INTERRELATIONSHIPS BETWEEN LEFT-VENTRICULAR VOLUME AND OUTPUT DURING EXERCISE IN HEALTHY-SUBJECTS

To better characterize the relationship between left ventricular volume response and improved ventricular ejection and output during supine exercise in normal subjects, 36 healthy asymptomatic volunteers (age 39 +/- 17 yr) were studied with radionuclide ventriculography during recumbent bicycle ergometry. Relative changes in left ventricular end-diastolic and end-systolic volume were measured at rest and during exercise by a modification of the radionuclide counts-based method that accounted for variability in stress blood pool counts. A biphasic response was noted in left ventricular end-diastolic volume with an initial increase in early exercise (8.5 +/- 11% at 200 kpm/min and 11 +/- 12% at 300 kpm/min) followed by a progressive and significant decline at peak exercise (-3.3 +/- 18% at 547 +/- 140 kpm/min; P < 0.05). There was substantial variation in end-diastolic volume response at peak exercise in the group as a whole, which could be more closely related to changes in end-systolic volume (r = 0.84, P < 0.0001) than in heart rate (r = -0.57, P < 0.01) or age (r = 0.36, P < 0.05) of the study subjects. Despite the decline in ventricular filling, systolic function appeared to improve dramatically at peak exercise (change in left ventricular ejection fraction 15.5 +/- 6.4, P < 0.0001). Although not directly related to increasing systolic ejection, end-diastolic volume was directly related to the percent change in stroke volume at peak exercise among the study subjects (r = 0.88, P < 0.0001). We conclude that progressive supine exercise is characterized by marked augmentation of left ventricular ejection, which is not directly related to increased left ventricular preload. In contrast, left ventricular end-diastolic volume was directly related to the change in stroke volume noted during progressive recumbent exercise.