Microconfined flow behavior of red blood cells

Red blood cells (RBCs) perform essential functions in human body, such as gas exchange between blood and tissues, thanks to their ability to deform and flow in the microvascular network. The high RBC deformability is mainly due to the viscoelastic properties of the cell membrane. Since an impaired RBC deformability could be found in some diseases, such as malaria, sickle cell anemia, diabetes and hereditary disorders, there is the need to provide further insight into measurement of RBC deformability in a physiologically relevant flow field. Here, RBCs deformability has been studied in terms of the minimum apparent plasma-layer thickness by using high-speed video microscopy of RBCs flowing in cylindrical glass capillaries. An in vitro systematic microfluidic investigation of RBCs in micro-confined conditions has been performed, resulting in the determination of the RBCs time recovery constant, RBC volume and surface area and RBC membrane shear elastic modulus and surface viscosity. It has been noticed that the deformability of RBCs induces cells aggregation during flow in microcapillaries, allowing the formation of clusters of cells. Overall, our results provide a novel technique to estimate RBC deformability and also RBCs collective behavior, which can be used for the analysis of pathological RBCs, for which reliable quantitative methods are still lacking.     

恒定磁场对家免血液流变学性质的影响

本文用激光衍射法研究了家兔离体血经不同磁场强度(0．05～0．35T)不同照射时间(10～50min)后血液流变性质的变化。结果表明当磁场强度低于0．25T时,不同磁场强度,不同照射时间处理后,血液粘度均有不同程度的降低;当磁场强度高于030T并长时间照射后,照射组的血液粘度与对照组相比有所升高;当磁场强度为0．25T时,血液粘度降低最显著;实验还表明经磁场照射后,红细胞的变形性并未有明显改变,但当照射时间为10分钟时,红细胞的变形性明显下降;红细胞的取向指数有一定程度的改善。因此,磁场增加了红细胞表面电荷,可能是磁场照射使血液粘度降低的一个主要原因。     

Viscoelasticity of pediatric blood and its implications for the testing of a pulsatile pediatric blood pump

Red blood cell hematocrit, aggregation and deformability, and plasma protein concentration influence the viscosity and elasticity of whole blood. These parameters affect the flow properties, especially at low shear rates (< 50 s(-1)). In particular, we have previously shown that the viscoelasticity of fluid affects the inlet filling characteristics and regions of flow separation in small pulsatile blood pumps. Although the viscosity of pediatric blood has been thoroughly studied, its elasticity has not been previously measured. Here we present the viscosity and elasticity of pediatric blood against shear rate for hematocrits from 19-56, measured using an oscillatory rheometer. There is little effect of patient age on blood viscoelasticity. A statistical analysis showed that when compared at constant hematocrit, blood from adult and pediatric patients had similar viscoelastic properties. We present blood analog solutions, as a function of hematocrit, constructed on the basis of the pediatric measurements. Flow field results for viscoelastic analogs of 20, 40 and 60% hematocrit and a Newtonian analog will be compared in the initial, in vitro testing of the Penn State pediatric blood pump, to determine the importance of incorporating a viscoelastic analog into the desigh interaction.     

Polyethylene glycol additives reduce hemolysis in red blood cell suspensions exposed to mechanical stress

Mechanical damage to blood cells is of considerable concern in the development and use of circulatory assist devices and other blood contacting systems. Furthermore, hemodilution with saline, dextran, and other plasma expanders applied during extracorporeal circulation and dialysis increases red blood cell (RBC) susceptibility to the high shear stresses associated with these procedures. In this paper, we present polyethylene glycol (PEG) as a potential erythrocyte protective agent against mechanically induced cellular trauma. Bovine RBCs were subjected to mechanical stress induced by rolling stainless steel shots through RBC suspensions for a constant exposure time. The suspensions were prepared at a hematocrit of 30% in various media: PEG (20,000 molecular weight), autologous bovine plasma, Dextran 40 solution, and phosphate buffered saline (PBS). RBC suspensions in Dextran 40 were prepared at a viscosity similar to the PEG suspensions. We found the hemolysis level of RBCs suspended in plasma and in PEG solutions to be several times lower (p < 0.001) than in the Dextran and PBS solutions. No statistically significant difference was found between the hemolysis that occurred in suspensions of RBCs in autologous plasma and in 2.0% PEG solutions. Even PEG concentration as low as 0.1% reduced hemolysis by more than 40% compared with PBS or the same concentration of Dextran in suspension medium. Our data demonstrate the efficacy of PEG molecules in reducing mechanical trauma to erythrocytes and suggest the potential for using PEG in assisted circulation, dialysis, and other procedures where RBCs are subjected to extensive mechanical stress.     

