Changes of Peritoneal Transport Parameters with Time on Dialysis: Assessment with Sequential Peritoneal Equilibration Test

2017 ◽  
Vol 40 (11) ◽  
pp. 595-601 ◽  
Author(s):  
Jacek Waniewski ◽  
Stefan Antosiewicz ◽  
Daniel Baczynski ◽  
Jan Poleszczuk ◽  
Mauro Pietribiasi ◽  
...  
Keyword(s):  
Solute Transport ◽  
Fluid Transport ◽  
Transport Processes ◽  
Model Parameters ◽  
Hydraulic Permeability ◽  
Transport Parameters ◽  
Peritoneal Equilibration Test ◽  
Transport Barrier ◽  
Pore Model ◽  
Peritoneal Transport

Background Sequential peritoneal equilibration test (sPET) is based on the consecutive performance of the peritoneal equilibration test (PET, 4-hour, glucose 2.27%) and the mini-PET (1-hour, glucose 3.86%), and the estimation of peritoneal transport parameters with the 2-pore model. It enables the assessment of the functional transport barrier for fluid and small solutes. The objective of this study was to check whether the estimated model parameters can serve as better and earlier indicators of the changes in the peritoneal transport characteristics than directly measured transport indices that depend on several transport processes. Methods 17 patients were examined using sPET twice with the interval of about 8 months (230 ± 60 days). Results There was no difference between the observational parameters measured in the 2 examinations. The indices for solute transport, but not net UF, were well correlated between the examinations. Among the estimated parameters, a significant decrease between the 2 examinations was found only for hydraulic permeability LpS, and osmotic conductance for glucose, whereas the other parameters remained unchanged. These fluid transport parameters did not correlate with D/P for creatinine, although the decrease in LpS values between the examinations was observed mostly for patients with low D/P for creatinine. Conclusions We conclude that changes in fluid transport parameters, hydraulic permeability and osmotic conductance for glucose, as assessed by the pore model, may precede the changes in small solute transport. The systematic assessment of fluid transport status needs specific clinical and mathematical tools beside the standard PET tests.

scholarly journals Peritoneal Fluid Transport rather than Peritoneal Solute Transport Associates with Dialysis Vintage and Age of Peritoneal Dialysis Patients

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Jacek Waniewski ◽  
Stefan Antosiewicz ◽  
Daniel Baczynski ◽  
Jan Poleszczuk ◽  
Mauro Pietribiasi ◽  
...  
Keyword(s):  
Peritoneal Dialysis ◽  
Solute Transport ◽  
Fluid Transport ◽  
Peritoneal Membrane ◽  
Transport Parameters ◽  
Patient Age ◽  
Pore Model ◽  
Peritoneal Transport ◽  
Patient Âgé ◽  
Dialysis Vintage

During peritoneal dialysis (PD), the peritoneal membrane undergoes ageing processes that affect its function. Here we analyzed associations of patient age and dialysis vintage with parameters of peritoneal transport of fluid and solutes, directly measured and estimated based on the pore model, for individual patients. Thirty-three patients (15 females; age 60 (21–87) years; median time on PD 19 (3–100) months) underwent sequential peritoneal equilibration test. Dialysis vintage and patient age did not correlate. Estimation of parameters of the two-pore model of peritoneal transport was performed. The estimated fluid transport parameters, including hydraulic permeability (LpS), fraction of ultrasmall pores (αu), osmotic conductance for glucose (OCG), and peritoneal absorption, were generally independent of solute transport parameters (diffusive mass transport parameters). Fluid transport parameters correlated whereas transport parameters for small solutes and proteins did not correlate with dialysis vintage and patient age. Although LpS and OCG were lower for older patients and those with long dialysis vintage,αuwas higher. Thus, fluid transport parameters—rather than solute transport parameters—are linked to dialysis vintage and patient age and should therefore be included when monitoring processes linked to ageing of the peritoneal membrane.

