WO2000045883A1

WO2000045883A1 - Computer-controlled portable ventilator

Info

Publication number: WO2000045883A1
Application number: PCT/US2000/000943
Authority: WO
Inventors: Nir Geffen
Original assignee: Versamed Medical Systems Ltd.; Friedman, Mark, M.
Priority date: 1999-02-04
Filing date: 2000-01-18
Publication date: 2000-08-10
Also published as: AU2506300A

Abstract

This invention is a ventilation system (20) with inspiration, and expiration support phases providing gas to a patient, including a compressor (54), which compresses the gas at a variable operating rate. The ventilator (30) conveys the gas from the compressor (54) to the patient, with a CPU (60) controlling the operating rate of the compressor so that the rate of gas supplied to the patient varies during a portion of the inspiration phase.

Description

COMPUTER-CONTROLLED PORTABLE VENTILATOR

FIELD OF THE INVENTION

The present invention relates generally to ventilators, and specifically to computer-controlled portable ventilators.

BACKGROUND OF THE INVENTION

Ventilation of patients with respiratory or cardiovascular pathologies is well known in the art. Adult Respiratory Distress Syndrome (ARDS), cardiac arrest, carbon monoxide poisoning, smoke inhalation, premature birth, and general anesthesia are among the many events which may mandate the use of a ventilator in order to bring air and/or oxygen into the body.

In response to ARDS (characterized by alveolar inability to prevent filling of the lungs with fluid), ventilators are often equipped with a capability to maintain Positive End Expiratory Pressure (PEEP). Unlike the typical situation in which there is negative pressure in the lungs at the end of expiration ~ allowing fluid to fill the lungs in ARDS patients ~ PEEP reduces the transalveolar fluid flow and thereby improves lung function. PEEP is commonly achieved by use of a PEEP valve, comprising a spring in an expiration circuit of the ventilator which must be compressed by the exhaled air in order to open the valve and allow the air to vent to atmosphere. Different PEEP levels are often attained by removing the PEEP valve and replacing it with one having a different effective resistance. Alternatively, PEEP is controlled by supplying air to the patient through one branch of a Y-tube and having the patient exhale through another branch, whose resistance is controlled by a valve coupled to the ventilator.

PCT Patent Publication WO 97/06843 to Geffen, whose disclosure is incorporated herein by reference, describes a ventilator wherein a CPU turns a compressor on and off cyclically in order to control the respiration of a patient.

PCT Patent Publication WO 89/10768 to Sipin, whose disclosure is incorporated herein by reference, describes a portable ventilator in which a CPU controls the respiratory cycle by varying the states of one or more valves. U.S. Patent 5,398,676 to Press et al., whose disclosure is incorporated herein by reference, describes a portable respirator in which the compressor is turned on and off by electronic circuitry in order to generate each respiratory cycle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved patient ventilator.

It is a further object of some aspects of the present invention to provide a portable ventilator which enables a broad set of ventilation parameters to be regulated under software control.

In preferred embodiments of the present invention, a ventilator which provides a gas to a patient comprises a compressor and a CPU which governs the speed of the compressor. Ventilators of the prior art substantially do not actively control the compressor operating speed. Instead they typically control parameters of ventilation by incorporating additional hardware to shunt output from a continuously operating compressor, or they turn the compressor on and off during each breathing cycle. In preferred embodiments of the present invention, software- controlled regulation of the operating speed of the compressor throughout the breathing cycle preferably gives an operator of the ventilator the ability to modify a set of ventilation parameters, such as respiration rate, flow rate, pressure, PEEP and Inspiration: Expiration time (I:E, the relative proportion of the breathing cycle allotted for inspiration and expiration). Feedback from a pressure sensor and/or a flow sensor coupled to a patient valve associated with the ventilator is continuously sent to the CPU, which modifies the compressor speed in order to maintain desired pressure and/or flow values throughout at least a substantial portion of the duration of the breathing cycle.

In a preferred embodiment of the present invention, the CPU monitors the flow and/or pressure measurements made at the patient valve in order to detect a "breathing effort" (an effort by the patient to inhale spontaneously). Generally, airflow or pressure changes occurring during a predetermined "dead time" following expiration are attributed to spontaneous breathing efforts by the patient. When, for example, negative pressure is detected during the dead time of the breathing cycle, the CPU preferably increases compressor output in order to minimize the magnitude of the negative pressure measured at the patient valve. This increase in compressor output consequently supports the spontaneous breathing effort.

In another preferred embodiment of the present invention, PEEP is regulated through software by maintaining during expiration a positive pressure in a variable PEEP valve coupled to the patient valve. Preferably, a continuous range of PEEP levels is available by setting the compressor speed to an appropriate value during expiration. Further preferably, the CPU frequently samples pressure measurements made at the patient valve, and modifies the compressor speed accordingly in order to keep the pressure measurements substantially equal to a desired PEEP level. In some ventilators of the prior art, for example the Drager Oxylog 2000, a variable PEEP valve is also used. However, in these prior art ventilators, an additional valve and a separate pressure regulation hose are needed to maintain the desired PEEP level.

In yet another preferred embodiment of the present invention, oxygen flow is verified at regular intervals by reducing or suspending an ambient air input to the compressor, in order to allow substantially only oxygen, or a relatively greater concentration of oxygen, to enter the compressor and go the patient valve. Routine pressure measurements made at the patient valve during this period verify sufficient oxygen flow.

In other preferred embodiments of the present invention, a system for controlling oxygen concentration in an air stream supplied to the patient comprises an ambient air input valve, whose operation is governed by the CPU to regulate the quantity of ambient air which is drawn into the ventilator. Preferably, the CPU controls a setting of regulating means (e.g., linear actuator or a worm gear) coupled to the ambient air input valve in order to achieve a desired oxygen concentration responsive to the quantity of ambient air drawn into the ventilator. The settings attainable by the regulating means can range from the ambient air input valve being completely open, to being completely closed, and includes a range of partially open settings. In applications wherein the regulating means comprises an electrically- powered linear actuator or a worm gear, electrical power is required to move the actuator or worm gear to a new position, but is preferably not required to maintain the actuator or worm gear in any given position. Alternatively, the regulating means is directly controlled by an operator of the ventilator, who manually changes the setting of the regulating means in order to attain a desired oxygen concentration.

