title: Modelling Transcapillary Transport of Fluid and Proteins in Hemodialysis Patients.
abstract: BACKGROUND
  The kinetics of protein transport to and from the vascular compartment play a major role in the determination of fluid balance and plasma refilling during hemodialysis (HD) sessions. In this study we propose a whole-body mathematical model describing water and protein shifts across the capillary membrane during HD and compare its output to clinical data while evaluating the impact of choosing specific values for selected parameters.
  
  
  METHODS
  The model follows a two-compartment structure (vascular and interstitial space) and is based on balance equations of protein mass and water volume in each compartment. The capillary membrane was described according to the three-pore theory. Two transport parameters, the fractional contribution of large pores (αLP) and the total hydraulic conductivity (LpS) of the capillary membrane, were estimated from patient data. Changes in the intensity and direction of individual fluid and solute flows through each part of the transport system were analyzed in relation to the choice of different values of small pores radius and fractional conductivity, lymphatic sensitivity to hydraulic pressure, and steady-state interstitial-to-plasma protein concentration ratio.
  
  
  RESULTS
  The estimated values of LpS and αLP were respectively 10.0 ± 8.4 mL/min/mmHg (mean ± standard deviation) and 0.062 ± 0.041. The model was able to predict with good accuracy the profiles of plasma volume and serum total protein concentration in most of the patients (average root-mean-square deviation < 2% of the measured value).
  
  
  CONCLUSIONS
  The applied model provides a mechanistic interpretation of fluid transport processes induced by ultrafiltration during HD, using a minimum of tuned parameters and assumptions. The simulated values of individual flows through each kind of pore and lymphatic absorption rate yielded by the model may suggest answers to unsolved questions on the relative impact of these not-measurable quantities on total vascular refilling and fluid balance.
authors.affiliation: Institute of Biocybernetics and Biomedical Engineering, Warsaw, Poland.
authors.forename: Mauro
authors.initials: M
authors.lastname: Pietribiasi
authors.affiliation: Institute of Biocybernetics and Biomedical Engineering, Warsaw, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Waniewski
authors.affiliation: Department of Rehabilitation and Physiotherapy, Medical University of Lublin, Lublin, Poland.
authors.forename: Alicja
authors.initials: A
authors.lastname: Załuska
authors.affiliation: Department of Nephrology, Medical University of Lublin, Lublin, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Załuska
authors.affiliation: Baxter Novum and Renal Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Bengt
authors.initials: B
authors.lastname: Lindholm
mesh_terms: D001798:Blood Proteins / Q000378:metabolism*; D002199:Capillary Permeability; D003198:Computer Simulation; D045604:Extracellular Fluid / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D021381:Protein Transport; D006435:Renal Dialysis; D014462:Ultrafiltration; D014867:Water / Q000378:metabolism*; D014882:Water-Electrolyte Balance
chemical_list: D001798:Blood Proteins; D014867:Water