Wall Shear Rate Research Articles

Cytidine-5-diphosphocholine reduces microvascular permeability during experimental endotoxemia.

BackgroundMicrovascular permeability and leukocyte adhesion are pivotal mechanisms in sepsis pathophysiology contributing to the development of shock and mortality. No effective pharmacological therapy is currently available to restore microvascular barrier function in sepsis. Cholinergic mediators have been demonstrated to exert anti-inflammatory effects during inflammation. Cytidine-5-diphosphocholine (CDP-choline) is an extensively studied cholinergic drug due to its brain protective characteristics in cerebrovascular diseases. This study evaluated the effect of CDP-choline on microvascular permeability and leukocyte adhesion during endotoxemia.MethodsMacromolecular leakage, leukocyte adhesion, and venular wall shear rate were examined in mesenteric postcapillary venules of rats by using intravital microscopy (IVM). Lipopolysaccharide (LPS) (4 mg/kg/h) or equivalent volumes of saline were continuously infused following baseline IVM at 0 min. IVM was repeated after 60 and 120 min in endotoxemic and nonendotoxemic animals. CDP-choline (100 mg/kg) was applied as an i.v. bolus. Animals received either saline alone, CDP-choline alone, CDP-choline 10 min before or 30 min after LPS administration, or LPS alone. Due to nonparametric data distribution, Wilcoxon test and Dunn's multiple comparisons test were used for data analysis. Data were considered statistically significant at p < 0.05.ResultsTreatment with LPS alone significantly increased microvascular permeability and leukocyte adhesion and decreased venular wall shear rate. CDP-choline significantly reduced microvascular permeability in animals treated with LPS. Leukocyte adhesion and venular wall shear rate were not affected by CDP-choline during endotoxemia.ConclusionCDP-choline has a protective effect on microvascular barrier function during endotoxemia. Considering the excellent pharmacologic safety profile of CDP-choline, its use could be an approach for the treatment of capillary leakage in sepsis.

Platelet glycoprotein VI binds to polymerized fibrin and promotes thrombin generation

AbstractFibrin, the coagulation end product, consolidates the platelet plug at sites of vascular injury and supports the recruitment of circulating platelets. In addition to integrin αIIbβ3, another as-yet-unidentified receptor is thought to mediate platelet interaction with fibrin. Platelet glycoprotein VI (GPVI) interacts with collagen and several other adhesive macromolecules. We evaluated the hypothesis that GPVI could be a functional platelet receptor for fibrin. Calibrated thrombin assays using platelet-rich plasma (PRP) showed that tissue factor–triggered thrombin generation was impaired in GPVI-deficient patients and reduced by the anti-GPVI Fab 9O12. Assays on reconstituted PRP and PRP from fibrinogen-deficient patients revealed a fibrinogen-dependent enhancement of thrombin generation, which relied on functional GPVI. The effect of GPVI was found to depend on fibrin polymerization. A binding assay showed a specific interaction between GPVI-Fc and fibrin, inhibited by the Fab 9O12. This Fab also reduced platelet adhesion to fibrin at low (300 s−1) and high (1500 s−1) wall shear rates. Platelets adherent to fibrin displayed shape change, exposure of procoagulant phospholipids, and the formation of small clots. When hirudinated blood was perfused at 1500 s−1 over preformed fibrin-rich clots, the Fab 9O12 decreased the recruitment of platelets by up to 85–. This study identifies GPVI as a platelet receptor for polymerized fibrin with 2 major functions: (1) amplification of thrombin generation and (2) recruitment of circulating platelets to clots. These so-far-unrecognized properties of GPVI confer on it a key role in thrombus growth and stabilization.

