Coronary hyperperfusion augments myocardial oxygen consumption
.
Ishibashi, Yutaka, Jianyi Zhang, Dirk J. Duncker, Christopher Klassen,
Todd Pavek, Robert J. Bache.
Cardiovascular Division, Department of Medicine, University of
Minnesota Medical School, Minneapolis, Minnesota, Current address:
Laboratory for Experimental Cardiology, Thoraxcenter, Erasmus
University Rotterdam, PO Box 1738, 3000 Dr, Rotterdam, The
Netherlands
APStracts 3:0116H, 1996.
This study was performed to test the hypothesis that increases in
myocardial oxygen consumption (MVO2) and myocardial contractile
function during exercise are flow-limited. Studies were performed in
fifteen chronically instrumented normal dogs. MVO2 and regional
percent systolic wall thickening were measured during control
conditions and during maximum vasodilation produced by infusion of
adenosine (20-75 [mu]g/kg/min) or adenosine combined with
nitroglycerine (0.4 [mu]g/kg/min) (TNG) into the left anterior
descending coronary artery during a three stage graded treadmill
exercise protocol. Adenosine and adenosine+TNG significantly
increased coronary blood flow by 298 +/- 26% and 306 +/-24%
(respectively) at rest, and by 135 +/- 7% and 146 +/- 9%
(respectively) during the heaviest level of exercise (each
p<0.01). Adenosine and adenosine plus TNG increased MVO2 at
rest, but this was associated with a parallel increase in heart rate,
so that MVO2/beat was not significantly changed. Systolic wall
thickening was also not changed by hyperperfusion during resting
conditions. However, MVO2/beat was increased by 12 +/- 4% with
adenosine and by 13 +/- 5% with adenosine+TNG during moderate
exercise, and by 23 +/- 5% with adenosine and by 27 +/- 4% with
adenosine+TNG during the heaviest level of exercise (each
p<0.05). Systolic thickening of the full left ventricular wall
did not change during hyperperfusion, but thickening in the
subepicardial layer was increased by 14 +/- 3% with adenosine and 18
+/- 3 % with adenosine+TNG during the heaviest level of exercise
(each p<0.05). There was no difference in wall thickening
between adenosine and adenosine+TNG. These findings imply that the
increases in myocardial oxygen consumption which occur during
exercise are limited by coronary blood flow.
Received 20 April 1995; accepted in final form 28 February 1996.
APS Manuscript Number H378-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96