Hydraulic resistance of red cell beds in an unstirred filtration cell

A stagnant batch filtration system, in which saline is filtered through an unstirred bed of red cells at constant pressure, was employed to study the hydraulic permeability of red cell beds as well as the extent of cellular blockage of membrane pores. Since red cells are highly deformable, the compressibility of the cell bed was characterized by porosity measurements in centrifuged cell beds. Red cell deformation was also examined by microscopic observation of the cell bed fixed during filtration. Photomicrographs provided evidence that the red blood cells deform into a hexagonal close-packed structure. A simple two-dimensional model for cell bed compressibility developed on the basis of this observation was in good agreement with porosity data taken in the centrifugal system. Filtration data were analyzed using an integrated form of Darcy's law which permits the effects of cell bed hydraulic resistance of pore blockage to be evaluated separately. Functional relationships between hydraulic permeability, porosity, and compressive pressure were developed which can be incorporated into a detailed model for the filtrate flux in cross-flow microfiltration of red cell suspensions.