Arterial distensibility and compliance in hypertension

Under normal circumstances arteries, especially the larger elastic ones, distend during systole, and hence are able to store volume energy during this phase of the cardiac cycle. In this way the increase in blood pressure during systole will be leveled off. The amount of energy that can be stored depends not only on the degree of distension (distensibility), but also on the initial diameter of the vessel--two parameters actually determining the compliance of an artery. In both established and borderline hypertension distensibility and compliance of the larger elastic arteries are reduced, as compared with normotensives, but not of the radial artery, at least in patients with established hypertension. In these patients this artery shows a pronounced increase in intima-media thickness. The elastic modulus of the radial artery is not different in hypertensive and normotensive subjects. In the present state of the art, it cannot be concluded whether the loss of artery wall distensibility is caused solely by the increase in blood pressure or that also structural wall changes are involved. In borderline hypertensive patients distensibility and compliance of the elastic arteries are diminished as compared with normotensive subjects. The loss of distensibility already occurs in the fourth age decade and is not homogeneous along the carotid artery bifurcation. The distensibility is significantly lower at all levels in the carotid artery bulb than in the common carotid artery, the proximal part of the bulb, where the baroreceptors are predominantly located, being most affected. This pattern is similar to that observed in normotensive subjects in the sixth age decade, indicating that the carotid arteries age faster in borderline hypertensive than in normotensive subjects.