Short-Term Effects of Carbon Monoxide Exposure on the Exercise Performance of Subjects with Coronary Artery Disease

Abstract

Patients with atherosclerotic cardiovascular disease may be adversely affected by the presence of carboxyhemoglobin, even at low concentrations. We investigated the effects of carbon monoxide exposure on myocardial ischemia during exercise in 63 men with documented coronary artery disease. On each test day, subjects performed two symptom-limited incremental exercise tests on a treadmill; the tests were separated by a recovery period and 50 to 70 minutes of exposure to either room air or air containing one of two concentrations of carbon monoxide (117 +/- 4.4 ppm or 253 +/- 6.1 ppm). The order of exposure was assigned randomly. On each occasion, neither the subjects nor the study personnel knew whether the subjects had been exposed to room air or to one of the concentrations of carbon monoxide. Exposure to room air resulted in a mean carboxyhemoglobin level of 0.6 percent, exposure to the lower level of carbon monoxide resulted in a carboxyhemoglobin level of 2.0 percent, and exposure to the higher level of carbon monoxide resulted in a level of 3.9 percent. An effect of carbon monoxide on myocardial ischemia was demonstrated objectively by electrocardiographic changes during exercise. We observed a decrease of 5.1 percent (90 percent confidence interval, 1.5 to 8.7 percent; P = 0.02) and a decrease of 12.1 percent (90 percent confidence interval, 9.0 to 15.3 percent; P less than or equal to 0.0001) in the length of time to a threshold ischemic ST-segment change (ST end point) after carbon monoxide exposures that produced carboxyhemoglobin levels of 2.0 percent and 3.9 percent, respectively. The length of time to the onset of angina decreased by 4.2 percent (90 percent confidence interval, 0.7 to 7.9 percent; P = 0.054) at the 2.0 percent carboxyhemoglobin level and by 7.1 percent (90 percent confidence interval, 3.1 to 10.9 percent; P = 0.004) at the 3.9 percent carboxyhemoglobin level. Significant dose-response relations were found in both the change in the length of time to the ST end point (P less than or equal to 0.0001) and the change in the length of time to the onset of angina (P = 0.02). We conclude that low levels of carboxyhemoglobin exacerbate myocardial ischemia during graded exercise in subjects with coronary artery disease.

The tar fraction of cigarette smoke does not promote arteriosclerotic plaque development.

“…With the exception of carbon monoxide, a vapor phase component that plays no direct role in arteriosclerosis in cockerels (43) and only a small role at best in exacerbating other manifestations of heart disease in humans (47), investigations of the cancer-and arteriosclerosis-associated effects of CS have long focused on the tar fraction and its components (25,48,49). Evidence for activation of cytochrome P450 enzymes, which is necessary for the metabolism of the PAH carcinogens, has been reported in the vascular system following in vivo and in vitro exposures to carcinogens that are present in cigarette tar (22,31,32,50).…”

Effect of air pollution on diabetes and cardiovascular diseases in São Paulo, Brazil

“…Allred and colleagues (27) pointed out an increase in carboxyhemoglobin levels in response to 8-h average 9-ppm CO concentrations when evaluated by time to onset of exercise-induced angina and shorter ST intervals among nonsmoking volunteers with ischemic heart diseases.…”

Cardiovascular diseases among foundry workers exposed to carbon monoxide.

“…There are controversial reports on the effect of different COHb levels on myocardial hypoxia in smoking and nonsmoking patients with coronary heart disease (9,10).…”