Alternatively or additionally, a dual-input, CPU-controlled valve performs generally the same function as the ambient air input valve, but is additionally coupled to receive oxygen, and to convey the air and/or oxygen to an inlet manifold. In a typical mode of operation, the compressor generates suction, which draws air and/or oxygen into the dual-input valve. A setting of the valve is determined by the CPU, such that a desired combination of oxygen and ambient air is provided to the patient.

In other preferred embodiments of the present invention, one or more physiological parameters of the patient, such as weight and/or height, are entered through a user interface into the CPU and are used by the CPU to select appropriate ventilation parameters.

In yet other preferred embodiments of the present invention , an internal solenoid valve is coupled to allow it to shunt air from the compressor away from the patient valve during expiration. This shunting allows patients (e.g., elderly patients, infants, or other high respiration rate patients) to exhale even though the inertia of the decelerating compressor blades continues to move air through the compressor after the CPU shuts the compressor off or reduces its speed to allow expiration to occur.

In some of these preferred embodiments, the internal solenoid valve incorporates a safety feature by which malfunction of the compressor resulting in excessive output pressure automatically triggers the solenoid to shunt the compressor output away from the patient and to give the patient access to ambient air and/or oxygen. It is understood that solenoid valve could be replaced by other mechanisms known in the art, such as a stepper motor-actuated valve, a digitally-controlled magnetic latching valve or another proportional valve known to regulate air flow. Additionally, the valve may be linearly or rotationally actuated.

In some preferred embodiments of the present invention, at least one CPU- controlled valve is coupled to cause a decrease in the pressure of air which has left the compressor. Typically, this pressure reduction is performed during an expiration phase of the ventilator, in order to: (a) help the patient to begin exhaling by overcoming pressure unavoidably generated during deceleration of the compressor's blades; and/or (b) allow the compressor to continue operating at a decreased but moderate speed while simultaneously allowing the patient to exhale. In this manner, when the inspiration phase is initiated (e.g., by a breathing effort or by the CPU), the compressor is quickly able to supply the patient with air at a rate sufficient for comfortable inhaling and/or sufficient to overcome high patient airway resistance. It is known that a patient may feel discomfort when a ventilator's output cannot increase in accordance with the patient's inspiration attempts.

There is therefore provided, in accordance with a preferred embodiment of the present invention, a ventilation system having inspiration and expiration phases for providing a gas to a patient, including: a compressor, which compresses the gas at a variable operating rate for supply to the patient; patient supply apparatus, through which the gas from the compressor is conveyed to the patient; and a CPU, which controls the operating rate of the compressor so that the rate of gas supply to the patient varied during a portion of the inspiration phase.

Preferably, the system includes a sensor, which generates a signal responsive to a characteristic of the gas supply, and the CPU receives the signal from the sensor and controls the operating rate of the compressor responsive to the signal.

Further preferably, the system includes a variable Positive End Expiratory Pressure (PEEP) valve which varies a PEEP level responsive to the operating rate of the compressor.

Still further preferably, the compressor is a rotary compressor, whose speed of rotation is varied so as to vary the rate of gas supply. Preferably, the compressor includes a turbine selected from the group consisting of: a radial blower turbine and a regenerative drag turbine.

In a preferred embodiment, the system includes a gas-mixing mechanism to provide a mixture of first and second gases to the patient, the mechanism including a valve, which is controlled to regulate a quantity of the first gas supplied to the patient, and a demand valve, which regulates a quantity of the second gas responsive to the quantity of the first gas. Preferably, the controlled valve includes an electrically- actuated valve, and the electrically-actuated valve includes a linear actuator or a worm gear, such that electricity is generally supplied to the electrically-actuated valve only to change the regulated quantity of the first gas.

In another preferred embodiment, the CPU receives a signal indicative of a physiological parameter of the patient and sets a ventilation parameter responsive to the signal.

In still another preferred embodiment, the system includes a shunt valve which shunts the gas leaving the compressor away from the patient supply apparatus during the expiration phase.

In yet another preferred embodiment, the system includes at least one valve, controlled by the CPU, which at least one valve is controlled to reduce a pressure of gas exiting the compressor during the expiration phase. Preferably, the at least one valve includes a plurality of valves, such that at least two of the plurality of valves are separately controlled by the CPU in order to regulate a level of the pressure reduction.

There is further provided, in accordance with a preferred embodiment of the present invention, an electrically-controlled mixing valve for use in a ventilation system to provide a mixture of first and second gases to a patient, including an electrically-actuated valve which regulates a quantity of the first gas supplied to the patient, such that electricity is generally supplied to the valve only to change the regulated quantity of the first gas. Preferably, the mixing valve includes a demand valve which regulates a quantity of the second gas responsive to the quantity of the first gas.

There is also provided, in accordance with a preferred embodiment of the present invention, gas mixing apparatus for use in a ventilation system to provide a mixture of first and second gases to a patient, including: a control valve, which regulates a quantity of the first gas supplied to the patient; and a demand valve which regulates a quantity of the second gas responsive to the quantity of the first gas.

Preferably, the demand valve includes a passive valve, which does not receive electrical power.

Further preferably, the demand valve reduces a pressure of the second gas. There is further provided, in accordance with a preferred embodiment of the present invention, gas mixing apparatus for use in a ventilation system to provide respective regulated quantities of two gases to a patient, including: a demand valve, which provides the regulated quantity of one of the gases responsive to a control pressure applied to the valve; and a control valve, coupled to the demand valve so as to convey the control pressure thereto, and which simultaneously regulates the quantity provided of the other of the gases.

There is additionally provided, in accordance with a preferred embodiment of the present invention, a ventilation system for providing a gas to a patient, including: a compressor, which is activated, responsive to a desired respiratory rate, so as to compress the gas for supply to the patient during an inspiration phase of the system and is deactivated so as substantially not to compress the gas during an expiration phase of the system, except for a residual amount of gas compressed during an initial portion of the expiration phase due to inertia of the compressor; patient supply apparatus, through which the gas from the compressor is supplied to the patient; and a shunting valve, which shunts gas leaving the compressor away from the patient supply apparatus during the initial portion of the expiration phase.

