Methods for non-invasivelyestimating pulmonary capillary blood flow or cardiac output

• US 20060129054A1
• Filed: 02/03/2006
• Published: 06/15/2006
• Est. Priority Date: 12/19/1996
• Status: Abandoned Application

• Current Assignee: Dwayne Westenskow, Joseph A. Orr, Michael B. Jaffe, Scott A. Kofoed
• Original Assignee: Dwayne Westenskow, Joseph A. Orr, Michael B. Jaffe, Scott A. Kofoed
• Inventors: Orr, Joseph A., Jaffe, Michael B., Westenskow, Dwayne, Kofoed, Scott A.
• Application Number:
  US11/346,913
• Publication Number:
  US 20060129054A1
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61M 16/0045 Means for re-breathing exhaled gases, e.g. for hyperventilation treatment
• CPC Class Codes: A61M 16/0833 T- or Y-type connectors, e.g. Y-piece
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: G01N 33/004 for CO, CO2
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

Methods for non-invasively determining the cardiac output or pulmonary capillary blood flow of a subject include monitoring the subject'"'"'s respiration during two ventilatory states. Such a method may include determining parameters of at least one of the ventilatory states based on one or more characteristics of the subject. Data obtained from monitoring the subject'"'"'s respiration, such as an amount of gas present in exhaled gases and respiratiory flow, may be used to estimate respiratory or blood gas parameters, such as an amount of gas exchanged between blood and gases in the subject'"'"'s lungs or an indicator of a content of the gas in the subject'"'"'s blood.

Claims

1. A method for estimating the cardiac output of an individual, comprising:

determining a carbon dioxide elimination (V_CO2) of the individual in a before phase before a change in effective ventilation and in a during phase during a change in effective ventilation;

calculating a carbon dioxide elimination difference between the carbon dioxide elimination of the before phase and the carbon dioxide elimination of the during phase;

estimating a partial pressure of carbon dioxide in alveoli (P_ACO₂) of the individual for the before phase and for the during phase based on partial pressure of end tidal carbon dioxide (PetCO₂) measurements of the individual from the before phase and the during phase, respectively;

converting each estimation of the partial pressure of carbon dioxide in alveoli to a carbon dioxide content (C_CO2);

calculating a carbon dioxide content difference between the carbon dioxide content of the before phase and the carbon dioxide content of the during phase; and

dividing the carbon dioxide elimination difference by the carbon dioxide content difference to estimate cardiac output.

2. The method of claim 1, wherein determining the carbon dioxide elimination comprises accounting for at least one of serial dead space and parallel dead space.

3. The method of claim 1, wherein determining the carbon dioxide elimination comprises accounting for functional residual capacity.

4. The method of claim 3, wherein accounting for functional residual capacity comprises determining a corrected carbon dioxide elimination (V_{CO2 corrected}) during at least one of the before rebreathing period and the during rebreathing period as follows:

V_{CO2 corrected}=V_CO2+FRC×

Δ

Pet_CO2/P_bar,

where V_CO2 is the carbon dioxide elimination that has been determined, Δ

Pet_CO2 is the breath-to-breath change in Pet_CO2, and P_bar is barometric pressure.

5. The method of claim 1, wherein determining the carbon dioxide elimination for at least one of the before phase and the during phase comprises determining an average carbon dioxide elimination over a period of time.

6. The method of claim 5, wherein determining the average carbon dioxide elimination over a period of time comprises determining the average carbon dioxide elimination over a plurality of breaths.

7. The method of claim 5, wherein determining the average carbon dioxide elimination is effected at at least about twenty-five seconds into the during phase.

8. The method of claim 1, wherein estimating the partial pressure of carbon dioxide in alveoli includes accounting for at least one of functional residual capacity and carbon dioxide in parallel dead space.

9. The method of claim 8, wherein accounting comprises employing the following formula:

P_{CO2 PDS}(n)=[FRC/(FRC+V_t)]·

P_{CO2 PDS}(n−

1)+(P_bar·

(([Vi_CO2+deadspace·

(Pet_CO2(n−

1)/P_bar)]/V_t) [V_t/(V_t+FRC)])),

where (n) represents one breath, (n−

1) represents a prior breath, FRC is the functional residual capacity, V_t is the tidal volume, Vi_CO2 is the volume of inspired carbon dioxide, P_{CO2 PDS} is the partial pressure of carbon dioxide in the parallel dead space, and P_bar is barometric pressure.

10. The method of claim 1, wherein converting at least one estimation of the partial pressure of carbon dioxide in alveoli to a carbon dioxide content comprises predicting a stable carbon dioxide content.

11. The method of claim 10, wherein predicting the stable carbon dioxide content comprises plotting the partial pressure of carbon dioxide in alveoli from at least one of the before rebreathing phase and the during rebreathing phase against a breath-to-breath change in a content of carbon dioxide in blood in the alveolar capillaries (Δ

C_ACO₂).

12. A rebreathing method, comprising:

monitoring a subject'"'"'s respiration during a non-rebreathing phase;

determining a selected amount of carbon dioxide to be collected based on at least one characteristic of the subject;

collecting the selected amount of carbon dioxide from gases exhaled by the subject;

introducing the selected amount of carbon dioxide into gases inhaled by the subject during a rebreathing phase; and

monitoring the subject'"'"'s respiration during the rebreathing phase.

13. The method of claim 12, wherein monitoring the subject'"'"'s respiration during the non-rebreathing phase and during the rebreathing phase include monitoring an amount of at least one gas and respiratory flow.

14. The method of claim 13, further comprising;

estimating an amount of the gas exchanged between the subject'"'"'s blood and gases in at least one lung of the subject; and

estimating an indicator of a content of the gas in the subject'"'"'s blood.

15. The method of claim 13, wherein monitoring an amount of at least one gas comprises monitoring an amount of carbon dioxide as the subject exhales.

16. The method of claim 15, wherein:

estimating the amount of the gas exchanged includes estimating carbon dioxide elimination; and

estimating the indicator of the content of the gas includes estimating carbon dioxide content of the subject'"'"'s blood.

17. The method of claim 16, further comprising:

dividing a difference between carbon dioxide elimination from the non-rebreathing and rebreathing phases by a difference between carbon dioxide content from the non-rebreathing and rebreathing phases to estimate pulmonary capillary blood flow or cardiac output.

18. The method of claim 12, further comprising:

defining a volume within which the act of collecting is to be effected.

19. A method for estimating a pulmonary capillary blood flow or cardiac output of a subject, comprising:

monitoring a subject'"'"'s respiration during a first ventilatory phase;

determining a selected amount of at least one gas to be administered to the subject based on at least one characteristic of the subject;

administering the selected amount of the at least one gas to the subject during a second ventilatory phase; and

monitoring the subject'"'"'s respiration during the rebreathing phase.

20. The method of claim 19, wherein administering the selected amount of the at least one gas includes inducing a change in effective ventilation.