Method of measuring cardiac related parameters non-invasively via the lung during spontaneous and controlled ventilation

• US 20070062531A1
• Filed: 02/18/2004
• Published: 03/22/2007
• Est. Priority Date: 02/19/2003
• Status: Active Grant

• Current Assignee: Thornhill Scientific Inc.
• Original Assignee: Thornhill Scientific Inc.
• Inventors: Fisher, Joseph, Somogyi, Ron, Preiss, David, Vesely, Alex, Azami, Takafumi, Prisman, Eltan, Nayot, Dan
• Granted Patent: US 8,460,202 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• 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 16/085 Gas sampling
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• 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 16/22 Carbon dioxide-absorbing devices ; Other means for removing carbon dioxidecartridges with absorbing substances for respiratory apparatus A62B19/00

Abstract

An apparatus to measure cardiac output (Q) and other parameters such as alveolar ventilation (VA), minute CO₂ elimination from the lung (VCO₂ ), minute oxygen consumption (VO₂), oxygenated mixed venous partial pressure of CO₂, (PvCO₂-oxy), true mixed venous partial pressure of CO₂(PvCO₂), PaCO₂, mixed venous oxygen saturation (SvO₂), pulmonary shunt, and anatomical dead space, consisting of: a) a breathing circuit with characteristics that: i. on exhalation, exhaled gas is kept substantially separate from inhaled gas; ii. oninhalation, when V_E is greater than FGS flow, the subject inhales FGS first and then inhales a gas that is substantially SGS, for the balance of inhalation; b) gas sensor means for monitoring gas concentrations at the patient-circuit interface c) a first gas set (FGS), and a second gas set (SGS), said second gas set which may comprise previously exhaled gases or exogenous gases or both d) a gas flow control means for controlling the rate of FGS flow into the breathing circuit e) means to identify phase of breathing, said means may consist of pressure sensors or analysis of signal generated by gas sensors or other means known to those skilled in the art; f) machine intelligence consisting of a computer or logic circuit capable of controlling the gas flow control means, receiving the output of the gas sensor means and means to identify phased of breathing, and performing the calculations for measuring cardiac output and other parameters as outlined in the disclosure.

Claims

1. A breathing circuit for use with a first gas set (FGS) and a second gas set (SGS), said circuit comprising means for keeping separate the FGS and SGS, an FGS reservoir, and a means for sequentially delivering to a patient on inspiration, first the FGS, and, when FGS reservoir is emptied, subsequently delivers substantially SGS for the balance of inspiration.

3. The circuit of claim 1 or claim 2 comprising:

a. an inspiratory limb with a port for entry of FGS, a FGS reservoir and FGS flow control means

b. an expiratory limb containing an exit port for exhaled gas, SGS reservoir, and SGS flow control means for directing the flow towards the SGS reservoir during exhalation, and for directing the flow of SGS in the expiratory limb towards the patient during a portion of inspiration.

4. The circuit of claim 3 where the FGS flow control means comprises at least one unidirectional valve that opens toward the patient.

5. The circuit of claim 3 where the FGS flow control means comprises a FGS controlled valve activated by a FGS valve control means, which allows FGS to flow to the subject during inspiration until the FGS reservoir has been emptied and then prevents FGS from flowing to the subject until the next inspiration begins.

6. The circuit of claim 5 where the FGS flow control means additionally comprises at least one uni-directional valve that opens toward the patient, located between the controlled valve and the patient.

7. The circuits of claims 4, 5 or 6 wherein the SGS flow control means comprises an exhalation valve on the expiratory limb, and a bypass valve on a bypass limb connected to the expiratory limb, said bypass limb bypassing said exhalation valve, whereby said bypass valve is opened during inspiration only once the FGS reservoir has been emptied.

8. The circuit of claims 4, 5 or 6 wherein the SGS control means comprises a SGS controlled valve activated by a SGS valve control means, said SGS valve control means which opens said SGS controlled valve to allow SGS to be inspired by the subject during inspiration once the inspiratory reservoir has been emptied and closes it after expiration.

15. The circuits of claims 1, 2 or 9 whereby the inspiratory and expiratory limbs are co-axial.

16. The circuits of claim 15 whereby one of the limbs is comprised of a material that allows passage of moisture to the other but keeps the gases in the limbs separate

17. The circuits of claim 1, 2 or 9 whereby the reservoirs are contained in a sealed container with openings for the inspiratory and expiratory limbs, and with opening for connection to a ventilator.