There is further provided, in accordance with a preferred embodiment of the present invention, a method for supplying a gas to a patient having inspiration and expiration phases, including: compressing the gas using a compressor which operates at an operating rate which is variable, responsive to a desired ventilation parameter; and controlling the operating rate of the compressor so as to vary the rate during a portion of the inspiration phase.

Preferably, the method includes receiving a signal responsive to a characteristic of the gas supply, and controlling the operating rate of the compressor responsive to the signal.

Further preferably, the method includes varying the operating rate of the compressor during the expiration phase in order to vary a pressure in a variable PEEP valve. Still further preferably, the method includes providing a desired mixture of first and second gases to the patient by actively regulating a quantity of the first gas supplied to the patient and passively regulating a quantity of the second gas responsive to the quantity of the first gas.

In a preferred embodiment, actively regulating includes supplying electricity generally only to a valve which changes the regulated quantity of the first gas, whereby the quantity of the second gas varies responsive to the quantity of the first gas.

Preferably, controlling the operating rate includes determining a physiological parameter and regulating the operating rate responsive thereto.

In a preferred embodiment, the method includes shunting the gas leaving the compressor away from the patient during the expiration phase.

In another preferred embodiment, the method includes: operating the compressor during the expiration phase; and controlling gas flow coming from the compressor during the expiration phase so as to reduce a pressure thereof.

In yet another preferred embodiment, controlling the gas flow includes controlling a plurality of valves coupled to the compressor, and at least two of the plurality of valves are separately controlled, in order to regulate a level of the pressure reduction.

There is still further provided, in accordance with a preferred embodiment of the present invention, a method for supplying a gas to a patient, including providing a mixture of first and second gases to a patient, and regulating a quantity of the first gas supplied to the patient, such that for the purpose of varying the mixture, electricity is generally supplied only to a valve regulating the quantity of the first gas.

Preferably, the method includes passively regulating a quantity of the second gas responsive to the quantity of the first gas.

There is also provided, in accordance with a preferred embodiment of the present invention, a method for supplying a mixture of first and second gases to a patient, including: actively regulating a quantity of the first gas supplied to the patient; and regulating a quantity of the second gas responsive to the quantity of the first gas.

In a preferred embodiment, regulating the quantity of the second gas includes passively regulating the quantity of the second gas, substantially not using electricity to control a valve regulating the second gas.

Preferably, the method includes verifying a supply of the second gas by changing the quantity of the first gas during a test period and measuring an amount of the second gas during the test period.

Further preferably, the method includes reducing a pressure of one of the gases.

There is further provided, in accordance with a preferred embodiment of the present invention, a method for supplying respective regulated quantities of two gases to a patient, including: actively regulating the quantity of one of the gases using a control valve; generating a control pressure using the control valve substantially simultaneously with regulating the quantity of the one of the gases; and providing the quantity of the other of the gases responsive to the control pressure.

Preferably, the method includes reducing a pressure of the other of the gases at the second site prior to providing the quantity thereof.

There is additionally provided, in accordance with a preferred embodiment of the present invention, a method for providing a gas to a patient using a ventilation system having inspiration and expiration phases, including: activating a compressor so as to cyclically compress the gas, responsive to a desired respiratory rate, for supply to the patient during the inspiration phase; deactivating the compressor so as substantially not to compress the gas during the expiration phase, except for a residual amount of gas compressed during an initial portion of the expiration phase due to inertia of the compressor; and shunting the gas compressed during the initial portion of the expiration phase away from the patient.

There is further provided, in accordance with a preferred embodiment of the present invention, a ventilation system for providing a gas to a patient, including: a compressor, which compresses the gas at a variable operating rate for supply to the patient; and a variable Positive End Expiratory Pressure (PEEP) valve, through which the gas is supplied to the patient, which varies a PEEP level responsive to the operating rate of the compressor.

There is still further provided, in accordance with a preferred embodiment of the present invention, a method for supplying a gas to a patient having an expiration phase, including compressing the gas using a compressor which operates at an operating rate which is variable, responsive to a desired Positive End Expiratory Pressure (PEEP) level.

The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1A is a schematic illustration of a computer-controlled ventilation system, in accordance with a preferred embodiment of the present invention;

Fig. IB is a schematic illustration of another computer-controlled ventilation system, in accordance with a preferred embodiment of the present invention;

Fig. 1C is a schematic illustration of yet another computer-controlled ventilation system, in accordance with a preferred embodiment of the present invention;

Fig. ID is a schematic illustration of still another computer-controlled ventilation system, in accordance with a preferred embodiment of the present invention;

Fig. 2A is a schematic illustration of a PEEP valve in the system of Fig. 1A, in an inspiration phase of the ventilator, in accordance with a preferred embodiment of the present invention;

Fig. 2B is a schematic illustration of the PEEP valve of Fig. 2A, in an expiration phase of the ventilator, in accordance with a preferred embodiment of the present invention; Fig. 2C is a schematic illustration of the PEEP valve of Fig. 2A, after the expiration phase of the ventilator, in accordance with a preferred embodiment of the present invention;

Fig. 3 A is a schematic, sectional illustration of an implementation of the PEEP valve of Fig. 2 A, in accordance with a preferred embodiment of the present invention;

Fig. 3B is an isometric, schematic illustration of the PEEP valve of Fig. 3A, showing internal components thereof, in accordance with a preferred embodiment of the present invention; and

Fig. 3C is an isometric, schematic illustration of the PEEP valve of Fig. 3 A, in accordance with a preferred embodiment of the preferred invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1A is a schematic illustration of a ventilation system 20 comprising a computer-controlled portable ventilator 30 and patient supply apparatus 80, in accordance with a preferred embodiment of the present invention. In this embodiment, ventilator 30, enclosed within a case 32, is coupled to a ventilation tube 82 in order to carry a gas to a patient 100. Gas inputs to the ventilator are determined by an operator of the ventilator, and preferably comprise ambient air and a high pressure oxygen source 46 or a low pressure oxygen source 44. It is understood that other gases, such as anesthetics, or pharmaceuticals, such as in the form of aerosols, may be included in a mixture supplied to the patient.

