动脉分叉管道血液流动的边界元分析

我们用边界元方法研究了一类动脉分叉血管中血液流动的流体动力特性,计算了分叉血管无病变和主支管有病变时血液流动的速度矢量分布,比较了主支管壁有病变和无病变两种情况下内外侧壁切应力的大小,同时计算了分叉附近有颗粒状绕流物时血液的流场分布,及颗粒物所受压力状况,给出了颗粒物的运动趋势,分析了引起粥样斑块病变的可能原因.     

Y型血管血流动力学边界元分析

目的：通过数值计算,判断Y型动脉血管中,血流动力学特性对分叉处粥样斑块病变产生和发展的影响。方法：利用边界元方法[4,5],计算了Y型动脉血管,主管病变前后的血液流场、血管壁切应力、压力等血液流体动力学特性,通过对计算结果的分析和比较对粥样病变产生和发展的原因做出了分析。边界元方法由于只在边界离散时作了近似,因而计算精度较高,对于象分叉血管这类复杂边界问题,有较强的适应性。结果：计算结果显示,分叉处管壁切应力明显大于主管壁切应力,说明了分叉处易产生粥样斑块的流体动力学原因;而病变的产生使血管腔变窄,病变斑块顶部血流速度、切应力变大,上、下游血流速度、切应力变小,说明了粥样斑块变厚和附壁延伸的流体动力学原因[7];另外,病变前后血管壁压力的计算结果显示,病变的产生对动脉血压有一定的影响。结论：通过对Y型分叉血管血液流体动力学特性的计算,进一步说明,边界元方法对分叉血管,以及分叉处有病变血管,这类复杂边界问题的计算,方便、快捷、精度高、节约机时,可为生物流体力学的深入研究提供一种可靠、有效的方法[8,9]。     

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。     

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。     

不同型式流体切应力对血管内皮细胞生理生化的影响

血管内皮细胞经常处于血液流动力的作用下,它能感知血流力的变化,在调节血管的功能和结构中起状重要作用。血液流动力的变化与某些血客性疾病的发生发展有着密切的关系,因此血液流动力对内皮细胞的影响受到广泛关注。本文就流体切应力对内皮细胞生理、生化影响的研究进展作一简要综述。     

磨牙根分叉病变对固定义齿应力分布的影响

目的：研究磨牙根分叉病变对固定桥应力大小分布的影响。方法：采取CT平描的方法获得健康年轻人下颌牙及其周围组织的二维数据．通过计算机三维重建技术生成下颌第二前磨牙缺失的双端三单位固定义齿的有限元数学模型,在同等水平向载荷和垂直向载荷下分析了磨牙根分叉病变对固定桥应力大小分布的影响。结果：当磨牙根分叉区牙槽骨无吸收时,固定桥双侧两基牙应力大小分布均匀;当磨牙端根分叉区牙槽骨吸收达30％,前磨牙端牙槽骨无病变时,磨牙端根分叉区表现为应力集中;当前磨牙端和磨牙端根分叉区牙槽骨同时吸收达10％时,固定桥两侧基牙均表现为应力集中。结论：磨牙根分叉病变对固定义齿应力分布的影响较为明显,尤其是与前磨牙端基牙牙槽骨同时吸收时对基牙应力分布的影响最大。     

TCD对200例糖尿病患者基底动脉血流动力学变化的评估

目的应用经颅多普勒超声（TCD）探讨200例糖尿病患者基底动脉血流动力学的变化。方法回顾性分析我院200例糖尿病患者,采用TCD检测患者基底动脉血流动力学变化。检测结果与200例高血压患者比较。结果糖尿病患者BA及MCA的血流速度异常率显著高于VA（P〈005）,而BA与MCA比较差异无统计学意义（P〉0．05）,糖尿病患者BA的血流速度异常率显著高于高血压患者（P〈0．05）,而vA与MCA无显著性差异（P〉0．05）。糖尿病患者BA的血流频谱及音频异常率显著高于vA及MCA（P〈0．05）,且MCA明显高于VA（P〈0．05）,糖尿病患者BA及MCA的血流频谱及音频异常率显著高于高血压患者（P〈0．05）,而vA无显著性差异（P〉0．05）。结论TCD检测有助子了解糖尿病患者各动脉血流动力学变化,为及早发现隐性糖尿病。以及评价病情的发展和预后提供了重要的客观依据。     

