Portable drag compressor powered mechanical ventilator

• US 20020005197A1
• Filed: 08/21/2001
• Published: 01/17/2002
• Est. Priority Date: 10/14/1994
• Status: Active Grant

• Current Assignee: Carefusion 202 Inc. (Becton, Dickinson & Co)
• Original Assignee: Douglas F. Devries, Malcolm R. Williams, Michael B. Holmes, Michael J. Ceqielski, Warner V. Graves Jr
• Inventors: Ceqielski, Michael J., DeVries, Douglas F., Graves, Warner V. Jr., Williams, Malcolm R., Holmes, Michael B.
• Granted Patent: US 6,526,970 B2
• Time in Patent Office: Days
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0057 Pumps therefor
• CPC Class Codes: A61M 16/0063 Compressors
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 16/1015 using a gas flush valve, e.g. oxygen flush valve
• CPC Class Codes: A61M 16/107 in the inspiratory path
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 16/125 Diluting primary gas with ambient air
• CPC Class Codes: A61M 16/20 Valves specially adapted to medical respiratory devices
• CPC Class Codes: A61M 16/202 electrically actuated
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 16/206 Capsule valves, e.g. mushroom, membrane valves
• CPC Class Codes: A61M 16/208 Non-controlled one-way valves, e.g. exhalation, check, pop-off non-rebreathing valves
• CPC Class Codes: A61M 16/209 Relief valves
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2016/0042 : in the expiratory circuit
• CPC Class Codes: A61M 2202/0208 : Oxygen
• CPC Class Codes: A61M 2205/16 : with back-up system in case of failure
• CPC Class Codes: A61M 2205/18 : with alarm
• CPC Class Codes: A61M 2205/3331 : Pressure; Flow
• CPC Class Codes: A61M 2205/3365 : Rotational speed
• CPC Class Codes: A61M 2205/3561 : local, e.g. within room or hospital
• CPC Class Codes: A61M 2205/3569 : sublocal, e.g. between console and disposable
• CPC Class Codes: A61M 2205/3592 : using telemetric means, e.g. radio or optical transmission
• CPC Class Codes: A61M 2205/42 : Reducing noise
• CPC Class Codes: A61M 2205/502 : User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2205/581 : by audible feedback
• CPC Class Codes: A61M 2205/587 : Lighting arrangements
• CPC Class Codes: A61M 2205/70 : with testing or calibration facilities
• CPC Class Codes: A61M 2205/8206 : battery-operated
• CPC Class Codes: A61M 2205/8212 : with means or measures taken for minimising energy consumption
• CPC Class Codes: A61M 2230/46 : Resistance or compliance of the lungs
• CPC Class Codes: G01F 1/40 : Details of construction of the flow constriction devices
• CPC Class Codes: G01F 1/42 : Orifices or nozzles

Abstract

A ventilator device and system comprising a rotating compressor, preferably a drag compressor, which, at the beginning of each inspiratory ventilation phase, is accelerated to a sufficient speed to deliver the desired inspiratory gas flow, and is subsequently stopped or decelerated to a basal flow level to permit the expiratory ventilation phase to occur. The ventilator device is small and light weight enough to be utilized in portable applications. The ventilator device is power efficient enough to operate for extended periods of time on internal or external batteries. Also provided is an oxygen blending apparatus which utilizes solenoid valves having specific orifice sizes for blending desired amounts of oxygen into the inspiratory gas flow. Also provided is an exhalation valve having an exhalation flow transducer which incorporates a radio frequency data base to provide an attendant controller with specific calibration information for the exhalation flow transducer.

Claims

1. A rotary drag compressor ventilator device for ventilating the lungs of a mammalian patient, said device comprising:

A. a rotary drag compressor comprising;

i. a housing having a gas inflow passageway and a gas outflow passageway;

ii. a rotor mounted within said housing, said rotor having a multiplicity of blades formed circularly therearound such that, when said rotor is rotated in a first direction, said blades will compress gas within said housing and expel said compressed gas out of said outflow passageway;

iii. a motor coupled to said compressor for rotating said rotor within said compressor housing; and

B. a controller apparatus to intermittently accelerate and decelerate the rotation of said rotor so as to deliver discrete periods of inspiratory gas flow through said outflow passageway.