Time-dependent effect of clonidine on microvascular permeability during endotoxemia

BackgroundEndothelial leakage with accompanying tissue edema and increased leukocyte adhesion are characteristics of the vascular inflammatory response. Tissue edema formation is a key mechanism in sepsis pathophysiology contributing to impaired tissue oxygenation and the development of shock. Sepsis mortality is directly associated with the severity of these microcirculatory alterations. Dysfunction of the sympathetic nervous system can have deleterious effects in generalized inflammation. This study evaluated the effect of the adrenergic alpha 2 agonist clonidine on microvascular permeability and leukocyte adhesion during endotoxemia. MethodsMacromolecular leakage, leukocyte adhesion, and venular wall shear rate were examined in mesenteric postcapillary venules of rats by using intravital microscopy (IVM). Lipopolysaccharide (LPS) (4mg/kg/h) or equivalent volumes of saline were continuously infused following baseline IVM at 0min. IVM was repeated after 60 and 120min in endotoxemic and nonendotoxemic animals. Clonidine (10μg/kg) was applied as an i.v. bolus. Animals received either (i) saline alone, (ii) clonidine alone, (iii) clonidine 45min prior to LPS, (iv) clonidine 10min prior to LPS, (v) clonidine 30min after LPS, or (vi) LPS alone. Due to nonparametric data distribution, Wilcoxon test and Dunn's multiple comparisons test were used for data analysis. Data were considered statistically significant at p<0.05. ResultsLPS significantly increased microvascular permeability and leukocyte adhesion and decreased venular wall shear rate. Clonidine significantly reduced microvascular permeability when applied 45min before or 30min after LPS administration. Leukocyte adhesion and venular wall shear rate were not affected by clonidine during endotoxemia. ConclusionClonidine reduces microvascular permeability in endotoxemic animals in a time-dependent manner. Adrenergic alpha 2 agonists might prove beneficial in stabilizing capillary leakage during inflammation.

Microfluidic assessment of functional culture-derived platelets in human thrombi under flow

Despite their clinical significance, human platelets are not amenable to genetic manipulation, thus forcing a reliance on mouse models. Culture-derived platelets (CDPs) from human peripheral blood CD34(+) cells can be genetically altered and may eventually be used for transfusions. By use of microfluidics, the time-dependent incorporation of CD41(+)CD42(+) CDPs into clots was measured using only 54,000 CDPs doped into 27μL of human whole blood perfused over collagen at a wall shear rate of 100sec(-1). With the use of fluorescence-labeled human platelets (instead of CDPs) doped between 0.25% and 2% of total platelets, incorporation was highly quantitative and allowed monitoring of the anti-αIIbβ3 antagonism that occurred after collagen adhesion. CDPs were only 15% as efficient as human platelets in their incorporation into human thrombi under flow, although both cell types were equally antagonized by αIIbβ3 inhibition. Transient transfection allowed the monitoring of GFP(+) human CDP incorporation into clots. This assay quantifies genetically altered CDP function under flow.

Passive control of wall shear stress and mass transfer generated by submerged lobed impinging jet

Particle image velocimetry was used to investigate the flow field in an impinging lobed daisy hemispherical nozzle jet in comparison to its counterpart round jet, at a Reynolds number of 5620 based on the exit velocity and the equivalent diameter D e of the nozzle. The limitations of the PIV technique in the vicinity of the target wall due to the laser scattering were addressed by using the electrodiffusion (ED) technique to determine the wall shear rate distribution. The distribution of the mass transfer coefficient is also obtained using the ED technique. The target wall is placed at a distance H = 2D e from the plane tangent to the nozzle, at the center of the orifice. The entrainment of ambient fluid in the free jet region, which is larger in the lobed jet compared to the round jet, feeds in turn the wall jet region. The maximum wall shear rate was found significantly higher in the daisy jet, with an excess of 93 % compared to the reference round jet. The maximum mass transfer is 35 % higher in the former compared to the latter. Therefore, the hemispherical daisy nozzle is an excellent candidate in passive strategies to enhance local skin-friction and the subsequent local mass transfer at a constant exit Reynolds number

Modelling of platelet-fibrin clot formation in flow with a DPD-PDE method.

