Biomedical subjects

J Waniewski

Publications and source records attributed to J Waniewski.

At least 55 records · Page 3Linked to original sources

PubMed1994

Dialysate to plasma solute concentration (D/P) versus peritoneal transport parameters in CAPD.

The relationship between dialysate to plasma solute equilibration ratio (D/P) and diffusive (diffusive mass transport coefficients, KBD) as well as convective (sieving coefficient, S, and net ultrafiltration) transport characteristics were studied in clinically stable CAPD patients and in patients with loss of ultrafiltration capacity (UFC). Forty-one 6-h single-dwell studies with standard glucose-based dialysis fluids containing 1.36% (n = 9), 2.27% (n = 9), and 3.86% (n = 23) anhydrous glucose were carried out in 33 clinically stable CAPD patients. Eleven patients with loss of UFC were studied with 3.86% glucose solution. Intraperitoneal dialysate volumes were calculated from the dilution of the tracer (131I-albumin) with a correction applied for its elimination from the peritoneal cavity. KBD and S were estimated using the Pyle-Popovich-Moncrief model with aqueous plasma concentrations. A theoretical D/P curve was derived with and without taking convective transport and peritoneal reabsorption into account. The three different glucose solutions yielded D/P curves which were similar for urea and potassium. For creatinine a slower equilibration and for glucose and sodium a faster decrease in dialysate concentration were observed with more hypertonic solutions. In general, there was a strong correlation which was best at 240 min between D/P (for glucose dialysate/initial dialysate concentration, D/Do) and KBD for all solutes (except sodium), whereas the correlation between D/P and convective transport parameters was much weaker. KBD for creatinine (with 3.86% glucose solution) could be estimated (r = 0.98) from aqueous D/P using the experimental formula: creatinine KBD = -1.8 - ln (1 - D240/P)/0.1. Patients with loss of UFC due to increased diffusive transport (n = 8) could be discriminated from the clinically stable patients using KBD and D/P (or D/D0) for creatinine and glucose or D/P for sodium. However, patients with loss of UFC associated with increased peritoneal reabsorption (n = 2) could not be identified using these parameters. Theoretically derived D/P curves were in excellent agreement with measured D/P for 1.36% glucose solution and simulations were satisfactory also for the 2.27% and 3.86% solutions provided that the effect of convective transport was taken into account. The standardized peritoneal equilibration tests (PET) as proposed by Twardowski et al. [17] seems to be appropriately designed as regards duration of the dwell and the choice of glucose and creatinine as investigated solutes. Thus, PET can be recommended as a sensitive routine investigation for the monitoring of normal/abnormal peritoneal transport behaviour in peritoneal dialysis patients.

Biological Transport↗

PubMed1994

Methods for estimation of peritoneal dialysate volume and reabsorption rate using macromolecular markers.

Reabsorption of fluid and solutes from the peritoneal cavity poses several problems for the correct estimation of peritoneal dialysate volume and ultrafiltration rate with macromolecular volume markers. Although physiological mechanisms of peritoneal reabsorption (direct lymphatic absorption vs reabsorption to the peritoneal tissue) are being currently discussed, many experimental and clinical studies have demonstrated that peritoneal reabsorption of the marker is mainly a bulk "backflow" out of the peritoneal cavity. Theoretical bases for the estimation of peritoneal dialysate volume and cumulative ultrafiltration of fluid including the correction for peritoneal reabsorption are reviewed. A widely applied simplified method which, however, neglects the impact of ultrafiltration on marker concentration is also discussed. The systematic errors involved in the application of the simplified method are usually less than 10% in the standard conditions; however, in specific cases they may be much higher. Therefore, the correct method is suggested for practical applications.

Absorption↗

PubMed1993

Kinetic analysis of cytotoxic lymphocyte-target cell interaction as quantified by dual parameter flow cytometry.

