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 (CPT_COA), and (iii) 2‐h CO and 1‐h 100% normobaric O₂ exposure followed by a CPT under CO conditions (CPT_COB). All exercise tests were performed at 85% of peak power output to exhaustion. Oxygenated (ΔO₂Hb]), deoxygenated (ΔHHb]) and total (ΔtHb]) 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 ΔO₂Hb] and ΔtHb] were lower in CPT_COA than in CPT. During the CPT_COB, the intercostal ΔO₂Hb] and ΔtHb] were higher than in the CPT_COA. 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.