The Analysis of Wall Shear Stress Modulated by Acute Exercise in the Human Common Carotid Artery with an Elastic Tube Model

Assessment of the magnitude and pattern of wall shear stress(WSS)in vivo is the prerequisite for studying the quantitative relationship between exercise-induced WSS and arterial endothelial function.In the previous studies,the calculation of the WSS modulated by exercise training was primarily based upon the rigid tube model,which did not take non-linear effects of vessel elastic deformation into consideration.In this study,with an elastic tube model,we estimated the effect of a bout of 30-minute acute cycling exercise on the WSS and the flow rate in the common carotid artery according to the measured inner diameter,center-line blood flow velocity,heart rates and the brachial blood pressures before and after exercise training.Furthermore,the roles of exerciseinduced arterial diameter and blood flow rate in the change of WSS were also determined.The numerical results demonstrate that acute exercise significantly increases the magnitudes of blood flow rate and WSS.Moreover,the vessel elastic deformation is a non-negligible factor in the calculation of the WSS induced by exercise,which generates greater effects on the minimum WSS than the maximum WSS.Additionally,the contributions of exercise-induced variations in blood flow rate and diameter are almost identical in the change of the mean WSS.

The Wall Shear Stress of a Pulsatile Blood Flow in a Patient Specific Stenotic Right Coronary Artery

A computer simulation of the blood flow in a patient specific atherosclerotic right coronary artery is carried out to study the blood flow pattern and the wall shear stress (WSS) distribution in the artery. Both temporal and special distribution patterns of the WSS of the non-Newtonian blood flow are presented and the regions on the lumen surface where the WSS is constantly lower than 1N/m2are identified.

彩色多普勒定量分析腘动脉参数在2型糖尿病患者下肢血管病变中的应用研究

目的:分析彩色多普勒定量分析腘动脉参数在2型糖尿病(T2DM)患者下肢血管病变中的应用价值。方法:采用回顾性分析法,将天津市河西医院2019年8月—2022年10月进行健康体检的25例志愿者纳入对照组,将51例T2MD患者纳入观察组。按腘动脉中膜厚度(IMT)情况将观察组分为A组(IMT正常)20例、B组(IMT增厚)6例、C组(斑块形成)25例。对比观察组与对照组患者腘动脉最大管径(R)、峰值血流速(peak systolic velocity,PSV)、壁剪应力(wall shear stress,WSS),对比A组、B组、C组患者病程、年龄、体重指数、血压、血糖等可能影响动脉斑块形成的因素,对比三组患者R、PSV、WSS。分析WSS预测T2DM患者效能以及WSS相关因素。结果:观察组患者PSV、WSS低于对照组,差异有统计学意义(P<0.05)。与A组比较,B组患者年龄更高,病程更长,甘油三酯、WSS更低,差异有统计学意义(P<0.05)。与A组比较,C组患者年龄更高,病程更长,PSV、WSS更低,差异有统计学意义(P<0.05)。与B组比较,C组患者年龄更高,PSV、WSS更低,差异有统计学意义(P<0.05)。WSS取1.82 dyne/cm^(2),预测T2DM患者下肢血管病变的特异度、灵敏度分别为84%、66%。WSS与病程、年龄、腘动脉IMT呈负相关(r=-0.370、-0.570、-0.592,P<0.05),与PSV呈正相关(r=0.601,P<0.05)。结论:彩色多普勒超声定量分析下腘动脉WSS能有效预测T2DM患者下肢血管病变,建议综合患者病程、年龄及腘动脉IMT提高诊断准确性。