Hypoxia and hemorheological properties in older individuals

Hypoxia is caused by insufficient oxygen availability for the organism leading to reduced oxygen delivery to tissues and cells. It has been regarded as a severe threat to human health and it is indeed implicated in pathophysiological mechanisms involved in the development and progression of many diseases. Nevertheless, the potential of controlled hypoxia interventions (i.e. hypoxia conditioning) for improving cardio-vascular health is gaining increased attention. However, blood rheology is often a forgotten factor for vascular health while aging and hypoxia exposure are both suspected to alter hemorheological properties. These changes in blood rheology may influence the benefits-risks balance of hypoxia exposure in older individuals. The benefits of hypoxia exposure for vascular health are mainly reported for healthy populations and the combined impact of aging and hypoxia on blood rheology could therefore be deleterious in older individuals.This review discusses evidence of hypoxia-related and aging-related changes in blood viscosity and its determinants. It draws upon an extensive literature search on the effects of hypoxia/altitude and aging on blood rheology. Aging increases blood viscosity mainly through a rise in plasma viscosity, red blood cell (RBC) aggregation and a decrease in RBC deformability. Hypoxia also causes an increase in RBC aggregation and plasma viscosity. In addition, hypoxia exposure may increase hematocrit and modulate RBC deformability, depending on the hypoxic dose, i.e, beneficial effect of intermittent hypoxia with moderate dose vs deleterious effect of chronic continuous or intermittent hypoxia or if the hypoxic dose is too high. Special attention is directed toward the risks vs. benefits of hemorheological changes during hypoxia exposure in older individuals, and its clinical relevance for vascular disorders.     

驻极体改善烫伤大鼠血液流变学指标的实验研究

本实验用自制模型造成大鼠局部烫伤，用锥板粘度计测定大鼠烫伤早期和应用驻极体治疗后全血表观粘度、血浆粘度及红细胞压积的变化，并对红细胞的聚集和变形性能等参量作了相应的讨论。结果表明，烫伤后大鼠的全血表现粘度、血浆粘度及红细胞压积均呈显著性升高（Ｐ＜０．００１），红细胞聚集程度增加，变形能力下降。应用驻极体治疗后，烫伤动物的血液粘度和红细胞压积均较烫伤后有明显下降（Ｐ＜０．００１），红细胞的变形能力和聚集性能得到改善，驻极体具有改善血液流变学指标的作用。     

Ultrastructural alterations in red blood cell membranes exposed to shear stress

In the mechanism of damage to red blood cells (RBCs) caused by a centrifugal pump, the prolonged effects to the RBC membrane caused by exposure to shear stress remain unclear. We focused on the band 3 protein (B3), one of the major proteins in the membrane skeleton, and investigated the ultrastructural alterations of the RBC membrane with loaded shear stress. Using flow cytometry, the relative amount of B3 was examined in relation to RBC deformability. The results, with continuous exposure to low shear stress, showed cell downsizing, an increase in B3 density, and a decrease in the deformability of the RBC membrane. Exposure to high shear stress does not appear to exert any influence on the membrane skeleton of the RBC. Therefore, in addition to conventional processes including the instantaneous destruction of a cell due to intense shear stresses, the results of the present study indicate the presence of another process based on changes in membrane proteins leading to cell fragmentation. Under low shear stress, the RBC membrane skeleton shows delayed destruction, which is exhibited as a disorder of B3 distribution, and the related membrane dysfunction includes decreases in RBC deformability and stability.     

The etiopathogenesis of premenstrual syndrome as a consequence of altered blood rheology: a new hypothesis

The multisystem symptoms of premenstrual syndrome (PMS), the variable nature of their occurrence and their relatively rapid disappearance with the onset of bleeding are highly suggestive of a systemic factor as the causal agent of the disorder. Reports of increased blood viscosity and enhanced red blood cell (RBC) hydration provide a basis for proposing that PMS is the consequence of an aberration of the change in blood viscosity which occurs in the third week of the normal menstrual cycle. The seriousness of the viscosity-impaired capillary blood flow will be greatest in organs and capillary beds with the smallest capillaries. Such an assumption implies that those women who suffer from PMS will be individuals whose capillaries are smaller in size than non-sufferers. The frequency of occurrence of fluid retention as a symptom suggests that the specific etiologic agent could be a reduction in RBC deformability as a consequence of impaired linoleic acid metabolism or high levels of noradrenaline or hypothyroidism or combinations of the three factors. If poorly deformable RBCs are involved then the use of agents such as evening primrose oil or fish oil to improve RBC deformability could ameliorate the symptoms of PMS. It is speculated that similar changes in RBC deformability should occur at other times of hormonal change. Health problems occurring during pregnancy, or after parturition, or after cessation of ovarian function might be caused by or exacerbated by reduced RBC deformability.     