The paper is devoted to mathematical modelling of clot growth in blood flow. Great complexity of the hemostatic system dictates the need of usage of the mathematical models to understand its functioning in the normal and especially in pathological situations. In this work we investigate the interaction of blood flow, platelet aggregation and plasma coagulation. We develop a hybrid DPD-PDE model where dissipative particle dynamics (DPD) is used to model plasma flow and platelets, while the regulatory network of plasma coagulation is described by a system of partial differential equations. Modelling results confirm the potency of the scenario of clot growth where at the first stage of clot formation platelets form an aggregate due to weak inter-platelet connections and then due to their activation. This enables the formation of the fibrin net in the centre of the platelet aggregate where the flow velocity is significantly reduced. The fibrin net reinforces the clot and allows its further growth. When the clot becomes sufficiently large, it stops growing due to the narrowed vessel and the increase of flow shear rate at the surface of the clot. Its outer part is detached by the flow revealing the inner part covered by fibrin. This fibrin cap does not allow new platelets to attach at the high shear rate, and the clot stops growing. Dependence of the final clot size on wall shear rate and on other parameters is studied.

In Vitro Measurement of Particle Margination in the Microchannel Flow: Effect of Varying Hematocrit

It has long been known that platelets undergo margination when flowing in blood vessels, such that there is an excess concentration near the vessel wall. We conduct experiments and three-dimensional boundary integral simulations of platelet-sized spherical particles in a microchannel 30 μm in height to measure the particle-concentration distribution profile and observe its margination at 10%, 20%, and 30% red blood cell hematocrit. The experiments involved adding 2.15-μm-diameter spheres into a solution of red blood cells, plasma, and water and flowing this mixture down a microfluidic channel at a wall shear rate of 1000 s−1. Fluorescence imaging was used to determine the height and velocity of particles in the channel. Experimental results indicate that margination has largely occurred before particles travel 1 cm downstream and that hematocrit plays a role in the degree of margination. With simulations, we can track the trajectories of the particles with higher resolution. These simulations also confirm that margination from an initially uniform distribution of spheres and red blood cells occurs over the length scale of O(1 cm), with higher hematocrit showing faster margination. The results presented here, from both experiments and 3D simulations, may help explain the relationship between bleeding time in vessel trauma and red blood cell hematocrit as platelets move to a vessel wall.

Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

It is well known that the transfer of heat, mass and momentum to a wall by an impinging jet is partially linked to the way in which jet generation is realized. The organization of the vortices at the jet exit depends on the upstream conditions and on the geometry of the nozzle. Particle image velocimetry (PIV) and electrodiffusion techniques were used to investigate the characteristics of different impinging jets and the resulting wall shear rates and mass transfer. Two cross-shaped orifice jets, one produced by a plane orifice nozzle (i.e. a cross-shaped orifice made on a flat plate, CO/P) and the second by a hemispherical orifice nozzle (i.e. a cross-shaped orifice made on a hemisphere, CO/H), were compared to a reference round jet produced by a convergent nozzle. The distance between the jet exit and the target wall was equal to two nozzle equivalent diameters (D e ), based on the free orifice area. The Reynolds number, based on D e and on the exit bulk-velocity, was 5620 for each flow. PIV measurements give an overall view of the flow characteristics in their free and wall regions. The switching-over phenomena observed in the CO/P nozzle case, and already described in the literature with similar nozzles, did not occur in the jet from the CO/H nozzle. Electrodiffusion measurements showed differences in the shape and level of radial distribution of the wall shear rates and mass transfer. One of the most important observations is the large difference in wall shear stress between the three jets. For the same exit bulk-velocity, the maximum wall shear rate in the CO/P and CO/H nozzle jets was almost two and three times higher, respectively, than that of the reference convergent jet. This higher wall shear rate is accompanied by higher mass transfer rate. It is demonstrated that the cross-shaped orifices enhance the mass transfer not only locally but also globally

