Computational Fluid Dynamics Analysis of Shroud Design on Hemodynamic Performance and Blood Damage in a Centrifugal Blood Pump

Patients with extracorporeal membrane oxygenation still suffer from high rates of complication that linked to the flow field within the blood pump.So it is essential to optimise the geometry of the pump.The specification of shroud design is arguably the necessary design parameter in the centrifugal pump.However,the hemodynamic performances of the different shroud designs have not been studied extensively.In this study,ten different shroud designs were made and divided into two groups as the different covering locations(A:Covering the blade leading edge,B:Covering the blade trailing edge).In every group,six shroud designs with the covering proportions of 0,1/5,2/5,3/5,4/5,1 were made.Detailed computational fluid dynamics(CFD)analyses were performed to investigate their effects on hemodynamics and hydraulic performance at the constant flow condition(4000 rpm,5 L/min).The percentage volumes of the scalar shear stress in specific threshold(τ<1 Pa:Thrombosis,τ>9 Pa:the destruction of von Willebrand factor,τ>50 Pa:Platelet activation,τ>150 Pa:Break of red blood)were used to compare the blood damage of the different shroud designs.Also,the modified index of hemolysis(MIH)were calculated based on a Eulerian approach for different pumps.CFD simulations predicted an increase in the pump head,hydraulic efficiency,a fraction of fluid volume with scalar shear stress values above a threshold(9 Pa,50 Pa,150 Pa)and MIH with increasing shroud covering proportions from 0 to 1 in the same covering location.Also,these above results were higher in group B than group A.This means that the risks of the hemolysis,thrombosis and bleeding increased as the rise of the covering proportion and they were higher in the pump whose shroud covers the blade trailing edge.

Computational fluid dynamics modeling in intracranial atherosclerotic disease

Intracranial atherosclerotic disease(ICAD)is an important cause for ischemic stroke and transient ischemic stroke(TIA)throughout the world,especially in Asians,which is not fully appreciated,partly due to its inaccessibility and limitations of current neuroimaging methods.The computational fluid dynamics(CFD)modeling technique provides a novel approach to reveal the hemodynamic characteristics in ICAD,e.g.,the distributions of pressure,wall shear stress and flow velocity.In this review article,we aim to provide an overview of the general methodology of CFD modeling in arterial stenotic diseases,the established application of this technique in coronary artery disease,and more importantly,perspectives and challenges of this technique in the investigation of ICAD.Promising findings of preliminary studies using a CFD model for hemodynamic analysis in ICAD warrant verifications.Further studies in this area will help rectify loopholes in the current secondary prevention strategy,and inform individualized treatment for ICAD patients in the near future.

Preliminary Evaluation of Hemodynamic Effects of Fontan Palliation on Renal Artery Using Computational Fluid Dynamics

Background:The assessment of renal function is important to the prognosis of patients needing Fontan palliation due to the reconstructed compromised circulation.To know the relationship between the kidney perfusion and hemodynamic characteristics during surgical design could reduce the risk of acute kidney injury(AKI)and the postoperative complications.However,the issue is still unsolved because the current clinical evaluation methods are unable to predict the hemodynamic changes in renal artery(RA).Methods:We reconstructed a three-dimensional(3D)vascular model of a patient requiring Fontan palliation.The technique of computational fluid dynamics(CFD)was utilized to explore the changes of RA hemodynamics under different possible blood flow rates.The relationship between the kidney perfusion and hemodynamic characteristics was investigated.Results:The calculated results indicated the declined tendency of the pressure and pressure drop as the flow rate decreased.When the flow rate decreased to two-thirds of its baseline,both the pressure of left renal artery(LRA)and the pressure of right renal artery(RRA)dipped below 50%,and the pressure of RRA fell more quickly than that of LRA.Uneven distribution of WSS was observed on the trunk of RA,and the lowest WSS was found at the distal of RA.The average WSS in RA dropped to around 50%as the flow rate reached one-third of its baseline.Conclusions:As a promising approach,CFD can be utilized to quantitatively evaluate the hemodynamic characteristics of RA and contribute to offsetting the drawbacks of clinical assessments of renal function,to help realize better prognosis for the patients with Fontan palliation.

