The Influence of Vascular Smooth Muscle on the Development of Post-Stenotic Dilatation
A segment of the thoracic aorta distal to a stenotic ring in four rabbits was frozen with liquid nitrogen in order to determine whether post-stenotic dilatation (PSD) would develop in the absence of viable vascular smooth muscle (VSM). Four animals were similarly prepared except that the rings did not constrict the aorta. Another four served as controls, having constricting rings but no aortic freezing. PSD developed as expected in the nonfrozen stenosed animals (60% diameter increase in 8 weeks). Freezing was associated with a rapid dilatation of the vessel when compared to the proximal segment (56% diameter increase) which regressed to normal dimensions during the next 8 weeks. In spite of marked fibrosis of the frozen areas their static elastic moduli did not differ significantly from that of their dilated counterparts, although in all cases the segments distal to the constriction had significantly greater modulus values than those proximal to it. The dynamic elastic modulus of the frozen segments was significantly greater than that of the PSD region and the untreated areas proximal to the stenosis site.
We conclude that destruction of VSM by freezing prevents the development of PSD and that this may be due in part to the increased dynamic stiffness of the frozen vessels.
KeywordsDistal Segment Proximal Segment Dynamic Elastic Modulus Disturbed Flow Stenosis Site
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