The effects of margination and red cell augmented platelet diffusivity on platelet adhesion in complex flow

The effects of platelet margination and enhanced platelet diffusivity, as induced by red blood cells, on the adhesion of platelets, were investigated for a range of haematocrits, under 2D axi-symmetric flow, simulating previous in vitro experiments [Microvasc. Res. 17 (1979), 238-262]. The effect of margination was incorporated via use of an elevated platelet inlet mass fraction, Phie, in a manner similar to that of Wootton [Ann. Biomed. Eng. 29 (2001), 321-329], and a shear and haematocrit dependent platelet diffusivity, according to the model presented by Zydney and Colton [Physico Chem. Hydrodyn. 10 (1988), 77-96] was used. A combination of the two models was required to simulate the deposition of platelets to a collagen coated surface, under the complex flow, which exhibited a recirculation zone and stagnation point. Results obtained showed qualitative agreement with in vitro results, for a range of haematocrits (11-50%), and also showed that the effects of margination were not linearly dependent on haematocrit. Agreement may be improved in future simulations by incorporating the effects of depleted cell concentrations in the vortex which have been observed previously [Phil. Trans. Roy. Soc. (Lond.) B279 (1977), 413-445]. It would also be advantageous to devise a full mathematical description for platelet margination effects as a function of shear rate and haematocrit and a description of the accompanying effect of apparent blood viscosity.