Shear induced platelet activation

Circulating blood elements encounter a range of fluid mechanical shearing forces which result from the variable flow conditions which occur normally in the vasculature, from disease processes, or from the implantation of medical devices (e.g. heart valves). This study will attempt to determine whether shear forces alone can directly produce platelet activation. Non-anticoagulated and anticoagulated human and baboon whole blood samples were evaluated under a wide range of shearing conditions in a simple test in which blood samples were perfused through siliconized stainless steel tubes of different length and diameter. Hematologic assays and platelet flow cytometry were performed on the perfusates. Platelet activation was negligible, except for very modest binding of annexin V to platelet phospholipids which may be expressed during platelet activation. At shear levels above 400,000 s^-1, severe hemolysis was observed. In conclusion, shear forces alone, generated in a tubular geometry, did not produce significant platelet activation