Bidimensional passive and active mechanical behavior of rat tail artery segments in vitro

The arterial wall mainly contains elastin, collagen, and smooth muscle arranged in concentric layers that are interconnected. Because of their interrelated architecture, circumferential and longitudinal deformations affect each other. Therefore, to develop a complete picture of arterial mechanics, whole vessel segments have to be studied under bidimensional states of deformation. The purpose of this study is to examine the passive and active mechanical behavior of intact segments of rat tail arteries subjected in vitro to various levels of pressures and longitudinal loads. Using photographic methods of deformation measurement, diameter and length of the segment were analyzed as a function of pressure and of longitudinal force under passive and active smooth muscle conditions. The passive pressure-diameter relationship shows maximum compliance around 6.6 kPa for all longitudinal loads investigated, while maximal contraction occurs at 13.3 kPa under in vivo longitudinal loads. The segment length increases with pressure at small longitudinal loads not only under passive, but even more markedly so under active smooth muscle conditions. On the other hand, at large longitudinal forces the artery length decreases on pressurization, both under passive as well as under active states of the smooth muscle. For the particular range of longitudinal loads corresponding to the individual prestretches found in situ, the length of the vessel segment not only remains constant with pressure, but also remains the same in magnitude, both under passive and active smooth muscle conditions.