The kinetics of conjugate formation between leukemic cell lines (K562 and Daudi) and lymphokine-activated killer (LAK) cells was studied. A flow cytofluorometry method using double immunofluorescence staining was applied. During the first 15 min of incubation of LAK effectors with leukemic targets, a rapid binding occurred, followed by a plateau phase lasting until 30 min of observation. A considerable, yet not statistically significant, between-donor variability was noticed. A mathematical model of conjugate formation kinetics, based on the analogy to enzyme kinetics, was formulated and validated. Parameters of the model were related to the binding capacity of effector and target cells, and to the lifetime of conjugates and free cells. The concordance of theoretical curves with experimental data proved that the described model can be considered as a useful tool for the evaluation of kinetic and dynamic characterization of conjugate formation between leukemic targets and LAK effectors.

Cell Adhesion↗

PubMed1993

Alternative descriptions of combined diffusive and convective mass transport in hemodialyzer.

Two alternative versions of the mathematical description of the combined diffusive and convective membrane transport in hemodialyzers were compared using the one-dimensional theory of hemodialyzers. The first version is based on the assumption of homogeneity of the membrane. The second version is a widely used "ad hoc" formulation, which can be interpreted as a description of the membrane as tighter at the dialysate side than at the blood side. Theoretical predictions of the increase of dialyzer clearance caused by ultrafiltration, as assessed by transmittance coefficient, were compared to experimental data about transport of small solutes (urea, creatinine, and sodium) as well as middle molecules (vitamin B12) in three types of hollow-fiber hemodialyzer. For one type of dialyzer, the theory assuming the homogeneous membrane yielded the correct predictions for the small solutes. For two other types of dialyzer, the alternative version of the theory was adequate. For vitamin B12, the experimental values of transmittance coefficient were between the values predicted by the two versions of the theory for all three types of hemodialyzer. Thus, the two versions should be considered as a possible adequate description of solute transport in hemodialyzers.

Membranes, Artificial↗

PubMed1993

Effect of alternative osmotic agents on peritoneal transport.

To investigate the impact of osmotic agents on solute transport in continuous ambulatory peritoneal dialysis single 6-hour dwell studies were performed in nondiabetic patients using different osmotic agents: glucose 3.86%, amino acids 2.70, and glycerol 2.50%. Diffusive mass transport coefficient (KBD) and sieving coefficient (S) were assessed for urea, creatinine, glucose, glycerol, potassium, sodium, and total protein using the Babb-Randerson-Farrell model. The estimated KBD values for small solutes were higher in peritoneal dialysis fluid based on amino acids than in both glucose- and glycerol-based dialysis solutions. S values for small solutes were higher in glucose-based peritoneal dialysis fluid than in dialysis solutions based on amino acids and glycerol. Moreover, nonphysical, i.e., out of the range 0-1, S values were obtained for urea and potassium in glucose-based peritoneal dialysis fluid and for glucose and glycerol applied as osmotic agents. No difference in the transport parameters for total protein was found between the three investigated dialysis fluids. We conclude that the composition of dialysis fluid (osmotic agent, buffer solute, pH) can change the transport characteristics of the peritoneum. Furthermore, other physiological processes besides the diffusive and convective transport can contribute to the net peritoneal transport of some solutes.

Adult↗

PubMed1993

Peritoneal transport during dialysis with amino acid-based solutions.

