Ventilation apparatus and anesthesia delivery system

• US 6,131,571 A
• Filed: 04/30/1997
• Issued: 10/17/2000
• Est. Priority Date: 04/30/1997
• Status: Expired due to Fees

• Current Assignee: University of Florida (State University System of Florida)
• Original Assignee: University of Florida (State University System of Florida)
• Inventors: Gravenstein, Joachim S., van Oostrom, Johannes Hugo Maria, Lampotang, Samsun
• Primary Examiner(s): Weiss, John G.
• Assistant Examiner(s): SRIVASTAVA, VIRENDRA KUMAR
• Application Number:
  US08/848,339
• Time in Patent Office: 1,266 Days
• Field of Search: 728/204.21, 728/205.18, 728/203.28, 728/205.12, 728/204.28, 728/203.12, 728/203.14, 728/205.25, 728/204.23, 728/204.24 , 728/205.19, 728/205.11, 728/202.27
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0009 with sub-atmospheric pressure, e.g. during expiration
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/0075 Bellows-type
• CPC Class Codes: A61M 16/0078 Breathing bags
• CPC Class Codes: A61M 16/009 Removing used or expired gases or anaesthetic vapours filtering, sterilising or disinfecting the exhaust air in drainage systems A61M1/784; bacterial filters in the expiratory path A61M16/1065
• CPC Class Codes: A61M 16/01 specially adapted for anaesthetising A61M16/104, A61M16/18 take precedence
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/08 Bellows; Connecting tubes having means for taking samples G01N1/22; Water traps; Patient circuits
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• CPC Class Codes: A61M 16/1015 using a gas flush valve, e.g. oxygen flush valve
• CPC Class Codes: A61M 16/1055 bacterial
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 16/22 Carbon dioxide-absorbing devices ; Other means for removing carbon dioxidecartridges with absorbing substances for respiratory apparatus A62B19/00
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2016/1025 the O2 concentration
• CPC Class Codes: A61M 2016/103 the CO2 concentration
• CPC Class Codes: A61M 2016/1035 the anaesthetic agent concentration
• CPC Class Codes: A61M 2205/3368 : Temperature
• CPC Class Codes: A61M 2205/3606 : cooled
• CPC Class Codes: A61M 2230/432 : partial CO2 pressure (P-CO2)
• CPC Class Codes: Y02C 20/10 : of nitrous oxide (N2O)

Abstract

A combination ventilation apparatus and anesthesia delivery system comprises a circulation loop within which oxygen and air or other clinical gas, or a mixture of air, oxygen, nitrous oxide or other clinical gas and anesthetics, are circulated by a variable speed centrifugal blower to a Y-piece which connects the circulation loop to an endotracheal tube or other airway device communicating with a patient. A proportional flow control valve is operative to actively control the pressure or flow at the Y-piece in response to signals from pressure or flow sensors which are positioned to provide measurements representative of the actual pressure and flow conditions within the patient'"'"'s lungs. Constant circuit volume is maintained by computer control of gas make-up valves in response to the movement of a weighted bellows located between the proportional flow control valve and centrifugal blower.

Claims

1. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a source of positive pressure and a source of negative pressure which are collectively operative to circulate a flow of gas within said circulation loop;

a control device having a variable-size orifice, said control device being located in said circulation loop between said airway device and said source of negative pressure;

a controller operatively connected to said control device, said controller being effective to selectively cause said variable-size orifice of said device to alternatively create a pressure at said airway device which permits gas to flow into said airway device, and then a pressure at said airway device which permits gas to flow out of said airway device.

2. The apparatus of claim 1 in which said source of positive pressure and said source of negative pressure are collectively comprised of a centrifugal blower having a negative pressure, intake side and a positive pressure, exhaust side.

3. The apparatus of claim 1 in which said control device is a proportional flow control valve having said variable-size orifice.

4. The apparatus of claim 3 in which said proportional control valve includes:

(i) a valve body having a hollow interior, an inlet and an outlet;

(ii) a conduit extending from said inlet of said valve body into said interior thereof, said conduit being formed with a discharge opening having a cross sectional area; and

(iii) a valve closure member movable with respect to said conduit to vary the effective cross sectional area of said discharge opening thereof.