How Accurate is the Description of Transport Kinetics in Peritoneal Dialysis According to Different Versions of the Three-Pore Model?

2008 ◽  
Vol 28 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Jacek Waniewski ◽  
Malgorzata Debowska ◽  
Bengt Lindholm
Keyword(s):  
Peritoneal Dialysis ◽  
Solute Transport ◽  
Peritoneal Fluid ◽  
Dwell Time ◽  
Transport Kinetics ◽  
Transport Parameters ◽  
Pore Model ◽  
Peritoneal Transport ◽  
Endogenous Protein ◽  
Dialysate Volume

Objective The three-pore model of peritoneal transport is used extensively for modeling peritoneal fluid and solute transport, but the currently used versions include certain modifications of the transport parameters that have not been validated quantitatively versus detailed data on fluid and solute kinetics. The aim of this study was to evaluate different versions of the three-pore model. Method Detailed clinical peritoneal fluid and solute transport data were obtained from 40 peritoneal dwell studies in clinically stable continuous ambulatory peritoneal dialysis patients in whom the dialysate volume was measured using a macromolecular volume marker (RISA). Results Using a new version of the three-pore model with several adjusted transport parameters, good agreement between the measured and the simulated values of dialysate volume and concentrations of small solutes and RISA (but not of endogenous protein) versus dwell time was obtained; however, the predicted peritoneal absorption for longer than the investigated dwell time would be too high. Conclusion The three-pore model, with some adjustments proposed in this study, may be used for detailed description of peritoneal transport kinetics, but it should be pointed out that, even after these adjustments, it still does not provide the correct description of peritoneal fluid absorption and transport of macromolecules.

Mathematical Models for Peritoneal Transport Characteristics

1999 ◽  
Vol 19 (2_suppl) ◽  
pp. 193-201 ◽  
Author(s):  
Jacek Waniewski
Keyword(s):  
Mathematical Models ◽  
Peritoneal Cavity ◽  
Fluid Transport ◽  
Driving Forces ◽  
Experimental Studies ◽  
Theoretical Description ◽  
Distributed Model ◽  
Transport Parameters ◽  
Pore Model ◽  
Peritoneal Transport

Four mathematical models and for the description of peritoneal transport of fluid solutes are reviewed. The membrane model is usually applied for (1) separation of transport components, (2) formulation of the relationship between flow components and their driving forces, and (3) estimation of transport parameters. The three-pore model provides correct relationships between various transport parameters and demonstrates that the peritoneal membrane should be considered heteroporous. The extended threepore model discriminates between heteroporous capillary wall and tissue layer, which are assumed to be arranged in series; the model improves and modifies the results of the three-pore model. The distributed model includes all parameters involved in peritoneal transport and takes into account the real structure of the tissue with capillaries distributed at various distances from the surface of the tissue. How the distributed model may be applied for the evaluation of the possible impact of perfusion rate on peritoneal transport, as recently discussed for clinical and experimental studies, is demonstrated. The distributed model should provide theoretical bases for the application of other models as approximate and simplified descriptions of peritoneal transport. However, an unsolved problem is the theoretical description of bi-directional fluid transport, which includes ultrafiltration to the peritoneal cavity owing to the osmotic pressure of dialysis fluid and absorption out of the peritoneal cavity owing to hydrostatic pressure.

Fluid and Solute Transport in CAPD Patients before and after Permanent Loss of Ultrafiltration Capacity

2005 ◽  
Vol 28 (10) ◽  
pp. 976-984 ◽  
Author(s):  
J. Waniewski ◽  
D. Sobiecka ◽  
M. DĘbowska ◽  
O. Heimbürger ◽  
A. Werynski ◽  
...  
Keyword(s):  
Solute Transport ◽  
Absorption Rate ◽  
Fluid Absorption ◽  
Transport Parameters ◽  
Normal Range ◽  
Peritoneal Transport ◽  
High K ◽  
Before And After ◽  
Permanent Loss ◽  
High Fluid

