AJP - Heart and Circulatory Physiology, Vol 243, Issue 3 379-H390, Copyright © 1982 by American Physiological Society
Epicardial deformation and left ventricular wall mechanisms during ejection in the dog
T. Arts, P. C. Veenstra and R. S. Reneman
Significant differences between epicardial and endocardial systolic stress
in the wall of the left ventricle (LV) have been predicted by various
models of LV mechanics. Yet a model incorporating transmural differences in
fiber orientation and torsion, defined as a rotation of the apex with
respect to the base around the long axis of the LV, predicts transmural
equalization of stress and shortening along the fiber direction during the
ejection phase. this equalization is due to an interplay between torsion
and myocardial contraction. To assess the model hypothesis, predicted
epicardial deformation during the ejection phase was compared with that
measured experimentally. For this purpose 45 sets of measurements were
performed in four open-chest dogs using a triangular array of inductive
gauges for the assessment of epicardial circumferential strain (epsilon c),
base-to-apex strain (epsilon z), and shear angle (gamma). Changes in shear
angle are directly related to LV torsion. LV end-diastolic pressure was
varied over a wide range (0-15 mmHg) by volume loading and bleeding. In the
control state, the slope of the shear angle vs. volume strain curve (volume
strain = 2 epsilon c + epsilon z), which is related to contraction, was
found to be 0.74 +/- 0.10 (mean +/- SD). This compares reasonably wih the
mathematical model prediction of a slope of 0.67. Due to an interplay
between torsion and contraction, left ventricular fiber stress and fiber
shortening might be uniformly distributed across the wall.
