Nondestructive evaluation by x-ray computed tomography of dialysate flow patterns in capillary dialyzers

It is hard to evaluate dialysate flow patterns inside the fiber bundle of capillary dialyzers. The current study describes a novel determination of dialysate flow by x-ray computed tomography. The authors did steady and nonsteady state tracer experiments with adipiodone to observe the dialysate flow pattern in capillary dialyzers held vertically and horizontally. The hollow fibers were filled with paraffin to avoid permeation of adipiodone from the dialysate to blood compartment. In steady state tracer experiments, adipiodone solution (50 vol%) was injected into the dialysate compartment at a flow rate of 1.5 ml/min. Horizontal sectional dialysate flow patterns were observed every 2 cm from the point of the adipiodone injection. Adipiodone solution flowed along broken and twisted fiber bundles at dialysate flow rates ranging from 200 to 600 ml/min. In nonsteady state tracer experiments, dialysate was switched from pure water to adipiodone solution by solenoid-controlled valves after a steady state was reached, and adipiodone solution (2.4 vol%) was infused into the dialysate compartment for 30 sec at a flow rate of 500 ml/min. Vertical sectional dialysate flow patterns were observed every 2 sec after the start of adipiodone infusion. Values for dialysate flow velocity at the outer and inner regions of the fiber bundle were 3.5 and 0.6 cm/sec for the CA-170, and 1.4 and 0.7 cm/sec for the HF-200 capillary dialyzer, respectively. This study demonstrates the usefulness of x-ray computed tomography in visually and quantitatively determining dialysate flow patterns in capillary dialyzers.