Initiate Platelet Aggregation Research Articles

Initial platelet aggregation in the complex shear environment of a punctured vessel model

To analyze flow conditions and cellular behavior at the onset of a hemostatic response in the injury of a microneedle-induced vessel puncture, a combined in silico and in vitro platform is created. A cell-resolved blood flow model is utilized for in-depth flow profile and cell distribution analyses, and a novel punctured vessel flow chamber is set up to complement the simulations with the evaluation of platelet aggregation around the wound neck of the puncture. The respective setups of the platform are explained, and the results of both experiments and simulations with various puncture diameters and pressure drops are combined, providing detailed insight into the basic processes of platelet transport and aggregation in the wound area. A special emphasis of the simulation evaluation is put on the cell distributions and the magnitude of shear rate and elongational flow in the wound neck area, as well as downstream from the puncture. Additionally, possible implications of wound size and pressure difference on the hemostatic response are discussed. The simulations display asymmetric cell distributions between the proximal and distal sides of the wound neck in regard to the flow direction. The flow chamber with the puncture diameter closest to the simulated domains confirms this asymmetry by displaying increased platelet aggregation at the wound neck's distal side. The presented punctured vessel in silico and in vitro experimental setups offer a platform to analyze the hemostatic environment of a vessel injured by a puncture and might assist in identifying differentiating factors between primary hemostasis and arterial thrombosis.

Use of n-acetylcysteine therapy in patients with relapsed refractory thrombotic thrombocytopenic purpura

There is limited data on the use of NAC in the literature. We would like to present the satisfactory results we obtained in our resistant and relapsed patients as a case series.Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy caused by ADAMTS13 (a disintegrin with thrombospondin type 1 motif and metalloprotease activity, member13) deficiency. Von Willebrand factor (vWF) initiates platelet aggregation and thus thrombus formation. The multimers of vWF are cleaved by ADAMTS13. Because of the decreased activity of ADAMTS13, ultra-large multimers accumulate and end-organ damage occurs. TTP is characterized by microangiopathic hemolytic anemia (MAHA), severe thrombocytopenia, and organ ischemia resulting from vascular occlusion caused by thrombi. Plasma exchange therapy (PEX) remains the mainstay of TTP therapy. Patients who do not respond to PEX and corticosteroids require additional treatments such as rituximab and caplacizumab. NAC reduces disulfide bonds in mucin polymers through its free sulfhydryl group. Thus, the size and viscosity of the mucins are reduced. VWF is structurally similar to mucin. Based on this similarity, Chen and colleagues showed that NAC can reduce the size and reactivity of ultralarge multimers of vWF, such as ADAMTS13. Currently, there is not much information to suggest that NAC has any clinical value in the treatment of TTP. In this case series of 4 refractory patients, we would like to present the responses we obtained with the addition of NAC therapy. NAC can be added to PEX and glucocorticoid therapy as supportive therapy, especially in unresponsive patients.

PAR4-Mediated PI3K/Akt and RhoA/ROCK Signaling Pathways Are Essential for Thrombin-Induced Morphological Changes in MEG-01 Cells.

Thrombin stimulates platelets via a dual receptor system of protease-activated receptors (PARs): PAR1 and PAR4. PAR1 activation induces a rapid and transient signal associated with the initiation of platelet aggregation, whereas PAR4 activation results in a prolonged signal, required for later phases, that regulates the stable formation of thrombus. In this study, we observed differential signaling pathways for thrombin-induced PAR1 and PAR4 activation in a human megakaryoblastic leukemia cell line, MEG-01. Interestingly, thrombin induced both calcium signaling and morphological changes in MEG-01 cells via the activation of PAR1 and PAR4, and these intracellular events were very similar to those observed in platelets shown in previous studies. We developed a novel image-based assay to quantitatively measure the morphological changes in living cells, and observed the underlying mechanism for PAR1- and PAR4-mediated morphological changes in MEG-01 cells. Selective inhibition of PAR1 and PAR4 by vorapaxar and BMS-986120, respectively, showed that thrombin-induced morphological changes were primarily mediated by PAR4 activation. Treatment of a set of kinase inhibitors and 2-aminoethoxydiphenyl borate (2-APB) revealed that thrombin-mediated morphological changes were primarily regulated by calcium-independent pathways and PAR4 activation-induced PI3K/Akt and RhoA/ROCK signaling pathways in MEG-01 cells. These results indicate the importance of PAR4-mediated signaling pathways in thrombin-induced morphological changes in MEG-01 cells and provide a useful in vitro cellular model for platelet research.

