Diabetic oxygen-hemoglobin equilibrium curves evaluated by nonlinear regression of the Hill equation

The oxygen-hemoglobin equilibrium curves ( OHECs ) were measured on whole blood samples from 131 individuals (33 normal and 26 diabetic adults and 30 normal and 42 diabetic juveniles) using a Radiometer Dissociation Curve Analyzer (DCA-1). All measurements were made in the morning following an overnight fast and without exogenous insulin. The saturation versus Po2 data were fitted to the Hill equation using a previously described nonlinear regression algorithm to yield the parameters describing the position (P50) and shape (n) of each OHEC . It was found that the Hill model could be used to describe OHECs of both normal and diabetic subjects. A small (approximately 10%) but significant decrease in P50 was found for the diabetic juveniles compared to normal juveniles. There appeared to be no change in P50 with diabetes in adults. However, in these diabetic subjects, the P50 had been increased by the somewhat elevated levels of 2,3-DPG. No difference in n was found between either group of diabetics and their corresponding group of normals but n was approximately 5% lower in juveniles than in adults. The ability of blood to release oxygen to tissue may be transiently impaired in diabetic juveniles because of the left shift of their OHECs .