Influence of oxygen and carbon dioxide on the plasma-erythrocyte pH relationship in normal human whole blood.

The influence of oxygenation level (oxyhaemoglobin saturation 0 or 100%) on the relationship between plasma pH and erythrocyte pH was studied, in vitro, in normal human blood submitted to changes in carbon dioxide tension. Firstly, the pH of both true and separated erythrolysates were compared: for the former, tonometry was carried out on whole blood, before red cells lysis; for the latter, equilibration was performed on erythrolysate, pH values appeared different: at PCO2 congruent to 21 and 38 Torr, separated erythrolysate was more alkaline than true one, and at PCO2 congruent to 0 it was more acid. Therefore, to estimate pHe-pHi relationship, pHi was evaluated on true erythrolysate. When haemoglobin passed from the reduced to the completely oxygenated state, a significant decrease of both pHe and pHi was observed for a given PCO2 (respectively about 0.05 and 0.08 pH unit), and of pHi for a given pHe (about 0.04 pH unit). In either extra or intraerythrocyte fluid, the oxygen-linked pH difference was negatively correlated to PCO2.