Transport of protein in the abdominal wall during intraperitoneal therapy. I. Theoretical approach

2001 ◽  
Vol 281 (2) ◽  
pp. G424-G437 ◽  
Author(s):  
Michael F. Flessner

Intraperitoneal therapies such as peritoneal dialysis or regional chemotherapy use large volumes of solution within the peritoneal cavity. These volumes increase intraperitoneal hydrostatic pressure (Pip), which causes flow of the solution into tissues that surround the cavity. The goal of this paper is to integrate new experimental findings in a rigorous mathematical model to predict protein transport from the cavity into tissue. The model describes non-steady-state diffusion and convection of protein through a deformable porous medium with simultaneous exchange with the microcirculation and local tissue binding. Model parameters are dependent on local tissue pressure, which varies with Pip. Solute interactions with the tissue in terms of local distribution volume (solute void space), local binding, and retardation relative to solvent flow are demonstrated to be major determinants of tissue concentration profiles and protein penetration from the peritoneal cavity. The model predicts the rate of fluid loss from the cavity to the abdominal wall in dialysis patients to be 94 ml/h, within the observed range of 60–100 ml/h. The model is fitted to published transport data of IgG, and the retardation coefficient f is estimated to be 0.3, which markedly reduces the rate of protein penetration and is far lower than previously published estimates. With the value of f = 0.3, model calculations predict that Pipof 4.4 mmHg and dialysis duration of 24 h result in several millimeters of protein penetration into the tissue.

1996 ◽  
Vol 270 (2) ◽  
pp. F377-F390 ◽  
Author(s):  
M. F. Flessner ◽  
A. Schwab

Ascites or dialysis fluid in the peritoneal cavity causes fluid loss from the cavity to the body. Experiments in animals and in humans have shown that the fluid loss rate increases with large increments in the intraperitoneal hydrostatic pressure (Pip). We hypothesized that there is a low-threshold Pip above which this fluid loss occurs. Because the full Pip force is exerted across the abdominal wall (AW), we further hypothesized that fluid movement into the abdominal wall would vary directly with the Pip. To address these questions, we dialyzed rats for 3 h in the supine position at constant levels of Pip with isotonic and hypertonic dialysis solutions containing a protein marker of fluid movement. We measured total fluid loss, AW fluid-marker concentration, and lymph flow. With variation of Pip from 0 to 8 cmH2O, we found that 1) lymph flows (0.61 +/- 0.03 ml/h) were not dependent on Pip, 2) measured isotonic fluid loss rate varied from 0.29 +/- 0.06 ml/h at 0 cmH2O to 0.62 +/- 0.02 at 2 cmH2O and then rose in a linear fashion to 5.06 +/- 0.10 ml/h at 8 cmH2O, 3) fluid movement into the AW paralleled the measured fluid loss rate, and 4) protein clearance from the cavity overestimated the true fluid loss because of adsorption of the marker to the peritoneal surface. We conclude that, although peritoneal lymph flow is not dependent on intraperitoneal hydrostatic or osmotic pressure, fluid loss from the cavity and fluid loss to the abdominal wall are directly proportional to Pip > 2 cmH2O. We also note that protein markers of fluid movement require correction for tissue surface adsorption for accurate results.


2004 ◽  
Vol 124 (6) ◽  
pp. 679-690 ◽  
Author(s):  
Toby W. Allen ◽  
O.S. Andersen ◽  
Benoit Roux

Proteins, including ion channels, often are described in terms of some average structure and pictured as rigid entities immersed in a featureless solvent continuum. This simplified view, which provides for a convenient representation of the protein's overall structure, incurs the risk of deemphasizing important features underlying protein function, such as thermal fluctuations in the atom positions and the discreteness of the solvent molecules. These factors become particularly important in the case of ion movement through narrow pores, where the magnitude of the thermal fluctuations may be comparable to the ion pore atom separations, such that the strength of the ion channel interactions may vary dramatically as a function of the instantaneous configuration of the ion and the surrounding protein and pore water. Descriptions of ion permeation through narrow pores, which employ static protein structures and a macroscopic continuum dielectric solvent, thus face fundamental difficulties. We illustrate this using simple model calculations based on the gramicidin A and KcsA potassium channels, which show that thermal atomic fluctuations lead to energy profiles that vary by tens of kcal/mol. Consequently, within the framework of a rigid pore model, ion-channel energetics is extremely sensitive to the choice of experimental structure and how the space-dependent dielectric constant is assigned. Given these observations, the significance of any description based on a rigid structure appears limited. Creating a conducting channel model from one single structure requires substantial and arbitrary engineering of the model parameters, making it difficult for such approaches to contribute to our understanding of ion permeation at a microscopic level.


