Modeling long-term solute transport in drained unsaturated zones

1992 ◽  
Vol 28 (10) ◽  
pp. 2799-2809 ◽  
Author(s):  
Hesham Kandil ◽  
Cass T. Miller ◽  
R. Wayne Skaggs
Keyword(s):  
Solute Transport ◽  
Unsaturated Zones

Monitoring of Long-Term Peritoneal Membrane Function

2001 ◽  
Vol 21 (2) ◽  
pp. 225-232 ◽  
Author(s):  
Simon J. Davies
Keyword(s):  
Peritoneal Dialysis ◽  
Solute Transport ◽  
Water Transport ◽  
Drop Out ◽  
Published Data ◽  
Peritoneal Membrane ◽  
Membrane Function ◽  
Technique Survival ◽  
Ultrafiltration Failure

Objective Peritoneal membrane function influences dialysis prescription and clinical outcome and may change with time on treatment. Increasingly sophisticated tools, ranging from the peritoneal equilibration test (PET) to the standard permeability analysis (SPA) and personal dialysis capacity (PDC) test, are available to the clinician and clinical researcher. These tests allow assessment of a number of aspects of membrane function, including solute transport rates, ultrafiltration capacity, effective reabsorption, transcellular water transport, and permeability to macromolecules. In considering which tests are of greatest value in monitoring long-term membrane function, two criteria were set: those that result in clinically relevant interpatient differences in achieved ultrafiltration or solute clearances, and those that change with time in treatment. Study Selection Clinical validation studies of the PET, SPA, and PDC tests. Studies reporting membrane function using these methods in either long-term (5 years) peritoneal dialysis patients or longitudinal observations (> 2 years). Data Extraction Directly from published data. Additional, previously unpublished analysis of data from the Stoke PD Study. Results Solute transport is the most important parameter. In addition to predicting patient and technique survival at baseline, there is strong evidence that it can increase with time on treatment. Whereas patients with initially high solute transport drop out early from treatment, those with low transport remain longer on treatment, although, over 5 years, a proportion develop increasing transport rates. Ultrafiltration capacity, while being a composite measure of membrane function, is a useful guide for the clinician. Using the PET (2.27% glucose), a net ultrafiltration capacity of < 200 mL is associated with a 50% chance of achieving less than 1 L daily ultrafiltration at the expense of 1.8 hypertonic (3.86%) exchanges in anuric patients. Using a SPA (3.86% glucose), a net ultrafiltration capacity of < 400 mL indicates ultrafiltration failure. While there is circumstantial evidence that, with time on peritoneal dialysis, loss of transcellular water transport might contribute to ultrafiltration failure, none of the current tests is able to demonstrate this unequivocally. Of the other membrane parameters, evidence that interpatient differences are clinically relevant (permeability to macro-molecules), or that they change significantly with time on treatment (effective reabsorption), is lacking. Conclusion A strong case can be made for the regular assessment by clinicians of solute transport and ultrafiltration capacity, a task made simple to achieve using any of the three tools available.

Impact of Peritoneal Membrane Function on Long Term Clinical Outcome in Peritoneal Dialysis Patients

1999 ◽  
Vol 19 (2_suppl) ◽  
pp. 91-94 ◽  
Author(s):  
Simon J. Davies ◽  
Louise Phillips ◽  
Anne M. Griffiths ◽  
Lesley H. Russell ◽  
Patrick F. Naish ◽  
...  
Keyword(s):  
Renal Function ◽  
Solute Transport ◽  
Residual Renal Function ◽  
Clinical Implications ◽  
Water Removal ◽  
Peritoneal Membrane ◽  
Dialysis Patients ◽  
Membrane Function

It is increasingly clear that peritoneal membrane transport status has clinical implications. The role of the peritoneum in dialysis delivery becomes para mount once residual renal function is lost, particularly as the membrane characteristics may change for the worse with time on treatment. These findings have several important implications: Clinicians need to take solute transport character istics into account as they assess their patients. Adverse effects of high solute transport include reduced ultrafiltration, solute removal (in particular, sodium), and increased peritoneal protein losses. A need exists to replace lost residual renal function, not just with enhanced solute removal, but also with adequate salt and water removal. The interpretation of urea and creatinine clear ances in anuric PD patients needs further consideration and validation. Hypoalbuminemia in PD patients will result from the combined effects of high protein losses, over hydration, comorbidity, and malnutrition.

scholarly journals Peritoneal Glucose Exposure and Changes in Membrane Solute Transport with Time on Peritoneal Dialysis

