Biomechanical Study of Vascular Walls

Abstract
It has been required to determine the stress distribution in a vascular wall because it may be one of the most important factors for cardiovascular diseases. The objective of this study is to analyze it by the finite element method which has been widely used in practical engineering problems.Vascular walls mainly consist of three structural components; elastin, collagen and smooth muscle. Each component is considered to have its unique and characteristic mechanical properties. It is necessary, therefore, to determine them as the fundamental data for the finite element analysis. Mechanical properties of bulk vascular walls and of each structural component were first studied experimentally by an extraction method. It was found that smooth muscle plays almost no role in the static mechanical properties of bulk vascular walls, and that elastin has high deformability and low strength, while collagen is a stiff and strong component. Stresses of elastin and of collagen can be related to their strains by exponential functions.Stresses developed in a vascular wall under static pressure were then analyzed by the finite element method. The structure of wall was assumed to be an aggregate of three different components; the elastin component, the collagen one and the one consisting of homogeneous mixtures of elastin, collagen and smooth muscle. An incrementally linear elastic model was used for the calculation. The results obtained showed that the stress distribution in a wall is very complicated and the elements of collagen in tunica media take remarkably higher stress values than the other two elements. These high stresses in collagen elements induce rather high stresses in the adjacent structures in tunica media. It can be considered from these results that a damage in a vascular wall is more easily caused in the tunica media than in the endothelium so far as the stress distribution is concerned.