OBJECTIVE: To evaluate the potential clinical role of amino acids as an osmotic agent. DESIGN: The peritoneal transport of fluid, amino acids, and other solutes was investigated during a 6-hour single-cycle peritoneal dialysis with PDA 1% versus 1.36% glucose (n = 6) or PDA 2.7% versus 3.86% glucose solution (n = 9). PATIENTS: Fifteen stable nondiabetic continuous ambulatory peritoneal dialysis (CAPD) patients. RESULTS: The fractional absorption of the osmotic agents at 6 hours was higher with PDA 2.7% versus glucose 3.86% (p < 0.005). The diffusive mass transport coefficient, KBD, calculated for a period of dialysate isovolemia was higher with PDA 2.7% versus PDA 1% for essential, nonessential (p < 0.005), and total (p < 0.05) amino acids. The intraperitoneal volume-over-time curves and KBD values for urea, creatinine, glucose, albumin, beta 2-microglobulin, and total protein did not differ between the amino acid solutions and the corresponding glucose solutions. KBD for urea was significantly higher during the dwell with PDA 2.7% versus PDA 1% (p < 0.05). Plasma amino acid concentrations increased substantially during the first 1-2 hours and then decreased gradually. Valine and methionine rose to 792% and 1119% of baseline values, respectively. CONCLUSIONS: We conclude that the peritoneal transport of fluid and investigated solutes, except amino acids, was not different with the amino acid solutions compared with the corresponding equimolar glucose solutions. However, ultrafiltration tended to be lower with amino acid solutions. Furthermore, the fractional absorption of amino acids and KBD values for amino acids was higher with PDA 2.7% versus PDA 1%, suggesting an effect of the hypertonic amino acid solution on the peritoneal membrane transport properties. Also, the hypertonic PDA 2.7% solution yielded nonphysiologically high plasma levels of several amino acids. We therefore consider this solution not to be safe enough for long-term clinical use.

Absorption↗

PubMed1992

A quantitative description of solute and fluid transport during peritoneal dialysis.

To investigate the relationship between dialysate glucose concentration and peritoneal fluid and solute transport parameters, 41 six-hour single dwell studies with standard glucose-based dialysis fluids containing 1.36% (N = 9), 2.27% (N = 9) and 3.86% (N = 23) anhydrous glucose were carried out in 33 clinically-stable continuous ambulatory peritoneal dialysis (CAPD) patients. Intraperitoneal dialysate volumes (VD) were determined from the dilution of 131I-albumin with a correction applied for its elimination from the peritoneal cavity (KE, ml/min). Diffusive mass transport coefficients (KBD) were calculated from aqueous solute concentrations (with a correction applied for the plasma protein concentration and, for electrolytes, also for the Donnan factor) during a period of dialysate isovolemia. The intraperitoneal amount calculated to be transported by diffusion was subtracted from the measured total amount of solutes in the dialysate, yielding an estimate of non-diffusive solute transport. The intraperitoneal dialysate volume over time curve was characterized by: initial net ultrafiltration (lasting on average 92 min, 160 min and 197 min and with maximum mean net ultrafiltration rates 6 ml/min, 8 ml/min and 14 ml/min, respectively, for the 1.36%, 2.27% and 3.86% solutions); dialysate isovolemia (lasting about 120 min for all three solutions) and fluid reabsorption (rate about 1 ml/min for all three solutions). KBD for glucose, potassium, creatinine, urea and total protein did not differ between the three solutions and the fractional absorption of glucose was almost identical for the three glucose solutions, indicating that the diffusive transport properties of the peritoneum is not influenced by the initial concentration of glucose or the ultrafiltration flow rate. About 50% of the total absorption of glucose occurred during the first 90 minutes of the dwell. The mean percentage of the initial amount of glucose which had been absorbed (%GA) at time t during the dwell could be described (r = 0.999) for all three solutions using the experimental formula %GA = 85 - 75.7 * e-0.005*t. After 360 minutes, about 75% of the initial intraperitoneal glucose amount had been absorbed corresponding to a mean (+/- SD) energy supply of 75 +/- 6 kcal, 131 +/- 18 kcal and 211 +/- 26 kcal for the three solutions. Non-diffusive (that is, mainly convective) transport was almost negligible for the less hypertonic solutions while it was estimated to account for 30 to 40% of the total peritoneal transport of urea, creatinine and potassium during the first 60 minutes of the 3.86% exchange.

Absorption↗

PubMed1992

Aqueous solute concentrations and evaluation of mass transport coefficients in peritoneal dialysis.

