左主干分叉病变严重程度的血流动力学功能性评价

目的无保护左主干分叉病变的治疗方式选择很大程度上依赖于病变的严重程度。SYNTAX评分是基于冠脉造影图像对冠脉病变严重程度进行评价的方法,是一种完全解剖学的评价,缺少功能性的分析。本文以总灌注量作为判断病变严重程度的参考量,从血流动力学的角度对不同类型分叉病变严重程度做出评价。方法采用患者三维模型(three-dimensional,3D)耦合个性化的集中参数模型(lumped parameter model,LPM,0D)对不同的分叉病变进行多尺度数值仿真计算,提取不同分支的流量、分叉区域的壁面切应力(wall shear stress,WSS)、壁面切应力振荡指数(oscillatory shear index,OSI)3个血流动力学参数,通过对比这些参数,从血流动力学的角度对不同类型分叉病变严重程度做出分析。结果分支(回旋支)是否病变对总灌注量是有影响的,当分支存在病变时,总灌注量会降低,与SYNTAX评分中对分叉病变严重程度的分类是一致的。从恶化风险(WSS,OSI)来看,当左主干存在狭窄时,分叉区域平均WSS相对比较大,OSI并没有呈现出一定的规律。结论分支存在狭窄的左主干分叉病变比分支不存在狭窄的病变总灌注量更小,心肌缺血程度更严重,狭窄进一步恶化并无明显差异。     

颈动脉分叉处血管粥样硬化斑块的体内应力分析

目的探究颈动脉分叉处血管斑块的体内应力分布,为颈动脉分叉处血管斑块破裂行为的研究和诊断治疗方案的设计提供力学机理参考。方法基于人体颈动脉分叉血管的平均几何参数,建立三维颈动脉分叉血管及其斑块的几何模型,通过"热-结构"耦合重建颈动脉分叉血管及其斑块的残余应力,并计算血压和血流分别作用下颈动脉分叉处血管斑块的体内应力。结果斑块的肩部同时存在着最大主应力和弹性剪切应力的应力集中。斑块肩部的弹性剪切应力随着狭窄率增大或血压升高均增加。斑块上游区域的流体壁面切应力明显高于斑块下游区域,斑块下游区域的振荡剪切指数则显著大于上游区域。且斑块的弹性剪切应力和流体壁面切应力大小随着狭窄率的变化呈现出不同的变化规律。结论斑块从内部中心位置到壁面肩部承受着非均匀的应力分布,血管严重狭窄时"内压外拉"的受力状态更容易导致斑块破裂。随着血压的变化,斑块结构应力的周期性变化可能使斑块产生结构疲劳,增加破裂风险。斑块上下游区域流体动力学参数的差异可能是斑块上下游组分、易损程度等性质不同的原因之一。     

基于病例研究冠状动脉扭曲对血流动力学的影响

目的探讨扭曲冠状动脉血流动力学的改变,从而阐明扭曲对冠状动脉血流灌注和壁面切应力(wall shear stress,WSS)的影响。方法选取冠状动脉左前降支(left anterior descending,LAD)扭曲和无扭曲两例个体病例,在Mimics软件中重建出LAD扭曲和无扭曲血管模型,并将模型导入ANSYS Fluent软件中进行血流动力学模拟计算,比较两种不同LAD模型的血流动力学情况。结果扭曲的冠状动脉在最大曲率大于1 mm~(-1)的弯曲处WSS下降较为明显,这种情况可能导致下游供血不足;弯曲外侧具有较低WSS(0~26 Pa),而弯曲内侧WSS相对较高(100 Pa);无扭曲和扭曲血管WSS均值分别为10.79、36.12 Pa,相比于无扭曲血管,扭曲血管整体WSS增高。结论扭曲冠状动脉整体WSS增高,从而可能延缓冠状动脉粥样硬化的进展。     