5. The apparatus of claim 4 in which said valve closure member comprises a woofer speaker including a diaphragm which mounts a profiled plug having a tapered outer wall whose diameter progressively increases from the tip thereof to a diameter at least equal to the diameter of said discharge opening of said conduit, said diaphragm of said woofer speaker being effective to move said profiled plug toward and away from said discharge opening of said conduit.

6. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of gas within said circulation loop, said blower having an intake side and an exhaust side;

a proportional flow control valve located in said circulation loop between said airway device and the intake side of said blower;

a gas storage reservoir located in said circulation loop between said proportional flow control valve and the intake side of said blower;

a controller operatively connected to said proportional flow control valve, said controller being effective to selectively move said proportional flow control valve to a position to alternatively create a pressure at said airway device which permits gas to flow into said airway device, and then a pressure at said airway device which permits gas to flow out of said airway device.

7. The apparatus of claim 6 in which said gas storage reservoir includes a collapsible bellows.

8. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

an endotracheal tube for intubating a patient, said endotracheal tube having a proximal end and a distal tip which is positionable near the carina of a patient;

a circulation loop connectable to said endotracheal tube;

a blower operative to circulate a flow of gas within said circulation loop, said blower having an intake side and an exhaust side;

a pressure sensor operative to produce a signal representative of the pressure at said distal tip of said endotracheal tube;

a proportion flow control valve located in said circulation loop between said endotracheal tube and the intake side of said blower; and

a controller operatively connected to said proportion flow control valve, said controller being effective in response to receipt of said signal from said pressure sensor to selectively move said proportion flow control valve to a position to alternatively create a pressure at said proximal end of said endotracheal tube which permits gas to flow into said endotracheal tube and then a pressure at said proximal end which permits gas to flow out of said endotracheal tube.

9. The apparatus of claim 8 in which said blower is selected from the group consisting of a variable speed, centrifugal blower and a fixed speed blower.

10. The apparatus of claim 8 in which said pressure sensor includes a lumen connected to said distal tip of said endotracheal tube, and a pressure transducer connected by a line to said lumen, said pressure transducer being effective to produce said signal representative of the pressure at said distal tip.

11. The apparatus of claim 8 further including a Y-piece interconnecting said circulation loop with said endotracheal tube, and at least one other flow/pressure sensor located at said Y-piece to provide an independent measurement of pressure thereat.

12. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of intermixed oxygen, a second gas and at least one anesthetic within said circulation loop;

a multi-gas sensor having an input located at a distal tip of a endotracheal tube, said multi-gas sensor being effective to sense the presence of oxygen, anesthetic gas, carbon dioxide and other gases within said flow and produce signals representative of the concentration of each gas;

first, second and third supply means for introducing oxygen, said second gas and said at least one anesthetic, respectively, into said circulation loop;

a controller operatively connected to each of said first, second and third supply means and to said multi-gas sensor, said controller being effective upon receipt of said signals from said multi-gas sensor to selectively control the operation of said first, second and third supply means to obtain the desired, relative concentration of oxygen, said second gas and said at least one anesthetic within said circulation loop.

13. The apparatus of claim 12 in which said first supply means is a gas make-up valve connected to said circulation loop, said gas make-up valve being adapted to connect to a source of oxygen.

14. The apparatus of claim 12 in which said second supply means is a gas make-up valve connected to said circulation loop, said gas make-up valve being adapted to connect a source of clinically usable gas such as nitrous oxide, nitrogen and helium.

15. The apparatus of claim 12 in which said third supply means is a motorized anesthetic syringe pump connected to said circulation loop, said syringe pump including:

a pump body having an interior carrying a movable plunger;

a needle connected at one end to said interior of said pump body;

a sintered metal insert carried within a copper block located in said circulation loop, said needle being connected to said sintered metal insert to deliver liquid anesthetic therein where it is vaporized and carried by said circulation loop to the patient'"'"'s lung.

16. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of gas within said circulation loop;

a supply device for introducing gas into said circulation loop;

a bellows having a hollow interior communicating with said circulation loop, said bellows being movable from a baseline position when the volume of gas within said circulation loop changes;

a sensor device for sensing the extent of movement of said bellows from said baseline position, and for producing a signal representative of said movement;

a controller operatively connected to said supply device, said controller being effective in response to receipt of said signal from said sensor device to open said supply device so that fresh gas is introduced into said circulation loop at a total flowrate proportional to the extent of movement of said bellows from said baseline position.

