Numerical simulation of blood flow and interstitial fluid pressure in solid tumor microcirculation based on tumor-induced angiogenesis

A coupled intravascular-transvascular-interstitial fluid flow model is developed to study the distributions of blood flow and interstitial fluid pressure in solid tumor microcirculation based on a tumor-induced microvascular network. This is generated from a 2D nine-point discrete mathematical model of tumor angiogenesis and contains two parent vessels. Blood flow through the microvascular network and interstitial fluid flow in tumor tissues are performed by the extended Poiseuille＇s law and Darcy＇s law, respectively, transvascular flow is described by Starling＇s law; effects of the vascular permeability and the interstitial hydraulic conductivity are also considered. The simulation results predict the heterogeneous blood supply, interstitial hypertension and low convection on the inside of the tumor, which are consistent with physiological observed facts. These results may provide beneficial information for anti-angiogenesis treatment of tumor and further clinical research.

Numerical Simulation of Blood Flow in Aorta with Dilation:A Comparison between Laminar and LES Modeling Methods

Computational modeling methods have been increasingly employed to quantify aortic hemodynamic parameters that are challenging to in vivo measurements but important for the diagnosis/treatment of aortic disease.Although the presence of turbulence-like behaviors of blood flow in normal or diseased aorta has long been confirmed,the majority of existing computational model studies adopted the laminar flow assumption(LFA)in the treatment of sub-grid flow variables.So far,it remains unclear whether LFA would significantly compromise the reliability of hemodynamic simulation.In the present study,we addressed the issue in the context of a specific aortopathy,namely aortic dilation,which is usually accompanied by disturbed flow patterns.Three patient-specific aortas with treated/untreated dilation of the ascending segment were investigated,and their geometrical models were reconstructed from computed tomography angiographic images,with the boundary conditions being prescribed based on flow velocity information measured in vivo with the phase contrast magnetic resonance imaging technique.For the modeling of blood flow,apart from the traditional LFA-based method in which sub-grid flow dynamics is ignored,the large eddy simulation(LES)method capable of incorporating the dissipative energy loss induced by turbulent eddies at the sub-grid level,was adopted and taken as a reference for examining the performance of the LFA-based method.Obtained results showed that the simulated large-scale flow patterns with the two methods had high similarity,both agreeing well with in vivo measurements,although locally large between-method discrepancies in computed hemodynamic quantities existed in regions with high intensity of flow turbulence.Quantitatively,a switch from the LES to the LFAbased modeling method led to mild(<6%)changes in computed space-averaged wall shear stress metrics(i.e.,SA-TAWSS,SA-OSI)in the ascending aortic segment where intensive vortex evolution accompanied by high statistical Reynolds stress was observed.In addition,comparisons among the three aortas revealed that the treatment status of aortic dilation or the concomitant presence of aortic valve disease,despite its remarkable influence on flow patterns in the ascending aortic segment,did not significantly affect the degrees of discrepancies between the two modeling methods in predicting SA-TAWSS and SA-OSI.These findings suggest that aortic dilation per se does not induce strong flow turbulence that substantially negates the validity of LFA-based modeling,especially in simulating macro-scale hemodynamic features.

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

A three-dimensional computational fluid dynamics (CFD) simulation of the physiological pulsatile blood flow in the human aortic arch and its three branches has been conducted by using commercial software StarCD. The blood flow, of a peak Reynolds number of 3289 and a Womersley parameter of 16.44, was simulated in a rigid aorta geometry that was built by computer aided design (CAD) reconstruction method based on autopsy data of a female adult. The purpose of this work is to further the understanding of the complex nature of aorta flow, therefore it mainly focuses on analysis of the spatial and temporal distributions of velocities and wall shear stresses. The results, illustrated by 3D visualization pictures and 2D graphs of the primary velocity profiles, wall shear stress and pressure distributions, as well as the secondary flow patterns, are in good agreement with those of other experimental and computational works. The distributions of pressure and wall shear stress support the correlation between high and low shear stresses and pressures and the atherosclerotic lesions.

