硅胶管流动腔系统的合理使用

硅胶管流动腔系统被用来研究培养血管内皮细胞在流体切应力和周向应力联合作用下的力学行为。如何选择硅胶管流动腔的几何和力学特性以及前、后负荷条件,真实模拟生理条件下血管内皮细胞的切应力和周向应力环境,是构建硅胶管流动腔系统须解决的关键问题。首先给出了确定硅胶管流动腔无载荷状态几何尺寸和硅胶管弹性模量的方法;其次给出了定常流条件下在硅胶管流动腔中模拟生理环境中壁面切应力和周向应力的过程;最后总结了装置中壁面切应力、周向应力的控制因素。     

磁场对人体三维分叉颈动脉血液流动的影响规律

目的 通过CT影像重构三维血管模型,研究外加均匀磁场对血液动力学行为的影响规律。方法 采用计算流体动力学理论和磁流体力学方法,建立体外均匀磁场对血液流动影响的数学模型,运用多物理场耦合模拟软件COMSOL Multiphysics进行仿真模拟,探究磁场强度对血液流动速度、压力和剪切应力的影响。结果 随着磁场强度的增加,血管中心处的流速受到了更加显著的抑制。壁面压力随着磁场强度的增加而减小,且磁场在血流分叉前对壁面处压力的影响明显,而在血流分叉后对壁面压力的影响减弱。血流进入分支血管后,壁面切应力显著增加,同时磁场对切应力的影响也显著增强。结论 人体血液具有磁流体力学特性,一定强度范围的磁场对血液流动产生了明显的影响。研究结果为设计人造强磁场设备、评估人造磁场环境对人体血液动力学的影响以及诊断人造磁场环境产生的疾病提供理论依据。     

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。     

剪切流动下内皮细胞变形的模拟

血液流动和内皮的耦合是重要的生物医学问题 ,引起了学者们的广泛的兴趣。目前已知内皮细胞能感知流场的剪切应力而改变其形态和功能。由于剪切应力被认为是引起内皮细胞重建的始发信号 ,所以了解内皮细胞与流动应力之间的相互作用机制是十分重要的。我们建立了一个理论模型来模拟内皮细胞与流场应力之间的相互作用。根据二维计算流体动力学方法研究了内皮细胞应力、压力的分布以及内皮细胞在剪切应力作用下的变形情况。结果表明 :( 1)内皮细胞的变形随 α(对应于流体作用于细胞表面的切应力 )的变化而变化。当 α>0 .0 2 1时 ,细胞的变形随 α的增大而显著增大 ;( 2 )流动引起了细胞表面应力和压力分布的不均匀 ,从而导致了细胞的变形。但内皮细胞的最大应力总是位于细胞的顶点。同时 ,我们用流室系统提供剪切流动 ,测量了不同剪切应力作用下培养的人主动脉内皮细胞的变形。所得到的实验结果与上述数值模拟结果是吻合的。本文结果提示 ,由于剪切流动引起细胞表面应力和压力分布的不均一 ,可能在细胞激活和细胞功能的调节 (如细胞骨架的调节 ,粘附分子的表达与分布等 )机制上具有特殊的作用。本研究为综合应用动力学方程来建立内皮细胞模型提供了工作框架     

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。     

基于三维医学影像的脑动脉瘤内血液流动的数值模拟

目的 利用数值模拟研究具有病人特异性的脑动脉瘤内的血液流动,为脑动脉瘤的破裂风险的评价和动脉瘤介入栓塞后复发风险的评价提供帮助。方法 从两例脑动脉瘤病人的3D-RA数据中重建动脉瘤几何模型,血液流变学模型选择假塑性非牛顿流体模型,利用商用CFD软件Fluent对两例动脉瘤内的血液流动进行数值模拟。结果 数值模拟给出了动脉瘤内的流线图、重要截面上的速度分布图、壁面上的切应力分布和压力分布图。并且绘制了在收缩期时刻动脉瘤颈部和瘤顶部各20个点上的壁面切应力和压力的变化情况。结论 血流动力学因素如流速、压力、壁面切应力、流动对壁面的冲击状况等因素与动脉瘤的生长和破裂密切相关,而由于脑动脉瘤形态各异、载瘤动脉与动脉瘤体的几何关系复杂,所以具有病人特异性的数值模拟对于研究动脉瘤破裂和复发风险具有重要价值。动脉瘤颈部的壁面切应力和壁面切应力的波动的变化规律并不相同,需要进一步研究壁面切应力的波动与脑动脉瘤生长与破裂之间的定量关系。     

