Effects of short-term exposure to carbon monoxide in subjects with coronary artery disease

Twenty-four male subjects with stable angina pectoris performed graded exercise tests after being exposed to either carbon monoxide (CO) or clean air in a randomized crossover double-blind experiment in which each subject acted as his own control. Subject's blood carboxyhemoglobin levels were increased from a baseline level of approximately 1.5% to 3% of saturation, post-CO exposure. Cardiographic and respiratory gas exchange data were obtained during the tests in which the subjects exercised to the point of onset of anginal pain. The goal of the study was to determine if low-level CO exposure compromised the ability of these individuals to perform work. Data were evaluated statistically using a two-factor analysis of variance with repeated measures; the factors were exposure ATMOSPHERE (clean air vs. CO) and ORDER of exposure (clean air first, CO second vs. CO first, clean air second). One-tailed tests were used, and differences were considered significant at the p less than .05 level. The time to onset of angina was reduced 6% (p = .046) after CO exposure relative to clean air. Oxygen uptake (VO2) at angina was reduced by approximately 3% (p = .04). A subgroup of individuals who exhibited depression in the ST segment of their electrocardiograph tracings showed a 12% reduction in time to onset of angina and a 20% reduction in the time to onset of 0.1 mV ST segment depression; both of these findings were also statistically significant.