Suction created by a compressor 52 draws ambient air through an optional NBC (Nuclear-Biological-Chemical) filter 34 and through an ambient air filter 36 into an ambient air input valve 38. The ambient air input valve, preferably under the control of a CPU 60, may restrict the flow of ambient air therethrough by regulating the position of an element 40 within the ambient air input valve. Element 40 preferably comprises a linear actuator or a worm gear. Preferably, the flow of oxygen through a demand valve 48, such as the demand valve described in the above- mentioned PCT Patent Publication WO 97/06843 to Geffen, is regulated responsive to the airflow through ambient air input valve 38. When element 40 is set to substantially restrict ambient air flow, more oxygen is drawn through the demand valve into an inlet manifold 42, where the oxygen and ambient air are mixed. Similarly, when more ambient air is allowed to pass through the ambient air input valve into manifold 42, correspondingly less oxygen enters the manifold. In this manner, ventilator 30 supplies a substantially continuous range of attainable oxygen concentrations in the gas passed to the patient, from atmospheric level 100%, which can be set by the CPU or by an operator of the ventilator. In another preferred embodiment (not shown), an active valve (such as a linear or rotating solenoid valve or other valve known in the art) is used instead of or in addition to element 40 to regulate the flow of ambient air into inlet manifold 42. In yet another preferred embodiment of the present invention, ambient air input valve 38 is controlled manually by an operator of ventilator 30 in order to attain a desired oxygen concentration.

Preferably, oxygen concentration is measured during inspiration by an optional oxygen sensor 89 coupled to a flow transducer 88 in patient supply apparatus 80. The concentration thereby ascertained is used by CPU 60 in a negative feedback loop to control operation of ambient air input valve 38, in order to give a desired oxygen output level. For example, if the desired oxygen concentration is 40%, and a measurement by oxygen sensor 89 determines that the concentration is 35%, then the CPU, having that measurement as an input, adjusts the position of element 40 to further restrict the flow of ambient air through ambient air input valve 38 in order to increase the oxygen concentration of the gas entering compressor 52, as described hereinabove. Frequent sampling of the output of oxygen sensor 89 and subsequent modifications of the position of element 40 when necessary maintain the oxygen concentration in the gas delivered to the patient substantially equal to the desired value.

Alternatively or additionally, the oxygen concentration measurement is performed: (a) by a sensor fixed to an exit port 83, which sensor is coupled to receive gas flow from compressor 52; and/or (b) within a sensor package 66 located inside ventilator 30. Further alternatively or additionally, blood oxygen levels are measured, preferably by a pulse oximetry unit 102 attached to the patient, and these measurements are used in a similar negative feedback loop to control operation of the ambient air input valve, in order to produce a desired blood oxygen level. In some preferred embodiments, other physiological measurements, such as blood pressure, pulse rate, carbon dioxide concentration, and ECG, may also be used by the CPU to modify operating parameters of ventilator 30. Alternatively or additionally, results from one or more of the above measurements are displayed to an operator of the ventilator, who optionally modifies operating parameters of ventilator 30 responsive to the measurements.

In some operation modes of ventilator 30, CPU 60 uses one or more formulae and/or a look-up table stored in a memory associated therewith when controlling input valve 38. In these modes, predominantly open-loop control of valve 38 is exercised, in contrast to the closed-loop control of valve 38 described hereinabove. For example, if an oxygen concentration of 40% is chosen by an operator of ventilator 30, CPU 60 performs a pre-programmed calculation and/or finds a value in the look-up table, using as inputs the .40% desired concentration and optionally other parameters (such as the respiration rate, pressure, and flow rate), in order to determine a new setting for ambient air input valve 38.

Under normal operating conditions, the gas from inlet manifold 42 is drawn into compressor 52, wherein the gas pressure is increased. A resultant pressure difference across the compressor is measured by a differential pressure sensor 56, which passes the result to CPU 60 to verify proper operation of the compressor and/or enable operation of a negative feedback loop based on the measurement. Unlike ventilators of the prior art, ventilation system 20 preferably utilizes high-speed control of a DC brushless motor 53 coupled to the compressor, and the compressor preferably comprises a radial blower turbine or a regenerative drag turbine. Both the radial blower turbine and the regenerative drag turbine are capable of operating at a range of speeds responsive to the operating speed of motor 53. This configuration is preferably used, as described in this disclosure, to regulate many aspects of air flow through ventilator 30 and patient supply apparatus 80, including parameters such as respiration rate, flow rate, pressure, I:E, and PEEP. For example, a desired flow or pressure profile in patient supply apparatus 80 is produced by CPU 60 by applying a voltage or current to motor 53 coupled to compressor 52, measuring the pressure generated in the patient supply apparatus using one or more pressure sensors and/or differential pressure sensors within sensor package 66, and adjusting the voltage or current accordingly. Frequent sampling of flow parameters during each breathing cycle preferably produces the desired pressure or flow profile. The ability of system 20 to actively and responsively control pressure levels throughout the respiratory cycle is particularly useful in application involving detecting breathing efforts by patient 100. For example, CPU 60 regulates compressor 52 so that reduced measured pressure in patient supply apparatus 80 due to an inspiration attempt by the patient is immediately compensated for by an increase in compressor output. CPU 60 continues to increase compressor output throughout the period of reduced pressure, and thereby reduces the "work of breathing." Similarly, some ventilator therapies require precise control of the onset rate of pressure or flow, which need is currently satisfied only by expensive, non-portable ventilators. Control of flow or pressure onset rates in some preferred embodiments of the current invention is achieved through CPU regulation of compressor speed.

