Damping is the conversion of mechanical energy of a structure into thermal energy, and it is related to the material viscous behavior. To evaluate the role of damping in the common carotid artery (CCA) wall in human hypertension and the possible improvement of angiotensin-converting enzyme (ACE) inhibition, we used noninvasive CCA pressure (tonometry) and diameter (B-mode echography) waveforms in normotensive subjects (NT group; n=12) and in hypertensive patients (HT group; n=22) single-blind randomized into HT-placebo (n=10) or HT-treated (ramipril, 5 to 10 mg/d during 3 months; n=12). Vascular smooth muscle (VSM) null tonus condition was achieved from in vitro pressure and diameter waveforms (Konigsberg microtransducer and sonomicrometry) measured in explanted human CCA (n=14). Arterial wall dynamics was described by viscous (eta), inertial (M), and compliance (C) parameters, mean circumferential wall stress, viscous energy dissipation (WD), peak strain energy (WSt), damping ratio (xi=WD/WSt), and modeling isobaric indexes CIso and WSt(Iso). The lack of VSM tonus isobarically increased wall stress and reduced eta, CIso, and damping (P<0.01). Wall stress, eta, and WD were greater in HT than in NT (P<0.015) and arrived near normal in HT-treated (P<0.032 respect to HT), with no changes in HT-placebo. Whereas CIso increased in HT-treated (P<0.01) approaching the NT level, xi did not vary among groups. During hypertension, because of the WSt increase, the arterial wall reacts increasing WD to maintain xi. ACE inhibition modulates VSM activation and vessel wall remodeling, significantly improving wall energetics and wall stress. This protective vascular action reduces extra load to the heart and maintains enhanced arterial wall damping.

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Abstract-Increases m arterial wall vlscoslty and mtlma-media thickness (IMT) were found m hypertensive patients Because smooth muscle cells are responsible for the viscous behavior of the artenal wall and they are involved m the process of thickening of the mtlma-media complex, this study evaluates the relationship between carotid thickness and wall vlscos~ty The simultaneous and nomnvaslve assessment of the mtlma-media complex and arterial diameter waveform was performed using high-resolution ultrasonography This technique was contrasted agamst sonomlcrometry m sheep, showmg that the waveforms obtained by both methods were surular The common carotid arteries of 11 normotenslve subjects (NTA) ayd 11 patients with rmld to moderate essential hypertension (HTA) were measured nomnvaslvely by usmg tonometry and Ian automatic densltometrlc analysis of B-mode Images to obtam IMT and instantaneous pressure and diameter loops A vlscoelastlc model was used to derive the wall vlscoslty mdex (7) using the hysteresis loop ehmmatlon criteria In NTA, 7 was 2 7321 66 (mm Hg * s/mm) and IMT was 0 58+0 08 ( mm , whereas m HTA, q was 5 91?2 34 (K 025) and ) IMT was 0 7020 12 (P< 025), respectively When all data of q versus IMT of NTA and HTA were pooled m a linear regression analysis, a correlation coefficient of r= 71 (P< 05) was obtained Partial correlation between q and IMT holding constant pressure was r= 59 (PC 05) In conclusion, wall vlscoslty increase was associated with a higher IMT even mamtammg blood pressure fixed, suggestmg that the mtlma-media thickening might be related to smooth muscle alterations manifested as an Increase m viscous behavior (H~~eutension.1998;31[part 2]:534-539.)Key Words: wall thickness n arterial wall vlscoslty n hypertension H tonometry A complete charactenzatlon of geometric, elastic, and VIS-COUS propertles of arteries has been proposed on the basis of mvaslve recordings of pressure and diameter pulses, allowing the determination of the pressure-diameter hysteresis loop m conscious chronically instrumented dogs ' Moreover, another study provided a complete m vlvo descnptlon of geometric, elastic, and viscous properties of carotid and femoral artenes m human hypertension' m which recent nonmvaslve vascular techniques, applanatlon tonometry, and Doppler postprocessmg M-mode images were applied for measurmg pressure and diameter pulses Wall v~scoslty was estimated as the area of the diameter-pressure hysteresis loop dunng the procedure of loop ehmmatlon Compared to normotenslve subJects, hypertensive patients had an increased wall vlscoslty index m the carotid artery This increased wall vlscoslty might be the consequence of hypertensive vascular hypertrophy and particularly of the partlclpatlon of the smooth muscle m that hypertrophy Moreover, the smooth muscle component among the arterial wall constituents has been demonstrated to be responsible for the viscous behavior of the diameter-pressure relatlonshlp',3 An increased wall thickness m carotid arteries of asymptomatlc hypertensive patients h...