Abstract:Dialyzer clearanceKis usually presented asK=KO+ Tr Qu, whereQuis ultrafiltration rate,K0is clearance forQu– 0, andTris transmittance coefficient. Although a simple and accurate mathematical description ofKois widely used, only a somewhat inaccurate formula forTrthat predicts a linear relationship betweenTrandKohas been proposed before. In this study the detailed investigation ofTrusing a one–dimensional theory of a dialyzer is presented. In general, the application of a one–dimensional theory requires sophisticated numerical methods, but for small and middle molecular weight solutes an analytical formula forKcan be derived.Trpredicted by the developed theory in comparison toTrpredicted by the previous linear formula is higher for small molecular weight solutes and lower for middle and large molecular weight solutes. These theoretical results were confirmed in experiments carried out in vitro for hollow–fiber dialyzers and small molecular weight solutes (urea, creatinine, sodium, TcO4) as well as middle molecular weight solutes (vitam
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