18. The circuits of claim 1, 2 or 9 additionally comprising means for detecting when SGS is being delivered to the patient, with FGS control means using said detecting means to determine when to direct FGS to the FGS reservoir and prevent FGS from being delivered to the patient.

19. The circuits of claims 1, 2 or 9 whereby the FGS consists of one or more gases in combination and in varying concentrations.

20. The circuits of claims 1, 2 or 9 whereby the FGS consists of air.

21. The circuits of claims 1, 2 or 9 whereby the FGS consists of O₂.

22. The circuits of claims 1, 2 or 9 whereby the FGS consists of air and O₂ mixed.

23. The circuits of claims 1, 2 or 9 whereby the FGS contains CO₂.

24. The circuits of claim 1, 2 or 9 whereby the SGS consists of one or more gases in combination and in varying concentrations.

25. The circuits of claim 1, 2 or 9 whereby the SGS comprises previously exhaled gas.

26. The circuits of claim 1, 2 or 9 whereby the SGS comprises a mixture of previously exhaled gas and an exogenous set of gases.

27. The circuits of claim 1, 2 or 9 further comprising means for altering the composition of SGS delivered to the patient.

28. The circuits of claim 27 wherein said SGS altering means comprises CO₂ absorbing material.

29. The circuits of claim 27 wherein said SGS altering means comprises Zeolite for elimination of anaesthetics or vapour anaesthetic agents.

30. The circuits of claim 27 wherein said SGS altering means comprises Hopcalite for elimination of carbon monoxide.

31. The circuits of claims 1, 2 or 9 whereby the portion of the inspiratory limbs and expiratory limbs that contain the valves or flow control means are contained within the SGS reservoir.

32. The circuits of claims 1, 2 or 9 wherein said SGS reservoirs are bags or extended tubes sufficiently large to provide the functions of SGS.

37. The apparatus of claim 33 wherein the breathing circuit is the circuit of claims 1, 2 or 9.

2. A breathing circuit for use with a first gas set (FGS) and a second gas set (SGS), said circuit comprising means for keeping separate the FGS and SGS, an FGS reservoir, and a means for sequentially delivering to a patient on inspiration, first the FGS, and, on inspiration, when FGS reservoir is emptied, subsequently delivers SGS for the balance of inspiration.

9. A breathing circuit comprising:

a. an inspiratory limb with a port for entry of FGS, a FGS reservoir and FGS flow control means, whereby the FGS control means directs FGS into the FGS reservoir during the portion of inspiration after the FGS reservoir is emptied preventing FGS flow to the patient prior to the beginning of the next inspiration,

b. an expiratory limb containing an exit port for exhaled gas, an SGS reservoir, and exhalation valve for directing the flow towards the SGS reservoir during exhalation,

c. a bypass limb connecting the inspiratory and expiratory limbs, containing a bypass flow control means which directs flow of the SGS from the SGS reservoir to the patient through the inspiratory limb during the portion of inspiration from when the FGS reservoir is emptied until the end of inspiration.

10. The circuit of claim 9 where the FGS flow control means comprises at least one unidirectional valve that opens toward the patient.

11. The circuit of claim 9 where the FGS flow control means comprises a FGS controlled valve activated by a FGS valve control means, which allows FGS to flow to the subject during inspiration until the inspiratory reservoir has been emptied and then prevents FGS from flowing to the subject until the next inspiration begins.

12. The circuit of claim 11 where the FGS flow control means additionally comprises at least one uni-directional valve that opens toward the patient, located between the controlled valve and the patient.

13. The circuits of claims 10, 11, or 12 wherein the SGS flow control means comprises an exhalation valve on the expiratory limb, and a bypass valve on a bypass limb connected to the expiratory limb, said bypass limb bypassing said exhalation valve, whereby said bypass valve is opened during inspiration only once the FGS reservoir has been emptied.

14. The circuit of claims 10, 11, or 12 wherein the SGS control means comprises a SGS controlled valve activated by a SGS valve control means, said SGS valve control means which opens said SGS controlled valve to allow SGS to be inspired by the subject during inspiration once the inspiratory reservoir has been emptied and closes it after expiration.