Background Two major types of permanent loss of ultrafiltration capacity (UFC) were previously distinguished among patients treated with CAPD: 1) type HDR with high diffusive peritoneal transport rate of small solutes and low osmotic conductance, but with normal fluid absorption rate, and 2) type HAR with high fluid absorption rate, but with normal diffusive peritoneal transport rate of small solutes and normal osmotic conductance. However, the detailed pattern of changes in peritoneal transport parameters in patients developing loss of ultrafiltration capacity is not known. Objective Analysis of solute and fluid transport parameters in the same patient before and after UFC loss. Patients Seven CAPD patients who had undergone repeated dwell studies, which were carried out before and/or after the onset of UFC loss. Methods Dialysis fluids (2 L) with glucose or a mixture of amino acids as osmotic agent at three basic tonicities were applied during 6 hour dwell studies. Fluid and solute transport parameters were previously shown not to be affected by these dialysis solutions (except by hypertonic amino acid-based solution). Intraperitoneal dialysate volume and fluid absorption rate were assessed using radiolabeled human serum albumin (RISA). Osmotic conductance (aOS) was estimated by a mathematical model as ultrafiltration rate induced by unit osmolality gradient. Diffusive mass transport coefficients, KBD, for glucose, urea, and creatinine were estimated using the modified Babb-Randerson-Farrell model. Results Five patients had increased KBD for small solutes after the onset of UFC loss, and three of them had decreased aOS, whereas two patients had normal aOS. In one of them, aOS decreased with time after the onset of UFC loss with concomitant normalization of glucose absorption. In all studies of these five patients the fluid absorption rate was within the normal range. Two other patients had increased fluid absorption rate (about 5 ml/min), and one of them also had increased KBD for small solutes, in two consecutive dwell studies in each patient with the second study being carried out at 1 and 7 months respectively after the first one. In all four studies in these two patients, the aOS was within the normal range. The sodium dip during dialysis with 3.86% glucose-based solution was lost, not only among most patients with UFC loss related to reduced osmotic conductance, but also in patients with increased KBD. Conclusions The occurrence of two major types of UFC loss was confirmed. However, a case of a mixed type of UFC loss with high fluid absorption rate and high KBD for small solutes, but normal osmotic conductance, and with normalization of initially high KBD for small solutes, linked with decreasing initially normal osmotic conductance, was also found. As a reduced sodium dip with hypertonic glucose solution is not only seen in patients with reduced osmotic conductance, it cannot reliably be used as a single measure of decreased aquaporin function. Permanent ultrafiltration capacity loss may be a dynamic phenomenon with a variety of alterations in peritoneal transport characteristics.

On the change of transport parameters with dwell time during peritoneal dialysis

2020 ◽  
pp. 089686082097151
Author(s):  
Jacek Waniewski ◽  
Joanna Stachowska-Pietka ◽  
Bengt Lindholm
Keyword(s):  
Peritoneal Dialysis ◽  
Clinical Data ◽  
Dwell Time ◽  
Dialysis Fluid ◽  
Transport Parameters ◽  
Satisfactory Description ◽  
Pore Model ◽  
Vasodilatory Effect ◽  
Peritoneal Transport ◽  
Molecular Radius

The transitory change of fluid and solute transport parameters occurring during the initial phase of a peritoneal dialysis dwell is a well-documented phenomenon; however, its physiological interpretation is rather hypothetical and has been disputed. Two different explanations were proposed: (1) the prevailing view—supported by several experimental and clinical studies—is that a vasodilatory effect of dialysis fluid affects the capillary surface area available for dialysis, and (2) a recently presented alternative explanation is that the molecular radius of glucose increases due to the high glucose concentration in fresh dialysis fluid and that this change affects peritoneal transport parameters. The experimental bases for both phenomena are discussed as well as the problem of the accuracy necessary for a satisfactory description of clinical data when the three-pore model of peritoneal transport is applied. We show that the correction for the change of transport parameters with dwell time provides a better fit with clinical data when applying the three-pore model. Our conclusion is in favor of the traditional interpretation namely that the transitory change of transport parameters with dwell time during peritoneal dialysis is primarily due to the vasodilatory effect of dialysis fluids.

