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Arterial hemodynamics in human hypertension. Effects of angiotensin converting enzyme inhibition
Insights
Essential hypertension involves abnormal hemodynamics like increased resistance. Angiotensin-converting enzyme inhibition with captopril normalized blood pressure and resistance but not all hemodynamic factors.
Area of Science:
- Cardiovascular Physiology
- Hypertension Research
Background:
- Essential hypertension is characterized by distinct hemodynamic alterations.
- These include increased resistance, wave reflections, pulse wave velocity, and decreased systemic compliance.
- The renin-angiotensin system is implicated in essential hypertension's altered hemodynamics.
Purpose of the Study:
- To investigate the role of the renin-angiotensin system in the altered hemodynamics of essential hypertension.
- To assess the hemodynamic effects of angiotensin-converting enzyme inhibition using captopril.
Main Methods:
- Comparison of a hypertensive patient group with a normotensive control group.
- Measurement of ascending aortic pressures and flows during cardiac catheterization.
- Administration of intravenous captopril to hypertensive patients and repeat measurements.
Main Results:
- Hypertensive patients exhibited increased peripheral resistance, wave reflections, and decreased systemic compliance.
- Captopril normalized blood pressure, resistance, and impedance phase angle zero crossing.
- Systemic compliance and wave reflections, while improved, remained abnormal compared to normotensive levels.
Conclusions:
- The renin-angiotensin system plays a significant role in the hemodynamic alterations of essential hypertension.
- Angiotensin-converting enzyme inhibition effectively improves key hemodynamic parameters.
- A complex interplay of factors contributes to increased smooth muscle tone in essential hypertension.
Abstract:
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 alpha- and beta-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.(ABSTRACT TRUNCATED AT 250 WORDS)