双路搭桥术的移植管直径对血液流动的影响

移植管直径对搭桥术的长期通畅率具有至关重要的作用.为了弄清楚移植管直径对双路搭桥术中血液流动的具体影响,利用数值仿真的方法对两个股动脉双路搭桥模型中的生理脉动流进行了研究.为便于比较,除移植管直径不同以外,两个模型均采用相同的几何参数来建模.我们将研究直径一小和一大两个模型.两个模型的流动仿真边界条件相同.峰值雷诺数为832.8,Wcmersley数为6.14.重点分析了下游缝合区流场.对速度场、上下游足尖的压力差、壁面切应力及其梯度、应力波动系数等血流动力学参数的时空分布进行了比较.研究表明,大直径移植管模型下游缝合区的纵向速度和二次流速度较为紊乱,而其足尖下游远端的轴向流动则具有较大而均匀的纵向速度.同时,大移植管模型具有较小的回流、较均匀的壁面切应力、较低的压力、较小的壁面切应力梯度等特点.然而在二次流分布和应力波动系数方面却没有优势.总之,大移植管模型在近壁部分具有更好、更均匀的血流动力学现象,可以有效地避免术后内膜增生和再狭窄的发生和发展.     

利用硅胶管流动腔系统模拟动脉脉动血流切应力和周向应力环境

目的选择硅胶管流动腔的前、后负荷,模拟生理脉动流条件下动脉内皮细胞所承受的切应力和周向应力环境。方法利用在体脉动血流切应力和周向应力波形,在求得硅胶管流动腔几何和力学特性的情况下,反向求解硅胶管流动腔内径、压力和流量波形;根据所求得的压力和流量波形,确定出硅胶管流动腔的后负荷(即输入阻抗)条件;利用冯忠刚等提出的三弹性腔九元件集中参数模型模拟该后负荷,并求出各元件参数。结果三弹性腔九元件集中参数模型模拟出的输入阻抗模和幅角与目标输入阻抗模和幅角能较好的吻合。结论该方法为选择合适的硅胶管流动腔前、后负荷,构建能较真实再现动脉脉动血流切应力和周向应力环境的硅胶管流动腔系统提供了一定的理论依据。     

黏附于血管壁表面的白细胞在稳定剪切流动下发生变形的生物力学模型

白细胞与血管表面的黏附是重要的生物医学工程问题，引起了学者们的广泛研究。我们用复合液滴来模拟黏附于血管表面的白细胞，根据二维计算流体动力方法研究了流体切应力作用下白细胞黏附引起的压力分布。同时，通过引入“变形指数”的概念，研究稳定剪切流动下白细胞变形的生物力学特性，数值结果表明：（1）随着初始接触角，毛细血管数，外界流场雷诺数的增大，细胞的变形也增大，而细胞浆比细胞核更易于变形，表明细胞核更能耐受切流动；（2）当切应力增大到一定值时，细胞不能进一步变形，变形指数达到峰值；（3）压力分布曲线表明，在细胞的下游形成一个高压区，提供促使细胞受力达到平衡的升力，从而阻止了细胞的进一步变形，我们关于细胞核变形的结果有助于理解白细胞如何将外界流体作用力（如切应力）等力学信号向核内转导的生物力学机理。     

粘性流体在弯曲管道内在交变压力梯度下的振荡流动

在血液动力学中，一般只有在微血管中才可把血液这似看作定常运动，而在大动脉或动脉中，血液的压力在同一位置上是随时间周期性变化的。考虑到血管具有一定的弯曲率，本引入了一种新的坐标系统，解决了弯管中的振荡流问题。给出了流体在弯管中运动的速度及切应力公式，并对切应力加以讨论。发现微弯管中的切应力将在壁面上获得极值。本还通过计算机计算，得知流体对弯管两侧的冲刷力也是振荡的。并且随着压力差的增大，流体对弯管两侧的冲剧力的差值也增大；随着曲率的减小，此差值也减小。此结果较好地解释了动脉硬化形成的主要原因：切应力的影响。对于进一步深入了解血液在血管中的流动，特别是血液在弯曲大动脉内流动特性的研究提供了理论依据。     

腹主动脉血管瘤的定常流动的模拟

目的 应用两维对称模型模拟腹主动肪血管瘤的定常流动。方法 运用计算力学软件（FLUENTv4.3.2)进行数值模拟。结果 该研究给出了各种情况下的流动状态、流线分布、壁面剪切力和壁面压降的分布。结论 结果表明，腹主动脉血管瘤的形状和大小对流动状态影响不大，而雷诺数的增大会增大腹主动脉血管瘤内涡的强度。     

