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Objective: Blood flow is considered one of the important parameters that contribute to venous thrombosis. We quantitatively test the relationship between initiation of coagulation and shear rate and suggest a biophysical mechanism to understand this relationship., Methods and Results: Flowing human blood and plasma were exposed to cylindrical surfaces patterned with patches of tissue factor (TF) by using microfluidics. Initiation of coagulation of normal pooled plasma depended on shear rate, not volumetric flow rate or flow velocity, and coagulation initiated only at shear rates below a critical value. Initiation of coagulation of platelet-rich plasma and whole blood showed similar behavior. At constant shear rate, coagulation of plasma also showed a threshold response to the size of a patch of TF, consistent with our previous work in the absence of flow., Conclusions: Initiation of coagulation of flowing blood displays a threshold response to shear rate and to the size of a surface patch of TF. Combined with the results of others, these results set the range of shear rates that limit initiation of coagulation by small surface areas of TF and by shear activation of platelets. This range fits the relatively narrow range of physiological shear rates described by Murray's law.

Aim: Arterial occlusion is a leading cause of cardiovascular disease. The main mechanism causing vessel occlusion is thrombus formation, which may be initiated by the activation of platelets. The focus of this study is on the mechanical aspects of platelet-mediated thrombosis which includes the motion, collision, adhesion and aggregation of activated platelets in the blood. A review of the existing continuum-based models is given. A mechanical model of platelet accumulation onto the vessel wall is developed using the dissipative particle dynamics (DPD) method in which the blood (i.e. colloidal-composed medium) is treated as a group of mesoscale particles interacting through conservative, dissipative, attractive and random forces., Methods: Colloidal fluid components (plasma and platelets) are discretized by mesoscopic (micrometre-size) particles that move according to Newton's law. The size of each mesoscopic particle is small enough to allow tracking of each constituent of the colloidal fluid, but significantly larger than the size of atoms such that, in contrast to the molecular dynamics approach, detailed atomic level analysis is not required., Results: To test this model, we simulated the deposition of platelets onto the wall of an expanded tube and compared our computed results with the experimental data of Karino et al. (Miscrovasc. Res. 17, 238-269, 1977). By matching our simulations to the experimental results, the platelet aggregation/adhesion binding force (characterized by an effective spring constant) was determined and found to be within a physiologically reasonable range., Conclusion: Our results suggest that the DPD method offers a promising new approach to the modelling of platelet-mediated thrombosis. The DPD model includes interaction forces between platelets both when they are in the resting state (non-activated) and when they are activated, and therefore it can be extended to the analysis of kinetics of binding and other phenomena relevant to thrombosis.

In this paper we apply the artificial compressibility method (ACM) in strongly coupled fluid-structure interaction (FSI) computation of blood flow in an elastic artery. Previously published and here referred to as the ACM/FSI method uses the idea of artificial compressibility by Chorin 1967, except the term of pressure time derivative in the continuity equation is used to mimic the response of the walls, thereby stabilizing the iterative coupling. To reach the aim, we present a new way, the test load method, to improve ACM/FSI computations. In the test load method, the compressibility parameter is computed locally and is based on the mesh deformation of the fluid domain. The functionality of the ACM/FSI coupling with the test load method is demonstrated in an arterial flow simulation, and the combination is shown to provide a robust convergence. In order to get the test cases to correspond better to human physiology, one-dimensional FSI models are combined with the higher dimensional test models.

Background: The severity of epicardial coronary stenosis can be assessed by invasive measurements of trans-stenotic pressure drop and flow. A pressure or flow sensor-tipped guidewire inserted across the coronary stenosis causes an overestimation in true trans-stenotic pressure drop and reduction in coronary flow. This may mask the true severity of coronary stenosis. In order to unmask the true severity of epicardial stenosis, we evaluate a diagnostic parameter, which is obtained from fundamental fluid dynamics principles. This experimental and numerical study focuses on the characterization of the diagnostic parameter, pressure drop coefficient, and also evaluates the pressure recovery downstream of stenoses., Methods: Three models of coronary stenosis namely, moderate, intermediate and severe stenosis, were manufactured and tested in the in-vitro set-up simulating the epicardial coronary network. The trans-stenotic pressure drop and flow distal to stenosis models were measured by non-invasive method, using external pressure and flow sensors, and by invasive method, following guidewire insertion across the stenosis. The viscous and momentum-change components of the pressure drop for various flow rates were evaluated from quadratic relation between pressure drop and flow. Finally, the pressure drop coefficient (CDPe) was calculated as the ratio of pressure drop and distal dynamic pressure. The pressure recovery factor (eta) was calculated as the ratio of pressure recovery coefficient and the area blockage., Results: The mean pressure drop-flow characteristics before and during guidewire insertion indicated that increasing stenosis causes a shift in dominance from viscous pressure to momentum forces. However, for intermediate (approximately 80%) area stenosis, which is between moderate (approximately 65%) and severe (approximately 90%) area stenoses, both losses were similar in magnitude. Therefore, guidewire insertion plays a critical role in evaluating the hemodynamic severity of coronary stenosis. More importantly, mean CDPe increased (17 +/- 3.3 to 287 +/- 52, n = 3, p < 0.01) and mean eta decreased (0.54 +/- 0.04 to 0.37 +/- 0.05, p < 0.01) from moderate to severe stenosis during guidewire insertion., Conclusion: The wide range of CDPe is not affected that much by the presence of guidewire. CDPe can be used in clinical practice to evaluate the true severity of coronary stenosis due to its significant difference between values measured at moderate and severe stenoses.