CPU 60 operates a solenoid valve 58, coupled to patient supply apparatus 80, in order to select whether patient 100 will receive the gas from compressor 52 (coupled to valve 58) or directly from inlet manifold 42 (coupled to valve 58 through a bypass line 50). Alternatively, other regulating means, as are known in the art (for example a stepper motor-actuated valve or a digitally-controlled magnetic latching valve), are used to perform essentially the same function as solenoid valve 58. In particular, it will be understood by one skilled in the art that valve 58, while shown as a linear valve in Fig. 1, could be replaced by a rotational valve. Preferably, under normal operating conditions, CPU 60 sets the solenoid valve to allow gas to flow to the patient from the compressor. In case of compressor malfunction, the CPU switches solenoid valve 58 to allow patient 100 to receive gas flow directly from the manifold. Alternatively, compressor malfunction automatically causes solenoid valve 58 to shunt flow away from the compressor without action by the CPU. Additionally, a negative pressure relief valve 62 and positive pressure relief valve 64 are preferably incorporated within ventilator 30 to allow the patient to inhale and exhale in the event of ventilator malfunction.

In high breathing rate applications, for example ventilation of infants, solenoid valve 58 is preferably used to shunt gas leaving compressor 52 away from ventilation tube 82 during expiration. By way of illustration and not limitation, high breathing rates may range from 40 to 70 breaths/minute. This shunting prevents residual pressure during deceleration of compressor blades 54 (located within the compressor) from preventing the patient from exhaling. In normal breathing rate applications, this shunting is generally not performed, because the deceleration of blades 54 requires substantially less time than the period designated for expiration.

Measurements of flow parameters within patient supply apparatus 80 are preferably made using flow transducer 88 connected to tube 82. Transducer 88, typically a differential pressure flow transducer, is coupled to a sensor package 66 in the ventilator by thin flexible tubes 90 and 92. Package 66 comprises one or more pressure sensors and, optionally, oxygen and carbon dioxide sensors. Sensor package 66 preferably sends electrical signals to CPU 60 responsive to the pressure and/or gas composition within tubes 90 and 92. Alternatively or additionally, oxygen and/or carbon dioxide sensors may be coupled directly to the patient supply apparatus. During inspiration, air leaving the flow transducer preferably passes through a bacterial filter 94 before entering a face-mask 96 or other means for bringing the gas to the patient, as are known in the art. Although most of the components of patient supply apparatus 80 are shown as separate from mask 96 in order to improve clarity, in practice they are preferably made as a single, integral unit.

Fig. IB is a schematic illustration of another computer-controlled ventilation system 21, comprising ventilator 30 coupled to patient supply apparatus 79, in accordance with a preferred embodiment of the present invention. Ventilator 30, according to this embodiment, is different from that described hereinabove with reference to Fig. 1A predominantly in that: (a) a CPU-controlled valve 81 is optionally coupled to ventilator case 32 and to patient supply apparatus 79; (b) an "internal bypass flow" valve assembly 106 is coupled to an output of compressor 52; and (c) solenoid valve 58 (Fig. 1 A) is generally not used to regulate flow. In order to clarify the roles of CPU-controlled valve 81 and valve assembly 106 in system 21, solenoid valve 58, patient valve 84, and an optional PEEP valve 86 (described hereinbelow with respect to Figs. 2A-C) are not shown in Fig. IB. It will nevertheless be understood by one skilled in the art that cooperation between controlled valve 81 and valve assembly 106 of system 21 and valves 58, 84 and/or 86 of system 20 is possible, can provide redundancy in case of failure of one of the valves, and is desirable for some applications of the present invention. Additionally, solenoid valve 58 is used in some embodiments to perform both shunting functions, as described hereinabove, and also functions, like those performed by controlled valve 81, relating to controlling air pressure in the patient supply apparatus during expiration, as described hereinbelow.

Patient supply apparatus 79 typically comprises a Y-tube 104, which couples flow transducer 88 to exit port 83 and CPU-controlled valve 81. More generally, Y- tube 104 preferably serves as a means for air flow to come from compressor 52 to patient 100 during inspiration, and for air flow to go from patient 100 and/or from compressor 52 to valve 81 during expiration, in order to be released therefrom into the atmosphere. Y-tube 104, as is known in the art, is particularly advantageous in some applications (e.g., those involving infants and elderly patients), because it allows air to continue to flow from compressor 52 through controlled- valve 81 while patient 100 exhales, and the compressor can use this flow of air as an immediate source of pressurized air for the patient by partially or completely closing valve 81 when the patient begins to inhale.

CPU-controlled valve 81, preferably comprising a linear or rotational proportional valve, as is known in the art, controls flow from compressor 52 and from patient 100. Valve 81 typically comprises a stepper motor-actuated valve or a digitally-controlled magnetic latching valve. Alternatively or additionally, valve 81 comprises a pneumatically-controlled valve, for example, a mushroom valve, as is known in the art. In some applications, valve 81 is used to control PEEP levels by controlling the pressure in patient supply apparatus 79. In a closed-loop mode of operation, dynamic pressure measurements made at flow transducer 88 and/or at exit port 83 are used by CPU 60 to regulate valve 81 and or the speed of compressor 52 in order to attain a desired PEEP level at transducer 88. Alternatively, in an open- loop mode of operation, CPU 60 selects a setting for valve 81 based on, for example, a value in a look-up table, and generally not responsive to a dynamic pressure measurement.

Simultaneous regulation of compressor speed and of CPU-controlled valve 81 is preferably used to increase the response speed of ventilation system 21 to a breathing effort by patient 100, as described hereinbelow. Generally, CPU 60 decreases the operating speed of compressor 52 during the ventilator's expiration phase from the high-speed operation associated with the inspiration phase. Detection of initiation of a breathing effort is preferably used as a trigger to begin the inspiration phase by increasing the compressor speed in order to support the patient's breathing effort. The speed with which the ventilator output can be increased is known to affect the patient's comfort while inhaling. In particular, a slow increase of ventilator output uncomfortably increases the patient's "work of breathing" at the beginning of inspiration.

Therefore, ventilation system 21 preferably increases the effective response rate of ventilator 30 to a breathing effort by maintaining an intermediate compressor speed during expiration. The intermediate-pressure are generated during the expiration phase is preferably released to the atmosphere through controlled valve 81 , which is in a partially or completely open position during expiration. Concurrently, patient 100 is exhaling, and the exhaled air is also released through controlled-valve 81. Upon detection by CPU 60 of a breathing effort by patient 100, valve 81 is preferably switched to a closed position in order to divert the compressor output to patient 100. Because compressor 52 was operating at an intermediate speed during expiration, a significant amount of pressure is provided upon closing valve 81 to support the initial breathing effort. Subsequently, compressor operation preferably increases from the intermediate speed to a higher speed, in accordance with a desired pressure or flow profile, as described hereinabove with respect to Fig. 1 A.