2. The ventilator of claim 1, further in combination with:

C. an oxygen blending apparatus connected to said inflow passageway for blending oxygen with ambient air to provide oxygen-enriched air to the inlet aperture of said compressor housing.

3. The ventilator of claim 2 wherein said oxygen blending apparatus comprises:

an ambient air receiving passageway;

an oxygen receiving passageway;

an accumulator for receiving ambient air through said ambient air passageway and oxygen through said oxygen passageway; and

,

a series of independently actuatable solenoid valves positioned, in parallel, within the oxygen receiving passageway of said bending apparatus, each of said solenoid valves having a predetermined flow rate when fully open, each of said solenoid valves thereby permitting passage therethrough of a predetermined amount of oxygen per time period; and

,

said oxygen blending apparatus being connected to said controller and said controller being further programmable to receive input of a desired oxygen concentration setting and to emit control signals to the solenoid valves to cause individual opening and closing of said solenoid valves to result in said desired oxygen concentration within said accumulator.

4. The ventilator system of claim 3 wherein said solenoid valves comprises three to five separate solenoid valves.

5. The ventilator system of claim 3 wherein said controller is programmed to apply a pulse-width modulation signal to control the opening and closing of said solenoid valves.

6. The ventilator of claim 1 wherein said controller comprises at least one microprocessor.

7. The ventilator of claim 1 wherein said compressor rotor comprises a dual-faced compressor rotor having first and second series of blades mounted opposite sides thereof;

and, wherein said compressor housing is configured to define first and second compressor flow paths which are positioned in relation to said first and second series of blades, respectively, such that rotation of said compressor rotor in said first direction will a) draw gas into said inflow passageway, b) concomitantly compress and move gas through both of said first and second flow paths and, c) expel the combined gas from said first and second compressor flow paths to compressor flow paths to provide inspiratory gas flow from said ventilator device.

8. The ventilator of claim 7 wherein said compressor rotor is round in configuration and has a diameter of 2-6 inches.

9. The ventilator of claim 7 wherein said blades are disposed at angles of attack of 30-60 degrees.

10. The ventilator of claim 9 wherein said blades are disposed at 55°

angles of attack.

11. The compressor of claim 7 wherein said blades are mounted within concave annular troughs formed on opposite sides of said dual-faced compressor rotor and wherein said first and second compressor flow paths are formed in relation to said first and second annular troughs such that the series of blades mounted within the first annular trough will compress gas within said first compressor flow path and the series of blades mounted within said second trough will compress gas within said second compressor flow path.

12. The ventilator of claim 7 wherein rotor, including said blades, had a mass of less than 40 grams.

13. The ventilator of claim 7 wherein said rotor further comprises:

the convex rotor hub having a central transverse motor shaft receiving aperture formed therein, to facilitate rotation of said rotor by said motor.

14. The ventilator of claim 7 wherein said rotor is formed of molded material.

15. The ventilator of claim 7 wherein said blades are formed of aluminum.

16. The ventilator of claim 7 wherein approximately 30-40 blades are positioned on either side of said rotor.

17. The ventilator of claim 1 further comprising:

a differential pressure transducer for measuring the difference in pressure between gas entering the inlet of said compressor and gas exiting the outlet of said compressor.

18. The ventilator of claim 1 further comprising:

a tachometer for measuring the rotational speed of said compressor.

19. The ventilator of claim 18 wherein said tachometer comprises an optical encoder.

20. The ventilator of claim 1 further comprising:

a differential pressure transducer for measuring the difference in pressure between gas entering the inlet of said compressor and gas entering the outlet of said compressor;

a tachometer for measuring the rotational speed of said compressor; and

said differential pressure transducer and said tachometer being in communication with said controller; and

said controller being programmed to determine the instantaneous flow rate and current accumulated volume of inspiratory gas flow delivered by said ventilator based on the pressure differential measured by said differential pressure transducer and the rotational speed measured by said tachometer.