17. The apparatus of claim 16 in which said supply device is a gas make-up valve adapted to connect to a source of clinical gas, and a gas make-up valve adapted to connect to a source of oxygen.

18. The apparatus of claim 16 in which said supply device is a gas make-up valve adapted to connect to a source of oxygen, a gas make-up valve adapted to connect to a source of clinical gas, and, a motor-driven anesthetic syringe pump containing a volatile anesthetic.

19. The apparatus of claim 16 in which said bellows is formed with a bottom wall and a hollow interior connected to said circulation loop, said bellows being received within a casing having a sidewall connected to a base formed with an opening, said bellows being connected to at least one weight.

20. The apparatus of claim 19 in which said sensor device is a linear optical encoder operative to sense the extent of movement of said bellows from said baseline position and produce said signal, and a microswitch mounted to said base of said casing in position offset from said baseline position of said bellows, said microswitch being triggered in the event said bellows bottoms out against said base of said casing to reinitialize said linear optical encoder.

21. Apparatus for use as a ventilator and/or anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of gas within said circulation loop;

a supply for introducing gas into said circulation loop;

a heating/cooling device for selectively heating or cooling the gas circulating within said circulation loop, said heating/cooling device including at least one temperature sensor operative to sense the temperature thereof and produce a signal representative of said temperature;

a controller operatively connected to said heater/cooler device and to said temperature sensor thereof, said controller being effective to operate said heater/cooler device to heat the circulating gas and adjust the heating operation thereof dependent on said signal, said controller being effective to operate said heater/cooler device to cool the circulating gas and adjust the cooling operation thereof dependent on said signal.

22. The apparatus of claim 21 in which said heating/cooling device comprises:

a housing having a hollow interior;

a core including a plurality of interconnected fins formed of a thermally conductive material, said core being mounted within said hollow interior of said housing;

a number of thermo-electric Peltier modules connected to said core, said Peltier modules being effective to heat or cool said core dependent on the direction of flow of electrical current therethrough;

at least one temperature sensor connected to said core.

23. The apparatus of claim 22 in which said controller is operative to direct electrical current through said Peltier modules of said heating/cooling device in a first direction to heat said core and the gas flowing therethrough, said controller being operative to direct electrical current through said Peltier modules of said heating/cooling device in a second direction to cool said core and the gas flowing therethrough.

24. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of gas within said circulation loop, said blower having an intake side and an exhaust side;

a purge valve connected to said circulation loop downstream from the airway device, said purge valve being movable between an open position wherein gas is discharged from said circulation loop, and a closed position;

a proportional flow control valve located in said circulation loop between said purge valve and the intake side of said blower, said proportional flow control valve including;

(i) a valve body having a hollow interior, an inlet and an outlet;

(ii) a conduit extending from said inlet of said valve body into said interior thereof, said conduit being formed with a discharge opening having a cross sectional area; and

(iii) a valve closure member movable with respect to said conduit to vary the effective cross sectional area of said discharge opening thereof;

a controller operatively connected to said proportional flow control valve, said controller being effective to move said valve closure member in a direction toward said discharge opening of said conduit to reduce the effective cross sectional area thereof and create a pressure at the airway device which permits a flow of gas into the airway device, said controller being effective to move said valve closure member in a direction away from said discharge opening of said conduit to increase the effective cross sectional area thereof and create a pressure at the airway device to permit a flow of gas out of the airway device.

25. The apparatus of claim 24 in which said valve closure member comprises a woofer speaker including a diaphragm which mounts a profiled plug having a tapered outer wall whose diameter progressively increases from the tip thereof to a diameter at least equal to the diameter of said discharge opening of said conduit, said diaphragm of said woofer speaker being effective to move said profiled plug toward and away from said discharge opening of said conduit in response to signals from said controller.

26. The apparatus of claim 25 in which a donut-shaped seal formed of flexible material is mounted to said woofer diaphragm in a position to engage said discharge opening of said conduit.