Alternatively or additionally, internal bypass flow valve assembly 106, coupled to the output of compressor 52, allows elevated air pressure, most preferably, intermediate air pressure generated during the expiration phase, to partially or completely bypass patient supply apparatus 79. The role of valve assembly 106 is generally similar to that of controlled-valve 81; e.g., it allows compressor 52 to continue operating at an intermediate speed during the expiration phase and optionally reduces pressure in the patient supply apparatus at the beginning of the expiration phase. It is noted that solenoid valve 58 in system 20 is used in some applications for similar response purposes to those served by controlled-valve 81 and valve assembly 106 in system 21.

Assembly 106 typically comprises independently-controlled solenoid valves 108 and 110. Although Fig. IB shows two solenoid valves in assembly 106, only one valve is used in some embodiments of the present invention, while three or more valves may be used in others. Preferably, valves 108 and 110 comprise CPU- controlled linear actuators, rotating actuators, stepper motors, digitally-controlled magnetic latching valves, and/or other means known in the art for regulating air flow. For some applications, typically those in which two or more solenoid valves are used in assembly 106, the valves are two-position valves. When controlled in combination, "n" two-position valves yield up to 2ⁿ levels of resistance to air flow through assembly 106. At least one of the n valves, in a closed position thereof, preferably does not completely occlude flow through assembly 106.

Preferably, internal bypass flow valve assembly 106 is additionally coupled to inlet manifold 42 (as shown in Fig. IB). It will be understood by one skilled in the art, however, that assembly 106 can also be coupled to conduct the output of compressor 52 to other elements within ventilator 30 or to an exit port (not shown) on ventilator case 32.

Fig. 1C is a schematic illustration of yet another computer-controlled ventilation system 23, comprising ventilator 30 coupled to patient supply apparatus 79, in accordance with a preferred embodiment of the present invention. Ventilator 30, according to this embodiment, is different from that described hereinabove with reference to Fig. IB predominantly in that CPU-controlled valve 81 is preferably replaced by a pneumatically-controlled valve 181, coupled to patient supply apparatus 79 and optionally coupled to ventilator case 32. Additionally, ventilator 30, according to this embodiment, preferably comprises a CPU-controlled valve 182, coupled to: (a) the output of compressor 52; (b) pneumatic regulating means of valve 181; and (c) a port to vent to atmosphere, which port is preferably fixed to ventilator case 32.

In another preferred embodiment (not shown),-controlled valve 81 (Fig. IB) is used at generally the same time as pneumatically-controlled valve 181 and CPU- controlled valve 182.

CPU-controlled valve 182 typically comprises a three-way solenoid valve, which, responsive to an electric signal from CPU 60, conveys gas from compressor 52 to valve 181, most preferably in order to convey thereto a control pressure. Preferably, pneumatically-controlled valve 181 comprises a standard mushroom valve, as is known in the art, such that expired air from patient 100 is allowed to vent to atmosphere only if the pressure of the expired air is greater than the control pressure generated by compressor 52.

In one mode of operation of ventilator 30, CPU-controlled valve 182 shunts substantially all of the output of compressor 52 to atmosphere during at least a portion of the expiration phase, in order to enable patient 100 to exhale with minimal effort. Typically, this mode is utilized at the beginning of the expiration phase and is optionally combined with control of PEEP during the remainder of the expiration phase. In applications wherein valve 181 comprises a mushroom valve, the shunting by valve 182 causes the PEEP pressure generated by the mushroom valve's membrane to be essentially zero. Alternatively, when valve 182 is actuated to convey gas from compressor 52 to pneumatically-controlled valve 181 during the expiration phase, the pressure generated by compressor 52 is generally equal or similar to the PEEP pressure.

Fig. ID is a schematic illustration of still another computer-controlled ventilation system 25, comprising ventilator 30 coupled to patient supply apparatus 80, in accordance with a preferred embodiment of the present invention. Ventilator 30, according to this embodiment, is different from that described hereinabove with reference to Fig. 1 A predominantly in that ambient air input valve 38 is replaced by a dual-input, CPU-controlled valve 39, coupled to demand valve 48 and ambient air filter 36. CPU 60 preferably regulates a setting of valve 39 and the operating rate of compressor 52 such that a gas mixture with a desired combination of ambient air and oxygen is conveyed to patient 100. Preferably, valve 39 comprises an actuating mechanism, such as a solenoid, stepper-motor, or worm gear, that can be set in a generally continuous manner over its operating range in order to enable valve 39 to provide a range of oxygen concentrations to the patient.

In some high flow-rate modes of operation, oxygen flow into inlet manifold 42 is restricted. In these modes, CPU 60 typically regulates the state of valve 39, in order to restrict or completely block the flow of oxygen to patient 100.

It will be understood by one skilled in the art that the various configurations of valves shown in Figs. 1A, IB, 1C, and ID are shown by way of example. For some applications, one or more valves shown in one of these figures are incorporated into the ventilation apparatus shown in another one of the figures. Fig. 2A is a schematic illustration of optional PEEP valve 86 during an inspiration phase of ventilator 30, in accordance with a preferred embodiment of the present invention. PEEP valve 86 preferably comprises a standard mushroom valve, as is known in the art, a connector 138, and an air flow modulator 140. In general, optional PEEP valve 86 allows an air flow parameter to be used to modulate a PEEP pressure, as described hereinbelow.

Typically, during the inspiration phase, a flow of gas comes from ventilator 30 through ventilator tube 82 and modulator 140, and is conveyed therefrom to patient 100. Preferably, modulator 140 comprises a one-way valve 118, which is in an open state when the air pressure thereacross is greater than a threshold value. Generally, during the inspiration phase, the air pressure across one-way valve 118 is greater than the threshold value, and gas from ventilator 30 passes through valve 118 and goes to patient 100. Alternatively or additionally, modulator 140 comprises a humidifier, preferably a heated humidifier, which generally functions as a one-way valve, as described hereinabove.