Improved methods are needed to identify patients at risk for thrombotic or bleeding events. Free oscillation rheometry (FOR) is a technique that offers information on coagulation, based on contributions of all blood components, by measurement of clotting time and changes in clot elasticity. This is the first study that evaluates FOR parameters in subjects likely to represent hypercoagulability (pregnant women) and hypocoagulability (thrombocytopenic patients). Clotting time and blood clot elasticity were measured by FOR in blood samples obtained from women in different pregnancy trimesters (n = 58), in thrombocytopenic patients before and after a platelet transfusion (n = 20) and in healthy blood donors (n = 60). The clotting time was shorter and the clot elasticity higher in pregnant women compared to the non-pregnant female blood donors. The elasticity was higher in late pregnancy compared to early pregnancy. Compared to the blood donors, the thrombocytopenic patients had lower elasticity, which was increased by a platelet transfusion, but there was no difference in clotting time. The results suggest that FOR can provide new information on the haemostatic status of patients at risk of thrombotic or bleeding events as well as information on the haemostatic effect of a platelet transfusion.

Hemolysis and thrombosis are among the most detrimental effects associated with mechanical heart valves. The strength and structure of the flows generated by the closure of mechanical heart valves can be correlated with the extent of blood damage. In this in vitro study, a tilting disk mechanical heart valve has been modified to measure the flow created within the valve housing during the closing phase. This is the first study to focus on the region just upstream of the mitral valve occluder during this part of the cardiac cycle, where cavitation is known to occur and blood damage is most severe. Closure of the tilting disk valve was studied in a "single shot" chamber driven by a pneumatic pump. Laser Doppler velocimetry was used to measure all three velocity components over a 30 ms period encompassing the initial valve impact and rebound. An acrylic window placed in the housing enabled us to make flow measurements as close as 200 microm away from the closed occluder. Velocity profiles reveal the development of an atrial vortex on the major orifice side of the valve shed off the tip of the leaflet. The vortex strength makes this region susceptible to cavitation. Mean and maximum axial velocities as high as 7 ms and 20 ms were recorded, respectively. At closure, peak wall shear rates of 80,000 s(-1) were calculated close to the valve tip. The region of the flow examined here has been identified as a likely location of hemolysis and thrombosis in tilting disk valves. The results of this first comprehensive study measuring the flow within the housing of a tilting disk valve may be helpful in minimizing the extent of blood damage through the combined efforts of experimental and computational fluid dynamics to improve mechanical heart valve designs.

This review considers various rheometrical approaches that have been adopted to study blood coagulation, with special reference to the rheological assessment of clotting time and studies of the evolution of viscoelasticity during the course of fibrin polymerization and cross-linking. The significance of the Gel Point in blood coagulation studies is discussed as a common feature of many of these studies in that they attempt to detect a liquid-to-solid transition during coagulation. Coagulation studies based on various forms of complex shear modulus measurements are considered, the latter being based principally on controlled stress and controlled strain rheometers. Also considered are the long established technique of thromboelastography and several emerging techniques such as wave propagation measurements, free oscillation rheometry, quartz crystal microbalance measurements and surface plasmon resonance.

Objective: Cardiac syndrome X (CSX) is of clinical interest, yet the underlying pathophysiological mechanisms have not been fully elucidated. It is well known that elevated blood viscosity and red blood cell (RBC) aggregation can adversely affect microcirculatory blood flow. The present study was designed to explore whether CSX is associated with abnormalities of blood rheology., Methods: Blood samples were obtained from 152 adult angina patients undergoing diagnostic coronary angiography; geometric and flow-velocity data were obtained. Rheologic measurements were performed in a blinded manner; 21 subjects were later identified with CSX. Hemorheologic and clinical laboratory data were compared to 21 age- and gender-matched healthy controls., Results: CSX patients had markedly abnormal blood rheology: (1) higher RBC aggregation and aggregability as judged by erythrocyte sedimentation rate and Myrenne indices at stasis and low shear (p < 0.001) and (2) elevated hematocrit-corrected blood viscosity, plasma viscosity (p < 0.001), and yield stress (p < 0.01). White blood cell counts and high-sensitivity C-reactive protein levels were significantly elevated in CSX; coronary-flow velocities were below normal., Conclusions: Abnormal hemorheologic parameters exist in subjects with CSX and may contribute to the pathophysiology of the disease, presumably via adversely affecting blood flow in the coronary microcirculation. Therapeutic measures aimed at normalizing blood rheology and hence microcirculatory flow should be explored.

