Hemoglobin-Oxygen Affinity and Erythrocyte 2,3-Diphosphoglycerate (DPG) Content in Hyaline-Membrane Disease (HMD) and Cardiac Malformations (CM)1

Abstract

The effect of DPG on the affinity of hemoglobin for oxygen, expressed as P50 (the PO2 at which Hb is 50% saturated with O2), is well known. In the present investigation whole blood from newborns with hyaline membrane disease (HMD) and cardiac malformations (CM) revealed a statistically significant difference between the two groups in both P50 and DPG content (HMD: P50 24.6 mm Hg = 3.5 S.D., DPG 0.78 mol/mol/Hb±0.16; CM: P50 29.1 mm Hg±3.4, DPG 1.31 mol/mol Hb±0.30). Patients with CM were more mature with higher birth weights and had lower arterial PO2 and O2 content (10.2 vol % O2 = 4.0 vs 16.7±4.9). BE, pH, PCO2, Hb and HbF were comparable. The effect of the observed difference in P50 between babies with HMD and CM can possibly explain the greater tolerance to hypoxemia of infants with CM since blood with P50 of 29.1 mm Hg can unload 15% more O2 to the tissues than blood with P50 of 24.1 assuming the same PvO2, CaO2 and cardiac output. Such differences in P50 have almost no effect on the amount of O2 loaded in the lungs. Further observations showed that DPG concentration varied directly with pH in normoxemic patients (> 90% saturation, > 15 vol% O2). Low pH could cause a decrease in DPG by inhibition of enzymes responsible for the synthesis, but also low DPG could produce a decrease in pH by impairment of unloading of O2 to the tissues. The hypoxemic patients showed a higher DPG concentration than predicted from their Hp, again suggesting that hypoxemia causes an increase in DPG concentration.