Functional imaging of shear-dependent activity of ADAMTS13 in regulating mural thrombus growth under whole blood flow conditions

Blood ◽  
2008 ◽  
Vol 111 (3) ◽  
pp. 1295-1298 ◽  
Author(s):  
Yasuaki Shida ◽  
Kenji Nishio ◽  
Mitsuhiko Sugimoto ◽  
Tomohiro Mizuno ◽  
Masaaki Hamada ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Whole Blood ◽  
Thrombus Formation ◽  
Arterial Occlusion ◽  
Generation Process ◽  
Flow Conditions ◽  
Normal Hemostasis

Abstract The metalloprotease ADAMTS13 is assumed to regulate the functional levels of von Willebrand factor (VWF) appropriate for normal hemostasis in vivo by reducing VWF multimer size, which directly represents the thrombogenic activity of this factor. Using an in vitro perfusion chamber system, we studied the mechanisms of ADAMTS13 action during platelet thrombus formation on a collagen surface under whole blood flow conditions. Inhibition studies with a function-blocking anti-ADAMTS13 antibody, combined with immunostaining of thrombi with an anti-VWF monoclonal antibody that specifically reflects the VWF-cleaving activity of ADAMTS13, provided visual evidence for a shear rate–dependent action of ADAMTS13 that limits thrombus growth directly at the site of the ongoing thrombus generation process. Our results identify an exquisitely specific regulatory mechanism that prevents arterial occlusion under high shear rate conditions during mural thrombogenesis.

Critical Role of Immobilized Factor VIII In Solid-Phase Blood Coagulation During Mural Thrombogenesis Under Whole Blood Flow Conditions

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2199-2199
Author(s):  
Masaaki Doi ◽  
Mitsuhiko Sugimoto ◽  
Hideto Matsui ◽  
Tomoko Matsumoto ◽  
Midori Shima
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Whole Blood ◽  
Solid Phase ◽  
Glass Plate ◽  
High Shear Rate ◽  
High Shear ◽  
Fibrin Deposition ◽  
Flow Conditions

Abstract Abstract 2199 Coagulation factor VIII (FVIII), lacking in hemophilic blood, plays an essential role in mechanisms of fibrin plug formation to arrest bleeding at sites of injured vessel walls. Physiologic activity of FVIII circulating in bloodstream (soluble FVIII; S-FVIII) could be extensively evaluated so far by classic plasma coagulation assays such as activated partial thromboplastin time. However, the in vivo functional relevance of FVIII bound to von Willebrand factor (VWF) which is immobilized in subendothelium (immobilized FVIII; I-FVIII) is more complex and remains to be addressed. Using an in vitro perfusion chamber system, we have therefore evaluated the function of I-FVIII in the process of mural thrombus generation under whole blood flow conditions. FVIII-free VWF was purified in the presence of 0.35 M CaCl2 from cryoprecipitate, and coated on a glass plate. Various concentrations (0 as a control, 0.1, 0.3, 1, or 3 U/ml) of recombinant FVIII (Kogenate FS provided by Bayer Pharmaceutical Co.) were reacted with the FVIII-free VWF-coated glass plate. After non-adherent proteins were washed out, the amount of FVIII immobilized to a glass surface via VWF (I-FVIII) was measured by ELISA-based assay using a peroxidase-conjugated anti-FVIII polyclonal antibody. Whole blood was then perfused over a glass plate described above in a parallel plate flow chamber with various shear rates, and the thrombus generation process on a glass surface was observed in real time by confocal laser scanning microscopy. The development of intra-thrombus fibrin deposition was assessed by immune-staining of thrombi with a fluorescence-labeled anti-fibrin specific monoclonal antibody (NYB-T2G1; Accurate Chem.), reflecting solid-phase blood coagulation reaction during mural thrombogenesis. In perfusion of control blood with a high shear rate (1500 s-1), the intra-thrombus fibrin deposition was found to increase as a function of I-FVIII, resulting in the 2.5-fold greater fibrin deposition at the plateau as compared to control thrombi generated in the absence of I-FVIII. This I-FVIII effect on intra-thrombus fibrin deposition was also confirmed in perfusion of synthetic hemophilic blood (S-FVIII activity < 1%) which was prepared by the incubation of control blood with an anti-FVIII human IgG (final inhibitor titer in synthetic blood; 5, 10, or 20 Bethesda U/ml). Indeed, I-FVIII normalized in a dose-dependent manner the reduced fibrin deposition (20-35% of normal control) within synthetic hemophilic thrombi generated in the absence of S-FVIII under a high shear rate condition. The improvement of impaired fibrin deposition by I-FVIII was unvarying regardless of the anti-FVIII inhibitor titer in synthetic hemophilic blood. In contrast, the direct addition of recombinant FVIII into synthetic hemophilic blood was poorly effective in this regard, due to the immediate neutralization of S-FVIII by an inhibitor involved in synthetic blood. Thus, these results clearly indicate that I-FVIII, independent of S-FVIII, does play a considerable role on the intra-thrombus fibrin-network formation in the process of mural thrombus generation under whole blood flow conditions with high shear rate, most relevant physiologically for the in vivo hemostasis and thrombosis. Our results might imply a possibility of novel strategic design targeting I-FVIII against hemophilic patients with a high titer anti-FVIII inhibitor. Disclosures: No relevant conflicts of interest to declare.