Although gas can flow from tube 82 into a compartment 120 of PEEP valve 86 through connector 138, at no time during the respiration cycle does any substantial quantity of gas enter compartment 120 through the connector, because a deformable membrane 122 located within the PEEP valve precludes such flow. Membrane 122 deforms according to the relative pressures in a patient chamber 130 and in compartments 120 and 128 of PEEP valve 86 located on opposite sides of the membrane. During inspiration, the pressure in compartment 120 is substantially equal to or greater than that within compartment 128 and chamber 130, and membrane 122 consequently presses against and closes an opening of chamber 130. Pressure by membrane 122 on chamber 130 thereby precludes any substantial flow through the chamber during inspiration.

In another preferred embodiment (not shown), connector 138 is coupled between compartment 120 and an output port of compressor 52. According to this alternate embodiment, ventilator 30 separately controls the pressure in tube 82 and in connector 138, such that tube 82 generally conveys gas from the ventilator to patient 100, while connector 138 conveys a control pressure from the ventilator to compartment 120. Fig. 2B illustrates PEEP valve 86 during the ventilator's expiration phase, showing the flow of exhaled air, in accordance with a preferred embodiment of the present invention. During the expiration phase, pressure generated by ventilator 30 is insufficient to maintain one-way valve 118 in the open state. Consequently, substantially no flow of gas goes from ventilator 30 to patient 100 during the expiration phase. The force of the patient's expired air generates a pressure within chamber 130 which is greater than that within compartment 120, and thereby displaces membrane 122 from its former position pressing against chamber 130. This displacement allows the exhaled air to flow through chamber 130, into compartment

128, and through an exit port 126. Preferably, the pressure required to displace membrane 122 is substantially equal to the desired PEEP level. Increased or decreased pressure in tube 82 during expiration produces respectively a higher or lower PEEP level.

Fig. 2C is a schematic illustration of PEEP valve 86 after the expiration phase of the ventilator (i.e, during the "dead time" of the respiration cycle), in accordance with a preferred embodiment of the present invention. Output from compressor 52 is set under software control to correspond to a desired PEEP level. Because the pressure generated by the compressor in compartment 120, even at the reduced level, is grreater than the pressure within compartment 128 and chamber 130, the position of membrane 122 on chamber 130 is maintained, and the membrane thereby substantially prevents any air flow within chamber 130. Additionally, the reduced output is insufficient to open one-way valve 118, and therefore this flow, as desired, is not conveyed to patient 100.

Reference is now made to Figs. 3A, 3B and 3C, which schematically illustrate an implementation of PEEP valve 86, for use as described hereinabove, in accordance with a preferred embodiment of the present invention. Fig. 3A is a schematic, sectional illustration of PEEP valve 86, Fig. 3B is an isometric, schematic illustration of PEEP valve 86, showing internal components thereof, and Fig, 3C is an isometric, schematic illustration of PEEP valve 86. Each numbered element in Fig. 2A corresponds functionally to the similarly-numbered element in Figs. 3A-3C.

Valve 86 according to the present embodiment preferably comprises molded plastic, and is most preferably formed substantially from only two, separately-molded, main pieces: a PEEP valve housing 87, and a PEEP valve cover 123. One-way valve

118 preferably comprises a shaped, flexible membrane 119, and generally permits air to flow from ventilator 30 through valve 118 when the pressure across membrane 119 is above a pre-determined threshold value. Otherwise, membrane 119 remains seated against a valve base 121, and substantially blocks all air flow through valve 118.

Membrane 122, according to the present embodiment, is coupled top a membrane mount 125, which generally constitutes the bottom of compartment 120. Membrane mount 125 and membrane 122 typically are embodied in one integral part, although it will be understood that other forms of construction are appropriate for some applications. PEEP valve cover 123 is enabled to snap onto the top of compartment 120, and to form thereby a substantially air-tight seal.

Although preferred embodiments are described hereinabove with reference to portable ventilator 30, it will be appreciated that elements of the present invention may be used in different combinations and configurations, in both portable and nonportable ventilators. It will be appreciated generally that the preferred embodiments described above are cited by way of example, and the full scope of the invention is limited only by the claims.

Claims

1. A ventilation system having inspiration and expiration phases for providing a gas to a patient, comprising: a compressor, which compresses the gas at a variable operating rate for supply to the patient; patient supply apparatus, through which the gas from the compressor is conveyed to the patient; and a CPU, which controls the operating rate of the compressor so that the rate of gas supply to the patient varies during a portion of the inspiration phase.

2. A ventilation system according to claim 1, and comprising a sensor which generates a signal responsive to a characteristic of the gas supply, wherein the CPU receives the signal from the sensor and controls the operating rate of the compressor responsive to the signal.

3. A ventilation system according to claim 1, and comprising a variable Positive End Expiratory Pressure (PEEP) valve which varies a PEEP level responsive to the operating rate of the compressor.

4. A ventilation system according to claim 1, wherein the compressor is a rotary compressor, whose speed of rotation is varied so as to vary the rate of gas supply.

5. A ventilation system according to claim 1, wherein the compressor comprises a turbine selected from the group consisting of: a radial blower turbine and a regenerative drag turbine.

6. A ventilation system according to claim 1, and comprising a gas-mixing mechanism to provide a mixture of first and second gases to the patient, the mechanism comprising a valve, which is controlled to regulate a quantity of the first gas supplied to the patient, and a demand valve, which regulates a quantity of the second gas responsive to the quantity of the first gas.

7. A ventilation system according to claim 6, wherein the controlled valve comprises an electrically-actuated valve, and wherein the electrically-actuated valve comprises a linear actuator or a worm gear, such that electricity is generally supplied to the electrically-actuated valve only to change the regulated quantity of the first gas.

8. A ventilation system according to claim 1, wherein the CPU receives a signal indicative of a physiological parameter of the patient and sets a ventilation parameter responsive to the signal.

9. A ventilation system according to claim 1 , and comprising a shunt valve which shunts the gas leaving the compressor away from the patient supply apparatus during the expiration phase.

