Hemoglobin affinity for oxygen during short-term exhaustive exercise

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Abstract
Hb affinity for O2 (standard [std] P50 [O2 partial pressure at 50% Hb saturation]: pH 7.40, PCO2 [CO2 partial pressure] 40 torr, temperature 37.degree. C) was assessed in 3 series of studies of 16 human male subjects who performed exhaustive treadmill exercise for 10 min. Std P50 was significantly elevated (0.7-2.5 torr) during the last minute of and for 30 min following exercise. Exercise while carboxyhemoglobin (HbCO) was acutely elevated to 5% did not affect std P50 any differently than exercise alone. 2,3-Diphosphoglycerate (2,3-DPG) was significantly elevated after exercise, but not during or 30 min postexercise, and it correlated significantly with P50 in 2 studies (r [correlation coefficient] 0.43-0.68). ATP (.mu.mol/100 ml) was significantly elevated only 3 min postexercise. Serum [Na+], [K+], [Cl-], osmolarity and (Hb) concentration were significantly elevated during exercise, with [Na+], osmolarity, and [Hb] remaining significantly elevated postexercise. There was no significant correlation between std P50 and any of these variables. Multiple correlation regression analysis between P50 and 2,3-DPG, ATP and [Na+] yields a coefficient of 0.86. This type of exercise is unique in causing a small change in std P50 which appears to be mediated by several factors.