Mass transfer and shear rate on a wall normal to an impinging circular jet

The electrodiffusion technique and the time-resolved tomographic PIV were used in impinging jet issued from a convergent conical nozzle at a Reynolds number of 2450 based on the nozzle diameter d and the jet exit velocity. The relative distance from the nozzle to the impinging wall was equal to h/d=2. The experimentally gained velocity fields provides information on the organization of coherent flow structures, which play a role in the wall shear rate and the mass transfer phenomenon at the impinged wall.Instantaneous wall shear rate and local mass transfer were measured at an impinging wall using platinum electrodes with a diameter of 0.5mm flush mounted into a platinum disc electrode with a diameter of 49.5mm. The small electrodes were used alternately for the measurement of wall shear rate and mass transfer. The proposed correction factor on the inertia of the concentration boundary layer, which is the ratio of the corrected fluctuations of wall shear rate to their primary values, along with the analysis of the signals history, provide valuable information on the state of the hydrodynamic boundary layer. The mean wall shear rate and local mass transfer exhibit their maximum values at the normalised radial positions r/d=0.6–0.7. There are the interactions of the primary Kelvin–Helmholtz (K–H) vortices with smaller structures issued from the breaking-down of these vortices, both rotating in the same direction. Counter-rotating secondary vortices form between the wall and primary K–H vortices at a radial distance about r/d=1.5. They are present in a wide region (r/d~1.5 to 2.5); around r/d=1.5 they are very close to the wall leading to a clear periodicity of wall shear rate, and at r/d=2.5 they are farther above the wall since no periodicity of the wall shear rate was observed. The local mass transfer rates were integrated and compared with the global mass transfer measured by a platinum disc electrode.

Material removal of glass by magnetorheological fluid jet

Magnetorheological (MR) fluid jet polishing is a material removal process for precision products such as optical elements. It is characterized by a jet flow that is stabilized by a magnetic field, and a highly predictable machining spot. The behavior of the particles in an MR fluid slurry near a target wall surface is conceptually described. In experiments with a BK7 glass specimen, various removal spots are created by impingement of MR fluid jets at velocities of 10~30 m/s, using MR fluids of different compositions, and different processing durations. The tangential MR fluid flow along the part surface is assumed to be responsible for material removal, and theoretical models for the prediction of material removal are developed, using the conventional wear model and granular flow theory. The constitutive relation between the shear stress and the shear rate changes as the jet velocity increases, which has a critical effect on the behavior of material removal. CFD analysis is performed to calculate the wall shear rate. The proposed models agree with the experimental results with respect to the distribution of the material removal rate. Additionally, the surface topographies of polished parts are discussed, with regards to the particle behavior.

Incidence and Risk Factors of Hemolysis After Transcatheter Aortic Valve Implantation With a Balloon-Expandable Valve

There are currently no data evaluating the hematologic and biocompatibility profile of transcatheter aortic valves invivo. We evaluated the incidence, predictive factors, and clinical consequences associated with hemolysis post-transcatheter aortic valve implantation (TAVI). A total of 122 patients who underwent TAVI with a balloon-expandable valve were included. Baseline blood sampling and echocardiography, followed by early post-TAVI echocardiography and repeat blood sampling, at 6 to 12months post-TAVI were performed. Hemolysis post-TAVI was defined according to the established criteria. The incidence of hemolysis post-TAVI was 14.8% yet no patient experienced severe hemolytic anemia requiring transfusion. Compared with the nonhemolysis group, those with hemolysis demonstrated significant reductions in hemoglobin (p= 0.012), were more frequently women (67% vs 34%, p= 0.016), and had a higher incidence of post-TAVI severe prosthesis-patient mismatch (PPM) (44% vs 17%, p= 0.026). The rate of mild or more prosthetic valve regurgitation did not significantly differ between those patients with and without hemolysis (56% vs 37%, p= 0.44). Wall shear rate (WSR) and energy loss index (ELI), both indirect measures of shear stress, were higher (p= 0.039) and lower (p= 0.004), respectively, in those patients with hemolysis. Increasing PPM severity was also associated with significant stepwise WSR increments and ELI decrements (p <0.01 for both). In conclusion, subclinical hemolysis occurred in 15% of patients following TAVI. Although prosthetic valve regurgitation had no impact on hemolysis, a novel association between PPM and hemolysis was found, likely driven by higher shear stress as determined by WSR and ELI. These hematologic and biomechanical findings may have long-term clinical implications and could affect future transcatheter aortic valve design.