10. A ventilation system according to claim 1, and comprising at least one valve, controlled by the CPU, which at least one valve is controlled to reduce a pressure of gas exiting the compressor during the expiration phase.

11. A ventilation system according to claim 10, wherein the at least one valve comprises a plurality of valves, such that at least two of the plurality of valves are separately controlled by the CPU in order to regulate a level of the pressure reduction.

12. An electrically-controlled mixing valve for use in a ventilation system to provide a mixture of first and second gases to a patient, comprising an electrically-actuated valve which regulates a quantity of the first gas supplied to the patient, such that electricity is generally supplied to the valve only to change the regulated quantity of the first gas.

13. A mixing valve according to claim 12, and comprising a demand valve which regulates a quantity of the second gas responsive to the quantity of the first gas.

14. Gas mixing apparatus for use in a ventilation system to provide a mixture of first and second gases to a patient, comprising: a control valve, which regulates a quantity of the first gas supplied to the patient; and a demand valve which regulates a quantity of the second gas responsive to the quantity of the first gas.

15. Apparatus according to claim 14, wherein the demand valve reduces a pressure to the second gas.

16. Apparatus according to claim 14, wherein the demand valve comprises a passive valve, which does not receive electrical power.

17. Gas mixing apparatus for use in a ventilation system to provide respective regulated quantities of two gases to a patient, comprising; a demand valve, which provides the regulated quantity of one of the gases responsive to a control pressure applied to the valve; and a control valve, coupled to the demand valve so as to convey the control pressure thereto, and which simultaneously regulates the quantity provided of the other of the gases.

18. Apparatus according to claim 17, wherein the demand valve reduces a pressure of the one of the gases prior to providing the quantity thereof.

19. A ventilation system for providing a gas to a patient, comprising: a compressor, which is activated, responsive to a desired respiratory rate, so as to compress the gas for supply to the patient during an inspiration phase of the system and is deactivated so as substantially not to compress the gas during an expiration phase of the system, except for a residual amount of gas compressed during an initial portion of the expiration phase due to inertia of the compressor; patient supply apparatus, through which the gas from the compressor is supplied to the patient; and a shunting valve, which shunts gas leaving the compressor away from the patient supply apparatus during the initial portion of the expiration phase.

20. A method for supplying a gas to a patient having inspiration and expiration phases, comprising: compressing the gas using a compressor which operates at an operating rate which is variable, responsive to a desired ventilation parameter; and controlling the operating rate of the compressor so as to vary the rate during a portion of the inspiration phase.

21. A method according to claim 20, and comprising receiving a signal responsive to a characteristic of the gas supply, and controlling the operating rate of the compressor responsive to the signal.

22. A method according to claim 20, and comprising varying the operating rate of the compressor during the expiration phase in order to vary a pressure in a variable PEEP valve.

23. A method according to claim 20, and comprising providing a desired mixture of first and second gases to the patient by actively regulating a quantity of the first gas supplied to the patient and passively regulating a quantity of the second gas responsive to the quantity of the first gas.

24. A method according to claim 23, wherein actively regulating comprises supplying electricity generally only to a valve which changes the regulated quantity of the first gas, whereby the quantity of the second gas varies responsive to the quantity of the first gas.

25. A method according to claim 20, wherein controlling the operating rate comprises determining a physiological parameter and regulating the operating rate responsive thereto.

26. A method according to claim 20, and comprising shunting the gas leaving the compressor away from the patient during the expiration phase.

27. A method according to claim 20, and comprising: operating the compressor during the expiration phase; and controlling gas flow coming from the compressor during the expiration phase so as to reduce a pressure thereof.

28. A method according to claim 27, wherein controlling the gas flow comprises controlling a plurality of valves coupled to the compressor, wherein at least two of the plurality of valves are separately controlled, in order to regulate a level of the pressure reduction.

29. A method for supplying a gas to a patient, comprising providing a mixture of first and second gases to a patient, and regulating a quantity of the first gas supplied to the patient, such that for the purpose of varying the mixture, electricity is generally supplied only to a valve regulating the quantity of the first gas.

30. A method according to claim 29, and comprising passively regulating a quantity of the second gas responsive to the quantity of the first gas.

31. A method for supplying a mixture of first and second gases to a patient, comprising: actively regulating a quantity of the first gas supplied to the patient; and regulating a quantity of the second gas responsive to the quantity of the first gas.

32. A method according to claim 31, wherein regulating the quantity of the second gas comprises passively regulating the quantity of the second gas, substantially without using electricity to control a valve regulating the second gas.

33. A method according to claim 31, and comprising verifying a supply of the second gas by changing the quantity of the first gas during a test period and measuring an amount of the second gas during the test period.

34. A method according to claim 31 , and comprising reducing a pressure of one of the gases.

35. A method for supplying respective regulated quantities of two gases to a patient, comprising: actively regulating the quantity of one of the gases using a control valve; generating a control pressure using the control valve substantially simultaneously with regulating the quantity of the one of the gases; and providing the quantity of the other of the gases responsive to the control pressure.

36. A method according to claim 35, and comprising reducing a pressure of the other of the gases prior to providing the quantity thereof.

37. A method for providing a gas to a patient using a ventilation system having inspiration and expiration phases, comprising: activating a compressor so as to cyclically compress the gas, responsive to a desired respiratory rate, for supply to the patient during the inspiration phase; deactivating the compressor so as substantially not to compress the gas during the expiration phase, except for a residual amount of gas compressed during an initial portion of the expiration phase due to inertia of the compressor; and shunting the gas compressed during the initial portion of the expiration phase away from the patient.

38. A ventilation system for providing a gas to a patient, comprising: a compressor, which compresses the gas at a variable operating rate for supply to the patient; and a variable Positive End Expiratory Pressure (PEEP) valve, through which the gas is supplied to the patient, which varies a PEEP level responsive to the operating rate of the compressor.

39. A method for supplying a gas to a patient having an expiration phase, comprising compressing the gas using a compressor which operates at an operating rate which is variable responsive to a desired Positive End Expiratory Pressure

(PEEP) level.