Platelet binding to polymerizing fibrin is avidity driven and requires activated αIIbβ3 but not fibrin cross-linking

AbstractThe molecular basis of platelet-fibrin interactions remains poorly understood despite the predominance of fibrin in thrombi. We have studied the interaction of platelets with polymerizing fibrin by adding thrombin to washed platelets in the presence of the peptide RGDW, which inhibits the initial platelet aggregation mediated by fibrinogen binding to αIIbβ3 but leaves intact a delayed increase in light transmission (delayed wave; DW) as platelets interact with the polymerizing fibrin. The DW was absent in platelets from a patient with Glanzmann thrombasthenia, indicating a requirement for αIIbβ3. The DW required αIIbb3 activation and it was inhibited by the αIIbβ3 antagonists eptifibatide and the monoclonal antibody (mAb) 7E3, but only at much higher concentrations than needed to inhibit platelet aggregation initiated by a thrombin receptor activating peptide (T6). Surface plasmon resonance and scanning electron microscopy studies both supported fibrin having greater avidity for αIIbβ3 than fibrinogen rather than greater affinity, consistent with fibrin's multivalency. mAb 10E5, a potent inhibitor of T6-induced platelet aggregation, did not inhibit the DW, suggesting that fibrin differs from fibrinogen in its mechanism of binding. Inhibition of factor XIII–mediated fibrin cross-linking by >95% reduced the DW by only 32%. Clot retraction showed a pattern of inhibition similar to that of the DW. We conclude that activated αIIbβ3 is the primary mediator of platelet-fibrin interactions leading to clot retraction, and that the interaction is avidity driven, does not require fibrin cross-linking, and is mediated by a mechanism that differs subtly from that of the interaction of αIIbβ3 with fibrinogen.

Electron microscopy shows that binding of monoclonal antibody PT25-2 primes integrin αIIbβ3 for ligand binding

The murine monoclonal antibody (mAb) PT25-2 induces αIIbβ3 to bind ligand and initiate platelet aggregation. The underlying mechanism is unclear, because previous mutagenesis studies suggested that PT25-2 binds to the αIIb β propeller, a site distant from the Arg-Gly-Asp-binding pocket. To elucidate the mechanism, we studied the αIIbβ3-PT25-2 Fab complex by negative-stain and cryo-electron microscopy (EM). We found that PT25-2 binding results in αIIbβ3 partially exposing multiple ligand-induced binding site epitopes and adopting extended conformations without swing-out of the β3 hybrid domain. The cryo-EM structure showed PT25-2 binding to the αIIb residues identified by mutagenesis but also to 2 additional regions. Overlay of the cryo-EM structure with the bent αIIbβ3 crystal structure showed that binding of PT25-2 creates clashes with the αIIb calf-1/calf-2 domains, suggesting that PT25-2 selectively binds to partially or fully extended receptor conformations and prevents a return to its bent conformation. Kinetic studies of the binding of PT25-2 compared with mAbs 10E5 and 7E3 support this hypothesis. We conclude that PT25-2 induces αIIbβ3 ligand binding by binding to extended conformations and by preventing the interactions between the αIIb and β3 leg domains and subsequently the βI and β3 leg domains required for the bent-closed conformation.

