Urban angina in the mountains: Effects of carbon monoxide and mild hypoxemia on subjects with chronic stable angina

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. Investigato rs conducted the tests at sea level, and they simulated 2.1-km altitudes (i .e., reduced arterial oxygen saturation by approximately 4%) in a randomize d double-blind experiment in which each subject acted as his or her own con trol. The duration of symptom-limited exercise, heart rate, indicators of c ardiac ischemia and arrhythmia, blood pressure, and respiratory gas exchang e were measured. Analyses of variance showed that both independent variable s-altitude and carbon monoxide-significantly (p less than or equal to .01) reduced total duration of exercise for the group as a whole (n = 17) and re duced the time to onset of angina for a subset of 13 subjects who experienc ed angina during ail four test conditions (p < .05). Time to onset of angin a 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 altitu de reduced the time to onset of angina, relative to clean air, by 18% (p < .05). Other cardiological, hemodynamic, and respiratory physiological param eters were also affected adversely by altitude and carbon monoxide exposure s. None of the parameters measured were associated significantly with eithe r altitude or carbon monoxide, indicating that the effects of carbon-monoxi de-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 a rtery disease.