冠状动脉斑块分型及分叉角度对斑块影响的血液动力学模拟

目的 分析斑块分布分型和血管分叉角度对冠状动脉分叉血管内血液动力学的影响,进一步探讨对斑块易损性发展的影响规律。方法 基于人体冠状动脉分叉血管的平均几何参数,构建不同斑块分布分型和血管分叉角度情况下的流固耦合模型,研究关键部位处的血流速度、压力以及剪切应力分布。结果 斑块上游的肩部是斑块表面剪切应力最大的部位,容易发生溃疡或破裂并进一步发展;当分叉血管单侧有斑块时,分叉脊处的剪切应力大于双侧有斑块的情况。血管分叉脊处的压力和剪切应力随分叉角度减小而逐渐增大。结论 分叉处单侧有斑块时,斑块溃疡或破裂的概率更大。主支血管内斑块的存在会促进分叉处斑块的形成和发展。血管分叉的角度越小,分叉脊处的血管内壁越易受损。研究结果可为易损斑块治疗方案的设计与优化提供理论参考。     

冠状动脉分叉病变单支架植入术后血流动力学分析

目的分叉病变在即刻手术成功率及远期心脏事件方面是最具有挑战的冠脉病变之一。血流动力学对动脉粥样硬化的形成有重要影响。对分叉病变单支架虚拟植入后的血流动力学参数分布进行分析,探讨其对支架后再狭窄的影响,可为临床治疗提供理论依据。方法本文选取一例冠状动脉分叉病变患者的冠状动脉血管造影(computed tomography angiography,CTA)图像,首先用Mimic软件对所获得冠脉CTA数据进行三维重建得到冠脉血流区域,然后运用类似虚拟去除斑块的方式建立不均匀壁厚血管壁模型,对所得模型在ABAQUS中进行单支架虚拟植入,最后根据虚拟植入前、后的冠脉模型分别生成支架前和真实变形后的血流域有限元模型,并利用ANSYS软件通过瞬态CFD分析模拟动脉血流的流动状态,获得目标血管段的血流动力学参数。结果支架植入后与支架植入前相比,目标血管段的血液流速、壁面剪切应力均降低;支架植入后主支血管远端有振荡的低剪切应力区域;支架边缘位置壁面剪切应力低于其他位置;分支血管直径变小;分支外侧壁壁面剪切应力低于内侧壁。结论分叉病变的单支架植入可改善冠脉主支的狭窄,但术后主支血管远端振荡的低剪切应力区域、支架边缘和边支外侧壁处的低壁面剪切应力,以及斑块和分叉嵴的移位有可能是分叉病变再狭窄的血流动力学机制。     

不同冠脉后负荷下竞争流对左乳内动脉桥血流动力学影响

目的研究冠状动脉在不同后负荷条件下,冠脉搭桥手术后竞争流对左乳内动脉(left internal mammary artery,LIMA)血流动力学影响。方法模拟LIMA到前降支(left anterior descending,LAD)搭桥手术三维模型(three-dimensional,3D),建立与冠脉模型相对应的集中参数模型(lumped parameter model,LPM,0D),为其提供1倍和1.2倍两种不同后负荷的边界条件,同时在LAD主干处设置了25%、40%、50%、60%、75%5种不同直径狭窄程度,使用计算流体力学(computational fluid dynamics,CFD)耦合计算冠脉3D模型和0D模型,从血流动力学角度分析不同后负荷时竞争流对LIMA的影响。结果 1倍后负荷时,LAD总流量约为80 m L/min,随狭窄率增加,RC/G从2.025减小到0.280,LIMA平均血流量从26.598 m L/min增加到62.310 m L/min,震荡剪切指数(oscillatory shear index,OSI)从0.1557减小到0.0020,狭窄率小于50%时,时间平均壁面切应力(time-average wall shear stress,TAWSS)低于1 Pa;1.2倍后负荷模型中,LAD总流量为71 m L/min,随狭窄率增加,RC/G从2.222减小到0.289,LIMA平均血流量从22.188 m L/min增加到54.810 m L/min,OSI从0.1790降低到0.0024,狭窄率小于60%时TAWSS低于1 Pa。后负荷改变时,相同狭窄程度下桥血管在收缩期血流量变化很小,但舒张期流量随后负荷增大而减小。结论当冠脉后负荷较大时,竞争流强度偏大。当血管管径和狭窄程度都相同时,后负荷大的患者LIMA桥血管会因偏低的WSS和较高的OSI更容易引起"线性征",降低桥血管远期通透性。     