不同型式流体切应力对血管内皮细胞生理生化的影响

血管内皮细胞经常处于血液流动力的作用下 ,它能感知血流力的变化 ,在调节血管的功能和结构中起着重要作用。血液流动力的变化与某些血管性疾病的发生发展有着密切的关系 ,因此血液流动力对内皮细胞的影响受到广泛关注。本文就流体切应力对内皮细胞生理、生化影响的研究进展作一简要综述。     

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。     

Finite element analysis of side branch access during bifurcation stenting

Stent implantation has become a widely accepted endovascular intervention for the treatment of stenosed arteries. This minimally invasive technique has shown excellent results in unbranched arteries. However, stenting bifurcation lesions remains a challenge in coronary intervention as it is associated with a lower success rate. Many different techniques have been proposed in medical practice but all the suggested methodologies have specific limitations. Numerical simulations may help to understand and eliminate the shortcomings of current clinical techniques and devices.In this study, one of the currently applied techniques is analysed which involves the implantation of a stent in the main branch, followed by subsequent inflation of a balloon through the side of the stent. This improves the side branch patency and provides access to the side branch for later stent implantations. The impact of using different balloon sizes and stent designs was investigated. The stent cell through which the balloon is inflated increases considerably and as intuitively expected, using a larger balloon results in a larger opening. Furthermore, it was observed that this procedure may compromise the downstream main branch lumen. These observations correspond well with previously reported results, which were based on in vitro studies. The added value of the proposed numerical model is the ability to study many different techniques/stents, without the need for various expensive stent samples.     

Theoretical analysis of arterial hemodynamics including the influence of bifurcations

Based on earlier theoretical studies, a new mathematical model is developed for the prediction of the pressure and flow pulses propagating in the arterial system. This model permits a more realistic simulation of bifurcation and stenoses than was possible previously. By making use of a computer, it allows us to calculate the pulse shapes along branching arteries. It is based on the assumption that each arterial conduit can be represented by a suitable combination of three basic segments, namely segments with no or only small-calibre side branches, short segments with big side branches, and short segments with pathological changes of the conduit. Along segments of the first type, the pulse propagation is calculated with the aid of the method of characteristics and a first order integration. For the other two types, the linearized mass balance and momentum equations are utilized together with the boundary conditions to determine the pressure and flow values at the ends of the segment. A standard case for the human arterial conduit extending from the heart to the foot, with eight major branches, is defined using published data and prescribing the ejection pattern from the heart. The computed pulse shapes and their changes with propagation exhibit the characteristic features observed in man under normal conditions. This work was supported in part by Grant 3. 121.–0.77 from the Swiss National Science Foundation.     

分叉和狭窄对颅内动脉血液流体动力学的影响

目的 基于颅内动脉数量众多且影响因素较多,本文重点研究了分叉角度、对称分支动脉狭窄度、不对称分支动脉狭窄度和斑块尺寸对颅内动脉粥样硬化形成和生长的影响作用,以期利用血流动力学参数的评估为动脉粥样硬化的预警、诊断及选择合适的血管内治疗等提供一定的指导作用.方法 基于计算流体动力学方法,构建主支动脉连接分支动脉的几何模型和有限元模型的边界条件,设计45°～135°区间共7种分叉角度,依托狭窄度λ来表征血管的狭窄程度,通过血液压力、流速和剪切力等血液流体力学参数对比分析各因素对颅内动脉粥样硬化的产生及发展过程的机制.结果 分叉角度对速度比最大值和剪切力最大值基本没有影响,对压力最小值影响也较小,最大振幅不超过5％.随着狭窄度的增加,最小压力下降而速度比最大值增加,当λ从0增加到0.5、0.67和0.75时,最小压力分别下降了1.6 Pa、1.8 Pa和3.6 Pa,速度比最大值分别上升了48％、1.2倍和1.9倍;狭窄度对最大剪切力的影响很小,直到当狭窄度增大到0.75时,最大剪切力提升了5％.非对称两个支路狭窄度的比值φ增加时,3个参数均逐渐增加且增加的幅度随φ的增加而增大.随着斑块长度的增加,压力最小值呈线性增加,速度比最大值则逐渐增加,剪切力最大值则是逐渐下降,最后趋势趋于平缓.结论 分叉角度对血液流体力学参数的影响较小;对称分支动脉狭窄度越大,或者不对称分支动脉的狭窄度比值越大,或者斑块长度越短,均引起血管壁剪切力越大,越容易造成血管内壁损伤,加速动脉粥样硬化.本研究为颅内动脉粥样硬化的形成机制、影响因素以及预测转归等方面提供有用信息.     