27. The apparatus of claim 24 further including a room air entrainment valve connected to said circulation loop at the intake side of said blower, said room air entrainment valve being movable to an open position to permit entrainment of ambient air by said blower into said circulation loop.

28. The apparatus of claim 24 further including a purge valve comprising:

a valve body having an inlet communicating with said circulation loop, and an outlet;

a flexible diaphragm movable with respect to said outlet of said valve body; and

means for moving said diaphragm between a closed position against said outlet, and an open position spaced from said outlet.

29. The apparatus of claim 28 in which said means for moving said diaphragm includes a pilot valve connected by a line to said valve body of said purge valve, and a pressure regulator connected to said pilot valve and to a source of pressurized gas, said pilot valve being effective to transmit pressurized gas from the source into said valve body to move said flexible diaphragm to said closed position and to vent pressurized gas from said valve body to allow said flexible diaphragm to move to said open position.

30. In an apparatus for use as a ventilator and/or anesthesia delivery system including an airway device to which a patient can be connected, a proportional flow control valve comprising:

a valve body having a hollow interior, an inlet and an outlet, said inlet of said valve body communicating with a source of gas and the airway device;

a conduit extending from said inlet of said valve body into said interior thereof, said conduit being formed with a discharge opening having a cross sectional area; and

a valve closure member movable with respect to said conduit to vary the effective cross sectional area of said discharge opening thereof, said valve closure member being movable in a direction toward said discharge opening of said conduit to reduce the effective cross sectional area thereof and create a pressure at the airway device which permits a flow of gas from the source into the airway device, and said valve closure member being movable in a direction away from said discharge opening of said conduit to increase the effective cross sectional area thereof and create a pressure at the airway device to permit a flow of gas out of the airway device.

31. The proportional flow control valve of claim 30 in which said valve closure member comprises a woofer speaker including a diaphragm which mounts a profiled plug having a tapered outer wall whose diameter progressively increases from the tip thereof to a diameter at least equal to the diameter of said discharge opening of said conduit, said diaphragm of said woofer speaker being effective to move said profiled plug toward and away from said discharge opening of said conduit.

32. The proportional flow control valve of claim 31 in which a donut-shaped seal formed of flexible material is mounted to said diaphragm in a position to engage said discharge opening of said conduit.

33. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of gas within said circulation loop;

a purge valve connected to said circulation loop downstream from the airway device, said purge valve being movable between an open position wherein gas is discharged from said circulation loop, and a closed position;

a scavenging system connected by a discharge line to said purge valve, said scavenging system including;

(i) a manifold having an inlet connected to said discharge line, and an outlet;

(ii) a sensor device for producing a signal representative of the pressure within said manifold; and

(iii) a proportional flow control valve connected to said manifold between said inlet and said outlet thereof, said proportional flow control valve being proportionately movable between open and closed positions;

a controller operatively connected to said proportional flow control valve and to said sensor device said controller being effective in response to receipt of said signal from said sensor device to selectively move said proportional flow control valve between said open and closed positions to maintain a substantially constant pressure within the manifold.

34. The apparatus of claim 33 in which said sensor device is a pressure transducer.

35. The apparatus of claim 33 in which said proportional flow control valve comprises:

a valve body having a hollow interior formed with an inlet connected to said manifold, and an outlet downstream from said inlet;

a conduit extending from said inlet into said interior of said valve body, said conduit being formed with a discharge opening having a cross sectional area;

a valve closure member movable with respect to said conduit to vary the effective cross sectional area thereof.

36. The apparatus of claim 35 in which said valve closure member comprises a woofer speaker including a diaphragm which mounts a profiled plug having a tapered outer wall whose diameter progressively increases from the tip thereof to a diameter at least equal to the diameter of said discharge opening of said conduit, said diaphragm of said woofer speaker being effective to move said profiled plug toward and away from said discharge opening of said conduit in response to signals from said controller.

37. The apparatus of claim 36 in which a donut-shaped seal formed of flexible material is mounted to said diaphragm in position to engage said discharge opening of said conduit.

38. The apparatus of claim 33 in which said scavenging system further includes a scavenging bag connected to said manifold between said inlet thereof and said proportional flow control valve.

