Apparatus and method for non-invasively measuring cardiac output

• US 20010031928A1
• Filed: 01/23/2001
• Published: 10/18/2001
• 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 6,648,831 B2
• Time in Patent Office: Days
• US Class Current: 600/526
• 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 cardiac output using partial re-breathing techniques are disclosed in which the apparatus is constructed with an instantaneously adjustable deadspace for accommodating differences in breathing capacities of various patients. The apparatus is constructed of inexpensive elements, including a single two-way valve which renders the apparatus very simple to use and inexpensive so that the unit may be readily disposable. The method of the invention provides a novel means of estimating cardiac output based on alveolar CO₂ values rather than end-tidal CO₂ values as previously practiced. A program for calculating cardiac output is also disclosed.

Claims

1. A re-breathing method, comprising:

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

adjusting a deadspace volume based on said characteristic, said adjusting being effected without

substantially changing airway pressure.

2. The re-breathing method of

claim 1

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

3. The re-breathing method of

claim 1

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

4. The re-breathing method of

claim 1

, wherein said adjusting 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 change in carbon dioxide elimination of the patient between carbon dioxide elimination of the patient during normal breathing and carbon dioxide elimination of the patient during re-breathing;

determining a change in partial pressure of end tidal carbon dioxide of the patient between partial pressure of end tidal carbon dioxide of the patient during said normal breathing and partial pressure of end tidal carbon dioxide of the patient during said re-breathing; 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 re-breathing.

8. The method of

claim 7

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

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 change in carbon dioxide elimination by a product of a slope of the carbon dioxide

dissociation curve and said change in partial pressure of end tidal carbon dioxide.

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 re-breathing method, comprising:

insufflating an airway of a patient with gas insufflation apparatus;

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

reducing said insufflating; and

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

13. The method of

claim 12

, further comprising adjusting a distance a catheter of said gas insufflation apparatus extends into the airway of the patient.

14. The method of

claim 13

, wherein said adjusting comprises varying a deadspace volume created during said reducing.

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

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;

a primary expiratory pathway through the breathing circuit;

a flow restrictor positioned along said primary expiratory pathway downstream from a junction of said deadspace portion with said primary expiratory pathway; and

a two-way valve positioned along or at an end of said deadspace portion, said two-way valve having;

a first, closed position for causing exhaled gases to flow through said flow restrictor; and

a second, opened position for causing at least a portion of exhaled 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 (PACO₂) of an individual, comprising:

calculating a concentration of carbon dioxide in the parallel deadspace (PDS_CO²) of an airway of the individual; and

determining an end tidal partial pressure of carbon dioxide (etCO₂) of the individual.

19. The method of

claim 18

, further comprising determining a perfusion ratio (r).

20. The method of

claim 19

, wherein:

PACO₂=[etCO₂−

(1−

r)×

PDS_CO²]/r.

21. The method of

claim 18

, wherein said calculating comprises calculating said concentration of carbon dioxide in the parallel deadspace of the individual on a breath-by-breath basis.

22. 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 (etCO₂) of a previous breath of the individual; and

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

23. The method of

claim 22

, wherein said calculating further comprises:

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

24. The method of

claim 23

, wherein

PDS_CO²(n)={[FRC/(FRC+V_t)]×

PDS_CO²(n−

1)}+({[ViCO₂+(deadspace×

etCO₂(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.

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

determining a carbon dioxide elimination (VCO₂) of the patient for a before re-breathing period and for a during re-breathing period;

estimating a partial pressure of carbon dioxide in alveolar blood (PACO₂) of the individual for said before re-breathing period and for said during re-breathing period;

converting each estimation of said partial pressure of carbon dioxide in alveolar blood to a carbon dioxide content (CCO₂);

calculating a carbon dioxide elimination difference between said carbon dioxide elimination of said before re-breathing period and said carbon dioxide elimination of said during re-breathing period;

calculating a carbon dioxide content difference between said carbon dioxide content of said before re-breathing period and said carbon dioxide content of said during re-breathing period; and

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