Trapped Volumes Research Articles

Assessment of sediment yield and deposition in a dry reservoir using field observations, RUSLE and remote sensing: Wadi Assarin, Oman

Soil erosion, sediment yield, and sediment transport associated with flash flooding in arid regions result in reservoir storage losses, decreased infiltration, high evaporation rates, and degradation of downstream channels. However, the lack of observational data from wadi systems and an empirical formula to compute sediment yield has hindered reservoir trapping evaluation, maintenance, and management. Therefore, this research aimed to estimate the annual soil loss in the upstream catchment area of a reservoir based on the Revised Universal Soil Loss Equation (RUSLE) with a remote sensing dataset. The sediment trapped in the Assarin Dam reservoir in Oman was estimated by coupling unmanned aerial vehicle (UAV) surveys with photogrammetry analysis to assess the reservoir siltation. Among the previous sediment trapping events, seven sets of field observation data were collected to investigate the relationship between soil loss at the catchment scale and sediment deposition volumes in the reservoir. The RUSLE method was applied to estimate soil erosion using independent factors such as rainfall erosivity, soil erodibility, topography, cover management and conservation practices. A remote sensing dataset and geographic information system (GIS) environments were used to analyse the quantitative and spatial distribution of the RUSLE parameters. Two drone surveys were conducted over the reservoir before and after a flash flood. The trapped sediment volume was estimated to be approximately 9,075 m3 (11,343 ton) per event, representing approximately 1.26 % of the total reservoir capacity. This computed volume was validated using measurements from monitored sediment scale bars sited throughout the Assarin Dam reservoir, yielding an accuracy of 79 %. From the RUSLE results, the annual soil erosion was estimated to be 196,599 ton/ha yr−1, of which approximately 5.8 % was trapped in the reservoir. Spatial-temporal variability in the rainfall patterns and the corresponding runoff discharges led to high sediment delivery at the outlet of the basin. After analysing available data from previous field surveys in Oman, a new formula for estimating the sediment yield in Wadi Assarin was developed. The results of this research, which represent the first of their type in the Middle East and North Africa (MENA) region, can support reservoir management practices and show that UAV-based photogrammetry is suitable for measuring trapped sediment volumes.

An improved multicomponent pseudopotential lattice Boltzmann method for immiscible fluid displacement in porous media

Immiscible fluid displacement in porous media occurs in several natural and industrial processes. For example, during petroleum extraction from porous rock reservoirs, water is used to displace oil. In this paper, we investigate the primary drainage and imbibition in a heterogeneous porous medium using an improved numerical model based on the multicomponent pseudopotential lattice Boltzmann method. We apply recent developments from the literature and develop new pressure boundary conditions. We show that the proposed model is able to simulate realistic viscosity ratios, and it allows independent tuning of surface tension from viscosity. Moreover, the model suppresses a nonphysical behavior of previous schemes, in which trapped fluid volumes significantly change with time. Furthermore, we show that the developed model correctly captures the underlying physical phenomena of fluid displacements. We simulate oil–water flows and verify that the measured values of irreducible water and residual oil saturations are realistic. Finally, we vary the wetting conditions of the porous medium to represent different wettability states. For the different scenarios, we show that the simulations are in good agreement with the experimental results.

Numerical prediction of structural damage due to pressure buildup in subsea oil and gas equipment