A numerical investigation on the steady and pulsatile flow characteristics in axi-symmetric abdominal aortic aneurysm models with some experimental evaluation

Steady and pulsatile flow characteristics in rigid abdominal aortic aneurysm (AAA)models were investigated computationally (using Fluent v.4.3) over a range of Reynolds number (from 200 to 1600)and Womersley number (from 17 to 22). Some comparisons with measurements obtained by particle image velocimetry under the pulsatile flow conditions are also included. A sinusoidal inlet flow waveform 1+sin omega t with thin inlet boundary layers was used to produce the required pulsatile flow conditions. The bulk features of the mean flow as well as some detailed features, such as wall shear stress distributions, are the foci of the present investigation. Recirculating vortices appeared at different phases of a flow cycle causing significant spatial and temporal variations in wall shear stresses and static pressure distributions. A high level of shear stresses usually appeared at the upstream and downstream ends of the bulge. Effects of pressure rise caused by the increase in crosssectional area were transmitted into the downstream tube. Further simulation studies were conducted using simulated physiological waveforms under resting and exercise conditions so as to determine the possible implication of vortex dynamics inside the AAA model.     

A numerical investigation on the steady and pulsatile flow characteristics in axi-symmetric abdominal aortic aneurysm models with some experimental evaluation

Steady and pulsatile flow characteristics in rigid abdominal aortic aneurysm (AAA) models were investigated computationally (using Fluent v. 4.3) over a range of Reynolds number (from 200 to 1600) and Womersley number (from 17 to 22). Some comparisons with measurements obtained by particle image velocimetry under the pulsatile flow conditions are also included. A sinusoidal inlet flow waveform 1 + sin omega t with thin inlet boundary layers was used to produce the required pulsatile flow conditions. The bulk features of the mean flow as well as some detailed features, such as wall shear stress distributions, are the foci of the present investigation. Recirculating vortices appeared at different phases of a flow cycle causing significant spatial and temporal variations in wall shear stresses and static pressure distributions. A high level of shear stresses usually appeared at the upstream and downstream ends of the bulge. Effects of pressure rise caused by the increase in cross-sectional area were transmitted into the downstream tube. Further simulation studies were conducted using simulated physiological waveforms under resting and exercise conditions so as to determine the possible implication of vortex dynamics inside the AAA model.     

A computer simulation of the blood flow at the aortic bifurcation.

A two-dimensional finite-difference numerical model is developed for the blood flow at the aortic bifurcation to determine the possible role of fluid dynamics in the atherogenesis. Arterial walls are assumed to be rigid, while the fluid is Newtonian. Parametric studies are performed to evaluate the effects of the area ratio, Reynolds number, corner curvatures, Womersley number, bifurcation angle and arterial pulsation on the flow and shear stresses. A high shear stress region exists on the inner wall distal to the vertex, while both high and low shear stress regions coexist along the outer wall. A temporary eddy is found along the outer wall, with more strength in the case of a higher area ratio. The results agree qualitatively with the existing experimental observations.     

腹主动脉瘤中定常流动的三维数值模拟

目的讨论定常流动情况下，三维腹主动脉瘤模型内的流动情况。方法应用三维非对称模型进行数值模拟。结果结果表明，在对称面上有一个涡而横截面上有两对涡的存在。壁面切应力在动脉瘤的出口处数值较高且变化大。结论流动和壁面切应力分布反应动脉瘤出口处为破裂的危险区域。     

A steady flow analysis on the stented and non-stented sidewall aneurysm models.

As part of a general investigation on the effects of blood flow patterns in sidewall aneurysm, in vitro steady flow studies on rigid aneurysm models have been conducted using Particle Image Velocimetry over a range of Reynolds number from 200 to 1600. Above Reynolds number 700, one large recirculating vortex would be formed, occupying the entire aneurysmal pouch. The centre of the vortex is located at region near to the distal neck. A pair of counter rotating vortices would however be formed at Reynolds numbers below 700. For all the aneurysm models considered, the vortex strength, in general, is stronger at higher Reynolds numbers but lower at larger aneurysm size. Maximum strength of the vortex is about 15% of the bulk mean velocity in the upstream parent tube. Estimates of the wall shear stresses are derived from the near wall velocity measurements. Highest level of wall shear stresses always appears at the distal neck of the aneurysmal pouch. Stents and springs of different porosity have been used to dampen the flow movement inside the aneurysm so as to induce the possible formation of thrombosis. It is found that the flow movement inside the aneurysmal pouch can be suppressed to less than 5% of the bulk mean velocity by both devices. Furthermore, regions of high wall shear stresses at the distal neck could also be suppressed by almost 90%. The present results would be useful for further improvements in stent (or spring) technology.     