冠状动脉旁路移植术后竞争血流对桥血管血流动力学的影响

目的 研究冠状动脉旁路移植术后,不同程度竞争血流对左侧胸廓内动脉管壁壁面切应力(wall shear stress, WSS)的影响。方法 基于阈值分割方法,通过采用SimVascular软件从CT图像提取并重建左侧胸廓内动脉(left internal mammary artery, LIMA) 左前降支（left anterior descending, LAD）吻合口模型。根据LAD的狭窄程度将竞争血流分为无竞争（100%狭窄）、轻度竞争（50%、75%狭窄）和高度竞争血流（0%、30%狭窄）3组。通过数值模拟方法观察上述情况下吻合口模型的血流动力学表现。结果 随着竞争血流的增加,LIMA桥血管管壁WSS逐渐降低,但是震荡程度逐渐增加。高度竞争血流组LIMA管壁平均WSS（0%狭窄：2.73 Pa,30%狭窄：2.85 Pa）明显低于轻度竞争血流组（50%狭窄：4.77 Pa,75%狭窄：6.01 Pa）和无竞争血流组(100%狭窄：8.64 Pa);而其震荡剪切指数(oscillatory shear index, OSI)（0%狭窄：0.206,30%狭窄：0.085）却明显高于轻度竞争血流组（50%狭窄：0.014,75%狭窄：0.013）和无竞争血流组(100%狭窄：0.006)。结论 当LAD狭窄程度小于50%时,大量的竞争血流会使LIMA管壁WSS明显降低,并且呈剧烈震荡的状态,这种不利的WSS表现会影响LIMA的远期通畅率,并造成手术远期疗效的下降。     

血管弯曲程度对内源性一氧化氮分布的影响

一氧化氮(NO)在血流调控中起着重要作用,目前关于血管弯曲程度对NO分布的影响尚不明确。建立11个不同弯曲程度的几何模型,利用多物理场耦合建模仿真的方法,对内源性NO在血液、血管壁及周围组织中的浓度分布进行数值模拟。数值结果表明,在血管弯曲处,NO径向分布不均,内外侧浓度存在差异,且随着弯曲程度的增加,浓度差值呈先上升后缓慢降低的趋势。在血管投影长度为定值20 mm 的情况下,当弯曲高度取2 mm、对应曲率为0.04时,NO在内外侧平滑肌区域的浓度差值达到最大,外侧边界比内侧高23.74%。研究揭示弯曲程度对内源性NO分布的影响,所产生的NO浓度分布差异可能是导致血管形态变化以及血管病变的重要因素,为进一步探究发病机理以及患病风险评估提供一定的理论依据。     

颈内动脉虹吸部血流的数值计算和模型实验

目的研究不同几何构型颈内动脉中的血流动力学因素,分析其构型和动脉狭窄的关系,为颈内动脉狭窄的风险预测和早期诊断提供一定的血流动力学基础。方法对两种常见形状的颈内动脉——U形和V形在定常流条件下的流场分别进行数值模拟和粒子成像测速的实验研究。结果在其中较上游的弯曲处,血流动力学因素与弯曲曲率存在单调的相关关系,V形在此处的狭窄风险小于U形。但是在下游的弯曲处,由于两个弯曲的叠加效应,其血流动力学因素与此处的曲率不存在单调的相关关系。结论弯曲动脉的曲率和动脉狭窄的风险成正相关关系。但是在连续多个弯曲的动脉中,则需考虑弯曲的叠加效应。对此叠加效应的研究有助于解释多弯血管内狭窄多发的原因。     

冠状动脉分叉角度对血液流体力学及斑块形成分布的影响

通过个体化正常人体左冠状动脉CT构建不同分叉角度的流体力学模型,应用计算流体动力学(computational fluid dynamics,CFD)的方法模拟研究不同分叉角度左冠状动脉的流体力学特性,从而探讨冠状动脉分叉角度与斑块形成分布的关系。应用有限元仿真模拟并分析不同分叉角度左冠状动脉的流动力学特性。不同分叉角度的冠状动脉在壁面压强(wall pressure,WP)、壁面剪切应力(wall shear stress,WSS)、血液流场分布均存在差异。左冠状动脉分叉模型中存在两处低剪切应力区域:分叉脊附近和分叉对侧。分叉脊附近剪切应力随分叉角度增大而逐渐减小,其范围相应的增大;分叉对侧的低剪切应力及其范围并没有相应的变化。冠状动脉分叉角度与血液流体力学及斑块形成及分布有一定的关系。     

