Blood HbO2 and HbCO2 Dissociation Curves at Varied O2, CO2, pH, 2,3-DPG and Temperature Levels

Abstract

New mathematical model equations for O2 and CO2 saturations of hemoglobin (S(HbO2) and S(HbCO2)) are developed here from the equilibrium binding of O2 and CO2 with hemoglobin inside RBCs. They are in the form of an invertible Hill-type equation with the apparent Hill coefficients K(HbO2) and K(HbCO2) in the expressions for S(HbO2) and S(HbCO2) dependent on the levels of O2 and CO2 partial pressures (P(O2) and P(CO2), pH, 2,3-DPG concentration, and temperature in blood. The invertibility of these new equations allows P(O2) and P(CO2) to be computed efficiently from S(HbO2) and S(Hbco2) and vice-versa. The oxyhemoglobin (HbO2) and carbamino-hemoglobin (HbCO2) dissociation curves computed from these equations are in good agreement with the published experimental and theoretical curves in the literature. The model solutions describe that, at standard physiological conditions, the hemoglobin is about 97.2% saturated by O2 and the amino group of hemoglobin is about 13.1% saturated by CO2. The O2 and CO2 content in whole blood are also calculated here from the gas solubilities, hematocrits, and the new formulas for S(HbO2) and S(HbCO2). Because of the mathematical simplicity and invertibility, these new formulas can be conveniently used in the modeling of simultaneous transport and exchange of O2 and CO2 in the alveoli-blood and blood-tissue exchange systems.