Haemodynamic flow conditions at the initiation of high-shear platelet aggregation: a combined in vitro and cellular in silico study.

The influence of the flow environment on platelet aggregation is not fully understood in high-shear thrombosis. The objective of this study is to investigate the role of a high shear rate in initial platelet aggregation. The haemodynamic conditions in a microfluidic device are studied using cell-based blood flow simulations. The results are compared with in vitro platelet aggregation experiments performed with porcine whole blood (WB) and platelet-rich-plasma (PRP). We studied whether the cell-depleted layer in combination with high shear and high platelet flux can account for the distribution of platelet aggregates. High platelet fluxes at the wall were found in silico. In WB, the platelet flux was about twice as high as in PRP. Additionally, initial platelet aggregation and occlusion were observed in vitro in the stenotic region. In PRP, the position of the occlusive thrombus was located more downstream than in WB. Furthermore, the shear rates and stresses in cell-based and continuum simulations were studied. We found that a continuum simulation is a good approximation for PRP. For WB, it cannot predict the correct values near the wall.

Design of a Microfluidic Bleeding Chip to Evaluate Antithrombotic Agents for Use in COVID-19 Patients.

IntroductionInterventions that could prevent thrombosis, clinical decompensation, and respiratory compromise in patients with novel coronavirus disease (COVID-19) are key to decrease mortality rate. Studies show that profound cytokine release and excessive activation of blood coagulation appear to be key drivers of COVID-19 associated mortality. Since limited in vitro methods exist for assessing the effects of anticoagulants on hemostasis, the development of novel therapies to safely prevent thrombosis in COVID-19 patients relies on preclinical animal models and early phase human trials. Herein we present the design of a microfluidic “bleeding chip” to evaluate the effects of antithrombotic therapies on hemostatic plug formation in vitro.MethodsThe design of the microfluidic device consists of two orthogonal channels: an inlet that serves as a model blood vessel, and a bleeding channel to model hemostatic plug formation at sites of compromised endothelial barrier function. This is achieved by placing a series of 3 pillars spaced 10 μm apart at the intersection of the two channels. The pillars and bleeding channel are coated with the extracellular matrix protein collagen.ResultsPerfusion of human whole blood through the microfluidic bleeding chip led to initial platelet adhesion and aggregation at the pillars followed by hemostatic plug formation and occlusion of the bleeding channel.ConclusionsSafe and effective mitigating agents are needed for treatment and prevention of thrombotic complications in COVID-19 patients. This simple microfluidic device holds potential to be developed into a tool for assessing the effects of anticoagulant therapy on hemostasis.

Hemodynamics in a bidirectional Glenn Shunt supplemented with a modified Blalock-Taussig shunt: Computational fluid dynamics assessment

The bidirectional Glenn Shunt (BGS), superior vena cava (SVC) to right pulmonary artery (RPA) is occasionally supplemented with a left modified Blalock-Taussig shunt (mBTS) when PA growth is inadequate. Little is known about hemodynamics when BGS's low-velocity steady flow interacts with mBTS's high-velocity pulsatile flow. We employed simulations of flow in cavopulmonary pathways consisting of internal jugular, subclavian and innominate veins, SVC, RPA, LPA and mBTS, using computational fluid dynamics (CFD) to numerically solve (finite volume method) the Navier-Stokes equations subject to in vivo flow rates at the inlets and measured or calculated pressures at the outlets of the cavopulmonary system. For normal size (9 mm) PAs and a BGS alone, SVC pressure was 12.3 mmHg, RPA and LPA 12.2 mmHg; PA outlets 12 mmHg. We then compared results for the BGS with a 4 mm mBTS. I) With normal-size PAs, SVC pressure was 14.3 mmHg, RPA 13.3 mmHg and LPA 12.9 mmHg; PA outlets 12 mmHg. Wall shear stress (WSS), RPA 6.2 Pa and LPA 53.7 Pa. II) With normal size (9 mm) RPA but small (5.1 mm) LPA, SVC pressure was 15.1 mmHg, RPA 13.8 mmHg and LPA 17.4 mmHg; RPA outlet 12 mmHg and LPA 14 mmHg. WSS, RPA 13.2 Pa and LPA 71 Pa. Normal PA WSS is ~ 2 Pa. *All parameters were averaged over the cardiac cycle. The mBTS created vortices which markedly elevated WSS. High WSS can induce PA luminal cell expression of coagulatory molecules and initiate platelet aggregation. However, WSS lessened as flow velocity decreased from LPA to RPA. This is important since in vitro studies demonstrate WSS's harmful effect on PA endothelium is ameliorated under decelerating flow. In conclusion, for a BGS with a mBTS, SVC pressure became cyclic and significantly increased and thrombogenic vortices were established in the PAs.

