NEWER THINKING ON THE HEMODYNAMICS OF HYPERTENSION

For more than 30 years there has been general agreement that in the es tablished phase of essential hypertension, the cardinal hemodynamic di sturbance is an increased total peripheral resistance with cardiac out put normal during rest, but subnormal during exercise. However, there are still different opinions about the hemodynamics in the starting ph ase of essential hypertension. Several studies from 1993-mainly perfor med in the offspring of hypertensive parents-reported high as well as low cardiac index values, depending on the patient selection and the m ethods used. Irrespective of whether the early phase of essential hype rtension is caused primarily by increased cardiac output or increased total peripheral resistance, an increased sympathetic activity is usua lly held responsible for either hemodynamic disturbance. Simultaneous recordings of central and regional hemodynamics and sympathetic nerve traffic in young subjects with mild hypertension did show increased ca rdiac output, reduced calf blood flow and increased nerve traffic as t he characteristic features. However, recent studies in subjects with b orderline hypertension have shown that if the subjects were aware of h aving hypertension, they showed higher blood pressure and higher react ivity to mental stress and cold-presser tests than uninformed subjects with similar blood pressures. With respect to regional circulation, s tudies have shown that the coronary reserve is reduced in early hypert ension, and also in subjects. without left ventricular hypertrophy. Th e role of the endothelium in the regulation of blood flow has attracte d great interest. Abnormalities in the production of vasoconstricting and vasodilating substances from the endothelial cells may be at least partially responsible for the increased vascular resistance character istic of essential hypertension.