Platelets
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Improved methods are needed to identify patients at risk for thrombotic or bleeding events. Free oscillation rheometry (FOR) is a technique that offers information on coagulation, based on contributions of all blood components, by measurement of clotting time and changes in clot elasticity. This is the first study that evaluates FOR parameters in subjects likely to represent hypercoagulability (pregnant women) and hypocoagulability (thrombocytopenic patients). ⋯ The elasticity was higher in late pregnancy compared to early pregnancy. Compared to the blood donors, the thrombocytopenic patients had lower elasticity, which was increased by a platelet transfusion, but there was no difference in clotting time. The results suggest that FOR can provide new information on the haemostatic status of patients at risk of thrombotic or bleeding events as well as information on the haemostatic effect of a platelet transfusion.
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Described 40 years ago as cell dust, microparticles (MPs) are now considered a key component in the haemostatic response. Owing to their plasma membrane reactivity, platelets are believed to constitute the main source of circulating procoagulant microparticles and behave as true sensors for the haemostatic response. Erythrocytes, leukocytes and endothelial cells are also able to shed MPs in the blood flow, their respective contribution varying with the pathophysiologic circumstances and extent of the cellular damage. ⋯ In specific pathophysiologic contents with elevated levels of circulating TF+-MPs, accessible TFPI at the MP surface would be overwhelmed. Beyond their procoagulant properties demonstrated in vitro, a number of pieces of evidence points to procoagulant MPs as efficient effectors in the haemostatic response, and as pathogenic markers of thrombotic disorders and vascular damage. This review will focus on the pathophysiological significance of platelet-derived MPs and their interaction with vascular cells.
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Platelet function and response to pharmacological inhibition are altered by cardiac surgery. For example, aggregation is increased early after aortic valve replacement (AVR) and platelet response to aspirin is often insufficient after coronary artery bypass grafting (CABG). We hypothesized that the effect of aspirin administration after cardiac surgery might be impaired due to platelet activation. ⋯ In conclusion, thromboxane formation increased after AVR but not after CABG. The antiplatelet effect of aspirin, therefore, may be impaired after CABG by increased platelet activity. An additional in vitro "resistance" of platelets was seen after both CABG and AVR.
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Thrombocytopenia is a common problem in critically ill patients, which is associated with increased mortality. Recently, Drotrecogin alfa (activated) (recombinant human activated protein C (APC)) was shown to reduce mortality in patients with severe sepsis. Only minimal effect of APC on coagulation markers was demonstrated. ⋯ In group APC-225, CD62P showed a non-significant decrease. This in vitro study demonstrates that therapeutic plasma concentrations of Drotrecogin alfa (activated) have neither influence on expression of platelet activation markers nor on platelet-granulocyte complexes in blood of volunteers and patients with severe sepsis. Thus, a direct drug-platelet interaction seems unlikely.
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We investigated the relationship between impedance platelet aggregometry (IPA) as measured by the Multiplate system and turbidimetric platelet aggregation (TPA) induced by ADP, arachidonic acid (AA), and collagen; blood cell counts; platelet function analyzer (PFA-100) closure times (CT), and von Willebrand factor (VWF) in 120 well-characterized healthy individuals. Pre-analytical and analytical conditions were standardized comprehensively. Analytical reliability of IPA and TPA and the influence of pre-analytical variables on assay results were also examined. ⋯ IPA results reflect interactions between platelets, red and white cells, while TPA does not. This explains discrepancies in associations of IPA and TPA with cell counts, time of day and blood donation. The clinical significance of IPA determined using the Multiplate device remains to be determined in studies on patients with platelet dysfunction and under treatment with antiplatelet agents.