Wyniki wyszukiwania - BazTech

1

Dialysis therapies: Investigation of transport and regulatory processes using mathematical modelling

Pstras Leszek, Stachowska-Pietka Joanna, Debowska Malgorzata, Pietribiasi Mauro, Poleszczuk Jan, Waniewski Jacek

Biocybernetics and Biomedical Engineering

|

2022

|

Vol. 42, no. 1

60--78

EN

Haemodialysis (HD) and peritoneal dialysis (PD) are the main kidney replacement therapies for patients with end-stage renal disease. Both of these life-sustaining therapies replace the key functions of the failing kidneys, i.e. the removal of the excess body water and waste products of metabolism as well as the restoration of fluid-electrolyte and acid-base balance. The dialysis-induced multi-scale transport and regulatory processes are complex and difficult to analyse or predict without the use of mathematical and computational models. Here, following a brief introduction to renal replacement therapies, we present an overview of the most important aspects and challenges of HD and PD, indicating the types and examples of mathematical models that are used to study or optimize these therapies. We discuss various compartmental models used for the study of intra- and interdialytic fluid and solute kinetics as well as distributed models of water and solute transport taking place across the peritoneal tissue or in the dialyzer. We also discuss models related to blood volume changes and cardiovascular stability during HD, including models of the thermal balance, likely related to intradialytic hypotension. A short overview of models of acid-base equilibration during HD and mineral metabolism in dialysis patients is also provided, along with a brief outline of models related to blood flow in arteriovenous fistulas and cardiovascular adaptations following the fistula creation. Finally, we discuss the model-based methods of assessment of dialysis adequacy in both HD and PD.

2

Modeling acid-base transport in hemodialyzers

Pietribiasi Mauro, Leypoldt John K.

Biocybernetics and Biomedical Engineering

|

2021

|

Vol. 41, no. 3

1150--1161

EN

One important objective of the hemodialysis treatment is the neutralization of interdialytic acid generation by transport of bicarbonate and other buffer bases from dialysis fluid to the patient via the hemodialyzer. Quantification of solute transport in hemodialyzers, in general, employs the concept of dialysance, a parameter that is often constant for given flow conditions, smaller than both the blood and dialysate flow rates, and independent of the solute concentration difference between blood and dialysate. This approach has been applied to bicarbonate transport in hemodialyzers, but such an approach neglects the transport of dissolved carbon dioxide (CO2) between dialysate and plasma, chemical equilibrium between bicarbonate and CO2, and other acid-base chemical reactions within blood. We describe a novel, one-dimensional model of bicarbonate and CO2 transport in hemodialyzers. The model equations were solved numerically and fitted to published data to estimate mass transfer-area coefficients for the relevant chemical species. Base excess in blood was assumed constant in the hemodialyzer. Simulations were performed for a dialysate bicarbonate concentration of 32 mEq/L at constant blood and dialysate flow rates and different plasma bicarbonate concentrations at the inlet of the hemodialyzer, both with and without CO2 transport. In the latter case, the bicarbonate mass transfer-area coefficient was adjusted to achieve the same total carbon dioxide transport. Calculated dialysance for CO2 exceeded the blood flow rate due to its conversion from bicarbonate in the hemodialyzer, and all calculated dialysances varied with inlet plasma bicarbonate concentration. We concluded that acid-base transport in hemodialyzers cannot be universally characterized by dialysances that are always less than the blood flow rate and independent of the concentration difference between dialysate and blood.

3

Comparison of two single-solute models of potassium kinetics during hemodialysis

Pietribiasi Mauro, Waniewski Jacek, Zaluska Wojciech, Wójcik-Zaluska Alicia, Leypoldt John K.

Biocybernetics and Biomedical Engineering

|

2020

|

Vol. 40, no. 3

938--949

EN

Optimal potassium removal in hemodialysis (HD) is an important but difficult to achieve goal, influenced by numerous factors. Two types of single-solute mathematical models have been previously proposed to assess potassium kinetics in HD: pseudo-one compartment ( p1) and two-compartment models (2c). We compared these two models in simulating potassium kinetics during HD sessions with different treatment settings. After estimation of unknown parameters via fitting to clinical data during 4 h sessions with a dialysate potassium of 2.6 ± 0.6 mmol/L, the models were used to simulate 4 HD sessions for each patient, resulting from the combination of session length (4 h vs. 8 h) and potassium dialysate concentration (2.6 vs. 0 mmol/L). The simulated potassium concentration profiles were similar under different treatment conditions, and predicted potassium removal during the treatments was 77 ± 24 mmol with the standard settings; both increases in session length and potassium dialysate to plasma concentration gradient resulted in a significant increase in potassium removed. Both models indicated similar minimum values of dialysate potassium concentration required to avoid post-HD hypokalemia: 1.18 ± 0.66 mmol/L for 4 h HD and 1.71 ± 0.52 mmol/L for 8 h HD. The models described similar kinetics for potassium during different combinations of treatment settings. Total removal of potassium and minimum dialysate concentration to avoid post-HD hypokalemia, were predicted without significant differences by both models. Although no model has a clear advantage in terms of describing clinical data, our analyses suggest that 2c might offer a better trade-off between physiological accuracy and over-parametrization.