21. The ventilator of claim 1 wherein said compressor incorporates a controller-readable data base containing specific rotational speed, differential pressure and flow rate data for that particular compressor;

and

wherein said controller is further programmed to read said data base and to utilize information obtained from said data base in the calculation of inspiratory flow, volume or pressure delivered by said ventilator.

22. The ventilator of claim 21 wherein said controller-readable data base comprises an EPROM.

23. The ventilator of claim 1 further in combination with a portable battery for supplying power to said device.

24. The ventilator of claim 23 wherein said portable battery contains sufficient power to operate said mechanical ventilator device for at least two hours.

25. A drag compressor apparatus for creating inspiratory gas flow in a mechanical ventilator, said compressor apparatus comprising:

a housing having a gas inflow passageway and a gas outflow passageway;

a rotor rotatably mounted within said housing, said rotor being configured and constructed such that rotation of said rotor in a first direction will cause said rotor to a) draw gas in said inflow passageway, b) compress said gas and c) expel said gas out of said outflow passageway;

a controller for controlling the rotation of said rotor within said housing, said controller being operative to cause said rotor to intermittently accelerate and decelerate so as to deliver discrete periods of inspiratory gas flow through said outflow passageway.

26. The compressor of claim 25 wherein said rotor incorporates at least one series of blades having leading edges, each of said blades being disposed at a positive angle of attack such that, when said rotor is rotated in said first direction, the leading edge of each blade will precede the remainder thereof.

27. The compressor of claim 26 wherein said blades are disposed at angles of attack of 30-60 degrees.

28. The compressor of claim 27 wherein said blades are disposed at 55 degree angles of attack.

29. The compressor of claim 26 wherein said blades are disposed at spaced intervals within an annular trough which extends about said rotor such that, when said rotor is rotating said first direction, said blades will serially contact and compress gas within said housing.

30. The compressor of claim 29 wherein said housing is further configured to define therewithin at least one compressor flow path said flow path being positioned in relation to said annular trough and being connected to said inflow and outflow passageways such that, when said rotor is rotated in said first direction, the blades of said rotor will a) draw gas inwardly through said inflow passageway into said compressor flow path, b) compress said gas within said compressor flow path, and c) expel said gas out of said outflow passageway.

32. The compressor of claim 30 wherein said at least one concave annular trough comprises:

a first annular trough which extends about the periphery of said rotor on a first side thereof; and

,

a second annular trough which extends about the periphery of said rotor on a second side thereof.

33. The compressor of claim 32 wherein said housing is configured to define therewithin:

a first compressor flow path which is at least partially within said first annular trough and is connected to said inflow passageway and said outflow passageway; and

,

a second compressor flow path which is at least partially within said second annular trough and is connected to said inflow passageway and said outflow passageway;

said first and second compressor flow paths being configured and positioned such that, when said rotor is rotated in said first direction, the blades mounted within said first annular trough will draw gas into said inflow passageway, compress said gas within said first flow path, and expel said gas out of said outflow passageway and the blades mounted within said second annular trough will draw gas into said inflow passageway, compress sid gas within said second flow path, and expel said gas out of said outflow passageway.

34. The compressor of claim 33 wherein said first concave trough and the blades mounted therewithin are mirror images of said second concave trough and the blades mounted therewithin.

35. The compressor of claim 25 further comprising a drive motor located within said compressor housing and coupled to said rotor to rotatably drive said rotor.

36. The compressor of claim 25 wherein said housing further comprises a number of heat dissipation fins formed on the outside of the portion of said housing wherein said motor is positioned to facilitate dissipation of heat from said motor.

37. The compressor of claim 35 further comprising a tachometer for measuring the rotational speed of said rotor.

38. The compressor of claim 37 wherein said tachometer comprises an optical encoder.

40. The compressor of claim 25 further comprising:

a differential pressure transducer for measuring the difference between the pressure of gas in said inflow passageway and the pressure of gas in said outflow passageway.

