Cardiovascular response to exercise in younger and older men.

Measurements of cardiac performance for humans at various ages is influenced by the variable examined, the population and techniques employed, and the factors that co-vary with age, including the presence of disease and physical conditioning. Interstudy differences in the extent to which occult coronary disease is present in older subjects and in the level of physical conditioning among subjects may underlie the variable perspectives contained in the literature of how aging affects cardiovascular function. In carefully screened, highly motivated but not athletically trained community-dwelling subjects, resting cardiovascular parameters are not age related except for systolic blood pressure, which increases with age. During vigorous exercise the mechanisms used to achieve a high level of cardiac output shift from a dependence on a catecholamine-mediated increase in heart rate and inotropy to a dependence on the Frank Starling mechanism. One reason for the age difference in cardiovascular response to exercise may be a diminished responsiveness to beta-adrenergic stimulation in these subjects. In other elderly subjects who cannot exercise to high work loads, a decline in stroke volume as well as heart rate at peak exercise has been observed. Whether the inability of these individuals to augment stroke volume is caused by a decrease in the ability of the heart to increase diastolic filling, by a decrease in systolic pump function caused by an increased afterload, by intrinsic myocardial contractile defects, or by a greater diminution of the cardiovascular response to beta-adrenergic stimuli is presently unknown.