scholarly journals Spatial model of convective solute transport in brain extracellular space does not support a “glymphatic” mechanism

2016 ◽  
Vol 148 (6) ◽  
pp. 489-501 ◽  
Author(s):  
Byung-Ju Jin ◽  
Alex J. Smith ◽  
Alan S. Verkman
Keyword(s):  
Solute Transport ◽  
Water Permeability ◽  
Extracellular Space ◽  
Fluid Transport ◽  
Volume Fraction ◽  
Convective Transport ◽  
Solute Diffusion ◽  
Model Parameters ◽  
Pulsatile Pressure ◽  
Brain Extracellular Space

A “glymphatic system,” which involves convective fluid transport from para-arterial to paravenous cerebrospinal fluid through brain extracellular space (ECS), has been proposed to account for solute clearance in brain, and aquaporin-4 water channels in astrocyte endfeet may have a role in this process. Here, we investigate the major predictions of the glymphatic mechanism by modeling diffusive and convective transport in brain ECS and by solving the Navier–Stokes and convection–diffusion equations, using realistic ECS geometry for short-range transport between para-arterial and paravenous spaces. Major model parameters include para-arterial and paravenous pressures, ECS volume fraction, solute diffusion coefficient, and astrocyte foot-process water permeability. The model predicts solute accumulation and clearance from the ECS after a step change in solute concentration in para-arterial fluid. The principal and robust conclusions of the model are as follows: (a) significant convective transport requires a sustained pressure difference of several mmHg between the para-arterial and paravenous fluid and is not affected by pulsatile pressure fluctuations; (b) astrocyte endfoot water permeability does not substantially alter the rate of convective transport in ECS as the resistance to flow across endfeet is far greater than in the gaps surrounding them; and (c) diffusion (without convection) in the ECS is adequate to account for experimental transport studies in brain parenchyma. Therefore, our modeling results do not support a physiologically important role for local parenchymal convective flow in solute transport through brain ECS.

Peritoneal Fluid Transport in CAPD Patients with Different Transport Rates of Small Solutes

2004 ◽  
Vol 24 (3) ◽  
pp. 240-251 ◽  
Author(s):  
Danuta Sobiecka ◽  
Jacek Waniewski ◽  
Andrzej Weryński ◽  
Bengt Lindholm
Keyword(s):  
Peritoneal Dialysis ◽  
Solute Transport ◽  
Osmotic Pressure ◽  
Absorption Rate ◽  
Fluid Transport ◽  
Transport Coefficients ◽  
Dialysis Fluid ◽  
Transport Parameters ◽  
Ultrafiltration Rate ◽  
Small Solute

