Mixing technique for study of oxygen-hemoglobin equilibrium: a critical evaluation

In the mixing technique for study of oxygen-hemoglobin equilibrium, the O2 saturation (SO2) of a blood mixture is calculated from the volume ratio at which an oxygenated sample is mixed with a deoxygenated sample, and the PO2 in the mixture is measured polarographically. Any predetermined level of SO2 may be obtained by proper choice of the volume ratio. It is shown that the volume and oxygen saturation of the mixed samples are by far the most critical parameters in calculating SO2, and a method is suggested by which the volume ratio is accurately measured by weighing the blood samples before mixing. Other parameters that influence determination of SO2, e.g., the O2 capacity of the blood, are much less important. The method has been applied to establish the O2 dissociation curve in human blood, and good reproducibility and agreement with standard curves were obtained. Measurements in rabbit blood yielded similarly satisfactory results. The technique is particularly applicable to problems that require exact adjustment of SO2 to a predetermined value, such as determination of the half-saturation pressure or of the Bohr effect at various levels of O2 saturation.