红细胞膜通道力学效应的探讨

在考察红细胞双凹碟形体形成的基础上,讨论了红细胞的输氧功能与红细胞变形的关系,揭示了红细胞膜通道的力学效应:当红细胞呈双凹碟形时,PiPo的地方,红细胞膜通道有释放出氧的现象,其氧的总流率为 J=Lo_2(Pio_2-Poo_2) Lp(Pi-Po) 式中Lo_2为O_2分压差引起的膜通道对氧的流导,PiO_2、Poo_2为膜内外的氧分压;Lp为由于压差引起的膜通道对氧的流导。     

基于液固耦合的光镊拉伸红细胞变形特性

目的:通过液固耦合的方法模拟红细胞在光镊拉伸过程中的变形情况,从而得到其剪切模量等力学参数,以探索其变形规律。方法:通过PRO/E建立血细胞三维双凹椭球模型,导入到ABAQUS软件中,采用超弹性材料,通过流体腔模型实现液固耦合,对光镊拉伸红细胞模型进行有限元计算。仿真再现红细胞变形的整个过程,拟合Suresh试验数据得到红细胞的剪切模量,进一步分析细胞质、细胞大小和形状与变形能力的关系。结果:仿真得到正常红细胞的剪切模量在5~9μN/m之间;细胞形状和直径均对变形能力有一定影响:直径越大,变形能力越差;双凹椭球细胞相对于球形细胞有更好的变形能力。结论:流体腔模型能够高效实现液固耦合,较好地模拟红细胞在光镊拉伸过程中的变形情况,直观地揭示细胞质、细胞大小和形状与变形的关系。为研究其他壳液提供了一种方法和参考。     

红细胞在毛细血管中的运动特征分析

目的 探究不同力学特性的红细胞在毛细血管中的运动变形,对相关血液流变学参数进行分析。方法 红细胞膜为超弹性膜,满足Skalak能量函数。采用浸入边界法将细胞膜与流场耦合,采用二阶精度的有限差分方法求解三维流场。同时,考虑了细胞膜内外的生理黏度比λ=5。结果 得到在不同硬度下细胞在毛细血管中的稳定变形。随细胞硬度的升高,细胞由轴对称形态转变为非对称屈曲形态。细胞变形随着毛细血管数的降低而减弱,流动阻力增大。结论 细胞变硬,细胞出现非对称变形,血液阻力上升。因此,在涉及红细胞硬度变化的疾病中,变硬的红细胞可能导致毛细血管堵塞,造成局部组织缺氧。     

基于浸入边界法研究超弹性红细胞在剪切流中的运动特性

目的 研究微血管中红细胞在剪切流中的运动特性,为阐明血管疾病的发病机制和开展血液循环实验研究提供理论参考。方法 建立具有膜厚度的超弹性红细胞模型,结合反馈力法和有限元浸入边界法,模拟红细胞在血液剪切流作用下的结构变形和运动方式。其中,固体采用超弹性材料,利用有限单元法进行求解;流体为不可压缩牛顿流体,利用有限差分法求解。结果 数值计算结果重现了细胞在剪切流中以“坦克履带式”向前滚动的运动方式。计算结果与文献结果吻合较好,验证了计算方法的可靠性。结论 所采用的浸入边界法对处理大变形问题的优势尤为明显,可以较好地展示红细胞在剪切流中的变形全过程。     

红细胞在单轴应变蠕动流中的轴对称变形

了解红细胞在流动中如何变形与破裂有重要的医学价值,它有助于确定大尺度血流中细胞的形状与膜张力,有助于设计人造心瓣膜,还有助于诊断某些血液病。本文把红细胞抽象为一个含有牛顿流体的囊袋,其薄膜只能承受各向同性张力并保持面积守恒,但不能承受弯矩。本文首先从理论上论证了在沿单轴方向引起应变的极慢流动中,红细胞的定常形状是长球。然后,用数值方法算出了细胞变形的非定常过程。计算表明,初始为长球或扁球形     

