One primary goal of the laboratory has been to determine the effects of age, gender, lifestyle variables and cardiovascular (CV) disease on cardiac performance, both at rest and during exhaustive dynamic exercise. We have utilized several techniques to accomplish this mission, including determination of maximal aerobic capacity (VO2MAX), blood volume measurements and gated cardiac blood pool scanning. Recent examples of these studies are shown. A. To determine whether expanded plasma, red cell and total blood volumes are major contributors to the augmented aerobic capacity of older endurance athletes, we measured these blood volume components in 7 endurance trained men age 63plus/minus5 years and 12 sedentary age matched controls. Plasma, red cell and total blood volumes, normalized for body weight, were all greater in the athletic men, each p lessor than .05. Furthermore, when the athletes and control subjects were combined, VO2MAX was directly related to plasma volume (r=0.61, p lesser than.01), red cell volume (r=0.46, p lesser than.05) and total blood volume (r=0.60, p lesser than .01) by linear regression analysis. In multivariate analyses incorporating conditioning status, fat-free body mass and blood volume components, plasma volume (or total blood volume) was independent predictor of VO2MAX. B. To evaluate CV performance throughout prolonged submaximal endurance exercise (PSE), 17 healthy BLSA volunteers aged 53plus/minus5 years performed upright cycle ergometry at 70% of peak VO2. Cardiac volumes were acquired by gated cardiac scans at rest and every 10 minutes during PSE until exhaustion. Although VO2 did not change during PSE at this constant work rate, arteriovenous oxygen difference declined 11% and cardiac output (CO) increased 19% between 10 minutes and end PSE. The CO increase was mediated by a 9% increase in both heart rate and stroke volume and a 7% increase in ejection fraction. Thus, cardiac performance increases progressively during PSE and peripheral factors, rather than cardiac fatigue, limit exercise performance.