A Locally Administered Novel Heparin Complex Attenuates Collagen-Induced Platelet Activation and Thrombosis In Vivo,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3361-3361
Author(s):  
Riitta Lassila ◽  
Annukka Jouppila ◽  
Ulla M Marzec ◽  
Stephen R Hanson
Keyword(s):  
Blood Flow ◽  
Platelet Aggregation ◽  
Thrombus Formation ◽  
Ptfe Graft ◽  
Thrombin Time ◽  
Thrombosis Model ◽  
Baboon Model ◽  
Induced Aggregation

Abstract Abstract 3361 We have developed a semi-synthetic antithrombotic heparin complex, APL001, to mimic mast cell-derived natural heparin proteoglycans (HepPG). HepPG attenuate platelet-collagen interactions under blood flow by inhibiting VWF- and GPIIb/IIIa -mediated platelet aggregation. In addition, rat-derived HepPG arrest platelet thrombus growth on collagen surfaces or at vascular injury sites, both in vitro and in vivo (Lassila et al.ATVB 1997, Kauhanen et al. ATVB 2000, Olsson et al. Thromb Haemost 2002). Our objective was to study the inhibitory capacity of APL001 for preventing human platelet aggregation in vitro and acute thrombosis in a baboon model in vivo. The effects of unfractionated heparin (UFH) and APL001 were compared in relevant coagulation assays (APTT, PT, thrombin time, anti-FXa activity, fibrinogen, FVIII:C and VWF activity (VWF:RCo) and antigen). Additionally, agonist-induced (collagen, ristocetin and ADP) platelet aggregation in citrate or hirudin-anticoagulated whole blood (Multiplate®) (n=10 healthy subjects), and platelet function analysis (PFA100®) in citrated platelet rich plasma (PRP) were assessed. In a well-established baboon thrombosis model a collagen-coated PTFE graft (length 2 cm, lumen 4 mm) was placed in an arterio-venous shunt. Prior to blood contact the thrombogenic surface was treated for 10 min with UFH or APL001 (both at 4 mg/mL). Thrombus formation was initiated by exposing the surface to blood flow (100 mL/min, shear rate 265−1), and the deposition of 111-In-labeled platelets and of fibrin was quantified continuously over 1h. Fibrin thrombus accumulation was assessed from the incorporation of circulating 125-I-fibrinogen. In the heparin-relevant coagulation tests APL001 was comparable or 20–30% more potent than UFH while FVIII, fibrinogen and VWF variables remained unaltered. In contrast to UFH, APL001 (300 μg/mL) consistently inhibited collagen- and ristocetin-induced platelet aggregation, whereas UFH had only a modest effect in comparison with PBS control (Table). ADP-induced aggregation was unaffected. Comparable results were observed in the PRP aggregation assay. PFA100 testing also demonstrated inhibitory effects. In the in vivo thrombosis model (n=4) APL001 reduced platelet deposition on collagen (vs. the results with UFH) by 34% (p=0.01), while platelet accumulation in distal propagated thrombus was reduced by 61% (p=0.16). APL001-treated surfaces accumulated 45% less fibrin than the UFH-treated surfaces (p=0.008). In conclusion, when compared with UFH APL001 inhibited both collagen- and ristocetin-induced platelet aggregation in human blood, while anticoagulant properties were comparable. In the absence of systemic antithrombotic drugs, exposure of APL001 to a highly thrombogenic collagen surface arrested thrombus formation in an in vivo baboon model. This finding suggests that locally administered APL001 alone, due to its dual antiplatelet and anticoagulant effects, may limit the growth and size of thrombus and thereby prevent subsequent thrombo-occlusion.TableAnticoagulantInhibition-% of platelet aggregation ± SDConc. 300 μg/mLnColl (3.2 μg/mL)Ristocetin (0.77 mg/mL)ADP (6.4 μM)CitrateAPL0011033 ± 1543 ± 166 ± 24UFH1011 ± 1323 ± 153 ± 7p value0.0030.0100.700HirudinAPL0011032 ± 1043 ± 178 ± 10UFH108 ± 1116 ± 166 ± 9p value0.0000.0020.600 Disclosures: Lassila: Aplagon: Chief Scientific Advisor.

