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。     

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。     

左前降支冠状动脉瘤搭桥手术血流动力学研究

目的采用计算流体力学方法,研究大隐静脉(saphenous vein graft,SVG)与左乳内动脉(left internal mammary artery,LIMA)分别作为移植管搭桥手术旷置与结扎冠脉瘤(coronary artery aneurysm,CAA)时移植管的血流动力学,并以此为根据探讨冠脉瘤搭桥手术移植管的选择与冠脉瘤的结扎与否,为临床手术提供可靠帮助。方法首先分别构建SVG和LIMA搭桥旷置冠脉瘤手术模型、SVG和LIMA搭桥结扎冠脉瘤手术三维模型(three-dimensional model,3D Model) 4个模型。然后在建立集中参数模型(lumped parameter model,LPM,zero-dimensional,0D)的基础上,采用几何多尺度方法,将0D集中参数模型与3D冠脉模型耦合计算。研究SVG和LIMA为移植管时流量、壁面切应力(wall shear stress,WSS)、振荡剪切指数(oscillatory shear index,OSI)血流动力学参数。结果不同手术术式左前降支总流量基本相同,约为82 m L/min。OSI:模型1为0. 014 044、模型2为0. 283 494、模型3为0. 0130 35、模型4为0. 023 263。一个周期内平均WSS:模型1为0. 474 5 Pa、模型2为0. 8600 Pa、模型3为0. 442 4Pa、模型4为1. 699 Pa。结论当采用SVG桥时,冠脉瘤旷置与结扎两种方式都有较好的手术效果;当采用LIMA桥时,结扎冠脉瘤有较好的手术效果。旷置冠脉瘤移植管会因高OSI与竞争流较高、桥流量不足导致较不利的血流动力学环境,从而影响手术预期效果。     

左冠状动脉曲率与左前降支狭窄对局部血流动力学的影响

目的 探究不同的左前降支(left anterior descending, LAD)狭窄程度和分叉血管曲率对血流动力学的影响。方法 建立不同分叉血管曲率半径和 LAD 分支狭窄率的理想模型,使用流固耦合( fluid-structure interaction, FSI)方法评估不同曲率半径和不同狭窄率情况下对血流和壁面剪切力相关指标的影响。 结果 LAD 发生狭窄后,高震荡剪切指数(oscillatory shear index, OSI)和高相对滞留时间(relative residence time, RRT)区域主要分布于 LAD 分叉脊对侧、弯曲外侧狭窄位置下游近端和弯曲内侧下游远端,并且随着狭窄程度的增加会扩大其区域与程度;由于曲率半径减小,弯曲内侧中的高 OSI 和 RRT 会向 LAD 下游远端分布,高 RRT 区域面积相对整个血管面积平均降幅能够达到 35. 68% 。 结论 LAD 狭窄的存在会增加狭窄位置下游和 LAD 分叉脊对侧发生继发性狭窄的风险。 曲率降低会促进弯曲内侧斑块的形成与发展,但从整个血管来看,又会细微地降低斑块形成概率。 研究结果可为治疗 LAD 病变与预防继发性狭窄提供方案设计与优化的理论参考。     

基于多孔介质模型的血流导向装置栓塞颅内动脉瘤的敏感性

目的 应用计算流体力学（computational fluid dynamics, CFD）技术模拟不同血流导向装置（flow diverter, FD）参数对血流动力学的影响,为术前制定合理治疗策略提供可行方法。方法 运用多孔介质模型模拟FD置入动脉瘤的过程,针对特定FD（Tubridge）计算其自身特有的多孔介质动量源参数（渗透率、惯性阻力）初始值。比较不同动量源参数值（初始值80%、90%、100%、110%、120%）情况下血流速度、壁面剪切应力（wall shear stress, WSS）、体积流量、瘤顶压力等血流动力学参数的变化,并进行多孔介质模型针对病人特异性颅内动脉瘤（intracranial aneurysm, IA）血流动力学参数的敏感性分析。结果 IA各血流动力学参数对多孔介质模型渗透率的敏感性为：载瘤动脉WSS＞瘤体WSS＞瘤顶压力,而各参数均对惯性阻力的敏感性较低。结论 应用多孔介质模型能够通过选择不同的渗透率参数模拟不同FD金属覆盖率（metal coverage, MC）,对不同MC的FD进行建模需要调整特定的渗透率设置。     

