To study the effects of smooth muscle contraction and relaxation on the
strain and stress distribution in the vascular wall, a mathematical
model was proposed. The artery was assumed to be a thick-walled
orthotropic tube made of nonlinear, incompressible elastic material.
Considering that the contraction of smooth muscle generates an active
circumferential stress in the wall, a numerical study was performed
using data available in the literature. The results obtained showed that
smooth muscle contraction affects the residual strains which exist in a
ring segment cut out from the artery and exposed to no external load.
When the ring specimen is cut radially, it springs open with an opening
angle. The predicted monotonic increase of the opening angle with
increasing muscular tone was in agreement with recent experimental
results reported in the literature. It was shown that basal muscular
tone, which exists under physiological conditions, reduces the strain
gradient in the arterial wall and yields a near uniform stress
distribution. During temporary changes in blood pressure, the increase
in muscular tone induced by elevated pressure tends to restore the
distribution of circumferential strain in the arterial wall, and to
maintain the dow-induced wall shear stress to normal level. (C) 1999
Biomedical Engineering Society. S0090-6964(99)00404-X.