Affiliations: Institute of Physiology, Medical University of Graz, Graz, Austria | Nephrology Section, Department of Internal Medicine, Ghent University Hospital, Gent, Belgium
Note: [] Corresponding author: Daniel Schneditz, Ph.D., Institute of Physiology, Center for Physiologic Medicine, Medical University of Graz, Harrachgasse 21/5, 8010 Graz, Austria. Tel.: +43 316 380 4269; Fax: +43 316 380 9630; E-mail: [email protected]
Abstract: It was the aim to examine the fluid flow in blood and dialysate compartments of highly permeable hollow fiber dialyzers where internal filtration contributes to solute removal but where excessive filtration bears a risk of cell activation and damage. Flow characteristics of high- (HF) and low-flux (LF) dialyzers were studied in lab-bench experiments using whole bovine blood. Measurements obtained under different operating conditions and under zero net ultrafiltration were compared to theoretical calculations obtained from a mathematical model. Experimental resistances in the blood compartment were within ±2% of those calculated from the model when dialysate was used as a test fluid. With whole blood, the experimental resistances in the blood compartment were only 81.8 ± 2.8% and 83.7 ± 4.3% of those calculated for the LF and HF dialyzer, respectively. Surprisingly, measured blood flow resistance slightly but significantly decreased with increasing flow rate (p < 0.001). Mathematical modeling confirmed this decrease both in LF and HF dialyzers which was accompanied by a concomitant decrease in internal filtration fraction, while overall internal filtration increased. The increase in internal filtration when increasing blood flow is associated with a beneficial reduction in internal filtration fraction. Concerns of increased hemoconcentration when increasing blood flow therefore appear to be unwarranted.