Characterization of Blood Flow in Capillaries by Numerical Simulation

This paper presents a numerical investigation of the axisymmetric, pressure driven motion of single file erythrocyte (i.e., red blood cell) suspensions flowing in capillaries of diameter 8-11 μm. Our study success-fully recreates several important in vivo hemodynamic and hemorheological properties of microscopic blood flow, such as parachute shape of the cells, blunt velocity profile, and the Fahraeus effect, and they have been shown to have strong dependence on cell deformability, hematocrit and vessel size.

Quantification of the distribution of blood flow pressure with postures

At a different angle, this study analyzed the contour chart of blood flow pressure, extreme pressure and its position to quantify DBFP in thirteen different postures with gravity considered or not (G ≠ 0 or G = 0). The aim was to determine the suitable body positions, in which the postural model of a single vessel could be simplified to two-dimensional (2D) symmetrical one while only considering such factors as posture and gravity. Computational fluid dynamic simulations were performed. Numerical results demonstrated that the DBFP showed 2D axisymmetry at ±90° and three-dimensional (3D) asymmetry at any other posture with G ≠ 0, and 2D axisymmetrical one at any posture with G = 0. Therefore, modeling a vessel as a 2D model is feasible in space and at ±90° posture on earth. In addition, the maximum pressure occurred between the inlet and the middle of the vessel, and its position variation mainly happened in the range of 0° - 15°. For a single vessel, this study provides the first theoretical evidence for cardiovascular modeling in microgravity and may help guide the researchers in designing defense devices for astronauts or patients clinically.

Exploratory study of non-invasive,high-resolution functional macular imaging in subjects with diabetic retinopathy

AIM:To evaluate a high-resolution functional imaging device that yields quantitative data regarding macular blood flow and capillary network features in eyes with diabetic retinopathy(DR).METHODS:Prospective,cross-sectional comparative case-series in which blood flow velocities(BFVs)and noninvasive capillary perfusion maps(nCPMs)in macular vessels were measured in patients with DR and in healthy controls using the Retinal Functional Imager(RFI)device.RESULTS:A total of 27 eyes of 21 subjects were studied[9 eyes nonproliferative diabetic retinopathy(NPDR),9 eyes proliferative diabetic retinopathy(PDR)and 9 controls].All diabetic patients were type 2.All patients with NPDR and 5 eyes with PDR also had diabetic macular edema(DME).The NPDR group included eyes with severe(n=3)and moderate NPDR(n=6),and were symptomatic.A significant decrease in venular BFVs was observed in the macular region of PDR eyes when compared to controls(2.61±0.6 mm/s and 2.92±0.72 mm/s in PDR and controls,respectively,P=0.019)as well as PDR eyes with DME compared to NPDR eyes(2.36±0.51 mm/s and 2.94±1.09 mm/s in PDR with DME and NPDR,respectively,P=0.01).CONCLUSION:The RFI,a non-invasive imaging tool,provides high-resolution functional imaging of the retinal microvasculature and quantitative measurement of BFVs in visually impaired DR patients.The isolated diminish venular BFVs in PDR eyes compared to healthy eyes and PDR eyes with DME in comparison to NPDR eyes may indicate the possibility of more retinal vein compromise than suspected in advanced DR.

Effect of tapered angles in an artery on distribution of blood flow pressure with gravity considered

The tapered angles of an artery significantly influence the local hemodynamics. However, as gravity is considered, little is known about the effect of tapered angles on the hemodynamics. In this study, we explored whether the effect of tapered angles on the distribution of blood flow pressure (DBFP) differed with gravity considered or not. Numerical simulations of the DBFP in a single vessel were performed based on such tapered angles as 0°, 0.5° and 1°. In the model used for simulation, gravity was introduced as a body force. We obtained the following simulations: i) The larger the tapered angles were, the better distributed the blood flow pressure;ii) The tapered effect was an important factor leading to nonlinearity in blood flow pressure;iii) Gravity affected DBFP coupling with the tapered angles, yet independently influenced the dimension of the DBFP. At the same time, the effective intensity of gravity decreased with the increase of tapered angles.

