Fundamentals and application of differential filtration

The fractionation of macrosolute mixtures into classes of graded molecular sizes is the most difficult and, at the same time, most desirable membrane moderated process, according to W.F. Blatt. The major problems originate from concentration polarization, pore plugging, and membrane fouling. Up until now there has been no comprehensive theory that describes these filtration effects satisfactorily. Thus, all accomplishments of differential filtration techniques are based mainly on empirical knowledge.

According to concentration polarization phenomena, increasing membrane wall concentrations of rejected macromolecules superimpose an additional membrane resistance. This dynamically formed “hybrid membrane” may govern the filtration process, exerting a dual effect upon hydraulic and solute permeability.

Experience obtained by studying the physics of differential filtration guided us to develop a system using currently available artificial membranes for clinical application. This system uses membrane modules with a nominal cutoff of 0.6 mega Dalton, which enables the separation of macroproteins out of the spectrum of plasma proteins. Thus, this system can be applied for the hemapheretic treatment of hypercholesterolemia with excessively high levels of low density lipoprotein (LDL).

This overview contains some basic principles of differential filtration and the data of its clinical use. Clinical observations as to regression of atherosclerotic lesions are not included, but are intended for separate publication.