Validation of a Two-Pool Model for the Kinetics of ß2-Microglobulin

2002 ◽  
Vol 25 (5) ◽  
pp. 411-420 ◽  
Author(s):  
S. Stiller ◽  
X.Q. Xu ◽  
N. Gruner ◽  
J. Vienken ◽  
H. Mann
Keyword(s):  
Standard Deviation ◽  
Plasma Concentrations ◽  
Generation Rate ◽  
Secondary Amyloidosis ◽  
Concentration Profiles ◽  
Dialysis Dose ◽  
Measured Concentration ◽  
Pool Model ◽  
Efficacy Parameters ◽  
Beta 2 Microglobulin

Secondary amyloidosis due to beta-2-microglobulin (ß2-m) is a serious long-term complication in patients on regular dialysis therapy. ß2-m can be considered a middle-molecule marker used to facilitate the assessment of dialysis efficacy. For this purpose, a validated model that calculates characteristic efficacy parameters, such as Kt/V, TAC and generation rate, is needed. There is general agreement that ß2-m-kinetics should be described by a two-pool model, but little has been published to validate such an approach. We measured the ß2-m concentration profiles of eight stable patients during hemodialysis (HD) at the start of treatment, after 30 minutes, after 60 minutes, and every hour until the end. Thereafter they were measured at 10-minute intervals for an hour. The dialyser clearances were determined from the plasma concentrations in front of and behind the dialyser twice during each session – after 1 hour, and 4 hours from the start of treatment. The kinetic parameters of a two-pool model (e.g. the compartment volumes V1 and V2, the mass transfer coefficient K12 and the generation rate G) were determined from the optimal fit of the measured concentration profile. The table below summarises the results by giving the mean and standard deviation for each parameter: V (liters) V1/V2 V % TBW K12 m(ml/min) G (mg/kg/day) 10.0 ± 1.6 4.60 ± 1.8 28.4 ± 3.1 56.3 ± 25.2 2.50 ± 0.66 Inter-individual differences in V1/V2 and K12 were high, ranging from 2.5 to 10.0 for V1/V2 and from 26 to 140 for K12. Error analysis suggested that these wide ranges were due to the method and that in reality the probable range of V is 25–36% of TBW, of V1/V2 3.5–5.3, and of K12 30–80 ml/min. With standard values for these three parameters (V = 30% of TBW, V1/V2 = 4.4 and K12 = 55 ml/m), equal for all patients, and their respective ranges, Kt/V can be calculated with a standard deviation of 13%. Kt/V > 1.2 secures the maximum possible ß2-m removal with three HD treatments a week. Conclusions The parameters of a two-pool model of ß2-m kinetics can be derived from concentration profiles obtained under routine dialysis conditions, but accuracy is not completely satisfactory. Similar to the dialysis dose for urea (Kt/Vurea) the dialysis dose for ß2-m (Kt/Vß2-m) can be calculated from the pre- and post-dialysis concentrations of ß2-m, body weight, ultrafiltration and dialysis time. Kt/Vß2-m > 1.2 secures the maximum possible removal of ß2-m in HD with three sessions per week.

Non-axisymmetric turbulent mass transfer in a circular tube

1969 ◽  
Vol 38 (3) ◽  
pp. 457-472 ◽  
Author(s):  
Alan Quarmby ◽  
R. K. Anand
Keyword(s):  
Mass Transfer ◽  
Circular Tube ◽  
Eddy Diffusivity ◽  
Concentration Profiles ◽  
Tracer Gas ◽  
Direct Evaluation ◽  
Measured Concentration ◽  
Eddy Diffusivities ◽  
Fluid Properties ◽  
Fully Developed Turbulent Flow

Theory and experiment are presented for mass transfer into a fully developed turbulent flow in a plain circular tube in two non-axisymmetric cases. The cases studied are a diametral line source and a discontinuous ring source, in which there is a uniform mass flux over rectangular areas of the tube wall. A comparison is made between the concentration profiles predicted by the solutions of the diffusion equation and experiments using nitrous oxide, Schmidt number S = 0·77, as a tracer gas in air. The range of experiments covers Reynolds numbers R from 20,000 to 120,000.In the analysis, the assumption is made that the tangential and radial eddy diffusivities of mass are equal at a point. The radial diffusivity of mass, which is a function of radial position, is related to the radial eddy diffusivity of momentum by a ratio, which takes account of fluid properties and the value of the radial eddy diffusivity of momentum. The satisfactory agreement between analysis and experiment establishes the correctness of this assumption. Further confirmation was obtained by direct evaluation of the tangential eddy diffusivity of mass from the measured concentration profiles.