Mechanical forces are known to affect the biomechanical properties of native and engineered cardiovascular tissue. In particular, shear stress that results from the relative motion of heart valve leaflets with respect to the blood flow is one important component of their mechanical environment in vivo. Although different types of bioreactors have been designed to subject cells to shear stress, devices to expose biological tissue are few. In an effort to address this issue, the aim of this study was to design an ex vivo tissue culture system to characterize the biological response of heart valve leaflets subjected to a well-defined steady or time-varying shear stress environment. The novel apparatus was designed based on a cone-and-plate viscometer. The device characteristics were defined to limit the secondary flow effects inherent to this particular geometry. The determination of the operating conditions producing the desired shear stress profile was streamlined using a computational fluid dynamic (CFD) model validated with laser Doppler velocimetry. The novel ex vivo tissue culture system was validated in terms of its capability to reproduce a desired cone rotation and to maintain sterile conditions. The CFD results demonstrated that a cone angle of 0.5 deg, a cone radius of 40 mm, and a gap of 0.2 mm between the cone apex and the plate could limit radial secondary flow effects. The novel cone-and-plate permits to expose nine tissue specimens to an identical shear stress waveform. The whole setup is capable of accommodating four cone-and-plate systems, thus concomitantly subjecting 36 tissue samples to desired shear stress condition. The innovative design enables the tissue specimens to be flush mounted in the plate in order to limit flow perturbations caused by the tissue thickness. The device is capable of producing shear stress rates of up to 650 dyn cm(-2) s(-1) (i.e., maximum shear stress rate experienced by the ventricular surface of an aortic valve leaflet) and was shown to maintain tissue under sterile conditions for 120 h. The novel ex vivo tissue culture system constitutes a valuable tool toward elucidating heart valve mechanobiology. Ultimately, this knowledge will permit the production of functional tissue engineered heart valves, and a better understanding of heart valve biology and disease progression.

The purpose of the study was to investigate relationships between sex, blood pressure level, duration of arterial hypertension (AH), 24-hour blood pressure (BP) rhythm, endothelial function (EF) and blood rheological parameters. 23 (mean age 50+/-8.73) outpatients with AH were included in the study. All subjects underwent off-therapy 24-hour ambulatory BP monitoring, investigation of blood rheological parameters and high resolution vascular dopplerography Dipper patients showed lower rate of platelet aggregation and platelet adhesion, than it was in non-dippers (86.42+/-8.20 vs. 99.36+/-5.93; P=0.0018 and 24.2+/-11.54 vs. 42.16+/-13.71; P=0.01). Viscosity was higher in patients with endothelial dysfunction, than it was in patients without it (0.064+/-0.01 vs. 0.051+/-0.0035; P=0.004). Compared with dippers, non-dippers showed an impaired EF (11.4+/-2% vs. 3.5+/-2.6%; p= 0.0006). The present data suggest the presence of disturbed endothelium-dependent vasodilatation and alterations in rheological indices in AH. According to the results obtained, the main factor, which leads to endothelial dysfunction and increase in platelet aggregative and adhesive activity, is the shortage in the lowering BP during the night. Consequently, hypertensive patients with non-dipper circadian blood pressure profile have to be assessed as a high risk group for development of future cardiovascular and cerebrovascular complications.

Background: Regions prone to atherosclerosis, such as bends and bifurcations, tend to exhibit a certain degree of non-planarity or curvature, and these geometric features are known to strongly influence local flow patterns. Recently, computational fluid dynamics (CFD) has been used as a means of enhancing understanding of the mechanisms involved in atherosclerotic plaque formation and development., Purpose: To analyze flow patterns and hemodynamic distribution in stenotic carotid bifurcation in vivo by combining CFD with magnetic resonance angiography (MRA)., Material and Methods: Twenty-one patients with carotid atherosclerosis proved by digital subtraction angiography (DSA) and/or Doppler ultrasound underwent contrast-enhanced MR angiography of the carotid bifurcation by a 3.0T MR scanner. Hemodynamic variables and flow patterns of the carotid bifurcation were calculated and visualized by combining vascular imaging postprocessing with CFD., Results: In mild stenotic cases, there was much more streamlined flow in the bulbs, with reduced or disappeared areas of weakly turbulent flow. Also, the corresponding areas of low wall shear stress (WSS) were reduced or even disappeared. As the extent of stenosis increased, stronger blood jets formed at the portion of narrowing, and more prominent eddy flows and slow back flows were noted in the lee of the stenosis. Regions of elevated WSS were predicted at the portion of stenosis and in the path of the downstream jet. Areas of low WSS were predicted on the leeward side of the stenosis, corresponding with the location of slowly turbulent flows., Conclusion: CFD combined with MRA can simulate flow patterns and calculate hemodynamic variables in stenotic carotid bifurcations as well as normal ones. It provides a new method to investigate the relationship of vascular geometry and flow condition with atherosclerotic pathological changes.

Perioperative monitoring of blood coagulation is critical to better understand causes of hemorrhage, to guide hemostatic therapies, and to predict the risk of bleeding during the consecutive anesthetic or surgical procedures. Point-of-care (POC) coagulation monitoring devices assessing the viscoelastic properties of whole blood, i.e., thrombelastography, rotation thrombelastometry, and Sonoclot analysis, may overcome several limitations of routine coagulation tests in the perioperative setting. The advantage of these techniques is that they have the potential to measure the clotting process, starting with fibrin formation and continue through to clot retraction and fibrinolysis at the bedside, with minimal delays. Furthermore, the coagulation status of patients is assessed in whole blood, allowing the plasmatic coagulation system to interact with platelets and red cells, and thereby providing useful additional information on platelet function. Viscoelastic POC coagulation devices are increasingly being used in clinical practice, especially in the management of patients undergoing cardiac and liver surgery. Furthermore, they provide useful information in a large variety of clinical scenarios, e.g., massive hemorrhage, assessment of hypo- and hypercoagulable states, guiding pro- and anticoagulant therapies, and in diagnosing of a surgical bleeding. A surgical etiology of bleeding has to be considered when viscoelastic test results are normal. In summary, viscoelastic POC coagulation devices may help identify the cause of bleeding and guide pro- and anticoagulant therapies. To ensure optimal accuracy and performance, standardized procedures for blood sampling and handling, strict quality controls and trained personnel are required.