PEAR1 polymorphisms as a prognostic factor in hemostasis and cardiovascular diseases.

Platelet Endothelial Aggregation Receptor (PEAR1), as a platelet receptor, plays a vital role in hemostasis. This receptor, by its extracellular part, causes platelet adhesion and consequently initiates platelet aggregation. Dysfunction of PEAR1 can disrupt platelet aggregation in patients with cardiovascular diseases (CVDs). The content used in this paper has been taken from English language articles (2005-2020) retrieved from Pubmed database and Google scholar search engine using "Cardiovascular Disease", "PEAR1", "Polymorphism", and "Platelet Aggregation" keywords. Some PEAR1 polymorphisms can disrupt homeostasis and interfere with the function mechanism of cardiac drugs. Since polymorphisms in this gene affect platelet function and the platelet aggregation process, PEAR1 could be further studied in the future as an essential factor in controlling the treatment process of patients with cardiovascular diseases. PEAR1 polymorphisms through disruption of the platelet aggregation process can be a risk factor in patients with CVDs. Therefore, controlling patients through genetic testing and the evaluation of PEAR1 polymorphisms can help improve the treatment process of patients. According to the studies on the PEAR1 gene and the effect of different polymorphisms on some crucial issues in CVDs patients (changes in platelet activity), it is clear that if there is a significant relationship between polymorphisms and CVDs, they can be used as prognostic and diagnostic markers. This study aims to evaluate the prognosis and drug treatment of the PEAR1 gene in CVDs patients.

Pleiotropic Activity of Metformin and Its Sulfonamide Derivatives on Vascular and Platelet Haemostasis.

As type 2 diabetes mellitus (T2DM) predisposes patients to endothelial cell injury and dysfunction, improvement of vascular function should be an important target for therapy. The aim of this study was to evaluate the effects of metformin, its sulfenamide and sulfonamide derivatives on selected parameters of endothelial and smooth muscle cell function, and platelet activity. Metformin was not found to significantly affect the viability of human umbilical vein endothelial cells (HUVECs) or aortal smooth muscle cells (AoSMC); however, it decreased cell migration by approximately 21.8% in wound healing assays after 24 h stimulation (wound closure 32.5 µm versus 41.5 µm for control). Metformin reduced platelet aggregation manifested by 19.0% decrease in maximum of aggregation (Amax), and 20% reduction in initial platelet aggregation velocity (v0). Furthermore, metformin decreased spontaneous platelet adhesion by 27.7% and ADP-induced adhesion to fibrinogen by 29.6% in comparison to control. Metformin sulfenamide with an n-butyl alkyl chain (compound 1) appeared to exert the most unfavourable effects on AoSMC cell viability (IC50 = 0.902 ± 0.015 μmol/mL), while 4-nitrobenzenesulfonamide (compound 3) and 2-nitrobenzenesulfonamide (compound 4) derivatives of metformin did not affect AoSMC and HUVEC viability at concentrations up to 2.0 μmol/mL. These compounds were also found to significantly reduce migration of smooth muscle cells by approximately 81.0%. Furthermore, sulfonamides 3 and 4 decreased the initial velocity of platelet aggregation by 11.8% and 20.6%, respectively, and ADP-induced platelet adhesion to fibrinogen by 76.3% and 65.6%. Metformin and its p- and o-nitro-benzenesulfonamide derivatives 3, 4 appear to exert beneficial effects on some parameters of vascular and platelet haemostasis.

