Oxygen transport in congenital heart disease: influence of fetal hemoglobin, red cell pH, and 2,3-diphosphoglycerate.

In 48 individuals (age 1 day to 13 years) with congenital heart disease, blood oxygen transport function was studied in order to evaluate adaptive changes in shunt hypoxemia and to investigate the in vivo regulation of erythrocyte 2, 3-diphosphoglycerate concentration (RBC 2, 3-DPG) in the presence of fetal hemoglobin (HbF). Arterial pO2 and oxygen content, oxygen capacity, acid base status, oxygen affinity, HbF fraction, plasma pH, red cell pH, and RBC 2, 3-DPG were determined. During the first 50 days of life values of standard P50 (stdP50) (37, pH 7.4), actual in vivo P50 (actP50), RBC 2, 3-DPG, O2 capacity, arterial plasma pH, and red cell pH were scattered around the normal range, although tending to low values for stdP50 and arterial plasma pH and to high values for O2 capacity. After the third month, stdP50 actP50, RBC 2, 3-DPG, O2 capacity, and red cell pH were found to be elevated. Plasma pH and actP50 were scattered around the normal range (Figs. 1 and 2). Intraerythrocytic pH in hypoxemic infants was increased compared with normal children when related to plasma pH (Fig. 3). A close to normal intraerythrocytic pH was therefore found in the hypoxemic infants with low plasma pH, and an increased intraerythrocytic pH in the hypoxemic children with normal plasma pH (Fig. 1). A significant negative correlation exists between erythrocyte H+ ion and 2, 3-DPG concentration (Fig. 5); regression constants derived from data at high (mean 47%) and low (mean 9%) fractions of HbF are not significantly different (Regression Equations 8 and 11 in Table 1). Thus, the known difference in 2, 3-DPG binding to fetal or adult deoxyhemoglobin does not measurably influence the erythrocyte 2, 3-DPG concentration, indicating that in vivo the 2, 3-DPG synthesis in hypoxia is virtually regulated by the erythrocyte pH, which in turn is determined by plasma pH and the oxygenation state of hemoglobin.