The volume fraction of red blood cells (RBCs) in a capillary affects the degree to which platelets are promoted to marginate to near a vessel wall and form blood clots. In this work we investigate the relationship between RBC hematocrit and platelet adhesion activity. We perform experiments flowing blood samples through a microfluidic channel coated with type 1 collagen and observe the rate at which platelets adhere to the wall. We compare these results with three-dimensional boundary integral simulations of a suspension of RBCs and platelets in a periodic channel where platelets can adhere to the wall. In both cases, we find that the rate of platelet adhesion varies greatly with the RBC hematocrit. We observe that the relative decrease in platelet activity as hematocrit falls shows a similar profile for simulation and experiment.

BackgroundAcute traumatic coagulopathy (ATC) has been linked to an increase in activated protein C (aPC) from 40 pM in healthy individuals to 175 pM. aPC exerts its activity primarily through cleavage of active coagulation factor Va (fVa). Platelets reportedly possess fVa which is more resistant to aPC cleavage than plasma fVa; this work examines the hypothesis that normal platelets are sufficient to maintain coagulation in the presence of elevated aPC.MethodsCoagulation responses of normal plasma, fV deficient plasma (fVdp), and isolated normal platelets in fVdp were conducted: prothrombin (PT) tests, turbidimetry, and thromboelastography (TEG), including the dose response of aPC on the samples.ResultsPT and turbidimetric assays demonstrate that normal plasma is resistant to aPC at doses much higher than those found in ATC. Additionally, an average physiological number of washed normal platelets (200,000 platelets/mm3) was sufficient to eliminate the anti-coagulant effects of aPC up to 10 nM, nearly two orders of magnitude above the ATC concentration and even the steady-state pharmacological concentration of human recombinant aPC, as measured by TEG. aPC also demonstrated no significant effect on clot lysis in normal plasma samples with or without platelets.ConclusionsAlthough platelet fVa shows slightly superior resistance to aPC's effects compared to plasma fVa in static models, neither fVa is sufficiently cleaved in simulations of ATC or pharmacologically-delivered aPC to diminish coagulation parameters. aPC is likely a correlative indicator of ATC or may play a cooperative role with other activity altering products generated in ATC.

We have adapted the corn-trypsin inhibitor whole-blood model to include EA.hy926 as an endothelium surrogate to evaluate the vascular modulation of blood coagulation initiated by relipidated recombinant tissue factor (rTf) and a cellular Tf surrogate, lipopolysaccharide (LPS)-stimulated THP1 cells (LPS-THP-1). Compared with bare tubes, EA.hy926 with rTf decreased the rate of thrombin formation, ITS accumulation, and the production of fibrinopeptide A. These phenomena occurred with increased rates of factor Va (fVa) inactivation by cleavages at R 506 and R 306 . Thus, EA.hy926 provides thrombin-dependent protein C activation and APC fVa inactivation. Comparisons of rTf with LPS-THP-1 showed that the latter gave reduced rates for TAT formation but equivalent fibrinopeptide A, and fV activation/inactivation. In the presence of EA.hy926, the reverse was obtained; with the surrogate endothelium and LPS-THP-1 the rates of TAT generation, fibrinopeptide release, and fV activation were almost doubled, whereas cleavage at R 306 was equivalent. These observations suggest cooperativity between the 2 cell surrogates. These data suggest that the use of these 2 cell lines provides a reproducible quasiendothelial quasi-inflammatory cytokinestimulated monocyte system that provides a method to evaluate the variations in blood phenotype against the background of stable inflammatory cell activator and a stable vascular endothelial surrogate.(Blood. 2010; 116(26):6082-6091) IntroductionVirchow postulated 3 phenomena that lead to venous thrombosis: (1) the components contained within the blood itself lead to systemic hypercoagulability; (2) alteration of the endothelium from injury or dysfunction; and (3) alterations of blood flow. 1 These postulates are the foundation for the physiologic understanding of blood coagulation and the maintenance of the hemostatic balance in the venous circulation.The maintenance of blood fluidity and vascular integrity is actively maintained by collaborations between the vascular wall and the procoagulant and anticoagulant functions in blood. Cellbound and soluble constituents cooperate to maintain this quasiequilibrium fluid state. Upon vascular perforation, multiple interactions initiate a local coagulant response, promoting platelet adhesion/ aggregation, the generation of membrane-bound catalysts, thrombin generation, and fibrin deposition that overcome local anticoagulants. These processes arrest blood loss with dimensions relevant to the injury. Subsequently, fibrinolysis and cellular proliferation repair 2 the injured tissue.The coagulation processes have been studied in vitro using anticoagulated phlebotomy blood, 3 derived plasma, 4,5 isolated component systems, [6][7][8] and numerical simulations. 9,10 We have used corn-trypsin inhibitor (CTI) stabilized whole blood to study the tissue factor (Tf)-initiated process in the absence of chelating anticoagulants. 11,12 Several hundred of these experiments have been performed to characterize the temporal dynamics of various blood clotting reactions...

Hemorrhagic shock and resuscitation produces time-dependent organ-specific trends of neutrophil sequestration as measured with tissue levels of myeloperoxidase, a marker of neutrophil infiltration. Modulation of the splanchnic blood flow by direct peritoneal resuscitation did not alter the time-dependent neutrophil infiltration in end-organs, suggesting a subordinate role of blood rheology in the hemorrhage-induced neutrophil sequestration. Vulnerable window for neutrophil-mediated tissue damage exists during the first 4 h following resuscitation from hemorrhagic shock in rats. Direct peritoneal resuscitation prevents the early obligatory fluid sequestration and promotes early fluid mobilization.

Extracorporeal life support (ECLS) is fast becoming more common place for use in adult patients failing mechanical ventilation. Management of coagulation and thrombosis has long been a major complication in the use of ECLS therapies. Scanning electron microscopy (SEM) of membrane oxygenators (MOs) after use in ECLS circuits can offer novel insight into any thrombotic material deposition on the MO. In this pilot study, we analyzed five explanted MOs immediately after use in a sheep model of different acute respiratory distress syndrome (ARDS). We describe our methods of MO dissection, sample preparation, image capture, and results. Of the five MOs analyzed, those that received continuous heparin infusion showed very little thrombosis formation or other clot material, whereas those that were used with only initial heparin bolus showed readily apparent thrombotic material.