Identifying the start of a platelet aggregate by the shear rate and the cell-depleted layer.

Computer simulations were performed to study the transport of red blood cells and platelets in high shear flows, mimicking earlier published in vitro experiments in microfluidic devices with high affinity for platelet aggregate formation. The goal is to understand and predict where thrombus formation starts. Additionally, the need of cell-based modelling in these microfluidic devices is demonstrated by comparing our results with macroscopic models, wherein blood is modelled as a continuous fluid. Hemocell, a cell-based blood flow simulation framework is used to investigate the transport physics in the microfluidic devices. The simulations show an enlarged cell-depleted layer at the site where a platelet aggregate forms in the experiments. In this enlarged cell-depleted layer, the probability to find a platelet is higher than in the rest of the microfluidic device. In addition, the shear rates are sufficiently high to allow for the von Willebrand factor to elongate in this region. We hypothesize that the enlarged cell-depleted layer combined with a sufficiently large platelet flux and sufficiently high shear rates result in an haemodynamic environment that is a preferred location for initial platelet aggregation.

The Role of Chemoprophylactic Agents in Modulating Platelet Aggregability After Traumatic Brain Injury

BackgroundThe pathophysiology behind the subacute but persistent hypercoagulable state after traumatic brain injury (TBI) is poorly understood but contributes to morbidity induced by venous thromboembolism. Because platelets and their microvesicles have been hypothesized to play a role in post-traumatic hypercoagulability, administration of commonly used agents may ameliorate this coagulability. We hypothesized that utilization of aspirin, ketorolac, amitriptyline, unfractionated heparin, or enoxaparin would modulate the platelet aggregation response after TBI. MethodsConcussive TBI was induced by weight drop. Mice were then randomized to receive aspirin, ketorolac, amitriptyline, heparin, enoxaparin, or saline control at 2 and 8 h after TBI. Mice were sacrificed at 6 or 24 h after injury to determine coagulability by rotational thromboelastometry (ROTEM), platelet function testing with impedance aggregometry, and microvesicle enumeration. Platelet sphingolipid metabolites were analyzed by mass spectrometry. ResultsROTEM demonstrated increased platelet contribution to maximum clot firmness at 6 h after TBI in mice that received aspirin or amitriptyline, but this did not persist at 24 h. By contrast, adenosine diphosphate– and arachidonic acid–induced platelet aggregation at 6 h was significantly lower in mice receiving ketorolac, aspirin, and amitriptyline compared with mice receiving saline at 6 h after injury and only arachidonic acid–initiated platelet aggregation was decreased by aspirin at 24 h. There were no differences in microvesicle production at either time point. Platelet sphingosine-1-phosphate levels were decreased at 6 h in the group receiving amitriptyline and increased at 24 h along with platelet ceramide levels at 24 h in the amitriptyline group. ConclusionAfter TBI, amitriptyline decreased platelet aggregability and increased contribution to clot in a manner similar to aspirin. The amitriptyline effects on platelet function and sphingolipid metabolites may represent a possible role of the acid sphingomyelinase in the hypercoagulability observed after injury. In addition, inhibition of platelet reactivity may be an underappreciated benefit of low molecular weight heparins, such as enoxaparin.

Platelet-Neutrophil Crosstalk in Atherothrombosis.