Computational Fluid Dynamics Simulation on Biomedical Stent Design

The stent was a major breakthrough in the treatment of atherosclerotic vascular disease. The permanent vascular implant of a stent, however, changes the intra-stent blood flow hemodynamics. There is a growing consensus that the stent implant may change the artery wall shear stress distribution and hence lead to the restenosis process. Computational fluid dynamics （CFD） has been widely used to analyze hemodynamics in stented arteries. In this paper, two CFD models （the axisymmetric model and the 3-D stent model） were developed to investigate the effects of strut geometry and blood rheology on the intra-stent hemodynamics. The velocity profile, flow recirculation, and wall shear stress distribution of various stent strut geometries were studied. Results show strong correlations between the intra-stent hemodynamics and strut geometry. The intra-stent blood flow is very sensitive to the strut height and fillet size. A round strut with a large fillet size shows 36% and 34% reductions in key parameters evaluating the restenosis risk for the axisymmetric model and the 3-D stent model, respectively. This suggests that electrochemical polishing, a surface-improving process during stent manufacturing, strongly influences the hemodynamic behavior in stented arteries and should be controlled precisely in order to achieve the best clinical outcome. Rheological effects on the wall shear stress are minor in both axisymmetric and 3-D stent models for the vessel diameter of 4 mm, with Newtonian flow simulation tending to give more conservative estimates ofrestenosis risk. Therefore, it is reasonable to simulate the blood flow as a Newtonian flow in stented arteries using the simpler axisymmetric model. These findings will provide great insights for stent design optimization for potential restenosis improvement.

Influence of Strut Cross-section of Stents on Local Hemodynamics in Stented Arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics（CFD） methods are performed to study how the shape and the aspect ratio（AR） of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress（WSS） in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.

Impacts of waveforms on the fluid flow, wall shear stress, and flow distribution in cerebral aneurysms and the development of a universal reduced pressure

The hydrodynamics of aneurysm blood flow is thought to be a critical factor in the evolution and potential rupture of blood vessel walls. The ability to predict which aneurysms may grow or rupture has eluded researchers and practicing clinicians. On the other hand, it is expected that local flow patterns, pressures, and wall shear stress play a role in the aneurysm life. In this study, the impact of waveform on these parameters was studied. A baseline waveform, taken from a patient, was applied to an aneurysm geometry. Then the waveform was modified by increasing and decreasing both the flowrates and the cardiac rate. In total, seven cases were investigated. It was found that there were remarkable similarities in the patterns of flow and wall stresses for the cases. These similarities existed throughout the cardiac cycle. It was also found that there was a reduced pressure variable that provides a universal relationship that characterizes all of the cases. It was seen that the maximum wall shear occurs at the neck of the aneurysm and scales with the peak systolic velocity. Finally, it is shown that the flow distribution to the multiple outlets does not appreciably depend on the details of the inlet waveform. All cases had a flow distribution that was within 2%.

主动脉穿刺型轴流血泵折边结构叶轮的数值模拟及溶血分析

为解决血泵因叶顶间隙泄漏而造成溶血和血栓等问题,引入了一种折边不等间距叶轮,采用计算流体力学(computational fluid dynamics, CFD)进行内部流场的数值模拟,并与非折边不等间距叶轮及折边等间距叶轮进行对比分析,研究了它们的内流场动力学特性和血液相容性.结果表明:折边叶片结构血泵避免了叶顶间隙泄漏流的产生,同时折边不等间距叶轮减少了叶轮入口和出口处的回流和涡流,流道内整体切应力低于其他2种叶轮;3种叶轮的溶血指数HI均满足血泵的溶血设计指标,其中,折边不等间距叶轮血泵壁面切应力在0~150 Pa的占比达96.84%,曝光时间相对集中且满足人工血泵设计要求,溶血指数较非折边不等间距叶轮血泵下降了3.50%,较折边等间距叶轮血泵下降了12.50%,溶血性能最优.提出的折边不等间距叶轮血泵可有效降低红细胞破损概率,减少溶血和血栓的发生,可为轴流血泵的结构设计和优化提供一定参考.

