Published Online
on October 17, 2005

A more recent version of this article appeared on November 1, 2005

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Submitted on April 26, 2005
Revised on May 31, 2005

Changes in Aortic Stiffness and Augmentation Index After Acute Converting Enzyme or Vasopeptidase Inhibition

Gary F. Mitchell^*; Yves Lacourcière; J. Malcolm O. Arnold; Mark E. Dunlap; Paul R. Conlin; and Joseph L. Izzo Jr

From Cardiovascular Engineering, Inc (G.F.M.,), Waltham, Mass; Centre hospitalier de l’Universite Laval (Y.L.), Ste. Foy, Quebec, Canada; London Health Sciences Centre (J.M.O.A.), London, Ontario, Canada; Louis Stokes VA Medical Center (M.E.D.), Cleveland, Ohio; Brigham and Women’s Hospital (P.R.C.), Boston, Mass; Erie County Medical Center (J.L.I.), Buffalo, NY.

^* To whom correspondence should be addressed. E-mail: GaryFMitchell{at}mindspring.com.

Abstract--Augmentation index (AI), a measure of enhanced wave reflection, has been proposed as a bedside measure of aortic stiffness. However, because AI is potentially sensitive to various factors other than vessel wall stiffness, the utility of AI as a stiffness indicator may be limited. To assess relations between AI and vascular properties, we used arterial tonometry and aortic Doppler flow to evaluate trough (24 hours) and peak (4 hours) pulsatile hemodynamics and pulse wave velocity in 159 individuals with systolic hypertension at the completion of a 12-week period of monotherapy with the vasopeptidase inhibitor omapatrilat (80 mg; n=75) or the converting enzyme inhibitor enalapril (40 mg; n=84). Characteristic impedance (Z_c) was calculated from the ratio of change in carotid pressure and aortic flow in early systole. Systolic ejection period (SEP), timing of wave reflection, and AI were assessed from the carotid waveform. Comparable acute reductions in mean pressure were associated with greater reductions in peripheral resistance with enalapril, whereas neither drug had an acute effect on Z_c. Both drugs reduced AI, but neither drug altered the timing of wave reflection. Both drugs increased heart rate and shortened SEP. Multiple regression analysis demonstrated that the acute reduction in AI was most affected by reductions in SEP and peripheral resistance. Change in AI was inversely related to change in Z_c and pulse wave velocity did not enter the model. Our findings indicate that AI is a complex surrogate marker that is inversely related to changes in proximal aortic stiffness in systolic hypertension.

Key words: angiotensin converting enzyme • aorta • clinical trials • hypertension • pulse

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