Brands P J, Hoeks A P, Hofstra L, Reneman R S
Department of Biophysics, Cardiovascular Research Institute Maastricht, University of Limburg, The Netherlands.
Ultrasound Med Biol. 1995;21(2):171-85. doi: 10.1016/s0301-5629(94)00111-1.
Wall shear stress (blood viscosity x wall shear rate), imposed by the flowing blood, and blood pressure are the main mechanical forces acting on a blood vessel wall. Accurate measurement of wall shear stress is important when investigating the development of vascular disease, since both high and low wall shear stresses have been cited as factors leading to vessel wall anomalies. Furthermore, in vitro studies have shown that endothelial cells, which play a key role in the function of the underlying arterial wall, undergo a variety of structural and functional changes in response to imposed shear stress. However, there is practically no knowledge about the influence of wall shear stress on the arterial wall in vivo because of the difficulty in measuring this stress in terms of magnitude and time variation. The method presented in this article to measure the time-dependent wall shear rate in the main arteries is based on the evaluation of velocity profiles determined by means of ultrasound, using off-line signal processing. Pulsed ultrasound is well suited for this application since it is noninvasive. The processing performed in the radio-frequency (RF) domain consists of a mean frequency estimator preceded by an adaptive vessel wall filter. In a pilot study (30 measurements in the carotid artery of five healthy volunteers) we investigated the reproducibility of our method to estimate wall shear rate as compared with the reproducibility of the measurement of blood flow velocity in the middle of the vessel. The coefficient of variation was on the order of 9% for blood flow velocity estimation, and for wall shear rate estimation on the order of 5%.
血流施加的壁面剪应力（血液粘度×壁面剪切速率）和血压是作用于血管壁的主要机械力。在研究血管疾病的发展时，准确测量壁面剪应力非常重要，因为高壁面剪应力和低壁面剪应力都被认为是导致血管壁异常的因素。此外，体外研究表明，在内皮动脉壁功能中起关键作用的内皮细胞会因施加的剪应力而发生各种结构和功能变化。然而，由于难以测量壁面剪应力的大小和随时间的变化，实际上对于体内壁面剪应力对动脉壁的影响知之甚少。本文提出的测量主动脉中随时间变化的壁面剪切速率的方法基于对通过超声确定的速度剖面的评估，并使用离线信号处理。脉冲超声非常适合此应用，因为它是非侵入性的。在射频（RF）域中进行的处理包括一个平均频率估计器，前面有一个自适应血管壁滤波器。在一项初步研究（对五名健康志愿者的颈动脉进行30次测量）中，我们将我们估计壁面剪切速率的方法的可重复性与测量血管中部血流速度的可重复性进行了比较。血流速度估计的变异系数约为9%，壁面剪切速率估计的变异系数约为5%。
