A model of blood flow distribution during filtration-reabsorption processes in capillaries

A model of blood flow in a capillary was constructed, which takes into account the movement of plasma through its porous wall. The functions of changes in pressure and the rate of blood flow along the capillary were calculated. It was shown that, in the general case, the distribution of hemodynamic parameters as a result of filtration-reabsorption processes is nonlinear. Possible mechanism of tissue edema resulting from the disturbance of the filtration-reabsorption equilibrium were analyzed.     

Plug Effect of Erythrocytes in Capillary Blood Vessels

As an idealized problem of the motion of blood in small capillary blood vessels, the low Reynolds number flow of plasma (a newtonian fluid) in a circular cylindrical tube involving a series of circular disks is studied. It is assumed in this study that the suspended disks are equally spaced along the axis of the tube, and that their centers remain on the axis of the tube and that their faces are perpendicular to the tube axis. The inertial force of the fluid due to the convective acceleration is neglected on the basis of the smallness of the Reynolds number. The solution of the problem is derived for a quasi-steady flow involving infinitesimally thin disks. The numerical calculation is carried out for a set of different combinations of the interdisk distance and the ratio of the disk radius to the tube radius. The ratio of the velocity of the disk to the average velocity of the fluid is calculated. The different rates of transport of red blood cells and of plasma in capillary blood vessels are discussed. The average pressure gradient along the axis of the tube is computed, and the dependence of the effective viscosity of the blood on the hematocrit and the diameter of the capillary vessel is discussed.     

肠淋巴液引流对失血性休克大鼠红细胞流变性的影响

目的:观察肠淋巴液引流对失血性休克大鼠红细胞流变性指标以及血液黏度的作用。方法:Wistar雄性大鼠均分为假休克组、休克组(复制失血性休克模型)、引流组(复制失血性休克模型,自低血压1 h引流休克肠淋巴液)。在低血压3 h或相应时间,经腹主动脉取血,检测红细胞参数、红细胞电泳、红细胞沉降率(ESR)以及血液黏度,计算红细胞聚集指数、红细胞变形指数。结果:与假休克组比较,休克组红细胞数量、红细胞比积(HCT)、血红蛋白(Hb)、平均红细胞血红蛋白浓度(MCHC)、红细胞电泳率与迁移率、红细胞变形指数、全血黏度、全血低切与高切相对黏度和还原黏度显著降低,休克组平均红细胞体积、红细胞电泳时间、ESR、血沉方程K值与校正K值、红细胞聚集性指数、血浆黏度显著升高;引流组MCHC、红细胞电泳率与迁移率、全血黏度、全血低切与高切还原黏度均显著降低,引流组红细胞体积分布宽度(RDW-SD)显著增加。同时,引流组HCT、RDW-SD、红细胞变形指数、全血黏度、全血低切与高切相对黏度显著高于休克组;ESR、血沉方程K值与校正K值、红细胞聚集性指数、血浆黏度显著低于休克组。结论:休克肠淋巴液引流可改善失血性休克大鼠红细胞流变行为,从而改善血液流变性。     

The tertiary endodermis in barley roots: Fine structure in relation to radial transport of ions and water

Summary The presence of numerous pits containing plasmodesmata in the inner tangential wall of the tertiary endodermis in barley roots is demonstrated by electron microscopy. The pit floor is covered by a thin layer of material which is continuous with and resembles the tertiary wall. The plasmodesmatal pore is constricted at its ends so that the plasmalemma lining the pore is appressed to the desmotubule. The frequency of plasmodesmata and their cross-sectional area is estimated, and phosphate and water fluxes through them are calculated on the assumption that they represent the only communication between the cortex and the vascular tissue. The pressure gradient across the ends of the plasmodesmata necessary to support the observed water flux is calculated for limiting cases of the pore radius and the viscosity of the fluid passing through the pore.     

Effects of inner solution viscosity and membrane stiffness on erythrocyte deformability on passing through a microchannel: prediction by two-dimensional simulation

We studied erythrocyte deformability in an effort to develop diagnostic methods based on its measurement and thus aid in the development of therapies for circulatory diseases. In the reported work, we performed two-dimensional numerical simulations of blood flow through a microchannel (MC) to evaluate erythrocyte deformability, applying the immersed boundary method to simulate erythrocyte movement and deformation. To evaluate deformability, MC transit capacity and shape recoverability were considered, defined as the time required to pass through the MC and the time constant during the shape-recovery process after exiting the MC, respectively. The simulation results showed that the erythrocyte MC transit time increased when the viscosity of the inner solution or the stiffness of the membrane increased. The time constant for erythrocyte shape recovery increased as the inner solution viscosity increased. In contrast, the time constant decreased as the erythrocyte membrane stiffness increased. These time-constant trends were in agreement with a theoretical equation derived using the Kelvin model and with previous experimental results. This diagnostic method of measuring erythrocyte shape recoverability and MC transit capacity is anticipated to have clinical application.     