Measurements of coastal dispersion in Ontario lakes

1976 ◽  
Vol 3 (1) ◽  
pp. 156-162 ◽  
Author(s):  
Merv. D. Palmer
Keyword(s):  
Cross Sections ◽  
Coastal Waters ◽  
Relative Dispersion ◽  
Concentration Profiles ◽  
Two Dimensional ◽  
Dispersion Coefficients ◽  
Measured Concentration ◽  
Power Growth ◽  
Constant Rate ◽  
Vertical Dispersion

A series of dye injection experiments were carried out near the surface in the coastal waters of lakes Erie, Ontario, and Simcoe. The purpose of the experiments was to determine whether the relative dispersion in these regions was similar to that obtained in other oceanographical experiment. Rhodamine BA dye was injected at a constant rate (approximately 150 mg/s) at a depth 1 m below the surface from a raft anchored in 9 m of water (approximately 1.5 km offshore) for 6 to 8 h. Two-dimensional dye plume concentrations were measured at cross sections 60 to 830 m from the source. Relative dispersion coefficients were determined numerically from the measured concentration profiles. The horizontal dispersion coefficients (80 to 4100 cm2/s) were comparable to oceanographical values and exhibited a 1.33 power growth with distance from the source. Vertical dispersion coefficients were very small (less than 1 cm2/s) and relatively independent of distance from the source.

scholarly journals A MODEL OF ION TRANSPORT IN CONJUGATED POLYMERS

2009 ◽  
Vol 50 (3) ◽  
pp. 355-364
Author(s):  
JOHN BURNELL
Keyword(s):  
Ion Transport ◽  
Conjugated Polymers ◽  
Conjugated Polymer ◽  
Experimental Studies ◽  
Cation Transport ◽  
Concentration Profiles ◽  
Measured Concentration ◽  
Micro Actuator ◽  
Micro Pump ◽  
Good Agreement

AbstractUnderstanding ion transport in conjugated polymers is essential for developing mathematical models of applications of these materials. Previous experimental studies have suggested that cation transport in a conjugated polymer could be either diffusion or drift controlled, with debate over which dominates. In this paper we present a new model of cation transport that explains most of the features seen in a set of recent experiments. This model gives good agreement with measured concentration profiles, except when the profile has penetrated the polymer by more than 60%. The model shows that both diffusion and drift processes can be present. An application of a micro-actuator based on a conjugated polymer is presented to demonstrate that this technology could be used to develop a micro-pump.

scholarly journals Calculated interdiffusivities resulting from different fitting functions applied to measured concentration profiles in Cu-rich fcc Cu-Ni-Sn alloys at 1073 K

2017 ◽  
Vol 53 (3) ◽  
pp. 255-262 ◽  
Author(s):  
Y. Liu ◽  
D. Liu ◽  
Y. Du ◽  
S. Liu ◽  
D. Kuang ◽  
...  
Keyword(s):  
Error Propagation ◽  
Scientific Method ◽  
Electron Probe ◽  
Bulk Diffusion ◽  
Ternary Systems ◽  
Concentration Profiles ◽  
Diffusion Couples ◽  
Green Method ◽  
Measured Concentration ◽  
Interdiffusion Coefficients

