Journal of Applied Physiology, Vol 51, Issue 5 1098-1102, Copyright © 1981 by American Physiological Society
Effect of exhaustive exercise on myocardial performance
G. K. Grimditch, R. J. Barnard and H. W. Duncan
Several investigators have reported ultrastructural changes in hearts of
animals exercised to exhaustion. The present study was designed to
determine whether functional changes occur in the intact heart at
exhaustion. Adult mongrel dogs (n = 8) were chronically instrumented to
measure cardiac output, coronary blood flow, aortic blood pressure, left
ventricular pressure, +dP/dtmax, and -dP/dtmax. After recovery, the dogs
were run to exhaustion at a constant work load, eliciting approximately 70%
of maximum heart rate. The exhaustive bouts were terminated when the
animals either refused or were unable to continue running, at which time
their rectal temperatures approaches 42.2 degree C. The mean exhaustion
time was 76.7 +/- 11.8 min. All parameters increased from rest to steady
state with the exception of stroke volume (23.2 +/- 4.9 vs. 20.5 +/- 1.6
ml), which remained constant. In the transition from steady state to
exhaustion, only +dP/dtmax (6,652 +/- 291 vs. 7,689 +/- 479 Torr/s) and
-dP/dtmax (4,110 +/- 227 vs. 4,890 +/- 215 Torr/s) increased significantly;
all other values exhibited no significant change. Similarly, when maximum
cardiovascular parameters were measured before and after exhaustion, no
significant changes were found. These data show that cardiac contractile
function is not depressed in dogs as a result of exhaustive exercise.
