Compliance

The term compliance is used to describe how easily a chamber of the heart or the lumen of a blood vessels expands expands when it is filled with a volume of blood. Physically, compliance (C) is defined as the change in volume (ΔV) divided by the change in pressure (ΔP).

C = ΔV / ΔP

For example, if a volume of blood is used to fill a cardiac chamber, the pressure within the chamber will increase, and it is the ratio of the change in volume to the change in pressure that represents the compliance of the chambers. The compliance of a biological tissue is not constant, meaning that at greater volumes there will be a disproportionate increase in pressure (i.e., compliance decreases as the chamber or blood vessel expands) as shown in the figure. Another way to view this is that the "stiffness" of the chamber or vessel wall increases at higher volumes and pressures.

Compliance is a fundamental property of a tissue; however, the compliance can be modified histological changes in the tissue (e.g., as occurs in cardiac and vascular disease) or by external influences that alter the mechanical properties of the tissue. Examples of this would be activation of smooth muscle in a blood vessel wall that decreases the compliance, or impaired relaxation of the ventricular chamber as it fills with blood.

Click below to learn more about the importance of compliance in

• Heart ventricles
• Blood vessels

Revised 04/06/07