Compliance (physiology) - Blood Vessels

Blood Vessels

The terms elastance and compliance are of particular significance in cardiovascular physiology and respiratory physiology. An increase in blood volume occurs in a vessel when the pressure in that vessel is increased. The tendency of the arteries and veins to stretch in response to pressure has a large effect on perfusion and blood pressure. This physically means that blood vessels with a higher compliance deform easier than lower compliance blood vessels under the same pressure and volume conditions. Venous compliance is approximately 30 times larger than arterial compliance. Compliance is calculated using the following equation, where ΔV is the change in volume, and ΔP is the change in pressure:

Physiologic compliance is generally in agreement with the above and adds dP/dt as a common academic physiologic measurement of both pulmonary and cardiac tissues. Adaptation of equations initially applied to rubber and latex allow modeling of the dynamics of pulmonary and cardiac tissue compliance.

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.