Abstract:
A multiple functionality pneumatically controlled medical ventilator provides precision regulation of tidal/forced breathing, and continuous positive airway pressure (CPAP)-based spontaneous breathing capability. The ventilator includes a patient breathing gas coupler that is adapted to be coupled to a patient airway breathing interface, and an input port to which a pressurized breathing gas is coupled, A pressure regulator supplies breathing gas at a positive pressure sufficiently higher than nominal lung pressure to prevent collapse of the patient&#39;s lungs. A tidal breathing gas supply unit periodically generates a volume-regulated tidal breathing gas for application to the patient airway breathing interface, while the CPAP valve supplies a pressure-regulated breathing gas to the patient airway breathing interface, in response to a patient demand for breathing gas that is exclusive of the tidal breathing supply.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Serial No. 60/060,187, filed Sep. 26, 1997, entitled: “Portable Medical Ventilator,” the disclosure of which is incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to an assisted breathing device or medical ventilator that may be used in a variety of human and animal patient applications, such as, but not limited to, medical facilities (e.g., hospitals, physicians′ and veterinary offices and the like), as well as medical field unit and emergency vehicle applications. The invention is particularly directed to a new and improved portable medical ventilator that provides both precision pneumatic regulation of tidal/forced breathing, and continuous positive airway pressure (CPAP)-based spontaneous breathing capability. 
     BACKGROUND OF THE INVENTION 
     Currently available portable medical ventilator units generally fall into one of two categories: i- relatively simple or limited capability pneumatically controlled units (typically carried by emergency vehicles), and ii-sophisticated electrically (both AC and battery) powered, electronically (microprocessor)-controlled systems, that are essentially comparable in function to in-house (e.g., hospital) devices. The former devices suffer from the fact that they are not much more that emergency oxygen supplies. An obvious drawback to the devices of the second category is the fact that, as electrically powered, system level pieces of equipment, they are relatively expensive and complex. Moreover, electronic systems are subject to a number of adverse influences, such as electromagnetic interference, handling abuse, and battery life-factors which do not affect a pneumatic system. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, drawbacks of conventional medical ventilator devices such as those described above are effectively obviated by a new and improved portable, pneumatically controlled medical ventilator that provides the multiple functionality of an electronically controlled ventilator, but without the need for any electrical power (including batteries), thereby making the unit especially suited for field and emergency vehicle applications. 
     For this purpose, the pneumatically controlled medical ventilator of the present invention has an input port coupled to a source of pressurized gas, such as an oxygen tank carried by a medical emergency vehicle. A pneumatic link from the input port is coupled to a system-priming gas flow control switch, which is operative to prime a pneumatic timing cartridge within a pneumatic timing unit, when the ventilator is initially coupled to the oxygen source. The input port is further coupled to a system gas flow pressure regulator. The output of the system gas flow pressure regulator is coupled to an input port of a tidal breathing control switch, the operation of which controls the flow of mandatory tidal breathing gas to the patient. 
     The system gas flow pressure regulator provides a prescribed elevated or positive driving pressure for the mandatory tidal breathing gas supply subsystem, so that a precisely regulated amount of breathing gas may be controllably supplied to the patient. This constant positive pressure is considerably higher than the nominal lung pressure of a patient, so that it is effective to prevent collapse of the patient&#39;s lungs, and is not affected by changes in the patient&#39;s lung compliance and resistance. 
     The filtered breathing gas supplied is further coupled to a continuous positive airway pressure (CPAP) valve. The CPAP valve has a sensing or control port coupled to the breathing gas supply throat of a patient air supply output coupler for sensing a drop in pressure when the patient initiates or demands a breath, separate from a mandatory tidal breathing cycle. A section of breathing gas supply tubing is coupled between the patient air supply output coupler and an airway breathing interface on the patient. In response to the patient spontaneously drawing a breath, the drop in pressure in the breathing gas supply throat of the output coupler will cause the CPAP valve to couple the breathing gas (oxygen) to a gated venturi unit installed at an upstream end of the patient air supply output coupler. The venturi unit includes an ambient air input port through which filtered ambient air is drawn into the patient air supply output coupler by the flow of pressurized oxygen supplied to input port, and thereby allow a prescribed spontaneous or on-demand oxygen-enriched breathing mixture to be supplied to the patient. 
