Predict Volume Changes Research Articles

Coupling of lung tissue tethering force to fluid dynamics in the pulmonary circulation

AbstractDynamic changes in lung volume during breathing and alteration of posture are both known to influence the distribution of perfusion within the lung. Here we couple computational models of pulmonary blood flow and parenchymal tissue mechanics to produce a novel flow model that predicts tissue deformation simultaneously with flow distributions at different lung volumes and postures. The model is used to study the effect of lung volume on flow distribution as a result of normal variation in axial and radial tethering forces. Finite deformation elasticity is used to predict volume changes of the lung tissue and resultant tethering pressures within the tissue. A finite element model of the pulmonary arterial network is embedded within the lung volume and deforms with the tissue. The spatial distribution of steady‐state blood flow is predicted using the Poiseuille resistance (including gravity), conservation of mass, and a vascular pressure–radius relationship. Blood flow gradients with respect to gravitationally dependent height are calculated. Gradients are predicted to be consistently steeper in the supine (compared with prone) model due to increased tissue deformation. Decreased lung volume resulted in increased gravitationally dependent flow gradients, predominantly due to the effect of axial vessel stretch on the length and the radius of the arterial vessels. Copyright © 2010 John Wiley & Sons, Ltd.

Effects of drug transporters on volume of distribution.

Recently, drug transporters have emerged as significant modifiers of a patient's pharmacokinetics. In cases where the functioning of drug transporters is altered, such as by drug-drug interactions, by genetic polymorphisms, or as evidenced in knockout animals, the resulting change in volume of distribution can lead to a significant change in drug effect or likelihood of toxicity, as well as a change in half life independent of a change in clearance. Here, we review pharmacokinetic interactions at the transporter level that have been investigated in animals and humans and reported in literature, with a focus on the changes in distribution volume. We pay particular attention to the differing effects of changes in transporter function on the three measures of volume. Further, trends are discussed as they may be used to predict volume changes given the function of a transporter and the primary location of the interaction. Because the liver and kidneys express the greatest level and variety of transporters, we denote these organs as the primary location of transporter-based interactions. We conclude that the liver is a larger contributor to distribution volume than the kidneys, in consideration of both uptake and efflux transporters. Further, while altered distribution due to secondary interactions at tissues other than the liver and kidneys may have a pharmacodynamic effect, these interactions, at least at the blood-brain barrier, do not appear to significantly influence overall distribution volume. The analysis provides a framework for understanding potential pharmacokinetic interactions rooted in drug transporters as they modify drug distribution.

High-pressure behavior ofTiO2as determined by experiment and theory

Using high-resolution synchrotron x-ray powder diffraction we have investigated the structural phase transitions and equations of state of titanium dioxide $({\text{TiO}}_{2})$ under high pressure before and after heating at high temperature. The phase sequence we observe experimentally is as follows: rutile $(\text{RT})\ensuremath{\rightarrow}\text{columbite}\text{ }(\text{CB})\ensuremath{\rightarrow}\text{baddeleyite}\text{ }(\text{MI})\ensuremath{\rightarrow}\text{orthorhombic}\text{ }\text{I}\text{ }(\text{OI})\ensuremath{\rightarrow}\text{orthorhombic}\text{ }\text{II}\text{ }(\text{OII})$. The equations of state as determined from our experiments are consistent with previous measurements and computations. The only exception is the OII phase for which we find a significantly lower room-pressure bulk modulus $({K}_{0})$ of 312 $(\ifmmode\pm\else\textpm\fi{}34)\text{ }\text{GPa}$ and room-pressure volume $({V}_{0})$ of 25.28 $(\ifmmode\pm\else\textpm\fi{}0.35)\text{ }{\text{\AA{}}}^{3}$ as compared to previous experiments. We find that the volume decreases across the $\text{OI}\ensuremath{\rightarrow}\text{OII}$ phase transition at room temperature by $\ensuremath{\sim}8.3%$, in very good agreement with our static first-principles calculations which predict volume changes of 8.2% and 7.6% for local-density approximation and generalized gradient approximation, respectively. This volume collapse is significantly higher than previously determined but consistent with the volume decrease observed in other dioxides across this transition.

