Impact of convective transport on dialyzer clearance.

The results of predictions of three mathematical models used to describe the impact of convective flow on dialyzer clearance are presented. These models are based on the ordinary differential equations, which describe changes of solute concentration and solute and fluid flows along the module length. One of the models takes into consideration the existence of the boundary layers on both sides of the membrane wall, by including in the equations two parameters kB and kD, which describe mass transport coefficients in blood and dialysate, respectively. In the second model, the boundary layers are included in one lumped membrane permeability parameter. The diffusive membrane permeability was calculated from pure diffusive clearance, which was taken from experimental results. In the third model, a linear dependence of transmittance coefficient and ultrafiltration flow was proposed. The theoretical results were compared with data obtained in experiments carried out in vitro with four types of high-flux hollow-fiber dialyzers. The comparisons demonstrate that the first two models are of similar accuracy and the third model is not suitable for small solutes.