Wall Shear Stress Assessment in the Common Carotid Artery of End-Stage Renal Failure Patients

Abstract

Under physiological circumstances in the common carotid artery (CCA), mean wall shear stress (WSS), defined as mean wall shear rate (WSR) times local whole blood viscosity (WBV), is maintained at approximately 1.5 Pa. In patients with end-stage renal failure (ESRF) whole blood viscosity is low and it is not unlikely that mean WSS is lower in these patients than in control subjects. Moreover, hemodialysis causes an acute increase in blood viscosity with possible effects on WSS. In this study WSS in the CCA was determined with the Shear Rate Estimating System, an apparatus based on ultrasound, in ESRF patients (n = 13) and in presumed healthy age- and sex-matched control subjects (n = 13). Prior to hemodialysis, mean WSS (0.67 ± 0.23 Pa) was significantly lower (p < 0.05) in patients with ESRF, due to both a lower WBV (2.80 ± 0.52 mPa·s) and mean WSR (271 ± 109 s^–1), than in the control subjects (mean WSS: 1.24 ± 0.20 Pa; WBV: 3.20 ± 0.29 mPa·s; WSR: 387 ± 51 s^–1). Hemodialysis induced an increase in WBV (up to 3.71 ± 1.54 mPa·s, p < 0.01), but mean WSS did not change significantly due to a reciprocal decrease in mean wall shear rate. These findings demonstrate that WSS is lower in hemodialysis patients than in control subjects, and that mean WSS is maintained at this low level despite an acute change in blood viscosity.

Flow-Mediated Vasodilation in End-Stage Renal Disease

“…On the arm opposite to the arteriovenous shunt, brachial artery (BA) internal diameter, stroke diameter changes, BA wall-intima-media thickness (IMT), and SR were independently measured with a high-resolution B-mode (7.5-MHz transducer) echotracking system (Wall-Track System, PIE Medical, Maastricht, the Netherlands), as described previously in detail (13)(14)(15)(16). Briefly, vessel walls are identified automatically and their displacement is tracked throughout the cardiac cycle.…”

“…The BA incremental elastic modulus (Einc) was determined according to the previously reported formula (16,17): Einc ϭ [(BA lumen cross-sectional area/BA-wall cross-sectional area ϩ 1)ϫ3)]/BA distensibility. SR was measured with the same device but with different settings, as previously reported (13)(14)(15)(16). The echo system is shifted to pulsed Doppler mode and a 30°oblique radiofrequency line is digitized at high frequency (24 MHz).…”

Local Shear Stress and Brachial Artery Functions in End-Stage Renal Disease

“…Shear rate was measured with the same device but with different settings, as previously reported (5,13,14,16). The echo system is shifted to pulsed Doppler mode, and a 30°oblique radiofrequency line is digitized at high frequency (24 MHz).…”

“…However, it was shown that, under conditions of similar blood flow changes, FMD depended on SS changes that were induced by whole-blood viscosity (WBV) modifications (12). Arterial SS is lower in ESRD (13), and we hypothesized that lower FMD in the context of ESRD could reflect diminished SS and not only endothelial alterations. SS is a major factor implicated in vascular remodeling (1,5) and, as such, could influence the mechanical properties of arteries (5).…”

“…The inclusion of arterial radius in the equations that are used to determine FMD and SS could generate an erroneous mathematical relationship between these variables that does not necessarily reflect a physiologic reality. Newly developed technologies enable direct in vivo ultrasound measurements of arterial wall shear rate and its distribution and SS determination (5,13,14). To define the interrelationships between local SS and BA wall properties, including capacitive (BA compliance [BAC]), and conduit functions (FMD), we measured in vivo shear rate, SS, BA diameter, and BAC changes in response to progressive hand warming in patients with ESRD and healthy control subjects.…”