33. An apparatus to measure cardiac output ({dot over (Q)}) and other parameters such as alveolar ventilation ({dot over (V)}A), minute ventilation ({dot over (V)}_E), minute CO₂ elimination from the lung ({dot over (V)}CO₂), minute oxygen consumption ({dot over (V)}O₂), oxygenated mixed venous partial pressure of CO₂, (P vCO₂-oxy), true mixed venous partial pressure of CO₂ (P vCO₂), PaCO₂, mixed venous oxygen saturation (SvO₂), pulmonary shunt, and anatomical dead space, comprises:

a) Any breathing circuit wherein when the subject'"'"'s minute ventilation exceeds a first gas set (FGS) flow into the circuit, the balance of his/her ventilation is supplied from a second gas set (SGS).

b) gas analyser means for monitoring gas concentrations of the patient'"'"'s breath

c) a gas flow control means for controlling the rate of FGS flow into the breathing circuit

d) optionally wherein FGS is provided to the patient first followed by SGS.

34. The apparatus of claim 33 further comprising a first gas set (FGS), and a second gas set (SGS), said second gas set which may comprise previously exhaled gases or exogenous gases or both.

35. The apparatus of claim 33 further comprising means to identify phase of breathing.

36. The apparatus of claim 33 further comprising machine intelligence capable of controlling the gas flow control means, receiving the output of the gas sensor means and means to identify phased of breathing, and performing the calculations for measuring cardiac output and other parameters.

38. The apparatus of claim 33 wherein the breathing circuit is that described by Fisher in U.S. Pat. No. 6,622,725.

39. The apparatus of claim 33, 34, or 36 where said gas flow control means is capable of controlling and mixing the flows of several component gases to constitute FGS.

40. The apparatus of claim 33, 34 or 36 where FGS comprises O₂.

41. The apparatus of claim 33, 34 or 36 where FGS comprises air.

42. The apparatus of claim 33, 34 or 36 where FGS comprises O₂ and air in any proportion.

43. The apparatus of claim 40, 41, or 42 where FGS further comprises any proportion of CO₂, anesthetic or other gas or vapour.

44. The method of using the apparatus of claims 33, 34 or 36 for determining {dot over (Q)}, {dot over (V)}A, {dot over (V)}_E, {dot over (V)}CO₂, {dot over (V)}O₂, P vCO₂-oxy, true P vCO₂, PaCO₂, SvO₂, pulmonary shunt, and anatomical dead space.

45. A method of identifying the alveolar ventilation ({dot over (V)}_A) using the apparatus of claim 33 comprising:

a. setting the FGS flow into the circuit at a rate greater than the subject'"'"'s minute ventilation {dot over (V)}_E

b. measuring one or more end tidal CO₂ concentrations (P_ETCO₂ ) in a steady state

c. progressively lowering the FGS flow into the circuit, either breath by breath or continuously while measuring PETCO₂ of the subject

d. identifying a rise in P_ETCO₂ above a threshold

e. determining {dot over (V)}_A as the rate of FGS flow into the circuit at the beginning of the rise in P_ETCO₂ above said threshold.

46. The method of claim 45 wherein the beginning of the rise in P_ETCO₂ is determined by:

a. after identifying the rise in PETCO₂ above said threshold, collecting one or more successive PETCO₂ values prior to a recirculation time

b. fitting a straight line to said values of P_ETCO₂ on a graph of PETCO₂ vs FGS flow.

c. determining the FGS flow at which the P_ETCO₂ of said line equals one of, or the average of several of, the P_ETCO₂ values at steady state, said FGS flow being equal to {dot over (V)}_A.

47. A method of measuring the alveolar ventilation ({dot over (V)}_A) using the apparatus of claim 33 comprising:

a. estimating a preliminary minimum {dot over (V)}A for the subject based on body weight, temperature, and sex.

b. Providing FGS flow greater than the patient'"'"'s resting {dot over (V)}E until steady state P_ETCO₂ is reached

c. Setting FGS flow below said estimated {dot over (V)}A, to a flow {dot over (V)}_Ax for a time less than or equal to a recirculation time, and measure P_ETCO_2x, the end tidal CO₂ concentration during equilibrium if an equilibrium end tidal value is reached within a recirculation time, otherwise measuring P_ETCO_2x the equilibrium value of end tidal CO₂ as extrapolated from the exponential rise in end tidal CO₂ values within the recirculation time.

d. Setting FGS flow above {dot over (V)}E until steady state P_ETCO₂ is reached.

e. Setting FGS Flow below estimated {dot over (V)}A, to flow {dot over (V)}A_y where {dot over (V)}A_y is not equal to {dot over (V)}A_x, for a time less than or equal to a recirculation time, and measuring P_ETCO_2y, the end tidal CO₂ concentration during equilibrium if an equilibrium end tidal value is reached within a recirculation time, otherwise measuring P_ETCO_2y as the equilibrium value of end tidal CO₂ as extrapolated from the exponential rise in end tidal CO₂ values within the recirculation time.

f. On a graph of P_ETCO₂ vs FGS flow, plot the points (P_ETCO_2y, {dot over (V)}A_y) and (P_ETCO_2x, {dot over (V)}A_x) extrapolate the line formed by connecting these two points to intersect a horizontal line at P_ETCO₂=resting P_ETCO₂.

g. Determining {dot over (V)}A to be the FGS flow corresponding to the intersection point .

