Haemodynamic Abnormalities in Hypertensive Patients: A Review of the Influence of Vasodilating Drugs

Mean arterial pressure is determined primarily by cardiac output and total peripheral resistance, in addition to blood volume and compliance of the arterial system. The regulation of these determinants occurs via reflex neurogenic mechanisms and metabolic or humoral mechanisms. The haemodynamic situation in the early stages of arterial hypertension is characterized by a slight hypercirculatory state due to a moderate increase in heart rate and cardiac output, whereas the total peripheral resistance is increased only moderately, if at all. In later stages, however, a progressive increase in total peripheral resistance prevails, accompanied by a decrease in left ventricular performance due to the development of left ventricular hypertrophy, changes in ventricle geometry and coronary heart disease. A pharmacologically-induced decrease of total peripheral resistance by means of vasodilators, therefore, represents a logical approach to therapy, at least of advanced hypertension. Vasodilators can be classified into three categories: those with preferential activity on the arterial resistance vessels, eg hydralazine, diazoxide, minoxidil; those with preferential activity on venous capacitance vessels, eg organic nitrates; and those with activities on both branches, eg sodium nitroprusside, urapidil, prazosin and other a-blockers. Brief reference is made to new and possibly more acceptable vasodilators--in particular carvedilol and prizidilol.