The CO_2 Dissociation Curve at Steady State in Vivo

概要

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The CO_2 content in blood ([CO_2]) depends not only on PCO_2, but also on the O_2 saturation ([SO_2]). Since SO_2 changes in parallel with [CO_2] in capillary blood ([CO_2]^* ) at steady state, the slope of [CO_2]^* against PCO_2 becomes steeper than that of [CO_2] measured in oxygenated or deoxygenated blood. In the preceding paper it was made clear that the change in [CO_2] due to that in SO_2 (i.e., the Haldane effect, [CO_2]_HE) became proportional to the respiratory quotient (RQ). Since the ratio of the arterial-venous (a-v) difference in SO_2 (av [SO_2]) to that in [CO_2]^* (av[CO_2]^*) was in inverse pro-portion to the RQ, the ratio of the a-v difference in [CO_2]_HE (av[CO_2]_HE) to av[CO_2]^* became constant irrespective of the RQ. Designating the PCO_2 dependent component of [CO_2] except for [CO_2]_HE by [CO_2]_P , the ratio av[CO_2]_P/[CO_2]^* also became constant. Thus, using [CO_2]_P measured in oxygenated blood in vitro, [CO_2]^* could be expressed by an exponential function of PCO_2　Key words : Carbonic anhydrase, O_2 saturation, Haldane effect, Respiratory quotient, Va/Q ratio
2004-02-16