Urban Angina in the Mountains: Effects of Carbon Monoxide and Mild Hypoxemia on Subjects with Chronic Stable Angina

Abstract

Seventeen men with stable angina pectoris who resided at or near sea level performed cardiopulmonary exercise stress tests after they were exposed to either carbon monoxide (3.9%), carboxyhemoglobin, or clean air. Investigators conducted the tests at sea level, and they simulated 2.1-km altitudes (i.e., reduced arterial oxygen saturation by approximately 4%) in a randomized double-blind experiment in which each subject acted as his or her own control. The duration of symptom-limited exercise, heart rate, indicators of cardiac ischemia and arrhythmia, blood pressure, and respiratory gas exchange were measured. Analyses of variance showed that both independent variables—altitude and carbon monoxide—significantly (p ≤ .01) reduced total duration of exercise for the group as a whole (n = 17) and reduced the time to onset of angina for a subset of 13 subjects who experienced angina during all four test conditions (p < .05). Time to onset of angina was reduced either after exposure to sea-level carbon monoxide (9%) or to simulated high-altitude clean-air exposures (11%), compared with clean air at sea level. Joint exposure to carbon monoxide at a simulated high altitude reduced the time to onset of angina, relative to clean air, by 18% (p < .05). Other cardiological, hemodynamic, and respiratory physiological parameters were also affected adversely by altitude and carbon monoxide exposures. None of the parameters measured were associated significantly with either altitude or carbon monoxide, indicating that the effects of carbon-monoxide-induced and high-altitude-induced hypoxia were additive. The results of this study suggest that high-altitude conditions exacerbate the effects of carbon monoxide exposures in unacclimatized individuals who have coronary artery disease.