Quantitative Analysis of the Relationship between Blood Vessel Wall Constituents and Viscoelastic Properties: Dynamic Biomechanical and Structural In Vitro Studies in Aorta and Carotid Arteries
The purposes of this work were to perform in sheep a quantification of the elastic, viscous, and inertial moduli obtained in carotid and aortic artery segments during in vitro dynamic studies that mimic the normal circulatory function; a quantitative determination of collagen, elastin, and vascular smooth muscle of the carotid and aortic segments analyzed in vitro; the correlation between the amounts of each arterial wall constituent and the viscoelastic properties. To this end, nine healthy sheep were included. One artery was selected from each animal to evaluate its biomechanical properties: (a) in three sheep the ascending aorta, (b) in three the thoracic descending aorta, and (c) in the remaining three the proximal segments of the carotid artery. Each selected artery was instrumented with pressure and diameter sensors. After excision, a small ring-shaped sample was set apart from each segment for histological analysis. In conclusion, (a) the arterial compliance showed a positive association with the absolute and relative amount of the parietal elastin, and (b) arterial viscosity was positively associated with the relative amount of smooth muscle, and this association was increased when the correlation was calculated considering the amount of collagen as well as the amount of smooth muscle. 1. Introduction The relationship between the structure and the function of the tissues of the arterial wall has been analyzed for more than 50 years, being the work of Alan Burton one of the most important among those that focused the attention on this basic subject [1]. Indeed, the structural bases for the static and dynamic mechanical properties of the vascular wall have been extensively studied both in in vitro experiments [2] and in in vivo experimental animals [3]. Furthermore, the influence of the specific constituents of the arterial wall on the mechanical properties of the vessel has been investigated, focusing the analyses on determining their role in the elasticity of arteries [4]. The aforementioned structure/function vascular studies evaluated both the parietal constituents and the physiology of the vessel, using the standardized methods and techniques available, to estimate (a) the amount of elastin, smooth muscle, and collagen and (b) the viscoelasticity of the vascular wall. Since the technology and methodologies that ensure accurate measurements are continuously in evolution, it is very important to focus on this important fact. For instance, at the time in which Wolinsky and Glagov described the structural basis for the static mechanical
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