Surface and bulk effects on platelet adhesion and aggregation during simple (laminar) shear flow of whole blood.

This study attempts to clarify the role of the artificial surface and the fluid bulk on platelet adhesion and aggregation events during simple shear flow of whole blood. The experimental approach involved the shearing of fresh whole blood samples over the shear rate range of 720-5680 s-1, which corresponded to a shear stress maximum of about 150 dyn cm-2. Results on platelet adhesion, measured as surface coverage by platelets, and platelet aggregation, measured in terms of reduction in platelet count and adenosine diphosphate (ADP) release, were determined as a function of the surface to volume ratio (S/V); and artificial surface used. Both shear-induced platelet adhesion and platelet count reduction showed significant variation over the range of S/V employed. The ratios between the three different S/V values used in this system (10:6:4) were about the same as the ratio of the shear rate-averaged results obtained. Also, for shear-induced hemolysis, an increase in the release of hemoglobin from red blood cells was found as S/V was increased, again with ratios between the shear rate-averaged values similar to the ratio of S/V values employed. The shear-induced release of ADP, presumably from platelets and from red blood cells indicated a different dependence of ADP release on S/V than was observed for the other parameters reported. Irreversible platelet aggregation was expected to occur because the amount of ADP that was released as a result of the shear was substantial. Models proposed to explain the experimental results were found to support a surface-controlled mechanism.