Two-pool physical simulator of the inter-compartmental mass transfer during dialysis

A two-pool simulator of fluid and mass transfer among patient body compartments during hemodialysis (HD) was developed to characterize commercial dialyzers taking into account dynamic mass transfer effects. Materials and Methods: The two-pool simulator replicates intra- and extra-vascular compartments: the former by means of a rigid reservoir and a set of semi permeable hollow fibers, the latter by means of a compliant reservoir. The simulator design was optimized (in terms of fiber number, reservoir dimensions, etc.) by an ad hoc developed computational model. The set-up was then tested by simulating HD procedures with commercial filters. Blood samples were withdrawn from the simulator to evaluate urea and electrolytes (Na, Ca, Cl-, Mg, K) concentration. Intra- and extra-vascular volumes were directly monitored on the set-up. The experimental results were compared with clinically measured data. Results: All electrolytes (except K) and urea concentrations showed good agreement with the clinical data (maximum shift 11%). K concentration instead showed shifts of nearly 22%, probably due to the non replicated active mass transfer through the cellular membrane. Plasmatic volume profile showed good correlation with clinical patterns (0,24% shift) despite the tangled ultrafiltration rate setting on the simulator. Conclusions: The patient simulator satisfactorily reproduced electrolytes and volume profiles during a simulated HD thus showing reliability in testing dialyzers dynamic response. The device accuracy can be improved by reproducing active mass transfer through the cellular membrane as well as defining easier procedures to set ultrafiltration rate.