Effect of temperature on the p50 value for human blood.

We investigated the effect of temperature (19, 30, 37, and 43 degrees C) on the p50 value for normal human blood at pco2 = 5.72 kPa (43 mmHg), at various pHs (range 7.0 to 7.6) and molar ratios of [2,3-diphosphoglycerate]/[Hb4] (range 0.4 to 2.4). The d(log p50)/d(pH) coefficient varied from 0.39 at 19 degrees C to 0.35 at 43 degrees C. The relationship between log p50 and 1/T (T = degrees Kelvin) was linear under the experimental conditions used, and the d(log p50)/d(1/T) coefficient varied between -2138 at pH 7.0 and -2162 at pH 7.6, independent of the concentration of 2,3-diphosphoglycerate. Assuming that the effect of pco2 on the p50 value is the same at 19, 30, and 43 degrees C as at 37 degrees C, one can use the reported coefficients to calculate the p50 value for normal human blood under conditions of temperature, pH, pco2, and 2,3-diphosphoglycerate concentrations prevailing under physiological and pathological conditions. The p50 value calculated by empirical equations, taking into account the effect of temperature, correlated well with the values for p50 determined experimentally (y = 0.9774x + 0.453; r = 0.998; n = 60), with an SD of 52 Pa (0.39 mmHg).