冠状动脉中氧输运的数值模拟研究

利用正常人的CT数据,通过图像分割和重建建立右侧冠状动脉的真实三维几何模型;利用专业的网格划分软件ICEM CFD 12.0对几何模型进行计算网格的划分;利用商用CFD软件Fluent12.0对模型中的血液流动和氧输运进行数值模拟,获得了在入口的平均速度为0.2m/s的定常流情况下,冠状动脉内的流线图、壁面切应力分布图、重要截面上的速度分布和氧浓度分布图。数值模拟结果发现,在血管曲率较大的区域和血管分叉区域的血液流动较为复杂,存在二次流、回流和死水区;在弯曲血管附近靠近内侧的区域的氧浓度显著降低、浓度梯度也降低。这些结果与临床上观察到的这些区域易形成冠状动脉粥样硬化斑块的结论相吻合。     

基于MATLAB的微循环数值分析－毛细血管几何特性对氧输送特性的影响

目的　考察毛细血管弹性和血管扭曲度对氧分布的影响,从而进一步考察肿瘤组织内形成乏氧区的机理,为肿瘤的放射线疗法提供理论帮助。方法　通过一维毛细血管模型与氧传输模型相结合,考察了Krogh模型和扭曲血管模型内毛细血管与组织内的氧分压分布。血管截面积尺寸由一维模型获得并传输给组织模型。通过有限元分析计算氧分布。结果　获得了在一定血流压力和不同毛细血管初始半径下,血管沿流动方向的尺寸变化,并计算了Krogh模型和扭曲血管模型中,毛细血管与组织内的氧分压分布。结论　当毛细血管较小时,血管弹性对氧分压分布的影响很小;随着管径增大,血管弹性的影响也加大。另外,随着毛细血管扭曲度的增加,组织内氧分压分布的不均一性也增加,计算结果与相关文献的结果一致。该工作将有助于进一步考察肿瘤组织内的氧传输。     

Fundamental Study of Ultrasonic-Measurement-Integrated Simulation of Real Blood Flow in the Aorta

Acquisition of detailed information on the velocity and pressure fields of the blood flow is essential to achieve accurate diagnosis or treatment for serious circulatory diseases such as aortic aneurysms. A possible way to obtain such information is integration of numerical simulation and color Doppler ultrasonography in the framework of a flow observer. This methodology, namely, Ultrasonic-Measurement-Integrated (UMI) Simulation, consists of the following processes. At each time step of numerical simulation, the difference between the measurable output signal and the signal indicated by numerical simulation is evaluated. Feedback signals are generated from the difference, and numerical simulation is updated applying the feedback signal to compensate for the difference. This paper deals with a numerical study on the fundamental characteristics of UMI simulation using a simple two-dimensional model problem for the blood flow in an aorta with an aneurysm. The effect of the number of feedback points and the feedback formula are investigated systematically. It is revealed that the result of UMI simulation in the feedback domain rapidly converges to the standard solution, even with usually inevitable incorrect upstream boundary conditions. Finally, an example of UMI simulation with feedback from real color Doppler measurement also shows a good agreement with measurement.     

Effects of an Artery/Vascular Graft Compliance Mismatch on Protein Transport: A Numerical Study

Small-diameter vascular graft failure by intimal hyperplasia and thrombosis may result from flow disturbances and disruption of chemical transport in the fluid at the distal anastomosis, because of compliance mismatch between the graft and host artery. In previous studies. lower-than-normal wall shear stress (WSS), particle trapping, and high particle residence times were observed at the distal anastomosis due to a pulsatile tubular expansion effect caused by nonuniform radial deformations. This study was undertaken to examine effects of compliance and radius mismatch on the distribution of a model protein released at the graft-fluid interface. Finite element simulations of end-to-end vascular grafting were performed under pulsatile flow, using fluid-structure coupling to give physiologic wall displacements. Results showed that protein is convected smoothly downstream in a uniform compliant tube. A compliance mismatch disturbed the transport, causing positive and negative gradients in the concentration profile at the distal anastomosis. This was seen when the graft and artery radii were matched at zero pressure and at mean arterial pressure; low WSSs were only observed in the former case. Thus the distal intimal hypertrophy seen in noncompliant grafts may be caused partly by decreased WSS, and partly by concentration gradients of dissolved chemicals affecting chemotaxis of cells.     

