A new approach to haemoglobin oxygen affinity research at high altitude: Determination of haemoglobin oxygen dissociation curves and 2,3-bisphosphoglycerate in an experimental human crossover hypoxic chamber study

Abstract

Purpose During rapid exposure to hypobaric hypoxia (HH), arterial oxygen tension and haemoglobin oxygen saturation decrease. The oxygen dissociation curve (ODC) describes the relationship of oxygen tension and haemoglobin oxygen saturation. Previous methods for ODC determination are mostly limited to standard conditions (40 mmHg PCO 2 , 37 °C), and measurements of 2,3-bisphosphoglycerate (2,3-BPG) and adenosine triphosphate (ATP) are omitted. This study aimed to investigate hypoxia-induced changes on the ODC in a strictly controlled hypobaric chamber setting utilising a novel method for ODC determination, incorporating innovative 2,3-BPG and ATP measurements. Methods In a randomised crossover design, ten healthy males completed two 4-day sojourns, one in HH (3,500 m) and one in normoxia (NX, 262 m). ODCs were determined from venous blood at 96 h using a highly customisable high-throughput microplate reader method. Haemoglobin half saturation pressure (P50) was measured for a standardised CO 2 tension of 40 mmHg (P50 st ) and individual end-tidal CO 2 tensions (P et CO 2 ) (P50 act ). 2,3-BPG and ATP were determined by liquid chromatography–tandem mass spectrometry. Results P50 st were increased in HH compared to NX but missed statistical significance (28.3 ± 2.0 mmHg vs. 26.8 ± 1.9 mmHg; p = 0.054), whilst P50 act was similar in HH and NX (26.4 ± 1.6 mmHg vs. 26.1 ± 2.7 mmHg; p = 0.360) despite reduced P et CO 2 (31.0 ± 2.1 mmHg vs. 38.4 ± 2.5 mmHg; p < 0.001). 2,3-BPG and pH were significantly increased in HH compared to NX (16.8 ± 1.6 µmol/gHb and 20.5 ± 1.1 µmol/gHb, p < 0.001; 7.36 ± 0.01 versus 7.39 ± 0.02, p < 0.001). Conclusion The 2,3-BPG increase after 96 h in HH compensates the effect of hypoxia-induced decrease in P et CO 2 /increase in pH on the ODC.

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