V Flow技术测量颈动脉壁面剪应力的一致性研究

目的评价血流向量成像(V Flow)技术在测量健康成年人颈动脉壁面剪应力(WSS)中的一致性。方法于2021年2月至2021年3月招募健康成年志愿者20人,由2名不同年资的超声医师使用配备V Flow功能的Mindray Resona 7超声仪和3~9 MHz线阵探头进行双侧颈动脉扫查,分别采集双侧颈总动脉远段、颈总动脉分叉至颈内动脉起始部两段动脉的动态V Flow图像,测量两侧颈总动脉远段的近心端、远心端、分叉处及颈内动脉起始部的前、后壁的WSS,使用组内相关系数(ICC)和Bland-Altman图评估组内一致性及组间一致性。结果双侧颈动脉前、后壁的4个不同节段之间WSS值差异均有统计学意义(P<0.05)。高年资超声医师2次测量结果的一致性结果显示,左侧颈总动脉远段的远心端一致性极好(ICC 0.779),右侧颈总动脉远段的近心端(ICC 0.605)、远心端(ICC 0.585)、颈内动脉起始部(ICC 0.457)、左侧颈总动脉分叉处(ICC 0.606)及颈内动脉起始部(ICC 0.702)一致性均较好;不同年资超声医师的测量结果显示,仅右侧颈总动脉分叉处(ICC 0.486)及左侧颈总动脉远段的远心端(ICC 0.576)一致性较好。结论V Flow技术可显示不同位点间颈动脉WSS之间的差异,其组内一致性较好,但在不同年资超声医师间存在一定的差异。

多重力学刺激作用下新内膜重塑模型构建和数值模拟研究

目的支架植入造成血管内膜损伤引起新内膜重塑。本文旨在构建支架植入后力学刺激新内膜重塑模型,探讨支架植入后动脉应力和壁面切应力对新内膜重塑的影响及新内膜重塑过程中的血管应力分布。方法建立支架植入模型、支架段血流模型,计算支架植入后血管壁力学刺激;通过促生长因子g描述力学刺激与细胞增殖的关系,并构建细胞增殖迁移模型,模拟细胞聚集形成新内膜过程。模拟动脉应力、壁面切应力单独作用下新内膜重塑,以探讨两种力学刺激作用效果的差异;模拟动脉应力和壁面切应力共同作用下新内膜重塑过程,得到重塑过程血管应力分布的变化。结果在动脉应力作用下,新内膜集中在支架段,对支架段管腔影响更大;在壁面切应力作用下新内膜重塑范围更广,除支架段还包括上、下游。新内膜重塑会使血管壁应力峰值和高应力区域减小,重塑后血管壁应力峰值由0.277 MPa下降至0.098 MPa,高应力区域体积减少了64.6%。结论新内膜重塑模型可得到支架植入后血管形貌和应力的动态变化。不同力学刺激作用下,新内膜位置与重塑速度有显著性差异,具有不同特征。新内膜可对血管壁起到一定程度的支撑作用,使血管壁的高应力区域明显减少。

SYNERGY OF WALL SHEAR STRESS AND CIRCUMFERENTIAL STRESS IN STRAIGHT ARTERIES

The Wall Shear Stress （WSS） generated by blood flow and Circumferential Stress （CS） driven by blood pressure have been thought to play an important role in blood flow-dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis. The WSS and CS in straight arteries were calculated by measuring the blood pressure, center-line velocity, wall thickness, and radius of vessels. The WSS and CS in the time domain were then decomposed into the amplitude and phase in the frequency domain. The CS amplitude to the WSS amplitude ratio （referred as stress ampli tude ratio, Zs ） and the phase difference between the CS and the WSS （referred as stress phase difference, SPA） in the fre quency domain were calculated to characterize the synergy of the CS and WSS. Numerical results demonstrated that the CS is not in phase with the WSS, a time delay in the time domain or a stress phase difference in the frequency domain between the WSS and the CS exists. Theoretical analysis demonstrated that the Zs and SPA are primarily determined by the local fac tors （blood viscosity, local inertial effects, local geometry, loeal elasticity） and the input impedance of whole downstream arterial beds. Because the arterial input impedance has been shown to reflect the physiological and pathological states of whole downstream arterial beds, the stress amplitude ratio Zs and stress phase difference SPA would be thought to be the appropriate indices to reflect the effects of states of whole downstream arterial beds on the local blood flow dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis.