通脉促活胶囊对兔红细胞流变性作用的实验研究

目的观察通脉促活胶囊对兔实验性高粘滞血症的红细胞流变性的作用。方法用高分子右旋糖苷对兔造成高粘滞血症，即血瘀证动物模型，通过对动物血液粘度和红细胞流变性指标的检测，观察通脉促活胶囊的药理作用。结果通脉促活胶囊具有降低血液粘度、降低红细胞聚集指数和提高红细胞变形能力的作用、给药后，红细胞聚集指数为１４．２９±５．０６％，红细胞变形指数为４５．５８±６．４１％，和生理盐水对照组比较有显著差异（Ｐ<０．０１）。结论通脉促活胶囊具有降低兔血液粘度，增加细胞流动性，改善红细胞流变性的作用，具有预防和治疗作用。     

角质层渗透性质的有限元数值模拟计算

角质层是皮肤屏障作用的最主要部分，它决定可外界物质对皮肤的渗透情况。本研究在假设角质层细胞为一种三维的十四面体（物理学经典的Tetrakaidecahedron体）下，进行对角质层渗透性质的数值模拟工作。为此，首先完成了对角质层空间结构的网格拆分，拆分过程分两步进行：首先对角蛋白细胞的网格拆分；然后对角蛋白细胞周围的网状脂质体的网格拆分。在数值模拟过程中，则用有限元法得到方程的离散格式，用多重网格算法降低高频误差，提高计算精度。最后，给出了数值模拟结果的可视化效果图。     

微型轴流血泵溶血的数值模拟

基于N-S方程和标准K-ε湍流模型,采用非结构网格技术,对微型轴流血泵内部三维流场进行了数值模拟,得到了速度场、压力场等流场细节;同时采用Lagrange粒子追踪法获得了沿不同流线的剪应力以及红细胞暴露接触时间的分布,并引入溶血计算的经验公式,计算对比了不同转速条件下血泵的溶血指标,重点分析了血泵在5L/min、8000r/min工况下的溶血性能,对于血泵溶血的估算,本方法是可行的.     

眼眶骨折手术修复的计算机辅助模拟系统构建

统开发的三角面片网格的几何模型.完成具有三维真实感的图像显示、三维截骨以及三维手术模拟功能.实现对健康成年男性眼眶进行三维测量和眼眶体积的计算,左眼眶体积21.07 cm3,右眼眶体积21.05 cm3.结论 3D-OFCAS系统为眼眶骨折临床诊断和整形修复手术设计提供了参考.     

眼眶骨折手术修复的计算机辅助模拟系统构建

统开发的三角面片网格的几何模型.完成具有三维真实感的图像显示、三维截骨以及三维手术模拟功能.实现对健康成年男性眼眶进行三维测量和眼眶体积的计算,左眼眶体积21.07 cm3,右眼眶体积21.05 cm3.结论 3D-OFCAS系统为眼眶骨折临床诊断和整形修复手术设计提供了参考.     

Cataract in a fetus at risk for oculo-cerebro-renal syndrome (lowe)

Summary A high-risk pregnancy for X-linked recessive inherited Lowe's syndrome was terminated due to a male karyotype in the cultured amniotic fluid cells. The eyes of the male fetus showed specific cataracteous changes of the lens. A posterior lenticonus was due to a defect of the lens capsule. The lenses were of normal size. Loss of lens material through a lens capsule defect could account for the small discoid lens usually seen in Lowe's syndrome. Amino acids in amniotic fluid had normal concentrations except lysine and proline which were markedly elevated.     

Morphological study by an 'in vivo cryotechnique' of the shape of erythrocytes circulating in large blood vessels

Changes in the shape of erythrocytes circulating in large blood vessels of mice were examined by our 'in vivo cryotechnique'. The abdominal aorta and inferior vena cava (IVC) were cut vertically with a precooled knife and simultaneously an isopentane–propane mixture (−193°C) was poured over them for freezing. They were freeze-substituted in acetone containing 2% osmium tetroxide. Some specimens were embedded in Quetol-812, and thick or ultrathin sections were examined by light or transmission electron microscopy. Serial ultrathin sections were used to reconstruct 3-dimensional images of native erythrocytes. Others were transferred into t-butyl alcohol and freeze-dried for scanning electron microscopy. The tissue surfaces were sufficiently frozen to prevent large ice crystal formation, and erythrocyte shapes were also preserved. The shapes of circulating erythrocytes appeared to be varied in the abdominal aorta but typical biconcave discoid shapes were rarely observed. Conversely, erythrocytes were approximately biconcave discoid in shape in the IVC. Our in vivo cryotechnique was useful for clarifying the in vivo morphology of erythrocytes circulating in large blood vessels.     