     An auxiliary anti-suffocation valve is coupled to the main airflow passageway of the patient air supply output coupler, to ensure that ambient air can be drawn into the main airflow passageway and supplied to the patient, in the event of a ventilator failure or depressurization of the oxygen source. Also, an overpressure valve is coupled to the main airflow passageway of the patient air supply output coupler, to prevent an excess pressure build up within the main airflow passageway of the coupler, and within the patient&#39;s lungs. 
     The presetable gas pressure provided at the output port of the CPAP valve is further coupled to a pneumatic conduit for inflating the diaphragm of an exhalation valve of an airway breathing interface on the patient. When a breath drawn in by the patient is patient-initiated, the pressured gas supplied by CPAP valve to the exhalation valve outlet inflates the exhalation valve&#39;s diaphragm and prevents the breathing gas in the tubing breathing gas tubing from being exhausted from the exhalation valve, and instead directed into the patient&#39;s airway, as intended. When the patient ceases inhaling, there is no longer a pressure drop in the coupler throat, causing the CPAP valve to close, and interrupt the positive pressure at the exhalation valve outlet. The exhalation valve&#39;s diaphragm thereby deflates to allow the patient to exhale. 
     The pneumatic timing unit supplies a periodic pneumatic control signal associated with a controllable (oxygen) concentration and rate of tidal breathing gas to a normally closed tidal breathing control switch. Tidal breathing parameters of the pneumatic control signal supplied to the pneumatic timing unit includes a pneumatic timing cartridge and a pneumatic time constant circuit for controlling the charge and bleed rates of the pressurized gas. The tidal breathing control switch receives the pressure-regulated oxygen from the system pressure regulator, and outputs a pressure-regulated oxygen to a dual position tidal air supply-mixture switch. 
     For a first position, the tidal air supply-mixture switch couples the pressure-regulated oxygen from the tidal breathing pneumatic circuitry to an oxygen concentration-reducing venturi, that is coupled to the output throat of the patient air supply coupler. To supply a pure (100%) oxygen breathing gas to the patient&#39;s airway breathing interface, the tidal air supply-mixture switch is turned, and thereby ported to a 100% oxygen outlet port, which is coupled through a section of oxygen supply tubing to a pure oxygen feed input port of the patient&#39;s airway breathing interface. 
     A manually setable, pressure regulator valve is coupled to the tidal breathing supply, and is operative to feed the exhalation valve outlet. As with the operation of the CPAP valve for an on-demand breath, this serves to inflate the exhalation valve&#39;s diaphragm, and prevent the breathing gas from being exhausted from the exhalation valve, but directed instead into the patient&#39;s airway. At the end of the tidal breath interval, the positive pressure at the output of the tidal breathing control switch is interrupted, terminating the positive pressure at the output of the pressure limit regulator valve necessary for inflating the diaphragm of the exhalation valve. The exhalation valves diaphragm deflates to allow the patient to exhale. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 diagrammatically illustrates the architecture of the medical ventilator of the present invention; and 
     FIG. 2 diagrammatically illustrates a patient airway breathing interface to which the medical ventilator of FIG. 1 may be coupled. 
    
    
     DETAILED DESCRIPTION 
     Before describing in detail the pneumatically controlled multifunction medical ventilator of the present invention, it should be observed that the invention resides primarily in what is effectively a prescribed combination of conventional pneumatic flow control and pressure regulation devices and components and interconnections therefor. As a result, for the most part, the configurations of such devices and components, and the manner in which they are interfaced with conventional breathing equipment have been illustrated in the drawings in readily understandable pneumatic flow control circuit block diagram form, which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with details which will be readily apparent to those skilled in the art having the benefit of the description herein. Thus, the pneumatic block diagram illustrations are primarily intended to show the major components of the ventilator system in a convenient functional grouping and flow control arrangement, whereby the present invention may be more readily understood. 
