PULSATILE FLOW AND OSCILLATING WALL SHEAR-STRESS IN THE BRACHIAL-ARTERY OF NORMOTENSIVE AND HYPERTENSIVE SUBJECTS

Study objective - The aim of the study was to examine oscillating arterial wall shear stress in hypertension.Design - Pulsatile flow and oscillating wall shear stress were measured in brachial artery in hypertensive υ normotensive subjects using pulsed Doppler apparatus. Methods were tested in four subjects using a micrometric procedure of Doppler probe displacement providing instantaneous real time velocity profiles.Subjects - 19 ambulatory male patients with mild to moderate hypertension (diastolic blood pressure 95-114 mm Hg) and 11 normotensive male controls of similar age were studied. All were non-smokers.Measurements and results - Arterial diameter and pulsatile centreline blood velocity were determined with pulsed Doppler, and blood viscosity was measured with a coaxial cylinder viscometer. Shear rates corresponding to maximum (γ Vmax), minimum (γ Vmin), and pulse (γ Vpulse) velocities were evaluated with a simplified method of computation of Womersley equations. Corresponding shear stresses (τ Vmax, τ Vmin, τ Vpulse) were calculated as the product between shear rate and viscosity. The differences in wall shear rates obtained with the Womersley method and with the micrometric procedure were less than 10%. Compared to normotensives, hypertensiveshad greater arterial diameter [0.508(SEM0.006) υ 0.446(0.014), p<0.001], lower maximum velocity [36.2(1.5) υ 46.3(2.4) cm·s-1, p<0.001], lower absolute value of minimum velocity [-8.3(1.2) υ -14.3(2.3) cm·s-1, p<0.01], lower pulse velocity [44.5(2.2) v 61.2(3.9) cm·s-1, p<0.001], and higher blood viscosity [4.77(0.08) v 4.25(0.09) mPa·s, p<0.001]. γ and τ VMAX, VMIN and Vpulse were all lower in absolute value in hypertensives. Overall mean blood pressure in all subjects was negatively correlated to γ VMAX (r=-0.65), τ VMAX (r=-0.46), γ VMIN (r=-0.45), τ Vmin (r=-0.37), τ Vpulse (r=-0.63), and τ Vpulse (r=-0.48). In hypertensives, age was correlated negatively γ VMAX (r=-0.44), τ VMAX (r=-0.46) γ VMIN (r=-0.57), τ VMIN (r=-0.57), γ Vpulse (r=-0.58), and τ Vpulse (r=-0.58). In normotensives, age was not correlated with shear parameters, except for τ VMAX (r=-0.60) and τ Vpulse (r=-0.66).Conclusions - The hypertensive state is associated with a reduction in oscillating wall shear in large arteries despite an increase in blood viscosity. Age in combination with hypertension also decreases wall shear conditions.