A Follow-up MRI-based Geometry and Computational Fluid Dynamics Study of Carotid Bifurcation

Cardiovascular disease is the leading causes of death in the developed world. Wall shear stress(WSS) is associated with the initiation and progression of atherogenesis. This study combined the recent advances in MR imaging and computational fluid dynanucs(CFD) and evaluated the patient-specific carotid bifurcation. The patient was followed up for 3 years. The geometry changes(tortuosity,curvature, ICA/CCA area ratios, central to the cross-sectional curvature, maximum stenosis) and the CFD factors(velocity distribute, wall shear stress(WSS) and oscillatory shear index(OSI) were compared at different time points.The carotid stenosis was a slight increase in the central to the cross-sectional curvature, and it was minor and variable curvature changes for carotid centerline. The OSI distribution presents a high-values in the same region where carotid stenosis and normal border,indicating complex flow and recirculation.The significant geometric changes observed during the follow-up may also cause significant changes in bifurcation hemodynamics.     

Hemodynamics of Stent Implantation Procedures in Coronary Bifurcations: An <Emphasis Type="Italic">In Vitro</Emphasis> Study

Stent implantation in coronary bifurcations presents unique challenges and currently there is no universally accepted stent deployment approach. Despite clinical and computational studies, the effect of each stent implantation method on the coronary artery hemodynamics is not well understood. In this study the hemodynamics of stented coronary bifurcations under pulsatile flow conditions were investigated experimentally. Three implantation methods, provisional side branch (PSB), culotte (CUL), and crush (CRU), were investigated using time-resolved particle image velocimetry to measure the velocity fields. Subsequently, hemodynamic parameters including wall shear stress, oscillatory shear index (OSI), and relative residence time (RRT) were calculated. The pressure field through the vessel was non-invasively quantified and pressure wave speeds were computed. The effects of each stented case were evaluated and compared against an un-stented case. CRU provided the lowest compliance mismatch, but demonstrated detrimental stent interactions. PSB, the clinically preferred method, and CUL maintained many normal flow conditions. However, PSB provided about a 300% increase in both OSI and RRT. CUL yielded a 10 and 85% increase in OSI and RRT, respectively. The results of this study support the concept that different bifurcation stenting techniques result in hemodynamic environments that deviate from that of un-stented bifurcations, to varying degrees.     

Bifurcation Model for Characterization of Pulmonary Architecture

A flexible mathematical model of an asymmetric bronchial airway bifurcation is presented. The bifurcation structure is automatically determined after the user specifies geometric parameters: radius of parent airway, radii of daughter airways, radii of curvature of the daughter branch toroids, bifurcation angles, and radius of curvature of carina ridge. Detailed shape in the region where the three airways merge is defined by several explicit functions and can be changed with ease in accordance with observed lung structure. These functions take into account the blunt shape of the carina, the smooth transition from the outer transition zone to the inner one, and the shift in carinal ridge starting position as a function of bifurcation asymmetry. We validated the bifurcation model by comparing it to a computed tomography image of a rat lung cast. Three‐dimensional representations of the bifurcation geometry can be viewed at http://mae.ucdavis.edu/wexler/lungs/bifurc.htm . Anat Rec, 291:379–389, 2008. © 2008 Wiley‐Liss, Inc.     

腹主动脉叉血流动力学边界元分析

本文利用边界元方法计算了腹主动脉叉。在动脉粥样硬化前后的血液流场、血管壁切应力等血液流体动力学特性,通过对动脉粥样硬化产生前后,左、右髂总动脉壁切应力的计算结果分析,对粥样斑块病变产生和发展的血液流体动力学原因做出了判断。结果显示:腹主动脉叉几何形状的不对称性导致分叉处血液流速、血管壁切应力分布的不对称,内侧壁切应力大于外侧壁,右髂总动脉内侧壁切应力大于左髂总动脉。动脉粥样硬化处由于血管腔变窄血液流速明显变大、切应力变大,容易使斑块表面撕裂出现组织增生,粥样斑块下游处血流速度、切应力减小,形成血液分离区,使血细胞聚集,造成动脉粥样硬化发展、加剧。     

