Circulation, Vol 83, 2029-2037, Copyright © 1991 by American Heart Association
DC Homans, DD Laxson, E Sublett, T Pavek and M Crampton
BACKGROUND. Transient reversible myocardial dysfunction has been documented
after episodes of exercise-induced ischemia. This study was undertaken to
determine whether the duration or intensity of exercise affects the
severity of postischemic dysfunction in this setting. METHODS AND RESULTS.
Ten dogs were instrumented with ultrasonic microcrystals for measurement of
wall thickening, with circumflex coronary artery flow probes, and with
hydraulic occluders. Dogs performed low-intensity exercise, which was
sufficient to increase coronary perfusion 50% above control, and
high-intensity exercise, which was sufficient to double coronary blood
flow. To investigate the effects of exercise intensity on postischemic
dysfunction, we had dogs perform high-intensity exercise for 5 minutes in
the presence of a stenosis. On the alternate day, dogs performed
low-intensity exercise for 10 minutes in the presence of a stenosis. These
two protocols provide equivalent coronary flow debts. Mean transmural blood
flow during high-intensity exercise without stenosis (2.61 +/- 0.54
ml/min/g) was significantly higher than that during low-intensity exercise
(1.74 +/- 0.61 ml/min/g, p less than 0.002). During high- intensity
exercise with coronary artery stenosis, subendocardial blood flow was
significantly lower than that during low-intensity exercise with stenosis
(0.64 +/- 0.40 versus 1.08 +/- 0.28 ml/min/g, p less than 0.02). This
difference in subendocardial perfusion was associated with greater degrees
of regional dysfunction during exercise (circumflex wall thickening was 44
+/- 23% of control for high-intensity exercise versus 60 +/- 18% of control
for low-intensity exercise, p less than 0.01). In addition, from 10 to 30
minutes after exercise, wall thickening in myocardium perfused by the
circumflex coronary artery remained significantly lower after
high-intensity exercise than that after low-intensity exercise. To assess
the effects of exercise duration on the severity of postischemic
dysfunction, we had dogs perform low-intensity exercise in the presence of
a coronary stenosis for 10 minutes and low-intensity exercise for only 5
minutes on alternate days. Systolic wall thickening was significantly lower
after low-intensity exercise for 10 minutes than after low-intensity
exercise for 5 minutes. CONCLUSIONS. High-intensity exercise results in
greater degrees of subendocardial hypoperfusion and greater degrees of
regional dysfunction both during and after exercise-induced ischemia than
does low-intensity exercise. Second, exercise duration also exerts an
effect on the severity of postischemic dysfunction, although the magnitude
of this effect is less important than the effect of exercise intensity.
ARTICLES
Effect of exercise intensity and duration on regional function during and after exercise-induced ischemia
Department of Medicine, University of Minnesota Medical School, Minneapolis.
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