Profound Increase in Longitudinal Displacements of the Porcine Carotid Artery Wall Can Take Place Independently of Wall Shear Stress: A Continuation Report

The mechanisms underlying longitudinal displacements of the arterial wall, that is, displacements of the wall layers along the artery, and the resulting intramural shear strain remain largely unknown. We have already found that these displacements undergo profound changes in response to catecholamines. Wall shear stress, closely related to wall shear rate, represents the viscous drag exerted on the vessel wall by flowing blood. The aim of the work described here was to study possible relations between the wall shear rate and the longitudinal displacements. We investigated the carotid arteries of five anesthetized pigs in different hemodynamic situations using in-house developed non-invasive ultrasound techniques. The study protocol included administration of epinephrine, norepinephrine and β-blockade (metoprolol). No significant correlation between longitudinal displacement of the intima–media complex and wall shear rate was found. This result suggests that one or multiple pulsatile forces other than wall shear stress are also working along arteries, strongly influencing arterial wall behavior.

Numerical investigation of the membrane fouling during microfiltration of semiconductor wastewater

Membrane fouling is a problem of vital importance in microfiltration. A numerical method was used to investigate the membrane fouling phenomenon during microfiltration of semiconductor wastewater. In the numerical model, the concentration-dependent physical properties were considered and a dynamically updating boundary condition was incorporated to deal with the flux variation with fouling resistance. The mechanism of suspension transition from liquid phase to gel phase was adopted to characterize the formation of membrane fouling. With this method, the flow field and the concentration distribution as well as the fouling resistance in the membrane module were obtained. The results revealed the mass transfer character in the concentration boundary layer and its influence on the formation of membrane fouling. The enhancement effect of cross-flow on membrane filtration was analyzed in terms of wall shear rate and dimensionless Peclet number. Agreement between the simulation and the experimental results demonstrated the applicability of this numerical method in evaluating membrane fouling during microfiltration.

Automated Assessment of Hemodynamics in the Conjunctival Microvasculature Network.

The conjunctival microcirculation is accessible for direct visualization and quantitative assessment of microvascular hemodynamic properties. Currently available methods to assess hemodynamics in the conjunctival microvasculature use manual or semi-automated algorithms, which can be inefficient for application to a large number of microvessels within the microvascular network. We present an automated image analysis method for measurements of diameter and blood velocity in microvessels. The method was applied to conjunctival microcirculation images acquired in 15 healthy human subjects. Frangi filtering, thresholding, and morphological closing were applied to automatically segment microvessels, while variance filtering was used to detect blood flow. Diameter and blood velocity were measured in arterioles and venules within the conjunctival microvascular network, and blood flow and wall shear rate were calculated. Repeatability and validity of hemodynamic measurements were established. The automated image analysis method allows reliable, rapid and quantitative assessment of hemodynamics in the conjunctival microvascular network and can be potentially applied to microcirculation images of other tissues.

Microcirculatory effects of physostigmine on experimental burn edema.

