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% O-2), 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 O-2 uptake kinetics ((V) over dot(o2)p). Surprisingly, however, HiOX was associated with faster fractional O-2 extraction (similar to 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 O-2 delivery (Q(O2)' mv)-to-utilization. These data indicate that, despite improved central O-2 delivery, Q(O2)' mv adapted at a slower rate than muscle (V) over dot(O2) under HiOX in non-hypoxaemic patients with COPD. Our results question the rationale of using supplemental O-2 to improve muscle oxygenation during the transition to high-intensity exercise in this patient sub-population. (C) 2010 Elsevier B.V. All rights reserved.