31. The compressor of claim 31 wherein each of said blades has a leading edge and at least one peripheral edge, and wherein said blades are mounted within said trough such that the leading edges of the blades extend transversely across the trough and the peripheral edge of said blades are in abutment with said trough.

41. An exhalation valve for controlling the expiratory gas flow from a mammalian patient, said exhalation valve comprising:

a housing defining an expiratory gas flow passageway therethrough;

a valve seat formed within said expiratory gas flow passageway;

an annular diaphragm movably disposed within said gas flow passageway, in juxtaposition to said valve seat, said diaphragm being variably movable back and forth to various positions between and including;

i) a fully closed position wherein said diaphragm is firmly seated against said valve seat to prevent gas from flowing through said passageway; and

ii) a fully open position wherein said diaphragm is retracted away from said annular valve seat so as to permit substantially unrestricted flow of expiratory gas through said pathway;

an elongate actuation shaft having a proximal end and a distal end, the distal end of said actuation shaft being contactable with said diaphragm, and said actuation shaft being axially moveable back and forth to control the positioning of said diaphragm between said fully closed and said fully open positions;

an electrical induction coil linked to said actuation shaft such that a decrease in the current passing into said induction coil will cause said shaft to advance in the distal direction and an increase in the current passing into said induction coil will cause said shaft to retract in the proximal direction;

means for determining the flow rate of expiratory gas passing out of said exhalation valve;

means for determining airway pressure;

a microprocessor controller connected to said means for determining airway pressure, said controller being provided with a positive expiratory pressure setting, and said controller being connected to said induction coil and adapted to emit control signals to said induction coil to control the movement of said actuation shaft in response to the current airway pressure, thereby maintaining the present amount of positive expiratory pressure;

a radio frequency transponder database containing flow characterization data for the means for determining the flow rate of expiratory gas passing out of said exhalation valve;

said controller being further connected to said means for determining the flow rate of expiratory gas passing out of said exhalation valve and being equipped to receive radio frequency input of the characterization data contained in the radio frequency transponder database, and to utilize such data to determine the instant flow rate of expiratory gas passing out of said exhalation valve.

44. The exhalation valve of claim 41 wherein said controller is further adapted to receive input signals from said means for determining the flow rate at which expiratory gas is passing outwardly through said expiratory gas flow passageway, and for emitting control signals to said induction coil to fully close said diaphragm when said flow rate has fallen to a predetermined basal level, thus signifying the end of the expiratory phase.

43. The exhalation valve of claim 42 wherein said controller is located separately from, said exhalation valve.

45. A method of providing pulmonary ventilation to a mammalian patient, said method comprising the steps of:

a) providing a rotary drag compressor device comprising;

i) a housing having an inflow passageway and an outflow passageway formed therein; and

,

ii) a rotor rotatably mounted within said housing such that rotation of said rotor in a first direction will draw gas into said inflow passageway, compress said gas, and expel said gas out of said outflow passageway;

b) connecting the outflow passageway of said rotary drag compressor to a conduit through which respiratory gas flow may be passed into the patient'"'"'s lungs;

c) accelerating said rotor to a first rotational speed for sufficient time to deliver a desired inspiratory gas flow through said conduit and into the patient'"'"'s lungs;

d) stopping said rotor or decelerating said rotor to a basal rotational speed to terminate the inspiratory gas flow through said conduit and to allow the expiratory phase of the ventilation cycle to occur.

46. The method of claim 45 wherein step b comprises connecting said outflow passageway to an endotracheal tube inserted into the trachea of the patient.

47. The method of claim 45 wherein step b comprises connecting said outflow passageway to a nasotracheal tube inserted into the trachea of the patient.

48. The method of claim 45 wherein step b comprises connecting said outflow passageway to a tracheostomy tube inserted into the trachea of the patient.

49. The method of claim 45 wherein step b comprises connecting said outflow passageway to a mask which is positioned over the nose and mouth of the patient.

