CARDIAC-OUTPUT AND LEFT-VENTRICULAR FUNCTION IN RESPONSE TO EXERCISE IN OLDER MEN

Studies of the cardiovascular response to exercise in older subjects have presented conflicting data regarding left ventricular function, the cardiac output - oxygen consumption (Q-Vo2) relationship, and the pattern of change in Q, stroke volume (SV), and arteriovenous O2 difference. We have examined the cardiovascular response to submaximal and strenuous exercise in 96 men of mean age 63 years during an incremental treadmill test with Q determined by CO2 rebreathing, and in 12 subjects studied during incremental supine exercise with left ventricular volumes evaluated by radionuclide angiocardiography. During treadmill exercise the Q was approximately 10% lower than reported for younger samples, with a lower intercept of the Q - Vo2 relationship. During near-maximal exercise Q was approximately 15 L . min-1, with SV of 95 mL plateauing or showing a small decline in heavy work. Peak arteriovenous 02 difference (150 + mL . L-1) approached values of the young. During the supine exercise SV increased from rest to exercise, with a consistent increase in ejection fraction (rest, 66%, to peak exercise, 76%). In contrast to a prior report, the end-diastolic volume was constant, with the increase of SV attributable to a reduced end-systolic volume. Also, in contrast to a number of reports in older subjects, our findings show only small losses in cardiovascular response, and in left ventricular performance during light through strenuous exercise.