High shear-induced platelet activation and inactivation: the importance of methodology.

High shear platelet activation may be conveniently studied by forcing blood through a fine filter in the filterometer. To achieve haemostasis in vivo platelets are activated. When haemostasis is achieved, inactivation must follow. In the filterometer, activation occurs with filter blocking (first phase) and after 100s inactivation ('rebleeding') may occur (second phase). We report the effect of different pressures, temperatures, incubation times, anticoagulants and aspirin in this system. Most 'rebleeding' occurred in citrate, followed by native blood, r-hirudin and low-molecular-weight heparin. Unfractionated heparin inhibited 'rebleeding' whereas aspirin potentiated it. These and other findings are technically and clinically relevant and contribute to an understanding of the mechanisms involved in 'rebleeding' and hence perhaps in thrombogenesis.