     Referring now to FIG. 1, the architecture of the pneumatically controlled medical ventilator of the present invention is diagrammatically illustrated as comprising a patient breathing gas (oxygen) inlet port  10 , to which a pressurized (e.g., within a range of 40-100 psi) source of a prescribed breathing gas (e.g., oxygen)  11  is coupled. This pressurized breathing gas source (such as a pressurized oxygen tank carried by a medical emergency vehicle) serves as a source of both (periodically metered) tidal and patient on-demand breathing gas for the patient, and to operate as a pneumatic supply for controlling the operation of the various components of the ventilator. By basing the operation of the ventilator exclusively upon mechanically and pneumatically driven components, without any need for electrical or electronic circuits, the ventilator of the invention is readily suited for the typical limited or no notice need of emergency medical personnel and eliminates any concern for the availability and or operability of batteries. All medical personnel require is a source of breathing gas (e.g., an oxygen gas tank). 
     A pneumatic link  12  from input port  10  is coupled directly through a flow-reducing orifice  13  to the flow control or signal input port  101  of a normally open (system-priming) gas flow control switch  100 , such as an Industrial Specialties Model No. AVAP2-1032NOM. Because it is normally open, the gas flow control switch  100  provides a gas flow path for pressurized gas from the gas supply source  11  that enables a pneumatic timing cartridge  200  within a pneumatic timing unit  110 , to be described, to be immediately pressurized when the ventilator is first connected to the breathing gas supply. 
     The pneumatic link  13  from the gas input port  10  is further coupled through an air filter  14  to a pneumatic link  15 , that is coupled to an input port  21  of a system gas flow pressure regulator  20  (such as a Norgen Model No. R07-100NKA regulator, as a non-limiting example). The output port  22  of the system gas flow pressure regulator  20  is coupled through a pneumatic supply link  99  to the control port  102  of the gas flow control switch  100  and to the input port  201  of the pneumatic timing cartridge  200 . It is also coupled to an input port  121  of a normally closed tidal breathing control switch  120 , the operation of which controls the flow of mandatory tidal breathing gas to the patient, as will be described. 
     The system gas flow pressure regulator  20  serves to provide a prescribed positive driving pressure for the mandatory tidal breathing gas supply subsystem, whereby a precisely regulated amount of breathing gas may be controllably and repetitively supplied at a prescribed rate and volume to the patient. Regardless of the breathing volume of the patient (which may typically vary from 120 to 1,500 milliliters per breath) the tidal volume settings do not change. 
     As will be described, the oxygen content of the tidal breathing gas may be varied between pure or 100% oxygen and a relatively reduced oxygen percentage (e.g., on the order e of 60%). This constant positive pressure (e.g., on the order of 30 psi) is considerably higher than the nominal lung pressure of a patient (which is zero psi), so that it is effective to prevent collapse of the patient&#39;s lungs a not uncommon condition in ill or injured patients. 
     The pneumatic link  15  is further coupled to a manually adjustable low pressure alarm switch  40  (such as a Pisco Model No. RPV-⅛-10-32 F unit), the output  41  of which is coupled through a flow orifice  42  to an alarm device, such as a pneumatic whistle  44 , which is activated if the input gas pressure drops below a prescribed minimum value. The filtered breathing gas supplied over the pneumatic link  15  is further coupled to an input port  31  of a continuous positive airway pressure (CPAP) valve  30 , such as a Bird Products Model No. 4715 valve, as a non-limiting example. The CPAP valve  30  is operative to maintain a continuous positive pressure regardless of the patient&#39;s effort to breath. CPAP valve  30  has a patient demand pressure-monitoring or control port  32 , that is coupled through a manually adjustable damping orifice  52  to a patient air supply-monitoring pneumatic link  50 . Pneumatic link  50  is coupled to an on-demand breath monitoring port  61 , which is coupled to the breathing gas supply throat  62  of a patient air supply output coupler  60 . 
     To allow the pressure in the patient airway to be visually monitored by attendant medical personnel, the pneumatic link  50  is also coupled through a flow orifice  54  to an airway-monitoring pressure gauge  56 . A section of hose or tubing  70  is coupled between the patient air supply output coupler  60 , and an airway breathing interface on the patient, diagrammatically illustrated at  68  in FIG.  2 . In addition, link  50  may be coupled to an external sensor (not shown) of an unobtrusive off-line microcontroller-based monitoring system, for monitoring the operation of the system by supervisory medical (e.g., hospital) personnel. 