不同生理条件下主动脉双叶机械心脏瓣膜血流动力学分析

采用计算流体动力学方法对不同生理条件下主动脉位置双叶机械心脏瓣膜下游的速度分布、涡演化、粘性剪切应力、雷诺剪切应力进行研究。收缩期峰值时,运动状态下血液射流较其他两种生理状态下更为强烈,最大血液流速为2.1 m/s。对于涡演化的分析表明3种生理状态下剪切层是比较明显的流动特征,在收缩期峰值时,血液与主动脉窦作用较为强烈。对于粘性剪切应力,当瓣叶完全打开时,瓣叶在瓣膜区阻碍了血液流过瓣膜,血流与瓣叶之间的相互作用导致了较高的剪切应力,3种生理状态下,观察到的最大粘性剪应力小于8 N/m^(2)。3种生理状态下观察到最大的雷诺剪切应力为700 N/m^(2)。本研究有助于为临床手术瓣膜选择以及术后康复提供理论依据。

基于CTA数据后处理对颈内动脉狭窄处血流动力学特点的研究

目的 基于头颈部CTA影像数据建立计算流体力学(CF)仿真模型,研究颈内动脉狭窄处的血流动力学特点。方法 回顾性分析蚌埠医学院第二附属医院2021-05—2023-03符合纳入标准的30例患者,运用脑血管三维重建技术对颈动脉及颈内动脉进行3D模型重建,并进行血流动力学参数分析测量及统计,测得颈内动脉狭窄处的壁面剪切应力(WSS)、时间平均壁面剪切应力(TAWSS)、震荡剪切指数(OSI)、相对滞留时间(RRT)并分析各项参数之间的相关性及差异性。结果 颈内动脉狭窄区域的WSS、TAWSS、OSI、RRT分别为58.669 3(43.882 0,65.979 2)、18.695 8(14.973 8,25.534 6)、0.074 6(0.063 3,0.085 4)、0.092 3(0.082 2,0.109 6),正常侧WSS、TAWSS、OSI、RRT分别为15.215 3(9.039 7,25.117 2)、5.138 2(3.373 4,6.139 9)、0.122 7(0.099 7,0.151 2)、0.712 3(0.519 0,0.821 7)。颈内动脉狭窄处的血流速度及血流量分别为1.925 9±0.125 5、4.374 1±0.277 9,正常侧的血流速度及血流量分别为0.992 6±0.074 7、6.190 7±0.260 9。狭窄区域的WSS、TAWSS明显增大,OSI和RRT相对较小,血流速度明显增大,同时伴随较小的血流量,差异均有统计学意义(P<0.05)。结论 颈内动脉狭窄处的血流动力学因素较正常侧发生明显变化,可通过CFD仿真模拟分析方法评估血流动力学因素变化程度,帮助分析颈内动脉狭窄患者的危险程度,辅助临床诊断、治疗及预后评估。

串联型颈动脉狭窄的血流动力学模拟分析

目的使用计算流体力学(computational fluid dynamic,CFD)对串联型颈动脉狭窄(tandem carotid artery stenosis,TCAS)进行模拟,比较不同手术方式术后的血流动力学改变情况。方法选取1例颈内动脉(internal carotid artery,ICA)和颈总动脉(common carotid artery,CCA)串联型狭窄患者,使用CFD技术对建立的4个颈动脉分叉三维模型(1个真实患者模型,3个假定手术模型)进行血流动力学分析,探索TCAS的发生发展机制并指导选择合适的手术方案。结果在串联型狭窄中,狭窄优先在CCA形成,随后导致ICA狭窄;TCAS较单个颈动脉狭窄的局部血流动力学情况更复杂,风险更高;串联型狭窄中,单个狭窄部位的治疗会影响第二个狭窄部位的血流,并可能导致再狭窄或斑块破裂。结论在规划TCAS手术方案时,对选定TCAS患者进行CFD模拟可帮助临床医生评估术后血流改变情况,指导选择合适的手术方案。

Stanford A型主动脉夹层的个体化血流数值模拟

目的研究Stanford A型主动脉夹层的血流动力学变化。方法收集4名Stanford A型主动脉夹层患者和2名健康志愿者的主动脉计算机断层扫描血管造影(computed tomography angiography,CTA)图像,建立主动脉三维模型并进行网格划分,使用流体仿真软件对模型进行数值模拟。结果健康志愿者主动脉内血流近似层流。夹层真腔的血流近似层流,位于破口附近的真腔和被假腔压迫的真腔会在局部形成湍流。真腔的壁面压力高于假腔。心脏收缩期,假腔的壁面压力峰值位于夹层第一个破口处,被假腔压迫的真腔和假腔破口处出现较高的壁面剪切力且破口处出现了应力集中。相比于单一破口的夹层,有2个破口的夹层其破口周围的壁面剪切力更低。结论个体化计算流体力学分析可以为主动脉夹层的个性化诊疗提供参考。

