Effects of exposure to low concentrations of carbon monoxide on exercise performance and myocardial perfusion in young healthy men.

Objective: To assess the effects of exposure to low concentrations of carbon monoxide (CO), as commonly measured in atmospheric urban air pollution and certain occupational environments, on exercise performance and myocardial perfusion in young healthy men, and the possible need for tighter restrictions on ambient concentrations of CO.

Methods: 15 young, healthy non-smoking men, 18-35 years old, were exposed blindly and randomly to air or to a mixture of CO and air, followed by an exercise treadmill test with thallium heart scintigraphy. Blood was drawn for determination of carboxyhaemoglobin before and at the end of the exposure, and for lactic and pyruvic acid at the beginning and the end of the exercise test. The main outcome measures include the duration of the exercise test, the maximal effort expressed in metabolic equivalent units (METs), the mean plasma lactic to pyruvic acid ratio at the end of the ergometry, ECG changes in the exercise test, and perfusion deficits in thallium heart scintigraphy.

Results: At the end of exposure to CO, the mean (SD) blood carboxyhaemoglobin concentration rose from 0.59% (0.08%) to 5.12% (0.65%) (p < 0.0001). At the end of the exercise period, the mean (SD) plasma lactate/pyruvate ratio, which reflects the level of anaerobic metabolism (69.9 (5.9) after air and 75.9 (7.0) after CO), was not significantly different between the two experimental groups. Exercise induced electrocardiographic changes were noted in only one subject after exposure to CO. No arrhythmias were detected in any of the subjects. Significant differences were found in the mean duration of the exercise test (p = 0.0012) and the METs (p = 0.0001). The mean adjusted difference of exercise duration between exposure to air and CO was 1.52 minutes 95% confidence interval (95% CI) 0.73 to 2.32 minutes. The mean adjusted difference of METs between exposure to air and CO was 2.04 95% CI 1.33 to 2.76. The models for duration of exercise and METs showed no significant sequence and period effects. Thallium myocardial perfusion imaging disclosed normal perfusion in all regions of the heart, with no significant differences in perfusion between the two exercise tests (after air or CO).

Conclusion: Acute exposure to a low concentration of CO which produces blood carboxyhaemoglobin concentrations of 4%-6% significantly decreases exercise performance in young healthy men. No ischaemic electrocardiographic changes or disturbances in myocardial perfusion were found by graded exercise with thallium scintigraphy. Our findings suggest that pollution of atmospheric air by CO at concentrations which are commonly found in urban and industrial environments may exert an adverse effect on skeletal muscles, manifesting as decreased exercise performance.