Platelet ADP receptors contribute to the initiation of intravascular coagulation

Blood ◽  
2004 ◽  
Vol 103 (2) ◽  
pp. 594-600 ◽  
Author(s):  
Catherine Leon ◽  
Meike Alex ◽  
Antje Klocke ◽  
Eberhard Morgenstern ◽  
Christine Moosbauer ◽  
...  
Keyword(s):  
Whole Blood ◽  
Ex Vivo ◽  
Thrombus Formation ◽  
Intravascular Coagulation ◽  
Adp Receptors ◽  
Adp Receptor ◽  
Deficient Mice ◽  
Storage Pools

Abstract While the adenosine 5′-diphosphate (ADP) pathway is known to enhance thrombus formation by recruiting platelets and leukocytes to the primary layer of collagen-adhering platelets, its role for the initiation of coagulation has not been revealed. Ex vivo inhibition of the P2Y12 ADP receptor by clopidogrel administration diminished the rapid exposure of tissue factor (TF), the major initiator of coagulation, in conjugates of platelets with leukocytes established by the contact of whole blood with fibrillar collagen. Under in vitro conditions, the P2Y12 and P2Y1 ADP receptors were both found to be implicated in the exposure of TF in collagen-activated whole blood. Immunoelectron-microscopy revealed that collagen elicited the release of TF from its storage pools within the platelets. Functional activation of the intravascular TF was reduced by inhibition of the ADP receptors, partially due to the disruption of the platelet-neutrophil adhesions. Injection of collagen into the venous system of mice increased the number of thrombin-antithrombin complexes, indicative for the formation of thrombin in vivo. In P2Y1-deficient mice, the ability of collagen to enhance the generation of thrombin was impaired. In conclusion, the platelet ADP pathway supports the initiation of intravascular coagulation, which is likely to contribute to the concomitant formation of fibrin at the site of the growing thrombus.

scholarly journals The distal carboxyl-terminal domains of ADAMTS13 are required for regulation of in vivo thrombus formation

Blood ◽  
2009 ◽  
Vol 113 (21) ◽  
pp. 5323-5329 ◽  
Author(s):  
Fumiaki Banno ◽  
Anil K. Chauhan ◽  
Koichi Kokame ◽  
Jin Yang ◽  
Shigeki Miyata ◽  
...  
Keyword(s):  
Shear Rate ◽  
Genetic Background ◽  
Thrombus Formation ◽  
Short Form ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Terminal Domains

Abstract ADAMTS13 is a multidomain protease that limits platelet thrombogenesis through the cleavage of von Willebrand factor (VWF). We previously identified 2 types of mouse Adamts13 gene: the 129/Sv-strain Adamts13 gene encodes the long-form ADAMTS13 having the same domains as human ADAMTS13, whereas the C57BL/6-strain Adamts13 gene encodes the short-form ADAMTS13 lacking the distal C-terminal domains. To assess the physiologic significance of the distal C-terminal domains of ADAMTS13, we generated and analyzed 129/Sv-genetic background congenic mice (Adamts13S/S) that carry the short-form ADAMTS13. Similar to wild-type 129/Sv mice (Adamts13L/L), Adamts13S/S did not have ultralarge VWF multimers in plasma, in contrast to 129/Sv-genetic background ADAMTS13-deficient mice (Adamts13−/−). However, in vitro thrombogenesis under flow at a shear rate of 5000 s−1 was accelerated in Adamts13S/S compared with Adamts13L/L. Both in vivo thrombus formation in ferric chloride–injured arterioles and thrombocytopenia induced by collagen plus epinephrine challenge were more dramatic in Adamts13S/S than in Adamts13L/L but less than in Adamts13−/−. These results suggested that the C-terminally truncated ADAMTS13 exhibited decreased activity in the cleavage of VWF under high shear rate. Role of the C-terminal domains may become increasingly important under prothrombotic conditions.