48. The method of claims 45, 46, or c wherein the {dot over (V)}_A so determiined is utilized to determine the {dot over (V)}CO₂ as {dot over (V)}_A×

F_ETCO₂ during the steady state.

49. The method of claims 45, or 46, wherein O₂ is used instead of CO₂ and the PETO₂ level drops below a threshold value, instead of PETCO₂ rising above a threshold value.

56. A method of measuring cardiac output in a subject using the apparatus of any of claims 33, 34 or 36 comprising:

i. Measuring {dot over (V)}CO₂ and P_ETCO₂ in a first state

ii. Changing {dot over (V)}CO₂ for a time less than or equal to a recirculation time to a new {dot over (V)}CO₂, designated as {dot over (V)}CO₂′

iii. Determining a new PETCO₂ at {dot over (V)}CO₂′

designated as P_ETCO₂′

wherein said PETCO₂′

is the steady state end tidal PCO₂ after a change in {dot over (V)}CO₂ to {dot over (V)}CO₂′

, or if no steady state is reached, then it is the extrapolated steady state end tidal PCO₂ from the exponential rise in end tidal PCO₂ within the recirculation time.

iv. Determining {dot over (Q)} using the Differential Fick relationship

57. The method of claim 56 wherein {dot over (V)}CO₂ in the first state is measured using the method of claim 48.

60. The method of claim 56 wherein the FGS flow during the first state is equal to the subject'"'"'s {dot over (V)}_A.

61. The method of claim 56 wherein the FGS flow during the second state is less than the subject'"'"'s {dot over (V)}_A.

62. The method of claim 60 or 61 wherein the {dot over (V)}_A is determined according to the method of claim 45.

63. The method of claim 60 or 61 wherein the {dot over (V)}_A is determined according to the method of claim 46.

64. The method of claim 60 or 61 wherein the {dot over (V)}_A is determined according to the method of claim 47.

65. The method of claim 56 wherein the {dot over (V)}CO₂is changed to {dot over (V)}CO₂′

by changing the concentration of CO₂ in FGS.

66. The method of claim 56 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

67. The method of claim 57 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

70. The method of claim 60 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

71. The method of claim 61 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

72. The method of claim 62 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

73. The method of claim 63 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

74. The method of claim 64 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

75. The method of claim 65 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

76. A method of measuring cardiac output in a subject using the apparatus of any of claims 33, 34 or 36 comprising:

i. Estimating the subject'"'"'s {dot over (V)}_A (denoted {dot over (V)}_{A PRELIM}) based on weight, height, temperature, and sex.

ii. setting the FGS flow into the circuit at a rate greater than the subjects minute ventilation ( {dot over (V)}E)

iii. for a time less than or equal to a recirculation time, changing FGS flow to a value {dot over (V)}A¹ which is below {dot over (V)}A _PRELIM.

iv. Calculating {dot over (V)}CO₂¹={dot over (V)}A¹×

F_ETCO₂¹, whereby F_ETCO₂¹ is the fractional end tidal CO₂ concentration during equilibrium if an equilibrium end tidal value is reached within a recirculation time, otherwise it is the equilibrium value of end tidal CO₂ as extrapolated from the exponential rise in end tidal CO₂ values within the recirculation time.

v. setting the FGS flow into the circuit at a rate greater than {dot over (V)}E and waiting for a steady state P_ETCO₂ to be reached.

vi. for a time less than or equal to a recirculation time, changing FGS flow to a value {dot over (V)}A² which is below {dot over (V)}A _PRELIM and not equal to {dot over (V)}A¹.

vii. Calculating {dot over (V)}CO₂²={dot over (V)}A²×

F_ETCO₂², whereby F_ETCO₂² is the fractional end tidal CO₂ concentration during equilibrium if an equilibrium end tidal value is reached within a recirculation time, otherwise it is the equilibrium value of end tidal CO₂ as extrapolated from the exponential rise in end tidal CO₂ values within the recirculation time.