Effect of head posture on the healthy human carotid bifurcation hemodynamics

Head and neck postures may cause morphology changes to the geometry of the carotid bifurcation (CB) that alter the low and oscillating wall shear stress (WSS) regions previously reported as important in the development of atherosclerosis. Here the right and left CB were imaged by MRI in two healthy subjects in the neutral head posture with the subject in the supine position and in two other head postures with the subject in the prone position: (1) rightward rotation up to 80°, and (2) leftward rotation up to 80°. Image-based computational models were constructed to investigate the effect of posture on arterial geometry and local hemodynamics. The area exposure to unfavorable hemodynamics, based on thresholds set for oscillatory shear index (OSI), WSS and relative residence time, was used to quantify the hemodynamic impact on the wall. Torsion of the head was found to: (1) cause notable changes in the bifurcation and internal carotid artery angles and, in most cases, on cross-sectional area ratios for common, internal and external carotid artery, (2) change the spatial distribution of wall regions exposed to unfavorable hemodynamics, and (3) cause a marked change in the hemodynamic burden on the wall when the OSI was considered. These findings suggest that head posture may be associated with the genesis and development of atherosclerotic disease as well as complications in stenotic and stented vessels.     

Image-based computational hemodynamics evaluation of atherosclerotic carotid bifurcation models

Widely accepted treatment for carotid artery stenosis includes stenting as well as carotid endoarterectomy (CEA), despite complications associated with distal embolism. Therefore pre-screening for evaluating the extent of a stenosis is critically important before undertaking surgical procedures. This study presents and evaluates the feasibility of implementing a virtual computational hemodynamics platform for clinical use to determine the severity of a stenosis and give guidance for surgical decision making. The virtual platform incorporates high-resolution three-dimensional angiography results with Computational Fluid Dynamics modeling to determine clinically related indicators. This includes wall shear stress (WSS), the spatial and temporal hemodynamic changes of blood flow within patient-specific carotid bifurcations, pressure drop coefficient, and severity stratification. The turn-around time for each computational modeling stage was examined which showed that the total time cost is practical and the proposed hemodynamics evaluation platform is reasonably efficient for clinical diagnosis. Furthermore the virtual platform may be used to detect the hemodynamic consequence of atherogenesis, which can then be addressed and quantified based on the distribution of WSS related flow indicators on the abnormal luminal fractions. Additional functional evidence and data can be used by the overseeing physician to enrich and complement the anatomical information for more in-depth evaluation of stenosis in a reasonable time duration.     

Computerised multiparametric analysis from images of blood flow through frog mesenteric arterial bifurcation

A computerised multiparametric procedure is developed to analyse the images of blood flow through various locations of the mesenteric arterial bifurcation of frog. The data are recorded by a video microscopic system and, after digitisation and pre-processing, are analysed by an IBM PC/AT based image processing system to obtain erythrocyte and velocity distribution profiles by axial tomographic and image velocimetry techniques respectively. The vessel radius, haematocrit, blood flow through main and branch arteries and flow separation zones are determined from the data by various analytical procedures. In contrast to the earlier techniques the data are obtained from the same location of the vessel and thus the variability in flow parameters is minimised.     

Ultrastructure of the renal arterial bifurcation of rabbits

Intimal thickenings at renal artery bifurcations of 30 rabbits were studied ultrastructurally. After localization of intimal pads, the forks were cut on several planes. No microthrombi were observed at the fork but the endothelium of the fork and stem contained bundles of cytoplasmic fibrils incorporating dense bodies like those in smooth muscle cells. The densities were at times arranged as cross striations with a fairly regular periodicity. The internal elastic lamina external to the pads appeared thinned or deficient with much collagen and fibrillary elastica between the strata of muscle cells in the intimal thickenings. The intimal pads contained quantities of cell debris seemingly derived from both endothelium and muscle. Degenerate and undifferentiated cells were observed in the intimal pads and calcification but rarely. Intimal pads are apparently sites of enhanced degeneration of endothelium, smooth muscle cells and elastic tissue.     