The role of ecto-ATPases of erythrocyte plasma membrane in hemodynamics of fishes

The review addresses varied aspects of physiological and biochemical mechanisms aimed at creating special rheological conditions for blood flow termed non-Newtonian blood properties. We conducted a comparative analysis of structural features and phospholipid repertoire of the erythrocyte plasma membranes and cytoskeleton, extracellular ATP pool, and ecto-ATPase enzymatic activity in nucleated and non-nucleated erythrocytes in vertebrates, as well as a study of thermal effects in nucleated red blood cells. Based on data from the literature and our own research, we hypothesize that the phenomenon of non-Newtonian blood properties is underlain by a decrease in the relative blood viscosity due to thermal hydrolysis of extracellular ATP that erythrocytes release onto their surface most actively under capillary deformation stress. We believe that in fishes an important role in this process may belong to erythrocyte plasma membrane ecto-ATPases. Due to a heat released during hydrolysis of extracellular ATP, the marginal blood plasma layer, adjoining the capillary wall, appears to warm up. This may modify the structure of the membrane bilayer and deform the cytoskeleton, thus providing special rheological conditions for blood flow. The heat-producing ability, that we found in fish nucleated erythrocytes, may serve an additional evidence for the existence of this mechanism.     

Hydrodynamics of bolus flow—An analytical approach to blood flow in capillaries

A model which was used by Prothero and Burton to simulate a particular configuration in capillary blood vessels is investigated from a hydrodynamic point of view. In this model, the erythrocytes are approximated by rigid pistons, and plasma is assumed to be an incompressible Newtonian fluid. An order of magnitude analysis using the physiologically realistic values for various parameters reduces the exact equations of motion to an equation describing the creeping motion of the fluid. An analytical approach to the solution of the equation is proposed and some results are reported here. The solution of the flow field is given in terms of a stream function which is represented by two infinite series composed of known functions. Two coupled infinite systems of algebraic equations determining the coefficients of the two series have been derived. This method of solution is proposed as an alternative to the entirely numerical procedure of solving the similar problem proposed by Bugliarelloet al. A limiting case of large aspect ratio (the ratio of the axial spacing of the two successive erythrocytes to the capillary diameter) is studied and the solution, valid away from the erythrocyte surface, has been obtained in simple form. It resembles the classical Poisenille flow, but the pressure gradient is related to the erythrocyte speed.     

肝郁脾虚证模型大鼠血流变及TXB_2、PGFla的变化（英文）

目的：探查中医肝郁脾虚证模型的血流变及相关调节因子的状态。方法：采用慢性束缚应激＋过度疲劳＋饮食失节法建立大鼠肝郁脾虚证模型,测定大鼠造模三周、自然恢复一周时的血流变和血浆TXB2、PGF1a。结果：与正常组相比,模型组大鼠造模三周150/s、38/s、10/s、5/s切变率下的全血粘度、还原粘度均显著升高（P〈0.001）,红细胞聚集指数显著降低（P〈0.001）,红细胞压积显著升高（P〈0.01）,红细胞变形指数无显著性差异（P〉0.05）;血浆TXB2显著升高（P〈0.001）,6-keto-PGF1a显著降低（P〈0.05）,TXB2/PGF1a显著升高（P〈0.01）;模型组大鼠第四周150/s、38/s、10/s、5/s切变率下的全血粘度、还原粘度仍显著升高（P〈0.001或P〈0.01）;红细胞聚集指数显著降低（P〈0.001）;红细胞压积与变形指数无显著性差异（P〉0.05）;血浆TXB2和TXB2/PGF1a显著降低（P〈0.05）,6-keto-PGF1a显著升高（P〈0.05）。结论：肝郁脾虚证大鼠存在血液高粘和血栓易形成状态,恢复期血液高粘同时伴有扩血管因素的加强。提示肝郁脾虚证有血流变的异常和血浆TXB2-PGI2的平衡失调,主要涉及到血小板和血浆因素的参与。     

Pulmonary edema: ischemia reperfusion endothelial injury and its reversal by c-AMP.

