Cardiovascular response to exercise in the healthy male septuagenarians: with reference to plasma norepinephrine

Hemodynamics during supine graded exercise were measured in 7 healthy aged and 20 young. The maximal work load in the aged was about one half of that in the young. Cardiac output (CO) increased linearly with increasing work load, but its maximal value was markedly lower in the aged than in the young (11.2 +/- 1.1 vs. 19.7 +/- 1.0 liter)min; M +/- S.E.) Although CO at each level of submaximal exercise was essentially the same in both groups, the aged had smaller increases in stroke volume (SV) and systemic vascular conductance (SC), corresponding to larger increases in heart rate and mean blood pressure. An increase in SV during exercise was achieved from a greater systolic emptying force rather than Frank-Starling effect. A small increase in SC suggested the decreased arteriolar vasodilation in the working muscles. Thus, in the aged, both the reduced myocardial contraction reserve and increased afterload contributed to a small increase in SV during exercise. Plasma norepinephrine concentration in the aged was higher than in the young at rest (240 +/- 37 vs. 159 +/- 30 pg/ml), and both groups showed similar high levels at exhaustion (715 +/- 121 vs. 702 +/- 99 pg/ml). These demonstrated that the sympathetic activity during exercise remained unchanged and the cardiac response to sympathetic stimulation declined with age.