2001 ◽  
Vol 12 (5) ◽  
pp. 1046-1051 ◽  
Author(s):  
SIMON J. DAVIES ◽  
LOUISE PHILLIPS ◽  
PATRICK F. NAISH ◽  
GAVIN I. RUSSELL
Keyword(s):  
Renal Function ◽  
Peritoneal Dialysis ◽  
Solute Transport ◽  
Residual Renal Function ◽  
Causative Role ◽  
Continuous Exposure ◽  
Hypertonic Glucose ◽  
Ultrafiltration Failure ◽  
Glucose Exposure

Abstract. Peritoneal solute transport increases with time on treatment in a proportion of peritoneal dialysis (PD) patients, contributing to ultrafiltration failure. Continuous exposure of the peritoneum to hypertonic glucose solutions results in morphologic damage that may have a causative role in changes in peritoneal function. The purpose of this analysis was to establish whether increased exposure to glucose preceded changes in solute transport in a selected group of long-term PD patients. Peritoneal solute transport, residual renal function, peritonitis rate, and peritoneal exposure to glucose were recorded prospectively in a cohort of 303 patients at a single dialysis center. A subgroup of individuals, treated continuously for 5 yr, were identified and defined retrospectively as having either stable or increasing transport status. Of the 22 patients who were treated continuously for 5 yr, 13 had stable solute transport (solute transport at start, 0.67 [±0.1]; at 5 yr, 0.67 [±0.1]), whereas 9 had a sustained increase (solute transport at start, 0.56 [±0.08]; at 5 yr, 0.77 [±0.09]). Compared with the stable patients, those with increasing transport had earlier loss in residual renal function and were exposed to significantly more hypertonic glucose during the first 2 yr of treatment that preceded the increase in solute transport. This was associated with greater achieved ultrafiltration compensating for the reduced urinary volumes in these patients. Further increases in glucose exposure were observed as solute transport continued to rise. Peritonitis, including severity of infection and causative organism, was similar in both groups. In this selected group of long-term survivors on PD, an increase in solute transport with time was preceded by increased peritoneal exposure to hypertonic glucose. This is supportive evidence that hypertonic glucose may play a causative role in alterations in peritoneal membrane function.

The Hydrogeologic Environment for a Proposed Deep Geologic Repository in Canada for Low and Intermediate Level Radioactive Waste

2011 ◽  
Author(s):  
Jonathan F. Sykes ◽  
Stefano D. Normani ◽  
Yong Yin ◽  
Mark R. Jensen
Keyword(s):  
Radioactive Waste ◽  
Solute Transport ◽  
Regional Scale ◽  
Intermediate Level ◽  
Geologic Repository ◽  
Site Specific ◽  
Ordovician Limestone ◽  
Intermediate Level Radioactive Waste ◽  
The Impact

A Deep Geologic Repository (DGR) for low and intermediate level radioactive waste has been proposed by Ontario Power Generation for the Bruce nuclear site in Ontario, Canada. As proposed the DGR would be constructed at a depth of about 680 m below ground surface within the argillaceous Ordovician limestone of the Cobourg Formation. This paper describes the hydrogeology of the DGR site developed through both site characterization studies and regional-scale numerical modelling analysis. The analysis provides a framework for the assembly and integration of the site-specific geoscientific data and examines the factors that influence the predicted long-term performance of the geosphere barrier. Flow system evolution was accomplished using both the density-dependent FRAC3DVS-OPG flow and transport model and the two-phase gas and water flow computational model TOUGH2-MP. In the geologic framework of the Province of Ontario, the DGR is located on the eastern flank of the Michigan Basin. Borehole logs covering Southern Ontario combined with site-specific data from 6 deep boreholes have been used to define the structural contours and hydrogeologic properties at the regional-scale of the modelled 31 sedimentary strata that may be partially present above the Precambrian crystalline basement rock. The regional-scale domain encompasses an approximately 18500km2 region extending from Lake Huron to Georgian Bay. The groundwater zone below the Devonian includes units containing stagnant water having high concentrations of total dissolved solids that can exceed 300g/L. The Ordovician sediments are significantly under-pressured. The horizontal hydraulic conductivity for the Cobourg limestone is estimated to be 2 × 10−14 m/s based on straddle-packer hydraulic tests. The low advective velocities in the Cobourg and other Ordovician units result in solute transport that is diffusion dominant with Peclet numbers less than 0.003 for a characteristic length of unity. Long-term simulations that consider future glaciation scenarios include the impact of ice thickness and permafrost. Solute transport in the Ordovician limestone and shale was diffusion dominant in all simulations. The Salina formations of the Upper Silurian prevented the deeper penetration of basal meltwater.