In order to further understand the role of the cholinergic anti-inflammatory pathway, the authors determined the effects of burn plasma from donor rats (DRs) on the microvascular circulation of healthy recipient rats and whether these could be altered by pretreatment with physostigmine (PT). DRs underwent thermal injury (100°C water, 12 seconds, 30% BSA) for positive controls. For negative controls DRs underwent sham burn (same procedure but water at 37°C). DR-plasma (harvested 4 hours posttrauma) was transferred to healthy rats. Bolus injection of PT (70 μg/kg body weight) was performed 15 minutes before starting the infusion of DR-plasma in the study group. Intravital microscopy was performed in mesenteric venules (0/60/120 minutes). Edema was assessed by fluorescein isothiocyanate (FITC)-albumin extravasation. Additionally, leukocyte rolling and sticking (cells/mm) as well as hemodynamic parameters were assessed. Burn plasma transfer significantly increases albumin extravasation in healthy individuals when compared with sham-burn treatment. Additional bolus administration of PT (70 μg/kg body weight) to burn plasma treatment reduces plasma extravasation to sham-burn levels. PT also attenuates leukocyte-endothelial interactions. After 120 minutes no significant changes in the systemic circulation (mean arterial pressure, heart rate, wall shear rate) were found between the groups. Burn plasma transfer results in significant increases in plasma extravasation and leukocyte-endothelial wall adherence, which are reversed by pretreatment with PT. These results suggest that the cholinergic anti-inflammatory pathway may play a role in the microcirculatory response to thermal injury.

High-speed particle image velocimetry for the efficient measurement of turbulence statistics

A high-frame-rate camera and a continuous-wave laser are used to capture long particle image sequences exceeding 100,000 consecutive frames at framing frequencies up to 20 kHz. The electronic shutter of the high-speed CMOS camera is reduced to $$10\,\upmu$$ s to prevent excessive particle image streaking. The combination of large image number and high frame rate is possible by limiting the field of view to a narrow strip, primarily to capture temporally resolved profiles of velocity and derived quantities, such as vorticity as well as higher order statistics. Multi-frame PIV processing algorithms are employed to improve the dynamic range of recovered PIV data. The recovered data are temporally well resolved and provide sufficient samples for statistical convergence of the fluctuating velocity components. The measurement technique is demonstrated on a spatially developing turbulent boundary layer inside a small wind tunnel with $$Re_\delta = 4{,}800,\, Re_\tau = 240$$ and $$Re_\theta = 515$$ . The chosen magnification permits a reliable estimation of the mean velocity profile down to a few wall units and yields statistical information such as the Reynolds stress components and probability density functions. By means of single-line correlation, it is further possible to extract the near-wall velocity profile in the viscous sublayer, both time-averaged as well as instantaneous, which permits the estimation the wall shear rate $$\dot{\gamma }$$ and along with it the shear stress $$\tau _w$$ and friction velocity $$u_\tau$$ . These data are then used for the calculation of space-time correlation maps of wall shear stress and velocity.

Self-regulation in flow-induced structure formation of polypropylene.

Flow-induced structure formation is investigated with in situ wide-angle X-ray diffraction with high acquisition rate (30 Hz) using isotactic polypropylene in a piston-driven slit flow with high wall shear rates (up to ≈900 s(-1) ). We focus on crystallization within the shear layers that form in the high shear rate regions near the walls. Remarkably, the kinetics of the crystallization process show no dependence on either flow rate or flow time; the crystallization progresses identically regardless. Stronger or longer flows only increase the thickness of the layers. A conceptual model is proposed to explain the phenomenon. Above a certain threshold, the number of shish-kebabs formed affects the rheology such that further structure formation is halted. The critical amount is reached already within 0.1 s under the current flow conditions. The change in rheology is hypothesized to be a consequence of the "hairy" nature of shish. Our results have large implications for process modelling, since they suggest that for injection molding type flows, crystallization kinetics can be considered independent of deformation history.

