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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A female baby sustained pneumopericardium after bronchoscopic CO2 laser surgery for tracheal stenosis. Perioperative pneumopericardium though rare is a life-threatening condition in babies. The symptoms are usually not specific such as hypotension, bradycardia, muffled heart sound, cardiovascular collapse, etc. The causes and clinical findings of pneumopericardium were reviewed, as are the radiographic features so as to differentiate the condition from pneumomediastinum. Early recognition of pneumopericardium is important, because emergent pericardiocentesis may be required if there is clinical evidence of cardiac tamponade.
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PMID:Pneumopericardium after bronchoscopic carbon dioxide laser surgery--a case report. 1147 81

We have constructed a model that predicts the evolution of CO2 on Mars from the end of the heavy bombardment period to the present. The model draws on published estimates of the main processes believed to affect the fate of CO2 during this period: chemical weathering, regolith uptake, polar cap formation, and atmospheric escape. Except for escape, the rate at which these processes act is controlled by surface temperatures which we calculate using a modified version of the Gierasch and Toon energy balance model (1973, J. Atmos. Sci. 30, 1502-1508). The modifications account for the change in solar luminosity with time, the greenhouse effect, and a polar and solar equatorial energy budget. Using published estimates for the main parameters, we find no evolutionary scenario in which CO2 is capable of producing a warm (global mean temperatures>250 K) and wet (surface pressures>30 mbar) early climate, and then evolves to present conditions with approximately 7 mbar in the atmosphere, <300 mbar in the regolith, and <5 mbar in the caps. Such scenarios would only exist if the early sun were brighter than standard solar models suggest, if greenhouse gases other than CO2 were present in the early atmosphere, or if the polar albedo were significantly lower than 0.75. However, these scenarios generally require the storage of large amounts of CO2 (>1 bar) in the carbonate reservoir. If the warm and wet early Mars constraint is relaxed, then we find best overall agreement with present day reservoirs for initial CO2 inventories of 0.5-1.0 bar. We also find that the polar caps can a profound effect on how the system evolves. If the initial amount of CO2 is less than some critical value, then there is not enough heating of the poles to prevent permanent caps from forming. Once formed, these caps control how the system evolves, because they set the surface pressure and, hence, the thermal environment. If the initial amount of CO2 is greater than this critical value, then caps do not form initially, but can form later on, when weathering and escape lower the surface pressure to a point at which polar heating is no longer sufficient to prevent cap formation and the collapse of the climate system. Our modeling suggests this critical initial amount of CO2 is between 1 and 2 bar, but its true value will depend on all factors affecting the polar heat budget.
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PMID:A model for the evolution of CO2 on Mars. 1153 35

A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact. Additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume, causing an early, intense pulse of sulfuric acid rain. Estimates of the conversion rate of stratospheric SO2 and water vapor to sulfate aerosol, based on volcanic production of sulfate aerosols, coupled with calculations of diffusion, coagulation, and sedimentation, demonstrate that the 200 Gt stratospheric SO2 and water vapor reservoir would produce sulfate aerosols for 12 years. These sulfate aerosols caused a second pulse of acid rain that was global. Radiative transfer modeling of the aerosol clouds demonstrates (1) that if the initial rapid pulse of sulfate aerosols was global, photosynthesis may have been shut down for 6 months and (2) that for the second prolonged aerosol cloud, solar transmission dropped 80% by the end of first year and remained 50% below normal for 9 years. As a result, global average surface temperatures probably dropped between 5 degrees and 31 degrees K, suggesting that global near-freezing conditions may have been reached. Impact-generated CO2 caused less than 1 degree K greenhouse warming and therefore was insignificant compare to the sulfate cooling. The magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool, sink, and are replaced by upwelling of deep ocean water. This upwelling apparently drastically altered ocean stratification and circulation, which may explain the global collapse of the delta 13C gradient between surface and deep ocean waters at the K/T boundary.
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PMID:Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact. 1154 Nov 45

