Impact of Pharmacologically Left Shifting the Oxygen-Hemoglobin Dissociation Curve on Arterial Blood Gases and Pulmonary Gas Exchange During Maximal Exercise in Hypoxia

Stewart, Glenn M., Troy J. Cross, Michael J. Joyner, Steven C. Chase, Timothy Curry, Josh Lehrer-Graiwer, Kobina Dufu, Nicholas E. Vlahakis, and Bruce D. Johnson. Impact of pharmacologically left shifting the oxygen-hemoglobin dissociation curve on arterial blood gases and pulmonary gas exchange during maximal exercise in hypoxia. High Alt Med Biol. 16:000-000, 2021. Introduction: Physiological and pathological conditions, which reduce the loading of oxygen onto hemoglobin (Hb), can impair exercise capacity and cause debilitating symptoms. Accordingly, this study examined the impact of pharmacologically left shifting the oxygen-hemoglobin dissociation curve (ODC) on arterial oxygen saturation (SaO(2)) and exercise capacity. Methods: Eight healthy subjects completed a maximal incremental exercise test in hypoxia (FIO2: 0.125) and normoxia (FIO2: 0.21) before (Day 1) and after (Day 15) daily ingestion of 900 mg of voxelotor (an oxygen/Hb affinity modulator). Pulmonary gas exchange and arterial blood gases were assessed throughout exercise and at peak. Data for a 1,500 mg daily drug dose are reported in a limited cohort (n = 3). Results: Fourteen days of drug administration left shifted the ODC (p50 measured under standard conditions, Day 1: 28.0 +/- 2.1 mmHg vs. Day 15: 26.1 +/- 1.8 mmHg, p < 0.05). Throughout incremental exercise in hypoxia, SaO(2) was systematically higher after drug (peak exercise SaO(2) on Day 1: 71 +/- 2 vs. Day 15: 81% +/- 2%, p < 0.001), whereas oxygen extraction (Ca-vO(2) diff) and consumption (VO2) were similar (peak exercise Ca-vO(2) diff on Day 1: 11.5 +/- 1.7 vs. Day 15: 11.0 +/- 1.8 ml/100 ml blood, p = 0.417; peak VO2 on Day 1: 2.59 +/- 0.39 vs. Day 15: 2.47 +/- 0.43 l/min, p = 0.127). Throughout incremental exercise in normoxia, SaO(2) was systematically higher after drug, whereas peak VO2 was reduced (peak exercise SaO(2) on Day 1: 93.9 +/- 1.8 vs. Day 15: 95.8% +/- 1.0%, p = 0.008; peak VO2 on Day 1: 3.62 +/- 0.55 vs. Day 15: 3.26 +/- 52 l/min, p = 0.001). Conclusion: Pharmacologically increasing the affinity of Hb for oxygen improved SaO(2) during hypoxia without impacting exercise capacity; however, left shifting the ODC in healthy individuals appears detrimental to exercise capacity in normoxia. Left shifting the ODC to different magnitudes and under more chronic forms of hypoxia warrants further study.