title: Concomitant bidirectional transport during peritoneal dialysis can be explained by a structured interstitium.
abstract: Clinical and animal studies suggest that peritoneal absorption of fluid and protein from dialysate to peritoneal tissue, and to blood and lymph circulation, occurs concomitantly with opposite flows of fluid and protein, i.e., from blood to dialysate. However, until now a theoretical explanation of this phenomenon has been lacking. A two-phase distributed model is proposed to explain the bidirectional, concomitant transport of fluid, albumin and glucose through the peritoneal transport system (PTS) during peritoneal dialysis. The interstitium of this tissue is described as an expandable two-phase structure with phase F (water-rich, colloid-poor region) and phase C (water-poor, colloid-rich region) with fluid and solute exchange between them. A low fraction of phase F is assumed in the intact tissue, which can be significantly increased under the influence of hydrostatic pressure and tissue hydration. The capillary wall is described using the three-pore model, and the conditions in the peritoneal cavity are assumed commencing 3 min after the infusion of glucose 3.86% dialysis fluid. Computer simulations demonstrate that peritoneal absorption of fluid into the tissue, which occurs via phase F at the rate of 1.8 ml/min, increases substantially the interstitial pressure and tissue hydration in both phases close to the peritoneal cavity, whereas the glucose-induced ultrafiltration from blood occurs via phase C at the rate of 15 ml/min. The proposed model delineating the phenomenon of concomitant bidirectional transport through PTS is based on a two-phase structure of the interstitium and provides results in agreement with clinical and experimental data.
authors.affiliation: Nalecz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Warsaw, Poland; jstachowska@ibib.waw.pl.
authors.forename: Joanna
authors.initials: J
authors.lastname: Stachowska-Pietka
authors.affiliation: Nalecz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Warsaw, Poland;
authors.forename: Jacek
authors.initials: J
authors.lastname: Waniewski
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland; and.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Flessner
authors.affiliation: Divisions of Renal Medicine and Baxter Novum, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Bengt
authors.initials: B
authors.lastname: Lindholm
mesh_terms: D000818:Animals; D001692:Biological Transport; D001786:Blood Glucose / Q000378:metabolism; D002196:Capillaries / Q000378:metabolism; D002199:Capillary Permeability; D003198:Computer Simulation; D015314:Dialysis Solutions / Q000378:metabolism*; D004058:Diffusion; D006801:Humans; D006874:Hydrostatic Pressure; D007700:Kinetics; D008954:Models, Biological; D009997:Osmotic Pressure; D065629:Peritoneal Absorption; D010530:Peritoneal Dialysis; D010537:Peritoneum / Q000098:blood supply* / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D015314:Dialysis Solutions; D012709:Serum Albumin
keywords: diffusion and convection; distributed model; peritoneal transport; tissue transport; two phases