Background Continuous ambulatory peritoneal dialysis (CAPD) patients with high peritoneal solute transport rate often have inadequate peritoneal fluid transport. It is not known whether this inadequate fluid transport is due solely to a too rapid fall of osmotic pressure, or if the decreased effectiveness of fluid transport is also a contributing factor. Objective To analyze fluid transport parameters and the effectiveness of dialysis fluid osmotic pressure in the induction of fluid flow in CAPD patients with different small solute transport rates. Patients 44 CAPD patients were placed in low ( n = 6), low-average ( n = 13), high-average ( n = 19), and high ( n = 6) transport groups according to a modified peritoneal equilibration test (PET). Methods The study involved a 6-hour peritoneal dialysis dwell with 2 L 3.86% glucose dialysis fluid for each patient. Radioisotopically labeled serum albumin was added as a volume marker. The fluid transport parameters (osmotic conductance and fluid absorption rate) were estimated using three mathematical models of fluid transport: ( 1 ) Pyle model (model P), which describes ultrafiltration rate as an exponential function of time; ( 2 ) model OS, which is based on the linear relationship of ultrafiltration rate and overall osmolality gradient between dialysis fluid and blood; and ( 3 ) model G, which is based on the linear relationship between ultrafiltration rate and glucose concentration gradient between dialysis fluid and blood. Diffusive mass transport coefficients (KBD) for glucose, urea, creatinine, potassium, and sodium were estimated using the modified Babb–Randerson–Farrell model. Results The high transport group had significantly lower dialysate volume and glucose and osmolality gradients between dialysate and blood, but significantly higher KBD for small solutes compared with the other transport groups. Osmotic conductance, fluid absorption rate, and initial ultrafiltration rate did not differ among the transport groups for model OS and model P. Model G yielded unrealistic values of fluid transport parameters that differed from those estimated by models OS and P. The KBD values for small solutes were significantly different among the groups, and did not correlate with fluid transport parameters for model OS. Conclusion The difference in fluid transport between the different transport groups was due only to the differences in the rate of disappearance of the overall osmotic pressure of the dialysate, which was a combined result of the transport rate of glucose and other small solutes. Although the glucose gradient is the major factor influencing ultrafiltration rate, other solutes, such as urea, are also of importance. The counteractive effect of plasma small solutes on transcapillary ultrafiltration was found to be especially notable in low transport patients. Thus, glucose gradient alone should not be considered the only force that shapes the ultrafiltration profile during peritoneal dialysis. We did not find any correlations between diffusive mass transport coefficients for small solutes and fluid transport parameters such as osmotic conductance or fluid and volume marker absorption. We may thus conclude that the pathway(s) for fluid transport appears to be partly independent from the pathway(s) for small solute transport, which supports the hypothesis of different pore types for fluid and solute transport.

Distributed modeling of osmotically driven fluid transport in peritoneal dialysis: theoretical and computational investigations

2009 ◽  
Vol 296 (6) ◽  
pp. H1960-H1968 ◽  
Author(s):  
Jacek Waniewski ◽  
Joanna Stachowska-Pietka ◽  
Michael F. Flessner
Keyword(s):  
Peritoneal Dialysis ◽  
Fluid Transport ◽  
Present Report ◽  
Capillary Wall ◽  
Distributed Model ◽  
Hydraulic Permeability ◽  
Transport Parameters ◽  
Distributed Modeling ◽  
Dialysis Solution ◽  
Osmotic Agent

Based on a distributed model of peritoneal transport, in the present report, a mathematical theory is presented to explain how the osmotic agent in the peritoneal dialysis solution that penetrates tissue induces osmotically driven flux out of the tissue. The relationships between phenomenological transport parameters (hydraulic permeability and reflection coefficient) and the respective specific transport parameters for the tissue and the capillary wall are separately described. Closed formulas for steady-state flux across the peritoneal surface and for hydrostatic pressure at the opposite surface are obtained using an approximate description of the concentration profile of the osmotic agent within the tissue by exponential function. A case of experimental study with mannitol as the osmotic agent in the rat abdominal wall is shown to be well described by our theory and computer simulations and to validate the applied approximations. Furthermore, clinical dialysis with glucose as the osmotic agent is analyzed, and the effective transport rates and parameters are derived from the description of the tissue and capillary wall.

Investigating surface morphology and transport parameters of single fractures

2020 ◽  
Author(s):  
Sascha Frank ◽  
Thomas Heinze ◽  
Mona Ribbers ◽  
Stefan Wohnlich
Keyword(s):  
Fracture Surface ◽  
Surface Morphology ◽  
Transport Processes ◽  
Coarse Grained ◽  
Hydraulic Permeability ◽  
Transport Parameters ◽  
Flow And Transport ◽  
Fracture Surfaces ◽  
Depth Analysis ◽  
Surface Images

