766: Is fetal hemoglobin designed to limit oxygen delivery to the fetus?

Abstract

Introduction: It has long been appreciated that adult hemoglobin and fetal hemoglobin differ in their ability to transport oxygen. Methods: We employed a highly accurate mathematical model of oxyhemoglobin dissociation (Kelman GR. Digital computer subroutine for the conversion of oxygen tension into saturation. J Appl Physiol 1966; 21: 1375-1376) to quantify oxyhemoglobin saturation values for adult and fetal hemoglobin under the conditions which normally pertain to arterial blood (borne to the fetus from the placenta via the umbilical vein) and mixed venous blood (borne from the fetus to the placenta via the umbilical artery). The values pertaining to homeostatic intrauterine conditions were obtained from an authoritative source (Siggard-Andersen O, Huch R. The oxygen status of fetal blood. Acta Anaesthesiol Scand 1995; 39 (Supplement 107): 129-135). Results: This analysis revealed that fetal hemoglobin unloads far less (46.1%) of its' oxygen content to fetal tissues, as compared to its' adult counterpart (64.0%). Conclusions: This striking dissimilarity in the efficiency of oxygen transport between the two forms of hemoglobin tempts us to speculate that fetal hemoglobin has a role in limiting oxygen delivery to fetal tissues.