Arterial hemodynamics in human hypertension: Effects of angiotensin converting enzyme inhibition

Previous studies have shown some distinct hemodynamic alterations in essential hypertension, including increased resistance, wave reflections, and pulse wave velocity and decreased systemic compliance. These abnormalities are completely normalized by nonspecific smooth muscle dilation with nitroprusside but not by combined α- and β-adrenergic blockade. The renin-angiotensin system, acting possibly via both circulating and local tissue effects, is thought to play an important role in essential hypertension, so its role in the altered hemodynamics deserves careful investigation. A hypertensive patient group was compared with a normotensive group similar in age, body size, and proportion of men and women. During diagnostic cardiac catheterization, ascending aortic micromanometer pressures and electromagnetic flows were measured in the baseline state. Intravenous captopril of a sufficient dosage (11 mg) to normalize blood pressure then was given to the hypertensive patients while measurements were repeated. From the pressures and flows, aortic input impedance, wave reflection magnitude, and compliance were computed. In the hypertensive group, the important hemodynamic alterations consisted of increased peripheral resistance, first zero crossing of aortic impedance phase angle, and wave reflections and decreased systemic compliance. Captopril had a pronounced hemodynamic effect. It normalized blood pressure, resistance, and impedance phase angle zero crossing. Compliance, although increased substantially by captopril, was still slightly lower than normotensive levels. The magnitude of wave reflections, although substantially lowered by angiotensin converting enzyme inhibition, was still persistently greater than normal. The present results, together with those previously reported, demonstrate that a complex interplay of factors underlies the increased smooth muscle tone in essential hypertension. Whereas nonspecific smooth muscle relaxation with nitroprusside is able to completely restore hemodynamics to a normal state, angiotensin converting enzyme inhibition alone, β-adrenergic blockade alone, or combined β- and α-blockade cannot do so. Therefore, if one wishes to completely normalize the hemodynamic alterations produced by hypertension in addition to treating the elevated blood pressure, one needs to appreciate the actions of these and other antihypertensive agents and select the appropriate combinations that will yield the desired results.