50. The method of claim 45 wherein step c is commenced upon the occurrence of a triggering event, said triggering event being selected from the group of triggering events consisting of:

i) the passing of a predetermined time period; and

ii) the initiation of spontaneous inspiratory effort by the patient.

51. The method of claim 45 wherein the inspiratory gas flow delivered in step c is limited by a limiting parameter selected from the group of limiting parameters consisting of:

i. a predetermined minimum airway pressure;

ii. a predetermined maximum airway pressure;

iii. a predetermined minimum flow rate;

iv. a predetermined maximum flow rate;

v. a predetermined minimum tidal volume; and

vi. a predetermined maximum tidal volume.

52. The method of claim 45 wherein step c is terminated and step d is commenced upon the occurrence of a selected terminating event, said terminating event being selected from the group of terminating events consisting of:

i. the passing of a predetermined period of time since the commencement of step c;

ii. the attainment of a predetermined airway pressure; and

iii. the passage of a predetermined tidal volume of inspiratory gas.

53. The method of claim 45 wherein step c further comprises controlling the speed to which said rotor is accelerated during the inspiratory phase by:

i. storing specific rotor speed, compressor differential pressure and flow rate characterization data for the compressor;

ii. providing a first input signal to said compressor which is intended to cause the rotor to rotate at a speed calculated to deliver a desired flow rate;

iii. determining the actual flow rate generated by said compressor in response to said first input signal;

iv. comparing the actual flow rate determined in step iii, to the desired flow rate;

v. adjusting the input signal to said compressor to provide the desired flow rate.

54. The method of claim 53 wherein step c further comprises:

vi. repeating steps ii-v, as necessary to achieve said desired flow rate.

55. A rotary drag compressor ventilator device for delivering inspiratory gas flow to a mammalian patient, said device comprising:

a) a rotary drag compressor having an intake port and an outflow port;

b) an inspiratory gas flow passageway for carrying gas from the outflow port of the compressor to the patient during the inspiratory phase of the ventilation cycle;

c) means for accelerating said compressor at the beginning of the inspiratory phase of the ventilation cycle to deliver inspiratory gas flow through said passageway to said patient;

d) means for controlling said compressor during the inspiratory phase of the ventilation cycle to maintain a desired inspiratory pressure and flow rate; and

,

e) means for decelerating said compressor at the end of the inspiratory phase of the ventilation cycle.

56. The ventilator device of claim 55 wherein said inspiratory gas flow passageway is devoid of valves for diverting the inspiratory gas flow away from said patient.

57. The ventilator device of claim 55 wherein said rotary drag compressor comprises:

a compressor housing having said intake and outflow ports formed therein;

a rotor mounted within said housing such that rotation of said rotor in a first direction will cause said inspiratory gas flow to be delivered out of said outflow port and through said inspiratory gas flow passageway to said patient; and

,

a motor for rotating said rotor within said housing.

58. The ventilator device of claim 55 wherein said means for accelerating, controlling and decelerating said compressor comprise:

a microprocessor controller connected to said compressor.

59. The ventilator device of claim 55 further comprising:

f) an exhalation conduit for carrying expiratory gas flow from said patient during the expiratory phase of the ventilation cycle;

g) an exhalation valve positioned on said exhalation conduit, said exhalation valve being constructed to;

i) open during the expiratory phase of the ventilation cycle to permit the expiratory gas flow to pass out of said exhalation conduit, and

ii) close during the inspiratory phase of the ventilation cycle to prevent gas from being drawn into said patient through said exhalation conduit.

60. The ventilator device of claim 55 further comprising:

f) an oxygen blending apparatus connected to said intake port to provide oxygen-enriched air to said compressor.

82. The oxygen blending apparatus of claim 76 wherein the ventilator device connected to the outlet of the accumulator chamber comprises the ventilator device of claim 55.

83. The oxygen blending apparatus of claim 82 wherein the controller which controls opening and closing of the solenoid valves is incorporated into the means for controlling the ventilator compressor.

