Effects of hemoglobin concentration, carbon dioxide tension, and lactic acid concentration on hydrogen ion activity of human blood in vitro

The current study assessed in vitro effects of changing hemoglobin concentration, carbon dioxide tension, and lactic acid concentration on normal human blood pH and bicarbonate concentration. Hemoglobin concentration was varied among separated plasma, normal blood, and high hematocrit blood samples with 0, 2.1, and 2.4 mM mean hemoglobin concentrations, respectively. The carbon dioxide tension was held constant at either 40 or 20 mm Hg while the oxygen tension was always 95 mm Hg. Lactic acid concentration was maintained within a low range of 1.0 to 2.7 mM and within a high range of 10.7 to 11.7 mM. The pH and bicarbonate responses to a constant lactic acid load among the three hemoglobin levels indicated that bicarbonate was the major buffer of lactic acid. Estimates were made of the relative contributions of plasma bicarbonate, plasma proteinate, erythrocyte bicarbonate, and erythrocyte proteinate to the total lactic acid buffering. There was no increase in lactic acid buffering when hemoglobin concentration was increased by 12.7%. There was also an indication that lactate participated in the chloride shift when lactic acid was added to blood.