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 PCO2, 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 CO2 tension of 40 mmHg (P50st) and individual end-tidal CO2 tensions (PetCO2) (P50act). 2,3-BPG and ATP were determined by liquid chromatography–tandem mass spectrometry. Results: P50st 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 P50act was similar in HH and NX (26.4 ± 1.6 mmHg vs. 26.1 ± 2.7 mmHg; p = 0.360) despite reduced PetCO2 (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 PetCO2/increase in pH on the ODC.