Dialysate flow distribution in hollow fiber hemodialyzers with different dialysate pathway configurations

The efficiency of a hemodialyzer is largely dependent on ifs ability to facilitate diffusion, since this is the main mechanism by which small solutes are removed. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. The objective of the paper was to study the impact of different dialysate compartment designs on dialysate flow distribution and urea clearances. Eighteen hollow fiber 1.3 m(2) hemodialyzers were studied, 6 each of 3 designs: Type A - standard fiber bundle (PAN 65DX Asahi Medical, Tokyo, Japan), Type B - spacing filaments external to the fibers (PAN 65SF Asahi Medical, Tokyo, Japan), Type C - fibers waved to give Moire structure (FB130 Nissho-Nipro, Osaka, Japan). In vitro studies: 3 dialyzers of each type were studied following dye injection into the dialysate compartment. Dynamic sequential imaging of longitudinal sections of the dialyzer were undertaken, using a new generation helical CT scanner (X-Press/HS1 Toshiba Corporation, Tokyo, Japan). In vivo studies: 3 dialyzers of each type were studied, in randomized sequence, in 3 different patients under standardized dialysis conditions. Blood- and dialysate-side urea clearances were measured at 30 and 150 minutes of treatment. Macroscopic and densitometrical analysis revealed that flow distribution was most homogeneous in the dialyzer with Moire structure (Type C) and least homogeneous in the standard dialyzer (Type A). Space yarns (Type B) gave an intermediate dialysate flow distribution. Significantly increased urea clearances (p<0.001) were seen with Types B and C, compared to the standard dialyzer. Type C (Moire) had the highest clearances although these were not significantly greater than Type B (space yarns). In conclusion, more homogeneous dialysate flow distribution and improved small solute clearances can be achieved by use of spacing yarns or waved (Moire structure) patterns of fiber packing in the dialyzer. These effects are achieved probably as a result of reduced dialysate channeling resulting in a lower degree of mismatch between blood and dialysate flows. The new radiological technique using the helical CT scanner allows detailed flow distribution analysis and has the potential for testing future modifications to dialyzer design.