2005 ◽  
Vol 20 (5) ◽  
pp. 347-352 ◽  
Author(s):  
Alberto Goldenberg ◽  
Jacques Matone ◽  
Wagner Marcondes ◽  
Fernando Augusto Mardiros Herbella ◽  
José Francisco de Mattos Farah

PURPOSE: Compare, in a rabbit model, the inflammatory response and adhesions formation following surgical fixation of polypropilene and Vypro mesh in the inguinal preperitoneal space. METHODS: Fourteen male New Zealand rabbits, weighing between 2.000 to 2.500 g were used. A midline incision was made and the peritoneal cavity was exposed. The 2,0X1,0 cm polypropylene mesh was fixed in the left flank and secured to the margins with 3-0 prolene in a separate pattern. In the right flank, a 2,0X1,0 cm Vypro II mesh was sewn in the same way. After the post surgical period, the animals were again anesthetized and underwent laparoscopic approach, in order to identify and evaluate adhesions degree. Both fixed prosthesis were excised bilaterally with the abdominal wall segment, including peritoneum, aponeurosis and muscle and sent to a pathologist RESULTS: Operative time ranged from 15 to 25 minutes and no difficulties in applying the mesh were found. From the 14 polypropylene meshes fixed to the intact peritoneum, 11 had adhesions to the abdominal cavity (78,6%). Concerning Vypro mesh, 12 animals developed adhesions from the 14 with mesh fixation (85,7%). Histological examination of tissues harvested revealed fibroblasts, collagen, macrophages and lymphocytes between the threads of the mesh. CONCLUSION: Polypropylene and Vypro mesh, when implanted in the peritoneal cavity of rabbits provoke similar amount of adhesions. Vypro mesh tissues had higher fibrosis resulting in better mesh incorporation to the abdominal wall.


2019 ◽  
Vol 33 (04) ◽  
pp. 1950012
Author(s):  
P. C. Baral

In this work, we report on theoretical study of the effect of electron-phonon (EP) interaction in THz frequency and temperature dependence of the electrical resistivity in heavy fermion (HF) systems. For this purpose, a model Hamiltonian is considered which consists of the Heisenberg type exchange interaction between localized moments and a tight binding model called the Kondo lattice model (KLM). The effect of EP coupling on electrical resistivity is presented by considering phonon interaction to bare f-electrons, band electrons and to the hybridization between band and f-electrons as a perturbed term. The phonon Hamiltonian in harmonic approximation is also included. The model Hamiltonian is solved by employing the mean-field theory (MFT) along with the Hubbard model of approximation. The temperature- and frequency-dependent electrical resistivity exhibits change in slopes at T[Formula: see text] as well as at T[Formula: see text]. The theoretical findings from the graphical analysis by varying the model parameters g[Formula: see text], g[Formula: see text] and g[Formula: see text] are compared to some of the experimental results in HF systems.


1993 ◽  
Vol 13 (2_suppl) ◽  
pp. 35-38 ◽  
Author(s):  
Bengt Rippe

The three-pore model of peritoneal transport treats the capillary membrane as a primary barrier determining the amount of solute that transports to the interstitium and the peritoneal cavity. According to the three-pore model, the principal peritoneal exchange route for water and water-soluble substances is a protein-restrictive pore pathway of radius 40–55 A, accounting for approximately 99% of the total exchange (pore) area and approximately 90% of the total peritoneal ultrafiltration (UF) coefficient (LpS). For their passage through the peritoneal membrane proteins are confined to so-called “large pores” of radius approximately 250 Å, which are extremely few in number (0.01% of the total pore population) and more or less nonrestrictive with respect to protein transport. The third pathway of the three-pore model accounts for only about 2% of the total LpS and is permeable to water but impermeable to solutes, a so-called “water-only” (transcellular?) pathway. In contrast to the classical Pyle-Popovich (P&P) model, the three-pore model can predict with reasonable accuracy not only the transport of water and “small solutes” (molecular radius 2.3–15 Å) and “intermediatesize” solutes (radius 15–36 Å), but also the transport of albumin (radius 36 Å) and larger molecules across the peritoneal membrane. The model operates with reflection coefficientsa (a's) for small solutes <0.1. These are approximately one order of magnitude lower than the & sigma's In the P&P model. Furthermore, the peritoneal LPS is one order of magnitude higher than In the P&P model. As a consequence, the major portion of the “fluid loss” from the peritoneal cavity In continuous ambulatory peritoneal dialysis (CAPD) can be explained by the operation of the so-called Starling forces (the transcapillary hydrostatic pressure gradient opposed by the plasma colloid osmotic pressure as multiplled by the LpS), and to a much lesser extent by lymphatic absorption (L). Furthermore, In contrast to the P&P model, the three-pore model can with reasonable accuracy predict the UF profiles produced when glucose Is substituted by high molecular weight solutes as osmotic agents In CAPO.


1996 ◽  
Vol 69 (1) ◽  
pp. 81-91 ◽  
Author(s):  
R. Ding ◽  
A. I. Leonov ◽  
A. Y. Coran

Abstract Vulcanization kinetics for a SBR compound was studied by using both curemeter and DSC methods by a kinetic approach. A simplified but realistic model reaction scheme was used to simulate both induction and curing periods simultaneously. Model parameters were extracted from isothermal curemeter experiments. The model prediction demonstrated a good agreement with isothermal curemeter data over a temperature range of 120°C to 180°C. The variation of equilibrium modulus with temperature, observed from cure curves, can also be predicted. However, DSC experiments showed a different reaction behavior in the curing period as compared to model calculations. This was explained by the assumption that the reaction heat observed in DSC is due to all possible exothermal reactions, and the formation of crosslinks is only a part of these reactions. Hence, the curemeter can provide a good indication of crosslink formation, while DSC displays the entire reaction heat released during the vulcanization process. The kinetic approach allows one to incorporate vulcanization kinetics into the practical simulation of reactive processing operations.


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