脉动流条件下动脉狭窄血管内脂质浓度极化现象的计算机数值模拟

在脉动流条件下,用计算机数值模拟的方法对低密度脂蛋白(LDL)在动脉狭窄血管段内的质量传输进行了研究。计算结果表明．无论是在定常流还是在脉动流条件下．LDL都将聚积于血管狭窄处峰口附近的流动分离点,LDL壁面浓度在此处最高。在脉动流条件下,LDL在血流受扰动区的聚积高于定常流的值;而且．流动分离点处LDL壁面浓度峰值覆盖的区域也宽于定常流。本文所揭示出的LDL在血管狭窄处的质量传输现象可能在动脉粥样硬化的局部性和动脉狭窄的形成中起着很重要的作用。     

消息与动态(十八)

血液在轴对称狭窄直圆管内的流动在动脉系内,由于血管内皮细胞的异常增生造成动脉狭窄,这是许多研究人员重视的问题。动脉狭窄和血液流动间存在耦合作用,许多学者在进行病理研究同时,对狭窄区血液流场进行理论分析,探索动脉狭窄的血液动力学依据。因问题的复杂性,绝大多数所研究的力学模型是轴对称狭窄直圆柱刚性管内牛顿流体的流动。     

消息与动态(十八)

血液在轴对称狭窄直圆管内的流动在动脉系内,由于血管内皮细胞的异常增生造成动脉狭窄,这是许多研究人员重视的问题。动脉狭窄和血液流动间存在耦合作用,许多学者在进行病理研究同时,对狭窄区血液流场进行理论分析,探索动脉狭窄的血液动力学依据。因问题的复杂性,绝大多数所研究的力学模型是轴对称狭窄直圆柱刚性管内牛顿流体的流动。     

消息与动态

血液在轴对称狭窄直圆管内的流动在动脉系内,由于血管内皮细胞的异常增生造成动脉狭窄,这是许多研究人员重视的问题。动脉狭窄和血液流动间存在耦合作用,许多学者在进行病理研究同时,对狭窄区血液流场进行理论分析,探索动脉狭窄的血液动力学依据。因问题的复杂性,绝大多数所研究的力学模型是轴对称狭窄直圆柱刚性管内牛顿流体的流动。     

分叉血管中动脉狭窄对血液流动的影响

利用血液流动的粘性不可压Navier-Stokes方程，采用有限元方法研究了分叉血管中动脉局部狭窄对血液流动的影响，分别对母血管壁有动脉狭窄病变和无病变时的血液流动进行了数值模拟。针对不同程度的动脉狭窄，得到了当狭窄度S分别为0.05、0.25、0.5时血液流动的流线图和压力图。一方面，从计算的压力图中可以看出当血液流经狭窄区域时，压力会迅速发生变化；另一方面，观察流线图可知，在血液流经狭窄的区域时会出现流动分离现象，产生涡的结构。根据上述结果，可以看出动脉局部狭窄会对血液流动产生很大的影响。动脉粥样硬化等某些血管疾病的发病机制和病变发展与血液流动的力学特征有密切关系。在动脉局部狭窄的初期，动脉狭窄邻近区域的血液几乎光滑地流过狭窄区，流动产生的分离小；随着狭窄区域半径的逐渐增大，血流流动产生比较明显的分离，在分离区内存在层流和回流；而当狭窄区域的半径进一步增大时，血管内血流流动分离区域扩大，而且在分离区内的血液流动会出现局部湍流。这种情况可能会使血液中的血小板、纤维蛋白、脂肪颗粒沉积，最终导致血流不畅或动脉粥样硬化等血管疾病。     

动脉狭窄对血液流速的影响

为了定量计算动脉局部狭窄对动脉管中血液流动速度的影响，本文分别对狭窄区域内定常流和非定常流动进行了求解，得出了狭窄区域内定常流和脉动流的速度表达式。本文将均匀段的流速形经Ｆｏｕｒｉｅｒ分解成定常和脉动两部分，然后分别计算出狭窄区域内对应的定常和脉动流速，经Ｆｏｕｒｉｅｒ合成还原成流速时域波形，同时针对各种情况将不同狭窄对不同的流速波形的作了分析比较。     

