CARDIOVASCULAR-RESPONSES TO EXERCISE - EFFECTS OF AGING AND EXERCISE TRAINING IN HEALTHY-MEN

Background Cardiac aging alters many of the acute responses to exercis e stress, but the extent to which chronic exercise tie, training) can alter or improve the effects of aging in humans is largely unknown. Me thods and Results Cardiovascular responses to graded supine exercise s tress (beginning at 200 kpm and increasing by 200 kpm every 3 minutes till exhaustion) were assessed using radionuclide ventriculography in 13 older (age, 60 to 82 years) and 11 young (age, 24 to 32 years) rigo rously screened healthy men before and after 6 months of endurance tra ining. Repeated-measures ANOVA was used to test significance. During e xercise, the old group had a lesser increase in heart rate (+105% old versus +166% young), a greater increase in mean blood pressure (+35% o ld versus +22% young), lesser increases in ejection fraction (+3 eject ion fraction units old versus +11 units young) and peak ejection rate (+62% old versus +119% young), a greater increase in end-diastolic vol ume index (+8% old versus -10% young), a lesser fall in end-systolic v olume index (-0% old versus -32% young), and a lesser increase in card iac index (+135% old versus +189% young) (all P<.01 young/old versus e xercise stage). Stroke volume index response to exercise was not diffe rent with aging (+14% old versus +6% young, P=NS). Exercise training i ncreased maximal oxygen intake by 21% in the older group (28.9+/-4.6 t o 35.1+/-3.8 mL.kg(-1).min(-1), P<.001) and by 17% in the young (44.5/-5.1 to 52.1+/-6.3 mL.kg(-1).min(-1), P<.001) and increased peak work load by 24% in the old and 28% in the young. Exercise training had no differential effects on old versus young men. Among all subjects, trai ning significantly reduced the resting heart rate by 12% (-8 beats per minute) and increased resting end-diastolic volume index by 13% (+9 m L/M(2)) and resting stroke volume index by 18% (+7 mL/M(2)) (all P<.O1 ). At peak,exercise, cardiac index increased by 16% (+1.07 L.M(-2).min (-1)) compared with before training, which was the result of an increa se in stroke volume of 18% (+7 mL/M(2)) (P<.001); peak heart rate was unchanged. The increase in stroke volume index at peak exercise was th e result of both a 12% increase in end-diastolic volume index (+8 mL/M (2)) (P<.01) and an increase in ejection fraction (+3 ejection fractio n units) (P<.05) at peak exercise. The increased ejection fraction at peak exercise occurred despite a 9% increase in systolic blood pressur e (+18 mm Hg) (P<.01), suggesting an increase in contractility. Thus, both the young and old increased peak exercise cardiac output by use o f the Frank-Starling mechanism tie, cardiac dilatation) as well as an increase in ejection fraction. Conclusions We conclude that there is a n age-associated decline in heart rate, ejection fraction, and cardiac output responses to supine exercise in healthy men. Although the stro ke volume responses of the young and old are similar, the old tend to augment stroke volume during exercise more through cardiac dilatation, with an increase in end-diastolic volume (+8%) but without much chang e in ejection fraction (+3 ejection fraction units), whereas the young rely more on an increase in the ejection fraction (+11 ejection fract ion units) with no cardiac dilatation (-10%). Despite the significant cardiovascular changes that occur in the response to a single bout of exercise with aging, adaptations to chronic exercise training were not different with aging and included improvements in maximal workload an d increases in ejection fraction, stroke volume index, and cardiac ind ex at peak exercise.