61. An exhalation valve comprising:

a) a housing defining a first exhalation passageway through which expiratory gas may outflow in a first direction;

b) a valve seat formed within said passageway;

c) a diaphragm having a front side and a back side, said diaphragm being sized and configured such that the front side thereof may abut against said valve seat valve seat to thereby block the flow of gas through said exhalation passageway, said diaphragm being moveable back and forth between;

i) a first position wherein said diaphragm is fully retracted from said valve seat to permit unrestricted flow through said passageway;

ii) a second position wherein said diaphragm is seated on said valve seat to block flow through said passageway;

iii) a range of intermediate positions between said first and second positions wherein said diaphragm will cause varying degrees of restriction of the flow through said passageway;

d) an elongate shaft having a first end and a second end, the first end of said shaft being adjacent to the back side of said diaphragm, said shaft being axially moveable back and forth between;

i) a first position wherein the first end of said shaft is at a location which will retain said diaphragm in its first position;

ii) a second position wherein the first and of said shaft is at a location which will allow said diaphragm to move to its second position; and

,

iii) a range of intermediate positions wherein said shaft is at a location which will allow said diaphragm to move to one of its intermediate positions;

e) an electrical induction coil slidably mounted within said housing so as to move back and forth in response to changes in current applied to the coil, said coil consisting essentially of multiple convolutions of wire upon which a rigidifying coating has been applied to hold said wire in a closely coiled substantially cylindrical configuration;

f) a mounting spider connecting said shaft to said coil, said spider configured to hold said shaft in co-axial alignment with the longitudinal axis of the coil, with the first end of the shaft protruding toward the back side of said diaphragm such that, when the coil moves forward, said shaft will move forward toward said first shaft position, and when said coil moves rearward, said shaft will be retracted toward said second shaft position.

62. The exhalation valve of claim 61 wherein the front surface of said diaphragm is planar and wherein said valve seat is angled relative to the plane of the front surface of the diaphragm such that, when said diaphragm is moving into said first diaphragm position, the front side of said diaphragm will initially contact only one side of said diaphragm and will subsequently move into contact with the remainder of said valve seat.

63. The exhalation valve of claim 61 further comprising:

g) a pliable dust barrier disposed between said valve seat and said induction coil, said pliable dust barrier being sealed to the surrounding housing to prevent particulate matter from passing around said shaft and into said induction coil, said dust barrier being in contact with said shaft and being sufficiently flexible to move back and forth in accordance with axial movement of said shaft.

64. The exhalation valve of claim 63 wherein said dust barrier comprises an elastomeric boot.

65. The exhalation valve of claim 63 wherein at least one vent hole is formed in said exhalation valve to prevent the creation of pressure on at least one side of said dust barrier as said dust barrier flexes back and forth.

66. An exhalation valve comprising:

a) a housing defining an expiratory gas flow path connectable to a mammalian patient such that expiratory gas exhaled by the patient will pass through said flow path in a first direction;

b) a valve associated with said flow path to permit gas exhaled by the patient to pass through said flow path in said first direction, but to prevent gas from being drawn through said flow path, in a second direction opposite said first direction, when said patient inhales;

c) a flow measuring apparatus for monitoring the flow rate of expiratory gas passing through said exhalation valve.

67. The exhalation valve of claim 66 wherein said flow measuring apparatus comprises:

a flapper disposed transversely within said flow path, said flapper being constructed such that at least a portion of said flapper will deflect in a first direction when exhaled gas is passed through said flow path in said first direction, the extent of flapper deflection being variable with the flow rate of gas passing through the exhalation valve, said flapper thereby creating a dynamic flow restricting orifice within said flow path;

means for determining gas pressure within said flow path upstream of said flapper;

means for determining gas pressure within said flow path downstream of said flapper; and

means for determining the then-current flow rate of gas passing through said exhalation valve, based on the difference in the pressures measured upstream and downstream of said flapper.