Pressure buildup/annular pressure buildup in subsea oil and gas equipment occurs primarily due to the thermal expansion of trapped liquids. With the advent of modern computers, it has become increasingly possible to numerically analyze such problems with commercial codes available in the market. The objective of the present study is to propose a methodology for numerical prediction of structural damage in subsea oil and gas equipment due to pressure buildup. A judicious combination of computational fluid dynamics (CFD) with structural finite element analysis code has been used to perform a sample numerical analysis that is truly representative of a wide class of problems encountered in subsea oil and gas applications. The mitigation of trapped pressure is one among the prime areas of concern in the subsea oil and gas industry. In the present study, CFD analysis is used to determine the maximum pressure buildup due to the thermal expansion of trapped liquids in small leak tight enclosed volumes with rigid walls and the pressure obtained is used as a boundary condition for the structural analysis. In a nutshell, the analysis has been split into three steps (1) a steady-state CFD analysis to determine the temperature distribution within the oil and gas equipment under consideration, (2) the temperature contours obtained from the steady-state analysis are imposed as a boundary condition for the transient analysis to calculate the trapped pressure in the small volumes of interest and finally and (3) a structural analysis is used to determine the damage to the oil and gas equipment. The methodology adapted is similar to a one-way coupled fluid structure interaction analysis, but provides the added advantage of a significant reduction in computational cost. In the present study, the proposed methodology has been extended to a subsea Christmas tree (XT) and the pressure buildup in the hydraulic lines has been calculated. The results obtained using the present technique has been compared with analytical solution. The proposed numerical technique can be applied to any subsea or surface oil and gas equipment where pressure buildup due to trapped volume is a major issue. The findings of this study can help for better understanding of pressure buildup in trapped volumes within subsea/surface oil and gas equipment. This study can be applied to predict the thermal expansion of trapped volumes in subsea XTs, manifolds, pipe line end manifolds (PLEM) and pipe line end termination (PLET) units.

The Use of Infant Pulmonary Function Tests in the Diagnosis of Neuroendocrine Cell Hyperplasia of Infancy

Infant pulmonary function tests (iPFTs) in subjects with neuroendocrine cell hyperplasia of infancy (NEHI) have demonstrated substantial expiratory airflow obstruction and air trapping. Can indices from iPFTs be used in the diagnosis of NEHI? This is an observational case-control study evaluating iPFT results from a registry of patients assessed at the Hadassah Hebrew University Medical Center between 2008 and 2018. iPFTs results in infants with NEHI were compared to two disease control infant groups (infants evaluated for recurrent wheezing and infants evaluated due to prematurity) and a spirometry control group of infants with normal expiratory airflow, using the Kruskal-Wallis test. Receiver operating characteristic (ROC) curves were used to assess the diagnostic accuracy of iPFT indices. We evaluated iPFT data in 481 infants (15, NEHI; 292, wheezing; 128, premature; and 46, spirometry control group). Infants with NEHI had significantly increased trapped air volumes (median functional residual capacity measured with infant whole-body plethysmography [FRCpleth] was 199%predicted; median ratio of residual volume to total lung capacity was 59%predicted) when compared with results in all evaluated groups of infants (P< .001), including multiple pairwise comparisons. Airflow limitation was demonstrated in infants with NEHI when compared with the infants in the spirometry control group but was similar to the two disease control groups. FRCpleth had the best discriminatory ability for NEHI diagnosis, with an FRCpleth≥ 150%predicted demonstrating a ROC of 0.91 (95%CI, 0.82-1.00), sensitivity of 86.7%(95%CI, 59.5%-98.3%), and specificity of 95.5%(95%CI, 93.2%-97.3%). Findings on iPFTs of markedly increased air trapping, out of proportion to the degree of airflow limitation, are characteristic of infants with NEHI. iPFT results demonstrating an FRCpleth≥ 150%predicted are highly specific for NEHI and may aid in early diagnosis. Further research is required to confirm these findings in a prospective cohort and to understand the pathophysiologic explanation for these findings.

An Interim Report on Predicting Pressure Rise due to the Thermal Expansion of Trapped Liquids in Subsea Oil and Gas Equipment

Summary The objective of the present work is to propose a methodology to predict pressure rise due to the thermal expansion of trapped liquids using computational fluid dynamics (CFD). The present study also provides a comparison between the various methods used for pressure buildup calculations that are widely used in oil and gas industries. A comparison of standard thermodynamic calculations with transient 3D CFD analysis reveals that transient CFD analyses can provide deeper insights on the temperature and velocity fields in trapped volumes. The application of the proposed method is not just restricted to a single component/equipment in the subsea field but can be applied to any trapped volume in subsea equipment. In the present study, the pressure buildup in a downhole (DH) port of a subsea Christmas tree (XT) is presented for demonstration purposes; the same methodology can be extended to other equipment or regions of interest. Because of a lack of literature on the topic of pressure rise due to thermal expansion of trapped fluids, engineers are forced to make several assumptions without knowing the effect of each term or parameter on the final pressure calculated. In this study, the percentage change/variation of the final pressure using the various forms of a standard analytical pressure rise equation is also discussed in detail.