Pulsatile blood flow in large arteries:comparative study of Burton's and McDonald's models

To get a clear picture of the pulsatile nature of blood flow and its role in the pathogenesis of atherosclerosis, a comparative study of blood flow in large arteries is carried out using the two widely used models, McDonald＇s and Burton＇s models, for the pressure gradient. For both models, the blood velocity in the lumen is obtained analytically. Elaborate investigations on the wall shear stress （WSS） and oscillatory shear index （OSI） are carried out. The results are in good agreement with the available data in the literature. The superiority of McDonald＇s model in capturing the pulsatile nature of blood flow, especially the OSI, is highlighted. The present investigation supports the hypothesis that not only WSS but also OSI are the essential features determining the pathogenesis of atherosclerosis. Finally, by reviewing the limitations of the present investigation, the possibility of improvement is explored.

PERFORMANCE MODELING AND ANALYSIS OF BLOOD FLOW IN ELASTIC ARTERIES

Two different non_Newtonian models for blood flow are considered,first a simple power law model displaying shear thinning viscosity,and second a generalized Maxwell model displaying both shear thinning viscosity and oscillating flow viscous_elasticity.These models are used along with a Newtonian model to study sinusoidal flow of blood in rigid and elastic straight arteries in the presence of magnetic field.The elasticity of blood does not appear to influence its flow behavior under physiological conditions in the large arteries,purely viscous shear thinning model should be quite realistic for simulating blood flow under these conditions.On using the power law model with high shear rate for sinusoidal flow simulation in elastic arteries,the mean and amplitude of the flow rate were found to be lower for a power law fluid compared to Newtonian fluid for the same pressure gradient.The governing equations have been solved by Crank_Niclson scheme.The results are interpreted in the context of blood in the elastic arteries keeping the magnetic effects in view.For physiological flow simulation in the aorta,an increase in mean wall shear stress,but a reduction in peak wall shear stress were observed for power law model compared to a Newtonian fluid model for matched flow rate wave form.Blood flow in the presence of transverse magnetic field in an elastic artery is investigated and the influence of factors such as morphology and surface irregularity is evaluated.

Couple stress nanofluid flow through a bifurcated artery—Application of catheterization process

In this article,we are exploring the hemodynamics of nanofluid,flowing through a bifurcated artery with atherosclerosis in the presence of a catheter.For treating obstruction in the artery,one can use the catheter whose outer surface is carrying the drug coated with nano-particles.The resultant solvent is considered as blood nano-fluid.Blood being a complex fluid,is modeled by couple stress fluid.In the presence of nano-particles,the temperature and the concentration distribution are understood in a bifurcated stenotic artery.The concluded mathematical model is governed by coupled non-linear equations,and are solved by using the homotopy perturbation method.Consequently,we have explored is the effects of fluid and the embedded geometric parameters on the hemodynamics characteristics.It is also realized that high wall shear stress exists for couple stress nano-fluid when compared to Newtonian nano-fluid.which is computed at a location corresponding to maximum constriction(z=12.5)of the artery.

Pulsatile MHD Flow in an Inclined Catheterized Stenosed Artery with Slip on the Wall

Catheter is commonly used by the surgeons for various reasons in the treatment of a patient suffering with cardiovascular diseases. Catheterization increases the mean flow resistance in the arterial blood flow and many other complications are associated with the presence of catheter in the artery. Effects of catheter in stenosed artery can be estimated non-invasively by means of hemo-dynamic indicator-WSS, WSSG, volume flow rate and impedance. The effect of slip at the arterial wall, inclination of the artery and magnetic field on the hemodynamic indicators and flow profiles are computed, presented and discussed through graphs.

