Ventriculoarterial Coupling During Exercise in Normal Human Subjects

To examine the relative roles of ventricular contractility and loading conditions for cardiovascular adjustment during exercise, 10 normal human subjects were studied using a framework of ventriculoarterial coupling. Anaerobic threshold was evaluated to determine the work rates of aerobic and anaerobic exercise. Ventricular contractile properties were quantified by the slope of the end-systolic pressure-volume relationship (ventricular elastance) and arterial system properties were expressed by the end-systolic pressure-stroke volume relationship (arterial elastance). During aerobic exercise, left ventricular end-diastolic volume and stroke volume were increased by 14 and 33%, with plasma norepinephrine levels being doubled. Arterial elastance was reduced by 30%, but ventricular elastance did not change significantly. During anaerobic exercise, ventricular end-diastolic volume returned to the resting value, while stroke volume remained increased by 31%. In contrast to aerobic exercise, ventricular elastance rose substantially by 89% in association with about a 10 times increase in plasma norepinephrine. Arterial elastance remained the same as in aerobic exercise. Thus, the increase in stroke volume was primarily mediated by changes in loading conditions during aerobic exercise and by enhanced contractility during anaerobic exercise.