A Mathematical Model for Pulsating Flow of Ionic Fluid under an Axial Electric Field： EMF Effect on Blood Flow

The present work introduces a mathematical model for ionic fluid that flows under the effect of both pulsating pressure and axial electromagnetic field. The fluid is treated as a Newtonian fluid applying Navier-Stokes equation. The fluid is considered as a neutral mixture of positive and negative ions. The effect of axial electric field is investigated to determine velocity profiles. Hydroelectric equation of the flow is deduced under dc and ac external electric field. Hence the effect of applied frequency （0-1 GHz） and amplitude （10-350 V/m） is illustrated. The ultimate goal is to approach the problem of EMF field interaction with blood flow. The applied pressure waveform is represented as such to simulate the systolic-diastolic behavior. Simulation was carried out using Maple software using blood plasma parameters; hence velocity profiles under various conditions are reported.

主动脉穿刺型轴流血泵折边结构叶轮的数值模拟及溶血分析

为解决血泵因叶顶间隙泄漏而造成溶血和血栓等问题,引入了一种折边不等间距叶轮,采用计算流体力学(computational fluid dynamics, CFD)进行内部流场的数值模拟,并与非折边不等间距叶轮及折边等间距叶轮进行对比分析,研究了它们的内流场动力学特性和血液相容性.结果表明:折边叶片结构血泵避免了叶顶间隙泄漏流的产生,同时折边不等间距叶轮减少了叶轮入口和出口处的回流和涡流,流道内整体切应力低于其他2种叶轮;3种叶轮的溶血指数HI均满足血泵的溶血设计指标,其中,折边不等间距叶轮血泵壁面切应力在0~150 Pa的占比达96.84%,曝光时间相对集中且满足人工血泵设计要求,溶血指数较非折边不等间距叶轮血泵下降了3.50%,较折边等间距叶轮血泵下降了12.50%,溶血性能最优.提出的折边不等间距叶轮血泵可有效降低红细胞破损概率,减少溶血和血栓的发生,可为轴流血泵的结构设计和优化提供一定参考.

颈内动脉狭窄血流动力学数值模拟

目的:基于血流动力学数值模拟条件,探究对颈内动脉进行不同程度人工干预狭窄的颈动脉模型的血流动力学特性,并从血流动力学角度分析颈内动脉位置处产生狭窄及由于其狭窄导致脑部供血疾病的原因。方法:采集内蒙古民族大学附属医院提供的健康个体二维CT数据,应用医学建模软件MIMICS20.0将二维的颈动脉CT数据进行三维模型重建,然后借助3-Matic Medical软件,对颈动脉模型中的颈内动脉同一位置进行不同程度的人为干预狭窄,得到颈内动脉25%、50%、75%狭窄程度的颈动脉模型。经格式转化、边界条件设置、网格划分等操作后,导入计算流体力学软件FLUENT14.5进行颈动脉血管及血液两相流血流动力学数值模拟与分析。结果:比较颈内动脉同一位置3种不同狭窄程度下的血液流线及速度矢量图可知,随着狭窄程度的增大,颈动脉窦处血液的涡旋流动现象迅速减弱,而颈内动脉狭窄处上方和下方血液出现明显的涡旋流动,并且血液流动出现选择性偏流。颈内动脉狭窄程度从25%到50%再到75%的过程中,狭窄处的血管壁面压力始终较低,狭窄下方的血管壁面压力逐渐增大,为高压力区域。狭窄处为高切应力区域,并且狭窄位置上方和下方的低切应力范围明显变大。结论:利用计算机软件进行人为干预狭窄获取模型的技术进行实验研究具有方便、快捷的特点。颈内动脉狭窄从25%到50%再到75%时,颈动脉的血液流场发生明显改变,颈内动脉出现明显的涡旋流动现象,血管壁面的力学性质也发生一定变化。

