Simulation of continuous blood O2 equilibrium curve over physiological pH, DPG, and Pco2 range

We analyzed 56 O2 equilibrium curves of fresh human blood, each from 0 to 150 Torr Po2. The data were collected over ranges of values for the 2,3-diphosphoglyceric acid-to-hemoglobin concentration ratio [DPG]/[Hb] of 0.2-2.7, for pH of 7.0-7.8, and for Pco2 of 7-70 Torr. Each curve was characterized according to the Adair scheme for the stepwise oxygenation of Hb, and the resulting constants (a1, a2, a3, a4) were analyzed to allow the simulation of the entire O2 equilibrium curve under any conditions of [DPG]/[Hb], pH, and Pco2 in the specified range. This analysis provides a powerful tool to study the affinity of Hb for O2 within the red blood cell and to predict the shape of the O2 equilibrium curve in various physiological and pathological states. Other attempts to predict blood O2 affinity have considered only P50 (the Po2 at one-half saturation with O2) or have provided too little data for continuous simulations.