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.

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.

Factors Influencing the Disturbed Flow Patterns Downstream of Curved Atherosclerotic Arteries

Pulsatile blood flows in curved atherosclerotic arteries are studied by computer 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 results 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 pattern in downstream is negligible.

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.

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。

基于颈动脉超声造影评估颈内动脉壁面切应力与颈动脉斑块内新生血管的关系

目的基于颈动脉彩色超声评估颈内动脉壁面切应力(WSS)与颈动脉斑块内新生血管(IPN)的关系。方法选择2021年7月至2023年9月河北医科大学第一医院收治的99例明确有颈动脉粥样硬化性斑块(CAP)的缺血性脑血管病患者。所有患者均接受颈动脉彩色超声、常规超声与颈动脉超声造影(CEUS)检查,根据缺血性脑血管病患者是否形成颈动脉IPN分为形成组与非形成组。对比形成组与非形成组WSS、临床资料,分析缺血性脑血管病患者形成颈动脉IPN的影响因素,分析平均WSS对缺血性脑血管病患者形成颈动脉IPN的预测价值。结果99例缺血性脑血管病患者中,形成颈动脉IPN 23例,剩余76例均未形成颈动脉IPN。形成组白细胞计数、斑块厚度、斑块长度、狭窄程度≥70%比例、C反应蛋白、基质金属蛋白酶-9与基质金属蛋白酶组织抑制剂-1比值(MMP-9/TIMP-1)高于非形成组(P<0.05)。Logistic回归分析结果显示,平均WSS(OR=4.545,95%CI:1.998~10.339)、狭窄程度(OR=2.765,95%CI:1.215~6.290)、C反应蛋白(OR=3.047,95%CI:1.339~6.930)、MMP-9/TIMP-1(OR=3.543,95%CI:1.558~8.060)为缺血性脑血管病患者形成颈动脉IPN的影响因素(P<0.05)。受试者工作特征曲线(ROC)结果显示,平均WSS预测缺血性脑血管病患者形成颈动脉IPN的AUC值为0.797(P<0.05),当平均WSS为10.23 dyne/cm^(2)时,最大特异度与灵敏度为85.53%和78.26%。结论颈内动脉平均WSS在预测缺血性脑血管病患者形成颈动脉IPN中具有良好价值。

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。

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.

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。

THE EFFECTS OF PHYSIOLOGICAL FLOW WAVEFORM ON WALL SHEAR STRESS IN CAROTID BIFURCATION MODEL

Numerical models of carotid bifurcation were constructed using a combination of tuning-fork bifurcation and straight or curved common carotid. The different inlet velocity profiles of the common carotid were generated for Bloch flow waveform and Holdsworth flow waveform, respectively. The effects of the different flow waveform for the common carotid on Wall Shear Stress （WSS） and Oscillatory Shear Index （OSI） of carotid bifurcation were studied by CFD method. The results show that the physiological flow waveform of curved common carotid has a significant effect on OSI. In particular, the OSI on the outer walls of carotid sinus and external carotid becomes higher in the inward-curved common carotid for Holdsworth flow waveform. But, in both cases of low WSS and high OSI, the effects of flow waveforms are smaller than those of the curved common carotid. The study reveals that the exact knowledge of the physiological flow waveform, vascular geometry and inlet velocity profile is important for hemodynamic numerical simulation of artery bifurcation.

局部狭窄动脉内血流动力学环境的动态数值研究

为了定量研究局部狭窄动脉内的血流动力学环境,进而寻求其与动脉粥样硬化发生发展的关联,本文推导并建立了针对该问题的差分数值求解体系。推导了控制方程在特定坐标系空间的表达,给出了适当的边界条件。最后选择猪的颈动脉为研究对象,利用高频电磁流量探头和压力探头在体测量了入口段一个心动周期的血流量、压力等数据。利用这些测量数据作为求解体系的输入数据,心动周期内局部狭窄动脉内的各种血流动力学数据被细致求解,心动周期不同时期的流场、轴向速度分布、壁面切应力被详细显示并作了生理层面的分析。

