Cardiovascular responses to lower body negative pressure in trained and untrained older men

To determine whether aerobic conditioning alters the orthostatic responses of older subjects, cardiovascular performance was monitored during graded lower body negative pressure in nine highly trained male senior athletes (A) aged 59-73 yr [maximum O₂ uptake (V̇O(2 max)) = 52.4 ± 1.7 ml · kg^-1 · min^-1] and nine age-matched control subjects (C) (V̇O(2 max) = 31.0 ± 2.9 ml · kg^-1 · min^-1). Cardiac volumes were determined from gated blood pool scintigrams by use of ^99mTc-labeled erythrocytes. During lower body negative pressure (0 to -50 mmHg), left ventricular end-diastolic and end- systolic volume indexes and stroke volume index decreased in both groups while heart rate increased. The decreases in cardiac volumes and mean arterial pressure and the increase in heart rate between 0 and -50 mmHg were significantly less in A than in C. For example, end-diastolic volume index decreased by 32 ± 4 ml in C vs. 14 ± 2 ml in A (P < 0.01), mean arterial pressure declined 7 ± 5 mmHg in C and increased by 5 ± 3 mmHg in A (P < 0.05), and heart rate increased 13 ± 3 beats/min in C and 7 ± 1 beats/min in A (P < 0.05). These data suggest that increased V̇O(2 max) among older men is associated with improved orthostatic responses.