基于两相流欧拉方法的中空纤维管血流动力学数值模拟

对人工肝中空纤维管内血液两相流动进行了三维数值模拟,研究了中空纤维管内血流速度分布、红细胞径向体积分数分布、黏度分布以及壁面条件对红细胞体积分数分布的影响.结果表明,红细胞在轴心附近处黏度高,在壁面处黏度低;红细胞流速略大于血浆流速;红细胞沿径向体积分数分布呈双峰状,随各截面与入口距离增加,邻近壁面处的红细胞体积分数逐渐减小,壁面处的红细胞体积分数逐渐增大;不同壁面条件下,壁面处的红细胞体积分数随所受升力减小而增大,远离壁面运动趋势减弱.

The simulation of multiphase flow field in implantable blood pump and analysis of hemolytic capability

The numerical simulation of the axial flow impeller blood pump NIVADIII is carried out by using a CFD multiphase flow model. The hydrodynamic performance of the pump and the flow field in the pump are analyzed, and the shear stress distribution is obtained. A hemolytic prediction model based on the shear stress is built based on the calculation results, and it can be used for qua- ntitative predictions of the hemolytic behavior of a blood pump. Hemolysis tests in vitro were performed 6 times with fresh bovine blood. At each time, the flow of the pump NIVADIII is 5 L/min and the outflow tract pressure is 100 mmHg. According to the tests, the plasma free hemoglobin （FHB） content and the hematocrit （HCT） are measured after 0 s, 0.5 s, 1 s, 1.5 s 4 s. At the end of each experiment Normal Index of Hemolysis （NIH） of NIVADIII is calculated. The average of NIH is 0.0055 g/100L, almost identi- cal with that obtained from the hemolytic prediction model. This method can be applied in the selection stage of a blood pump.

Comparison of blood rheological models in patient specific cardiovascular system simulations

Newtonian, Quemada and Casson blood viscosity models are implemented in order to simulate the rheological behavior of blood under pulsating flow conditions in a patient specific iliac bifurcation. The influence of the applied blood constitutive equations is monitored via the wall shear stress （WSS） distribution, magnitude and oscillations, non-Newtonian importance factors, and viscosity values according to the shear rate. The distribution of WSS on the vascular wall follows a pattern which is independent of the theological model chosen. On the other hand, the WSS magnitude and oscillations are directly related to the blood constitutive equations applied and the shear rate. It is concluded that the Newtonian approximation is satisfactory only in high shear and flow rates. Moreover, the Newtonian model seems to overestimate the possibility for the formation of atherosclerotic lesions or aneurysms at sites of the vascular wall where the WSS are oscillating.

应用CFD对人工血泵流场进行数值仿真

发展人工心脏以便在某些情况下代替心脏进行供血已成为医学界的普遍要求。血泵研制和改进中所面临的主要难点之一是血液在血泵中的流动分离等复杂流动情况 ,对人工血泵中血液的流体动力分析是发展先进人工血泵的前提。本文应用计算机求解三维Navier Stokes方程 ,对某型血泵叶片通道间内部流场进行了数值仿真。研究分析结果表明 ,血泵中流体具有非常复杂的流动情况。为避免流动中分离造成流体升压比下降和血细胞破坏 ,对通道的进口和小叶片的安放位置以及叶片高度的变化都提出了很高的要求。