<p>In order to obtain a deeper understanding of flow and transport processes in fractures, experimental investigations and numerical modelling have been carried out focusing on the effects of fracture surface morphology. To determine a possible relationship between the roughness of fracture surfaces and hydraulic and transport parameters, two different types of sandstones has been investigated. The sandstones were a coarse-grained, inhomogeneous and strongly anisotropic Flechtinger sandstone (Bebertal, Germany) and a fine-grained, rather homogeneous, isotropic Remlinger sandstone (Würzburg, Germany).</p><p>The sandstones were first cored with a diameter of 100 mm and a height of 150 mm and split into individual fissures. The resulting fracture surfaces were scanned using a 3D scan and surface images were generated. These surface images were used to determine the Joint Roughness Coefficient (JRC) and other measures of roughness. The roughness has been characterized along 1D profiles in each direction. Mean values and spread have been calculated for each surface. The fracture surfaces are self-affine so that little variation along both surfaces has been determined. Both sandstone halves were then joined together and the reassembled fractured rock core was examined experimentally. Darcy and tracer tests were carried out for the investigations and hydraulic (permeability, fracture opening width) and transport parameters (flow velocity, dispersivity, dispersion coefficient) were derived from the results and compared with each other and with the surface roughness. For the Darcy experiments, the cores were clamped in a specially designed Darcy cell and calculations were done based on equations for the cubic law. The transport parameters were determined using a salt tracer and by evaluating the breakthrough curves, recorded by measuring the electrical conductivity, with the moment analysis.</p><p>First results show a very clear separation between Remlinger and Flechtinger sandstone. Thus, the finer-grained Remlinger cores show lower JRC than the coarser-grained Flechtinger, as expected. Further, the Flechtinger cores have larger aperture opening widths than the Remlinger cores. First comparisons show a tendency to higher dispersivity with higher JRC, and thus with the Flechtinger than in the case of the Remlinger cores. Though, in-depth analysis reveals that the JRC alone might not be sufficient to characterize transport processes along fractures, as anisotropy, as well as roughness variability along the fracture surface can influence flow and transport. Numerical modeling of flow paths across the fracture surface are used to relate experimental results with the flow pattern across the rough surface.</p>

Influence of the Preceding Dwell Time on the Peritoneal Equilibration Test with 3.86% Glucose Solution in Automated Peritoneal Dialysis

2010 ◽  
Vol 30 (1) ◽  
pp. 95-98 ◽  
Author(s):  
Trijntje Cnossen ◽  
Charles Beerenhout ◽  
Watske Smit ◽  
Constantijn Konings ◽  
Jeroen Kooman ◽  
...  
Keyword(s):  
Peritoneal Dialysis ◽  
Solute Transport ◽  
Dwell Time ◽  
Fluid Transport ◽  
Glucose Solution ◽  
Automated Peritoneal Dialysis ◽  
Peritoneal Equilibration Test ◽  
Sodium Sieving ◽  
Transport Type

ObjectiveThe peritoneal equilibration test (PET) using 3.86% glucose solution is preceded by a long dwell with 3.86% glucose solution. A point of concern in patients treated with automated peritoneal dialysis (APD) is the influence of the preceding short nightly dwells on the results of a standardized PET. The aim of the study was to compare net ultrafiltration, small solute transport, sodium sieving, and solute transport type between a PET preceded by a long night dwell and one preceded by short (APD) dwells.Patients and Methods13 stable APD patients (mean age 60 ± 15 years; mean duration of peritoneal dialysis 31 ± 15 months) underwent 2 PETs: 1 preceded by short nightly dwells (PET A) and 1 preceded by a long night dwell (PET B).ResultsBoth PETs were performed within a mean period of 8 (range 5 – 11) days. Mean total ultrafiltration of PET A was 626 ± 218 mL and PET B was 644 ± 223 mL (NS). The 4-hour results of both tests for dialysate-to-plasma (D/P) ratios of creatinine and urea, Dt/D0ratios of glucose, and the dip in D/P sodium (sodium sieving) were similar. Classification of transport categories was identical for 10 of 13 patients.ConclusionIn APD, the preceding dwell time of a 3.86% glucose PET does not influence fluid transport, solute transport, or transport type.

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