Simulations of light scattering from a biconcave red blood cell using the finite-difference time-domain method

Numerical simulations of light scattering by a biconcave shaped human red blood cell (RBC) are carried out using the finite-difference time-domain (FDTD) method. A previously developed FDTD code for the study of light scattering by ice crystals is modified for the current purpose and it is validated against Mie theory using a spherically shaped RBC. Numerical results for the angular distributions of the Mueller scattering matrix elements of an RBC and their dependence on shape, orientation, and wavelength are presented. Also calculated are the scattering and absorption efficiencies. The implication of these results on the possibility of probing RBC shape changes is discussed.     

Numerical Simulation of Cell Motion in Tube Flow

A theoretical model is presented for describing the motion of a deformable cell encapsulating a Newtonian fluid and enclosed by an elastic membrane in tube flow. In the mathematical formulation, the interior and exterior hydrodynamics are coupled with the membrane mechanics by means of surface equilibrium equations, and the problem is formulated as a system of integral equations for the interfacial velocity, the disturbance tube-wall traction, and the pressure difference across the two ends to the tube due to the presence of the cell. Numerical solutions obtained by a boundary-element method are presented for flow in a cylindrical tube with a circular cross-section, cytoplasm viscosity equal to the ambient fluid viscosity, and cells positioned sufficiently far from the tube wall so that strong lubrication forces do not arise. In the numerical simulations, cells with spherical, oblate ellipsoidal, and biconcave unstressed shapes enclosed by membranes that obey a neo-Hookean constitutive equation are considered. Spherical cells are found to slowly migrate toward the tube centerline at a rate that depends on the mean flow velocity, whereas oblate and biconcave cells are found to develop parachute and slipper-like shapes, respectively, from axisymmetric and more general initial orientations.     

电阻抗法测量红细胞的流变特性

本文在ＦＲＩＣＫＥ悬浮液电导理论基础上,利用北医设计研制的红细胞流行特性测定仪测量红细胞的松驰过程。     

Effects of an ionophore, A23187, on the surface morphology of normal erythrocytes

A23187, an ionophore which selectively transports divalent cations across biologic membranes, was found in previous studies to cause exchange of calcium for hydrogen ions in erythrocytes, loss of potassium, and a decrease in cell volume due to escape of water without hemolysis. The present investigation has evaluated the influence of A23187 on erythrocyte morphology in the scanning electron microscope. The findings demonstrate that A23187 causes a time- and concentration-dependent conversion of biconcave erythrocytes into echinocytes and spheroechinocytes. The changes induced in erythrocytes by the ionophore required the presence of extracellular calcium. Red cells exposed to ionophore at low temperature were moderately resistant to its effects, and low pH (5.5 or less) virtually blocked the action of the drug. The findings support an important role for calcium in maintaining the discoid configuration of normal erythrocytes.     

Detrended fluctuation analysis of membrane flickering in discocyte and spherocyte red blood cells using quantitative phase microscopy

Dynamic analyses of vibrational motion in cell membranes provide a lot of information on the complex dynamic motilities of a red blood cell (RBC). Here, we present the correlation properties of membrane fluctuation in discocyte and spherocyte RBCs by using quantitative phase microscopy (QPM). Since QPM can provide nanometer sensitivity in thickness measurement within a millisecond time scale, we were able to observe the membrane flicking of an RBC in nanometer resolution up to the bandwidth of 50 Hz. The correlation properties of the vibrational motion were analyzed with the detrended fluctuation analysis (DFA) method. Fractal scaling exponent α in the DFA method was calculated for the vibrational motion of a cell surface at various surface points for normal discocyte and abnormal spherocyte RBCs. Measured α values for normal RBCs are distributed between 0.7 and 1.0, whereas those for abnormal spherocyte RBCs are within a range from 0.85 to 1.2. We have also verified that the vibrational motion of background fluid outside of a cell has an α value close to 0.5, which is a typical property of an uncorrelated white noise.     

