Abstract

Arterial elasticity is a common index of medical semiology, easier to understand than blood pressure measurement. This chapter summarizes the most classical aspects which are important to understand in vascular medicine.

Copyright © 2007 S. Karger AG, Basel

In biophysics, the theory of elasticity deals with the relations between the forces applied to a body and its subsequent deformations [1-3]. The force per unit area is called the 'stress'. The deformation, described as the ratio of the deformation to its original form, is called the 'strain'. Because it is a ratio, strain is dimensionless. The slope of the strain-stress relationship is called 'elastic modulus'.

When forces act on a given solid body without displacing it, they will deform it, that is, cause a movement of the various parts of the body relative to one another. If the body regains its original form exactly when the force is removed it is said to be 'perfectly elastic'. If the body retains the deformation, then it is said to be 'plastic'. A large number of substances exhibit properties appropriate to both an elastic solid and a viscous liquid, and the deformation suffered by such a material will depend on both the magnitude of the stress and on the rate at which it is applied. Such substances are called 'visco-elastic'. It is to this large class that the arterial wall belongs.

In the case of biology of arterial vessels, the stress-strain relationship is simplified in terms of pressure relationship applied to a cylindrical vessel of constant length. The mechanical stress is represented by pressure and the strain by the change in 'diameter' (or volume). Because the relationship is nonlinear, the slope of the curve at a given pressure represents the elasticity (or its inverse, the stiffness) of the system. Elasticity and stiffness are both qualitative terms. The corresponding establishing quantitative values are called 'compliance' or 'distensibility'. The purpose of this chapter is to define the visco-elas-tic properties of the large artery walls in relation to their principal applications in vascular medicine, mainly in subjects with atherosclerosis. Arterial stiffness is the qualitative and most widely used term to define the visco-elastic properties of the vascular wall.

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