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

Abstract

The Haldane effect coefficient in vivo and arterial-venous 02 content difference ((a-v)Co2) are, more or less, influenced by the contact time (ta), Po2 and P~o2 differences between venous blood and alveolar air. To increase the accuracy of the (a-v) Cot 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 02 and C02 diffusions in the red blood cell. Both the factors were complicated functions of t~, the difference in P~o2 between venous blood and alveolar air, as well as (a-v)Co2. For simplicity, we eliminated t~ from the above functions by using the standardized relation between the t~ and (a-v)Co2 measured from a rebreathing experiment in man. The F(H) was a linear function of (av)Co2. The (a-v)Co2 was calculated by dividing the product of F(H) and the slope of the C02 dissociation curve by that of a gas exchange ratio against the P~o2 in rebreathing air. The F(avCo2) was given by a ratio of (a-v)Co2 at any alveolar P~o2 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 P~o2 between venous blood and alveolar air, whose slope was inversely related to the (a-v)Co2 itself.Key words : 02 and C02 diffusion in RBC, Haldane effect, arterialvenous 02 difference, R-P02 relation, contact time.MocHizuK! and KAGAWA (1986) clarified that the coupled 02 and C02 diffusions in the red blood cell (RBC) are not so fast, that the C02 equilibrium is hardly established between alveolar air and capillary blood during the contact time (ta).•The venous-arterial C02 content difference due to the Haldane effect ((va)C~o2(H)) has hitherto been expressed by multiplying the slope of the C02 dissociation curve (a') by the difference between the true-and oxygenated-venous Pco2 (oxPv~o2 -trPv~o2) (CHRISTIANSEN et al., 1914). Using this relation,

A method for estimating contact time of red blood cells through lung capillary from O2 and CO2 concentrations in rebreathing air in man.

“…(12a) is used to correct the linear experimental R-P02 line. As shown in the preceding paper (KAGAWA and MOCHIZUKI, 1987, Fig. 8), the theoretical R-P02 line deviates upwards as the PAco2 is decreased against the constant trPvC02.…”

“…The effect usually decreases as the PAco2 approaches the trPvco2 during the rebreathing, since the intracellular pH (pH) decreases with increasing PAco2. KAGAWA and MOCHIZUKI (1987) designated the (a-v)Co2 at the PAco2, where the pH~ in arterial blood equals that in venous blood, as the standard (a-v)Co2 ((a-v)Co2*). Furthermore, they developed a method to obtain the (a-v)Co2* by a modification of the method originated by MOCHIZUKI et al (1984).…”

“…MOCHIZUKI et al (1984) estimated the (a-v) Cot by dividing the a'(Pm2) by 8. Since the (a-v)Co2 thus obtained, however, was not accurate enough, KAGAWA and MOCHIZUKI (1987) derived a correcting factor (F(H)) from the numerical solution of 02 and C02 diffusions in the RBC and attempted to estimate the (a-v)Co2*:…”

“…First, the trPVco2 was determined by the following equation for HEC (KAGAWA and MOCHIZUKI, 1987 (18a)-(18d) and as illustrated in Fig. 8.…”

“…8 of the preceding paper (KAGAWA and MOCHIZUKI, 1987), the resistance of the alveolar membrane to the CO2 diffusion was ignored. Provided that the CO2 transfer in the lung is, more or less, limited by the diffusion across the capillary wall, the difference between Pm 1 and Pm2 in Eqs.…”