Willis环瞬态血液流体动力特性数值分析

针对左颈内动脉在无狭窄和完全阻塞情况下交通动脉中的血液瞬态流动采用颅内Willis环二维模型进行计算分析.计算得到完整环、交通动脉大脑前动脉缺失情况下各交通动脉血液流量变化趋势.结果表明交通动脉中血液流量变化最大的情况为:右侧大脑前动脉缺失同时左颈内动脉阻塞;在左(右)大脑前动脉近端缺失时前交通动脉中血液流量变化趋势与左(右)大脑前动脉远端相同;左侧后交通动脉在左颈内动脉狭窄比较严重时血液流动方向就会发生改变;在完整环、左颈内动脉阻塞时前交通动脉中的血液流量大于后交通动脉.     

颅内Willis环二维血液动力学计算分析

采用颅内二维Willis环模型,对血管在不同程度狭窄情况下的血液流动进行稳态计算与分析,计算中采用了进出口处的压力边界条件和无滑移固壁条件.计算得到完整环和交通动脉缺失情况下各进出口血管流量变化曲线.所获结果表明,完整Willis环中,前交通动脉的代偿能力在左颈内动脉狭窄率达到25%以后才能得到比较明显的体现;后交通动脉缺失情况下前交通动脉的代偿能力变弱;Willis环的前部和后部有相对独立性,只有在主要进口动脉严重阻塞的时候,单侧的独立性才丧失.     

定常流下动脉狭窄局部流场的有限元分析

本文利用有限元数值模拟对定常流下动脉狭窄的局部流场进行了系统研究。在数值模拟中求解非线性轴对称Navier-Stokes方程,并对不同狭窄率、不同雷诺数、不同狭窄形状下的流场速度分布、压力降分布和壁面剪应力分布进行了全面细致的分析和讨论。     

具有缓变狭窄直圆管内的脉动流——早期动脉粥样硬化区的血流动力学机制讨论

六十年代末期以来D.F.Young等人提出了各种数学力学模型对动脉狭窄区血液流动进行理论分析,寻求血流动力学诸因素的定量关系,力图为动脉粥样硬化的发展提供力学上的解释根据。动脉粥样硬化易发区通常在主动脉的较大分枝处及脑动脉和冠状动脉内,血流是脉动的,Reynolds数是O(1)或以上的量级。但D.F.Young等人的研究多数考虑定常流或小Reynolds数的流动,所得结果对动脉粥样硬化狭窄区的血流并不适合。本文考虑Reynolds数为O(1)的量级的冠状动脉狭窄区的脉动流,初步探讨早期动脉粥样硬化狭窄区的血流动力学机制。     

Effects of fluid recirculation on mass transfer from the arterial surface to flowing blood

The effect of disturbed flow on the mass transfer from arterial surface to flowing blood was studied numerically,and the results were compared with that of our previous work.The arterial wall was assumed to be viscoelastic and the blood was assumed to be incompressible and non-Newtonian fluid,which is more close to human arterial system.Numerical results indicated that the mass transfer from the arterial surface to flowing blood in regions of disturbed flow is positively related with the wall shear rates and it is significantly enhanced in regions of disturbed flow with a local minimum around the reattachment point which is higher than the average value of the downstream.Therefore,it may be implied that the accumulation of cholesterol or lipids within atheromatous plaques is not caused by the reduced efflux of cholesterol or lipids,but by the infiltration of the LDL(low-density lipoprotein) from the flowing blood to the arterial wall.     

