Relationship between Hematocrit and CO₂ Contents in Whole Blood and True Plasma

Abstract

The amount of CO₂ liberated out of the red cell was measured by decreasing P_CO2 in human blood with different fractional hematocrits of about 0.24, 0.45, and 0.75, respectively, in order to elucidate whether it depends on the hematocrit and the intracellular pH. From a venous P_CO2 level the P_CO2 of the sample bood was lowered to 12Torr. P_CO2, CO₂ content, pH, Cl^-, and Na⁺ were measured in whole blood and true plasma before and after the reduction of P_CO2. Change in water concentration in plasma was calculated from change in plasma Na⁺ concentration. The bicarbonate shift well counterbalanced to the Cl^- shift. As the hematocrit was decreased, the amount of CO₂ released per mol of hemoglobin increased, while the change in intracellular bound CO₂ concentration decreased. That is, the intracellular bound CO₂ became higher in the lower hematocrit blood than in the higher hematocrit one. This fact suggested that the intracellular pH became higher as the hematocrit was lowered, and thus the amount of alkali bound with hemoglobin or the CO₂ release was enhanced. The Donnan ratio of the bound CO₂ at 12Torr was independent of the hematocrit, though the pH was inversely related to the hematocrit.