Carbon monoxide exposure during exercise performance: muscle and cerebral oxygenation

Aim: To investigate the effect of carbon monoxide (CO) in the inspired air as anticipated during peak hours of traffic in polluted megalopolises on cerebral, respiratory and leg muscle oxygenation during a constant-power test (CPT). In addition, since O2 breathing is used to hasten elimination of CO from the blood, we examined the effect of breathing O2 following exposure to CO on cerebral and muscle oxygenation during a subsequent exercise test under CO conditions. Methods: Nine men participated in three trials: (i) 3-h air exposure followed by a control CPT, (ii) 1-h air and 2-h CO (18.9 ppm) exposure succeeded by a CPT under CO conditions (CPTCO A), and (iii) 2-h CO and 1-h 100% normobaric O2 exposure followed by a CPT under CO conditions (CPTCO B). All exercise tests were performed at 85% of peak power output to exhaustion. Oxygenated (D[O2Hb]), deoxygenated (D[HHb]) and total (D[tHb]) haemoglobin in cerebral, intercostal and vastus lateralis muscles were monitored with near-infrared spectroscopy throughout the CPTs. Results: Performance time did not vary between trials. However, the vastus lateralis and intercostal D[O2Hb] and D[tHb] were lower in CPTCO A than in CPT. During the CPTCO B, the intercostal D[O2Hb] and D[tHb] were higher than in the CPTCO A. There were no differences in cerebral oxygenation between the trials. Conclusion: Inspiration of 18.9 ppm CO decreases oxygenation in the vastus lateralis and serratus anterior muscles, but does not affect performance. Breathing normobaric O2 moderates the CO-induced reductions in muscle oxygenation, mainly in the intercostals, but does not affect endurance.