Theoretical analyses for arterial-venous O2 content difference and haldane effect during rebreathing.

The Haldane effect coefficient in vivo and arterial-venous O2 content difference [a-v)Co2) are, more or less, influenced by the contact time (tc), PO2 and PCO2 differences between venous blood and alveolar air. To increase the accuracy of the (a-v)CO2 and the cardiac output measured by means of the rebreathing technique, factors to correct the Haldane effect (F(H] and (a-v)CO2 (F(avCO2] were obtained theoretically from the numerical solutions of simultaneous O2 and CO2 diffusions in the red blood cell. Both the factors were complicated functions of tc, the difference in PCO2 between venous blood and alveolar air, as well as (a-V)CO2. For simplicity, we eliminated tc from the above functions by using the standardized relation between the tc and (a-v)CO2 measured from a rebreathing experiment in man. The F(H) was a linear function of (a-v)CO2. The (a-v)CO2 was calculated by dividing the product of F(H) and the slope of the CO2 dissociation curve by that of a gas exchange ratio against the PCO2 in rebreathing air. The F(avCO2) was given by a ratio of (a-v)CO2 at any alveolar PCO2 to the standard one, in which arterial blood has the same intracellular pH as that in venous blood. It was a linear function of the difference in PCO2 between venous blood and alveolar air, whose slope was inversely related to the (a-v)CO2 itself.