Modelling and experimental verification of pressure relief synchronous control for small trapped fluid volumes

This paper presents a pressure relief synchronous control method for four small entrapped high-pressure fluid volumes on a huge hydraulic machine. Firstly, as the existing pressure relief methods cannot behave well for small entrapped high-pressure fluid volumes, a novel electrohydraulic proportional pressure relief circuit is proposed. The electrohydraulic proportional pressure relief circuit is composed of a proportional pressure relief valve, a damping orifice and a constant pressure source, through which the pressure can be relieved proportionally to the command signal. Secondly, as the machine is a manned hydropower carrier, a very safety-critical application, a simple and easy to implement hybrid control scheme consisting of a synchronization controller and a pressure tracking controller is developed. As the pressure relief circuit has a wide range of operating conditions and parameter uncertainties, a practical self-tuning fuzzy proportion integration (PI) pressure tracking controller with feedforward is proposed, and a master–slave PI synchronization pressure controller with dead band is employed for the four entrapped fluid volumes. Finally, the experimental verification is implemented on a test stand to demonstrate the effectiveness of the proposed synchronous control system. The experimental results confirm that the pressure deviations among the four small entrapped high-pressure fluid volumes are bound within [Formula: see text].

Pore-level influence of micro-fracture parameters on visco-capillary behavior of two-phase displacements in porous media

Abstract In this work, coupled Cahn–Hilliard phase field and Navier–Stokes equations were solved using finite element method to address the effects of micro-fracture and its characterizations on water-oil displacements in a heterogeneous porous medium. Sensitivity studies at a wide range of viscosity ratios (M) and capillary numbers (Ca), and the resultant log Ca–log M stability phase diagram, revealed that in both media, with/without fracture, the three regimes of viscous fingering, capillary fingering and stable displacement similarly occur. However, presence of the fracture caused water channeling phenomenon which resulted in reduction of the number of active fingers and hence the final oil recovery factor. At high Ca (especially in the stable regime, with log Ca ≥ −2.5 and log M ≥ 0), recovery factor for the fractured medium was relatively identical with the non-fractured one. At log M ≥ 0, the fracture was fully swept, but flow instabilities were observed inside the fracture at lower M values, especially for log Ca > −4.6. In the case of the fractured medium at log Ca = −4.6 and log M = 0 (capillary dominant flow), it is observed that the primary breakthrough took place by a finger progressed through the matrix, not those channeled through the fracture. Geometrical properties of the fracture, including length, aperture and orientation, highly affected both displacement profile and efficiency. The fracture length inversely influenced the oil recovery factor. It was observed that there is a critical fracture width (almost half of the medium average pore diameter) at which the recovery factor of the medium during displacement is minimum, compared to the media having thinner and thicker fractures. Minor channeling effect in the media with thinner fracture and larger fracture swept volume as well as high fracture/matrix cross flow in the media with thicker fracture were detected as the main cause of this non-monotonic behavior. In the models with thick fractures (with the thickness higher than the average pore diameter), considerable trapped oil volumes were observed inside the fracture at low M values. The fracture orientation had the most impressive effect on oil recovery compared to the other studied parameters; where the oil recovery factor incremented more than 20% as the fracture rotated 90° from flow direction. Due to the dominant effect of the channeling phenomenon, the change in the medium wettability from slightly oil-wet to slightly water-wet, did not considerably affect the displacement profile in the fractured medium. However, oil recovery factor increased as the medium became more water-wet. The fracture area was fully swept by the injected water in the oil-wet and neutral-wet media. However, flow instabilities were observed inside the fracture of the water-wet medium due to counter-current imbibition between fracture/matrix. Micro-scale mechanisms of pore doublet effect, interface coalesce, snap-off and reverse movements were captured during the studied unstable displacements.