Employing six groups of bulk diffusion couples together with electron probe microanalysis technique, the compositiondependences of ternary interdiffusion coefficients in Cu-rich fcc Cu-Ni-Sn alloys at 1073 K were determined via the Whittle and Green method. Different fitting functions applied to the measured concentration profiles are utilized to extract the interdiffusion coefficients of fcc Cu-Ni-Sn alloys. The errors for the obtained interdiffusivities are evaluated by a scientific method considering the error propagation. The calculated diffusion coefficients using the Boltzmann and additive Boltzmann functions are found to be with reasonable errors and show a general agreement with those using other fitting functions. Based on the Boltzmann and additive Boltzmann functions, the interdiffusivities in Cu-rich fcc Cu-Ni-Sn alloys at 1073 K are obtained and validated by thermodynamic constraints. The Boltzmann and additive Boltzmann functions are recommended to be used for the fitting of measured concentration profiles in other ternary systems for the sake of extracting ternary diffusivities.

Prediction of the Depletion Zone due to Selective Oxidation of P91 Steel

2005 ◽  
Vol 237-240 ◽  
pp. 965-970 ◽  
Author(s):  
Marek Danielewski ◽  
Robert Filipek ◽  
Barbara Kucharska
Keyword(s):  
Selective Oxidation ◽  
Computer Modelling ◽  
Average Concentration ◽  
Concentration Profiles ◽  
Unique Determination ◽  
Measured Concentration ◽  
P91 Steel ◽  
Calculated Concentration ◽  
Key Factor ◽  
Limitation Method

Experimental measurements do not allow for a unique determination of the concentration profiles, e.g., in case of multi-layer systems. The measured concentration of the elements at the alloy/scale interface is an average concentration in an alloy and in a scale near the spot of the beam [1]. The knowledge of the concentration of the elements at the boundary is necessary for the understanding corrosion of alloys. This essential obstacle of experimental techniques can be overcome by computer modelling. Namely, by combining the different methods (non-unique measurement with unique modelling). The Danielewski-Holly model of interdiffusion has a unique solution. This model enables to predict the evolution of component distributions in the reacting alloy. The model is valid for time dependent boundary conditions and consequently can be used for modelling the more complex reactions, eg., the formation of complex oxides. To avoid the nonphysical values of fluxes in reacting alloy the kinetic constraint on all fluxes was introduced, i.e., the flux limitation method. The results of the selective oxidation of the P91 steel (0,1 wt.% C, 8,6 wt.% Cr, 0,25 wt.% Ni) are presented. Calculated concentration profiles are compared with the experimental data. We show the evolution of chromium distribution in oxidizing steel up to 3 000 hours. The computations demonstrate that chromium depletion is the key factor determining the scale composition.

Solute transport in sub-irrigated peat-based growing media

2009 ◽  
Vol 89 (3) ◽  
pp. 301-313 ◽  
Author(s):  
J. Boudreau ◽  
J. Caron ◽  
D. Elrick ◽  
J. Fortin ◽  
J. Gallichand
Keyword(s):  
Solute Transport ◽  
Transport Model ◽  
Water Solution ◽  
Concentration Profiles ◽  
Measured Concentration ◽  
Growing Media ◽  
Flow Experiment ◽  
1D Model ◽  
Solute Movement ◽  
Efficient Water Use

New legislation to reduce the amount of fertilizer leached into the environment by horticultural growers and the need to implement water-saving irrigation systems require an understanding of salt build-up and of nutrient cycles in order to develop efficient water-use strategies for growers. Solute transport in growing media is central to this process, but has received little attention thus far. The objectives of this study were to determine how solutes behave in sub-irrigated growing media and to assess a solute transport model for these media. A steady state evaporation (upward water flow) experiment was carried out with three different growing media in packed columns in the laboratory. Bromide, potassium and copper concentrations were determined using in-column pore water solution samplers and by sectioning the columns at the end of the experiment to obtain concentration profiles. The Hydrus-1D model was fitted to the solution sampler data assuming non-linear Freundlich adsorption, and then used to obtain favorable predictions of the measured concentration profiles. Independent adsorption isotherm results from batch experiments were found to be inadequate when used to predict solute movement and the results indicate that the preferred approach is an in-column evaluation of the transport parameters.Key words: Solute transport, sub-irrigation, peat, growing media

Optical Estimation of Beta 2 Microglobulin during Hemodiafiltration - Does It Work?