     By ‘on-demand’ is meant a breath that is drawn by the patient, in addition to the ‘mandatory’ tidal breathing breath periodically supplied by the pneumatic timing unit  110 . As a non-limiting example, this auxiliary source of breathing gas is particularly useful where medical treatment involves ‘weaning’ the patient off the tidal breathing supply, by gradually reducing the number of tidal breaths supplied per minute, and forcing the patient to begin to initiate more breathing on his own. 
     For this purpose, in response to the patient spontaneously drawing a breath (at a time other than at the occurrence of the periodic supply of a prescribed quantity of tidal breathing gas), there will be a drop in pressure in the breathing gas supply throat  62  of the output coupler  60 . This drop in pressure will be coupled by the pneumatic link  50  to the patient demand pressure-monitoring port  32  of the CPAP valve  30 , causing that valve to open and couple the breathing gas (oxygen) in the pressurized gas link  15  to its output port  33 , at a prescribed pressure, manually setable by a valve control knob  36 . 
     The presetable gas pressure provided at the output port  33  of the CPAP valve  30  is coupled through a pneumatic link  72  and an adjustable proportioning orifice  73  to a pneumatic conduit  75  for inflating the diaphragm of an exhalation valve  106  of the patient airway breathing interface  68  of FIG.  2 . CPAP output port  33  is further coupled over link  72  to an input port  74  of a gated venturi unit  76  installed at an upstream end of the patient air supply output coupler  60 . As a non-limiting example, the gated venturi unit  76  may comprise a venturi unit available from Bird Products, referenced above. 
     The gated venturi  76  includes an ambient air input port  78  in which an air filter  82  is installed. It is through the venturi&#39;s air input port  78  that filtered ambient air is drawn into the patient air supply output coupler  60  by the flow of pressurized oxygen supplied to input port  74 , to allow a prescribed spontaneous or on-demand oxygen-enriched breathing mixture to be supplied to the patient. For this purpose, the output of the gate venturi  76  is coupled (through an overpressure valve  88 ) into the main airflow passageway  64  of the patient air supply output coupler  60 , so that a prescribed mixture of pure oxygen supplied from CPAP valve  30  and ambient air, as drawn into the venturi  76 , is coupled into the throat  62  of the patient air supply output coupler  60  for delivery to the patient airway breathing interface  68 . 
     An auxiliary anti-suffocation valve  86  (such as a Bird Product&#39;s Model No. 5536, as a non-limiting example) is coupled to the main airflow passageway  64  of the patient air supply output coupler  60 . This auxiliary valve ensures that ambient air can be drawn into the main airflow passageway and supplied to the patient, in the event of a failure or depressurization of the oxygen source. As long as a positive air/oxygen flow for the patient is provided in the main airflow passageway  64  of the coupler, the anti-suffocation valve  86  remains closed, so that the air supply to the patient is controlled by the demand or tidal pneumatic control components of the invention. An overpressure or pressure limit valve  88  (such as a Halkey-Roberts Model No. 780 RPA 125, as a non-limiting example) is coupled to the main airflow passageway  64  of the patient air supply output coupler  60 , to prevent an excess breathing mixture pressure build up within the main airflow passageway of the coupler  64 . 
     As pointed out above, the output port  33  of the CPAP valve  30  is coupled through a pneumatic link  72  and a proportioning (pressure reduction) orifice  73  to pneumatic conduit  75  for inflating the diaphragm of exhalation valve  106  of patient airway breathing interface  68 . For this purpose, the conduit  75  is coupled through an orifice  91  to an exhalation valve outlet  93 . It is also ported to the atmosphere via a coupling orifice  97  and an air filter  98 . The exhalation valve outlet  93  is coupled to a section of tubing  95  that is ported to a diaphragm inflation control port  104  of an exhalation valve  106  of the patient&#39;s breathing interface  68 . 
