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 restricti ons on ambient concentrations of CO. Methods-15 young, healthy non-smoking men, 18-35 years old, were exposed bl indly and randomly to air or to a mixture of CO and air, followed by an exe rcise 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 exercis e test. The main outcome measures include the duration of the exercise test , the maximal effort expressed in metabolic equivalent units (METs), the me an plasma lactic to pyruvic acid ratio at the end of the ergometry, ECG cha nges in the exercise test, and perfusion deficits in thallium heart scintig raphy. Results-At the end of exposure to CO, the mean (SD) blood carboxyhaemoglobi n 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, w hich reflects the level of anaerobic metabolism (69.9 (5.9) after air and 7 5.9 (7.0) after CO), was not significantly different between the two experi mental 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 di fference of exercise duration between exposure to air and CO was 1.52 minut es 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 se quence and period effects. Thallium myocardial perfusion imaging disclosed normal perfusion in all regions of the heart, with no significant differenc es 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 exercis e performance in young healthy men. No ischaemic electrocardiographic chang es or disturbances in myocardial perfusion were found by graded exercise wi th thallium scintigraphy. Our findings suggest that pollution of atmospheri c air by CO at concentrations which are commonly found in urban and industr ial environments may exert an adverse effect on skeletal muscles, manifesti ng as decreased exercise performance.