viii. Determine P_ETCO₂¹ from F_ETCO₂¹×

ambient pressure, and P_ETCO₂² from F_ETCO₂²×

ambient pressure

ix. Using the values of {dot over (V)}CO₂¹, {dot over (V)}CO₂², P_ETCO₂¹, and P_ETCO₂² in the Differential Fick equation to determine cardiac output

77. The method of claim 56 or 76 whereby the P_ETCO₂ values in the Fick equation are replaced by the PaCO₂ using the Kim Rahn Farhi method to identify the P_ETCO₂-PaCO₂ gradient

78. The method of determining P vCO₂-Oxy in a subject using the apparatus of any of claims 33, 34 or 36 comprising:

i. Determining {dot over (V)}A according to any of the methods in claims method of claims 45, 46, or c

ii. Setting the FGS flow in the circuit equal to {dot over (V)}A and measuring inspired concentration of CO₂ and P_ETCO₂

iii. For a series of breaths no longer than a recirculation time changing the CO₂ concentration in the FGS and measuring inspired concentration of CO₂ and P_ETCO₂

iv. Using the values of inspired and expired concentrations as described by Fisher to calculate P vCO₂-Oxy

79. The method of claim 45 wherein the {dot over (V)}_A so determined is utilized to determine the {dot over (V)}O₂ as {dot over (V)}_A×

[F₁O₂−

F_ETO₂] during the steady state where F₁O₂ is the O₂ concentration in FGS.

80. The method of claim 46 wherein the {dot over (V)}_A so determined is utilized to determine the {dot over (V)}O₂ as {dot over (V)}_A×

[F₁O₂−

F_ETO₂] during the steady state where F₁O₂ is the O₂ concentration in FGS.

81. The method of claim 47 wherein the {dot over (V)}_A so determined is utilized to determine the {dot over (V)}O₂ as {dot over (V)}_A×

[F₁O₂−

F_ETO₂] during the steady state where F₁O₂ is the O₂ concentration in FGS.

83. A method of determining the anatomical dead space comprising

a. Measuring {dot over (V)}_A using any of the methods of claims 45

b. Measuring {dot over (V)}E

c. Measuring the respiratory rate

d. Determining anatomical dead space=({dot over (V)}E−

{dot over (V)}_A)/respiratory rate

84. A method of determining the anatomical dead space comprising

a. Measuring {dot over (V)}_A using any of the methods of claims 46

b. Measuring {dot over (V)}E

c. Measuring the respiratory rate

d. Determining anatomical dead space=({dot over (V)}E−

{dot over (V)}_A)/respiratory rate

85. A method of determining the anatomical dead space comprising

a. Measuring {dot over (V)}_A using any of the methods of claims 47

b. Measuring {dot over (V)}E

c. Measuring the respiratory rate

d. Determining anatomical dead space=({dot over (V)}E−

{dot over (V)}_A)/respiratory rate

86. The method of determining physiological parameters in a subject using the apparatus of claims 33, 34 or 36 wherein the Kim Rahn Farhi approach is used to determine

i) P vCO₂-oxy

ii) true P vCO₂

iii) PaCO₂

iv) {dot over (Q)}

v) true P vCO₂ plus the information from a pulse oximeter to determine mixed venous hemoglobin O₂ saturation

87. The method of determining physiological parameters in a subject using the apparatus of claim 33, 34 or 36 wherein the differential CO₂ Fick technique of Gedeon and Orr is utilized to determine any combination of

i) Pv CO₂-oxy

ii) {dot over (Q)}

iii) {dot over (V)}CO₂

iv) {dot over (V)}CO₂′

v) PETCO₂-PaCO₂ gradient determined using the PaCO₂ as determined by the Kim Rahn Farhi method from data collected while reducing the {dot over (V)}CO₂ in order to perform the differential Fick method.

92. The method of claim 33, 34 or 36 wherein the O₂ saturation of haemoglobin in mixed venous blood, as determined therewith, is utilized to reveal a condition in a patient such as septic shock, or heart failure.

93. The method of claims 44, 45, 47, 51, 53, 56, 82, 83, 84, 85, 88 which is automated by gauges, controls, and computer assisted devices in conjunction with at least one computer in order to control, activate and measure the variables and determinates thereof.

94. The Method of claims 44, 45, 47, 51, 53, 56, 82, 83, 84, 85, 88 which is automated with at least one computing device.

