Bulk filtration through micropore membranes for analysing blood cell rheology in clinical research

The flow rate of suspensions of blood cells through micropore filters is widely used for assessing the deformability of red and white blood cells. Mathematical models have been described as a theoretical basis for the technique. There is conflicting data concerning the filterability of red cells in a number of disorders. Part of the confusion stems from the use of different models for various experimental systems and results being expressed in a variety of ways. Confusion also arises from the use of models, derived for studying red blood cells, for the analysis of mixed populations of blood cells e.g. blood filterability being equated with red blood cell deformability. Successful attempts to analyse the flow of heterogeneous populations of blood cells require the use of complex models which seem too daunting for routine clinical use. The current trend is to isolate cells and, as far as possible, work with a homogeneous preparation with allowance for a small degree of permanent pore occlusion. From the known properties of isolated cells, it is apparent that the analysis of the filtration of unfractionated blood cells can be reduced to a series of three relatively simple analyses of this type. The time may therefore be right to return to blood filtration for investigating the filterability of blood cells in clinical disorders of suspected microcirculatory flow.