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G Stelin

Publications and source records attributed to G Stelin.

7 recordsLinked to original sources
PubMed1991

Computer simulations of peritoneal fluid transport in CAPD.

To model the changes in intraperitoneal dialysate volume (IPV) occurring over dwell time under various conditions in continuous ambulatory peritoneal dialysis (CAPD), we have, using a personal computer (PC), numerically integrated the phenomenological equations that describe the net ultrafiltration (UF) flow existing across the peritoneal membrane in every moment of a dwell. Computer modelling was performed according to a three-pore model of membrane selectivity as based on current concepts in capillary physiology. This model comprises small "paracellular" pores (radius approximately 47 A) and "large" pores (radius approximately 250 A), together accounting for approximately 98% of the total UF-coefficient (LpS), and also "transcellular" pores (pore radius approximately 4 to 5 A) accounting for 1.5% of LpS. Simulated curves made a good fit to IPV versus time data obtained experimentally in adult patients, using either 1.36 or 3.86% glucose dialysis solutions, under control conditions; when the peritoneal UF-coefficient was set to 0.082 ml/min/mm Hg, the glucose reflection coefficient was 0.043 and the peritoneal lymph flow was set to 0.3 ml/min. Also, theoretical predictions regarding the IPV versus time curves agreed well with the computer simulated results for perturbed values of effective peritoneal surface area, LpS, glucose permeability-surface area product (PS or "MTAC"), intraperitoneal dialysate volume and dialysate glucose concentration. Thus, increasing the peritoneal surface area caused the IPV versus time curves to peak earlier than during control, while the maximal volume ultrafiltered was not markedly affected. However, increasing the glucose PS caused both a reduction in the IPV versus time curve "peak time" and in the "peak height" of the curves. The latter pattern was also seen when the dialysate volume was reduced. It is suggested that computer modelling based on a three-pore model of membrane selectivity may be a useful tool for describing the IPV versus time relationships under various conditions in CAPD.

Ascitic Fluid↗
PubMed1991

Clinical implications of a three-pore model of peritoneal transport.

The peritoneal barrier exchange characteristics are in this article described in terms of a three-pore model of membrane permselectivity. The peritoneal membrane during continuous ambulatory peritoneal dialysis (CAPD) is thus simulated to have a large number of small pores of radius 40-55 A, a small number of large pores of radius 200-300 A, and an abundance of transcellular pores of radius 4-5 A. Due to the heteroporous nature of the peritoneal membrane, peritoneal small solute sieving coefficients are of the order of 0.5-0.6, and not near unity, as predicted for a homoporous membrane having 50 A (radius) equivalent pores, but lacking transcellular pores. As a consequence, the dialysate during CAPD is diluted during the first 50-100 minutes of the dwell. Furthermore, there is a marked coupling between the increased net transperitoneal volume flow, occurring early in the cycle, and the transfer of "small" macromolecules, such as beta 2-microglobulin and albumin, across the peritoneal membrane. This coupling is, however, small for "large" macromolecules, such as IgG and IgM, or for small solutes. Increasing the peritoneal surface area, in computer simulations of peritoneal transport according to the three-pore model, causes the simulated intraperitoneal (i.p.) volume vs. time (V(t)) curves to peak earlier than during control, while the maximum volume ultrafiltered is not markedly affected. However, selectively increasing the glucose PS (mass transfer area coefficient) causes a reduction both in the peak time and the peak "height" of the V(t) curves. The latter pattern is also seen when the dialysate volume is reduced. It is concluded that a three-pore model of membrane permselectivity selectivity can adequately describe the kinetics of peritoneal transport of small and large solutes and of fluid.

Ascitic Fluid↗
PubMed1990

A phenomenological interpretation of the variation in dialysate volume with dwell time in CAPD.

Intraperitoneal fluid volume (IPV) changes versus time were followed in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) using a simple volume recovery method. In each patient dialysates containing 1.36 and 3.86 percent glucose as an osmotic agent were investigated. The patients' IPV versus time data were fitted to a function determined by four "arbitrary" coefficients, from which both the initial ultrafiltration (UF) rate immediately following intraperitoneal (i.p.) fluid instillation and the "final" peritoneal-to-blood fluid absorption rate could be assessed. The peritoneal osmotic conductance to glucose, that is, the peritoneal ultrafiltration coefficient (Kf), times the peritoneal osmotic reflection coefficient to glucose (sigma g), Kf sigma g, was determined using two related approaches. Kf sigma g is a major determinant of the transperitoneal volume exchange, and it was calculated to be 3.54 +/- 0.85 (+/- SE) and 3.81 +/- 0.52 microliters/min/mm Hg, respectively, depending on the assumption employed. Kf sigma g was further analysed according to a three-pore model of membrane permeability to determine the possible range of Kf and sigma g compatible with a peritoneal small solute sieving coefficient (phi) ranging from 0.3 to 0.61. According to these calculations both Kf and sigma g ranged from 0.043 to 0.081 (ml/min/mm Hg and dimensionless, respectively). The maximal peritoneal lymph flow (L) realistic according to this analysis, and compatible with a measured total peritoneal-to-blood fluid absorption rate of 1.25 +/- 0.14 ml/min, was 0.75 ml/min, the most plausible values, however, falling between 0.3 to 0.5 ml/min.

Biological Transport↗
PubMed1989

Simulations of peritoneal solute transport during CAPD. Application of two-pore formalism.

Blood peritoneal clearances of various endogenous solutes in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) were evaluated according to recent developments of the two-pore theory of membrane permeability, using a non-linear transport formalism for the analysis. Based on results obtained from these calculations and taking lymphatic drainage into account, transport from peritoneal cavity to the blood was also simulated. With respect to solute transport the data were compatible with a functional blood-peritoneal barrier consisting of a two-pore membrane containing a large number of paracellular "small pores" of radius 40 to 55 A and a small number of "large pores" of radius 200 to 300 A. Solutes smaller than 25 A in radius were found to be permeating across the peritoneal membrane mainly by means of diffusion across the small pores, whereas solutes larger than 40 A were calculated to reach the peritoneal cavity exclusively by unidirectional convection across the large pores. In addition, water was simulated to be transported through transcellular "ultrapores" (radius less than 8 A) not accessible to hydrophilic solute permeation. Small solute absorption from the peritoneal cavity was found to occur by diffusion across small pores. Molecules larger than 25 to 30 A in radius (molecular weight above 25,000) were simulated to be absorbed from the peritoneal cavity exclusively via non-size-selective lymphatic drainage.

Biological Transport↗