The Reason for the Shape of the Distensibility Curves of Arteries

Abstract

It is characteristic of arteries that they do not obey Hooke's law, but resist further stretch more strongly, the more they are stretched. It appears that this might be due to the combination of elastin fibers in the elastic laminae, with the much less distensible collagenous libers in the media and adventitia, more and more of which reach their 'unstretched length' as distension is increased. This has been verified on human iliac arteries, from autopsy, by comparing the 'elastic diagrams' (tension vs. circumference) before and after differential digestion of collagen by formic acid, and digestion of elastin by crude trypsin (containing an elastase). This proved that the resistance to stretch at low pressures was almost entirely due to elastin fibers, that at physiological pressures due to both collagenous and elastin fibers, but dominantly to collagen, and that at high pressures almost entirely due to collagenous fibers. In future work on the effect of age on the elasticity of iliac arteries, the initial slope of the elastic diagram can be taken as an index of the state, or number, of the elastin fibers, and the final slope as an index of the state, or number, of collagenous fibers.

Determination of the layer-specific distributed collagen fibre orientations in human thoracic and abdominal aortas and common iliac arteries

“…Figure 2 shows a tissue sample mounted in the fixture before stretching it biaxially. Applying a controlled stretch was essential during tissue preparation since it not only approximates the in vivo conditions of the vessel wall, but also straightens the collagen fibres, resulting in an increasingly coherent orientation necessary to perform accurate angular measurements [26,40,45]. The stretched sample and fixture were then put into a bath of 4 per cent formaldehyde for chemical fixation.…”

“…To approximate the in vivo strain state of the blood vessel, all of the samples investigated were pre-stretched biaxially with a specially designed fixture, followed by chemical fixation in formalin while distended [2]. This process resulted in improved fibre orientation coherence [26,30,40]. The measurements were performed using a Zeiss universal stage attached to a Zeiss polarizing microscope (Carl Zeiss IMT GmbH, Vienna, Austria) [27], enabling the measurement of two Euler angles and thus fully defining the local orientation of the mostly straightened fibres in the three-dimensional space.…”

Biomechanical Rupture Risk Assessment - A consistent and objective decision-making tool for Abdominal Aortic Aneurysm patients

“…Due to the aneurysm-related proteolytic degeneration of structural proteins [83], an AAA wall mechanically differs significantly from a normal aorta. Specifically, the AAA wall is less anisotropic, and, at the same time, the nonlinearity of the stress-strain relation is more pronounced [47].…”

“…Collagen fibers in the vascular wall have a major impact on the mechanical properties at higher loads (i.e., at the condition experienced by the aneurysm wall) [82,83]. Specifically, it seems that collagen is the only remaining histologic structure able to carry the high mechanical load of later-stage aneurysms [84,85].…”

“…Collagen is under continuous turnover and the maintenance of the collagen network relies on a delicate balance between synthesis by fibroblasts and degradation by metalloproteinases. A malfunction of collagen turnover could fail to result in homeostasis and determine AAA disease (i.e., collagen synthesis is insufficient to counteract the increasing mechanical stress), such that aneurysm growth further accelerates [83].…”