Evolution of Rhonegletscher, Switzerland, over the past 125 years and in the future: application of an improved flowline model

AbstractTo study the past and future evolution of Rhonegletscher, Switzerland, a flowline model was developed to include valley shape effects more accurately than conventional flowband models. In the model, the ice flux at a gridpoint was computed by a two-dimensional ice-flow model applied to the valley cross-section. The results suggested the underestimation of the accumulation area, which seems to be a general problem of flowline modelling arising from the model’s one-dimensional nature. The corrected mass balance was coupled with the equilibrium-line altitude (ELA) change, which was reconstructed for the period 1878–2003 from temperature and precipitation records, to run the model for the past 125 years. The model satisfactorily reproduced both changes in the terminus position and the total ice volume derived from digital elevation models of the surface obtained by analyses of old maps and aerial photographs. This showed the model’s potential to simulate glacier evolution when an accurate mass balance could be determined. The future evolution of Rhonegletscher was evaluated with three mass-balance conditions: the mean for the period 1994–2003, and the most negative (2003) and positive (1978) mass-balance values for the past 50 years. The model predicted volume changes of –18%, –58% and +38% after 50 years for the three conditions, respectively.

05/00899 Phase behavior applications of SAFT based equations of state — from associating fluids to polydisperse, polar copolymers

A molecular-thermodynamic model is presented to predict volume change transitions in temperature-sensitive polymer gels. The model uses an extended Flory-Huggins theory as a mixing contribution and a new interpolated affine model suggested by Birshtein as an elastic contribution. The Flory χ parameter is given by the product of a temperature-dependent and a composition-dependent term. Our model also differs from those presented previously because the temperature-dependent term is given by the incompressible lattice-gas model by ten Brinke and Karasz that accounts for specific interactions such as hydrogen bonding. Following conventional practice, the van't Hoff equation is introduced to represent the effect of a small number of ionizable segments in the network chain. Calculated swelling-ratio curves for neutral and weakly ionized aqueous N-isopropylacrylamide gels use molecular parameters obtained from phase-equilibrium data for (non-crosslinked) polymer solutions. In agreement with experiment, the calculated volume-transition temperature of the gel is about 1°C higher than the lower critical solution temperature of the (non-crosslinked) polymer solution.

Numerical analysis of cure temperature and internal stresses in thin and thick RTM parts

Abstract Resin transfer molding (RTM) is a widely used manufacturing technique of composite parts. Proper selection of processing parameters is critical in order to produce successful molding and to obtain a good part. Notably, when thermosetting resins are processed, the shrinkage that results from resin polymerization increases the complexity of the problem. Numerical prediction of internal stresses during composite manufacturing has three objectives: (1) to improve knowledge about the process; (2) to analyze the effects of processing parameters on the mechanical integrity of the part; and (3) to validate the principles of thermal optimization. This investigation aims to predict residual stresses and part deformation (i.e. warpage) in thin and thick composites. Accurate characterization of materials is essential for effective numerical analysis of phenomena which determine the generation of processing stresses. For this purpose, a reaction kinetics model of the resin is presented, together with a description of mechanical properties as a function of the degree of polymerization and glass transition temperature. A linear model is used to predict volume changes in glass–polyester composites. A finite difference analysis is used to simulate the effect of thermal and rheological changes during the processing of sample plates. Classical laminate theory is applied to calculate the internal stresses that result from processing conditions. These stresses are compared to determine different curing strategies for thick composite parts. Finally, a thermal optimization algorithm is applied to demonstrate the advantages of transient heating and cooling, to minimize processing stresses and avoid thermal degradation of the material or composite delamination.

