The effect of respiratory and metabolic acid-base changes on ionized calcium concentration: in vivo and in vitro experiments in man and rat.

Abstract

Correlation of ionized calcium concentration, [Ca2+] and blood pH has long been recognized. So far no distinction of the acid-base changes, i.e. respiratory changes or metabolic changes seemed necessary. The present study, with the use of a recently developed system for in vivo analysis of [Ca2+], and with in vitro experiments reinvestigates this question. In a first series respiratory and metabolic changes were induced in rats. Changes of [Ca2+] (delta [Ca2+]) and of plasma pH (delta pH) were recorded continuously in vivo, plasma bicarbonate, [HCO-3] was measured in vitro. In a second series respiratory and metabolic changes were induced in sixteen volunteers and, separately, in vitro in plasma and modified Ringer solution, and the same parameters were determined. In all experiments delta [Ca2+] correlates negatively with delta pH. However, the correlation in respiratory changes was significantly less as compared to that in metabolic changes. As expected, delta [HCO-3] correlates positively with pH in metabolic and negatively in respiratory changes. We conclude from these experiments that in metabolic changes the effects of calcium-albumin interaction and calcium complexation with bicarbonate are additive, whereas both effects oppose each other in respiratory changes. This might explain the blunted effect of pH changes on [Ca2+] in respiratory changes.