Apparatus and method for non-invasively measuring cardiac output

• US 6,908,438 B2
• Filed: 09/08/2003
• Issued: 06/21/2005
• Est. Priority Date: 12/19/1996
• Status: Expired due to Term

• Current Assignee: RIC INVESTMENTS LLC (Koninklijke Philips N.V.)
• Original Assignee: Respironics Novametrix, Inc.
• Inventors: Orr, Joseph A., Jaffe, Michael B., Westenskow, Dwayne, Kofoed, Scott A.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US10/657,909
• Publication Number:
  US 20040049113A1
• Time in Patent Office: 652 Days
• Field of Search: 600/532, 73/233, 422/84
• 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 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 method for estimating the partial pressure of carbon dioxide in alveoli (P_ACO₂) of an individual, comprising:

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

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

estimating the partial pressure of carbon dioxide in alveolar blood using the concentration of carbon dioxide in the parallel dead space of an airway and end tidal partial pressure of carbon dioxide.

2. The method of claim 1, further comprising determining a perfusion ratio (r).

3. The method of claim 2, wherein:

(P_ACO₂)=[etCO₂−

(1−

r)×

PDS_CO2]/r.

4. The method of claim 1, wherein calculating comprises calculating the concentration of carbon dioxide in the parallel deadspace of an airway of the individual on a breath-by-breath basis.

5. The method of claim 1, wherein calculating comprises:

determining a 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.

6. The method of claim 5, wherein calculating further comprises:

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

7. The method of claim 9, wherein ${\mathrm{PDS}}_{{\mathrm{CO}}_2}$

(n)⁢

={⁢

[FRC/(FRC+Vt)]×

PDSCO2⁡

(n-1)}+({[ViCO2+ ⁢

(deadspace×

et⁢

 

⁢

CO2⁡

(n-1)]/Vt}×

[Vt/(Vt+FRC)]),

where (n) indicates a parameter for a current breath and (n−

l) represents a parameter for an immediately preceding breath.