Mechanical factors in large artery disease and antihypertensive drugs

Hypertension may induce early alterations in large arteries by 2 mechanical stresses: one related to intravascular pressure, the other to blood flow dynamics. Distending pressure force acts in a circumferential direction, inducing decreased arterial distensibility. Arterial distensibility can be evaluated in humans by measurement of arterial compliance and pulse-wave velocity. It is well established that in chronic hypertension age and elevated pressure act together to increase arterial rigidity. Blood flow dynamics induce frictional forces in the endothelial surfaces of arteries. These forces, expressed by shear stress, are proportional to the viscosity of the blood and to the velocity gradient at the arterial wall. Measurement of blood viscosity and evaluation of velocity profile in the brachial arteries of hypertensive subjects have shown a reduction in wall shear rate and stress despite the elevation in blood viscosity. Several studies have shown that drug therapy that successfully reduces blood pressure does not necessarily improve arterial compliance. In contrast, few data are available on the effects of antihypertensive medication on arterial wall shear in humans. Arterial compliance and wall shear stress are 2 main therapeutic targets of potential importance in the physiopharmacologic approach to the effects of hypertension on atherogenesis.