The quantitative description of diffusive and convective mass transport of small solutes in peritoneal dialysis is dependent on accurate determination and appropriate expression of the concentration of investigated substances. For small solutes which easily equilibrate between dialysate and plasma the solute concentration in plasma should be expressed per volume of plasma water (aqueous concentration) and not per volume of whole plasma. Furthermore, the Donnan effect should be taken into account for electrolytes if measured by flame photometry. The common practice of expressing solute concentration per volume of whole plasma (plasma concentration) may result in substantial errors in calculated values of peritoneal transport parameters. To quantify these errors we compared plasma versus aqueous dialysate to plasma ratios (D/P), diffusive mass transport coefficients (KBD), and sieving coefficients (S) for 28 6-h single-dwell studies using glucose 3.86% dialysis fluid. For all substances except glucose non-corrected plasma D/P overestimated corrected aqueous D/P at 360 min by 2% (potassium and sodium) to 8% (creatinine) and, as assessed by the Pyle-Popovich model, non-corrected KBD overestimated true KBD by 12% (potassium) to 41% (urea). Similar results were also obtained for KBD estimation using the Garred model and KBD estimated during dialysate isovolaemia. The use of aqueous instead of plasma concentrations resulted in a substantial change of S for urea but not for the other investigated solutes. These results emphasise the importance of expressing small solute concentrations per volume of plasma water and not per volume of whole plasma in calculations of D/P ratios and mass transport coefficients.

Biological Transport, Active↗

PubMed1991

Theoretical basis and experimental verification of the impact of ultrafiltration on dialyzer clearance.

Dialyzer clearance K is usually presented as K = K0 + Tr Qu, were Qu is ultrafiltration rate, K0 is clearance for Qu = 0, and Tr is transmittance coefficient. Although a simple and accurate mathematical description of K0 is widely used, only a somewhat inaccurate formula for Tr that predicts a linear relationship between Tr and K0 has been proposed before. In this study the detailed investigation of Tr using a one-dimensional theory of a dialyzer is presented. In general, the application of a one-dimensional theory requires sophisticated numerical methods, but for small and middle molecular weight solutes an analytical formula for K can be derived. Tr predicted by the developed theory in comparison to Tr predicted by the previous linear formula is higher for small molecular weight solutes and lower for middle and large molecular weight solutes. These theoretical results were confirmed in experiments carried out in vitro for hollow-fiber dialyzers and small molecular weight solutes (urea, creatinine, sodium, TcO4) as well as middle molecular weight solutes (vitamin B12).

Hemofiltration↗

PubMed1991

Simple models for description of small-solute transport in peritoneal dialysis.

The convective component in the general description of transport of solutes across the peritoneal membrane can be expressed as SQuc, where S is the sieving coefficient, Qu is the ultrafiltration flow rate, and c is the average concentration in the membrane (c = (1-F)cB + FcD, where cB and cD are blood plasma and dialysate solute concentration, respectively). F is a weighing function dependent on Qu, S, and the diffusive mass transport coefficient KBD. In this study a class of simple models of solute transport was considered in which S = 1 (justified for small solutes) was chosen, and F was selected as follows: F = 0 (as in the S = 1 (justified for small solutes) was chosen, and F was selected as follows: F = 0 (as in the widely used model of Garred and coworkers), F = 0.5 (theoretically justified model), F = 0.33 (theoretically justified for a high ultrafiltration period), and F = 1 (for convective transport from dialysate to blood). For all these models the estimation of KBD from clinical data can be performed with the aid of linear regression. The simple models were compared with the Pyle-Popovich model which takes into account the general expression for convective solute transport, for both the accuracy of the KBD determination (using linear regression) and the accuracy of theoretically calculated dialysate to plasma concentration ratios (D/P) to experimental D/P. Clinical evaluation of the new models was carried out in 28 6-hour dwell studies in 21 nondiabetic patients using 2 liters of hypertonic (glucose 3.86%) dialysis fluid. The differences between the simple models were small from the clinical point of view for urea, creatinine, glucose, and potassium, whereas for sodium the predictions were not satisfactory for any of the models. For urea and creatinine the model with F = 0.5 yielded the best fit of theoretical predictions to experimental data. For glucose and potassium small but systematic deviations of theoretical D/P from experimental D/P were observed for all simple models. The protein transport could be satisfactorily described by a model in which F = 1, as shown for total protein.