动脉局部狭窄时脉动流的有限元分析

本文利用有限元方法研究动脉局部狭窄下的脉动流流场,重点考查在50％与80％面积狭窄下的速度分布、压力分布、壁面剪应力分布及流动分离情况。几何形状及边界条件均模拟相应的脉动流实验模型。采用测得的随时间变化的速度分布作为入口端条件,并利用罚函数和逆风格式等计算技巧得出了光滑的与实验基本相符的速度、压力波形。本文讨论了不同狭窄下速度、压力、壁面剪应力的分布形态,给出了脉动流中狭窄处局部流动分离的间歇性变化规律,并结合实验与临床应用进行了讨论。     

Viscoelastic blood flow through arterial stenosis—Effect of variable viscosity

Current theoretical investigation deals with mathematical model of unsteady non-Newtonian flow of blood through a stenosed artery. The flowing blood is considered as a viscoelastic fluid having shear-thinning rheology and characterized by generalised Oldroyd-B model. The arterial wall is considered to be rigid having cosine shaped stenosis in its lumen. The governing equations of motion accompanied by appropriate choice of the initial and boundary conditions are solved numerically by MAC (Marker and Cell) method and the results are checked for numerical stability with desired degree of accuracy. The quantitative analysis has been carried out finally which includes the respective profiles of the flow-field. The key factors like the wall shear stress and flow separation are also examined for further qualitative insight into the flow through arterial stenosis. The present results show quite consistency with several existing results in the literature which substantiate sufficiently to validate the applicability of the model under consideration.     

Effect of surface irregularities on unsteady pulsatile flow in a compliant artery

Of concern in the paper is an analytical study of pulsatile blood flow in an irregular stenosed arterial segment through a mathematical model. The model is two-dimensional and axisymmetric with an outline of the stenosis obtained from a three-dimensional casting of a mildly stenosed artery [L. Back, Y. Cho, D. Crawford, R. Cuffel, Effect of mild atherosclerosis on flow resistance in a coronary artery casting of man, J. Biomech. Eng. 106 (1984) 48–53]. The combined influence of an asymmetric shape and surface irregularities of the constriction has been explored in a computational study of blood flow through arterial stenosis with 48% areal occlusion. The moving wall of the artery is included to be anisotropic, linear, viscoelastic, incompressible circular cylindrical membrane shell. The effect of the surrounding connective tissues on the motion of the arterial wall is also paid due attention. Results are also obtained for a smooth stenosis model and also for a stenosis model representative by the cosine curve. An extensive quantitative analysis has been performed in non-uniform non-staggered grids through numerical computations for the effect of surface irregularities on the flow velocity, the flux, the resistive impedance and on the wall shear stress through their graphical representations so as to validate the applicability of such an improved mathematical model.     

A New Unsteady Three Dimensional Model for Macromolecular Transport and Water Filtration Across the Arterial Wall

ＩｎｔｒｏｄｕｃｔｉｏｎＡｔｈｅｒｏｇｅｎｅｓｉｓ,ｏｎｅｏｆｔｈｅｍａｊｏｒｃａｕｓｅｓｆｏｒｔｈｅｄｅａｔｈｏｆｐｅｏｐｌｅｉｎｗｅｓｔｅｒｎｃｏｕｎｔｒｉｅｓ,ｈａｓｔｗｏｐｒｏｍｉｎｅｎｔｐｒｏｐｅｒｔｉｅｓ.Ｆｉｒｓｔ,ｉｔｕｓｕａｌｌｙｔａｋｅｓｐｌａｃｅａｔｔｈｅｂｒａｎｃｈｅｓｏｒｃｕｒｖａｔｕｒｅｓｏｆｔｈｅｂｉｇａｒｔｅｒｉｅｓ,ｗｈｅｒｅｔｈｅｒｅｉｓａｎａｂｒｕｐｔｃｈａｎｇｅｏｆｂｌｏｏｄｆｌｏｗ .Ｓｅｃｏｎｄｌｙ ,ｔｈｅｒｅｉｓａｎａｃｃｕｍｕｌａｔｉｏｎｏｆｌｏｃａｌｆ…     