脐血红细胞免疫功能及流变特性的变化

目的 :研究脐血 4℃保存 3周红细胞免疫功能及流变特性的变化。方法 :取正常孕妇脐血 36份 ,无菌采血、4℃保存。在采血后 2h、1周末、2周末、3周末应用红细胞C3b受体花环试验和红细胞免疫复合物花环试验检测红细胞C3b受体活性 (RBC C3b)和红细胞粘附免疫复合物 (IC)率 ,同时应用LBY N6A旋转式粘度仪检测红细胞粘度、红细胞聚集指数 (AI)、刚性指数 (IR)及红细胞压积。结果 :脐血保存 2周内RBC C3b、IC、高切粘度和IR无显著性变化 ,3周末差异显著 ;AI则在 2周末显著上升 ,第 3周末上升更加明显 ;红细胞压积 3周内无显著变化。结论 :随着脐血保存时间的延长 ,红细胞的免疫功能在逐渐下降 ,同时对红细胞的变形性及红细胞的聚集性会产生重要影响 ,特别是第 3周出现显著性变化     

红细胞非惯性升力对血液流动的影响

目的 为准确模拟血流,研究红细胞变形性对血液流动的影响。方法 基于血液流变特性和红细胞力学特性分析,对现有血液两相流流动模型进行改进,改进模型中考虑了易变形红细胞受剪切流场或血管壁面作用而产生的非惯性升力的影响。利用改进模型对多个不同直径血管内的血液流动进行模拟。结果 由红细胞所受非惯性升力导致的径向运动对血管内红细胞体积分数、运动速度分布有明显影响;当血管直径为0.1~3.0 mm时,用改进模型得到的血液相对黏度的模拟值与测量值接近。结论 非惯性升力是血流呈现Fahraeus-Lindqvist效应的主要原因之一。考虑非惯性升力的改进模型可以准确模拟血液流动,为循环系统诊疗机制和细胞分选等过程的模拟提供更为准确的方法。     

红细胞非惯性升力对血液流动的影响

目的为准确模拟血流,研究红细胞变形性对血液流动的影响。方法基于血液流变特性和红细胞力学特性分析,对现有血液两相流流动模型进行改进,改进模型中考虑了易变形红细胞受剪切流场或血管壁面作用而产生的非惯性升力的影响。利用改进模型对多个不同直径血管内的血液流动进行模拟。结果由红细胞所受非惯性升力导致的径向运动对血管内红细胞体积分数、运动速度分布有明显影响;当血管直径为0.1~3.0 mm时,用改进模型得到的血液相对黏度的模拟值与测量值接近。结论非惯性升力是血流呈现Fahraeus-Lindqvist效应的主要原因之一。考虑非惯性升力的改进模型可以准确模拟血液流动,为循环系统诊疗机制和细胞分选等过程的模拟提供更为准确的方法。     

红细胞非惯性升力对血液流动的影响

目的 为准确模拟血流,研究红细胞变形性对血液流动的影响。方法 基于血液流变特性和红细胞力学特性分析,对现有血液两相流流动模型进行改进,改进模型中考虑了易变形红细胞受剪切流场或血管壁面作用而产生的非惯性升力的影响。利用改进模型对多个不同直径血管内的血液流动进行模拟。结果 由红细胞所受非惯性升力导致的径向运动对血管内红细胞体积分数、运动速度分布有明显影响;当血管直径为0.1~3.0 mm时,用改进模型得到的血液相对黏度的模拟值与测量值接近。结论 非惯性升力是血流呈现Fahraeus-Lindqvist效应的主要原因之一。考虑非惯性升力的改进模型可以准确模拟血液流动,为循环系统诊疗机制和细胞分选等过程的模拟提供更为准确的方法。     

住院治疗男性冠心病患者血液流变性变化的特点

２８例男性住院治疗冠心病（ＣＨＤ）患者，接受１０～４０天流变药物的治疗，虽然患者比积明显低于对照组（Ｐ＜０．０５），而血浆粘度明显高于对照组（Ｐ＜０．０１），但患者表观全血粘度及红细胞聚集指数与对照组无显著区别。若采用固定比积（０．５０）的红细胞ＰＢＳ，悬液，患者血样的表观粘度则明显高于对照组（Ｐ＜０．０５或＜０．０１）；红细胞聚集指数也明显高于对照组（Ｐ＜０．０５）。结果表明，红细胞变形性明显减弱和聚集性显著升高是住院男性冠心病患者血液流变性异常的主要特点，并提示，改善红细胞流变性异常和降低血浆粘度对冠心病患者可能是一种有益的治疗措施。     