39. The apparatus of claim 33 in which said scavenging system further includes a gravity pressure relief valve, and a gravity vacuum relief valve, both connected to said manifold.

40. The apparatus of claim 33 in which said scavenging system further includes a tube having an inlet connected to said manifold, and an outlet covered by a removable cap.

41. Apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device with which a patient can be intubated;

a blower operative to circulate a flow of gas within said circulation loop;

oxygen supply device for introducing oxygen into said circulation loop, including;

(i) at least one tank containing oxygen;

(ii) a gas make-up valve connected to said recirculation loop;

(iii) a transfer line interconnecting said tank and said gas make-up valve, said transfer line mounting a one-way valve and a pressure reducing device for supplying oxygen to said transfer line at a predetermined pressure, said pressure reducing device being located between said gas make-up valve and said one-way valve;

(iv) a pressure gauge connected to said transfer line between said one-way valve and said tank;

a controller operative to open and close said gas make-up valve to selectively introduce oxygen into said circulation loop.

42. The apparatus of claim 41 in which said pressure reducing device is a pressure reducing one-way valve, said valve permitting the flow of oxygen only in a direction from tank to said gas make-up valve.

43. The apparatus of claim 41 in which said oxygen supply device further includes:

a primary oxygen supply including a supply line having one end connected to said transfer line and an opposite end adapted to connect to a source of oxygen;

a one-way valve connected to said supply line; and

a pressure gauge connected to said supply line between said transfer line and said one-way valve.

44. The apparatus of claim 41 in which said oxygen supply device further includes:

first and second oxygen tanks each connected by a feed line to said transfer line;

each of said feed lines mounting a one-way valve and a pressure gauge, each of said pressure gauges being positioned in a respective feed line between an oxygen tank and a one-way valve.

45. An anesthetic delivery system, comprising:

a circulation loop connectable to an endotracheal tube with which a patient can be intubated, said endotracheal tube having a proximal end and a distal tip which is positionable near the carina of the patient;

a blower operative to circulate a flow of gas within said circulation loop, said blower having an intake side and an exhaust side;

a supply device for introducing a volatile anesthetic into said circulation loop, said supply device being located at the exhaust side of said blower;

a first device for introducing oxygen into said circulation loop, and second device for introducing another clinical gas into said circulation loop, said first and second device being located on the intake side of said blower;

a carbon dioxide absorber connected to said circulation loop to receive the flow of gas therethrough, and means for permitting the flow of gas within said circulation loop to bypass said carbon dioxide absorber;

a bacterial filter connected to said circulation loop between said blower and the endotracheal tube;

a heater/cooler connected to said circulation loop;

a manual breathing bag connected to said circulation loop upstream from the endotracheal tube;

at least one pressure sensor located at said distal tip of said endotracheal tube, said pressure sensor producing a signal representative of the pressure at said distal tip;

a multi-gas sensor having an input located at said distal tip of said endotracheal tube, said multi-gas sensor being effective to produce individual signals representative of the respective concentration of oxygen, volatile anesthetic, nitrous oxide and carbon dioxide within said flow of gas;

a flow sensor located at said proximal end of said endotracheal tube, said flow sensor being effective to produce a first signal representative of the direction of flow of gas into or out of said endotracheal tube and a second signal representative of the magnitude of gas flow into or out of said endotracheal tube;

a purge valve having an inlet connected to said circulation loop downstream from said endotracheal tube and an outlet, said purge valve being movable between an open position and a closed position;

a scavenging system connected to said outlet of said purge valve;

a proportional flow control valve located in said circulation loop between said purge valve and the intake side of said blower;

a bellows having a hollow interior communicating with said circulation loop, said bellows being located between said proportional flow control valve and the intake side of said blower;

a room air entrainment valve connected to said circulation loop at said intake side of said blower; and

a controller operatively connected to said blower, said supply device, said first and second devices, said heater/cooler, said at least one pressure sensor, said multi-gas sensor, said flower sensor, said purge valve, said scavenging system, said proportional flow control valve and said room air entrainment valve.

46. The anesthesia delivery system of claim 45 in which said blower is a variable speed, centrifugal blower.

47. The anesthesia delivery system of claim 45 in which said pressure sensor includes a lumen connected to said distal tip of said endotracheal tube, and a pressure transducer connected by a line to said lumen, said pressure transducer being effective to produce said signal representative of the gas pressure at said distal tip.

