Estimation of Internal Filtration Flow Rate in a Dialyzer by a Doppler Ultrasonography

Several types of dialyzers with enhanced internal filtration have been introduced in order to increase solute clearance, especially in relatively larger molecular solutes. In these dialyzers, enhanced internal filtration increased convective transport of the solute in addition to diffusive transport. The internal filtration flow rate (QIF) has not, however, been measured in clinical situations, because none of monitoring techniques can measure this value. Herein, the QIF value was estimated during an experimental and an analytical study. Namely, we measured blood flow velocity in a cross-sectional plane of the dialyzer by pulse Doppler ultrasonography. An in vitro study with bovine blood was carried out to determine the local blood flow velocity profile with a newly designed probe slider that enables parallel movement of the probe along the dialyzer. Furthermore, an analytical model was newly introduced to calculate changes in flow rate and pressure of blood and dialysate streams and solute concentrations along the dialyzer. The QIF value could be estimated by a simulation analysis to the experimental data using the analytical model.