# Definition of arterial stiffness

## Stiffness of an object

Stiffness of an object is the measure that characterizes its resistance to deformation in response to the application of a force. In other words, it is physical (mechanical) property of being inflexible and hard to bend. The idea of flexibility is relative to stiffness: the more flexible an object is the less stiff it is. Stiffness of an object such as one on the figure (A) can be calculated as the ratio wherein the numerator is the force (1) applied on the body (in newtons or in pound force, lbf) and the denominator is displacement (2) produced by the force (in meters or inches).

## Arterial stiffness

In the simplest model arterial stiffness may be described as the rigidity of arterial wall that is an object in form of tube (B). Accordingly, the forces applied to the object (3) intend from the inside and increase the tube size (4) depending on the stiffness. The stressing force in large arteries is the pressure of pulsatile blood flow. The change in arterial size may be calculated as the change in cross-sectional area or the change in volume.

## Nota bene!

It should be noted that many terms exist in this field of knowledge, often with different interpretations. Therefore the term "arterial stiffness" is used as a generic term to avoid confusion. Some terms are also used. For example:

Compliance. This is the ratio of any volume change caused by a given pressure change in an artery. Compliance increases can be misleading because, whether stiff or elastic, a larger artery, with its greater cross-sectional area and volume, will tend to accommodate more volume for given pressures increase than will a smaller artery. The term "arterial stiffness" is sometimes used to signify the inverse of compliance. Distensibility. This is the relationship between the fractional change in compliance and the corresponding change in cross-sectional area or volume. The property of distensibility is useful in comparing arteries of different sizes.