The viscosity of blood obtained by using a rotational viscometer decreases with the time elapsed from the beginning of measurement until it reaches a constant value determined by the magnitude of shear rate. It is not possible to obtain an initial value of viscosity at time t = 0 that is considered to exhibit an intrinsic property of the fluid by this method. Therefore, we devised a new method by which one can obtain the viscosity of various fluids that are not affected by both the time elapsed from the beginning of measurement and the magnitude of shear rate by considering the balance of the forces acting on a solid spherical particle freely falling in a quiescent viscous fluid. By using the new method, we studied the rheologic behavior of corn syrups, carboxy-methyl cellulose, and human blood; and compared the results with those obtained with a cone-and-plate viscometer. It was found that in the case of corn syrups and washed red cell suspensions in which no red cell aggregate (rouleau) was formed, the viscosity obtained with the two different methods were almost the same. In contrast to this, in the case of the whole blood in which massive aggregates were formed, the viscosity obtained with a falling-ball viscometer was much larger than that obtained with a cone-plate viscometer.

Twenty monkeys (macaccus rhesus) were examined by the following parameters: deformability of erythrocytes and mononuclear leukocytes, hemolytic activity of the serum, free hemoglobin of the serum and viscosity of plasma. The data obtained are accepted as standard because literature data on hemorrheology of monkeys are absent. Compared to relevant indices in humans, monkeys have increased hematocrit, serum hemolytic activity, erythrocytic rigidity index. Seven monkeys were used as the model of "donor" (6-8% blood loss). The above indices were measured before exfusion and on days 2, 7, 14 and 21 after exfusion. Maximal changes in rheology and hemolysis were observed on day 2 and 7 after blood loss which correlated with deviations of the red sprout of hemogeny.

Anastomotic haemodynamics, which plays an important role in the performance of bypass graft, is known to be profoundly affected by the diameter ratio (Phi) and angle (alpha) between the graft and host artery in the peripheral region. We hypothesize that these geometric factors would play similar roles in distal coronary anastomoses and that they could be improved for clinical applications through parametric studies. Anastomotic models covering a range of Phi (1:1, 1.5:1 and 2:1) and alpha (15 degrees , 30 degrees , 45 degrees and 60 degrees ) were investigated numerically in physiological coronary flow conditions. The transient flow patterns, cycle-averaged wall shear stress (WSS), oscillatory shear index (OSI), spatial and temporal WSS gradients (SWSSG and TWSSG) were compared. Results show a stronger influence of Phi than alpha on haemodynamics in distal coronary artery anastomoses. Substantially higher SWSSG and TSSWG occur on the artery floor when Phi=1:1 compared to larger Phi. High levels of OSI occur in critical regions when Phi=1:1 and 2:1. The largest area of high OSI is found in the anastomotic region when alpha=15 degrees , whereas the highest level of SWSSG appears on the artery floor when alpha=60 degrees . The study suggests the clinical relevance of optimizing geometric parameters of coronary anastomoses to improve their haemodynamic performance. We speculate that for a distal coronary anastomosis with a 20:80 proximal-distal flow division ratio maintained in the host artery, Phi=1.5 and alpha=30-45 degrees would enhance its long-term performance.

I present an historical overview beginning with Prof. Harry L. Goldsmith, my first summer research supervisor in 1963 in microrheology, evolving years later to introduction into my laboratories at McGill University of the coaxial cylinder couette flow device for dynamic, real-time measurements of platelet aggregation in platelet suspensions sheared up to 8000/s, analyzed with a flow cytometer, and finally to a technology transfer of this rheological approach toward the marketplace. I and collaborators observed the shear-dependent roles of different adhesive receptors in mediating human platelet aggregation, and the importance of shear in evaluating efficacy of antiplatelet drugs, in contrast to studies with a classical aggregometer. I outline the well-published rationale for using flow devices, such as the coaxial cylinder couette, to assist clinicians and health managers assess the drug and clinical outcome efficacy of antithrombotic drugs in cardiovascular diseases, as well as their future applications.

Computational fluid dynamics (CFD) methods based on in vivo three-dimensional vessel reconstructions have recently been shown to provide prognostically relevant hemodynamic data. However, the geometry reconstruction and the assessment of clinically relevant hemodynamic parameters may depend on the used imaging modality. This study compares geometric reconstruction and calculated wall shear stress (WSS) values based on magnetic resonance imaging (MRI) and computed tomography (CT). Both imaging methods were applied to a same 2.5-fold upscale silicon model of the left coronary artery (LCA) main bifurcation. The original model is an optically digitized post mortem vessel cast. This digitized geometry is considered as a "gold standard" or original geometry for the MRI versus CT comparative study. The use of the upscale model allowed generating a high resolution CT raw data set with voxel size of 0.156 x 0.156 x 0.36 mm(3) and a high resolution MRI data set with an equivalent voxel size of 0.196 x 0.196 x 0.196 mm(3) for corresponding in vivo conditions. MRI based reconstruction achieved a mean Hausdorff surface distance of 0.1 mm to the original geometry. This is 2.5 times better than CT based reconstruction with mean Hausdorff surface distance of 0.252 mm. A comparison of the calculated mean WSS shows good correlation (r = 0.97) and good agreement among the three modalities with a WSS of 0.65 Pa in the original model, of 0.68 Pa in the CT based model and of 0.67 Pa in the MRI based model.

