Oxygen dissociation curves for whole blood, recorded with an instrument that continuously measures pO2 and sO2 independently at constant t, pCO2, and pH.

We describe a method for recording oxygen dissociation curves for whole-blood specimens. The blood sample is placed in a thermostated measuring chamber, and pO2 and SO2 are measured continuously by polarography and by reflectometry, respectively. During the recording of an oxygen dissociation curve, the pO2 and SO2 signals are stored in a data-acquisition system, while pH, pCO2, and temperature are kept constant. Determination of precision and error discussion indicated that the coefficient of variation (CV) of the determination of the oxygen dissociation curve is mainly determined by the error in the measurement of SO2. The overall CV of pO2 values belonging to the lower, mid-, and upper parts of the SO2 range is estimated to be about 2.6, 3.1, and 2.1%, respectively. In practice the measurements are about 30% more precise than estimated. With our method, the fixed-acid-induced Bohr effect (H+ factor) can be determined over the entire SO2 range with much greater precision than hitherto.