Compliance (physiology)

Overview
Compliance is a measure of the tendency of a hollow organ to resist recoil toward its original dimensions upon removal of a distending or compressing force. It is the reciprocal of "elastance".

Blood vessels
The terms elastance and compliance are of particular significance in cardiovascular physiology. Specifically, the tendency of the arteries and veins to stretch in response to pressure has a large effect on perfusion and blood pressure.

Compliance is calculated using the following equation, where ΔV is the change in volume, and ΔP is the change in pressure:
 * $$C = \frac{ \Delta V}{ \Delta P} $$

Veins have a much higher compliance than arteries (largely due to their thinner walls.) Veins which are abnormally compliant can be associated with edema. Pressure stockings are sometimes used to externally reduce compliance, and thus keep blood from pooling in the legs.

The higher the compliance the more squishable the material, therefore steel has a lower compliance than a blood vessel.