Comparison of hemodynamic effects of exercise and isoproterenol infusion in normal young and old men

Hemodynamic comparison of ergometer exercise with isoproterenol infusion was carried out in normal young and old men, and age associated difference in responses to exercise and isoproterenol was evaluated. Ergometer exercises of 50, 100 and 150 W in young men, averaging 23.0 years, increased heart rate in linear fashion from 73.8 to 149.2, while stroke index was raised at 50 W and remained at the same level thereafter. The isoproterenol infusion of 0.02 and 0.04 microgram/kg/min increased heart rate, stroke index and cardiac index by similar amount to 50 and 100 W or ergometer exercise respectively. Ergometer exercise elevated systolic, diastolic and mean blood pressure linearly, while isoproterenol infusion lowered diastolic and mean blood pressure. In old men, averaging 73.0 years, the tolerable limit of ergometer exercise was 40 W. The increases in heart rate, cardiac index and blood pressure at the comparable work level were by similar amount to the young subjects, indicating the identical hemodynamic responses in young and old men at the same work load. Cardiac index to isoproterenol infusion of 0.02 microgram/kg/min showed less increase than ergometer exercise of 40 W in the aged. Furthermore, the increase in cardiac index to isoproterenol was less in old than young men, showing a decreased response to beta adrenergic stimulation in the aged.