Atherothrombosis is a frequent cause of cardiovascular mortality. It is mostly triggered by plaque rupture and exposure of the thrombogenic subendothelial matrix, which initiates platelet aggregation and clot formation. Current antithrombotic strategies, however, target both thrombosis and physiological hemostasis and thereby increase bleeding risk. Thus, there is an unmet clinical need for optimized therapies. Neutrophil activation and consecutive interactions of neutrophils and platelets contribute mechanistically to thromboinflammation and arterial thrombosis, and thus present a potential therapeutic target. Platelet-neutrophil interactions are mediated through adhesion molecules such as P-selectin and P-selectin glycoprotein ligand 1 as well as glycoprotein Ib and macrophage-1 antigen, which mediate physical cell interactions and intracellular signaling. Release of soluble mediators as well as direct signaling between platelets and neutrophils lead to their reciprocal activation and neutrophil release of extracellular traps, scaffolds of condensed chromatin that play a prothrombotic role in atherothrombosis. In this article, we review the role of neutrophils and neutrophil-derived prothrombotic molecules in platelet activation and atherothrombosis, and highlight potential therapeutic targets.

Porewater salinity effect on flocculation and desiccation cracking behaviour of kaolin and bentonite considering working condition

Cracking behaviour of clays at a local working climate and soils' evolution under seepage boundary is very important for the geological engineering. In coastal regions, pore water salinity is incorporated into above processes. In this study, the properties of typical clays (kaolin and bentonite) in saline environments, including the consistency limits, particle sedimentation and crack pattern, were investigated. The consistency limits of kaolin remain constant regardless of the pore water salinity, while the liquid limits of bentonite noticeably decrease with increasing salinity. Flocculation of kaolin occurs in both distilled water and NaCl solution, whereas the fine particles in bentonite disperse in distilled water but aggregate in saline water. At the end of the evaporation process, the total crack area of bentonite is obviously decreased, and the total crack length increases with pore water salinity, whilst that of kaolin is not influenced. In the subsequent wetting process, the bentonite clods disperse easily in saline environment, but the collapse of kaolin clods is not significantly influenced by the water salinity. The above observations are explained by the initial aggregation of clay platelets for the interactive forces between particles.

VWA proteins of Leptospira interrogans induce hemorrhage in leptospirosis by competitive inhibition of vWF/GPIb-mediated platelet aggregation.

BackgroudLeptospira interrogans is the major causative agent of leptospirosis, a worldwide zoonotic disease. Hemorrhage is a typical pathological feature of leptospirosis. Binding of von Willebrand factor (vWF) to platelet glycoprotein-Ibα (GPIbα) is a crucial step in initiation of platelet aggregation. The products of L. interrogans vwa-I and vwa-II genes contain vWF-A domains, but their ability to induce hemorrhage has not been determined.MethodsHuman (Hu)-platelet- and Hu-GPIbα-binding abilities of the recombinant proteins expressed by L. interrogans strain Lai vwa-I and vwa-II genes (rLep-vWA-I and rLep-vWA-II) were detected by flowcytometry, surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). Hu-platelet aggregation and its signaling kinases and active components were detected by lumiaggregometry, Western analysis, spectrophotometry and confocal microscopy. Hu-GPIbα-binding sites in rLep-vWA-I and rLep-vWA-II were identified by SPR/ITC measurements.FindingsBoth rLep-vWA-I and rLep-vWA-II were able to bind to Hu-platelets and inhibit rHu-vWF/ristocetin-induced Hu-platelet aggregation, but Hu-GPIbα-IgG, rLep-vWA-I-IgG and rLep-vWA-II-IgG blocked this binding or inhibition. SPR and ITC revealed a tight interaction between Hu-GPIbα and rLep-vWA-I/rLep-vWA-II with KD values of 3.87 × 10−7-8.65 × 10−8 M. Hu-GPIbα-binding of rL-vWA-I/rL-vWA-II neither activated the PI3K/AKT-ERK and PLC/PKC kinases nor affected the NO, cGMP, ADP, Ca2+ and TXA2 levels in Hu-platelets. G13/R36/G47 in Lep-vWA-I and G76/Q126 in Lep-vWA-II were confirmed as the Hu-GPIbα-binding sites. Injection of rLep-vWA-I or rLep-vWA-II in mice resulted in diffuse pulmonary and focal renal hemorrhage but this hemorrhage was blocked by rLep-vWA-I-IgG or rLep-vWA-II-IgG.InterpretationThe products of L. interrogans vwa-I and vwa-II genes induce hemorrhage by competitive inhibition of vWF-mediated Hu-platelet aggregation.

