Structural and Functional Properties of Venous Wall: Relationship between Elastin, Collagen, and Smooth Muscle Components and Viscoelastic Properties

The aims of this work were (1) to analyze the viscoelastic behavior of different venous segments and their differences, considering the structural characteristics (elastin, collagen, and smooth muscle content) of the venous wall; (2) to analyze the venous biomechanical behavior by means of the histological characteristics of the veins. Nine healthy male Corriedale sheep were included. One vein was selected from each animal to evaluate its biomechanical properties: (a) anterior vena cava, (b) right jugular vein, and (c) right femoral vein. Each selected vein was instrumented with pressure and diameter sensors. After excision, a small ring-shaped sample was set apart from each segment for histological analysis. The amounts of elastin, collagen and smooth muscle were correlated to calculated biomechanical parameters (high- and low-pressure compliance and viscosity). Conclusions are the following: (1) the viscoelastic behavior of the venous wall varies depending on the vascular territory, and it is associated with the variation of the histological structure. These differences involve muscle (both smooth and striated), elastin, and collagen contents. (2) In addition, the quantity of collagen was negatively correlated with high- and low-pressure compliances, and (3) the smooth muscle content was higher in peripheral veins and is positively correlated with venous wall viscosity. 1. Introduction The use of veins as grafts has been introduced in clinical practice with several purposes: (a) aortocoronary saphenous vein grafts in myocardial direct revascularization [1]; (b) to perform arteriovenous fistulae in hemodialyzed patients [2]; (c) to perform peripheral revascularization, including the confection of interposing vein cuffs in expanded polytetrafluoroethylene bypasses [3]. For the aforementioned reasons, the use of veins has been extensively indicated in both ischemic and hemodialyzed patients. However, there are several complications, such as intimal hyperplasia, which has been considered to be produced by a mechanical mismatch between the native arteries and the grafts [4]. Consequently, the functional parietal biomechanical behavior of blood vessels has an essential role determining the performance of the cardiovascular system, both in physiological and pathological conditions. Even though this is true for both veins and arteries, there is an imbalance between the existing studies and available information regarding the arterial wall and those related to the venous wall mechanics, which could be explained through several factors (e.g., methodological