Cell adhesion, mediated by specific receptor-ligand interactions, plays an important role in biological processes such as tumor metastasis and inflammatory cascade. For example, interactions between beta 2-integrin (lymphocyte function-associated antigen-1 and/or Mac-1) on polymorphonuclear neutrophils (PMNs) and ICAM-1 on melanoma cells initiate the bindings of melanoma cells to PMNs within the tumor microenvironment in blood flow, which in turn activate PMN-melanoma cell aggregation in a near-wall region of the vascular endothelium, therefore enhancing subsequent extravasation of melanoma cells in the microcirculations. Kinetics of integrin-ligand bindings in a shear flow is the determinant of such a process, which has not been well understood. In the present study, interactions of PMNs with WM9 melanoma cells were investigated to quantify the kinetics of beta 2-integrin and ICAM-1 bindings using a cone-plate viscometer that generates a linear shear flow combined with a two-color flow cytometry technique. Aggregation fractions exhibited a transition phase where it first increased before 60 s and then decreased with shear durations. Melanoma-PMN aggregation was also found to be inversely correlated with the shear rate. A previously developed probabilistic model was modified to predict the time dependence of aggregation fractions at different shear rates and medium viscosities. Kinetic parameters of beta 2-integrin and ICAM-1 bindings were obtained by individual or global fittings, which were comparable to respectively published values. These findings provide new quantitative understanding of the biophysical basis of leukocyte-tumor cell interactions mediated by specific receptor-ligand interactions under shear flow conditions.

Introduction: The Intercept Blood System, using InterSol as additive solution, is used for inactivation of contaminating pathogens in PCs, thus reducing the risk for transfusion transmitted infection and making it possible to prolong the storage period. This study aimed at investigating the ability of Intercept treated platelets to induce clot formation, as measured by coagulation time using free oscillation rheometry (FOR), and to compare with that of platelets in concentrates with the additive solution T-Sol or plasma., Methods: Seventy-four single-donor platelet units were diluted in InterSol (n=27) or T-Sol (n=47) to a mean plasma concentration of 38%. The Intercept treatment was performed by addition of amotosalen HCl to the InterSol PCs followed by UVA irradiation and treatment with a compound adsorption device (CAD). Forty-six units were collected and stored in 100% plasma for comparison. Clotting time was measured by FOR in fresh PCs (within 26h after collection) after stimulation by a platelet activator. Soluble P-selectin was analysed as a marker of platelet activation in the Intercept and T-Sol PCs., Results: The clotting time was shorter for Intercept treated platelets compared to platelets in T-Sol and plasma (p<0.05). There was no difference in clotting time between T-Sol and plasma PCs. Soluble P-selectin was higher for Intercept platelets than platelets in T-Sol (p<0.05)., Conclusions: The platelets treated with the Intercept procedure had good clot promoting capacity.

The longitudinal transport of nanoparticles in blood vessels has been analyzed with blood described as a Casson fluid. Starting from the celebrated Taylor and Aris theory, an explicit expression has been derived for the effective longitudinal diffusion (Deff) depending non-linearly on the rheological parameter xi(c), the ratio between the plug and the vessel radii; and on the permeability parameters pi and omega, related to the hydraulic conductivity and pressure drop across the vessel wall, respectively. An increase of xi(c) or pi has the effect of reducing Deff, and thus both the rheology of blood and the permeability of the vessels may constitute a physiological barrier to the intravascular delivery of nanoparticles.

The aim of the study was to evaluate the possible relationship of the hemorheological disturbances with the clinical symptoms and some risk factors (RF) for cerebrovascular diseases (CVD). The study included 68 patients with CVD, 29 with transient ischemic attacks (TIA) and 39 with chronic unilateral cerebral infarctions (UCI) and 47 healthy control subjects. A questionnaire for RF for CVD was filled. Hemorheological variables: leucocytes, hemoglobin, hematocrit, fibrinogen (Fib), plasma (PV) and whole blood viscosity (WBV) at different shear rates by Couette rotational viscometer Contraves Low Shear 30 were investigated and the hemorheological indices of erythrocyte aggregation (IEA), erythrocyte deformability (IED) and of oxygen transport to tissues (TO(2)) were calculated. The arterial hypertension was the most frequent RF in the examined patients'. The hemorheological investigation showed significant increase of Fib in the patients with TIA and of PV and WBV in both patients' groups. The comparative study of the hemorheological variables with the RF for CVD showed predominating significant correlations with blood pressure (systolic, diastolic and mean) values, with age, cholesterol, physical activity and the body mass index. Our study confirms the possibility the hemorheological variables to be accepted as RF for development of stroke and for its recurrences.

We report studies of the coagulation of samples of whole human blood by oscillatory shear techniques, including Fourier Transform Mechanical Spectroscopy (FTMS). These techniques are used herein to identify the Gel Point of coagulating blood in terms of the Chambon-Winter Gel Point criterion which provides a rheometrical basis for detecting the establishment of an incipient clot. A comparison of the results of FTMS with those obtained from measurements involving a Thromboelastograph (TEG) and a Free Oscillation Rheometer (FOR) indicate that the latter techniques are not capable of detecting the incipient clot, whose establishment occurs several minutes prior to TEG or FOR-based assessments of clot formation time. The results of the present study suggest that FTMS is a useful tool in blood clotting research, being capable of providing a global coagulation profile in addition to detecting the instant of incipient clot formation.