48. The anesthesia delivery system of claim 45 further including at least one other pressure sensor located at a Y-piece which interconnects said circulation loop to said endotracheal tube to provide an independent measurement of pressure thereat.

49. The anesthesia delivery system of claim 45 in which each of said first and second device includes a gas make-up valve connected to said circulation loop, said gas make-up valves being operatively controlled by said controller.

50. The apparatus of claim 45 in which said third supply device is a motorized anesthetic syringe pump connected by a needle to a sintered metal insert carried by a copper block within said circulation loop, said syringe pump being effective to introduce volatile anesthetics in liquid form into said sintered metal insert where they are vaporized.

51. The apparatus of claim 45 in which said bellows is formed with a bottom wall and a hollow interior connected to said recirculation loop, said bellows being received within a casing having a sidewall which is connected to a base formed with an opening, said bottom wall of said bellows being connected to at least one weight.

52. The anesthesia delivery system of claim 51 further including sensor device including a linear optical encoder operative to sense the extent of movement of said bellows from said baseline position and produce said signal, and a microswitch mounted to said base of said casing in position offset from said baseline position of said bellows, said microswitch being triggered in the event said bellows bottoms out against said base of said casing to reinitialize said linear optical encoder.

53. The apparatus of claim 45 in which said heater/cooler comprises:

a housing having a hollow interior;

a core including a plurality of interconnected fins formed of a thermally conductive material, said core being mounted within said hollow interior of said housing;

a number of thermoelectric Peltier modules connected to said core, said Peltier modules being effective to heat or cool said core dependent on the direction of flow of electrical current therethrough;

at least one temperature sensor connected to said core.

54. The apparatus of claim 45 further including a purge valve including:

a valve body having an inlet communicating with said circulation loop, and an outlet;

a flexible diaphragm movable with respect to said outlet of said valve body; and

means for moving said diaphragm between a closed position against said outlet, and an open position spaced from said outlet.

55. The apparatus of claim 54 in which said means for moving said diaphragm includes a pilot valve connected by a line to said valve body of said purge valve, and a pressure regulator connected to said pilot valve and to a source of pressurized gas, said pilot valve being effective to transmit pressurized gas from the source into said valve body to move said flexible diaphragm to said closed position and to vent pressurized gas from said valve body to allow said flexible diaphragm to move to said open position.

56. The anesthesia delivery system of claim 45 in which said proportional flow control valve includes:

a valve body having a hollow interior, an inlet and an outlet;

a conduit extending from said inlet of said valve body into said interior thereof, said conduit being formed with a discharge opening having a cross sectional area;

a valve closure member movable with respect to said conduit to vary the effective cross sectional area of said discharge opening thereof.

57. The apparatus of claim 56 in which said closure member comprises a woofer speaker including a diaphragm which mounts a profiled plug having a tapered outer wall whose diameter progressively increases from the tip thereof to a diameter at least equal to the diameter of said discharge opening of said conduit, said diaphragm of said woofer speaker being effective to move said profiled plug toward and away from said discharge opening of said conduit in response to signals from said controller.

58. The apparatus of claim 56 in which a donut-shaped seal formed of flexible material is mounted to said diaphragm in position to engage said discharge opening of said conduit.

59. The apparatus of claim 45 further including a room air entrainment valve connected to said circulation loop at the intake side of said blower, said room air entrainment valve being movable to an open position to permit entrainment of ambient air by said blower into said circulation loop.

60. The anesthesia delivery system of claim 45 in which said scavenging system includes:

(i) a manifold having an inlet connected to said discharge line, and an outlet;

(ii) a sensor device for producing a signal representative of the pressure within said manifold; and

(iii) a proportional flow control valve connected to said manifold between said inlet and said outlet thereof, said proportional flow control valve being proportionately movable between open and closed positions.

61. The apparatus of claim 60 in which said proportional flow control valve comprises:

a valve body having a hollow interior formed with an inlet connected to said manifold, and an outlet downstream from said inlet;

a conduit extending from said inlet into said interior of said valve body, said conduit being formed with a discharge opening having a cross sectional area;

a valve closure member movable with respect to said conduit to vary the effective cross sectional area thereof.