Anesthetic Care of a Patient With Bernard-Soulier Syndrome for Posterior Spinal Fusion

Bernard-Soulier syndrome (BSS), a rare autosomal recessive disorder first identified in 1948, is characterized by excessive and prolonged bleeding due to thrombocytopenia and platelet dysfunction with increased platelet size and deformability. The primary defect in BSS involves the glycoprotein (GP) Ib-IX-V complex, which is important in initiating platelet aggregation and thrombosis after vascular injury by facilitating the adhesion of platelets to von Willebrand factor. The coagulation defect in BSS can lead to significant bleeding during traumatic injury or surgical intervention. We present a 17-year-old adolescent with BSS who presented for posterior spinal fusion for idiopathic scoliosis. Previous reports of perioperative care of patients with BSS are reviewed and options for anesthetic care including perioperative control of the coagulation defect are presented. J Med Cases. 2018;9(10):341-344 doi: https://doi.org/10.14740/jmc3142w

Abstract 12056: Computational Fluid Dynamics Description of Blood Flow in a Bidirectional Glenn Shunt Supplemented With a Modified Blalock-Taussig Shunt: Relevance to Thrombosis and Power Loss

Introduction: A bidirectional Glenn shunt (BGS) has been supplemented with a modified Blalock-Taussig shunt (BTS), to enhance growth of the pulmonary arteries (PAs). However, the hemodynamics is incompletely understood. Hypothesis: High velocity BTS flow imposed on low velocity BGS flow can create secondary currents (vortices) in the PAs conducive to clot deposition and power dissipation. Methods: We employed a computational model (Fluent) of pulsatile flow (viscosity 5 cPa-s), using the finite volume method, and a schematic representation of a BGS with a BTS, to determine velocity field, wall shear stress (WSS) and power (W) efficiency (PE). The region studied included the internal jugular, subclavian and innominate veins, BGS (12.5 mm), BTS (4 mm) and PAs (9 mm). Vessel sizes and flow rates were derived from reported values. Flow rates were fixed at the inlet of the veins, and in the BGS was 1L/min. Aortic pressure (82/42 mmHg) was used at the inlet to the BTS, and a mean pressure (12 mmHg) at the outlets of the PAs. Results: Fig 1 shows velocity magnitude at peak systole. The BTS jet (red) enters the LPA, where it gives rise to dissipative counter-rotating velocity fields, which augment local WSS. Fig (2) shows the velocity fields (arrows) in cross-sectional planes where the BGS and BTS connect to the PAs. The high WSS (350 Pa) is sufficient (> 100 Pa) to initiate platelet aggregation leading to thrombus formation. PE (1-W loss /W in ) for the BGS alone was 97%; whereas, with the BTS it decreased to 29%. The BTS increased BGS pressure, 12.3 to 14.0 mmHg. Conclusion: Supplementing a BGS with a BTS can: 1) elevate BGS pressure, 2) create regions at risk for thrombus formation and 3) worsen power loss.