升主动脉黏弹性实验研究

对正常国人急性头部外伤致死的新鲜尸体升主动脉进行应力松驰，蠕变实验研究，得出了升主动脉的应力松驰，蠕变数据和曲线。用回归分析的方法处理实验数据，得出了归一化应力松驰函数和归一化蠕变函数，并对实验结果进行分析讨论。     

Finite-Element Analysis of Oxygen Transport in the Systemic Capillaries

A mathematical model is formulated for the transport of O₂ inthe systemic capillaries and surrounding tissue. The model takesinto account molecular diffusion, the convective effect of theblood, the nonlinear effects of oxyhaemoglobin, and the consumptionof O₂ in the metabolic process. A finite-element formulationfor solving the equations governing the mass transfer in thecapillary is described. A fixed-point iterative technique isused to deal with the nonlinearities in the model. The concentrationof O₂ is found to decrease from the axis of the capillary tothe periphery of the tissue. It is shown that, owing to thenonlinear effects of oxyhaemoglobin, the partial pressure ofoxygen (PO₂) in the capillary and tissue increases. It is alsoshown that the tissue PO₂ increases as (i) the arterial bloodPO₂ increases, (ii) the Péclet number increases, and(iii) the diffusive flux of O₂ from the capillary decreases.     

平行平板流动腔入口和出口结构对流场影响的数值研究

本研究针对现有平行平板流动腔的结构特点，在相同流量和压差的情况下，分别研究了三种不同入口和出口结构对流动腔内流场的影响。结果显示，采用对称的入口和出口结构，流动腔内部的压力值可由计算公式得到；流体进入流动腔时，均匀的流场可以减小入口长度；在设计平行平板流动腔时，合理的选择几何尺寸比选择入（出）口结构更重要。研究还发现，为了保证细胞在流动腔内的力学环境尽可能相同，流动腔的高度不宜过小。     

Finite Element Modeling of Three-Dimensional Pulsatile Flow in the Abdominal Aorta: Relevance to Atherosclerosis

The infrarenal abdominal aorta is particularly prone to atherosclerotic plaque formation while the thoracic aorta is relatively resistant. Localized differences in hemodynamic conditions, including differences in velocity profiles, wall shear stress, and recirculation zones have been implicated in the differential localization of disease in the infrarenal aorta. A comprehensive computational framework was developed, utilizing a stabilized, time accurate, finite element method, to solve the equations governing blood flow in a model of a normal human abdominal aorta under simulated rest, pulsatile, flow conditions. Flow patterns and wall shear stress were computed. A recirculation zone was observed to form along the posterior wall of the infrarenal aorta. Low time-averaged wall shear stress and high shear stress temporal oscillations, as measured by an oscillatory shear index, were present in this location, along the posterior wall opposite the superior mesenteric artery and along the anterior wall between the superior and inferior mesenteric arteries. These regions were noted to coincide with a high probability-of-occurrence of sudanophilic lesions as reported by Cornhill et al. (Monogr. Atheroscler. 15:13--19, 1990). This numerical investigation provides detailed quantitative data on hemodynamic conditions in the abdominal aorta heretofore lacking in the study of the localization of atherosclerotic disease. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 0270Dh, 8710+e     

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 …     

国内氧传输研究的进展与展望

国内氧传输研究的进展与展望ＡｄｖａｎｃｅｓａｎｄＰｒｏｓｐｅｃｔｓｉｎＲｅｓｅａｒｃｈｏｎＯｘｙｇｅｎＴｒａｎｓｐｏｒｔｉｎＣｈｉｎａ张叔伦微循环的基本功能之一是向组织传输所需要的氧，微循环的机能状态直接影响氧的传输；反之，氧传输状态又是从本质上反映...     

低密度脂蛋白在颈动脉中输运与沉积的数值模拟及其影响因素

目的研究低密度脂蛋白(low-density lipoproteins,LDL)在颈动脉中的输运和壁面沉积规律,分析其与血流动力学、形态学参数的关联性,为基于LDL壁面沉积特征及其关联因素评估颈动脉粥样硬化风险和易感位置提供理论参考。方法基于医学图像对6名健康志愿者的颈动脉构建个性化模型,数值模拟LDL在脉动流条件下的输运及其在血管壁的沉积过程,并量化分析LDL壁面沉积浓度、浓度极化区域面积等与血流速度和颈动脉形态学参数的关联性。结果 LDL沉积常出现在靠近颈总动脉远端的颈动脉窦部,其沉积程度和分布特征存在明显的个体差异。沉积程度主要由流速决定,流速越小,LDL壁面沉积程度越高,相应的浓度极化区域面积越大;而沉积的空间分布主要受几何形态特别是分叉偏心率的影响,依分叉偏心率可呈环状分布和单侧分布两种典型的形式。结论颈动脉血流速度和形态学特征是分别决定LDL沉积程度和分布特征的主要因素,对其进行个性化测量有助于识别颈动脉粥样硬化高风险个体及易感区域。     