Excess hemoglobin digestion and the osmotic stability ofPlasmodium falciparum–infected red blood cells

AbstractDuring their asexual reproduction cycle (about 48 hours) in human red cells, Plasmodium falciparum parasites consume most of the host cell hemoglobin, far more than they require for protein biosynthesis. They also induce a large increase in the permeability of the host cell plasma membrane to allow for an increased traffic of nutrients and waste products. Why do the parasites digest hemoglobin in such excess? And how can infected red cells retain their integrity for the duration of the asexual cycle when comparably permeabilized uninfected cells hemolyse earlier? To address these questions we encoded the multiplicity of factors known to influence host cell volume in a mathematical model of the homeostasis of a parasitized red cell. The predicted volume changes were subjected to thorough experimental tests by monitoring the stage-related changes in the osmotic fragility of infected red cell populations. The results supported the model predictions of biphasic volume changes comprising transient shrinkage of infected cells with young trophozoites followed by continuous volume increase to about 10% lower than the critical hemolytic volume of approximately 150 fL by the end of the asexual cycle. Analysis of these results and of additional model predictions demonstrated that the osmotic stability of infected red cells can be preserved only by a large reduction in impermeant solute concentration within the host cell compartment. Thus, excess hemoglobin consumption represents an essential evolutionary strategy to prevent the premature hemolysis of the highly permeabilized infected red cell.

Molecular thermodynamics for volume-change transitions in temperature-sensitive polymer gels

A molecular-thermodynamic model is presented to predict volume change transitions in temperature-sensitive polymer gels. The model uses an extended Flory-Huggins theory as a mixing contribution and a new interpolated affine model suggested by Birshtein as an elastic contribution. The Flory χ parameter is given by the product of a temperature-dependent and a composition-dependent term. Our model also differs from those presented previously because the temperature-dependent term is given by the incompressible lattice-gas model by ten Brinke and Karasz that accounts for specific interactions such as hydrogen bonding. Following conventional practice, the van't Hoff equation is introduced to represent the effect of a small number of ionizable segments in the network chain. Calculated swelling-ratio curves for neutral and weakly ionized aqueous N-isopropylacrylamide gels use molecular parameters obtained from phase-equilibrium data for (non-crosslinked) polymer solutions. In agreement with experiment, the calculated volume-transition temperature of the gel is about 1°C higher than the lower critical solution temperature of the (non-crosslinked) polymer solution.

Effect of development and cultivation on physical properties of peat soils in New Zealand

The effect of development and cultivation on the physical properties of two peat soils formed from restiad/sedge and sphagnum peat and developed for agriculture in the Hauraki Plains, New Zealand is reported by comparing physical properties of the plough layer (0–15 cm) and the relatively unaffected underlying peat (15–40 cm). Drainage and cultivation reduced soil moisture content, increased bulk density and reduced organic matter content. Bulk density was correlated with organic matter content only for the plough layer and indicates that bulk density alone is not a good indicator of decomposition in weakly decomposed peat soils in this region. Moisture retention curves indicated that a large amount of the water in the soil could not be removed at high suctions (up to 65% of the water was retained at suction oof 1500 kPa) and may cause moisture stress for plants, particulary in the plough layer of sphagnum peat, despite the high water content of the soil. This has important implications for maintaining a water table which maintains an adequate available water content for plants in the unsaturated zone immediately above the water table. Hydraulic conductivity differed between peat types in both the plough layer and the underlying peat. The presence of a root layer at 35–40 cm in the restiad/sedge peat was considered to substantially influence the readings and has important implications for drainage design in the soil. A simple method for measuring shrinkage in peat soils which involves coating natural clods in a saran resin is presented. A shrinkage curve indicated that shrinkage in peat is directly related to the gravimetric water content and does not contain zones of residual or structural shrinkage which are often associated with mineral soils. It is suggested, therefore, that a simple linear model based upon normal shrinkage will successfully predict volume changes associated with drainage of peat soils for agriculture.

Osmotic effects of protein polymerization: Analysis of volume changes in sickle cell anemia red cells following deoxy-hemoglobin S polymerization

Polymerization-depolymerization of proteins within cells and subcellular organelles may have powerful osmotic effects. As a model to study these we analyzed the predicted volume changes following hemoglobin (Hb) S polymerization in sickle cell anemia (SS) red cells with different initial volumes. The theoretical analysis predicted that dehydrated SS red cells may sustain large polymerization-induced volume shifts whose direction would depend on whether or not small solutes were excluded from polymer-associated water. Experiments with SS cells from promptly fractionated venous blood showed oxygenation-induced swelling, maximal in the densest cells, in support of nonexclusion models. The predicted extent of cell dehydration on polymerization was strongly influenced by factors such as the dilution of residual soluble Hb and the increased osmotic contribution of Hb in cells dehydrated by salt loss, largely overlooked in the past. The osmotic effects of polymer formation may thus play an important part in microcirculatory infarction by dense SS cells, as they become even denser and stiffer during deoxygenation in the capillaries.