Observations of the behavioral reactions of laying hens and broilers to different gas stunning atmospheres were made. Sixty Hy-Line W-36 hens and 60 market-weight commercial broilers were placed individually into a plexiglass gas stunning unit and exposed to one of six gas atmospheres: air, concentrations of 30, 45, or 60% CO2 in air, a mixture of 70% argon and 30% CO2, and 100% argon. Video records were made during each test, which lasted until the subject became unconscious or for 2 min in the air treatment. Behavior in the 100% argon atmosphere resembled that in air, until birds became impaired by anoxia. All treatments involving CO2, including 70% argon/30% CO2, caused deep breathing and head shaking. The concentration of CO2 in air in the range tested did not affect the tendency to perform different actions, except that birds in 60% CO2 were more likely to exhibit a convulsive flip at the point of collapse. Chickens in 70% argon/30% CO2 tended to demonstrate less sedation and performed more sudden efforts to regain balance during tests than did chickens in CO2 mixtures in air and were more likely to perform a convulsive flip. Deep breathing and head shaking have been suggested as being indicative of respiratory distress and aversive reaction to CO2. The data in this study are consistent with the possibility that head shaking is an alerting response functioning to promote arousal in the face of reduced sensibility during exposure to CO2-enriched atmospheres. Nonetheless, if the view is correct that deep breathing and head shaking indicate distress, the 70% argon/30% CO2 gas mixture was at least as distressing as even 60% CO2 in air. The relative prevalence of sudden efforts to regain balance in 70% argon/30% CO2 suggest that this gas mixture might cause even more distress than up to 60% CO2 in air.
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PMID:Reactions of laying hens and broilers to different gases used for stunning poultry. 1155 25

The NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase (2-KPCC) is the terminal enzyme in a metabolic pathway that results in the conversion of propylene to the central metabolite acetoacetate in Xanthobacter autotrophicus Py2. This enzyme is an FAD-containing enzyme that is a member of the NADPH:disulfide oxidoreductase (DSOR) family of enzymes that include glutathione reductase, dihydrolipoamide dehydrogenase, trypanothione reductase, thioredoxin reductase, and mercuric reductase. In contrast to the prototypical reactions catalyzed by members of the DSOR family, the NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase catalyzes the reductive cleavage of the thioether linkage of 2-ketopropyl-coenzyme M, and the subsequent carboxylation of the ketopropyl cleavage product, yielding the products acetoacetate and free coenzyme M. The structure of 2-KPCC reveals a unique active site in comparison to those of other members of the DSOR family of enzymes and demonstrates how the enzyme architecture has been adapted for the more sophisticated biochemical reaction. In addition, comparison of the structures in the native state and in the presence of bound substrate indicates the binding of the substrate 2-ketopropyl-coenzyme M induces a conformational change resulting in the collapse of the substrate access channel. The encapsulation of the substrate in this manner is reminiscent of the conformational changes observed in the well-characterized CO2-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxidase (Rubisco).
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PMID:Structural basis for CO2 fixation by a novel member of the disulfide oxidoreductase family of enzymes, 2-ketopropyl-coenzyme M oxidoreductase/carboxylase. 1239 15

The feasibility of ultrasound-induced in situ radical formation in liquid carbon dioxide was demonstrated. The required threshold pressure for cavitation could be exceeded at a relatively low acoustic intensity, as the high vapor pressure of CO2 counteracts the hydrostatic pressure. With the use of a dynamic bubble model, the formation of hot spots upon bubble collapse was predicted. Cavitation-induced radical formation was used for the polymerization of methyl methacrylate in CO2, yielding high-molecular-weight polymers. These results show that sonochemical reactions can be performed in dense-phase fluids, which allows the environmentally benign CO2 to replace conventional organic solvents in many reaction systems.
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PMID:Cavitation-induced reactions in high-pressure carbon dioxide. 1247 Dec 51

Single-lung anaesthesia for thoracotomy is usually achieved with endobronchial intubation, a double-lumen tube or an endobronchial blocker. High-frequency jet ventilation (HFJV) is seldom described for thoracotomy in children, although it is used for both laryngology procedures in the operating room and as a ventilation mode in intensive care. HFJV was used in three children, aged 10-12 years, who presented for scoliosis correction involving thoracotomy. The jet ventilation catheter was passed through a tracheal tube to reduce the risk of outflow obstruction and allow a smooth conversion to intermittent positive-pressure ventilation when required. Mean airway pressures measured at the tip of the HFJV catheter were at or below 4 cmH2O. Surgical opening of the nondependent lung pleura resulted in sufficient collapse of the pulmonary parenchyma with the patient in the lateral decubitus position for the surgical procedure. Arterial blood gas analyses performed during thoracotomy were within normal limits, with no CO2 retention. HFJV is an alternative ventilation strategy for thoracotomy in children because of its unique ability to deliver small tidal volumes at low mean airway pressures via a narrow catheter.
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PMID:Jet ventilation for anterior paediatric scoliosis surgery. 1247 11