增强型体外反搏对早期动脉粥样硬化斑块局部应力环境影响的实验与仿真研究

采用动物实验与数值仿真相结合的方法,研究增强型体外反搏（EECP）对发生早期粥样硬化斑块动脉的局部应力水平的影响,评价临床中该疗法增加粥样硬化斑块失稳的风险.首先以3.5月龄左右雄性猪2头为实验体,进行反搏前后状态的基础血流动力学在体测量,反搏压介于0.025 ～0.04MPa;进而建立血流动力学数值仿真模型,模拟斑块出现及生长过程中,EECP对其局部应力水平及应力震荡特性的影响.模拟计算结果显示,EECP使动脉的应力水平及应力震荡特性均有显著增加;早期小规模斑块的存在令局部应力水平进一步提升,但将降低应力的震荡水平.EECP使两实验体的动脉内压峰值水平最高提升10.62％及16.18％,此时若动脉存在斑块（H=0.2D）,其局部壁面切应力（WSS）峰值水平将分别提高135.54％及235.71％,震荡剪切指数（OSI）达到0.083及0.069.由于反搏产生的高舒张压明显提升了斑块的局部应力水平,同时反搏的“双脉冲”作用模式使动脉的OSI水平大幅增加,我们推测其慢性作用可能会促进斑块本身疲劳的进程,从而对斑块的稳定性产生不利影响;但EECP对心动周期里壁面切应力水平的提升可能对斑块本身的发展具有抑制作用.

T型分叉血管中血液流动对动脉血栓形成的影响

目的从血流速度、分支直径、T型分叉角度及血液黏度的血流动力学角度,并结合相关医学病例,研究T型分叉血管中血液流动对血栓形成的影响,从多学科角度分析并验证医学研究中的有关血栓形成机理的猜测。方法建立T-型动脉血管的几何模型,采用计算流体动力学方法对血管内流场进行数值分析研究,分析不同条件的流动对血栓形成影响。结果在分叉血管附近的支血管和主血管中分别形成了两处较大区域的涡流区域,另外,在分叉交接处的下游位置也出现了一处较小的区域,这些区域速度较低,剪应力出现突然增大趋势,符合血栓形成,因此成为"最适成栓位置"。结论血栓在"最适成栓位置"的形成还与分支血管直径、血管中血流速度、分叉角度以及血液黏度等有密切关系。

弯曲动脉血管中血液流动对血栓形成的影响

血栓性疾病大多发生在弯曲和血管分叉的位置附近,其形成机制和原因比较复杂,目前的研究主要集中在临床病例的治疗护理方面。临床观测表明,动脉疾病的发病机制和病变发展与血流动力学特征(如流场分布、壁面剪应力等)密切相关。采用计算流体力学方法,从血流动力学角度研究了弯曲血管中血液流动的改变对血管栓塞形成的影响。主要从血流入口初始速度、弯曲曲率半径、血管管径及血液黏度方面研究血液流动对血栓形成的影响。同时结合相关医学病例,从多学科角度分析并验证医学研究中有关血管弯曲对血栓形成机理的猜测。

S形动脉中的血流动力学研究

目的探索动脉直径大小对S形动脉血流动力学的影响。方法利用数值模拟方法,对具有不同直径的大小两种S形动脉模型在相同的边界条件下的血流动力学时空分布进行了分析。结果在大S形动脉中的二次流比小S形动脉中的要复杂;在弯曲动脉的内弯区存在较强的涡流;弯曲动脉中的压力和壁面切应力变化很剧烈,特别是在大模型中。结论S形弯曲动脉中的血流呈现复杂回流、二次流、压力和壁面切应力剧烈变化等特性,这些都可能影响到动脉内皮的功能及内膜增生。在利用人造或自体血管修复旁路狭窄动脉的手术中,应尽量避免采用S形动脉模型。

Y型分叉冠状动脉血管中血液流动对血栓形成的影响

为研究Y型分叉血管中血液流动对血栓形成的影响,根据黏性流体稳定流动的Navier-Stokes方程,建立了冠状动脉分叉血管中血液流动的数学模型,并采用计算流体力学(computational fluid dynamics,CFD)的方法,数值模拟了不同Y型分叉冠状动脉血管中血液流动情况,并考虑了分叉角度、血液黏度、入口血流初始速度对血流速度场、壁面剪应力、壁面压强的影响.结果表明:分叉角度越小成栓可能性越大,存在最易成栓的血流速度,但血液黏度对血柱形成的影响不大.