These observations suggest that the reduction in mean wall shear stress with age results from the concomitant increase in diameter in an attempt of the arterial system to limit the reduction in storage capacity of the arterial system with increasing age.

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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.