Influences of graft diameter on the blood flow in 2-way bypassing surgery

The graft diameter plays a critically important role in the long-term patency rates of bypass surgery. To clarify the influence of graft diameter on the blood flows in the femoral 2-way bypass surgery, the physiologically pulsatile flows in two femoral bypass models were simulated with numerical methods. For the sake of comparison, the models were constructed with identical geometry parameters except the different diameters of grafts. Two models with small and large grafts were studied. The boundary conditions for the simulation of blood flow were constant for both models. The maximum Reynolds number was 832.8, and the Womersley number was 6.14. The emphases of results were on the analysis of flow fields in the vicinity of the distal anastomosis. The temporal-spatial distributions of velocity vectors, pressure drop between the proximal and distal toe, wall shear stresses, wall shear stress gradients and oscillating shear index were compared. The present study indicated that femoral artery bypassed with a large graft demonstrated disturbed axial flow and secondary flow at the distal anastomosis while the axial flow at its downstream of toe was featured with larger and more uniform longitudinal velocities. Meanwhile, the large model exhibits less refluences, relatively uniform wall shear stresses, lower pressure and smaller wall shear stress gradients, whereas it does not have any advantages in the distributions of secondary flow and the oscillating shear index. In general, the large model exhibits better and more uniform hemodynamic phenomena near the vessel wall and may be effective in preventing the initiation and development of postoperative intimal hyperplasia and restenosis.     

腹主动脉瘤的数值计算模型比较研究

目的分别采用纯流体模型和流固耦合模型来计算腹主动脉瘤的血流动力学特征,比较两种数值模型的不同,并讨论在研究腹主动脉瘤中的应用。方法使用Gambit 2.2.30和COMSOL Multiphysics 4.2建立腹主动脉瘤的理想模型,分别基于有限体的方法分析纯流体模型,基于任意拉格朗日-欧拉算法(Arbitrary Lagrangian-Eulerian)计算流固耦合模型。结果同样的入口速度下,纯流体模型出现4个涡流和6个局部压力集中;流固耦合模型只有2个涡流和局部压力集中,且涡流中心更接近腹主动脉瘤的远端。在边界层分离点、血流回帖位置以及腹主动脉瘤的近端和远端,两种模型均出现壁剪切力极值。血管壁的最大形变和最大壁应力出现在腹主动脉瘤的近端和远端。结论两种模型的涡流个数和涡流中心的位置均不一样,与瘤体的生长有着密切的关联;流固耦合模型中的最大壁剪切力比纯流体模型要小36%;最大壁应力和最大血管壁的形变量与出口血压呈正相关。在研究血管瘤生长与血流动力学的关系时需要考虑使用流固耦合模型。     

腹主动脉瘤几何形态对血液动力学影响的三维数值分析

目的研究腹主动脉瘤不同形态学对瘤内血液动力学的影响,为临床预估动脉瘤的破裂提供参考。方法根据动脉瘤影像学上的特点建立不同几何形态的数学模型,采用计算流体动力学(CFD)方法,在周期性脉动速度入流、刚性壁面以及血液为牛顿流体的条件下,对一个心动周期内瘤内流场进行数值分析研究,比较不同几何形态腹主动脉瘤内血液动力学。结果非轴对称模型可造成相对较大的壁面剪应力;带有峰值偏移和曲率半径偏转的腹主动脉瘤,瘤内漩涡的发展变化会随着几何形态的不同而产生变化。结论腹主动脉瘤内流场特征的变化受到不同形态学的影响。     

3D CFD Simulation of Pulsatile Blood Flow in the Human Aorta

INTRODUCTION　　The human aorta is the majorblood vessel of complex geometry including curva-tures in multiple planes,branches at the apex of the arch,significant tapering andwith distensible vessel wall ( as shown in Fig.1 ) . The blood flow structures in theaorta are very complex and attribute a lot to the development of atherosclerotic le-sions,which always occur in the vicinity of arterial branches,curvatures and bifur-cations〔1～ 5〕.In order to understand the complex nature of the …