Doxycycline treatment prevents alveolar destruction in VEGF‐deficient mouse lung

In vivo lung-targeted VEGF gene inactivation results in pulmonary cell apoptosis, airspace enlargement, and increased lung compliance consistent with an emphysema-like phenotype. The predominant hypothesis for the cause of lung destruction in emphysema is an imbalance between active lung protease and anti-protease molecules. Therefore, we investigated the role of protease (e.g., matrix metalloproteinases--MMPs) and anti-protease (e.g., tissue inhibitors of metalloproteinases--TIMPs) expression in contributing to the lung structural remodeling observed in pulmonary-VEGF-deficient mice. VEGFLoxP mice instilled through the trachea with an adeno-associated virus expressing Cre recombinase (AAV/Cre) manifest airspace enlargement and a greater (P < 0.05) mean linear intercept (MLI: 44.2 +/- 4.2 microm) compared to mice instilled with a control virus expressing LacZ (31.3 +/- 2.5 microm). Airspace enlargement was prevented by the continuous administration of the general MMP inhibitor, doxycycline (Dox) (Cre + Dox: 32.6 +/- 2.5 microm), and MLI values were not different from either control (LacZ + Dox: 30.5 +/- 1.2 microm). In situ magnetic resonance imaging of VEGF gene inactivated mouse lungs revealed uneven inflation, residual trapped gas volumes upon oxygen absorption deflation/re-inflation, and loss of parenchymal structure; effects that were largely prevented by Dox. Five weeks after AAV/Cre infection Western blot revealed a 9.9-fold increase in pulmonary MMP-3, and 2-fold increases in MMP-9 and TIMP-2. However, the increase in MMP-3 was prevented by Dox administration and was associated with a 2-fold increase in serpin b5 (Maspin) expression. These results suggest that doxycycline treatment largely prevents the aberrant lung remodeling response observed in VEGF-deficient mouse lungs and is associated with changes in protease and anti-protease expression.

Estimation of Trapped Thrombus Volumes in Retrievable Inferior Vena Cava Filters: A Visual Scale

To establish a visual, objective scale for estimating trapped thrombus volumes in five types of retrievable inferior vena cava filters. Silicone-based radiopaque polymer volumes of 0.25, 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0 mL were created. Both sphere and cone shapes were used. Polymer volumes were confirmed by means of the water displacement method. The volumes were then positioned to simulate trapped thrombus in five retrievable filters: Recovery and G2 (Bard Peripheral Vascular, Tempe, Ariz), Günther Tulip and Celect (Cook, Bloomington, Ind), and OptEase (Cordis Endovascular, Warren, NJ). Radiographs were obtained by using conventional parameters. Visual scales of thrombus volume were created for each filter type. Visual scales for each retrievable filter type were created with simulated thrombi in typical trapping positions. The authors developed a visual, objective scale for estimating trapped thrombus volume in five types of retrievable IVC filters. This could facilitate standardized reporting of thrombus volumes in studies of optional vena cava filters.

Method for assessment of volume of trapped gas in infants during multiple-breath inert gas washout.

A breath-by-breath inert gas washout method for assessment of the volume of trapped gas in the lungs (V(TG)) in sedated sleeping infants is described. It is based on washin using a gas mixture containing 4% sulfur hexafluoride (V(TG,SF6)) and washout with air. A mass spectrometer was used for continuous gas concentration measurements, and a Fleisch no. 0 pneumotachometer for flow measurement. When equilibration of the tracer gas was achieved with tidal breathing washin, five passive inflations with a maximum positive airway pressure of 20 cm of H(2)O were performed to ensure filling of lung spaces not communicating during tidal breathing. After tidal washout of the tracer gas by air until the end-tidal concentration was 1/40th of its starting concentration, five passive inflations with air were instituted again. The V(TG,SF6) was calculated from the volume of SF(6) mobilized by these large breaths, and expressed as the corresponding volume of air. Triplets of V(TG,SF6) determination in 8 infants aged 9-31 months with varying degrees of airway obstruction showed an average volume of 13.7 mL (range, 4.7-25.0). The average SD of the triplets was 2.1 mL (range, 0.1-5.5 mL). Subjects with high V(TG,SF6)/FRC results demonstrated lower maximal expiratory flow at FRC (V'(max)FRC) results (Z-scores) and greater inhomogeneity of ventilation distribution than those with low trapped gas volumes. It is concluded that gas trapping can be assessed with acceptable precision with this washout method. Further studies are needed to establish the sensitivity and usefulness of the method in infants with various types of airway pathology.

