Effects of hyperoxia on the dynamics of skeletal muscle oxygenation at the onset of heavy-intensity exercise in patients with COPD

This study addressed whether hyperoxia (HiOX = 50% O2), compared to normoxia, would improve peripheral muscle oxygenation at the onset of supra-gas exchange threshold exercise in patients with chronic obstructive pulmonary disease (COPD) who were not overtly hypoxemic (resting PaO2>60 mmHgPaO2>60 mmHg). Despite faster cardiac output and improved blood oxygenation, HiOX did not significantly change pulmonary O2 uptake kinetics (V˙O2p). Surprisingly, however, HiOX was associated with faster fractional O2 extraction (∼Δ[deoxy-Hb + Mb] by near-infrared spectroscopy) (p < 0.05). In addition, an “overshoot” in Δ[deoxy-Hb + Mb] was found after the initial fast response only in HiOX (7/11 patients) thereby suggesting impaired intra-muscular O2 delivery (Q′O2mvQ′O2mv)-to-utilization. These data indicate that, despite improved “central” O2 delivery, Q′O2mvQ′O2mv adapted at a slower rate than muscle V˙O2 under HiOX in non-hypoxaemic patients with COPD. Our results question the rationale of using supplemental O2 to improve muscle oxygenation during the transition to high-intensity exercise in this patient sub-population.