determined on the based on a subject's respiratory response to the forced oscillating pressure variation, the respiratory mechanics processor being configured to provide the controller with the at least one respiratory parameter.

The ventilator of claim 15, wherein the respiratory mechanics processor is configured to determine a real-time natural respiratory rate from the subject's respiratory response over a predetermined period and wherein the respiratory mechanics processor is configured to determine an average natural respiratory rate by averaging the determined real-time natural respiratory rate of the subject over the predetermined period.

The respirator of claim 16, wherein the controller is adapted to control the rotational speed of the impeller to provide as the basal pressure an oscillating basal pressure pattern having the average natural respiratory rate at the gas outlet.

A respirator according to at least one of claims 5-7 and claim 16 or 17, wherein the respiratory mechanics processing unit is adapted to determine the respective frequencies of the one or more periodic oscillating pressures,

such that the respective frequencies are spectrally separated, or at least differ from the mean natural respiratory frequency and, preferably, its higher harmonic.

A respirator according to claim 18, wherein the respective frequencies of the one or more periodic oscillating pressures are spectrally apart, or at least differ from the mean natural respiratory rate by at least 5%, preferably at least 10%, more preferably at least 20% of the mean natural respiratory rate.

The ventilator of at least claim 10, wherein the controller comprises a feedback control loop for controlling the fan speed based on the measured flow rate and/or the sensed pressure supplied by the blower.

A respirator according to at least one of the preceding claims 15 - 20, wherein the respiratory mechanics processing unit is adapted to determine, as the at least one respiratory parameter, a frequency response function, an impedance function, an elasticity function, an inertia function and/or a resistance function. of the respiratory system.

A respirator according to at least one of the preceding claims 15 - 21, wherein the respiratory mechanics processing unit is adapted to calculate a spectral input function from at least the forced oscillating pressure variation and to calculate a spectral output function from at least the measured respiratory response of the subject and wherein the respiratory mechanics processor is configured to determine the at least one respiratory parameter based on a complex relationship between the spectral input function and the spectral output function.

Respiratory device according to at least one of the preceding claims 15 - 22, wherein the respiratory mechanics processing unit is adapted to determine a subject-specific pressure amplitude, subject-specific pressure pattern and/or subject-specific flow rate based on the determined at least one respiratory parameter. determine the flow of breathing gas, and wherein the controller is further adapted to control the rotational speed of the impeller to provide the subject-specific pressure amplitude, the subject-specific pressure pattern and/or the subject-specific flow rate of the flow of breathing gas breathing gas.

A respirator according to at least one of the preceding claims, wherein the bladder module further comprises a housing comprising the gas inlet, the gas outlet and a compression chamber, the impeller being rotatably mounted in the housing between the gas inlet and the compression chamber.

A respirator according to at least one of the preceding claims, wherein said impeller comprises a conical frontal surface which is substantially axisymmetric with respect to a central axis, wherein a plurality of fin-shaped members extend from the frontal surface in at least one direction. which is parallel to the central axis and wherein the impeller is arranged to rotate about the central axis.

Respiratory device according to at least one of the preceding claims, wherein the drive mechanism comprises an electric motor, the impeller being connected to an output shaft of the electric motor and wherein the controller is adapted to supply electric current to the electric motor and adjust the rotational speed. of the electric motor is controlled by varying the current, voltage and/or frequency of the supplied electrical power.

A method for obtaining at least one respiratory parameter, the method comprising the steps of: - providing a respiration device according to any one of the preceding claims; - controlling a rotational speed of the impeller to provide a flow of breathing gas with a basal pressure at the gas outlet and varying the rotational speed of the impeller to superimpose a forced oscillating pressure variation on the basal pressure; - determining, based on a particular respiratory response of the subject, at least one respiratory parameter indicative of the subject's respiratory mechanics.

The method of claim 27, wherein the step of determining the at least one respiratory parameter comprises: - determining the respiratory response of a subject based on at least a measured flow rate and/or pressure of an expired gas flow;

- determining the at least one respiratory parameter based on the determined respiratory response and the superimposed forced oscillating pressure variation.