Shear stress depends on vascular territory: comparison between common carotid and brachial artery

Abstract

Shear stress (SS) is thought to be constant throughout the vascular system. Evidence for this supposition is scarce, however. To verify this hypothesis in vivo, we assessed common carotid (CCA) and brachial artery (BA) peak and mean wall shear rate (SR) noninvasively in 10 healthy volunteers (23.7 +/- 3.4 yr) with an ultrasound SR estimation system. SS was estimated from SR and calculated whole blood viscosity. SR was higher (P < 0.05) in the CCA (mean: 359 +/- 111 s(-1); peak: 1,047 +/- 345 s(-1)) than in the BA (mean: 95 +/- 24 s(-1); peak: 770 +/- 170 s(-1)). Whole blood viscosity was higher in the BA than in the CCA (5.1 +/- 0.7 vs. 3.3 +/- 0.6 mPa. s; P < 0.001). Peak SS did not differ between the CCA and the BA, whereas mean SS was significantly higher in the CCA (1.15 +/- 0.21 Pa) than in the BA (0.48 +/- 0.15 Pa; P < 0.001). These results demonstrate that BA SS strongly deviates from CCA SS in vivo.

Model-based assessment of dynamic arterial blood volume flow from ultrasound measurements

“…[9,13,33]). Considering the group mean BVF, the value obtained in this study is comparable to the value of 30.6 ml/min reported by Green [13] for a group of healthy volunteers at rest conditions.…”

“…Furthermore, the distensibility of the brachial artery is relatively small [7,8], unlike that of the common carotid artery [9], so the effect of wall motion on the velocity distribution is assumed to be so small that it can be neglected.…”

Use of Ultrasound for Non-Invasive Assessment of Flow-Mediated Dilation

“…Shear rate has been used as a surrogate measure of shear stress in a number of previous studies 36,[48][49][50][51] . Fourth, in arteries, the velocity profile will generally not develop to a full parabola as a consequence of flow unsteadiness and short vessel entrance lengths; however, in the brachial artery, under resting conditions, the underestimation is less pronounced, likely due to a more parabolic velocity profile in this artery, i.e., n (velocity profile) is closer to 2 52) . However, this may only be true for resting conditions; the occurrence of flow turbulence is possible during reactive hyperemia 53) .…”

The viscous behaviour of HES 130/0.4 (Voluven®) and HES 260/0.45 (Pentaspan®)

“…22,23 Initial maximum flow was to be restricted to a Reynolds Number (Re = inertial fluid forces / viscous fluid forces) of 1500 to negate potential transitional effects in the circulating fluid (transition to turbulence often commencing at Re * 2000). It was found, however, that Re could be increased safely to 1635 before transitional disturbances appeared.…”