Water stress conditioning of corn (Zea mays) in the field and the greenhouse

Leaf water potential, osmotic potential, and leaf conductance were measured on corn (Zea mays L.) under water stress in the field and the greenhouse. Field-grown plants were subjected to several cycles of moderate water stress during vegetative growth, while greenhouse plants were well watered until just before the measurement period began following tasselling. In both the field and the greenhouse, leaf water potential declined at midday. Comparison of leaf water potential and osmotic potential measurements indicated that in both environments, the midday decline in leaf water potential was accompanied by a decline in osmotic potential. Since the decline in osmotic potential was greater than that accounted for by predicted volume changes resulting from normal daily dehydration, it was assumed to indicate osmotic adjustment. Despite these similarities, field-grown plants showed a greater response to water stress. Field plants underwent larger daily changes in leaf water potential and these were accompanied by larger changes in osmotic potential. As a result of this greater osmotic adjustment in the field, conductivity was higher at equivalent leaf water potentials and the critical leaf water potential was lower than in greenhouse-grown plants. In both environments, osmotic adjustment maintained leaf turgor (or pressure potential) in a narrow positive range. Although there was no direct relation between turgor potential and leaf conductivity, we hypothesize that the maintenance of a positive turgor potential during daylight hours is significant for growth since it may allow the moisture- and temperature-sensitive process of leaf expansion to proceed during the warmer daylight hours, even under moderate water stress.

The shape of red blood cells as a function of membrane potential and temperature

It is well known that a pH shift of the outside medium from 5 to 9 produces a shape transformation of washed human red blood cells from stomatocytes to echinocytes in isotonic salt solutions. In addition, a stomatocytogenic effect is demonstrated here due to solutions of low ionic strength (below 70 mM). An analysis of the true cell state in these situations, proved by measurements of predicted volume changes, indicates a good correlation between transmembrane potential and cell shape. The fact that amphotericin B acts as echinocytogenic agent in low ionic strength medium at pH 7.4 but not at pH 5.1 underlines this explanation. Therefore, a transmembrane potential positive inside produces stomatocytes, slightly negative inside (below--10 mV), normocytes, and strongly negative, echinocytes. The temperature dependence of this process underlines the rigidity-pattern hypothesis of red blood cell shape (Glaser & Leitmannová, 1975, 1977).

Volume of mixing effect on solvent shifts in fluorine magnetic resonance spectra

Fluorine chemical shifts have been determined for dilute solutions of 1,1,1,10,10,10-hexafluorodecane in twenty saturated hydrocarbon solvents. The van der Waals contribution to the solvents shifts was found to depend on the cohesive energy density of the solvent in an unexpected way. After correcting for bulk magnetic susceptibility effects, the shifts are fairly well correlated by an equation of the form δ s = A + B(1 − 2 ζ)( n 2 − 1)/( n 2 + 2), where A and B are empirical constants, n is the solvent refractive index, and ζ is a function of the cohesive energy density closely related to that used to predict volume changes on mixing for dilute solutions of fluorocarbons in hydrocarbon solvents.

Elastoplastic analysis of hollow spheres subjected to external pressure loading

AbstractThe elastoplastic deformation of spherical shells of uniform thickness acted upon by external pressure is investigated in this paper. A deformation theory of plasticity is combined with the classical elasticity equations and a solution is obtained by the method of successive elastic solutions. A logarithmic effective stress‐effective plastic strain diagram is used to determine the volume change for thick polypropylene spheres under the action of external pressure. These results are compared with previously published experimental volume changes in polypropylene spheres. This comparison shows that the predicted volume changes are similar to the experimental results.