Key result
Acute exposure to carbon monoxide (3.8% carboxyhemoglobin) did not significantly affect time to angina (306 vs 312 sec) but slightly reduced the change in ejection fraction (2% vs 3.5%, p=0.049).
Why the study?
Does acute exposure to low levels of carbon monoxide affect cardiovascular function during exercise in patients with ischemic heart disease?
RCT (n=30)
Double-blind
Randomized
Does acute exposure to low levels of carbon monoxide affect cardiovascular function during exercise in patients with ischemic heart disease?
Acute elevation of carboxyhemoglobin to 3.8% does not have a clinically significant effect on cardiovascular function or exercise tolerance in nonsmoking patients with ischemic heart disease.
We studied 30 patients 38-75 yr of age who had ischemic heart disease to assess the effect of acute elevation of carboxyhemoglobin (COHb) concentration. Patients were nonsmokers with ischemia defined by exercise-induced ST depression (ST decreases)--25/30, angina--23/30, or abnormal ejection fraction (EF) response--18/30. After an initial familiarization and exercise session patients were exposed to air (carboxyhemoglobin [COHb] = 1.5 +/- 0.05%) and to carbon monoxide (CO) (100 ppm-COHb-average = 3.8 +/- 0.1%) on successive days in a double blind, randomized fashion. There was no significant difference in time to onset of angina (air = 312 sec, CO = 306 sec), maximal exercise time (air = 711 sec, CO = 702 sec), maximal ST decreases (1.5 mm for both), or time to significant ST decreases (air = 474 sec, CO = 475 sec). Double product at ST decreases and maximal double products were similar for both conditions. Resting ejection fraction was slightly but nonsignificantly higher after CO exposure (air = 53.9%, CO = 55.2%). Maximal ejection fraction was similar for both conditions (air = 57.4%, CO = 57.1%). Change in ejection fraction was slightly lower for CO exposure (air = 3.5%, CO = 2%), p = .049. In conclusion, there is no clinically significant effect of 3.8% COHb (representing a 2.2% increase from resting values) on the cardiovascular system in this study.
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Sheps et al. (1987) conducted an RCT in Ischemic heart disease (n=30). Carbon monoxide vs. Air was evaluated on Time to onset of angina. Acute exposure to carbon monoxide (3.8% carboxyhemoglobin) did not significantly affect time to angina (306 vs 312 sec) but slightly reduced the change in ejection fraction (2% vs 3.5%, p=0.049).
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