Apparatus and method for non-invasively measuring cardiac output

• US 20010029339A1
• Filed: 02/06/2001
• Published: 10/11/2001
• Est. Priority Date: 12/19/1996
• Status: Active Grant

• Current Assignee: RIC INVESTMENTS LLC (Koninklijke Philips N.V.)
• Original Assignee: RIC INVESTMENTS LLC (Koninklijke Philips N.V.)
• Inventors: Orr, Joseph A., Jaffe, Michael B., Westenskow, Dwayne, Kofoed, Scott A.
• Granted Patent: US 6,648,832 B2
• Time in Patent Office: Days
• US Class Current: 600/529
• 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 CO or 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

Apparatus and methods for non-invasively determining the cardiac output or pulmonary capillary blood flow of a patient using partial re-breathing techniques. The apparatus includes a substantially instantaneously adjustable deadspace volume for accommodating differences in sizes or breathing capacities of various patients. The apparatus may be constructed of inexpensive elements, including one or more two-way valves, which render the apparatus very simple to use and inexpensive so that the unit may be employed as a disposable product. The method of the invention includes estimating the cardiac output or pulmonary capillary blood flow of a patient based on partial pressure of alveolar CO₂, rather than on the partial pressure of end tidal CO₂, as previously practiced. A computer program for calculating the cardiac output or pulmonary capillary blood flow of a patient is also disclosed.

Claims

1. A rebreathing method, comprising:

evaluating at least one of a lung capacity of the patient, a size of the patient, a respiratory flow condition of the patient, and a respiratory carbon dioxide condition of the patient; and

selecting a deadspace volume to be used in rebreathing based on said evaluating, said selecting being effected without substantially changing airway pressure.

2. The rebreathing method of

claim 1

, wherein said selecting comprises defining a volume of a deadspace receptacle communicating with a breathing circuit in communication with an airway of the patient.

3. The rebreathing method of

claim 1

, wherein said selecting comprises selecting a concentration of exhaled gases to remain within at least one of a breathing circuit in a communication with an airway of the patient and the airway.

4. The rebreathing method of

claim 1

, wherein said selecting comprises adjusting a deadspace within an airway of the patient.

5. A method for noninvasively determining at least one of a cardiac output and a pulmonary capillary blood flow of a patient, comprising:

determining a carbon dioxide elimination difference between a carbon dioxide elimination of the patient during normal breathing and a carbon dioxide elimination of the patient during rebreathing;

determining an end tidal carbon dioxide difference between a partial pressure of end tidal carbon dioxide of the patient during said normal breathing and a partial pressure of end tidal carbon dioxide of the patient during said rebreathing; and

compensating for functional residual capacity in lungs of the patient.

6. The method of

claim 5

, wherein said compensating comprises accounting for eliminated carbon dioxide not exhaled from the airway of the patient.

7. The method of

claim 6

, wherein said accounting comprises modifying at least one of said carbon dioxide elimination during said normal breathing and said carbon dioxide elimination during said rebreathing.

8. The method of

claim 7

, wherein said modifying comprises adding to a carbon dioxide elimination measurement a product of said functional residual capacity and a partial pressure of end tidal carbon dioxide.

9. The method of

claim 5

, comprising estimating said functional residual capacity as a function of body weight of the patient, said estimating including accounting for airway and apparatus deadspace.

10. The method of

claim 5

, further comprising:

dividing said carbon dioxide elimination difference by a product of a slope of a carbon dioxide dissociation curve and said end tidal carbon dioxide difference.

11. The method of

claim 5

, comprising measuring carbon dioxide elimination and partial pressure of end tidal carbon dioxide over a plurality of breaths.

12. A rebreathing method, comprising:

insufflating an airway of a patient;

monitoring at least one aspect of the patient'"'"'s breathing during said insufflating;

reducing a volume of said insufflating; and

monitoring said at least one aspect of the patient'"'"'s breathing with said volume of said insufflating reduced.

13. The method of

claim 12

, wherein said insufflating is effected with gas insufflation apparatus.

14. The method of

claim 13

, wherein said reducing comprises adjusting a distance a catheter of said gas insufflation apparatus extends into the airway of the patient.

15. An apparatus for introducing deadspace into a breathing circuit, comprising:

a primary expiratory pathway through the breathing circuit;

a deadspace portion of the breathing circuit located to receive gases exhaled by a patient upon positioning the breathing circuit in communication with an airway of the patient, said deadspace portion communicating with said primary expiratory pathway at least one junction thereof with said primary expiratory pathway;

a flow restrictor positioned along said primary expiratory pathway, downstream from said junction; and

a two-way valve located and positionable so as to, along with said flow restrictor, prevent gases from flowing into said deadspace portion and allow gases to flow into said deadspace portion.

16. The apparatus of

claim 15

, wherein said deadspace portion comprises at least a volume adjustable section.

17. The apparatus of

claim 16

, wherein said volume adjustable section is length expandable and length contractible.

18. A method for estimating the partial pressure of carbon dioxide in the alveolar blood (PSC ACO₂) of an individual, comprising:

calculating a concentration of carbon dioxide in the parallel deadspace (PDS_CO2) of an airway of the individual on a breath-by-breath basis; and

determining an end tidal partial pressure of carbon dioxide (PetCO₂) of the individual.

19. The method of

claim 18

, further comprising determining a perfusion ratio (r).

20. The method of

claim 19

, wherein:

PSC ACO₂=[PetCO₂−

(1−

r)×

PDS_CO2]/r.

21. The method of

claim 18

, wherein said calculating comprises:

determining the mixed inspired volume of carbon dioxide (ViCO₂) inhaled by the individual;

at least estimating an airway deadspace of the individual;

determining a partial pressure of end tidal carbon dioxide (PetCO₂) of a previous breath of the individual; and

determining a tidal volume (V_t) of the individual'"'"'s breathing.

22. The method of

claim 21

, wherein said calculating further comprises:

at least estimating a functional residual capacity (FRC) of alveoli of the individual'"'"'s lungs.

23. The method of

claim 22

, wherein

PDS_CO2(n)={[FRC/(FRC+V_t)]×

PDS_CO2(n−

1)}+({[ViCO₂+(deadspace×

PetCO₂(n−

1)]/V_t}×

[V_t/(V_t+FRC)]),

where (n) indicates a parameter for a current breath and (n-1) represents a parameter for an immediately preceding breath.

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

determining a carbon dioxide elimination (V_CO2) of the individual for a before rebreathing period and for a during rebreathing period;

calculating a carbon dioxide elimination difference between said carbon dioxide elimination of said before rebreathing period and said carbon dioxide elimination of said during rebreathing period;

calculating a carbon dioxide content difference between said carbon dioxide content of said before rebreathing period and said carbon dioxide content of said during rebreathing period; and

estimating a partial pressure of carbon dioxide in alveolar blood (P_ACO2) of the individual for said before rebreathing period and for said during rebreathing period respectively based on partial pressure of end tidal carbon dioxide (PetCO₂) measurements of the individual during said before rebreathing period and during said during rebreathing period;

converting each estimation of said partial pressure of carbon dioxide in alveolar blood to a carbon dioxide content (C_CO2);

dividing said carbon dioxide elimination difference by said carbon dioxide content difference.