A red cell deformation model for hemolysis in cross flow membrane plasmapheresis

Hemolysis is a serious potential problem in continuous flow membrane plasmapheresis, which is increasingly used for plasma collection and for therapeutic treatment of a variety of immunologic and metabolic disorders. Previously developed theory, which is based upon the notion that red cells hemolyze upon contact with the membrane, does not correctly predict experimental observations of the effects of transmembrane pressure drop, membrane pore size, and wall shear rate on hemolysis in this process. We propose that hemolysis occurs by deformation of red blood cells as they are forced into membrane pores. The cells hemolyze if the strain in the cell membrane caused by this deformation is sufficient to rupture the cell membrane. This strain is a function not only of the transmembrane pressure drop which forces the cells into the pores but also of the residence time for the cells in the pores, which is assumed to be a function of wall shear rate. Predictions of the model agree well with data. The model provides both a fundamental understanding of hemolysis and a rational basis for the design of improved plasmapheresis devices.