锁骨下动脉、颈总动脉和椎动脉分叉处血流动力学数值模拟

目的:探讨锁骨下动脉、颈总动脉和椎动脉分叉处的血流动力学特性,分析该处发生血管狭窄引起大脑供血不足的 血流动力学原因。方法:采用内蒙古民族大学附属医院神经内科提供的CT数据,应用医学建模软件MIMICS20.0将患者 二维CT数据进行三维血管重建,经过网格划分及边界条件设置后导入计算流体力学软件FLUENT14.5中。计算和分析 不同血液入口速度的锁骨下动脉、颈总动脉和椎动脉分叉处的血流动力学特性。结果:在血液入口速度不同的情况下,锁 骨下动脉、颈总动脉和椎动脉分叉处的血液流场分布、血液压力分布和血管壁面切应力分布有显著变化。在血液入口速 度增大时,锁骨下动脉分叉处和颈总动脉分叉处的血液流速快、血管壁压力大,颈总动脉内侧血管壁面切应力大,但锁骨 下动脉分叉处和颈总动脉分叉处血管壁面切应力数值和变化幅度小,属于低切应力区。结论:通过血流动力学数值模拟 研究,分析锁骨下动脉、颈总动脉和椎动脉分叉处易发生粥样斑块病变导致大脑供血不足的血流动力学原因。     

Derivation of flow related risk indices for stenosed left anterior descending coronary arteries with the use of computer simulations

The geometry of the coronary vessel network is believed to play a decisive role in the initiation, progression and outcome of coronary artery disease (CAD) and the occurrence of acute coronary syndromes (ACS). It also determines the flow field in the coronary artery which can be linked to CAD evolution.In this work geometric 3D models of left anterior descending (LAD) coronary arteries associated with either myocardial infarction (MI) or stable (STA) CAD were constructed. Transient numerical simulations of the flow for each model showed that specific flow patterns develop in different extent in the different groups examined. Recirculation zones, present distal the stenosis in all models, had larger extent and duration in MI cases. For mild stenosis (up to 50%) areas with low time averaged wall shear stress TAWSS (<0.15 Pa) as well as areas with high TAWSS (>3 Pa) appeared only in MI models; in moderate and severe stenosis (>50%) these areas were present in all models but were significantly larger for MI than STA models. These differentiations were expressed via numerical indices based on TAWSS, oscillating shear index (OSI) and relative residence time (RRT). Additionally we introduced the coagulation activation index (CAI), based on the threshold behaviour of coagulation initiation, which exceeded the suggested threshold only for MI models with intermediate stenosis (up to 50%). These results show that numerical simulations of flow can produce arithmetic indices linked with the risk of CAD complications.     

Correlation between local hemodynamics and lesion distribution in a novel aortic regurgitation murine model of atherosclerosis

Following surgical induction of aortic valve regurgitation (AR), extensive atherosclerotic plaque development along the descending thoracic and abdominal aorta of Ldlr ^−/− mice has been reported, with distinct spatial distributions suggestive of a strong local hemodynamic influence. The objective of this study was to test, using image-based computational fluid dynamics (CFD), whether this is indeed the case. The lumen geometry was reconstructed from micro-CT scanning of a control Ldlr ^−/− mouse, and CFD simulations were carried out for both AR and control flow conditions derived from Doppler ultrasound measurements and literature data. Maps of time-averaged wall shear stress magnitude (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT) were compared against the spatial distributions of plaque stained with oil red O, previously acquired in a group of AR and control mice. Maps of OSI and RRT were found to be consistent with plaque distributions in the AR mice and the absence of plaque in the control mice. TAWSS was uniformly lower under control vs. AR flow conditions, suggesting that levels (>100 dyn/cm²) exceeded those required to alone induce a pro-atherogenic response. Simulations of a straightened CFD model confirmed the importance of anatomical curvature for explaining the spatial distribution of lesions in the AR mice. In summary, oscillatory and retrograde flow induced in the AR mice, without concomitant low shear, may exacerbate or accelerate lesion formation, but the distinct anatomical curvature of the mouse aorta is responsible for the spatial distribution of lesions.