Gel layer limited haemofiltration rates can be increased by vortex mixing.

Haemofiltration has been used since 1976 as an alternative to haemodialysis in the treatment of chronic renal failure (1). Ultrafiltration flow rates (UFR) from blood are slow and it has been observed that when blood or plasma is ultrafiltered using highly permeable membranes, the UFR reaches a maximum which is independent of trans-membrane pressure (delta Pm) (2). We have confirmed this result during steady flow through an ultrafilter employing polyacrylonitrile membrane (Rhône Poulenc AN 69) but have also shown that this maximum can be exceeded by a factor of eight in the same device when vortex mixing is induced by pulsing the blood flow over furrowed channels.