A review of the factors that oppose pulmonary edema formation (alveolar flooding) when capillary pressure is elevated are presented for a normal capillary endothelial barrier and for damaged endothelium associated with ischemia/reperfusion in rabbit, rat, and dog lungs. Normally, tissue pressure, the plasma protein osmotic pressure gradient acting across the capillary wall and lymph flow (Edema Safety Factors) increase to prevent the build-up of fluid in the lung's interstitium when capillary pressure increases. No measureable alveolar edema fluid accumulates until capillary pressure exceeds 30 mmHg. When the capillary wall has been damaged, interstitial edema develops at lower capillary pressures because the plasma protein osmotic pressure will not change greatly to oppose capillary filtration, but lymph flow increases to very high levels to remove the increased filtrate and the result is that capillary pressures can increase to 20-25 mmHg before alveolar flooding results. In addition, the mechanisms responsible for producing pulmonary endothelial damage with ischemia/reperfusion are reviewed and the effects of O2 radical scavengers, neutrophil depletion or altering their adherence to the endothelium, and increasing cAMP on reversing the damage to the pulmonary endothelium is presented.     

Brain spectrin fragments and crosslinks actin filaments

The effect of brain spectrin (fodrin) on actin has been studied using viscometry and fluorimetry. Brain spectrin resembles erythrocyte spectrin tetramer in its action on actin. Both proteins crosslink actin filaments giving rise to a large increase in the viscosity but fluorimetry shows that neither affects actin polymerization significantly. In addition, brain spectrin as well as erythrocyte spectrin fragments preformed actin filaments. Actin filaments incubated in the presence of either of the two proteins incorporate actin monomers at a much higher rate showing that more filament ends are generated.     

Relationships between hemorheology, erythrocyte metabolism, and von willebrand factor in athletes and patients with peripheral arterial disease

The relationship between hemorheology, erythrocyte ATP and 2,3-diphosphoglycerate (2,3-DPG) concentrations, and von Willebrand factor antigen was studied in athletes and peripheral arterial disease patients. Lower blood viscosity, mainly due to a higher erythrocyte deformability, was found in athletes compared to control subjects. Higher 2,3-DPG/Ht levels in athletes were correlated with blood viscosity, erythrocyte deformability, the rigidity index, and erythrocyte suspension viscosity at low shear stress. It is suggested that these relationships might be determined by the predominance of immature erythrocytes in the blood circulation of the athletes. In the group of patients, a decrease in ATP/Ht was related to increased erythrocyte aggregation and a higher erythrocyte suspension viscosity. Moreover, the concentration of von Willebrand factor was positively correlated with the erythrocyte aggregation index, erythrocyte suspension viscosity, and plasma viscosity. The results show that alterations in erythrocyte and plasma rheology may be involved in the modification of the functional state of the vascular endothelium and the development of atherosclerosis.     

A Working Model of a Sieve Tube

A working model of a sieve tube is described, based upon thePressure-Flow Hypothesis. The flow of solution in the sievetube is envisaged as being due to the joint influence of anaxial turgor pressure gradient and a lateral water potentialdifference which causes an intake of water along the tube. Inthis second respect the model differs from that originally suggestedby Münch. The model comprises a length of dialysis tubing rendered semi-permeable,incorporating capillary resistances at regular intervals. Asucrose solution is pumped into one end and collected at theother, the whole being submerged in water. Turgor pressures and concentrations along the model were recordedat intervals; thus the approach to the steady state was followed.In the steady state ¹⁴C-sucrose was introduced to the solutionbeing pumped and its approach to a steady distribution in themodel was followed. Important conclusions reached are that the Munch Pressure-FlowHypothesis implies a pressure profile convex upwards, a velocityincrease down the phloem, and an exponential fall in tracerconcentration without its lateral leakage.     

A mechanism for erythrocyte-mediated elevation of apparent viscosity by leukocytes in vivo without adhesion to the endothelium

In spite of the relatively small number of leukocytes in the circulation, they have a significant influence on the perfusion of such organs as skeletal muscle or kidney. However, the underlying mechanisms are incompletely understood. In the current study a combined in vivo and computational approach is presented in which the interaction of individual freely flowing leukocytes with erythrocytes and its effect on apparent blood viscosity are explored. The skeletal muscle microcirculation was perfused with different cell suspensions with and without leukocytes or erythrocytes. We examined a three-dimensional numerical model of low Reynolds number flow in a capillary with a train of erythrocytes (small spheres) in off-axis positions and single larger leukocytes in axisymmetric positions. The results indicate that in order to match the slower axial velocity of leukocytes in capillaries, erythrocytes need to position themselves into an off-axis position in the capillary. In such off-axis positions at constant mean capillary velocity, erythrocyte axial velocity matches on average the axial velocity of the leukocytes, but the apparent viscosity is elevated, in agreement with the whole organ perfusion observations. Thus, leukocytes influence the whole organ resistance in skeletal muscle to a significant degree only in the presence of erythrocytes.     

