NL2027208B1 - Ventilation system for respiratory support - Google Patents

Ventilation system for ventilating a patient, wherein the ventilation system comprises: - a blower module comprising a gas inlet, a gas outlet, an impeller rotatably mounted 5 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 gas at the gas outlet at a first pressure and wherein the controller is arranged for varying the rotational speed of the impeller for superimposing a dynamic oscillating pressure variation around said first 10 pressure.

Ventilation system for respiratory support 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 towards a patient. In some sitaations the systems are used to only assist the patient in breathing more easily, whereas in other situations the ventilation system is driving the supply of fresh air to the patient’s fungs.

A downside of the currently applied tidal-volume or pressure controlled respiratory systems is that they can lead to damaging the lung tissue, as high pressures may be needed to supply sufficient oxygen to the patient.

For an efficient gas-exchange in the lungs, a minimum replacement of gas per minute has to be maintained to assure the refreshment of the gasses O2 and CO2 in the alveoli in the lungs. It is possible to increase the breathing frequency, which enables the decrease of the tidal volume, but this combination can only be changed in a limited range, because of the influence of the dead space effect. Dead space is commonly referred to the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways (anatomic dead space) or reaches alveoli that are not perfused or poorly perfused (alveolar dead space). The total of anatomic dead space and alveolar dead space is called physiological dead space.

A method of so-called High Frequency ventilation has been developed which enables to ventilate the patient with a much higher breathing frequency, around 10 to 15 times the normal breathing frequency, and much lower tidal volumes. This method requires, however, in addition to a source of breathable gas, the use of a strong oscillating actuator with a membrane, like a loudspeaker, which can generate rather high positive and even negative pressures around a positive mean pressure at the relatively high frequencies.

It is a goal of the present invention, next to other goals, to provide for an improved ventilation system and method for controlling the ventilation system, wherein at least one of the above- mentioned problems is at least partially alleviated.

Ina first aspect, the invention relates to a ventilation system for ventilating a patient, wherein the ventilation system comprises:

- 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 gas atthe gas outlet at a first pressure and wherein the controller is arranged for varying the rotational speed of the impeller for superimposing a dynamic oscillating pressure variation around said first pressure. A dead space effect does not only exist in the patient's airways, but also, although having a different physical effect, in the components of the ventilation system that is connected to the patient requiring ventilation. Whereas, the dead space of the patient’s airways refers to the situation wherein the expired gas remains in the respiratory system and is inhaled again, a dead space of the ventilation system refers to the compressible volume of the entire system that influences the time response and the oscillatory amplitude of the ventilation system. The latter effect will, for a clear distinction between the different dead spaces, be referred to as compressible volume hereafter. In systems according to the prior art, the addition of such an oscillator further adds to the compressible volume (or dead volume) of the system. Furthermore, this oscillator needs to be strong (i.e. large enough) to be able to excite the compressible volume in the ventilation system in order to create pressure oscillations having the desired effect in the lungs of the patient. Hence, the additional compressible volume due to the addition of sach a strong oscillator actually reduces the overall capability of the system to achieve the desired oscillations in the lungs, where they are needed. In order to overcome this, one could add an even larger oscillator. However, this larger oscillator will (again) increase the compressible volume only further, thereby further reducing the efficiency.

The system according to the invention, however, uses the impeller of the blower module for generating both the flow of breathable gas at a first (or base) pressure for the patient as well as for generating the oscillations around said first pressure. Thereby, no additional oscillator is required that increases the compressible 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 oscillations that are superimposed onto the first pressure. The first pressure may relate to a normal breathing pattern of a patient, whereby the delivered pressure (i.e. the first pressure) consecutively varies, at for instance an (average) natural breathing frequency of the patient, between a lower mean pressure during the expiration phase of the patient and a higher mean pressure during the inhalation phase of the patient.

Furthermore, by arranging the controller such that is can vary the rotational speed of the impeller for superimposing a dynamic oscillating pressure variation around said first pressure, the pressure oscillations are 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 created 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.

The system thus allows for a relatively strong oscillatory pressure swing (i.e. oscillation) that can be superimposed onto the pressure delivered to the patient, thereby stimulating a better gas- exchange in the lungs of the patient and enabling the clinician to treat the patient in a better way that reduces the negative effects for the lungs and helps to prevent from possible VILI (Ventilator Induced Lung Injury).

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 patient, 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 frequency range wherein the overall system is able to accurately deliver the required pressure oscillations to the patient.

In a preferred embodiment, the controller is arranged for generating a target pressure control signal for controlling the driving mechanism, wherein said target pressure control signal is obtained by superimposing a first pressure signal and a second oscillating pressure signal, wherein said second oscillating signal has a predefined frequency and a predefined pressure amplitude. Hereby, the driving mechanism of the blower is controlled on the basis of a single signal that results in driving the impeller with a varying rotation speed in such a way that the first pressure and the superimposed oscillating pressure is directly generated by the impeller in the blower. Hereby, there is no need for adding further pneumatic control measures for fine tuning of the oscillating pressure that is superimposed on the first pressure signal.

Preferably, the superimposed dynamic pressure variation has a higher rate of change than said first pressure. Hereby, a better gas-exchange in the lungs of the patient can be obtained without the need for high pressures on the hung, which could harm the sensitive lung tissues, as is also described above.

