Estimation of internal filtration flow rate in high-flux dialyzers by Doppler ultrasonography.

Several types of dialyzer with enhanced internal filtration have been introduced for clinical application as a means of improving the efficiency of solute removal, and the enhanced internal filtration in these dialyzers has increased the convective transport of the solute besides the diffusive transport. The internal filtration flow rates (Q(IF)) of the dialyzer, however, have never been evaluated precisely. In this study, blood flow velocity in a cross-sectional plane of a dialyzer was measured by pulse Doppler ultrasonography to evaluate Q(IF). An in vitro study using bovine blood was carried out to determine the local blood flow velocity profile with a probe slider that enables the probe to move in parallel along a dialyzer. A good correlation between observed blood velocity (u(B)(0)) and blood flow rate (Q(B)(0)) at the inlet portion of the dialyzer was obtained during the in vitro study. Blood flow rate profiles along the dialyzer (Q(B)(z)) could be estimated from the product of blood velocity u(B)(z) and the total cross-sectional area of the blood flow path (S(B)) of the hollow fibers. The maximum internal filtration flow rate value (Q(IF-Max)) was estimated as Q(B)(0) - [Q(B)(z)](Min), where [Q(B)(z)](Min) is the minimum value of Q(B)(z). The Doppler ultrasonography described in this paper is a useful method for bedside monitoring of Q( IF) in several dialyzers, because it is noninvasive to the patient and produces reliable data with higher reproducibility.