scholarly journals Loss of talin1 in platelets abrogates integrin activation, platelet aggregation, and thrombus formation in vitro and in vivo

2007 ◽  
Vol 204 (13) ◽  
pp. 3113-3118 ◽  
Author(s):  
Bernhard Nieswandt ◽  
Markus Moser ◽  
Irina Pleines ◽  
David Varga-Szabo ◽  
Sue Monkley ◽  
...  
Keyword(s):  
Vascular Injury ◽  
Thrombus Formation ◽  
Cellular Functions ◽  
High Affinity ◽  
Direct Binding ◽  
Normal Hemostasis ◽  
Necessary And Sufficient ◽  
Aggregation Of Platelets

Platelet adhesion and aggregation at sites of vascular injury are essential for normal hemostasis but may also lead to pathological thrombus formation, causing diseases such as myocardial infarction or stroke. Heterodimeric receptors of the integrin family play a central role in the adhesion and aggregation of platelets. In resting platelets, integrins exhibit a low affinity state for their ligands, and they shift to a high affinity state at sites of vascular injury. It has been proposed that direct binding of the cytoskeletal protein talin1 to the cytoplasmic domain of the integrin β subunits is necessary and sufficient to trigger the activation of integrins to this high affinity state, but direct in vivo evidence in support of this hypothesis is still lacking. Here, we show that platelets from mice lacking talin1 are unable to activate integrins in response to all known major platelet agonists while other cellular functions are still preserved. As a consequence, mice with talin-deficient platelets display a severe hemostatic defect and are completely resistant to arterial thrombosis. Collectively, these experiments demonstrate that talin is required for inside-out activation of platelet integrins in hemostasis and thrombosis.

scholarly journals Shear rate gradients promote a bi-phasic thrombus formation on weak adhesive proteins, such as fibrinogen in a VWF-dependent manner

Haematologica ◽  
2019 ◽  
Vol 105 (10) ◽  
pp. 2471-2483 ◽  
Author(s):  
Nicolas Receveur ◽  
Dmitry Nechipurenko ◽  
Yannick Knapp ◽  
Aleksandra Yakusheva ◽  
Eric Maurer ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Steady Flow ◽  
Thrombus Formation ◽  
Fiber Formation ◽  
Second Phase ◽  
Dependent Manner ◽  
Flow Acceleration ◽  
Adhesive Proteins

Blood flow profoundly varies throughout the vascular tree due to its pulsatile nature and to the complex vessel geometry. While thrombus formation has been extensively studied in vitro under steady flow, and in vivo under normal blood flow conditions, the impact of complex hemodynamics such as flow acceleration found in stenosed arteries has gained increased appreciation. We investigated the effect of flow acceleration, characterized by shear rate gradients, on the function of platelets adhering to fibrinogen, a plasma protein which plays a key role in hemostais and thrombosis. While we confirmed that under steady flow, fibrinogen only supports single platelet adhesion, we observed that under shear rate gradients, this surface becomes highly thrombogenic, supporting efficient platelet aggregation leading to occlusive thrombus formation. This shear rate gradient-driven thrombosis is biphasic with an initial step of slow platelet recruitment supported by direct plasma VWF adsorption to immobilized fibrinogen and followed by a second phase of explosive thrombosis initiated by VWF fiber formation on platelet monolayers. In vivo experiments confirmed that shear rate gradients accelerate thrombosis in a VWF-dependent manner. Together, this study characterizes a process of plasma VWF-dependent accelerated thrombosis on immobilized fibrinogen in the presence of shear rate gradients.

Reduced thrombus stability in mice lacking the α2A-adrenergic receptor

Blood ◽  
2006 ◽  
Vol 108 (2) ◽  
pp. 510-514 ◽  
Author(s):  
Miroslava Požgajová ◽  
Ulrich J. H. Sachs ◽  
Lutz Hein ◽  
Bernhard Nieswandt
Keyword(s):  
Blood Flow ◽  
Adrenergic Receptor ◽  
Thrombus Formation ◽  
Fold Increase ◽  
Wild Type ◽  
Perfusion Studies ◽  
G Protein Coupled ◽  
Deficient Mice