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。     

新一代左心室磁悬浮辅助泵血流动力学分析

目的降低左心室磁悬浮辅助泵的血栓形成概率和溶血风险,提升辅助泵供血效率。方法利用计算流体动力学方法,研究泵体出口直径、出口角度、出口与泵内壁面连接处圆角尺寸和转子与壳体间间隙对流场的影响,优化泵体内部结构,改善流体动力学性能。结果新一代左心室磁悬浮辅助泵与上一代辅助泵相比,泵内壁面最大壁面剪切应力(wall shear stress,WSS)降低约23. 6%,辅助泵内转子壁面最大WSS降低约47. 4%,WSS200 Pa区域面积降低约76. 2%,出口流量提升约14. 4%。结论新一代左心室磁悬浮辅助泵内部血流流迹趋于平缓,血流流体动力学性能有综合提升。研究结果为今后左心室磁悬浮辅助泵的优化设计及相关实验研究提供参考依据。     

基于血液流量波及Womersley 算法的动脉血液脉动流研究

目的 建立相对便利的血流动力学理论研究体系,进行多状态的综合血液脉动流研究。方法 在完全发展脉动流Womerseley算法的基础上引入数值算法,建立基于心动周期里动脉血液流量波的血流动力学求解及分析体系;进而采用理想化的正弦波以及正常生理状态和增强型体外反搏（enhanced external counterpulsation EECP）状态下的在体测量小猪颈动脉血液流量波,进行较全面的血流动力学研究。结果 对各状态下的轴向速度分布、壁面切应力（wall shear stress, WSS）分布、震荡剪切指数（oscillatory shear index, OSI）等重要血流动力学量进行心动周期里的求解分析。流量波波形对WSS分布尤其是OSI水平有一定的影响;EECP作用能明显提升心动周期里的动脉WSS水平尤其是WSS峰值,同时也提高了OSI水平。结论 所建立的基于血液流量波的求解体系能方便有效地应用于血流动力学研究中;EECP作用在生理范围内大幅提升动脉的WSS水平可能是其良好临床效果的最重要生物力学机制之一;作为当前备受关注的血流动力学指标,OSI对于动脉内皮功能的影响作用可能远小于WSS本身,OSI可能并不是理想的预测动脉粥样硬化病变的血流动力学指标。     

分支血管直径对颅内动脉瘤置入血流导向装置后血流动力学参数的影响

目的综合考虑血流导向装置(flow diverter,FD)置入对动脉瘤瘤体及分支血管的影响,为临床制定更加合理的FD栓塞颅内动脉瘤手术策略提供参考。方法基于计算流体动力学(computational fluid dynamics,CFD)方法,创新应用多孔介质模型模拟FD栓塞颅内分叉动脉瘤的过程。分析和比较不同分支血管直径条件下FD置入动脉瘤前后瘤体与分支血管血液流场、血流速度、壁面压力、壁面剪切力(wall shear stress,WSS)等血流动力学参数的变化。结果 FD置入改变动脉瘤内的血流动力学特征,血流速度减小,动脉瘤壁尤其是顶部压力减小,瘤颈口WSS增大,但瘤颈远侧端与近侧端WSS的差异减小。且不同分支血管直径对血流动力学特征改变的影响程度不同,直径越大,FD置入后流入分支血管内血流的减少量越大,但瘤体内血液流速与瘤顶压力的减少量越小,同时瘤颈部WSS增加量越小。结论分支血管直径越大,FD对动脉瘤的栓塞治疗效果与对血管粥样硬化的改善作用越差,越易造成分支闭塞或其他缺血性并发症的发生。此类情况下进行FD介入栓塞术尤其需要引起临床医师注意。     

缺血性脑卒中的体外反搏血流动力学效应及治疗策略优化

目的 探究增强型体外反搏(enhanced external counterpulsation,EECP)对于不同狭窄程度脑动脉的血流动力学效应。 方法 建立 4 个不同狭窄程度的 0D/ 3D 耦合几何多尺度血流动力学模型,开展不同反搏模式下的 EECP数值模拟,定量计算脑动脉各血流动力学指标。 其中,处于 4 ~ 7 Pa 范围的狭窄下游 TAWSS 均值、低 TAWSS 危险区域百分比、高狭窄支流量被认为可抑制动脉粥样硬化的发展,形成良好的血流动力学环境。 结果 对于 50% 、60% 、70% 、80% 狭窄,在反搏气囊放气时刻分别为心动周期内 0. 5、0. 6、0. 7、0. 7 s 的反搏模式下,血流动力学环境最优。 结论 对于 50% 狭窄脑动脉,应选择放气时刻为 0. 5 s 的反搏模式;对于 60% 狭窄脑动脉,应选择放气时刻为 0. 6 s 的反搏模式;对于 70% 、80% 狭窄脑动脉,应选择放气时刻为 0. 7 s 的反搏模式。 随着脑动脉狭窄程度增加,应当适当延长加压时长。 研究结果可为临床上对不同狭窄程度缺血性脑卒中患者 EECP 治疗方案提供理论参考。     

Effect of the degree of LAD stenosis on “competitive flow” and flow field characteristics in LIMA-to-LAD bypass surgery