Determination of Critical Parameters in Platelet Margination

An investigation of margination dependence on hematocrit, platelet shape, and viscosity ratio of plasma to cytoplasm is presented. Whole blood is modeled as a suspension of deformable red blood cells (RBCs) and rigid platelets in a viscous liquid. The fluid phase is simulated using the lattice-Boltzmann method, the RBC membranes are modeled with a coarse-grained spectrin-link method, and the dynamics of rigid particles are updated using Newton’s equations of motion for axisymmetric shapes. The results emphasize that an increase in hematocrit increases the rate of margination. The viscosity ratio between the interior cytoplasm and suspending fluid can considerably alter the rate of margination. The aspect ratio of surrogate platelet particles influences the rate of margination as well. Spherical particles tend to migrate more quickly than disks. Highly viscous or rigid RBCs slow down margination.     

用电阻抗法研究红细胞的松弛过程

提出用“红细胞流变特性测定义”测量红细胞在中粘悬浮介质中的松弛过程。并从Ｆｒｉｃｋｅ－Ｖｅｌｉｃｋ悬浮液电导理论出发，对该方法测量结果进行了理论探讨，证明所测得的ΔＲ／Ｒ０－ｔ曲线确能间接反映红细胞群体的变形性及变形后的粘弹性。     

The acute hemorheologic effect of calcium dobesilate

In a series 40 subjects without manifest vascular disorders received 1000 mg Calcium dobesilate (Doxium). Before and 3 hours after application the viscoelasticity of whole blood as well as plasma viscosity and the hematocrit were determined. The statistical analysis was performed by Wilcoxon-test. The viscosity of whole blood and the hematocrit decreased with a significance of p less than or equal to 0.001, whereas the elasticity decreased in a significance manner of p less than or equal to 0.01. Plasma viscosity remained uncharged. The results show an effect of hemodilution, which could be very important for treatment of hyperviscosity.     

Extensional flow-based assessment of red blood cell deformability using hyperbolic converging microchannel

The deformability of the red blood cell (RBC), is known to be closely related to microcirculation and diagnosis of specific diseases such as malaria, arterial sclerosis, sepsis, and so on. From the viewpoint of the flow type, conventional methods to measure the cell deformability have exploited simple shear or complex flow field with little focus on extensional flow field. In this paper, we present a new approach to assess cell deformability under the extensional flow field. For this purpose, a hyperbolic converging microchannel was designed, and the cell deformation in the extensional flow region was continuously monitored. It overcomes the limitation of conventional methods by reducing experiment time. As quantified by the degree of deformation, the extensional flow (Deformation Index = 0.51 at 3.0 Pa) was found to be more efficient in inducing cell deformation compared to the shear flow (Deformation Index = 0.29 at 3.0 Pa). This indicates the insufficiency of the existing models that predict the blood damage in artificial organs, which only consider shear flow. Also, this method could detect the heat-induced difference in deformability of RBCs. It provides a new platform to study the clinical effect of RBC deformability under extensional flow, and is expected to contribute the association of several diseases and deformability of RBCs.     

Effects of temperature and transfer from seawater to freshwater on blood microrheology in Pacific salmon

Blood of Pacific salmon was studied with particular interest in red blood cell (RBC) deformability in relation to migration. Blood samples were taken via cardiac puncture or chronic cannula placed in the dorsal aorta and heparinized. As an index of RBC deformability the mean passage time of single RBCs through micropores of 8 micron in diameter and 10 micron in length was determined under a pressure difference of 10 cmH2O. Despite about 100 mOsmol/l difference in plasma osmolality, there was no marked difference in RBC passage time between fish in seawater and those well acclimatized to freshwater. However, it seemed probable that a transient decrease in RBC passage time, i.e., an increase in RBC deformability, occurred immediately following transfer from seawater to freshwater. Plasma osmolality decreased to about 300 mOsmol/l within 1 hr after the transfer and showed no fluctuations thereafter. The temperature dependence of RBC deformability was much smaller in comparison with those previously observed in yellowtail and carp; salmon RBCs were still highly deformable even at 5 degrees C, a possible temperature of cold river water.     

白蛋白对红细胞力学性质影响的微观机理研究

作者采用激光衍射法、荧光分光光度法及电子顺磁共振法（ＥＳＲ）、从生物物理角度研究白蛋白地红细胞力学性质影响的机理。实验结果表明，不同深度的白蛋白处理红细胞后，可不同程度改善红细胞的变形性。在低浓度白蛋白条件下、白蛋白有较好改善红细胞变形性的作用。白蛋白浓度大于０．５ｍｇ／ｍｌ时，红细胞变形怀趋于稳定，如果红细胞呈棘形变形稍有减小。光学显微镜观察及荧光分光光度法及电子顺磁共振法测量红细胞流动性的实验