Platelet activation plays a central role in hemostasis and thrombosis. Many platelet agonists function through G-protein–coupled receptors. Epinephrine activates the α2A-adrenergic receptor (α2A) that couples to Gz in platelets. Although α2A was originally cloned from platelets, its role in thrombosis and hemostasis is still unclear. Through analysis of α2A-deficient mice, variable tail bleeding times were observed. In vitro, epinephrine potentiated activation/aggregation responses of wild-type but not α2A-deficient platelets as determined by flow cytometry and aggregometry, whereas perfusion studies showed no differences in platelet adhesion and thrombus formation on collagen. To test the in vivo relevance of α2A deficiency, mice were subjected to 3 different thrombosis models. As expected, α2A-deficient mice were largely protected from lethal pulmonary thromboembolism induced by the infusion of collagen/epinephrine. In a model of FeCl3-induced injury in mesenteric arterioles, α2A–/– mice displayed a 2-fold increase in embolus formation, suggesting thrombus instability. In a third model, the aorta was mechanically injured, and blood flow was measured with an ultrasonic flow probe. In wild-type mice, all vessels occluded irreversibly, whereas in 24% of α2A-deficient mice, the initially formed thrombi embolized and blood flow was reestablished. These results demonstrate that α2A plays a significant role in thrombus stabilization.

FcγRIIa Enhances Thrombus Growth in Vitro and in Vivo

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 191-191
Author(s):  
Huiying Zhi ◽  
Lubica Rauova ◽  
Vincent M Hayes ◽  
Jimmy Crockett ◽  
Cunji Gao ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Platelet Function ◽  
Whole Blood ◽  
Thrombus Formation ◽  
Flow Chamber ◽  
Wild Type ◽  
Integrin Αiibβ3 ◽  
Platelet Thrombus

Abstract Abstract 191 Outside-in signal transduction is one of several autocrine amplification loops that platelets employ to stabilize and consolidate a platelet thrombus following their adhesion to each other or to components of the extracellular matrix. Binding of soluble fibrinogen to activated integrin αIIbβ3 on the platelet surface, or binding of αIIbβ3 to platelet-immobilized fibrinogen, initiates an outside-in signaling cascade that results in the activation of integrin β3-associated Src family kinases, which in turn phosphorylate tyrosine residues within the cytoplasmic domain of the immunoreceptor tyrosine-based activation motif (ITAM)-containing adaptor protein, FcγRIIa. “Activation” of FcγRIIa sets off a cascade of events that result in the assembly and activation of other key signaling intermediates, including the tyrosine kinase Syk and phospholipase Cγ2(PLCγ2), through its lipase activity, generates lipid products that support a multitude of cellular activation responses, including cytoskeletal rearrangements leading to platelet shape change and spreading, secretion of platelet granules, and activation of additional cell surface integrins. We have previously shown that either antibody-mediated or genetic disruption of the functional interaction between integrin αIIbβ3 and FcγRIIa blocks tyrosine phosphorylation of FcγRIIa, Syk, and PLCγ2, and inhibits platelet spreading on immobilized fibrinogen. The physiological significance of FcγRIIa in supporting platelet thrombus formation, however, remains unknown. To further explore the importance of FcγRIIa in platelet function, we compared the relative ability of wild-type FcγRIIa-negative and transgenic FcγRIIa-positive (FcγRIIaTGN) murine platelets to support thrombosis and hemostasis in a number of well-accepted models of platelet function. FcγRIIaTGN platelets exhibited increased tyrosine phosphorylation of Syk and PLCγ2 and increased spreading upon interaction with immobilized fibrinogen. FcγRIIaTGN platelets also retracted a fibrin clot faster than did wild-type FcγRIIa-negative platelets. When anti-coagulated whole blood was perfused over a collagen-coated flow chamber under conditions of arterial shear, the rate and extent of adhesion, aggregation, and thrombus formation was significantly increased for FcγRIIaTGN platelets compared to their wild-type murine counterparts. Addition of Fab fragments specific for FcγRIIa to whole blood derived from either humans or FcγRIIaTGN mice strongly inhibited thrombus formation in the arterial in vitro flow chamber assay. Finally, to examine the in vivo relevance of FcγRIIa, mice were subjected to two models of vascular injury: electrolytic injury of the femoral vein and laser injury of cremaster arterioles. In both in vivo models, FcγRIIaTGN mice displayed increased thrombus formation compared with their wild-type, FcγRIIa-negative counterparts. Taken together, these data establish FcγRIIa as a physiologically-important functional conduit for αIIbβ3–mediated outside-in signaling, and suggest that modulating the activity of this novel integrin/ITAM pair might be effective in controlling thrombosis. Disclosures: No relevant conflicts of interest to declare.