Factors Influencing the Disturbed Flow Patterns Downstream of Curved Atherosclerotic Arteries

Pulsatile blood flows in curved atherosclerotic arteries are studied by com- puter simulations.Computations are carried out with various values of physiological parameters to examine the effects of flow parameters on the disturbed flow patterns downstream of a curved artery with a stenosis at the inner wall.The numerical re- suits indicate a strong dependence of flow pattern on the blood viscosity and inlet flow rate,while the influence of the inlet flow profile to the flow pattem in downstream is negligible.

急性缺血性脑血管病患者颈内动脉壁面切应力与复发的相关性

目的 研究伴有颈内动脉粥样斑块的急性缺血性脑血管病患者颈内动脉壁面切应力(wall shear stress,WSS)与复发的相关性。方法 收集广州医科大学附属第二医院神经内科2018年1月至2020年12月住院的98例首发急性缺血性脑血管病患者,筛选出彩超提示颈内动脉斑块形成者,计算壁面切应力,并随访2年记录复发情况。结果 左侧WSS(WSS-L)、右侧WSS(WSS-R)、平均WSS(WSS-M)复发组均高于对照组[(10.16±5.02)vs.(7.82±2.50);(10.22±2.09)vs.(7.82±2.82);(10.19±3.16)vs.(7.82±2.24)]dyne/cm^(2),复发组白细胞计数高于对照组(8.67±1.67 vs. 6.35±1.93)×109/L,差异有统计学意义(P值分别为0.039,0.015,0.008,0.001)。复发与WSS-R(r=0.372,P=0.007)、WSS-M(r=0.305,P=0.029)及白细胞计数(r=0.466,P=0.001)正相关。ROC曲线分析法分析WSS-M对复发的预测价值:当WSS-M为7.95时,最大敏感度和特异度为80%和56%。结论 伴颈内动脉粥样斑块的急性缺血性脑血管病患者颈内动脉WSS与疾病复发相关。

流固耦合分析脉压差对颈内动脉狭窄处壁面剪切力的影响

目的基于流固耦合(fluid structure interaction,FSI)的方式,分析不同脉压差对颈内动脉狭窄处壁面剪切力(wall shear stress,WSS)的影响。方法建模为颈内动脉轻度狭窄的CT血管造影(computed tomography angiography,CTA)图像,将模型导入FSI分析软件中。入口条件设定为A、B两组,A组8种入口条件:舒张压设定为80 mmHg,收缩压间隔10 mmHg由90~160 mmHg递增;B组8种入口条件:收缩压设定为120 mmHg,舒张压间隔10 mmHg由110~40 mmHg递减。获取两组数据后,分别测量颈内动脉狭窄处截面收缩期和舒张期的WSS数值和差值。结果两组WSS差值随着脉压差增大而增大,当压差为80 mmHg时,A组WSS差为92.821 Pa,B组WSS差为98.203 Pa,远高于正常压差(40 mmHg)的WSS差值52.041 Pa;B组脉压差越小,一个心动周期内的整体WSS越高,B组脉压差为10 mmHg时,收缩期和舒张期的WSS分别为220.384 Pa和204.744 Pa。结论颈内动脉狭窄处的脉压差增高,WSS的振荡幅度也会增大,易造成斑块破裂;当脉压差低且收缩压和舒张压同时偏高时,WSS整体也偏高,同样是斑块的易损因素,通过FSI分析脉压差对颈内动脉狭窄处的WSS数值,有助于临床预防和治疗。