Two-Dimensional Simulation of Red Blood Cell Deformation and Lateral Migration in Microvessels

A theoretical method is used to simulate the motion and deformation of mammalian red blood cells (RBCs) in microvessels, based on knowledge of the mechanical characteristics of RBCs. Each RBC is represented as a set of interconnected viscoelastic elements in two dimensions. The motion and deformation of the cell and the motion of the surrounding fluid are computed using a finite-element numerical method. Simulations of RBC motion in simple shear flow of a high-viscosity fluid show “tank-treading’’ motion of the membrane around the cell perimeter, as observed experimentally. With appropriate choice of the parameters representing RBC mechanical properties, the tank-treading frequency and cell elongation agree closely with observations over a range of shear rates. In simulations of RBC motion in capillary-sized channels, initially circular cell shapes rapidly approach shapes typical of those seen experimentally in capillaries, convex in front and concave at the rear. An isolated RBC entering an 8-μm capillary close to the wall is predicted to migrate in the lateral direction as it traverses the capillary, achieving a position near the center-line after traveling a distance of about 60 μm. Cell trajectories agree closely with those observed in microvessels of the rat mesentery.     

Relation of discoid lateral meniscus and cord-like anterior intermeniscal ligament: morphological and clinical study

Discoid lateral meniscus is a rare disorder and its association with other variations in the knee joint has been reported. The anterior intermeniscal ligament has also been described as connecting the anterior convex margin of the lateral meniscus to the anterior horn of the medial meniscus. In the normal population, it was observed at 53–94%. Although the functional properties of the anterior intermeniscal ligament are not yet clarified, two distinct types of the ligament have been described according to their morphological characteristics as cord-like and membranous types. The purpose of this study was to evaluate any possible association between morphologic types of anterior intermeniscal ligament and discoid lateral meniscus. A retrospective study was designed; 20 discoid lateral menisci were operated using routine arthroscopic examination. Upon arthroscopic examination the thickness of the ligament and associated morphological changes were recorded systematically. The cord-like anterior intermeniscal ligament was an associated structure in 15 of the 20 knees with discoid lateral meniscus (75%). Patients with discoid lateral meniscus apparently have cord-like type anterior intermeniscal ligament, thus we conclude that cord-like type of anterior intermeniscal ligament is a frequent accompanying structure to discoid lateral meniscus and may have a potential stabilizing effect on its anterior stability.     

Micro-scale Dynamic Simulation of Erythrocyte–Platelet Interaction in Blood Flow

Platelet activation, adhesion, and aggregation on the blood vessel and implants result in the formation of mural thrombi. Platelet dynamics in blood flow is influenced by the far more numerous erythrocytes (RBCs). This is particularly the case in the smaller blood vessels (arterioles) and in constricted regions of blood flow (such as in valve leakage and hinge regions) where the dimensions of formed elements of blood become comparable with that of the flow geometry. In such regions, models to predict platelet motion, activation, aggregation and adhesion must account for platelet–RBC interactions. This paper studies platelet–RBC interactions in shear flows by performing simulations of micro-scale dynamics using a computational fluid dynamics (CFD) model. A level-set sharp-interface immersed boundary method is employed in the computations in which RBC and platelet boundaries are tracked on a two-dimensional Cartesian grid. The RBCs are assumed to have an elliptical shape and to deform elastically under fluid forces while the platelets are assumed to behave as rigid particles of circular shape. Forces and torques between colliding blood cells are modeled using an extension of the soft-sphere model for elliptical particles. RBCs and platelets are transported under the forces and torques induced by fluid flow and cell–cell and cell–platelet collisions. The simulations show that platelet migration toward the wall is enhanced with increasing hematocrit, in agreement with past experimental observations. This margination is seen to occur due to hydrodynamic forces rather than collisional forces or volumetric exclusion effects. The effect of fluid shear forces on the platelets increases exponentially as a function of hematocrit for the range of parameters covered in this study. The micro-scale analysis can be potentially employed to obtain a deterministic relationship between fluid forces and platelet activation and aggregation in blood flow past cardiovascular implants.