FXII Promotes Coagulation in a FXI and FIX Independent Manner

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3362-3362 ◽  
Author(s):  
Cristina Puy ◽  
Zoë C Wong ◽  
Erik I Tucker ◽  
Andras Gruber ◽  
David Gailani ◽  
...  
Keyword(s):  
Thrombus Formation ◽  
Arterial Occlusion ◽  
Coagulation Factors ◽  
Independent Manner ◽  
Procoagulant Effect ◽  
Antithrombotic Effects ◽  
Recalcification Time ◽  
Deficient Mice

Abstract Abstract 3362 Activation of coagulation factors (F) XII and XI support thrombogenesis through multiple pathways. FXII-deficient mice are more resistant to FeCl3-induced arterial occlusion than either FIX or FXI deficient mice, suggesting that the resistance of FXII-deficient mice to experimental thrombosis is not completely explained by the FXII-FXI-FIX pathway, suggesting the existence of a pathological FXII by-pass, in vivo. The APTT of FXII deficient plasma is longer than the APTT of FXI, FIX, or FX deficient plasmas. We found that addition of 150 nM activated FXII (FXIIa) decreased the recalcification time of FXI or FIX-deficient plasma by up to 85%. In a purified system FXIIa could activate prothrombin but not FX. Addition of rivaroxaban, a FXa inhibitor, to FXI or FIX-deficient plasma blocked the observed procoagulant effect of FXIIa, suggesting that FXIIa promotes the activation of FX independent of FXI or FIX, but the ability of FXIIa alone to induce coagulation is insufficient in plasma, in vitro. Addition of long polyphosphate (polyP), typically found in bacteria, but not short polyP, which is secreted by activated platelets, decreased the recalcification time of FXI or FIX-deficient plasma. The presence of either corn trypsin inhibitor (CTI), that inhibits FXIIa, or rivaroxaban blocked the procoagulant effect of long polyP, suggesting that the activation of FXII by long polyP promotes coagulation in an FXI- and FIX-independent manner. Addition of CTI or an antibody that inhibits FIX activation by FXIa, but not addition of an antibody that inhibits activation of FXI by FXIIa, increased the time of occlusive thrombus formation in recalcified human blood that was driven through collagen and tissue factor (TF)-coated capillary tubes, consistent with the thrombogenic roles of FXIIa and feedback activation of FXI. Only CTI inhibited the prothrombotic effect of long polyP, also suggesting that FXIIa could be thrombogenic independent of FXI and FIX. In summary, we propose that pathological FXII activation, e.g., by foreign surfaces or long polyP, is thrombogenic both in FXI/FIX-dependent and -independent manners. Provided that FXII has no significant physiological function in humans, our data support the hypothesis that inhibition of FXII activity or activation may have safe antithrombotic effects. Disclosures: Morrissey: No organization, but the speaker is co-inventor on pending patent applications on the medical uses of polyphosphate: Patents & Royalties.

Determination of microvascular flow pattern formation in vivo

2000 ◽  
Vol 278 (4) ◽  
pp. H1142-H1152 ◽  
Author(s):  
Kurt Osterloh ◽  
Peter Gaehtgens ◽  
Axel R. Pries
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Power Spectra ◽  
Flow Patterns ◽  
Microvascular Blood Flow ◽  
Pattern Size ◽  
Branching Points ◽  
Glass Tubes

Blood flow in microvessels differs significantly from that of red blood cells (RBC) flowing through long, straight glass tubes in vitro. The in vivo situation is characterized by the presence of plasma favoring aggregation, by the irregular geometry of vessel segments, and by frequent branching points. Here, a method is presented to characterize flow patterns in microvascular blood flow during intravital microscopy based on Fourier analysis of recorded light intensity patterns. The interpretation of the resulting power spectra in terms of pattern size distribution was validated by model experiments employing artificial textures and by reverse transformation of idealized spectra. The determined size of RBC flow patterns in microvessels ranged from ∼8 μm in capillaries to ∼14 μm in vessels of >30 μm. With increasing shear rate above ∼100 s−1 pattern size increased, possibly reflecting formation of short-lived flow clusters. Below ∼100 s−1 an increase of pattern size with decreasing shear rate was found in experiments using local occlusion and treatment with high-molecular-weight dextran, suggesting the formation of aggregates. The dynamic process of generation and destruction of RBC flow patterns could well contribute to flow resistance in vivo in peripheral vascular beds.

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