The long-term patency of the left internal mammary artery (LIMA) in left anterior descending (LAD) coronary stenosis bypass surgery is believed to be related to the degree of competitive flow between the LAD and LIMA. To investigate the effect of the LAD stenosis severity on this phenomenon and on haemodynamics in the LIMA and anastomosis region, a numerical LIMA-LAD model was developed based on 3D geometric (obtained from a cast) and hemodynamic data from an experimental pig study. Proximal LAD pressure was used as upstream boundary condition. The model counted 13 outlets (12 septal arteries and the distal LAD) where flow velocities were imposed in systole, while myocardial conductance was imposed in diastole via an implicit scheme. LAD stenoses of 100 (total occlusion), 90, 75 and 0 % area reduction were constructed. Low degree of LAD stenosis was associated with highly competitive flow and low wall shear stress (WSS) in the LIMA, an unfavourable hemodynamic regime which might contribute to WSS-related remodelling of the LIMA and suboptimal long-term LIMA bypass performance.     

Fluid Dynamic Analysis in a Human Left Anterior Descending Coronary Artery with Arterial Motion

A computational fluid dynamic (CFD) analysis is presented to describe local flow dynamics in both 3-D spatial and 4-D spatial and temporal domains from reconstructions of intravascular ultrasound (IVUS) and bi-plane angiographic fusion images. A left anterior descending (LAD) coronary artery segment geometry was accurately reconstructed and subsequently its motion was incorporated into the CFD model. The results indicate that the incorporation of motion had appreciable effects on blood flow patterns. The velocity profiles in the region of a stenosis and the circumferential distribution of the axial wall shear stress (WSS) patterns in the vessel are altered with the wall motion introduced in the simulation. The time-averaged axial WSS between simulations of steady flow and unsteady flow without arterial motion were comparable (–0.3 to 13.7 Pa in unsteady flow versus –0.2 to 10.1 Pa in steady flow) while the magnitudes decreased when motion was introduced (0.3–4.5 Pa). The arterial wall motion affects the time-mean WSS and the oscillatory shear index in the coronary vessel fluid dynamics and may provide more realistic predictions on the progression of atherosclerotic disease.     

结扎犬冠脉左前降支后局部血管及心肌的病理生理变化

目的：探讨结扎犬冠状动脉左前降支(LAD)方法制作典型局部冠状动脉狭窄及急性心梗模型的合理性、安全性。 方法： 将30只老龄健康杂交犬随机分为A、B、C 3组，结扎LAD，分别阻断25%、50%、75%的血流。测定结扎前及结扎后各时段内皮因子一氧化氮(NO)、内皮素-1(ET-1)、肌钙蛋白T(CTnT)及P-选择素(P-selectin)的含量变化，Western blotting方法检测心肌组织P-selectin基因表达情况，两周后切取结扎处远段动脉及局部供血区心肌行电镜观察。 结果： 与结扎前对比，A组4种检测指标含量变化不显著，B、C两组NO、ET-1、CTnT及P-selectin含量均有显著变化，3组组间差异显著，P-selectin基因表达增加，以C组最为显著，所有犬均无因心梗发生死亡；电镜观察：A组冠脉内膜及心肌损伤较轻， B、C两组损伤严重，C组呈典型冠状动脉狭窄及心肌缺血梗死及纤维化病变。 结论： 结扎LAD阻断血流75%后损伤显著，形成典型的局部LAD狭窄及急性心梗病变,是适合CABG术外科研究安全、合理的模型方法。     

管径比对全阻塞动脉旁路移植流场影响的数值研究

目的 研究管径比对全阻塞动脉旁路移植流场的影响,为指导动脉旁路移植手术,减少术后再狭窄提供理论依据。方法 采用数值方法研究5种不同移植管与主血管的管径比对全阻塞情况下动脉旁路移植流场的影响,分析速度、二次流、壁面切应力和壁面切应力梯度等血流动力学参数的分布及其随管径比增大的改变。同时,为表明本文所采用模型的合理性,针对目前常使用的两类模型,比较在管径比1.0情况下全阻塞完整模型（Model A）、全阻塞局部模型（Model B）和75％狭窄完整模型（Model C）之间的血流动力学差异。结果 Model A和Model C的血流动力学特性是完全不同的;移植管顶部截面内的速度分布对下游吻合处的主血管底部壁面切应力的影响是显著的,最大相差达79％。大管径比时,主血管底部的壁面低切应力区较大,但壁面切应力分布均匀,壁面切应力梯度较小。而小管径比时,主血管底部的壁面低切应力区较小,但壁面切应力梯度较大。结论 采用整体模型单独研究全阻塞情况下的管径比对流场的影响是有必要的。管径比对全阻塞动脉旁路移植的流场具有显著影响,采用大管径比进行动脉旁路移植将有助于缓解吻合口处由于再狭窄而产生的阻塞。     