In a preferred embodiment, the impeller and controller are arranged for generating a dynamic 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. Oscillation frequencies can thereby be modulated between preferably 2 and 25 Hz. Oscillating pressures in this frequency ranges have been shown to improve the gas exchange in the lungs of the patient. Pressure amplitudes of the superimposed oscillating pressures around the first (or base) pressure are preferably in the range of 1 hPa - 50 hPa, more preferably 5 hPa - 40 hPa, even more preferably 10 hPa - 30 hPa, most preferably around 20 hPa. Pressures amplitudes of the superimposed oscillating pressures in these ranges have been shown to improve the gas exchange in the lungs of the patient. 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 a pressure control signal. The generated first pressure, and the dynamic oscillating pressure variation around said first pressure, is generated by rotating the impeller while varying the rotational speed for superimposing the pressure variations. A speed converter unit is therefore preferably arranged for determining, in dependence of the requested first 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 dynamic oscillating pressure variation around said first pressure, the speed variations of the impeller that are needed for superimposing said dynamic 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 ventilation system comprises an output pressure sensor arranged for measuring the pressure of a flow of exhaled gas of the patient, and/or for measuring a flow of gas that is to be inhaled, for obtaining an output pressure signal. Hereby, the respiratory response of the patient can be monitored. In addition, it enables implementing a feedback control loop for accurately controlling the pressures supplied to a patient. In order to achieve the before mentioned improved control, it is further preferred that the controller comprises a feedback control loop for providing a feedback pressure control signal to the speed converter unit and wherein the controller is arranged for obtaining the feedback pressure control signal on the basis of the output pressure signal and an input pressure signal. It is hereby preferred that the input pressure signal is the target pressure control signal, such that pressure at which the flow of gas that is provided to the patient accurately corresponds to the target pressure control signal.

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 rotatable mounted in the housing between the gas inlet and the compression chamber. Hereby, a compact blower module is obtained, wherein the compressible volume can be reduced, such that the overall compressible 5 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 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 dynamic 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 dynamic pressure oscillations can be imposed around a base rotational speed of the impeller for generating the first pressure.

Preferably, the controller is arranged for controlling the dynamic oscillating pressure variations 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 oscillations that are superimposed onto the first pressure.

Said first pressure is preferably a base pressure or a first variable pressure pattern that is arranged by rotating said impeller at a base speed or according to a first variable speed pattern. Said first variable pressure can be the normal breathing pattern of a patient, whereby the delivered pressure (i.e. the first pressure) of the first variable pressure pattern consecutively varies, at for instance an (average) natural breathing frequency of the patient, between a lower mean pressure during the expiration phase of the patient and a higher mean pressure during the inhalation phase of the patient. In a second aspect, the invention relates to a method of controlling a pressure and/or flow using a ventilations system, wherein the method comprises the steps of: - providing a ventilation system according to any of the embodiments described; - determining a first pressure and a dynamic oscillating pressure variation; - rotating the impeller of the ventilation system at a first speed for generating a flow of gas at the first pressure; - superimposing oscillation rotational speed variations onto the impeller for generating the dynamic oscillation pressure variations around said first pressure. This enables generating relatively strong oscillatory pressure oscillations that can be superimposed onto the pressure delivered to the patient, thereby stimulating a better gas-exchange in the lungs of the patient and enabling the clinician to treat the patient in a better way that reduces the negative effects for the lungs and helps to prevent from possible VILI (Ventilator Induced Lung Injury). 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. - Figure 2 schematically shows an overview of a controller for the ventilation system of an embodiment of the ventilation system according to the invention. - Figure 3 schematically shows a pressure-time signal of a flow of breathable gas that is generated by the embodiment of a ventilation system according to the invention.

- Figure 4 schematically shows a perspective view of an embodiment of the ventilation system according the invention. - Figure 5 schematically shows a first exploded view of the centrifugal blower. - Figure 6 schematically shows a second exploded view of the centrifugal blower. - Figure 7 schematically shows a cross-sectional view of the centrifugal blower along a first plane, - Figure 8 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) 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.

Figure 2 schematically shows an overview of the blower module controller 116 that is arranged for controlling a driving mechanism (not shown) of the centrifugal blower 113. 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 Tmp 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 Lmp during the expiration phase of the patient and an upper mean pressure Ump during the inhalation phase of the patient 300. The blower module controller 116 is further arranged for receiving a target frequency Tf and a target amplitude Ta. The target frequency Tf and amplitude Ta define a dynamic oscillating pressure variation around said target mean pressure Tmp, as is also seen in figure 3. The blower 113 and controller 116 are arranged for generating dynamic pressure variations having a target 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.

A target pressure control signal Tps is obtained by superimposing the target mean pressure Tmp and the dynamic oscillating pressure signal Ops that has a predefined target frequency Tf and a predefined target pressure amplitude Ta. A feedback loop with the target pressure control signal Tps and the measured pressure at the patent output Ppo can be used for obtaining the actual control signal Cs that is converted, by means of speed converter unit 1162, to rotor speed signal Rss, comprising the average rotational speed of the blower 113 and the superimposed rotational speed variations. The rotor speed signal Rss is used by the motor controller 1163 for driving the electric motor 1131 of the centrifugal blower 113.

Figure 3 shows a pressure-time signal of a flow of breathable gas that is generated by the centrifugal blower 113. Herein, the pressure signal is seen to vary, at a slow rate, between the lower mean pressure Lmp and upper mean pressure Ump, while at the same time a higher frequent pressure variation is superimposed on the Target mean pressure Tmp. The superimposed higher frequent pressure variation has a target amplitude Ta and a period dt that is equal to 1/Tf.

Figure 4 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 5 — 8.

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 1 (in figure 5). 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 5 — 8 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.