颈动脉斑块血流动力学成像技术及新进展

颈动脉粥样硬化性狭窄是引起缺血性脑卒中(ischemic stroke,IS)的主要疾病之一,尽早发现狭窄并识别易损斑块可以显著改善疗效,降低致死率和致残率。血流动力学改变与斑块的形成、发展、破裂有着密切关系。利用血流动力学参数来评估动脉粥样硬化斑块破裂的风险及指导临床治疗方式的选择已经成为动脉粥样硬化精确诊疗的研究焦点。然而,血流动力学参数与斑块相互作用的机制尚未被完全阐明,血流动力学相关影像学技术也未广泛开展。本文通过对既往文献进行回顾,进一步梳理颈动脉斑块血流动力学的影像进展,以及血流动力学变化与斑块形成、发展、破裂之间的相互作用机制,并探讨了这些特征与缺血性卒中的关系,旨在评估综合分析斑块成分和血流动力学对颈动脉粥样硬化性狭窄引起脑卒中事件的预测价值。

腹主动脉瘤血流动力学流固耦合分析

利用医学建模软件MIMICS对内蒙古民族大学附属医院提供的腹主动脉瘤CT数据进行三维模型重建,借助流固耦合仿真软件Workbench15.0进行血流动力学数值模拟,得到一个心动周期梭状腹主动脉瘤的管壁形变量、血液流场、壁面切应力。计算结果显示,在心动收缩期瘤内存在明显的涡旋和低流速区域,长此以往易造成瘤腔内壁出现血细胞堆积、细胞炎症等问题,动脉瘤大部分为低壁面切应力区域,区域长期处于低切应力会使瘤壁弹性蛋白降低,并且发现形变集中区域中心的形变量最大,在该区域极易发生动脉瘤破裂。借助双向流固耦合方法对弹性壁的腹主动脉瘤进行数值模拟,可以从血流动力学角度分析动脉瘤产生、发展及破裂的原因,为腹主动脉瘤的诊断和治疗提供依据。

计算流体力学在颅内动脉瘤中的研究进展

计算流体力学作为一种研究血流动力学的辅助工具,尽管在观察颅内动脉瘤发生、发展,评估破裂风险等方面具有重要作用,但目前仍有许多值得探讨之处。本文旨在归纳计算流体力学在颅内动脉瘤相关研究中的历史、应用及与三维打印技术的结合,探讨其对临床实际工作的指导意义。

Influence of high-porosity mesh stent on hemodynamics of intracranial aneurysm:A computational study

This paper studies the influence of a High-Porosity Mesh （HPM） stent on the hemodynamic characteristics in the intracranial aneurysm based on the Computational Fluid Dynamics （CFD）. An idealized basilar tip aneurysm model and a HPM stent model are built. The pulsating blood flow in a cardiac cycle is computationally simulated for non-stented and stented models, to provide a wealth of information of the spatio-temporally varying blood flow field. The influence of the stent placement on the hemodynamic characteristics is analyzed in terms of distributions of velocity, pressure, Wall Shear Stress （WSS） and Energy Loss （EL）, which are believed to play an important role in the development and rupture of the aneurysm. The numerical results clearly show that the velocity, pressure, WSS and EL of the blood flow in the aneurysm are reduced by 30%-40% when the HPM stent is implanted. These computational results may provide valuable hemodynamic information for clinical neurosurgeon.

Different treatment modalities of fusiform basilar trunk aneurysm： study on computational hemodynamics

Background Unclippable fusiform basilar trunk aneurysm is a formidable condition for surgical treatment.The aim of this study was to establish a computational model and to investigate the hemodynamic characteristics in a fusiform basilar trunk aneurysm.Methods The three-dimensional digital model of a fusiform basilar trunk aneurysm was constructed using MIMICS,ANSYS and CFX software.Different hemodynamic modalities and border conditions were assigned to the model.Thirty points were selected randomly on the wall and within the aneurysm.Wall total pressure （WTP）,wall shear stress （WSS）,and blood flow velocity of each point were calculated and hemodynamic status was compared between different modalities.Results The quantitative average values of the 30 points on the wall and within the aneurysm were obtained by computational calculation point by point.The velocity and WSS in modalities A and B were different from those of the remaining 5 modalities; and the WTP in modalities A,E and F were higher than those of the remaining 4 modalities.Conclusions The digital model of a fusiform basilar artery aneurysm is feasible and reliable.This model could provide some important information to clinical treatment options.

