Introduction

Compliance of a vessel is the amount by which it will increase in volume for a given increase in distending pressure and is determined by the elastic properties of the vessel wall. A compliant vessel will accommodate a large volume of blood at low pressure and show little rise in pressure when a large volume of blood is ejected into it. It has long been appreciated that vascular compliance has an important influence on circulatory haemodynamics. The compliance of the large veins enables them to accommodate blood returning to the heart and thus influences preload on the heart and hence cardiac output. Similarly, the compliance of the aorta and large arteries enables them to accommodate blood ejected from the left ventricle. This reduces afterload, preventing an excessive rise in systolic blood pressure, and increases flow to the peripheral and coronary circulation when the aorta contracts as distending pressure falls during diastole. In this context the aorta has been referred to as the ‘second heart’. It has recently been appreciated that reduced compliance of the aorta may represent one of or, in certain groups, the most important predictor of cardiovascular mortality. This has renewed interest in the determinants and consequences of large artery compliance. In this chapter we focus on large artery compliance, reviewing its measurement, influence on haemodynamics, biomechanical determinants, alterations in physiological and pathophysiological conditions, importance as a cardiovascular risk factor and interventions which may modify large artery compliance.