AJP - Heart and Circulatory Physiology, Vol 243, Issue 5 698-H707, Copyright © 1982 by American Physiological Society
Myocardial blood flow and function with critical coronary stenosis in exercising dogs
K. P. Gallagher, G. Osakada, M. Matsuzaki, W. S. Kemper and J. Ross Jr
Critical stenosis of coronary arteries does not alter myocardial blood flow
(MBF) at rest, but eliminates hyperemia and corresponds to a degree of
arterial narrowing that expends subendocardial vasodilator reserve. Because
subepicardial vasodilator reserve remains with critical stenosis at rest,
we tested the significance of this reserve in six exercising dogs
chronically instrumented to measure MBF (microspheres), regional function
(systolic wall thickening with sonomicrometers), and coronary blood flow
velocity (CBFV, pulsed Doppler). Critical stenosis produced with a
hydraulic occluder limited CBFV and mean MBF to the resting level during
treadmill exercise, but MBF was maldistributed. Subendocardial MBF
decreased 50% (P less than 0.05) and subepicardial MBF increased 104% (P
less than 0.01) compared with resting control conditions, suggesting that a
transmural "steal" phenomenon had occurred, with augmented MBF in the
subepicardial region at the expense of subendocardial MBF. Systolic wall
thickening decreased markedly from 31.5 +/- 6.8 to 9.4 +/- 2.0% (P less
than 0.01) during exercise, indicating that use of subepicardial
vasodilator reserve with critical stenosis had little sustaining effect on
regional contractile performance. Rather, subepicardial vasodilator reserve
is potentially deleterious, inasmuch as a steal effect could contribute to
reduced subendocardial perfusion, the primary determinant of systolic wall
thickening.
