Rheophoresis--a broader concept of platelet dispersivity

Interactions among red cells and platelets in flowing blood result in significant dispersive motions of the platelets, which are commonly modelled by an effective diffusion coefficient. This paper examines an additional platelet flux, termed rheophoresis, to model platelet motions due to the gradient of hematocrit. Rheophoretic effects occur near walls because geometric exclusion and fluid mechanical repulsion of red cells create a hematocrit gradient there. Models using rheophoretic flux show that platelet concentration near walls is elevated; such models provide a consistent interpretation of available experimental data. Estimates show the coefficients for traditional effective diffusivity and the rheophoretic diffusivity have similar magnitudes. The effects of rheophoresis on axial development of platelet concentration profiles and on surface deposition are discussed.