加温加湿经鼻导管高流量氧疗的研究

氧疗在呼吸系统疾病的治疗中占有重要地位,其包括有创机械通气及无创通气。有创机械通气是指通过行气管插管或气管切开的有创操作给予呼吸机通气支持。无创通气是指经口鼻、面罩或鼻导管连接呼吸机进行呼吸通气支持。近年来,经鼻高流量加温加湿氧疗作为一种新型氧疗方式,因其装置简便易行及独特的生理学效应得到广泛关注。本文对国内外经鼻高流量加温加湿氧疗的研究现状作一综述,为经鼻高流量氧疗在临床中的应用提供参考。     

人工晶体开孔孔径对晶体变形及前房内流场影响的数值模拟研究

目的 研究不同人工晶体(implantable collamer lens,ICL)开孔孔径对晶体变形和前房内流场的影响。 方法 从医工结合角度出发,采用流固耦合数值模拟方法,研究人工晶体不同开孔孔径对其变形及眼内房水流场(流量、速度场、压力场、温度场)的影响。 结果 流体动力学方面,房水通过 ICL 中央孔的房水流量从大到小对应的孔径依次为 0. 36、0. 40、0. 30、0. 20、0. 10 mm,该流量与孔径呈非线性关系。 后房压力略高于前房,前后房压差随孔径增大逐渐降低。 眼内温度分布对孔径的影响并不敏感。 固体静力学方面,0. 36 mm 孔径的 ICL 变形量最小,其变形量受房水通过中央孔的流量所主导,该流量越大,ICL 的变形越小。 结论 本文综合流体动力学和固体静力学分析,验证了现有 0. 36 mm 孔径的合理性,并提出理想的孔径范围为 d≥0. 36 mm。 研究结果有助于探明 ICL 的失效机制,提高临床手术的成功率,为未来人工晶体的国产化提供经验。     

楔形平板流动腔测量细胞硬度的数值模拟研究

细胞硬度或形变能力的测量对深入研究细胞的生物学功能及甄别细胞产生病变有着重要意义。以楔形平板流动腔作为细胞形变的加载装置,通过分析细胞在楔形平板流动腔中的运动情况,建立数学模型,通过数值模拟方法研究细胞形变系数与细胞在楔形平板流动腔内移动速度的关系,并以此测量细胞硬度或形变能力。结果表明,细胞在楔形平板流动腔内不同观测点的细胞移动速度可以作为细胞形变能力的测量依据。     

Influence of Pulsatile Flow on LDL Transport in the Arterial Wall

The accumulation of low-density lipoprotein (LDL) is one of the important factors in atherogenesis. Two different time scales may influence LDL transport in vivo: (1) LDL transport is coupled to blood flow with a pulse cycle of around 1 s in humans; (2) LDL transport within the arterial wall is mediated by transmural flow in the order of 10⁻⁸ m/s. Most existing models have assumed steady flow conditions and overlooked the interactions between physical phenomena with different time scales. The objective of this study was to investigate the influence of pulsatile flow on LDL transport and examine the validity of steady flow assumption. The effect of pulsatile flow on transmural transport was incorporated by using a lumen-free cyclic (LFC) and a lumen-free time-averaged (LFTA) procedures. It is found that the steady flow simulation predicted a focal distribution in the post-stenotic region, differing from the diffuse distribution pattern produced by the pulsatile flow simulation. The LFTA procedure, in which time-averaged shear-dependent transport properties calculated from instantaneous wall shear stress (WSS) were used, predicted a similar distribution pattern to the LFC simulations. We conclude that the steady flow assumption is inadequate and instantaneous hemodynamic conditions have important influence on LDL transmural transport in arterial geometries with disturbed and complicated flow patterns.     

人参皂甙对大鼠离体主动脉活动的影响

在一定GS浓度下对大鼠离体主动脉存在双向性作用。正常状态下使其收缩,而在NA收缩的基础上则引起其舒张。 GS对大鼠离体主动脉活动影响的作用途径及其机制目前尚不清楚,其收缩和舒张均与胰岛素的效应相似,由此提示可能是类胰岛素样的作用。GS的舒张效应可能不需动脉壁内膜参与,而GS收缩效应可被阿托品所阻断,可能与平滑肌上胆碱能M受体激活有关。