68. The exhalation valve device of claim 72 wherein said flapper is mounted within a flapper assembly which comprises:

a sheet of pliable material having a first side, a second side and an outer peripheral edge, a semi-annular cut being formed in said sheet to divide said sheet into i) an outer peripheral portion which is outboard of said cut and ii) an inner flapper portion which is inboard of said cut, and which remains attached on one side thereof to the surrounding peripheral portion of said sheet, said inner flapper portion of said sheet being thereby deflectable back and forth while the outer peripheral portion of said sheet is held in substantially stationary position;

a first frame member having a central aperture formed therein, said first frame member being juxtaposed to the first side of said sheet such that said first frame member is in contact with the first side of the peripheral portion of said sheet such that said first frame member is in abutment with the first side of the peripheral portion of said sheet and the central aperture of said first frame member surrounds the first side of the flapper portion of said sheet;

a second frame member having a central aperture formed therein, said second frame member being juxtaposed to the second side of said sheet such that said frame member abuts against the second side of the peripheral portion of said sheet, and the central aperture of said second frame member surrounds the second side of the flapper portion of said sheet;

said first and second frame members thereby holding the peripheral portion of said sheet in a substantially fixed position between said frame members while the flapper portion of said sheet extends transversely into the space between the axially aligned apertures of said frame members and is deflectable back and forth therein.

69. The exhalation valve device of claim 68 wherein said flapper assembly is positioned transversely within the flow path of said exhalation valve and is held in such position by engagement to the surrounding exhalation valve housing.

70. The exhalation valve device of claim 66 further comprising:

specific flow-pressure calibration information for the flow measuring apparatus stored on a storage medium contained within the exhalation valve housing.

71. The exhalation valve device of claim 70 wherein said storage medium comprises a radio-frequency transponder.

72. The exhalation valve device of claim 70 wherein the characterization information stored on said storage medium comprises a data base of predetermined pressure differences for specific flow rates of exhalation valve.

73. The exhalation valve device of claim 70 wherein the information stored on said storage medium comprises an equation for calculating specific flow rates based on measured pressure differentials for that exhalation valve.

74. The exhalation valve device of claim 68 further comprising:

a cushioning washer and a third frame member disposed on at least one of the first and second frame members which abut against the same so as to evenly distribute stresses applied to said sheet by said frame members.

75. The exhalation valve device of claim 74 wherein said cushioning washer comprises an elastomeric material disposed on said third frame member.

76. An oxygen blending apparatus for delivering oxygen enriched air to a ventilator, said apparatus comprising:

a) an accumulator chamber;

b) an air inlet conduit connected to said accumulator chamber;

c) an oxygen inlet conduit connected to said accumulator chamber;

d) a series of solenoid valves connected, in parallel, within said oxygen inlet conduit, each of said solenoid valves having a predetermined orifice size; and

e) a controller for independently opening and closing each of the solenoid valves to control the amount of oxygen which flows into the accumulator chamber during a time period.

77. The oxygen blending apparatus of claim 76 further in combination with a ventilator device connected to the outlet of said accumulator chamber, said ventilator device being operative to intermittently draw inspiratory gas from said accumulator chamber to compress and expel said gas to provide an inspiratory flow.

78. The oxygen blending apparatus of claim 77 wherein said controller is further programmed to repeatedly determine the volume of oxygen enriched gas which has been drawn from the accumulator chamber during the then-current inspiratory phase, and to subsequently adjust the opening and closing of the solenoid valves to maintain the prescribed oxygen concentration of gas drawn from the accumulator chamber during the reminder of that inspiratory phase.

79. The oxygen blending apparatus of claim 78 wherein said controller is further programmed to repeatedly compare the then-current accumulated volume of oxygen enriched gas to a predetermined trigger volume for each of the solenoid valves, and to open each solenoid valve for a predetermined period of time when it is determined that the accumulated volume of oxygen-enriched air has exceeded the trigger volume for that individual solenoid valve.

80. The oxygen blending apparatus of claim 76 wherein said solenoid valves comprise at least first, second, third and fourth solenoid valves, and wherein a predetermined oxygen pressure is constantly passed into said oxygen inlet conduit.