颈动脉斑块的流固耦合数值模拟

目的 提出一种基于真实颈动脉狭窄患者的双向流固耦合计算方法,用于分析不同类型颈动脉斑块在病变处的血流动力学参数以及斑块自身的变形和应力变化。方法 对颈动脉中度狭窄病人CT血管造影数据进行3D建模,分离出颈动脉血管壁模型和斑块模型,并进行瞬态流固耦合计算。模拟颈动脉粥样硬化的早期到形成斑块,将斑块类型分为增厚斑块、脂质斑块、混合斑块和钙化斑块,其中增厚斑块视为无斑块的情况,代表血管内膜-中膜的增厚,并对不同斑块类型的狭窄颈动脉进行对比分析。结果 不同类型斑块对整体血流流动影响不大,但是脂质斑块病变处的壁面剪切应力低于其余斑块;以增厚斑块作为对照,斑块出现会抑制动脉的扩张,其中脂质斑块最为明显;钙化斑块有最高的平均结构应力,相反脂质斑块平均结构应力则是最低。结论 本文所提出的计算方法能够同时对流体和固体区域进行分析。研究结果有助于更好理解不同斑块类型对于颈动脉病变处的影响。

基于冠状动脉CT造影的生物机械应力在斑块评估及不良心血管事件预测中的应用

冠状动脉长期暴露于危险因素会引起粥样硬化,进而导致斑块形成与进展。通过早期识别高危斑块特征将有助于预防斑块破裂或糜烂,从而避免急性心血管事件的发生。而生物机械应力(biomechanical stress)在动脉粥样硬化斑块进展及破裂中发挥重要的作用。近些年,已经可以通过无创冠脉CT血管造影(coronary computed tomography angiography,CCTA)利用计算流体力学(computational fluid dynamic,CFD)进行建模,从而得到相应的生物机械应力参数,尤其是壁面剪切应力(wall shear stress,WSS)将有助于更好地构建临床模型从而预测斑块进展及主要不良心血管事件(major adverse cardiac events,MACE)。本文重点介绍生物机械应力以及CCTA所计算得出的WSS在动脉粥样硬化中的作用,并讨论有关CCTA生物机械应力与冠心病相关的研究。

大鼠动脉螺旋血流的荧光成像

目的建立大鼠动脉螺旋血流的实时荧光成像法。方法随机将SD大鼠分为静脉造影组(股静脉注射,1 mL/kg)与小剂量动脉造影组(腹主动脉注射,0.1 mL/kg),其中小剂量动脉造影组又分为荧光素钠组、罗丹明B组、FITC-dextran组和量子点组(每组n=7)。通过体式荧光显微镜实时观察大鼠股动脉血液流动现象,用高速摄像机拍摄动态图像,通过图像阈值分割算法及形态学后处理算法标定荧光区域,测算大鼠股动脉螺旋血流的轴向速度与切向速度,并计算其螺距和壁剪切应力。结果与静脉造影组相比,小剂量动脉造影组可以清晰显示大鼠股动脉的血流呈顺时针螺旋样流动,在FITC-dextran造影剂组可计算出大鼠螺旋血流的轴向速度为(198.4±112.7)mm/s,切向速度为(3.3±0.8)mm/s,螺距为(126.1±76.3)mm,壁剪切应力为(9.5±5.6)Pa。每只大鼠重复3次注射,测得的轴向、切向速度结果无差异。结论实时荧光成像法可以用于在体观察大鼠动脉螺旋血流并对螺旋血流的血流动力学特征进行定量分析。

冠状动脉粥样斑块几何构型对粥样病变发展的影响

目的基于计算流体力学方法,计算左冠状动脉粥样斑块的几何构型与局部血流动力学指标的相关性,探讨粥样斑块几何构型对粥样病变发展的影响。方法将CT冠状动脉造影数据进行图像分割重建,获取每一例模型冠状动脉左前降支中粥样斑块的横断面偏心(cross-sectional eccentricity,CE)指数和纵向偏心(longitudinal eccentricity,LE)指数。对重建后的三维模型进行计算流体力学(computational fluid dynamics,CFD)数值模拟,得到时间平均壁面剪应力(time-averaged wall shear stress,TAWSS)、振荡剪切指数(oscillatory shear index,OSI)和相对保留时间(relative residence time,RRT)等血流动力学指标;将以上指标与CE指数和LE指数进行相关性分析。结果CE指数与TAWSS的倒数显著相关(P<0.001,r=0.97),与OSI显著相关(P=0.001,r=0.89),与RRT相关(P=0.011,r=0.76)。呈现近端偏心时,粥样斑块的LE指数与TAWSS显著相关(P=0.011,r=0.956),与OSI显著相关(P=0.023,r=0.928)。呈现远端偏心时,LE指数与TAWSS显著负相关(P=0.021,r=-0.931),与OSI显著负相关(P=0.012,r=-0.954)。结论基于计算流体力学分析表明,当CE指数升高,LE指数趋近于0或1时,更易引发血管狭窄程度的增加,导致粥样硬化病变继续发展,为该疾病的预防、诊断和治疗提供了参考依据。