Abstract PR132

Background & Objectives: It’s known that deep vein thrombosis of lower extremities and pulmonary embolism occupies an important place in the structure of postoperative morbidity and mortality. Materials & Methods: After Ethics approval and informed consent (Research Ethical Board number 3747-Л of Odessa National Medical University on 15 of April 2015), was studied the functional state of hemostasis in a group of 60 healthy volunteers, who were not receiving drugs affecting coagulation. Monitoring of hemostasis was by low-frequency piezoelectric thromboelastography (LPTEG) (fig. 1), platelet aggregation test (PAT), standard coagulation tests (SCT) and thromboelastogram (TEG). Results: It was found that the indexes of LPTEG as the intensity of the contact phase of coagulation (ICC), the time the contact phase of coagulation (t1), and initial rate of aggregation of blood (A0) were correlated with PAT indexes as the spontaneous platelet aggregation and epinephrine-induced platelet aggregation (0.59 – 0.76); the intensity of coagulation drive (ICD) correlate with activated partial thromboplastin time of SCT (0.56) and reaction time to initial fibrin formation of TEG (0.64), maximum density of the clot (MDC) with fibrinogen level of SCT (0.67) and maximal amplitude of TEG (0.86) a constant thrombin activity (CTA) with thrombin time of SCT (0.78) and clotting time of TEG (0.93), and the intensity of the retraction and clot lysis (IRCL) with the total fibrinolytic activity of SCT (0.83) and clot lysis of TEG (0.74). Conclusion: LPTEG allows make the total assessment of all parts hemostasis: from initial viscosity and platelet aggregation to coagulation and lysis of clot, as well as their interaction. We can use the indexes ICC, A0, t1 for control aggregation, ICD, MDC, CTA for control coagulation and IRCL for control fibrinolysis. His figures are objective and informative, as evidenced by close correlation with the performance of traditional coagulation methods. Disclosure of Interest: None declared

Primary haemostasis: newer insights.

At the same time as biophysical and omics approaches are drilling deeper into the molecular details of platelets and other blood cells, as well as their receptors and mechanisms of regulation, there is also an increasing awareness of the functional overlap between human vascular systems. Together, these studies are redefining the intricate networks linking haemostasis and thrombosis with inflammation, infectious disease, cancer/metastasis and other vascular pathophysiology. The focus of this state-of-the-art review is some of the newer advances relevant to primary haemostasis. Of particular interest, platelet-specific primary adhesion-signalling receptors and associated activation pathways control platelet function in flowing blood and provide molecular links to other systems. Platelet glycoprotein (GP)Ibα of the GPIb-IX-V complex and GPVI not only initiate platelet aggregation and thrombus formation by primary interactions with von Willebrand factor and collagen, respectively, but are also involved in coagulation, leucocyte engagement, bacterial or viral interactions, and are relevant as potential risk markers in a range of human diseases. Understanding these systems in unprecedented detail promises significant advances in evaluation of individual risk, in new diagnostic or therapeutic possibilities and in monitoring the response to drugs or other treatment.

An Adaptation of Prostaglandin Endoperoxide H Synthases in Binding to Endogenous Ligands and Nonsteroidal Anti-Inflammatory Drugs

Prostaglandins play critical roles in a number of physiological and pathophysiological processes. These molecules are involved in regulating blood flow to organs, initiating platelet aggregation in blood clotting, and mainly mediating the classical symptoms of inflammation. Biosynthesis of prostaglandins is initiated by prostaglandin endoperoxide H synthases (PGHS) −1 and −2, which catalyze the conversion of arachidonic acid to PGH2. PGHSs are homodimers comprised of ∼72 kDa monomers of identical primary sequence and recently have been investigated in the respect of allosteric communications between two subunits during ligand binding. The nonsteroidal anti-inflammatory drugs show multiple inhibition modalities against PGHSs. Their time-dependent and subunit-preferential bindings to PGHSs complicate the interactions of PGHSs with the cognate substrates and their regulations by natural and synthetic ligands. Accordingly, a paradigm shift in the analysis of PGHS-ligand complex during PGHS catalysis is required and their theoretical revaluation and biological functioning in vivo are described in this paper.