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 Pa O₂> 60 mmHg ). Despite faster cardiac output and improved blood oxygenation, HiOX did not significantly change pulmonary O2 uptake kinetics ( VO₂p ). Surprisingly, however, HiOX was associated with faster fractional O2 extraction ( approximately Delta[deoxy-Hb+Mb] by near-infrared spectroscopy) (p<0.05). In addition, an "overshoot" in Delta[deoxy-Hb+Mb] was found after the initial fast response only in HiOX (7/11 patients) thereby suggesting impaired intra-muscular O2 delivery ( Q'O ₂mv)-to-utilization. These data indicate that, despite improved "central" O2 delivery, Q'O₂mv adapted at a slower rate than muscle VO₂ 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.