62. The apparatus of claim 60 in which said scavenging system further includes a scavenging bag connected to said manifold between said inlet thereof and said proportional flow control valve.

63. The apparatus of claim 60 in which said scavenging system further includes a gravity pressure relief valve, and a gravity vacuum relief valve, both connected to said manifold.

64. The apparatus of claim 60 in which said scavenging system further includes a tube having an inlet connected to said manifold, and an outlet covered by a removable cap.

65. The anesthesia delivery system of claim 45 further including an oxygen supply device for introducing oxygen into said circulation loop, said oxygen supply device including:

(i) at least one tank containing oxygen;

(ii) a gas make-up valve connected to said recirculation loop;

(iii) a transfer line interconnecting said tank and said gas make-up valve, said transfer line mounting a one-way valve and a pressure reducing means for supplying oxygen to said transfer line at a predetermined pressure, said pressure reducing means being located between said gas make-up valve and said one-way valve; and

(iv) a pressure gauge connected to said transfer line between said one-way valve and said tank.

66. The apparatus of claim 65 in which said oxygen supply device further includes:

first and second oxygen tanks each connected by a feed line to said transfer line;

each of said feed lines mounting a one-way valve and a pressure gauge, each of said pressure gauges being positioned in a respective feed line between an oxygen tank and a one-way valve.

67. A method of ventilating a patient, comprising:

providing a source of positive pressure and a source of negative pressure;

circulating a flow of gas within a circulation loop connectable to a patient by an airway device with the positive and negative pressures, respectively;

positioning a control device having a variable-sized orifice within the circulation loop between the patient airway device and the source of negative pressure;

operatively connecting a controller to said control device and selectively using the controller to cause the variable-sized orifice to alternatively create a pressure at the airway device which permits a flow of gas into the airway device, and then a pressure at the airway device which permits gas to flow out of the airway device.

68. The method of claim 67 in which the step of using said controller with said variable-sized orifice comprises the step of operating a proportional flow control valve to create the flow of gas into, and the flow of gas out of the patient airway device.

69. A method of ventilating a patient, comprising:

circulating a flow of gas within a circulation loop which is connectable to a patient by an airway device;

sensing one of the pressure and flow rate within said circulation loop at said airway device, and producing a corresponding signal;

controlling the operation of a variable-orifice control device, dependent on said signal, to alternatively direct a portion of the gas flow within the circulation loop through the airway device and into the lungs of the patient, and then permit gas to flow out of the patient'"'"'s lungs and through the airway device into the circulation loop.

70. The method of claim 69 in which said step of circulating a flow of gas includes circulating a flow of gas within a circulation loop connected to an endotracheal tube having a distal tip positionable near the carina of a patient.

71. The method of claim 70 further including the step of sensing one of the flow and pressure of the gas at the distal tip of the endotracheal tube, and producing a corresponding signal.

72. The method of claim 71 in which said step of controlling a variable-orifice control device includes controlling the variable-orifice control device dependent on the signal.

73. The method of claim 69 in which said step of sensing one of the pressure and flow rate comprises sensing the flow rate within the circulation loop at said airway device during inspiration of the patient.

74. The method of claim 69 in which said step of sensing one of the pressure and flow rate comprises sensing the pressure within the circulation loop at said airway device during exhalation of the patient.

75. A method of ventilating a patient, comprising:

circulating a flow of gas within a circulation loop connected to the proximal end of an endotracheal tube whose distal tip is located near the carina of the patient;

sensing one of the pressure and flow rate of the gas at the distal tip of the endotracheal tube, and producing a signal representative thereof;

controlling the operation of a proportional flow control valve mounted within the circulation loop, dependent on said signal, to alternatively direct a flow of gas into and out of the endotracheal tube.

76. The method of claim 75 in which said step of controlling the operation of a proportional flow control valve comprises;

causing a valve closure member of said proportional flow control valve to move to a selected, at least partially closed position, to create a pressure at the proximal end of the endotracheal tube which permits a portion of the flow of gas to flow into said endotracheal tube and the lungs of the patient; and

causing said valve closure member to thereafter move to a selected, at least partially closed position, to create a pressure within said circulation loop at the proximal end of the endotracheal tube which permits the inspired gas to flow out of the patient'"'"'s lungs and said endotracheal tube.