81. The oxygen blending apparatus of claim 80 wherein said first, second, third, and fourth solenoid valves have flow rates, at a predetermined oxygen inlet operating pressure, of 5 liters/min., 14.7 liters/min.;

40 liters/min. and 80 liters/min., respectively.

84. A flow transducer for measuring the flow rate of a fluid, said transducer comprising:

a housing defining a first fluid flow path therethrough;

a deflectable flapper disposed transversely within said fluid flow path such that said flapper will deflect in the direction of fluid flow, thereby creating a fluid flow restriction permitting some fluid to flow past said flapper and through said flow path;

a first pressure port located upstream of said flapper for measuring the pressure of fluid within said flow path, upstream of said flapper;

a second pressure port downstream of said flapper for measuring the pressure of fluid flowing through said flow path, downstream of said flapper;

means associated with first pressure port for determining the pressure of fluid flowing upstream of said flapper;

means associated with said second pressure port for determining the pressure of fluid flowing downstream of said flapper;

means for determining the difference between the pressure of fluid flowing upstream of said flapper and the pressure of fluid flowing downstream of said flapper; and

means for computing the flow rate of fluid through said flow path, based on the measured difference in pressures upstream and downstream of said flapper.

85. The fluid flow transducer of claim 84, wherein said deflectable flapper comprises:

a rigid frame having a central aperture formed therein;

a flat sheet of pliable material mounted within said frame member and forming a flapper disposed transversely within the central aperture of said frame and deflectable in at least one direction to permit fluid to flow past said flapper and through said central aperture;

said frame being mounted transversely within said flow path such that fluid flowing in a first direction through said flow path will strike said flapper, thereby causing said flapper to deflect in the direction of flow such that the flowing fluid may pass through said central aperture.

86. The flow transducer of claim 85 wherein:

said flat sheet of pliable material comprises an outer peripheral portion, an inner flapper portion, and a semi-annular cut formed in said sheet to free most of said peripheral portion from said flapper portion; and

said rigid frame comprises first and second frame members disposed on opposite sides of the peripheral portion of said flat sheet, said frame members being compressed inwardly to compressively hold said peripheral portion of said flat sheet between said frame members such that the flapper portion of said flat sheet is transversely disposed and deflectable within the central aperture of said frame.

87. The flow transducer of claim 84 further comprising:

a cushioning member associated with said flapper to distribute the force exerted on said flapper thereby distributing any stresses created within said flapper.

88. The flow transducer of claim 85 further comprising:

a cushioning member associated with said frame to distribute the force exerted by said frame on said flat sheet of pliable material, thereby distributing any stresses of created within said flat sheet of pliable material.

89. The flow transducer of claim 84 wherein said housing comprises a portion of an exhalation valve through which a mammalian patient is permitted to exhale, said flow transducer being disposed within said exhaltion valve to measure the flow rate of expiratory gas passing through said exhalation valve.

90. The flow transducer of claim 84 further comprising:

a deflector member positioned on at least one of said first and second pressure ports to deter fluid from being forced directly into the pressure port on which deflector insert is positioned.

91. The flow transducer of claim 84 wherein said means for computing flow rate comprises a microprocessor.

92. The flow transducer of claim 86 wherein:

said housing incorporates first and second abutment ridges formed about said flow path;

said first and second frame members, having said flat sheet of pliable material therebetween, being positioned between said abutment ridges such that said abutment ridges will exert inward compressive force on said first and second frame members to compressively hold said flat sheet therebetween.

93. The flow transducer of claim 84 further comprising:

specific flow-pressure calibration information for the flow transducer stored on a storage medium contained within said housing.

94. The flow transducer of claim 93 wherein said storage medium comprises a radio-frequency transponder.

95. The flow transducer of claim 93 wherein the specific flow-pressure calibration information stored on said storage medium comprises a data base of predetermined pressure differences for specific flow rates of fluid through said flow path.

96. The flow transducer of claim 93 wherein the calibration information stored on said storage medium comprises an equation for calculating specific flow rates based on measured differences in pressure upstream and downstream of said flapper.