A broad diversity in oxygen affinity to haemoglobin

Oxygen affinity to haemoglobin is indicated by the p50 value (pO₂ at 50% O₂Hb) and critically determines cellular oxygen availability. Although high Hb-O₂ affinity can cause tissue hypoxia under conditions of well O₂ saturated blood, individual differences in p50 are commonly not considered in clinical routine. Here, we investigated the diversity in Hb-O₂ affinity in the context of physiological relevance. Oxyhaemoglobin dissociation curves (ODCs) of 60 volunteers (18-40 years, both sexes, either endurance trained or untrained) were measured at rest and after maximum exercise (VO₂max) test. At rest, p50 values of all participants ranged over 7 mmHg. For comparison, right shift of ODC after VO₂max test, representing the maximal physiological range to release oxygen to the tissue, indicated a p50 difference of up to 10 mmHg. P50 at rest differs significantly between women and men, with women showing lower Hb-O₂ affinity that is determined by higher 2,3-BPG and BPGM levels. Regular endurance exercise did not alter baseline Hb-O₂ affinity. Thus, p50 diversity is already high at baseline level and needs to be considered under conditions of impaired tissue oxygenation. For fast prediction of Hb-O₂ affinity by blood gas analysis, only venous but not capillary blood samples can be recommended.