Jet tritium inventory-control and measurement during DT, shutdown and DD operational phases

DT plasma operations took place at Joint European Torus (JET) from May to November 1997. The site tritium inventory was 20 g, and this was recycled several times using the active gas handling system (AGHS) to recover tritium from mixed exhaust gases. The amount of tritium available for use at any time was determined by the hold-up in the in-vessel components, in-process inventory, and losses via permeation and transfer to waste. It was therefore necessary, to continually assess the tritium inventory through on-line and batch measurements. During the shutdown periods, tritium continued to be evolved from the machine and its trapped volumes. This meant that a large number of specific measurements were necessary to ensure that the safety requirements were met and that the waste could be properly characterised. During DD operations, the exhaust gas from the machine contained quantities of tritium, too great to be discharged to atmosphere and must continue to be processed by the AGHS. The techniques for tritium inventory assessment are reviewed, taking into account continuing uncertainties and plans for resolutions of these. The JET experiment is used to highlight issues of tritium inventory control, which will apply to future fusion reactors.

A breathless toddler

A 3-year-old, previously healthy boy was admitted to hospital in September, 1992, in Turkey, where he was on holiday, with vomiting, fever, and dyspnoea. He had travelled to Turkey on a commercial airline 2 days before. During the flight, he drank three or four glasses of carbonated soft drinks. 2 h after take-off, he suddenly developed dyspnoea. On admission he was centrally cyanosed, had diminished breath sounds on the left side, and intercostal retraction. A chest radiograph was done, which was interpreted as showing a left-sided pneumothorax (figure). A pleural puncture on the midclavicular line in the sixth intercostal space did not lead to expansion of the left lung; however, a greenish fluid was aspirated. A second puncture on the midclavicular line in the second intercostal space also did not result in lung expansion. Further procedures, including placement of a nasogastric tube and upper gastrointestinal contrast radiography, showed that the air in the left hemithorax was air in a gastric bubble and in the duodenum. After returning to Germany by air ambulance, jet pressurised to sea level, the boy was successfully operated on, and a left-sided dorsolateral diaphragmatic hernia containing prolapsed stomach, part of the duodenum, spleen, and part of the left kidney, was closed. The left lung proved moderately hypoplastic and a non-rotation of the gut, which almost always accompanies congenital diaphragmatic hernia, was diagnosed. He was extubated 60 h after the operation, but had to be reintubated 12 h later because of respiratory insufficiency. 4 days later a further laparotomy became necessary as he developed an ileum invagination. 4 days after the second operation he was finally weaned from the ventilator. After 3 weeks of intensive physiotherapy, chest radiographs became normal. During air travel in commercial airliners, reduction of cabin pressure to about 595 mm Hg (2300 m) leads to a 30% increase in expansion of trapped gas volumes. Together with the consumption of carbonated soft CASE REPORT

The Improved Volumetric-Efficiency of an Axial-Piston Pump Utilizing a Trapped-Volume Design

In this research, the volumetric efficiency of the axial-piston pump is examined as it relates to the compressibility losses of the fluid. In particular, two valve-plate geometries are compared to show that alterations in the valve-plate design can cause differences in the operating efficiency of the pump. In this paper, a standard valve-plate design which utilizes slots is compared to a trapped-volume design which eliminates the slots altogether. In the analytical result of this paper, it may be shown that the standard valve-plate design introduces a volumetric loss which may be accounted for by the uncontrolled expansion and compression of the fluid that occurs through the slots themselves. By eliminating these slots, and utilizing a trapped volume design, it may be shown that improvements in the operating efficiency can be achieved. Though this paper does not claim to provide the ideal valve-plate design for all pump applications, it does provide the theoretical reason for utilizing trapped volumes and lends general insight into the overall problem of valve-plate design.