Therapeutic Amelioration of Vaso-Occlusion and Blood Flow Impairment in Transgenic Sickle Mice By the Antioxidant Flavonoid Quercetin

Sickle cell disease (SCD) is characterized by painful vaso-occlusive crises, which are, at least in part, due to an interaction of the sickle RBC (sRBC) with the vascular endothelium. Abnormal red blood cells (RBCs) impair blood flow and contribute to microcirculatory complications. Oxidative stress and/or oxidants generated via hemoglobin S (HbS) auto-oxidation play a vital role in the vaso-occlusive event in SCD. Antioxidant therapy mediated free radical scavenging and attenuation of oxidative stress may reduce red cell sickling and be beneficial for SCD. Several studies have described an antioxidant effect of flavonoids on the attenuation of free radical mediated biological membrane damage and the consumption of flavonoids reduces the prevalence of vascular diseases. Among flavonoids, quercetin (QUE) pentahydroxy flavone is the major representative. In vitro, QUE is a strong antioxidant with alkoxyl and peroxy radical scavenging ability. Due to the high susceptibility of sickle RBC to oxidation, QUE could be a useful therapy for SCD. Based on this concept, we examined the potential effect of QUE to improve microvascular function in a murine model of SCD.Methods: To confirm the protective effect of quercetin in vivo, we used Berkeley (Berk) sickle transgenic mice which express exclusively human α- and βS-globins with low levels of γ-globin (∼ 3-5%) generated by Paszty et al 1997. C57BL /6J were used as control wild type. We injected a single dose of QUE at different concentrations (50, 100, 200mg/kg body weight) intraperitoneally under normoxic conditions. Three hours after QUE administration, in vivo intra-vital microscopic observation of post-capillary venules in cremaster muscle was performed. The luminal diameters of the venules (∼ 20-40 µm diameter), centerline red blood cell velocity (Vrbc), adherent, emigrated and rolling leukocytes were measured by the technique described by Kaul et al 2004. Wall shear rate was calculated by Lipowsky et al, 1980.Results: QUE treatment restored blood flow, as evidenced by complete disappearance of vaso-occlusion in the postcapillary venules of Berk mice (Figure 1). However, no significant differences in venular diameter were noted with QUE treatment at any of the dose levels tested (50, 100, 200mg/kg) when compared to untreated Berk and wild type mice. But, when compared to untreated Berk mice, a significant increase in the RBC velocity was demonstrated in a dose dependent fashion (treated: 1.74 ±1.3 mm/sec, 3.02± 1.2 mm/sec, 3.4±0.90 mm/sec for 50, 100, 200 mg/kg dosing respectively vs. untreated 1.01± 1.05mm/sec, p<0.05). A dose of 200 mg level completely neutralized the vaso-occlusion. Increases in wall shear rate (650.01± 252.05 s-1 vs. 180.12± 165.02 s-1, p<6.03x10-6) was also observed in QUE treated vs. untreated Berk. This improvement of blood flow in the postcapillary venules correlated well with observed decreases in leukocyte adhesion (Figure 2A) and leukocyte emigration (Figure 2B) in QUE treated Berk mice (for doses 50, 100, and 200mg/kg) when compared to untreated Berk mice. Leukocyte rolling was also decreased for doses 100 and 200mg/kg (p<0.007, p<0.0002 respectively) after treatment with QUE when compared to untreated Berk and wild type. [Display omitted] [Display omitted] [Display omitted] Conclusion: We observed an improvement in RBC velocity and wall shear rate, as well as a complete attenuation of leukocyte adhesion, rolling and emigration at the highest dose of QUE treated transgenic sickle Berk mice. We suggest that these effects may be due to a decreased sickle RBC interaction with the vascular bed. Our present data provide a strong basis for the therapeutic application of flavonoids in SCD. Further studies are needed to better understand the mechanism of action in vivo for therapeutic effect in SCD. DisclosuresThangaswamy:AMI Life Sciences Private Ltd: Drug supplied Other. Billett:Selexys Pharmaceuticals: Research Funding.