Apoptosis induced by high shear stress has been reported for the dysfunction of various vascular endothelial cells. We investigated the protective effects of tetramethylpyrazine (TMP) and salvianolic acid B (SAB) from Chinese medicine on the shear-induced early and late stages of apoptosis in cultured rat cerebral microvascular endothelial cells (rCMECs) under pathological high shear stress. Near-confluent cultures of rCMECs were pretreated with TMP or SAB and their combinational dosages, and exposed to high shear stress generated by a rheometer. Apoptotic death rate of rCMECs was assessed by immunofluorescence microscopy of Annexin V-FITC and propidium iodide (PI). We found that early and late stage apoptosis occurred at 3.0 Pa for a short duration of 450 sec but did not occur at 1.5 Pa. SAB inhibited the cells from apoptosis at concentrations from 10 microM to 20 microM in a dose-dependent manner, while effect of TMP at 0.37 mM and 0.73 mM did not significantly differ. Moreover, the combined use of TMP and SAB had synergistic anti-apoptotic effects (P<0.01). The results indicate that the anti-apoptotic effect of TMP and SAB on rheologically induced endothelial injury is likely involved in their efficacy.

Red blood cell aggregation affects the flow of blood at low shear rates; not only the behaviour of the fluid deviates from its Newtonian characteristics, but, depending on the shearing history of the flow, the non-Newtonian characteristics may be influenced. It is not clear how the time and flow-dependent characteristics of the microstructural network developed in blood affect its mechanical properties. The present study aims to improve understanding of the effect of dynamic flow conditions on microstructural characteristics and consequently on the mechanical properties of the fluid. Viscosity measurements on blood samples from healthy volunteers (H=0.45) were taken with a double-walled Couette rheometric cell, under unsteady and quasi-unsteady flow conditions. The aggregation extent index A(alpha), and the microstructural integrity index A(I) were assessed with an optical shearing system and image analysis. Results showed that energy losses in Couette geometries may depend on the structural integrity of the developed RBC network.

Accepted methods of the ESR methodology (the Westergren mode and ZSR mode) and its alternative the plasma viscosity were tested for diagnostic utility in pregnancy induced hypertension and pre-eclampsia. The receiver-operating characteristic curve (ROC) analysis approved moderate diagnostic accuracy for the ESR methodology and supplied support for its preliminary estimated cutoff values but failed to indicate cogent discernment of pathology by values of plasma viscosity. Likely pathological whole blood alterations boost the erythrocyte aggregation while the concomitant depletion of macromolecules degrades plasma viscosity values.

Background: This study sought to describe and quantify microcirculatory changes in the mucosal surfaces of patients with severe malaria, by direct in vivo observation using orthogonal polarization spectral (OPS) imaging., Methods: The microcirculation in the rectal mucosa of adult patients with severe malaria was assessed by use of OPS imaging, at admission and then daily. Comparison groups comprised patients with uncomplicated falciparum malaria, patients with bacterial sepsis, and healthy individuals., Results: Erythrocyte velocities were measured directly in 43 adult patients with severe falciparum malaria, of whom 20 died. Microcirculatory blood flow was markedly disturbed, with heterogeneous obstruction that was proportional to severity of disease. Blocked capillaries were found in 29 patients (67%) and were associated with concurrent hyperdynamic blood flow (erythrocyte velocity, >750 mm/s) in adjacent vessels in 27 patients (93%). The proportion of blocked capillaries correlated with the base deficit in plasma and with the concentration of lactate. Abnormalities disappeared when the patients recovered. In healthy individuals and in patients with uncomplicated malaria or sepsis, no stagnant erythrocytes were detected, and, in patients with sepsis, hyperdynamic blood flow was prominent., Conclusion: Patients with severe falciparum malaria show extensive microvascular obstruction that is proportional to the severity of the disease. This finding underscores the prominent role that microvascular obstruction plays in the pathophysiology of severe malaria and illustrates the fundamental difference between the microvascular pathophysiology of malaria and that of bacterial sepsis.

The coronary slow flow phenomenon (CSFP) is an angiographic finding that is characterised by delayed progression of the contrast medium during coronary angiography. The mechanism of this phenomenon remains unknown. In the present paper, we revise the current evidence regarding this phenomenon and discuss recent findings from our group reporting increased resting resistances in patients with the CSFP. We report that these patients had preserved blood flow responses to the intracoronary infusion of the vasodilator papaverine, demonstrating that the CSFP is not necessarily associated with an abnormal coronary flow reserve. Based on these findings and on the review of the current literature, we concur with the concept proposed by Beltrame et al. that the CSFP should be considered a separate clinical entity. Further studies are necessary to describe the clinical characteristics, including the prognosis, of these patients and to identify potential treatments.

