Cardiac response to combined moderate heat and exercise in men with coronary artery disease

The effect of moderate heat stress on cardiac performance during sustained moderate physical work was evaluated in men greater than or equal to 6 weeks after a cardiac event. Subjects (n = 10) performed upright leg cycle ergometer exercise at approximately 50% of peak oxygen uptake for up to 60 minutes in warm (30.0 +/- 0.9 degrees C) and thermoneutral (21.5 +/- 0.3 degrees C) environments. Cardiac output (carbon dioxide rebreathing method), left ventricular ejection fraction and relative left ventricular end-diastolic volume (portable nuclear VEST monitor) were periodically determined. In both environments, heart rate increased (p less than 0.05), stroke volume decreased (p less than 0.05), and cardiac output remained unchanged with exercise time. In the warmer environment, heart rate was increased (p less than 0.05) and stroke volume tended to be decreased (p less than 0.08), with no difference in cardiac output. In both environments, left ventricular ejection fraction did not change from minute 6 to 60 of exercise, whereas relative left ventricular end-diastolic volume decreased (p less than 0.05) with exercise time. Arterial blood pressure was unchanged from minute 6 to 60 in the warm environment. Arrhythmias were not altered by exercise time or environment, and no subjects had evidence of myocardial ischemia. The data indicate that although heart rate increased and stroke volume and relative left ventricular end-diastolic volume decreased with exercise time, cardiac output and left ventricular ejection fraction remained unchanged in both thermoneutral and warm environments.(ABSTRACT TRUNCATED AT 250 WORDS)