50. The method of claims c wherein PETO₂ values are measured instead of PETCO₂ values.

51. A method for measuring {dot over (V)}CO₂ of a subject breathing on any breathing circuit wherein when the subject'"'"'s minute ventilation exceeds a first gas set (FGS) flow into the circuit, the balance of his/her ventilation is supplied from a second gas set (SGS).comprising:

a. Setting the FGS flow into the circuit at a rate equal to or above the subject'"'"'s {dot over (V)}_A

b. Measuring the average CO₂ concentration of gas exiting the circuit

c. Determining said {dot over (V)}CO₂ to be the average CO₂ concentration×

FGS flow rate

52. A method for determining {dot over (V)}_A of a subject comprising measuring {dot over (V)}CO₂ using the method of claim 51, measuring the subjects FETCO₂ and determining {dot over (V)}_A as {dot over (V)}CO₂/FETCO₂.

54. The method of claim 51 wherein the circuit is a SGDB circuit.

58. The method of claim 56 wherein {dot over (V)}CO₂ in the first state is measured using the method of claim 51.

59. The method of claim 56 wherein {dot over (V)}CO₂ in the first state is measured using the method of claim 54.

68. The method of claim 58 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

69. The method of claim 59 wherein {dot over (V)}CO₂′

is determined as F_ETCO₂′

×

FGS flow, where F_ETCO₂′

is the end tidal CO₂ of the subject either at equilibrium or as extrapolated to equilibrium from the exponential rise in end tidal CO₂ values.

53. A method for measuring {dot over (V)}O₂ of a subject breathing on any breathing circuit wherein when the subject'"'"'s minute ventilation exceeds a first gas set (FGS) flow into the circuit, the balance of his/her ventilation is supplied from a second gas set (SGS) comprising:

a. Setting the FGS flow into the circuit at a rate equal to or above the subject'"'"'s {dot over (V)}_A

b. Measuring the average O₂ concentration of gas exiting the circuit

c. Determining said {dot over (V)}O₂ to be the FGS flow rate×

[average O₂ concentration of FGS−

average O₂ concentration of gas exiting the circuit]

55. The method of claim 53 wherein the circuit is a SGDB circuit.

82. A method of identifying the minute ventilation ({dot over (V)}_E) using any breathing circuit wherein when the subject'"'"'s minute ventilation exceeds a first gas set (FGS) flow into the circuit, the balance of his/her ventilation is supplied from a second gas set (SGS) comprising

i. setting the FGS flow into the circuit at a rate greater than the subject'"'"'s minute ventilation ( {dot over (V)}E)

ii. progressively lowering the FGS flow into the circuit, either breath by breath or continuously, until the FGS reservoir bag in the breathing circuit first collapses. The FGS flow when the bag first collapses is determined to be {dot over (V)}E.

88. An improved method for determining {dot over (Q)}, {dot over (V)}_A, {dot over (V)}CO₂, PvCO₂-oxy, true PvCO₂, PaCO₂, pulmonary shunt, anatomical dead space, and O₂ saturation in mixed venous blood in a subject breathing on any breathing circuit wherein when the subject'"'"'s minute ventilation exceeds a first gas set (FGS) flow into the circuit, the balance of his/her ventilation is supplied from a second gas set (SGS) comprising

i) setting the flow of FGS to the circuit to create two sets of data for said determination utilizing the Fick equations;

(or)

ii) determining the P_ETCO₂-PaCO₂ gradient from two independently derived values in the same subject;

(or)

iii) utilizing the Kim-Rahn-Farhi technique a series of reduced FGS flows simulates complete or partial breath holding, wherein the P_ETCO₂ of each breath is equivalent to a sequential alveolar sample;

89. The method of 33, 34 or 36 used to measure {dot over (Q)} wherein {dot over (Q)} is used to determine SvO₂ using the relationship SvO₂=SaO₂−

{dot over (V)}O₂/[Hb×

CC×

{dot over (Q)}], where Hb is haemoglobin, and CC (in ml O₂/gm Hb) is the capacity of haemoglobin to carry oxygen.

90. The method or apparatus of claim 89 wherein the arterial O₂ hemoglobin saturation, is utilized with the O₂ saturation value in the pulmonary artery to calculate the fraction of shunted blood (assuming fully oxygenated blood in the end pulmonary capillary) thereof.

91. The method or apparatus of claim 90 utilized to determine the fraction of shunted blood {dot over (Q)}_S, which in conjunction with determination of cardiac output {dot over (Q)}_T may be used to determine {dot over (Q)}_P the pulmonary output via the relationship {dot over (Q)}_T={dot over (Q)}_P+{dot over (Q)}_S