Efficient calculation of trapped volumes in the layered manufacturing process

Prototypes of a design are always needed for the purposes of visualisation and evaluation for manufacturability, functionality, and aesthetic appearance. Since the prototyping process requires a significant amount of cost and time, various rapid prototyping processes have recently been introduced. However, it is usually necessary for a part built up by a rapid prototyping system to be finished by a post-processing process, in which the stair steps on the surfaces, the support structures (if they exist), and the unprocessed material are eliminated. This post-processing is usually done manually and is a time-consuming task. Eliminating the trapped volumes (the volume of the unprocessed material entrapped by the solidified portion) is sometimes impossible in some processes. This study provides a designer with a tool to detect the existence of trapped volumes and to calculate the quantity in a given build-up direction, so that a suitable build-up direction is chosen or the part is built in pieces to avoid the problems caused by the trapped volumes. Since the proposed algorithm can efficiently calculate the amount of the trapped volumes in any build-up direction, it has the potential for such applications as optimising the build-up direction to minimise the trapped volumes.

Retardation of Dissolved Oxygen Due to a Trapped Gas Phase in Porous Media

AbstractInformation on the transport of dissolved gases in ground water is needed to design ways to increase dissolved gas concentrations in ground water for use in in situ bioremediation (e.g., O2 and CH4) and to determine if dissolved gases are conservative tracers of ground‐water flow (e.g., He). A theoretical model was developed to describe the effect of small quantities of trapped gas bubbles on the transport of dissolved gases in otherwise saturated porous media. Dissolved gas transport in porous media can be retarded by gas partitioning between the mobile aqueous phase and a stationary trapped gas phase. The model assumes equilibrium partitioning where the retardation factor is defined as R = 1 + H′(Vg/Vw) where H' is the dimensionless Henry's Law constant for the dissolved gas, and Vg and Vw are the volumes of the trapped gas and water phases, respectively. At 15°C and with Vg/ Vw= 0.05, the predicted retardation factors for He, O2, and CH4 are 5.8, 2.4, and 2.3, respectively. The validity of the model was tested for dissolved oxygen in small‐scale column experiments over a range of trapped gas volumes. Retardation factors of dissolved oxygen increased from 1 to 6.6 as Vg/Vw increased from 0 to 0.123 and are in general agreement with model predictions except for the larger values of Vg/Vw. The theoretical and experimental results suggest that gas partitioning between the aqueous phase and a trapped gas phase can greatly influence rates of dissolved gas transport in ground water.

Efficient Encapsulation of Proteins within Liposomes for Slow Release in Vivo

A highly efficient method for the liposome encapsulation of granulocyte colony stimulating factor (rhG-CSF) was developed. The method was found to be gentle and led to no protein aggregation, denaturation or loss of protein activity. The liposomes obtained were judged to be oligolamellar based on a comparison of the actual with the theoretical trapped volumes. Slow release of encapsulated material from the liposomes was demonstrated both in vitro (90% serum, 37°C) and in vivo after subcutaneous injection.

Bilayer curvature and certain amphipaths promote poly(ethylene glycol)-induced fusion of dipalmitoylphosphatidylcholine unilamellar vesicles.

Unilamellar vesicles of varying and reasonably uniform size were prepared from 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC) by the extrusion procedure and sonication. Quasi-elastic light scattering was used to show that different vesicle preparations had mean (Z-averaged) diameters of 1340, 900, 770, 630, and 358 A (sonicated). Bilayer-phase behavior as detected by differential scanning calorimetry was consistent with the existence of essentially uniform vesicle populations of different sizes. The response of these different vesicles to treatment with poly(ethylene glycol) (PEG) was monitored using fluorescence assays for lipid transfer, contents leakage, and contents mixing, as well as quasi-elastic light scattering. No fusion, as judged by vesicle contents mixing and change in vesicle size, was detected for vesicles of diameter greater than 770 A. The diameters of smaller vesicles increased dramatically when treated with high concentrations of PEG, although mixing of their contents could not be detected both because of their small trapped volumes and because of the extensive leakage induced in small vesicles by high concentrations of PEG. Lipid transfer was detected between vesicles of all sizes. We conclude the high bilayer curvature does encourage fusion of closely juxtaposed membrane bilayers but that highly curved vesicles appear also to rupture and form larger structures when diluted from high PEG concentration, a process that can be confused with fusion. Despite the failure of PEG to induce fusion of large, uncurved vesicles composed of a single phosphatidylcholine, these vesicles can be induced to fuse when they contain small amounts of certain amphiphathic compounds thought to play a role in cellular fusion processes. Thus, vesicles which contained 0.5 mol % L-alpha-lysopalmitoylphosphatidylcholine, 5 mol % platelet activating factor, or 0.5 mol % palmitic acid fused in the presence of 30%, 25%, and 20% (w/w) PEG, respectively. However, vesicles containing 1,2-dipalmitoyl-sn-glycerol, 1,2-dioleoyl-sn-glycerol, 1-oleoyl-2-acetyl-sn-glycerol, or monooleoyl-rac-glycerol at surface concentrations up to 5 mol % did not fuse in the presence or absence of PEG. There was no correlation between the abilities of these amphipaths to induce phase separation or nonlamellar phases and their abilities to support fusion of pure DPPC unilamellar vesicles in the presence of high concentrations of PEG. The results are discussed in terms of the type of disrupted lipid packing that could be expected to favor PEG-mediated fusion.