     When a breath drawn in by the patient is a patient-initiated (spontaneous or on-demand) breath, to which the CPAP valve  30  responds in the manner described above, the pressured gas supplied by CPAP valve  30  (through conduit  75 ) to the exhalation valve outlet  93  inflates the exhalation valve&#39;s diaphragm and prevents the breathing gas in the tubing  70  from being exhausted via the output port  108  of exhalation valve  106 , and instead directed into the patient&#39;s airway, as intended. When the patient ceases inhaling, there is no longer a pressure drop in the coupler throat  62  and link  50 , causing the CPAP valve  30  to close. This interrupts the positive pressure at the exhalation valve outlet  93  necessary for inflating the diaphragm of the exhalation valve  106 . The diaphragm thereby deflates to allow the patient to exhale though the exhalation valve. 
     As described briefly above, the pneumatic timing unit  110  serves to generate a periodic pneumatic control signal associated with a controllable (oxygen) concentration and rate (e.g., in a range of from two to sixty breaths per minute) of tidal breathing gas. This tidal breathing pneumatic control signal is supplied via a pneumatic link  119  to a control port  122  of the normally closed tidal breathing control switch  120 . (As a non-limiting example, tidal breathing control switch flow  120  may comprise a Decker Model No. 1003 flow switch.) As pointed out above, the input port  121  of the tidal breathing control switch  120  is coupled to receive the pressure-regulated oxygen supplied via pneumatic link  99  from the system pressure regulator  20 . Switch  120  has an output port  123  through which the pressure-regulated oxygen flow in pneumatic link  99  is periodically coupled to a tidal breathing supply pneumatic link  125 . 
     The tidal breathing supply pneumatic link  125  is coupled to an input port  131  of a dual position tidal air supply-mixture switch  130 , such as a Norgren Model No. 5CV-022-000 air mix switch, as a non-limiting example. The tidal air supply-mixture switch  130  has a first output port  132  coupled to a first, pressurized oxygen input port  141  of a tidal oxygen/air mixture feed venturi  140 , such as a Festo Model No. 9394 venturi, as a non-limiting example. The venturi  140  is controllably coupled in the breathing gas supply path to the patient when the oxygen concentration of the breathing gas is to be less than 100% (pure O 2 ). e.g., on the order of 60%, as a non-limiting example. For this purpose, venturi  140  has an output port  143  coupled to a tidal gas mixture feed port  65  installed in the output throat of the patient air supply coupler  60 . The pneumatic signal input at control port  122  is reduced in pressure by an orifice  148  and enters the tidal mixture feed port  65  of the patient air supply coupler  60 . This link serves to exhaust the gas signal delivered to control port  122 . It may be noted that with the pressure (e.g., 35 psi) at control port  122  being higher than the pressure at tidal mixture feed port  65  (e.g., less than or equal to 1 psi), gas always flows from port  122  to port  65 . 
     Venturi  140  has a second, ambient air input port  144  coupled through a check valve  145  and a filter  146 . As in the gated venturi  76  employed for on-demand breathing, ambient air for a reduced oxygen concentration tidal breathing mixture supplied to tidal mixture feed port  65  of the patient air supply coupler  60  is drawn into the input port  144  of venturi  140  by the flow of pressurized oxygen supplied to the venturi&#39;s input port  141 , so as to provide a prescribed oxygen-enriched tidal breathing air mixture to the patient. 
     In order to supply pure (100%) oxygen breathing gas to the patient&#39;s airway breathing interface  68  (associated with a 90° clockwise rotation of the valve relative to that shown in FIG.  1 ), the tidal air supply-mixture switch  130  has a second output port  133  coupled through an oxygen feed orifice  135  to a 100% oxygen outlet port  136 . The pure oxygen outlet port  136  is coupled through a section of oxygen supply tubing  138  to a pure oxygen feed input port  107  of the patient&#39;s airway breathing interface  68 . 
     A manually setable, pressure regulator valve  150  (such as an Airtrol Model No. R-900-10-W/S) has a pressure input port  151  coupled to the tidal breathing supply pneumatic link  125 . An output port  152  of pressure regulator valve  150  is coupled through a check valve  154  to pneumatic supply conduit  75 , that feeds the exhalation valve outlet  93 . The pressure limit regulator valve  150  is operative to supply a prescribed level of exhalation valve pressurizing gas to the exhalation valve outlet  93  during a tidal breathing interval, which prevents excessive pressure build-up in the patient&#39;s lungs. 