Recent advances in the application of computational fluid dynamics in the development of rotary blood pumps

In recent years,ventricular assist devices(VADs,also known as blood pumps)have gradually entered clinical practice and provide effective treatment for heart failure patients.However,adverse events related to mechanical blood damage in patients receiving the VAD treatment,were often reported and have become a major concern during the development of VADs,limiting their clinical and economic benefits.Compared with bench and in-vivo testing,computational fluid dynamics(CFD)is flexible and inexpensive,offering the possibility to predict hemodynamics and mechanical blood damage in a purely numerical manner.Thus,CFD has become an important tool for the design,optimization and evaluation of blood pumps.The stringent requirements of blood pumps require high fidelity simulations.Thus,this article reviews the current state of the art in high-fidelity methodologies for simulating blood flow and blood damage for the development and evaluation of rotary blood pumps;design and optimization methods of rotatory blood pumps using CFD,as well as future challenges.

血管内支架构型变化对血流动力学及支架内再狭窄形成的影响

目的研究血管内支架的构型变化对血管壁面剪切力、血流速度及流动方式的作用,探讨支架构型对于支架内再狭窄形成的影响。方法应用三维实体建模软件Pro/engineer wildfire3.0建立5种支架模型,其中A为对照组,B加入横向连接结构,C加入纵向连接结构,D的支架厚度为A的2倍,E的网格密度为A的2倍,将其导入计算流体动力学(computational fluid dynamics,CFD)软件Ansys11.0-CFX,建立流体模型。设定边界条件后进行计算流体动力学分析,比较不同构型的支架植入后引起的血管壁面剪切力、管腔内血流速度及流动方式的变化。结果支架模型A、B、C、D、E植入后血管壁面低剪切力区域所占比率分别为:7.78%、6.65%、1.48%、16.52%、12.12%,D、E的低剪切力区域比率明显大于A,B的低剪切力区域比率明显小于A。支架横截面流速矢量(velocity vector)图显示,D、E中的血流低流速涡流区明显大于A,C中低流速涡流区明显小于A。结论支架构型变化能够引起植入血管血流动力学的明显改变,支架厚度和(或)网格密度增加是引起低剪切力区形成的主要因素,能够促进支架内再狭窄的发生,在支架中加入纵向连接结构能明显减少低剪切力区,可以降低再狭窄形成概率。

支架孔率对脑动脉瘤血流动力学影响的三维数值模拟研究

目的探讨不同支架网孔密度对支架植入后脑动脉瘤内血流动力学的影响。方法建立宽颈的弯曲管侧壁型动脉瘤血流动力学三维数值模型,比较不同网孔密度支架植入前后,动脉瘤内血流动力学变化。结果动脉瘤远侧壁的速度峰值与壁面剪应力随着支架孔率下降而降低,瘤颈远侧壁及瘤顶部的压力场与支架孔率无明确的相关性。结论数值模拟研究证实支架孔率是影响动脉瘤内血流动力学的关键因素,合适的支架孔率设计对动脉瘤血管重建治疗至关重要。

DeBakey Ⅲ型主动脉夹层血流动力学数值模拟分析初步研究

目的探索血流动力学因素在DeBakeyⅢ型主动脉夹层发生、发展以及临床预后评估中的作用。方法通过CT扫描获取临床常见典型形态的DeBakeyⅢ型主动脉夹层断层图像序列,重建出三维主动脉夹层血流动力学分析计算机模拟模型,采用计算流体力学数值模拟方法对主动脉夹层真假腔内的血液流场进行数值模拟分析。结果①单破口型夹层假腔压强持续高于真腔压强,呈现"吹气球"效应;②当DeBakeyⅢ型主动脉夹层真腔受压狭窄时,真腔内压强将低于假腔内压强,夹层真腔内血流流线也会出现部分中断;③夹层撕破口附近的动脉管壁局部血流动力学因素可出现失衡现象。结论 DeBakeyⅢ型主动脉夹层真假腔压强失衡可导致假腔持续扩张、压迫真腔。夹层管壁局部血流动力学改变可能是慢性期B型夹层破裂的危险因素。