Response of blood flow through an artery under stenotic conditions

This paper presents an analytical study on the behavoiur of blood flow in an artery having a stenosis. This is basically formulated through the use of a suitable mathematical model. The arterial segment under consideration is simulated by an anisotropically elastic cylindrical tube filled with a viscous incompressible fluid representing blood. The analysis is carried out for an artery with mild local narrowing in its lumen forming a stenosis. Particular emphasis has been paid to the effect of the surrounding connective tissues on the motion of the arterial wall. Blood is treated as a Newtonian fluid. The analysis is restricted to propagation of small amplitude harmonic waves, generated due to the flow of blood whose wave length is large compared to the radius of the arterial segment. The effect of the shape of stenosis on the resistance to blood flow has been well illustrated quantitatively through numerical computations of the resulting expressions. A quantitative analysis is also made for the variation of the phase velocity, as well as the velocity of wave propagation and the flow rate, in order to illustrate the applicability of the model.     

Oxygen transfer in human carotid artery bifurcation

Arterial bifurcations are places where blood flow may be disturbed and slow recirculation flow may occur. To reveal the correlation between local oxygen transfer and atherogenesis, a finite element method was employed to simulate the blood flow and the oxygen transfer in the human carotid artery bifurcation. Under steady-state flow conditions, the numerical simulation demonstrated a variation in local oxygen transfer at the bifurcation, showing that the convective condition in the disturbed flow region may produce uneven local oxygen transfer at the blood/wall interface. The disturbed blood flow with formation of slow eddies in the carotid sinus resulted in a depression in oxygen supply to the arterial wall at the entry of the sinus, which in turn may lead to an atherogenic response of the arterial wall, and contribute to the development of atherosclerotic stenosis there. The project supported by the National Natural Science Research Council of China (10632010, 10572017, 30670517).     

窦部对称狭窄对颈动脉内流场影响的数值研究

以颈动脉分岔血管为例，采用数值方法研究了窦部环缩狭窄之后的流场分布情况，并和正 常血管情况下的流场分布进行了比较. 结果表明，采用环缩方式给颈动脉分岔血管施加对称 的狭窄改变了颈动脉窦内流场，特别是壁面剪应力的分布规律. 低剪应力区出现在狭窄段之 后的窦内，并且沿整个周向均匀分布. 根据低剪应力和动脉粥样硬化的关系，指出： 若人为地给颈动脉窦内施加对称狭窄，则脂质沉积将在狭窄下游的窦内沿周向轴对称 发展. 为了更真实地反映颈动脉窦内的狭窄，建议根据动脉血管中的实际狭窄情况，采用非 对称的狭窄分布模式.     

Numerical simulation of mass transfer to micropolar fluid flow past a stenosed artery

A mathematical model of unsteady non‐Newtonian blood flow together with the mass transfer through constricted arteries has been developed. The mass transport refers to the movement of atherogenic molecules, i.e. blood‐borne components, such as low‐density lipoproteins from flowing blood into the arterial walls or vice versa. The flowing blood is represented as the suspension of all erythrocytes assumed to be Eringen's micropolar fluid and the arterial wall is considered to be rigid having cosine‐shaped stenosis in its lumen. The mass transfer to blood is controlled by the convection–diffusion equation. The governing equations of motion accompanied by the appropriate choice of the boundary conditions are solved numerically by Marker and Cell method and the results obtained are checked for numerical stability with the desired degree of accuracy. The quantitative analysis carried out finally includes the respective profiles of the flow‐field and the mass concentration along with their distributions over the entire arterial segment as well. The key factors, such as the wall shear stress and Sherwood number, are also examined for further quantitative insight into the flow and the mass transport phenomena through arterial stenosis. The present results show consistency with several existing results in the literature which substantiate sufficiently to validate the applicability of the model under consideration. Copyright © 2010 John Wiley & Sons, Ltd.