Evaluation of plasma viscosity has been underutilized in the clinical practice. Plasma viscosity is determined by water-content and macromolecular components. Plasma is a highly concentrated protein solution, therefore weak protein-protein interactions can play a role that is not characterized by electrophoresis. The effect of a protein on plasma viscosity depends on its molecular weight and structure. The less spheroid shape, the higher molecular weight, the higher aggregating capacity, and the higher temperature or pH sensitivity a protein has, the higher plasma viscosity results. Plasma is a Newtonian fluid, its viscosity does not depend on flow characteristics, therefore it is simple to measure, especially in capillary viscosimeters. Its normal value is 1.10-1.30 mPa s at 37 degrees C and independent of age and gender. The measurement has high stability and accuracy, thus little alterations may be pathologically important. Inflammations, tissue injuries resulting in plasma protein changes can increase its value with high sensitivity, though low specificity. It can increase in parallel with erythrocyte sedimentation rate (ESR), but it is not influenced by hematocrit (anemia, polycytemia), or time to analysis. Based on these favorable features, in 1942 plasma viscosity was recommended to substitute ESR. In hyperviscosity syndromes plasma viscosity is better in follow-up than ESR. In rheumatoid arthritis, its sensitivity and specificity are better than that of ESR or C-reactive protein. Plasma fibrinogen concentration and plasma viscosity are elevated in unstable angina pectoris and stroke and their higher values are associated with higher rate of major adverse clinical events. Elevation of plasma viscosity correlates to the progression of coronary and peripheral artery diseases. In conclusion, plasma viscosity should be measured routinely in medical practice.

The coupling of intravascular and interstitial flow is a distinct feature of tumor microcirculation, due to the high vessel permeability, the low osmotic pressure gradient as well as the absence of functional lymphatic system inside tumors. In this paper, a coupled mathematical model of tumor microcirculation is developed, which provides the link between microvasculature and interstitial space perfusion through the matrices determining a neighbor point belonging to either connected vessel (matrix B) or interstitial space (matrix A), and combines the intravascular and interstitial flow by vascular leaky terms. In addition, the compliance of tumor vessels, blood rheology with hematocritic distribution at branches is also considered. The microvascular network, on which the microcirculation calculation is carried out, is generated from our two-dimensional 9-point (2D9P) model of tumor angiogenesis, improved from the previous 2D5P one. A specific coupling procedure is developed in the study to couple the intravascular and interstitial flow. It is based on the iteratively numerical simulation techniques, including local iterations at individual parameter level and one global loop to provide coupling and simulation convergence. The simulation results not only present the basic features and characteristics of tumor microcirculation, which agree with the corresponding experimental observations reported, but also predict an intimate relationship between the tumor intravascular and interstitial flow quantitatively. Among the parameters, the vascular leakiness is a key to govern the systemic flowing pattern, influence the tumor internal environment and contribute to the metastasis of tumor cells, which could not be presented by the previous uncoupled models.

The interactions between membrane, peripheral and cytoskeleton proteins are responsible for the maintenance of erythrocyte deformability (EEI) and some of these interactions are modulated by PKC activity. Protein band 3 of the erythrocyte membrane is phosphorylated by phosphotyrosine kinases (PTK) and dephosphorylated by phosphotyrosine phosphatase (PTP). It was previously described by us a signal transduction mechanism that describes a possible pathway connecting an erythrocyte external membrane protein, acetylcholinesterase (AChE), with protein band 3. So how does PKC activity modulate EEI when protein band 3 is phosphorylated or dephosphorylated in absence or presence of AChE effectors?To answer this we used phorbol 12-myristate 13-acetate (PMA) as an activator and chelerythrine chloride as inhibitor of PKC and also band 3 modulators of band 3 phosphorylation degree, in presence and absence of AChE effectors in order to measure in whole blood samples EEI. Our results showed that erythrocyte deformability was significantly (i) decreased by inhibition of PKC, in absence and presence of AChE inhibitor velnacrine (ii) increased with PMA in absence and presence of ACh and (iii) decreased in presence of calpeptin in absence and presence of either chelerythrine or PMA. These results establish dependence between cytoskeleton proteins, PKC activity, band 3 phosphorylation degrees and EEI. Better understanding of those proteins interactions on transduction mechanisms might trigger possible targets for drug action that would modulate EEI.

Mural thrombus generation at sites of damaged vessel walls is essential for both physiological haemostasis and pathological intravascular thrombosis. While thrombi are established by the concerted action of platelet aggregation and blood coagulation, most previous in vitro coagulation assays have evaluated fibrin clot formation in a closed stirring situation that lacks blood cells including platelets. We describe here a modified flow chamber system, established originally for platelet functional studies, that enables real-time observation of intra-thrombus fibrin accumulation during platelet thrombogenesis under flow conditions. Analysis by confocal laser scanning microscopy during perfusion of whole blood anticoagulated to various extents revealed that the size and shape of mural thrombi can depend on the intra-thrombus fibrin development under high shear rate conditions. These observations were confirmed by perfusion of heparinized blood or blood from haemophilia patients with or without addition of activated factor VII. Thus, our experimental system provides visual evidence supporting the concept of "cell-based coagulation under whole blood flow", which might be the most physiologically relevant model of comprehensive thrombogenicity in vivo to date. This system promises to help formulate strategies for haemostatic management of congenital coagulation disorders as well as for antithrombotic therapy targeting fatal arterial thrombosis.

We have analysed the influence of acute alcohol exposure in vivo and in vitro on blood flow properties and platelet function. 12 healthy male volunteers drank either 4.36 ml red wine/kg body weight (=0.5 g ethanol/kg) or water at 06.00 p.m. under fasting conditions. Blood was drawn immediately before, and 1, 2, 4 and 13 h after alcohol ingestion. Alcohol had a detectable osmotic effect on erythrocytes; the mean cellular volume (MCV) was significantly smaller 1-4 h after ingestion. Whole blood viscosity remained unaffected, but blood viscosity at a standardized Hct of 45% measured at a high shear rate (94.5 s(-1)) was increased 2 h after wine ingestion. In the morning, 13 h after wine drinking, platelet aggregation measured with a platelet function analyser PFA-100 was increased to a greater extent than after water drinking. In vitro, no effect was seen when blood was incubated with 0, 12.5, 25, 50 and 100 mmol/l ethanol for 1 h at 37 degrees C. We conclude that an acute exposure to alcohol has only modest effects on hemorheological parameters and platelet aggregation in vivo and no effect in vitro, which suggests that other factors must be involved in both beneficial and harmful effects of wine drinking.