scholarly journals Groundwater-surface water interaction and the climatic spatial patterns of hillslope hydrological response

1999 ◽  
Vol 3 (3) ◽  
pp. 375-384 ◽  
Author(s):  
C. P. Kim ◽  
G. D. Salvucci ◽  
D. Entekhabi
Keyword(s):  
Water Table ◽  
Perturbation Analysis ◽  
Lateral Flow ◽  
Discharge Zone ◽  
Minor Importance ◽  
Phreatic Surface ◽  
Groundwater Surface Water Interaction ◽  
Temporal Perturbation ◽  
Unsaturated Zones

Abstract. A transient, mixed analytical-numerical model of hillslope hydrological behaviour is used to study the patterns of infiltration, evapotranspiration, recharge and lateral flow across hillslopes. Computational efficiency is achieved by treating infiltration and phreatic surface movement analytically. The influence of dynamic coupling of the saturated and unsaturated zones on the division of hillslopes into units of distinct hydrological behaviour is analyzed. The results indicate the importance of downhill groundwater flow on the lateral distribution of soil moisture and hydrological fluxes; unsaturated lateral flow is shown to be of relatively minor importance. For most conditions, the hillslope organizes itself into three distinct regions; an uphill recharge and a downhill discharge zone separated by a midline zone over which there is, on average, no recharge or discharge. A temporal perturbation analysis of the phreatic surface, made to quantify the deviations between the equivalent-steady water table derived by Salvucci and Entekhabi (1995) and the long-term mean water table, shows that the equivalent-steady water table effectively couples the unsaturated and saturated zone dynamics across storm and interstorm periods and divides the hillslope into distinct hydrological regions. The second order closure terms in the perturbation analysis, expressed as the gradient of water table variance, quantify the deviations and tend to make the hydrological zones relatively less distinct.

Biocompatibility of Peritoneal Dialysis Fluids: Long-term Exposure of Nonuremic Rats

2004 ◽  
Vol 24 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Barbara Musi ◽  
Magnus Braide ◽  
Ola Carlsson ◽  
Anders Wieslander ◽  
Ann Albrektsson ◽  
...  
Keyword(s):  
Peritoneal Dialysis ◽  
Growth Factor ◽  
Solute Transport ◽  
Transforming Growth Factor ◽  
Cell Damage ◽  
Mesothelial Cell ◽  
Mesothelial Cells ◽  
Vascular Density ◽  
Tissue Thickness

Objectives Long-term peritoneal dialysis (PD) leads to structural and functional changes in the peritoneum. The aim of the present study was to investigate the long-term effects of PD fluid components, glucose and glucose degradation products (GDP), and lactate-buffered solution on morphology and transport characteristics in a nonuremic rat model. Methods Rats were subjected to two daily intraperitoneal injections (20 mL/day) during 12 weeks of one of the following: commercial PD fluid (Gambrosol, 4%; Gambro AB, Lund, Sweden), commercial PD fluid with low GDP levels (Gambrosol trio, 4%; Gambro AB), sterile-filtered PD fluid (4%) without GDP, or a glucose-free lactate-buffered PD fluid. Punctured and untreated controls were used. Following exposure, the rats underwent a single 4-hour PD dwell (30 mL, 4% glucose) to determine peritoneal function. Additionally, submesothelial tissue thickness, percentage of high mesothelial cells (perpendicular diameter > 2 μm), vascular density, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF) β1 mRNA expression were determined. Submesothelial collagen concentration was estimated by van Gieson staining. Results Submesothelial tissue thickness and vascular density, mediated by VEGF and TGFβ production, in the diaphragmatic peritoneum increased significantly in rats exposed to any PD fluid. Gambrosol induced a marked increased fibrosis of the hepatic peritoneum. A significant increase in high mesothelial cells was observed in the Gambrosol group only. Net ultrafiltration was reduced in the Gambrosol and in the glucose-free groups compared to untreated controls. Small solute transport was unchanged, but all groups exposed to fluids showed significantly increased lymph flow. Conclusions Our results show that long-term exposure to different components of PD fluids leads to mesothelial cell damage, submesothelial fibrosis, and neoangiogenesis. Mesothelial cell damage could be connected to the presence of GDP; the other changes were similar for all fluids. Peritoneal transport characteristics did not change in any consistent way and the neoangiogenesis observed was not paralleled by increased solute transport.

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