Recombinant VWF Promotes Platelet Adhesion Under Shear Stress Dependent on Its Multimer Size

Baxter has developed BAX 111, a recombinant von Willebrand factor (rVWF) currently being evaluated for the treatment of von Willebrand disease based on the results of a phase 3 clinical trial. BAX 111 contains ultra-large molecular weight multimers (ULMWM), which are the most hemostatically active type of multimer. ULMWM demonstrate higher functional activity than the multimers present in commercially available plasma-derived VWF (pdVWF) products in terms of VWF:RCo and VWF:CB activity. To investigate the contribution of VWF multimer size on BAX 111 hemostatic activity, fractions containing distinct portions of VWF multimers were generated and analyzed for their ability to mediate platelet adhesion under shear stress in vitro.rVWF fractions of varying VWF multimer size were purified by size-exclusion chromatography; size distribution was determined using low and high resolution agarose gel electrophoresis. A parallel-plate perfusion chamber system was used to investigate the rVWF-mediated adhesion of platelets from human blood to fibrillar collagen type I under shear stress. For this purpose, a VWF sample of 1.0 IU/mL VWF:Ag was added to healthy donor blood and the time course of surface coverage was determined by microscopy using fluorescent labeled platelets. Multiple pictures were taken every 5 seconds. Perfusion was performed for 3 minutes at +37°C and at a defined wall shear rate of 1500 s-1. Different batches of BAX 111, rVWF fractions of distinct multimer size, and three commercially available pdVWF products with low and high FVIII content were investigated.The endogenous VWF present in human whole blood mediated initial platelet adhesion with approximately 5% surface coverage after 120 seconds of perfusion. Additionally spiking human blood with 1.0 IU/mL of BAX 111 or rVWF fractions of different multimeric size resulted in increased, time-dependent platelet binding. The amount of platelets that became attached to collagen was clearly dependent on the size of rVWF. While highly multimerized BAX 111 effectively promoted platelet binding, lower-sized rVWF fractions containing VWF multimers of lower molecular weight showed decreased platelet adhesion properties. pdVWF products lacking ultra-large molecular weight multimers were less effective in mediating platelet adhesion to collagen, as observed by delayed platelet binding kinetics. After 60 seconds of perfusion, approximately twice the surface coverage was measured for BAX 111 compared to pdVWF products. The amount of FVIII contained in the pdVWF products had no influence on platelet adhesion.These results demonstrate that the improved hemostatic activity of BAX 111 over pdVWF is due to the presence of ULMWM and confirms their importance in mediating intact platelet binding. DisclosuresSchrenk:Baxter Innovations GmbH, Vienna, Austria: Employment. Schreiner:Baxter Innovations GmbH, Vienna, Austria: Employment. Gritsch:Baxter Innovations GmbH, Vienna, Austria: Employment. Turecek:Baxter Innovations GmbH, Vienna, Austria: Employment. Dockal:Baxter Innovations GmbH, Vienna, Austria: Employment. Scheiflinger:Baxter Innovations GmbH, Vienna, Austria: Employment.

An improved estimation of shear rate for yield stress fluids using rotating concentric cylinder Fann viscometer

Abstract This paper deals with the estimation of wall shear rates for yield stress fluids using rotating coaxial-cylinder viscometer readings. The estimation is based on the generalized difference equation for rotating narrow gap coaxial cylinder Fann Viscometer under purely steady, laminar and isothermal tangential fluid flow condition. Rotor rotations and bob deflections are the two important viscometer readings and these are used to predict wall shear rates. The proposed equations are used to calculate shear rates for several Herschel–Bulkley type fluids involving polymer (for example, xanthan gum, poly-anionic cellulose and carbomethoxy cellulose) solutions with varying concentration and bentonite suspension, which are frequently used as drilling fluid additives. Parametric sensitivity is made for stability analysis of the proposed shear rate equations. Finally, the predicted shear rates are compared with the conventional method of estimating the rate of shear for drilling fluids.