AJP - Heart and Circulatory Physiology, Vol 263, Issue 2 597-H605, Copyright © 1992 by American Physiological Society
Time-varying wall stress: an index of ventricular vascular coupling
L. J. Dell'Italia, G. G. Blackwell, B. T. Thorn, D. J. Pearce, S. P. Bishop and G. M. Pohost
Department of Medicine, University of Alabama, Birmingham 35294.
Previous work in the isolated heart and intact circulation has suggested
that the relationship between wall stress and time during left ventricular
(LV) ejection is linear and that the slope, which will be referred to as
time-varying wall stress, increases in response to augmentation in
afterload. However, the etiology of the increase in slope has not been
determined in an intact animal. Magnetic resonance imaging coupled with
high-fidelity LV pressure measurement using a nonferrous catheter-tip
manometer generates a detailed assessment of wall stress in an animal model
where the thorax and pericardium have never been disturbed. Accordingly,
six anesthetized dogs were studied during autonomic blockade with atropine
and propranolol during angiotensin infusion, producing three widely
disparate left ventricular systolic pressures (87 +/- 7 vs. 124 +/- 13 vs.
152 +/- 10 mmHg, P less than 0.001). Time-varying wall stress did not
change from low to medium load (-42.4 +/- 9.5 to -27.3 +/- 22.3
g.cm-2.ms-1) but increased significantly at high load (-21.7 +/- 14.9
g.cm-2.ms-1, P less than 0.05). Analysis of the relative contribution of
pressure, chamber radius, wall thickness, and long-axis dimension to the
changes in time-varying wall stress demonstrated only the pressure
component to change its relative contribution at medium (P less than 0.001)
and high load (P less than 0.001). Therefore, we conclude that the increase
in time-varying wall stress results from augmentation of pressure in the
latter one-half of systole that is incompletely offset by shortening and
wall thickening.(ABSTRACT TRUNCATED AT 250 WORDS)