基于有限元分析腰椎内固定的生物力学特征

BACKGROUND: Posterior lamina resection often causes loss of spinal stability, so screw rod internal fixation technology is needed to maintain the stability of lumbar spine. Finite element analysis can be used to simulate the stress distribution of the spine and internal fixation system after spinal surgery. OBJECTIVE: To build three-dimensional finite element model of spinal L1 to L3, analyze the spinal stability and stress distribution after the total laminectomy and insertion of bilateral pedicle screw using finite element method. METHODS: L1-L3 CT data could be collected from an adult healthy male volunteer. Mimics14.01, 3-matic(V6.0) and Ansys 15.0 could be used to set up the intact lumbar spine finite element model of L1-L3 (group A), the L1-L3 finite element model after L2 total laminectomy (group B), and the finite element model of L2 total laminectomy and insertion of bilateral pedicle screw (group C). We used software to simulate flexion, extension, lateral bending and axial rotation, and three kinds of models received finite element analysis. RESULTS AND CONCLUSION: (1) Based on the maximum of Von Mises under different motion states, the maximum stress was significantly lower in group A than in group B (P < 0.05). The maximum stress was significantly lower in group B than in group C (P < 0.05). (2) Based on the total deformation under different motion states, the total deformation was significantly lower in group A than in group B (P < 0.05). The total deformation was significantly lower in group C than in groups A and B (P < 0.05). (3) After the total laminectomy, vertebral body stress increased, especially in the lamina, pedicle and joints. The range of motion of the vertebral body increased, which influenced the stability of the vertebral body. Internal fixation could decrease range of motion. Stress concentrated on the screw. Stress on the vertebral plate and pedicle decreased. The stability of vertebral body increased. Excessive stress concentrated on screw system will increase the risk of screw breakage.      

髓核摘除术对腰椎生物力学特性影响的有限元研究

目的　采用三维有限元模型分析方法,探讨腰椎间盘突出症髓核摘除术对腰椎生物力学特性的影响。 方法 采用新型CAD方法精确建立腰椎L4～5活动节段有限元模型,构建正常模型、退变模型、髓核摘除模型和疤痕长入模型分别模拟正常椎间盘、退变椎间盘、髓核摘除后即刻和术后中长期时的椎间盘;并比较其生物力学特征。 结果　(1)髓核摘除模型的刚度较退变模型减小,但较正常模型提高;　(2)疤痕长入模型腰椎节段刚度大幅回升并超过退变模型;(3)髓核摘除后即刻小关节突接触力减小,而疤痕长入模型则表现为小关节突接触力增加。 结论　腰椎间盘髓核摘除术后即刻对腰椎稳定性和后部结构应力影响较小,而髓核摘除中长期后则可有腰椎运动节段变硬和关节突的应力增加。     

沙疗对不同狭窄程度股动脉分叉管血流脉动动力学影响

文题释义： 埋沙疗法(简称沙疗)：是利用新疆天然的环境与资源,通过沙子的传热与磁性作用进行治疗的非药物性理疗方法。沙疗可以治疗风湿病,并且具有镇痛、镇静、消炎、消肿、降压、降血脂、止泻等作用。 双向流固耦合：在流体运动时所产生的力会使固体变形,与此同时固体的形变又会施加给流体,如此往复,持续不断。数值模拟中,双向流-固耦合是对流体模块以及固体模块的同时求解,计算流体模块的结果导入到固体模块,固体模块的结果再作用到流体模块中不断迭代。 背景：研究表明,维医沙疗对降低股动脉粥样硬化及血栓形成有一定的积极作用。 目的：通过对比沙疗前后4种狭窄模型的血流速度以及壁面切应力,研究沙疗对股动脉分叉管不同狭窄模型的血流动力学参数的影响。 方法：研究方案的实施符合新疆大学机械工程学院对研究的相关伦理要求,受者均对试验过程完全知情同意。采用医用软件Mimics10.01、逆向工程软件Geomagic Studio 2012与三维CAD软件UG 8.5将1名受试者的下肢CT数据进行分离、优化,得到人体股动脉分叉血管几何模型。依照下肢股动脉粥样硬化斑块所致的血管狭窄分级标准,将位于股动脉分叉管侧壁的斑块狭窄程度分别设置为0%(正常)、15%(正常)、30%(轻度)和50%(中度)。运用计算流体力学(CFD)方法进行数值模拟仿真,沙疗前血液流态选择Laminar层流模型,沙疗后血液选择标准κ-ε紊流模型,进行沙疗前后血流速度和壁面切应力分析。 结果与结论：①沙疗后的血流最大速度较沙疗前增大了0.35-0.45 m/s;②沙疗后动脉狭窄处的壁面切应力较沙疗前增大了5-11 Pa,50%狭窄率模型中狭窄处的壁面切应力达到了41 Pa;③结果说明,沙疗后动脉粥样硬化斑块扩大的趋势有所减弱,但50%(中度)以上狭窄率的患者沙疗后有斑块破裂的危险。 ORCID: 0000-0002-5540-4112(乔钰淇) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程