Abnormal wall shear conditions in the brachial artery of hypertensive patients

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Abstract
Brachial artery wall shear phenomena were studied in 20 untreated essential hypertensive patients and in 11 normotensive controls of similar age. A pulsed-Doppler velocimeter was used to measure brachial artery internal diameter and mean cross-sectional and systolic centreline blood velocities. A coaxial-cylinder viscometer was used to measure blood viscosity at a shear rate of 96 s–1. A Poiseuille model of velocity distribution across the arterial lumen was used to determine wall shear rate and stress from, respectively, the ratio of blood velocity to arterial diameter and the product of shear rate and blood viscosity. Mean and systolic shear rates and stresses were calculated using, respectively, mean cross-sectional and systolic centreline blood velocities. Hypertensive patients had larger brachial artery diameters (P<0.001), lower systolic centreline and mean cross-sectional blood velocities (P<0.001, P<0.05), higher blood viscosity (P<0.001), lower mean and systolic wall shear rates (P<0.01, P<0.001) and lower systolic wall shear stress (P<0.05) than normotensive controls. In all subjects, mean blood pressure was negatively correlated both with mean and systolic shear rates (r = – 0.49, P<0.01; r = – 0.68, P<0.001) and with mean and systolic shear stresses (r = – 0.39, P<0.05; r =– 0.45, P<0.01). Thus the hypertensive state was associated with decreases in both mean and systolic wall shear rates, and in systolic wall shear stress. These shear abnormalities merit attention because of the atherogenic effect of low-shear conditions.