Attenuation of cardiovascular adaptations to exercise in frail octogenarians

To determine the mechanisms underlying increased aerobic power in response to exercise training in octogenarians, we studied mildly frail elderly men and women randomly assigned to an exercise group (n = 22) who participated in a training program of 6 mo of physical therapy, strength training, and walking followed by 3 mo of more intense endurance exercise at 78% of peak heart rate or a control sedentary group (n = 24). Peak O-2 consumption ((V)over dotO(2 peak)) increased 14% in the exercise group (P < 0.0001) but decreased slightly in controls. Training induced 14% increase (P = 0.027) in peak exercise cardiac output ((Q)over dot), determined via acetylene re-breathing, and no change in arteriovenous O-2 content difference. The increase in (Q)over dot was mediated by increases in heart rate (P = 0.009) and probably stroke volume (P = 0.096). Left ventricular stroke work also increased significantly. In the men, the increase in V. O-2 peak was exclusively due to a large increase in peak (Q)over dot (22%). In the women, the gain in (V)over dotO(2 peak) was due to small increases in (Q)over dot and O-2 extraction from skeletal muscles. Pulse pressure normalized for stroke volume and arterial elastance during peak effort did not change with training. Controls showed no changes. The results suggest that, although frail octogenarians have a diminished capacity for improvement in aerobic power in response to exercise training, this adaptation is mediated mostly by an increase in (Q)over dot during peak effort. Furthermore, (Q)over dot likely plays a greater role in the adaptive increase in (V)over dotO(2 peak) in old men than old women.