A mathematical model for simulation of solute transport within the patient-artificial kidney system

The advent of the Middle Molecule Theory of Uremic Toxicity has introduced the need for hemodialyzers capable of efficiently removing metabolites with molecular weights between 300 and 2000. The rate at which these solutes can be removed from the body depends not only upon the efficiency of the dialyzer, but also upon the ability of the metabolites to diffuse from innerbody compartments into the patient's blood stream. In an effort to characterize innerbody transport during hemodialysis, a multicompartmental patient-artificial kidney model has been developed. In vivo clinical data in the form of solute-plasma concentration decline measurements following an impulse IV injection of Dextran-1500 (1500 molecular weight dextran fraction) and Vitamin B-12 have been obtained. These data were used to determine model parameters in the form of compartmental volumes and intercompartmental mass transfer coefficients. Analysis of the dextran data indicated that two intracellular pools, the interstitial pool, and the plasma pool were involved in DX-1500 solute kinetics. Further analysis of the data yielded a transcapillary mass transfer coefficient of 502 ml/min and two transcellular coefficients of 141 and 7 ml/min. The Vitamin B-12 data produced a similar compartmental arrangement. A transcapillary mass transfer coefficient of 470 ml/min and two transcellular coefficients of 30 ml/min and 5 ml/min were obtained. The DX-1500 parameters were used to simulate various modes of dialysis. The model predicted that innerbody mass transfer barriers begin to limit solute removal even for moderate dialyzer clearances. In contrast to this, the model predicted that innerbody mass transfer has little effect on the dialysis of urea.