失重对脑血流影响的仿真研究

目的应用计算机仿真探讨失重对脑血流的影响。方法根据流体力学参数与电学变量等效的原理,利用Pspice语言建立人体心血管系统模型,包括人体心脏模型、动脉系统模型、静脉系统模型以及外周血管模型等四部分。仿真了0G与1G下脑血流、颈动脉血压与主动脉弓血压的变化曲线。结果0G时脑血流量比1G时增加10%左右,颈动脉血压比1G时增高10mmHg。结论本模型可以较好地模拟失重条件下脑血流的变化,为进一步研究失重对脑血流的影响提供了新方法。

轴流式磁悬浮血泵流场数值模拟及溶血预测

血泵流体动力分析是研发先进人工心脏泵的前提,血泵叶轮旋转时会对血细胞造成不同程度的机械损伤,从而导致溶血和血栓,严重时甚至危及患者生命。以设计的一种轴流式磁悬浮血泵为例,结合计算流体力学和结构优化设计,采用κ-ε模型、动网格技术和用户自定义函数技术,在轴流式磁悬浮血泵内部三维流场数值模拟的基础上,分析轴流式磁悬浮血泵流道的剪应力分布,探索血液流量与叶轮转速的关系,利用粒子追踪法获取血液细胞流动轨迹,建立一种轴流式磁悬浮血泵的溶血数学模型,阐述轴流式磁悬浮血泵溶血性能预测的方法和机理。研究结果可为轴流式磁悬浮血泵的结构设计和降低溶血提供重要依据。

轴流血泵叶轮结构CFD仿真优化研究

轴流血泵内部流场形态产生的高剪切力是导致血液溶血的重要因素,因此,对轴流血泵中血液的流体动力分析有助于血泵性能的优化及减少血液细胞的损伤。应用计算机求解RNGk-ε方程,对所设计的微型轴流血泵叶轮中血液的流线及速度、压力、应力等分布情况进行了仿真分析。研究结果表明:血泵中的流体具有非常复杂的流动情况,为了避免流动分离、压力变化过大等情况,减少切应力,对血泵叶轮结构提出了相应的改进意见,并给出了优化后的叶轮结构。

锥形血管内血液脉动流的数值模拟

将锥形血管与人体血液的脉动流动联系起来研究发展中的血液流动问题 ,给出了锥形血管的几何模型、血液流动的理论模型、生理边界条件以及计算条件 ;根据人体生理脉动流条件 ,建立了血流平均速度函数 ,并就此对三维锥形血管内的血液脉动流动进行了数值模拟 ,获得心动周期不同时刻的轴向速度、径向速度、断面压力和轴向压力分布曲线。将数值模拟计算结果与实验和分析计算结果进行对照 ,讨论了锥形血管内血液脉动流的特点。

头低位卧床7天中脑循环功能的变化

为观察短期头低位卧床前、中、后脑循环的变化，进一步了解模拟失重对脑循环及其调节功能的影响。６名健康青年男性被试者，头低位－６°卧床７ｄ。脑循环观察采用ＴＣ２０００ＴＣＤ仪，分别检测头低位卧床前、中、后双侧脑中动脉血流速度。结果表明：头低位卧床期间双侧脑中动脉血流速度均呈升高趋势，２４ｈ内升高明显，４ｈ达最高值，第５ｄ呈最低值，第６～７ｄ又有升高趋势；双侧脑中动脉血流速度基本趋势相同，但存在部分差异。

冠状动脉移植管的血流动力学数值模拟

采用有限元数值计算的方法,模拟了冠状动脉搭桥术中移植管内的生理流动。计算模型包括了冠状动脉狭窄,并考虑了由于移植管直径大于冠状动脉直径而在两者缝合时移植管的变形。计算结果分析了缝合区附近的流场、二次流、壁面切应力在心动周期内的时空分布情况。计算结果表明,在缝合前端下游,存在一个低切应力、高切应力梯度的区域,在缝合区底部存在一个高切应力、高切应力梯度的区域。这两个区域都是内皮细胞增生并造成移植管术后再阻塞的危险部位。