Creatinine↗

PubMed1991

Mathematical modeling of antigen and immune complex kinetics during extracorporeal removal of autoantibody.

The extracorporeal removal of circulating auto-antibodies by repeated plasma exchange or continuous lymph drainage is modeled by single-pool kinetics. Total amounts of antigenic determinants, k-valent antibodies and immune complexes are variables of the model. Factors influencing the course of therapy are included: production rate of antigen and antibody and their natural catabolism. This model can give useful formulae for clinical practice. The effect of treatment can be predicted from the relative depletion of antibody and the actual severity of the disease. Another formula shows how the changed catabolism of antigen after antibody binding can influence the amount of immune complexes. As an example, lymph drainage in myasthenia gravis is calculated using averaged data from three patients.

Antigen-Antibody Complex↗

PubMed1990

Peritoneal transport in CAPD patients with permanent loss of ultrafiltration capacity.

During a 10 year period, 14 out of 227 patients (6.2%) undergoing continuous ambulatory peritoneal dialysis (CAPD) developed permanent loss of ultrafiltration capacity (UFC). The risk of UFC loss increased from 2.6% after one year to 30.9% after six years of treatment. A six hour, single dwell study with glucose 3.86% dialysis fluid was carried out in nine of the UFC loss patients and in 18 CAPD patients with normal UFC. Intraperitoneal dialysate volumes were calculated using 131I-tagged albumin (RISA) as volume marker with a correction applied for its elimination from the peritoneal cavity. The RISA elimination coefficient (KE), which can serve as an estimation of the upper limit of the lymphatic flow, was also calculated. Diffusive mass transport coefficients (KBD) for investigated solutes (glucose, creatinine, urea, potassium, total protein, albumin and beta 2-microglobulin) were calculated during a period of dialysate isovolemia. Two patterns of UFC loss were observed: (a) seven patients had high KBD values for small solutes resulting in rapid uptake of glucose, whereas KBD values for proteins were normal; (b) two patients had normal KBD values but a threefold increase both in the fluid reabsorption rate and KE. We conclude that loss of the osmotic driving force (due to increased diffusive mass transport for small solutes) and increased fluid reabsorption (possibly due to increased lymphatic reabsorption) are the two major causes of permanent loss of UFC in CAPD patients.

Biological Transport↗

PubMed1989

Peritoneal ultrafiltration and fluid reabsorption during peritoneal dialysis.

Peritoneal ultrafiltration and fluid reabsorption characteristics for 18 patients undergoing continuous ambulatory peritoneal dialysis (CAPD) were investigated in single dwell studies of 6 h duration with 21 of 3.86% glucose dialysis fluid. Dialysate volumes were determined in situ using radioiodinated serum albumin (RISA) as volume marker with a correction applied for the total elimination of RISA from the peritoneal cavity. The RISA elimination rate was calculated as 2.1 +/- 0.5 ml/min. The true dialysate volume after 360 min was on average 28% less than the apparent volume calculated without correction for the elimination of RISA. The mean maximum true volume plus sampling losses was 3255 ml at 240 min, corresponding to a mean net ultrafiltration volume of 762 ml between 3 min and 240 min. The mean net fluid reabsorption rate between 240 min and 360 min was 1.2 +/- 0.7 ml/min. This study of standard dialysate volume/time curves in clinically stable CAPD patients using hypertonic dialysis fluid shows that about 90% of the total net ultrafiltration is achieved during the first 90 min of the dwell. After an extended period of dialysate isovolaemia, usually lasting as long as between 120 min and 240 min, fluid reabsorption is observed in all patients.