77. The method of claim 76 in which said steps of causing a valve closure member to move to said at least partially closed and partially open positions, comprises causing a profiled plug to move toward and away from a discharge opening within the interior of said proportional flow control valve through which said flow of gas from said circulation loop is directed.

78. A method of anesthetizing a patient, comprising:

circulating a flow of gas containing oxygen and at least one anesthetic within a circulation loop connected to an airway device to which the patient is connected;

producing a signal in response to the failure of a bellows connected to said circulation loop to return to a baseline position at end expiration;

introducing additional gas into said recirculation loop in response to production of said signal.

79. The method of claim 78 in which said step of producing a signal comprises sensing the movement of said bellows from said baseline position by operation of a linear optical encoder.

80. The method of claim 79 in which said step of introducing additional gas into said circulation loop comprises opening a first gas make-up valve connected to a source of oxygen, and opening a second gas make-up valve connected to a source of clinical gas.

81. The method of claim 78 in which said step of introducing additional gas further comprises introducing a volatile anesthetic into said circulation loop.

82. A method of anesthetizing a patient, comprising:

circulating a flow of gas containing oxygen and at least one anesthetic within a circulation loop connected to an airway device to which the patient is connected;

transmitting at least a portion of said flow of gas out of said circulation loop and into a scavenging system connected to a vacuum source;

maintaining a substantially constant pressure within said scavenging system independent of any fluctuations in the negative pressure provided by said vacuum source or inflow from the circulation loop into the scavenging system.

83. The method of claim 82 in which said step of maintaining a substantially constant pressure within said scavenging system comprises selectively moving a proportional flow control valve proportionately between an open position and closed position within a scavenger system manifold in response to signals generated by a pressure sensor connected to said manifold.

84. A method of ventilating a patient, comprising:

circulating a flow of gas within a circulation loop and into an airway device communicating with the lungs of a patient;

operating a variable-orifice control device, located within the circulation loop, so that the peak end expiratory pressure in the lungs of the patient does not fall below a selected level above ambient pressure.

85. The method of claim 84 in which said step of operating a variable-orifice control device comprises adjusting a variable-orifice flow device in the course of exhalation by the patient so that a selected pressure above ambient pressure is maintained in the patient'"'"'s lungs at end exhalation.

86. A method of ventilating a patient, comprising:

circulating a flow of gas within a circulation loop and into an airway device communicating with the lungs of patient;

operating a variable orifice control device, located within the circulation loop, to permit gas within the circulation loop to flow in a direction downstream from the airway device and through the variable orifice control device in the event the pressure at the airway device exceeds a selected maximum level.

87. The method of claim 86 in which said step of operating a variable orifice control device comprises selectively opening the variable orifice control device in the event the pressure at the airway device exceeds a selected maximum level to permit the passage of gas through the variable orifice control device.

88. An apparatus for use as a ventilator and/or an anesthesia delivery system, comprising:

a circulation loop connectable to an airway device to which a patient can be connected;

a blower operative to circulate a flow of intermixed oxygen, a second gas and at least one anesthetic within said circulation loop;

a multi-gas sensor having an input located at a distal tip of an endotracheal tube, said multi-gas sensor being effective to sense the presence of at least oxygen, anesthetic gas and carbon dioxide;

first, second and third supply means for introducing oxygen, the second gas and the at least one anesthetic, respectively, into said circulation loop, said third supply means being a motorized anesthetic syringe pump connected to said circulation loop, said syringe pump including a pump body having an interior carrying a movable plunger, a needle connected at one end to said interior of said pump body, and a sintered metal insert carried within a copper block located in said circulation loop, said needle being connected to said sintered metal insert to deliver liquid anesthetic therein where it is vaporized and carried by said circulation loop to a lung of the patient; and

a controller operatively connected to each of said first, second and third supply means and to said multi-gas sensor, said controller being effective upon receipt of signals from said multi-gas sensor to selectively control the operation of said first, second and third supply means to obtain the desired, relative concentration of oxygen, the second gas and said the at least one anesthetic within said circulation loop.