2015 ◽  
Vol 40 (2) ◽  
pp. 113-119 ◽  
Author(s):  
Fredrik Uhlin ◽  
Jana Holmar ◽  
Pia Yngman-Uhlin ◽  
Anders Fernström ◽  
Ivo Fridolin
Keyword(s):  
Correlation Analysis ◽  
Uv Radiation ◽  
Relative Error ◽  
The Other ◽  
Uv Absorbance ◽  
Dialysis Dose ◽  
Spent Dialysate ◽  
Beta 2 ◽  
Beta 2 Microglobulin ◽  
Surrogate Substances

Background: Currently, urea reduction seems to be the most widely used dialysis dose parameter. The aim of this study was to investigate the possibility to monitor beta 2-microglobulin (β2-M) elimination by utilizing the ultraviolet (UV) absorbance of spent dialysate. Methods: Blood and spent dialysate were collected during two week's sessions in 8 patients, one week in hemodialysis (HD) and one in hemodiafiltration (HDF). Correlation analysis between UV-wavelengths and concentrations of solutes in spent dialysate was performed. The reduction ratio (RR) of concentrations in blood, dialysate and UV-absorbance were compared. Results: Differences between HD and HDF were discovered in wavelength correlation maxima for the solutes. Relative error in RR (%) was larger (p < 0.05) for β2-M than for the other solutes. The most reasonable explanation is that β2-M does not absorb UV-radiation; instead, the absorbance of surrogate substances is measured. Conclusion: A high correlation between UV-absorbance and β2-M can be achieved for HDF but not for HD. Still, UV-absorbance could perhaps be used in solely HDF mode for estimation of β2-M removal.

scholarly journals DETERMINATION OF TERIFLUNOMIDE ACROSS A WIDE DYNAMIC CONCENTRATION RANGE IN HUMAN PLASMA BY LC–MS/MS

2019 ◽  
Vol 16 (32) ◽  
pp. 608-620
Author(s):  
Natalia E. MOSKALEVA ◽  
Natalia V. MESONZHNIK ◽  
Roman M. KUZNETSOV ◽  
Pavel A. MARKIN ◽  
Svetlana A. APPOLONOVA
Keyword(s):  
Blood Plasma ◽  
High Performance ◽  
Plasma Concentrations ◽  
Internal Standard ◽  
The Body ◽  
Human Blood Plasma ◽  
Measured Concentration ◽  
Wide Range ◽  
The Difference ◽  
Acquity Uplc

Leflunomide is an antirheumatic drug with anti-inflammatory and antirheumatic properties, it is rapidly metabolized in the body to the active metabolite teriflunomide, which causes its pharmacological activity. At the usual 20-mg daily dosage of leflunomide, the expected teriflunomide plasma concentration is about 35 μg/ml. The pharmacokinetics of the drug is characterized by a large interindividual variability and a long half-life, which in combination with possible side effects creates the need to control the concentration of teriflunomide in the blood plasma. Teriflunomide may increase the risk of fetal death or teratogenic effects when administered to pregnant women. Teriflunomide plasma concentrations less than 0.02 μg/ml are preferred for patients anticipating pregnancy. In this study, a sensitive and high-performance method for analyzing teriflunomide in human blood plasma in a wide range of concentrations was developed and validated using a triple quadrupole liquid chromatography-mass spectrometer (HPLC-MS/MS). Sample preparation was performed by protein precipitation with acetonitrile, followed by chromatographic separation using an Acquity UPLC BEN C8 1.7 mm, 2.1 × 50 mm column (Waters, USA). D4-teriflunomide was used as an internal standard. The developed method was validated in the concentration range from 0.001 μg/ml to 200 μg/ml teriflunomide in plasma. Accuracy (%), defined as the difference between the nominal and measured concentration and reproducibility (coefficient of variation CV) ranged from -5.02% to 5.00% and from 0.47% to 9.30%, respectively, within the series and between series of samples. The developed method was successfully used to analyze volunteer blood plasma samples after taking 20 mg of leflunomide.

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