Covalent binding of poly(ethylene glycol), abbreviated as PEG, to red blood cells (RBC) surface leads to masking of the RBC blood group determinants and the PEG layer on the cell surface sterically hinders RBC-RBC and RBC-plasma protein interactions. We cross-linked linear mPEG-SPA of various molecular mass (2000, 5000, 20000) to washed human RBC under varying incubation ratios polymer to RBC. The electrophoretic mobility (EM) of the modified RBC decreases with increasing of chain length and concentration of PEG up to 50%. It may reflect the alteration in the surface layer thickness and friction. The aggregation behaviour of the pegylated RBC was studied with the Zeta sedimentation technique modifying the cell-cell interactions pressing them toward each other under centrifugal forces of various magnitudes. As a rule at low centrifugation forces the increase in chain length and concentration of PEG linked to RBC surface reduces the dextran-induced aggregation probably via elevation of the steric repulsion, which counteracts the depletion force generated by the free polymer. This effect was reversed to some extent by elevation of free dextran concentration and centrifugation forces. If cell-cell polymer bridging starts playing a role under these conditions requires further experimental and theoretical investigations.

Time variation of whole human blood conductivity and shear stresses were investigated at rectangular and trapezium-shaped Couette viscometric flow under electric field of 2 kHz. The kinetics of conductivity signals were recorded both under transient flow and after the complete stoppage of shearing at shear rates from 0.94 to 94.5 s(-1) and temperatures T=25 degrees C and 37 degrees C. Contraves Low Shear 30 rotational viscometer as a base unit and a concurrent measuring system, including a device, developed by the conductometric method with a software for measurement of conductivity of biological fluids (data acquisition system), previously described (IFMBE Proceedings Series, Vol. 11, 2005, pp. 4247-4252; Clin. Hemorheol. Microcirc. 35(1/2) (2006), 19-29), were used for the experiments. The obtained experimental relationships show that the human blood conductivity is time, shear rate, hematocrit and temperature dependent under transient flow. It is also dependent on the regime of the applied shear rates. Non-linear curve approximation of the growth and relaxation curves is done. The results show that valuable information could be received about the kinetics of "rouleaux formation" and the time dependences of the blood conductivity follow the structural transformations of RBC aggregates during the aggregation-disaggregation processes. The results suggest that this technique may be used to clarify the mechanism of dynamics of RBC aggregates.

The role played by hemorheological alterations on acute myocardial infarction (AMI) in young patients remains a question of debate. We have carried out a case-control study of 84 AMI patients aged <45 years and 135 sex and age matched controls, in which blood viscosity (BV), plasma viscosity (PV), erythrocyte aggregation (EA) performed with the Myrenne (EA0, EA1) and the Sefam aggregometer (Ta, AI10, gammaD), erythrocyte deformability (ED) along with fibrinogen (Fbg), C-reactive protein (CRP) and plasmatic lipids i.e. total cholesterol (T-Chol) and triglycerides (TG) were determined. AMI patients showed higher, Fbg, TG, EA0, EA1, IA10, gammaD and lower Ta than controls (p=0.029, p<0.001, p=0.013, p=0.003, p=0.010, p=0.025) respectively. No differences in the other rheological parameters were observed. No differences in any rheological parameter were observed regarding the AMI type, number and score of stenosed vessels and the time elapsed since the thrombotic event. After multivariate adjustment, Fbg>380 ml/dl and TG>185 ml/dl were independently associated with a higher risk of erythrocyte hyperaggregability (OR: 5.5 CI 95% 1.04-29.27 and OR: 7.3 CI 95% 2.66-20.03) respectively. EA>8.85 was associated with a increased AMI risk (OR: 5.3 CI 95% 1.98-14.5). These results reinforces the view that in young AMI patients increased Fbg and TG may promote the development of ischaemic events not only through its known mechanism but also by altering rheological blood behaviour, mainly increasing EA.

Hemorheological factors play an important role in the pathogenesis of severe complications of diabetes. The diabetic retinopathy is the leading cause of blindness in patients aged 20-65 years. In our study we investigated the effect of aspirin on the hemorheological parameters in patients with different diabetic retinopathies. Hemorheological parameters (hematocrit, fibrinogen, plasma and whole blood viscosity, red blood cell aggregation) of diabetic patients with non-proliferative (n=14, mean age: 66 years) and proliferative retinopathy (n=8, mean age: 48 years) were measured. The results between the two groups were compared: twelve patients were taking aspirin (group A), while ten patients were not (group B).Hematocrit, fibrinogen, plasma and whole blood viscosity were significantly higher (p < 0.05-0.001) in patients with diabetic retinopathy who did not take aspirin than in those who took. No significant difference was observed in red blood cell aggregation parameters between the two groups. We could not find any significant difference in the measured parameters between patients with non-proliferative and proliferative diabetic retinopathy. According to our results, all the measured hemorheological parameters were in the pathological range, although aspirin treatment could decrease these factors and thus may help to prevent the progression of severe diabetic retinopathy and perhaps blindness.