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Query: UMLS:C0020672 (hypothermia)
 17,327 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cold is supposed to be associated with alterations in blood coagulation and a pronounced risk for thrombosis. We studied the effect of clinically encountered systemic hypothermia on microvascular thrombosis in vivo and in vitro. Ferric chloride-induced microvascular thrombus formation was analyzed in cremaster muscle preparations from hypothermic mice. Additionally, flow cytometry and Western blot analysis was used to evaluate the effect of hypothermia on platelet activation. To test whether preceding hypothermia predisposes for enhanced thrombosis, experiments were repeated after hypothermia and rewarming to 37 degrees C. Control animals revealed complete occlusion of arterioles and venules after 742 +/- 150 and 824 +/- 172 s, respectively. Systemic hypothermia of 34 degrees C accelerated thrombus formation in arterioles and venules (279 +/- 120 and 376 +/- 121 s; P < 0.05 vs. 37 degrees C). This was further pronounced after cooling to 31 degrees C (163 +/- 57 and 281 +/- 71 s; P < 0.05 vs. 37 degrees C). Magnitude of thrombin receptor activating peptide (TRAP)-induced platelet activation increased with decreasing temperatures, as shown by 1.8- and 3.0-fold increases in mean fluorescence after PAC-1 binding to glycoprotein (GP)IIb-IIIa and 1.6- and 2.9-fold increases of fibrinogen binding on incubation at 34 degrees C and 31 degrees C. Additionally, tyrosine-specific protein phosphorylation in platelets was increased at hypothermic temperatures. In rewarmed animals, kinetics of thrombus formation were comparable to those in normothermic controls. Concomitantly, spontaneous and TRAP-enhanced GPIIb-IIIa activation did not differ between rewarmed platelets and those maintained continuously at 37 degrees C. Moderate systemic hypothermia accelerates microvascular thrombosis, which might be mediated by increased GPIIb-IIIa activation on platelets but does not cause predisposition with increased risk for microvascular thrombus formation after rewarming.
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PMID:Sustained hypothermia accelerates microvascular thrombus formation in mice. 1610 Feb 48

Deep Hypothermic Circulatory Arrest (DHCA) is employed during thoracic aortic and congenital heart surgery, and can induce postoperative neurological damage probably caused by microthrombembolism. Hypothermia has been reported to induce platelet activation and aggregation. The platelet activation marker P-selectin mediates binding of platelets to leukocytes. Tirofiban and eptifibatide, short-acting inhibitors of the platelet fibrinogen receptor GP IIb/IIIa, have recently been shown to protect platelet function without increasing bleeding during heart surgery using cardiopulmonary bypass. The aim of this study was to investigate the effect of tirofiban and eptifibatide on platelets and platelet-leukocyte interaction under DHCA conditions in vitro. Platelet aggregation, binding of the GP IIb/IIIa activation specific antibody PAC-1, P-selectin expression as well as monocyte and granulocyte content of aggregates were investigated in unstimulated and ADP-stimulated samples using flow cytometry. Tirofiban and eptifibatide inhibited massive platelet aggregation and PAC-1 binding which were induced by DHCA conditions. P-selectin expression was inhibited by tirofiban but increased by eptifibatide at hypothermia. Platelet-bound leukocytes were present in all samples. Eptifibatide increased granulocyte content of aggregates at hypothermia in ADP-stimulated samples. We conclude that under conditions of DHCA both tirofiban and eptifibatide inhibit platelet aggregation but have different effects on platelet P-selectin expression and platelet-leukocyte interaction. Application of a short-acting and non-activating GP IIb/IIIa inhibitor should be considered during DHCA in vivo to prevent occlusion of the microvasculature and subsequent organ damage.
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PMID:Glycoprotein IIb/IIIa inhibition reduces prothrombotic events under conditions of deep hypothermic circulatory arrest. 1611 94

We systematically evaluated the effects of test temperature and storage temperature on platelet aggregation using flow cytometry and impedance aggregometry. Aliquots of citrated whole blood from 27 healthy adult male volunteers were stored at 37 degrees C and 22 degrees C. Aliquots were subjected to impedance aggregometry in response to collagen, adenosine diphosphate, ristocetin, and arachidonic acid performed at 22 degrees C, 34 degrees C, 37 degrees C, and 40 degrees C. The expression of activated fibrinogen receptor was determined on adenosine diphosphate-activated platelets at 22 degrees C and 37 degrees C by whole blood flow cytometry using PAC-1 for fluorescent staining. Aggregation induced by collagen, ristocetin, and arachidonic acid was not significantly different at the test temperatures of 34 degrees C and 37 degrees C but was significantly impaired at 22 degrees C. In contrast, adenosine diphosphate-induced aggregation was significantly increased at both 34 degrees C and 22 degrees C. Hyperthermia exclusively impaired collagen-induced aggregation. Storage temperature of 22 degrees C exclusively enhanced adenosine diphosphate- and collagen-induced aggregation compared with storage at 37 degrees C. The binding of PAC-1 was enhanced at test temperatures below 37 degrees C. Prewarming the antibody above 22 degrees C significantly decreased binding. Our results suggest that mild hypothermic test conditions have no relevant effect, whereas profound hypothermia induces defects in adhesion, thromboxane generation, and activation. The pathomechanism for the increased response to adenosine diphosphate at mild and profound hypothermia remains unclear. Storage temperature considerably affects the aggregation response to the agonists adenosine diphosphate and collagen but not to arachidonic acid and ristocetin. Flow cytometry using the temperature-labile antibody PAC-1 fails to assess temperature effects on platelet aggregability.
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PMID:The effects of test temperature and storage temperature on platelet aggregation: a whole blood in vitro study. 1655 37