PATHOPHYSIOLOGY AND NATURAL HISTORY EXERCISE Elfect of isotonic exercise training on left ventricular volume during upright exercise

To determine the changes in left ventricular volume and their time course during exercise we studied 30 runners. Left ventricular end-diastolic and end-systolic volumes were measured from biapical two-dimensional echocardiograms recorded during graded upright bicycle exercise. The validity of this echocardiographic technique was assessed by comparing measurements at rest and exercise with results obtained by gated equilibrium radionuclide angiography in 10 patients with coronary artery disease. Although the absolute volume measurements were lower by echocardiography, ejection fraction was not significantly different and the directional changes in volume during exercise were comparable. In the runners, resting left ventricular end-diastolic volume measurements by echocardiography correlated with their maximum bicycle exercise endurance times (r = .80). Left ventricular end-diastolic volume, stroke volume, and ejection fraction increased during exercise with the most marked changes occurring in the first half of exercise. Systolic blood pressure/end-systolic volume (SBP/ESV) also increased during exercise, but the largest change occurred during the second half of exercise. Left ventricular volumes were larger in the 12 competitive marathon runners (maximum exercise duration 27 min) as compared with the 18 noncompetitive runners (exercise duration < 23 min): resting end-diastolic volume 130 ± 29 (SD) ml vs 87 ± 20 ml (p < .001), respectively. During exercise the competitive runners exhibited a larger increase in end-diastolic volume and the noncompetitive athletes showed a greater increase in SBP/ESV. Therefore, highly trained competitive marathon runners make greater use of the less energy-consuming Frank-Starling mechanism to accomplish high levels of isotonic exercise performance as compared with less well-trained runners. Circulation 72, No. 6, 1237-1243, 1985. LONG-TERM isotonic exercise training results in a reduction in resting heart rate and an increase in left ventricular end-diastolic volume.`' Also, isotonically trained individuals are able to achieve higher values for stroke volume, cardiac output, and exercise workload as compared with untrained individuals, despite similar values for peak exercise heart rate, blood pressure, and ejection phase indexes of left ventricular performance.5' 6 However, it is unclear whether the increased left ventricular output during exercise in athletes is related simply to the larger resting end-diastolic volume that persists during exercise, or whether further From the Division of Cardiology, Department of Medicine, University of Texas Health Science Center, and The Veterans Administration Hospital, San Antonio. Supported in part by The Veterans Administration and NIH training grant 5T32 HL07350-05. Address for correspondence: Michael H. Crawford, M.D., Department of Medicine, Division of Cardiology, University of Texas Health Science Center, 7703 Floyd Curl Dr., San Antonio, TX 78284. Received Jan. 30, 1985; revision accepted Sept. 5, 1985. Vol. 72, No. 6, December 1985 increases in left ventricular volume occur. If the latter is the case, what is the time course of volume changes during exercise? The relative contribution of increases in contractile state as estimated by the systolic pressure-volume relationship and the time course of these changes are poorly understood. Therefore we sought to determine whether the large ventricular end-diastolic volume of the trained individual can be increased further to take advantage of the less energy-consuming Frank-Starling effect and if so, to determine when it occurs during exercise. We also wished to evaluate changes in the systolic pressure-volume relationship during exercise and compare these with the changes in end-diastolic volume. Finally, the response of the left ventricle during exercise in highly trained competitive athletes was compared with that in less well-trained individuals to ascertain any differences during exercise that would explain the greater performance of the former. For this study, two-dimensional echocardiography was used during exercise to measure left ven1237 by gest on A ril 7, 2017 http://ciajournals.org/ D ow nladed from