TWO-POOL VIRTUAL PHYSICAL SIMULATOR TO REPRODUCE FLUID AND MASS TRANSFER DURING DIALYSIS

Aim: Hemodialysis (hd) induces fast changes of fluid volumes and electrolyte concentrations in patients’ body compartments. The aim of this work is to develop a two-pool virtual patient physical simulator (tvps) reproducing intracorporeal transport phenomena during hd. Methods: the main function of the tvps is to replicate the patient intra- and extra-vascular compartments (ivc and evc). ivc is reproduced by a rigid reservoir and a set of semi-permeable hollow fibers, representing the large arterial and venous vessels and the capillary system respectively; evc is simulated by rigid reservoirs, connected to a compliance. the hollow fibers are arranged in ad-hoc designed modular filters, placed in the ivc. test fluids reproduces rheological properties, oncotic pressure (by using polygelin and dextran), electrolytes and catabolites contents of an uremic patient. A Gambro AK200 machine was used to test the TVPS, performing a 3.5 hours HD (average duration). Fluid samples were collected from TVPS at scheduled intervals to evaluate the IVC and EVC solutes concentrations, for comparison with clinical average data. Results: All the electrolytes and urea concentrations showed good agreement with clinical data (dextran: max shift 10%, polygelin: 20%). Plasmatic volume profile showed good correlation with clinical patterns, also replicating the plasma- refilling phenomenon. Conclusions: The tests proved the TVPS capable to reproduce fluid and mass transfer during HD. Such a system would be useful to characterize commercial or new dialyzers, accounting for the dynamic effects of mass transport induced by the patient-machine interaction.