Lack of Effect of Low Levels of Carboxyhemoglobin on Cardiovascular Function in Patients with Ischemic Heart Disease

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Abstract
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 ↓)—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 ↓ (1.5 mm for both), or time to significant ST ↓ (air = 474 sec, CO = 475 sec). Double product at ST ↓ 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.