Aggravation of angina pectoris by two percent carboxyhemoglobin

A double-blind, randomized, crossover study was performed in 15 patients with stable angina to evaluate the effect of breathing carbon monoxide (CO), which raised the carboxyhemoglobin (COHb) from 1.09% to 2.02%, versus breathing compressed, purified air, which lowered the COHb from 1.07% to 1.00% on exercise duration until angina. The exercise duration until angina was 324.5 seconds in the air control period and 330.3 seconds after purified air compared to 321.7 seconds in the CO air control period and 289.7 seconds after CO. Breathing CO to raise the COHb from 1.09% to 2.02% caused a decrease in exercise duration until angina pectoris (p less than 0.001) and a reduction in product of systolic blood pressure times heart rate at the onset of angina (p less than 0.001). These data indicate that a 2% COHb level aggravates angina pectoris due to coronary artery disease.