Patent ID: 8460202

Claim:
A method of measuring pulmonary blood flow or true mixed venous content of CO 2 in a subject, comprising: using a gas sensor operatively connected to a processor to: determine a first value of an end-tidal partial pressure of CO 2 (P ET CO 2 ) that approximates a steady state P ET CO 2 value that corresponds to a first alveolar ventilation ({dot over (V)} A ); determine at least a second value of P ET CO 2 that approximates a steady state P ET CO 2 value that corresponds to at least a second {dot over (V)} A ; and determine a value for minute elimination of CO 2 corresponding to said first {dot over (V)} A ({dot over (V)}CO 2 ) and a value for minute elimination of CO 2 corresponding to said at least second {dot over (V)} A ({dot over (V)}CO 2 ′): wherein the processor uses the values of P ET CO 2 and minute CO 2 elimination so determined to calculate pulmonary blood flow or true mixed venous content of CO 2 (C v CO 2 ) using a differential Fick method; and wherein the at least second {dot over (V)} A and the corresponding second value of PetCO 2 (PetCO 2 ′) are generated by providing to the subject for breathing, a first gas set (FGS) at a flow rate below the subject's resting {dot over (V)} A , and a second gas set (SGS) that has a partial pressure of CO 2 that approximates the partial pressure of CO 2 in the subject's previously expired breath, wherein on each breath, the FGS is provided first to the subject, and wherein the SGS is provided to the subject for the balance of that breath to the extent that the subject's inhalation exceeds the provision of the FGS.