Introduction

Since 1990 a growing interest has developed for the dimensions, composition and structure of the arterial wall, specifically of such elastic arteries as the ascending and descending aorta and the carotid arteries. Functionally, the elastic arteries dampen the pressure pulse associated with a given volume pulse as ejected by the heart by an increase in cross-sectional area, thereby absorbing temporarily the volume pulse. The arterial wall will respond to a chronically elevated blood pressure by an increase in wall thickness to maintain wall stress at the same level. To what extent the increase in wall thickness is associated with a change in wall structure and composition, or can be regarded as a prelude to pathophysiological changes, like atherosclerosis, is still subject to debate. To be able to shed light on these relations, if any, direct and local information, among others, about the end-diastolic artery diameter and its change during the cardiac cycle, wall thickness and local blood pressure are required. These data allow the computation of the Young's modulus, a measure of elasticity, which characterizes the mechanical properties of the wall independent of wall mass, as well as the compliance, a measure of blood volume storage capacity which is of relevance for the hemodynamics.

The dimensions, mass and composition of the arterial wall do not only change in response to the transmural (pulsatile) pressure, but also in relation to the prevailing wall shear stress, i.e. the drag exerted by the flowing blood on the wall.