The surgical requirement for thoracoscopy is a good view of the contents of the thorax. This is achieved by capitalizing on natural consequences and the skills of anaesthesiologists to produce a pneumothorax and collapse the ipsilateral lung--a process that is commonly enhanced by insufflating carbon dioxide. Insufflating CO2 to actively promote lung collapse creates the dynamics of a tension pneumothorax. Complications are clinically insignificant if CO2 is used judiciously. There is a body of experience using ordinary endotracheal tubes and two-lung ventilation. Techniques of one-lung ventilation are more widely reported. All the factors known to contribute to the significant increase in shunt fraction associated with one-lung ventilation apply. The manoeuvre of collapsing a lung is no longer regarded as benign. Chemical attempts to produce a reversible post-pneumonectomy pulmonary circulation have not been shown to be an improvement. Post-operative pain can be severe. The mechanism is not defined but it differs from that associated with thoracotomy. Epidural analgesia and opioids may be required. Chronic pain syndromes have been described as complications.
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PMID:Anaesthesia for thoracoscopic surgery. 1249 43

The aim of this work is to evaluate the feasibility of hydrophilic silica aerogels as drug carriers and to investigate the influence of the aerogels properties on the release rate of poorly water-soluble drugs. Hydrophilic silica aerogels of different densities were loaded with two model drugs, ketoprofen and griseofulvin, by adsorption from their solution in supercritical CO2. It is demonstrated that up to 30 wt% of ketoprofen and 5.4 wt% of griseofulvin can be deposited on hydrophilic aerogels through physical adsorption. The obtained drug-aerogel formulations were characterized by IR- and UV-spectroscopy, X-ray diffraction and scanning electron microscopy. Release kinetics of both drugs were studied in vitro. The release rate of ketoprofen from the drug-aerogel formulation is much faster than that of the corresponding crystalline drugs. The release rate of ketoprofen increases in 500% and that of griseofulvin in 450%, respectively. The reasons for the release enhancement are the enlarged specific surface area of drugs by adsorption on aerogels compared to their crystalline form and the immediate collapse of aerogel network in aqueous media. The dissolution rate of poorly water soluble drugs can be significantly enhanced by adsorption on highly porous hydrophilic silica aerogels.
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PMID:Dissolution rate enhancement by adsorption of poorly soluble drugs on hydrophilic silica aerogels. 1558 Oct 80

An intravenous respiratory support catheter, the next generation of artificial lungs, is being developed in our laboratory to potentially support acute respiratory failure or patients with chronic obstructive pulmonary disease with acute exacerbations. A rapidly pulsating 25 ml balloon inside a bundle of hollow fiber membranes facilitates supplemental oxygenation and CO2 removal. In this study, we hypothesized that non-uniform gas exchange in different regions of this fiber bundle was present because of asymmetric balloon collapse and the interaction of longitudinal flow. Four quarter regions and two rings around the central balloon were selectively perfused to evaluate local gas exchange in a 3.18 cm test section using helium as the sweep gas. Quarter region CO2 exchange rates at 400 beats per minute were 156.8 +/- 0.8, 162.5 +/- 1.8, 157.2 +/- 0.2, and 196.6 +/- 0.8 ml/min/m2 (top, front, bottom, and back, respectively). The back section, adjacent to convex balloon collapse, had 17-20% higher exchange than the other sections caused by higher relative velocities past its stationary fibers. Inner and outer ring maximum pulsation gas exchange rates were 174.4 +/- 1.8 and 174.6 +/- 0.9 ml/min/m2, respectively, showing that fluid flow was equally distributed throughout the fiber bundle.
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PMID:Evaluation of local gas exchange in a pulsating respiratory support catheter. 1583 40


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