     As pointed out previously, this serves to inflate the exhalation valve&#39;s diaphragm, and thereby prevents the breathing gas in the tubing  70  from being exhausted from the exhalation valve  106 , but directed instead into the patient&#39;s airway, as intended. At the end of the tidal breath interval, the positive pressure at the output  123  of the tidal breathing control switch  120  is interrupted, thereby terminating the positive pressure in link  125  and at the output port  152  of pressure limit regulator valve  150  necessary for inflating the diaphragm of the exhalation valve  106 . The exhalation valves diaphragm thereby deflates to allow the patient to exhale. 
     In order to define the (volume and timing) parameters of the tidal breathing control signal supplied to the control input  121  of the tidal breathing control switch  120 , the input port  201  of the pneumatic timing cartridge  200  (such as Bird Products Model No. 6830 pneumatic timing cartridge, as a non-limiting example) of the pneumatic timing unit  110  is coupled to the pressure-regulated oxygen flow pneumatic link  99 . Port  201  is used to continuously pressurize the timing cartridge  200  during repetitive tidal breathing cycles, subsequent to the initial charging of the pneumatic timing cartridge  200  via a control port  202  that is coupled to the output port  103  of the normally open gas flow control switch  100 , as described above. 
     The pneumatic timing cartridge  200  has an output port  203  coupled to the pneumatic link  119 , and through a check valve  211  to a variable pneumatic resistor element  213 , and through a check valve  215  to a pneumatic timing circuit  220 . The pneumatic timing circuit  220  includes a volume balance orifice  221  and a pneumatic flow time constant control path  222 , that is comprised of a variable pneumatic resistor element  224  and a variable pneumatic capacitor element  226 , which is charged by the output  203  of the pneumatic timing cartridge  200 . A check valve  228  is coupled between the pneumatic timing circuit  220  and the variable pneumatic resistance element  213 . The variable pneumatic resistor  213  provides a pressure bleed path to ambient air through an air filter/muffler  230 . The tidal breathing rate and the duty cycle of a respective tidal breath interval are preset by the time constant parameters of the components of the pneumatic timing circuit  220 . 
     In operation, regulated pressure gas enters the input port  201  of the pneumatic timing cartridge  200 . Since the timing cartridge  200  is normally open, the gas immediately exits to both the flow control switch  120  and through the check valves  211  and  215  to the pneumatic timing circuit  220 . As the gas flows through the timing circuit it flows through the variable resistors  224  and  221  and variable capacitor  226  and begins to meter into timing cartridge  200 . As described above, the parameters of the pneumatic resistor and capacitor components of the timing circuit may be set to provide a controllable breathing rate in a range of from two to sixty breaths per minute. At the same time, this gas pressure is delivered downstream of check valve  228  through rate control variable resistor  213 . Since the volume of gas transferred by the high pressure cannot escape through the rate control path fast enough (the orifice is essentially saturated), the high pressure is maintained against the check valve  228 , holding it closed. 
     With check valve  228  held closed, absent leaks, gas entering port  202  of the timing cartridge  200  by way of the volume control components cannot escape. As a consequence, the pressure inside the ‘sealed’ timing chamber increases at a rate determined by the settings of the volume control variable resistors  224  and  221 . The pressure continues to rise, until it reaches that required to turn off the timing cartridge  200  (e.g., between 10 and 15 psi). When the gas flow is terminated, the gas exits from the timing chamber  200  through the check valve  228  and the rate control variable resistor  213  and air filter/muffler  230  of the rate control path. Once the pressure drops low enough in its timing chamber, the timing cartridge  200  turns back on. 
     As will be appreciated from the foregoing description, drawbacks of conventional medical ventilator devices described above are effectively obviated by the exclusively pneumatically controlled medical ventilator of the invention. By means of a dual, regulated positive pressure, tidal/on-demand breathing gas supply architecture, that requires no electrical power (including batteries), the invention is especially suited for a variety of hospital, field and emergency vehicle applications. 
     While I have shown and described an embodiment in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as are known to a person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.