Aged↗

PubMed1989

A mathematical model of extracorporeal antibody removal in autoimmune disease.

A mathematical model of T-B cell cooperation is adopted to describe autotolerance and autoimmunity. The model describes the development of plasma cells and T-helper cells from their precursors through activated and proliferating cells. A state of autotolerance is simulated by reducing the rate of T precursors supply (partial clonal deletion theory), while the normal rate yields a stable state of autoimmunity. During the state of autoimmunity extra-corporeal removal of autoantibody and immunosuppression are simulated. Removal of auto-antibody alone results in stimulation of the immune system and quick return to the previous state, mainly on account of activation of memory cells. Antibody overshooting is negligible. Immunosuppression leads to a slow decline in the antibody level. Synergy is clearly demonstrated between both therapies.

Autoantibodies↗

PubMed1988

Autoimmunity and its therapy: mathematical modelling.

A mathematical description of autotolerance and autoimmunity based on the previous model of immune response for normal antigen stimulation is given. In particular, the clonal deletion theory and non-specific stimulation of T-helper cells are included. Thus, an idea about the origin of autoimmune disease and the qualitative description of its course is presented. Possible therapies, such as immunosuppression and extracorporeal removal of autoantibodies, are also discussed.

Antigens↗

PubMed1988

Membrane plasma fractionation: effect of the surface area.

The influence of the surface area on the performance of plasma filters for dead-end mode of filtration is presented in this paper. Theoretical analysis of the dead-end filtration was performed and verified experimentally (using ENKA cellulose-diacetate PF-100 membranes) in respect to beta-lipoprotein. The theoretical model allows to optimize the course of the transmembrane pressure during plasma fractionation procedure in dependence of the surface area, initial concentration of macromolecules, total volume of the feed and membrane structure. The results indicate that the surface area effect is an important factor in the operation of membrane plasma fractionation and should be considered in the design of the plasma fractionation filter.

Blood Volume↗

PubMed1985

Theoretical formulation of sieving coefficient evaluation for membrane plasma separation.

Three different sieving coefficient definitions were theoretically investigated. It has been shown that the local sieving coefficient, characterizing membrane property, can be calculated under specified assumptions from input-output measurements. In contrast, the evaluation of the device sieving coefficient, useful in kinetic modeling, is validated in a situation in which calculation of the local sieving coefficient is connected with substantial error. The relationship between different sieving coefficient definitions is also given.

Blood↗

PubMedDate not supplied

Simple membrane models for peritoneal dialysis. Evaluation of diffusive and convective solute transport.

Currently used mathematical models to estimate parameters describing diffusive (diffusive mass transport coefficient, KBD) and convective (sieving coefficient, S) solute transport during peritoneal dialysis, as proposed by Pyle, Popovich, and Moncrief (PPM model) and Babb, Randerson, and Farrell (BRF model), require nonlinear regression and advanced numerical methods for parameter estimation. In this study, a simplified approach to the evaluation of KBD and S, using the same transport equation used in the PPM and BRF models but based on two-dimensional linear regression, is proposed. This new approach can be extended to generate a family of membrane models that differ in assumption concerning the average solute concentration (c) inside the peritoneal membrane. In particular, c was assumed to be equal to the arithmetic mean value of the dialysate and blood concentrations (PPM model), the blood concentration (BRF model), or the dialysate concentration (D model). The investigated family of models was used to study the transport of urea, creatinine, glucose, sodium, potassium, and total protein in 20 single, 6 hr dwell studies carried out in 20 nondiabetic patients in stable clinical condition using hypertonic (3.86%) glucose solution. For the PPM model, the linear and nonlinear regressions were able to provide almost identical values of KBD and S. The theoretical dialysate to plasma concentration ratio (D/P) was adequately fitted to experimental D/P for both the PPM and BRF models, but the fit was worse for the D model. However, unphysiologic (i.e., out of the 0-1 range) values of S were found for urea, potassium, and glucose independent of the version of the model used.

Adult↗