杜仲绿原酸对高脂小鼠血液流变学作用研究

旨以研究杜仲绿原酸对高脂高胆固醇诱导的高血脂模型小鼠血液流变学的影响,以昆明小鼠为实验动物,随机分成5组:阴性对照组,模型对照组和低剂量(25 mg/kg BW)、中剂量(50 mg/kg BW)、高剂量(100 mg/kg BW)杜仲绿原酸组,每组10只.后4组饲以高脂饲粮,同时小鼠灌胃杜仲绿原酸4周,实验结束,分别测定各组小鼠血液流变学参数、血清和肝脏的抗氧化酶活性和脂质过氧化产物MDA含量及其总抗氧化能力和羟自由基清除率.高脂血症小鼠的全血粘度、血浆粘度、红细胞压积、血沉、纤维蛋白原、红细胞刚性指数和聚集指数显著降低(P＜0.05),红细胞变形指数显著提高(P＜0.05),小鼠血清和肝脏SOD、GSH-Px水平、总抗氧化能力和羟自由基清除能力均显著升高(P＜0.05),MDA水平显著降低(P＜0.05).在高脂膳食条件下,杜仲绿原酸能有效提高血液的抗氧化防御功能(包括抗氧化力、抗氧化酶活性)、改变血液流变学参数等,降低血液粘度、红细胞刚性和聚集,增强变形能力,使细胞膜的流动性增高,其中以中剂量效果相对较好.     

Microvascular pressure and functional capillary density in extreme hemodilution with low- and high-viscosity dextran and a low-viscosity Hb-based O2 carrier

Blood losses are usually corrected initially by the restitution of volume with plasma expanders and subsequently by the restoration of oxygen-carrying capacity using either a blood transfusion or possibly, in the near future, oxygen-carrying plasma expanders. The present study was carried out to test the hypothesis that high-plasma viscosity hemodilution maintains perfused functional capillary density (FCD) by preserving capillary pressure. Microvascular pressure responses to extreme hemodilution with low- (LV) and high-viscosity (HV) plasma expanders and an exchange transfusion with a polymerized bovine cell-free Hb (PBH) solution were analyzed in the awake hamster window chamber model (n = 26). Systemic hematocrit was reduced from 50% to 11%. PBH produced a greater mean arterial blood pressure than the nonoxygen carriers. FCD was higher after a HV plasma expander (70 +/- 15%) vs. PBH (47 +/- 12%). Microvascular pressure spanning the capillary network was higher after a HV plasma expander (16-19 mmHg) compared with PBH (12-16 mmHg) and a LV plasma expander (11-14 mmHg) but lower than control (22-26 mmHg). FCD was found to be directly proportional to capillary pressure. The use of a HV plasma expander in extreme hemodilution maintained the number of perfused capillaries and tissue perfusion by comparison with a LV plasma expander due to increased mean arterial blood pressure and capillary pressure. The use of PBH increased mean arterial pressure but reduced capillary pressure due to vasoconstriction and did not maintain FCD.     

Effects of plasma- and cell-free perfusates on filtration coefficient of perfused canine lungs

The filtration coefficient (Kf,c) of the microvessels in isolated dog lungs were studied for whole and diluted blood, whole and diluted plasma, Tyrode's solution, and Tyrode's plus dextran (4%, 63,000 mol wt) perfusates. When whole blood and plasma were diluted, Kf,c increased abruptly at a plasma protein concentration between 4 and 5 g/l, an effect which was not dependent on the erythrocyte mass. Both Tyrode's and Tyrode's plus dextran produced increases in Kf,c (60 and 30%, respectively). The difference in Kf,c measured between these latter perfusates was completely abolished when Kf,c were corrected for viscosity differences. Thus the pulmonary microvasculature responds similarly to the systemic circulation in that complete removal of plasma proteins from the perfusate increases Kf,c by 50%. This effect is independent of erythrocyte mass or colloid osmotic pressure of the perfusate, since perfusion with dextran solutions alone also increased Kf,c.     

