Acid-base balance and the effect of oxyhemoglobin reduction on CO 2 transport

Abstract

The CO 2 content and [H+] of oxygenated and reduced whole blood of the dog were measured in vitro at constant P CO 2 but at varying levels of [H+]. The magnitude of increase in CO 2 content and decrease in hydrogen ion concentration at constant P CO2, which results from oxyhemoglobin reduction (CDH effect), is a decreasing linear function of the [H+] at which reduction takes place. The relationship is expressed by the equation CDH effect = −0.0034 [H+] + 0.518 and is similar at P CO 2's of 43 and 60 mm Hg. This effect is presumably the result of the influence of hydrogen ion concentration on formation of carbamino-bound CO 2 and explains the variations in the magnitude of the C-D-H effect which have been previously reported. The decreases in hydrogen ion concentration which accompanied oxyhemoglobin reduction were small and consistent with the hypothesis that carbamino-bound CO 2 is derived from oxylabile α-NH 2 groups with pK's between 6.5 and 8. Since carbamate formation results in the release of hydrogen ion, the relationship between its formation and the existing hydrogen ion concentration represents a mechanism for hydrogen ion homeostasis.