The effects of aging after coronary arterial bypass grafting on the regulation of cardiac output during upright exercise

We examined the effects of age on cardiac performance and the mechanisms that regulate cardiac output during upright exercise in patients free of myocardial ischemia after coronary revascularization. There were 90 subjects, aged 36 to 75 years, of whom 27 were greater than or equal to 60 years. There were no age-related changes in resting heart rate, systolic blood pressure, left ventricular end-diastolic volume index, left ventricular end-systolic volume index, stroke volume index, cardiac index and left ventricular ejection fraction. There were, however, age-related changes in exercise capacity (y = 20 - 0.21x, r = -0.52, P less than 0.001); exercise heart rate (y = 185 - 1x, r = -0.42, P less than 0.001); exercise end-systolic volume index (y = 11 + 0.46x, r = 0.28, P less than 0.01) and exercise ejection fraction (y = 81 - 0.31x, r = -0.28, P less than 0.01). In a subgroup of 54 patients with comparable exercise workload (27 aged less than 60 and 27 greater than or equal to 60 years), the age-related differences in exercise end-systolic volume index, exercise ejection fraction and exercise cardiac index were not observed, but the exercise heart rate was still higher in the younger patients (y = 168 - 0.76x, r = -0.34, P less than 0.01). Thus, age modifies the compensatory mechanisms that regulate the cardiac output during exercise. Young and old patients alike show increases in end-diastolic volume and ejection fraction to maintain exercise cardiac output. The higher exercise heart rate in the younger subjects suggests a decrease in cardiac responsiveness to adrenergic stimulation associated with aging.