Effect of erythrocyte aggregation at normal human levels on functional capillary density in rat spinotrapezius muscle

Previous studies have shown that functional capillary density (FCD) is substantially reduced by erythrocyte aggregation. However, only supranormal levels of aggregability were studied. To investigate the effect of erythrocyte aggregability at the level seen in healthy humans, the FCD of selected capillary fields in rat spinotrapezius muscle was determined with high-speed video microscopy under normal (nonaggregating) conditions and after induction of erythrocyte aggregation with Dextran 500 (200 mg/kg). To examine shear rate dependence, the effect was studied both at normal and reduced arterial pressures (50 and 25 mmHg), the latter achieved by short periods of hemorrhage. In a separate study, volume flow was determined in arterioles (52.1 +/- 3.7 microm) under the same conditions. Before Dextran 500 infusion, FCD fell to 91% and 76% of control values, respectively, when arterial pressure was reduced to 50 and 25 mmHg. After Dextran 500 infusion, FCD was 96% at normal arterial pressure and fell to 79% and 37% of normal control values at 50 and 25 mmHg. All FCD values were significantly lower after dextran infusion. FCD reduction after lowering arterial pressure or dextran infusion appeared to be due to plasma skimming rather than capillary plugging. Reduction of FCD by dextran at reduced pressure was compensated by increased red blood cell flux in capillaries with red blood cell flow. We conclude that the level of aggregability seen in healthy humans is an important determinant of FCD only at reduced arterial pressure.     

The mechanism of erythrocyte sedimentation in Westergren's examination.

The authors deduced the equation that describes the sedimentation of erythrocytes as the function of time, hematocrit, hemoglobin and some plasma protein concentrations and the citrate viscosity and density. This values served to describe plasma and erythrocyte density, plasma viscosity, erythrocyte aggregation and the influence of suspension concentration on the erythrocyte sedimentation rate. The influence of citrate on blood dilution (the reduction of hematocrit and plasma protein concentrations) was also considered. A good agreement between the observed and predicted values was obtained.     

Analysis of abnormalities of capillary CO2 exchange in vivo

Capillary CO2 exchange in vivo is affected by several interdependent reactions and transport processes. A mathematical model that includes all the significant chemical and transport events that are presumed to occur during capillary gas exchange has been used to investigate the effect of inhibition of 1) erythrocyte HCO(3-)-Cl- exchange, 2) lung carbonic anhydrase (CA) activity with access to plasma, and 3) erythrocyte CA activity on overall pulmonary CO2 excretion (VCO2) during rest and moderate exercise. Any decrement in VCO2 due to inhibition of HCO(3-)-Cl- exchange and/or CA activity, should result in compensatory alterations in cardiac output and/or an increase in the mixed venous blood-to-alveolar PCO2 gradient [(delta PCO2)V-A] to restore steady-state VCO2. Our computations show that complete inhibition of erythrocyte anion exchange would require a compensatory increment in cardiac output of approximately 30-40% or an increase in (delta PCO2)V-A from 6 to 8.3 Torr at rest and from 12 to 15.6 Torr during moderate exercise, if lung CA activity is intact. In the absence of availability of lung CA activity to plasma, the necessary (delta PCO2)V-A is 10.5 Torr at rest and 19.5 Torr during moderate exercise. Complete inhibition of lung and erythrocyte CA activity is predicted to require (delta PCO2)V-A of 39.1 Torr at rest and 74.2 Torr during moderate exercise. These results suggest that HCO(3-)-Cl- exchange might not be vital to maintenance of CO2 transfer and perhaps has a more important role in minimizing the changes in plasma pH associated with microvascular gas exchange in vivo.     

Ethephon-Induced Gummosis in Sour Cherry (Prunus cerasus L.) : II. Flow Characteristics of Gum Solutions

Flow of sour cherry (Prunus cerasus L. cv. Montmorency) gum solutions through a glass capillary was Newtonian for pressure gradients from 0 to 1.8 megapascals per meter, and hydraulic conductance was inversely proportional to solution viscosity in this range. However, flow became plastic at pressure gradients above 1.8 megapascals per meter, resulting in a decrease in solution viscosity. The magnitude of this effect diminished as gum concentration increased. Flow of water, a solution of the component sugar monomers of sour cherry gum, and sucrose solutions remained Newtonian over the entire pressure gradient range examined (0-4 megapascals per meter). Plastic flow of gum solutions in the vessels of intact sour cherry shoots is possible under pressure gradients induced by transpiration when high resistance to flow occurs over short distances.