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To assess the respective roles of the antihypertensive and blood pressure-independent effects of angiotensin converting enzyme (ACE) inhibition in the changed arterial haemodynamics observed in hypertensive patients with end-stage renal disease (ESRD) treated by haemodialysis.and methods Twelve hypertensive patients with ESRD were included in a double-blind, cross-over study comparing a single 20 mg dose of the ACE inhibitor quinapril versus placebo. Two study periods each of 172 h duration were separated by a 2-week placebo period. Repeated measurements of the following parameters were performed: brachial artery systolic blood pressure (SBP); diastolic blood pressure and mean blood pressure (using a mercury sphygmomanometer); carotid artery SBP and pulse pressure (by applanation tonometry); aortic stiffness (by pulse wave velocity); and the effect of arterial wave reflections in the common carotid artery (the augmentation index, by applanation tonometry). A radioimmunoassay was used to determine plasma angiotensin II levels. Quinaprilat pharmacokinetics were studied using a specific assay. Twoway (time-treatment) analysis of variance for repeated measures, analysis of covariance for two within-factors and a covariate changing with the level of the factor time (pressures measured at each time) and baseline values of the studied parameter as a second covariate were used for statistical analysis.Quinapril treatment induced a long-lasting decrease in arterial wave reflections, which was still observable 172h after quinapril administration and still present after removing the effect of the decrease in blood pressure. The effect on wave reflections was associated with a more pronounced and sustained decrease in carotid SBP and pulse pressure than that in brachial SBP and pulse pressure. Quinapril administration also induced a long-lasting decrease in aortic pulse wave velocity, but this effect was entirely dependent on parallel changes in blood pressure. Arterial haemodynamic changes were not related to plasma angiotensin II or quinaprilat levels.The results of this controlled study indicate that, in ESRD patients, ACE inhibition results in a longlasting, blood pressure-independent decrease in arterial wave reflections. The consequence of this was a decrease in pulsatile pressure load in the central arteries with increased aortic distensibility. The increased aortic distensibility resulted from the decrease in blood pressure. The observed arterial haemodynamic alterations suggest that ACE inhibition induces alterations in arterial wave reflections in the distal parts of the arterial tree.