Intermittent high frequency ventilation. Clinical evaluation of a new mode of ventilation

In this first clinical study of a new mode of ventilation, called intermittent high frequency ventilation (IHFV), a comparison was made in ten patients after myocardial revascularization, between normal ventilation, high frequency ventilation (HFV) and IHFV at 15, 60, 100 and 160 breaths per min (b.p.m.). During IHFV the ventilation was interrupted for 3 s 7 times per min. The measured mean trapped gas volumes were 219 ml at 60 b.p.m. and 716 ml at 160 b.p.m. At 160 b.p.m. during IHFV, the mean, mean airway pressures, pulmonary artery (PAP) and capillary wedge pressures and the Paco2 were decreased, while the cardiac output increased. When the Paco2 was maintained constant, IHFV also allowed a reduction in the mean peak and mean airway pressures. This new mode of ventilation can prevent sustained increases in the lung volume and provide a reduction in intrapulmonary pressures. It also permits the measurement of the trapped gas volume and end-tidal CO2 gas concentrations several times a minute for the clinical management of patients during high frequency ventilation.

Generation of multilamellar and unilamellar phospholipid vesicles

Multilamellar and unilamellar vesicles can be generated by a variety of techniques which lead to systems with differing lamellarity, size, trapped volume and solute distribution. The straight-forward hydration of lipid to produce multilamellar vesicles (MLVs) results in systems which exhibit low trapped volumes and where solutes contained in the aqueous buffer are partially excluded from the MLV interior. Large trapped volumes and equilibrium solute distributions can be achieved by freeze-thawing or by ‘reverse phase’ procedures where the lipid is hydrated after being solubilized in organic solvent. Unilamellar vesicles can be produced directly from MLVs by extrusion or sonication or, alternatively, can be obtained by reverse phase or detergent removal procedures. The advantages and limitations of these techniques are discussed.

Effects of ozone and sulfuric acid aerosol on gas trapping in the guinea pig lung.

Four groups of 20 guinea pigs were sequentially exposed by inhalation to either air followed by sulfuric acid aerosol, ozone followed by sulfuric acid aerosol, ozone followed by air, or air followed by air to determine whether ozone preexposure sensitizes guinea pigs to the airway constrictive effects of sulfuric acid aerosol. All first exposures to ozone or air were 2 h in duration; all second exposures to sulfuric acid or air were for 1 h. All ozone and sulfuric acid exposures were 0.8 ppm and 12 mg/m3, respectively. Animals were observed for respiratory distress during exposure, and excised lungs were quantitated for trapped gas and wet/dry ratios. None of the guinea pigs developed dyspnea, and wet/dry ratios were not altered. Ozone significantly (p less than 0.05) increased trapped gas volumes, which were 44% (ozone-acid) to 68% (ozone-air) greater than in the air-air group. Trapped gas volume was 23% greater in the ozone-acid group than in the air-acid group, but the difference was not statistically significant (p less than 0.20). Thus, ozone increased gas trapping but did not significantly sensitize guinea pigs to the bronchoconstrictive action of sulfuric acid.