Hollow fiber shape alters solute clearances in high flux hemodialyzers

The mass transfer properties of hemodialyzers containing hollow fiber membranes are known to be influenced by membrane chemical composition, surface area, and pore size; however, the effects of hollow fiber shape (or configuration) and packing density within the dialyzer housing have not been well characterized. We determined, both in vitro and ex vivo (clinical), solute clearances and mass transfer-area coefficients (K(O)A) for high flux dialyzers containing polysulfone hollow fibers of identical chemical composition but different shapes. Hemoflow F80A (1.8 m(2) of membrane surface area) dialyzers contained hollow fibers with a conventional shape, but Optiflux F180A (1.8 m(2)), F200A (2.0 m(2)), and F200NR (2.0 m(2)) dialyzers contained hollow fibers with a wavy shape. Clearances and K(O)A values determined in vitro for urea and creatinine increased with increasing dialysate flow rate and were higher for Optiflux F180A and F200A dialyzers than for Hemoflow F80A dialyzers. In vitro clearances for lysozyme and myoglobin were also higher for Optiflux F180A and F200A dialyzers than for Hemoflow F80A dialyzers, suggesting that a wavy hollow fiber shape increases mass transfer by increasing effective membrane surface area, conceivably by altering dialysate flow patterns. Urea clearances and K(O)A values determined ex vivo were higher for Optiflux F200NR dialyzers than for Hemoflow F80A dialyzers, confirming that the in vitro results are applicable to clinical hemodialysis. These increases in mass transfer efficiency for dialyzers containing hollow fibers with a wavy shape are consistent with improved mass transfer within the dialysate compartment as evidenced by the manufacturer-reported dialysate pressure-flow relationships. We conclude that the mass transfer characteristics of high flux dialyzers can be altered by the shape of the hollow fibers.