A parametric numerical investigation on haemodynamics in distal coronary anastomoses

Anastomotic haemodynamics, which plays an important role in the performance of bypass graft, is known to be profoundly affected by the diameter ratio (Phi) and angle (alpha) between the graft and host artery in the peripheral region. We hypothesize that these geometric factors would play similar roles in distal coronary anastomoses and that they could be improved for clinical applications through parametric studies. Anastomotic models covering a range of Phi (1:1, 1.5:1 and 2:1) and alpha (15 degrees , 30 degrees , 45 degrees and 60 degrees ) were investigated numerically in physiological coronary flow conditions. The transient flow patterns, cycle-averaged wall shear stress (WSS), oscillatory shear index (OSI), spatial and temporal WSS gradients (SWSSG and TWSSG) were compared. Results show a stronger influence of Phi than alpha on haemodynamics in distal coronary artery anastomoses. Substantially higher SWSSG and TSSWG occur on the artery floor when Phi=1:1 compared to larger Phi. High levels of OSI occur in critical regions when Phi=1:1 and 2:1. The largest area of high OSI is found in the anastomotic region when alpha=15 degrees , whereas the highest level of SWSSG appears on the artery floor when alpha=60 degrees . The study suggests the clinical relevance of optimizing geometric parameters of coronary anastomoses to improve their haemodynamic performance. We speculate that for a distal coronary anastomosis with a 20:80 proximal-distal flow division ratio maintained in the host artery, Phi=1.5 and alpha=30-45 degrees would enhance its long-term performance.     

Technical achievement: transthoracic Doppler echocardiography can be used to detect LAD restenosis after coronary angioplasty.

We investigated the capability of transthoracic Doppler echocardiography (TTE) to detect and quantify the severity of restenosis in the left anterior descending coronary artery (LAD) after percutaneous transluminal coronary angioplasty (PTCA). We studied 10 consecutive patients assigned for quantitative coronary angiography (qCA) due to a recurrent angina pectoris after PTCA of the LAD. The LAD was visualized by TTE, and the presence of local turbulence and an increase in the blood flow velocity was regarded to indicate coronary stenosis. To assess the severity of the stenosis, the increase of blood flow velocity was measured. Angiography showed stenoses of various degrees (27-100%) in all patients. All stenoses were detectable using TTE. Moreover, the ratio of maximal blood flow velocity at the site of stenosis to the pre-stenotic blood flow velocity (M/P-ratio) correlated significantly with the reduction of the luminal diameter of LAD (r = 0.85, P < 0.003). A M/P-ratio higher than 3.0 predicted a diameter reduction of 50% or higher with sensitivity and specificity of 100% in patients with a subtotal stenosis (n = 9). Our results indicate that stenoses in the LAD could be found and the severity of the stenoses could be quantified reliably with TTE. This approach is totally non-invasive and less expensive than coronary angiography and can be used clinically in clarifying restenosis after coronary angioplasty.     

Proper Orientation of the Graft Artery Is Important to Ensure Physiological Flow Direction

Arterial grafts such as right internal mammary artery (RIMA), radial artery (RA) or epigastric artery are being used with increasing frequency as free grafts or as composite grafts with left internal mammary artery (LIMA). Currently, there is no consideration of the orientation of the free artery graft to mimic the in vivo state. Hence, some grafts may be oriented such that the direction of blood flow exerted on the endothelium is reversed relative to the in vivo condition. Previous studies have shown that transient flow reversal lead to atherogenesis. A recent study demonstrated that nitric oxide is significantly reduced during reverse flow and the reduction is mediated through an increase in superoxide production. In light of these data, we suggest that the flow direction is important and recommend the assurance of proper orientation of the free arterial graft. Furthermore, we propose a new surgical procedure to modify the composite LIMA-RA or LIMA-RIMA configuration as a horseshoe or K composite graft to ensure proper orientation of the flow direction relative to the endothelium.     

Influence of graft-host diameter ratio on the hemodynamics of CABG

The graft-host diameter ratios have impacts on the flow patterns of bypass graft. In order to clarify the influence of graft-host diameter ratios on the flow patterns and the wall shear stress in coronary artery bypass graft (CABG), the pulsatile blood flows in three CABG models, with the graft diameter larger than, equal to and smaller than that of the coronary artery, were simulated with finite element method. The temporal-spatial distributions of flow patterns, wall shear stresses (WSS), wall shear stress gradients (WSSG), oscillating shear index and shear stress ratio were depicted and compared. Of the three models evaluated, large model can bring about better hemodynamics to some extent with relatively large positive longitudinal velocity, uniform and large WSS, and small WSSG. The results suggest that larger or isodiametric graft is favorable. However, no distinct difference of WSS based temporal parameters was found between all the three models. Alternative anastomotic designs are necessary for the improvement of CABG patency rates.