壁面剪切力在动脉夹层形成中的作用与机制研究进展

动脉夹层(arterial dissection,AD)的发生是多因素共同作用的结果,壁面剪切力(wall shear force,WSS)是血流与血管壁的摩擦力,是AD发生的重要始动因素。异常WSS通过多种机制引起动脉壁各层结构(内膜、中膜、外膜)的病理性改变,如内皮细胞结构和功能障碍、内弹力板损伤、平滑肌细胞数量减少和表型转化、细胞外基质降解等,最终导致AD的发生。为了更好地了解AD的发病机制,本文对异常WSS引起动脉壁各层结构病理性改变的调控机制进行综述。

头颈部CT血管成像评估颈动脉几何形态对颈内动脉起始部粥样斑块的影响

目的基于头颈部CT血管成像(CTA)探讨不同颈动脉几何形态与缺血性卒中患者颈内动脉(ICA)起始部粥样斑块形成的相关性。方法回顾性收集因缺血性卒中住院并完成头颈部CTA检查患者的资料。纳入92例单侧ICA起始部粥样硬化斑块患者为斑块组,并选择人口统计学变量相似的30例双侧ICA正常者为对照组。同时将单侧ICA起始部粥样硬化斑块分为斑块侧和非斑块侧。分别比较2组间和斑块组内斑块侧及非斑块侧的颈动脉几何形态差异。结果斑块组患者的颈内动脉角、颈动脉扩张度和ICA/颈总动脉(CCA)直径比等颈动脉几何形态学参数与对照组比较,差异有统计学意义(P<0.05)。与非斑块侧比较,斑块侧的颈内动脉角更大,颈动脉扩张度更高,ICA/CCA直径比更低,差异有统计学意义(P<0.05)。多因素Logistic回归分析结果显示,较大的颈内动脉角和颈动脉扩张度及低ICA/CCA直径比与ICA起始部粥样斑块形成相关。结论不同个体间颈动脉几何形态特征存在差异。在轻度ICA粥样硬化病变患者中,较大的颈内动脉角、颈动脉扩张度和较小的ICA/CCA直径比是ICA起始部粥样斑块形成的独立危险因素。

Distribution of wall shear stress in carotid plaques using magnetic resonance imaging and computational fluid dynamics analysis： a preliminary study

Background Wall shear stress is an important factor in the destabilization of atherosclerotic plaques. The purpose of this study was to assess the distribution of wall shear stress in advanced carotid plaques using high resolution magnetic resonance imaging and computational fluid dynamics.Methods Eight diseased internal carotid arteries in seven patients were evaluated. High resolution magnetic resonance imaging was used to visualize the plaque structures, and the mechanic stress in the plaque was obtained by combining vascular imaging post-processing with computational fluid dynamics.Results Wall shear stresses in the plaques in all cases were higher than those in control group. Maximal shear stresses in the plaques were observed at the top of plaque hills, as well as the shoulders of the plaques. Among them,the maximal shear stress in the ruptured plaque was observed in the rupture location in three cases and at the shoulder of fibrous cap in two cases. The maximal shear stress was also seen at the region of calcification, in thrombus region and in the thickest region of plaque in the other three cases, respectively.Conclusion Determination of maximal shear stress at the plaque may be useful for predicting the rupture location of the plaque and may play an important role in assessing plaque vulnerability.