Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GAS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1992

Conducting airway gas exchange: diffusion-related differences in inert gas elimination.

We studied CO2 and inert gas elimination in the isolated in situ trachea as a model of conducting airway gas exchange. Six inert gases with various solubilities and molecular weights (MW) were infused into the left atria of six pentobarbital-anesthetized dogs (group 1). The unidirectionally ventilated trachea behaved as a high ventilation-perfusion unit (ratio = 60) with no appreciable dead space. Excretion of higher-MW gases appeared to be depressed, suggesting a MW dependence to inert gas exchange. This was further explored in another six dogs (group 2) with three gases of nearly equal solubility but widely divergent MWs (acetylene, 26; Freon-22, 86.5; isoflurane, 184.5). Isoflurane and Freon-22 excretions were depressed 47 and 30%, respectively, relative to acetylene. In a theoretical model of airway gas exchange, neither a tissue nor a gas phase diffusion resistance predicted our results better than the standard equation for steady-state alveolar inert gas elimination. However, addition of a simple ln (MW) term reduced the remaining residual sum of squares by 40% in group 1 and by 83% in group 2. Despite this significant MW influence on tracheal gas exchange, we calculate that the quantitative gas exchange capacity of the conducting airways in total can account for less than or equal to 16% of any MW-dependent differences observed in pulmonary inert gas elimination.

Animals↗
PubMed2001

Intratracheal gas analysis for volatile substances by gas chromatography/mass spectrometry--application to forensic autopsies.

Intratracheal gas analysis was carried out by gas chromatography/mass spectrometry (GC/MS) in 20 burned body cases (13 males and 7 females). Volatile aromatic and aliphatic hydrocarbons were detected by GC/MS using a GS-Q column with the intratracheal gas as well as the blood in 19 cases. The characteristic patterns of mass chromatograms for gasoline, kerosene (gas oil), and liquid petroleum gas could be differentiated from each other using the intratracheal gas. The burned body in one case showed no presence of volatile substances in the intratracheal gas, nor intratracheal soot, although high concentrations (1 microg/g and more) of volatile substances were detected on the clothes. The victim also had normal CO-Hb concentrations (0.1 to 0.2%) in the heart blood. The results of intratracheal gas analysis were consistent with signs of the vital reaction. In conclusion, intratracheal gas analysis provides a supportive method for diagnosing the cause of death in burned bodies, and yields for at least 48 hours valuable information on volatile hydrocarbons (being detected in deliberate or accidental fire cases) to which the body had been exposed just before death.

Adolescent↗
PubMed1994

[The usefulness of transcutaneous gas monitoring during hemorrhagic shock; discrepancy between the two transcutaneous gas tensions of anterior thorax and femur].

We measured transcutaneous gas tensions of both anterior thorax and femur. The differences between the two transcutaneous gas tensions were compared, as well as the relationship between the two transcutaneous and mixed venous blood gas tensions, in 10 dogs during hemorrhagic shock. The changes in femoral transcutaneous gas tensions correlated better with the changes in mixed venous gas tensions. The correlation between the two transcutaneous gas tensions were fairly good (oxygen tensions; r = .827, carbon dioxide tensions; r = .867). However, the discrepancy between the two gas tensions became greater in severe shock. Hence, oxygen tensions became smaller and carbon dioxide tensions became greater on femur than on anterior thorax. This indicates the possibility of "maldistribution of blood flow", which has already been detected between vital organs and skin, also exists between peripheral and central skin. Therefore, transcutaneous gas tensions should be monitored at peripheral skin, where gas tensions show greater changes and reflect systemic perfusion precisely than at central skin, during shock.

Animals↗
PubMed2004

Gas-phase mercury reduction to measure total mercury in the flue gas of a coal-fired boiler.

Gaseous elemental and total (elemental + oxidized) mercury (Hg) in the flue gas from a coal-fired boiler was measured by a modified ultraviolet (UV) spectrometer. Challenges to Hg measurement were the spectral interferences from other flue gas components and that UV measures only elemental Hg. To eliminate interference from flue gas components, a cartridge filled with gold-coated sand removed elemental Hg from a flue gas sample. The Hg-free flue gas was the reference gas, eliminating the spectral interferences. To measure total Hg by UV, oxidized Hg underwent a gas-phase, thermal-reduction in a quartz cell heated to 750 degrees C. Simultaneously, hydrogen was added to flash react with the oxygen present forming water vapor and preventing Hg re-oxidation as it exits the cell. Hg concentration results are in parts per billion by volume Hg at the flue gas oxygen concentration. The modified Hg analyzer and the Ontario Hydro method concurrently measured Hg at a field test site. Measurements were made at a 700-MW steam turbine plant with scrubber units and selective catalytic reduction. The flue gas sampled downstream of the selective catalytic reduction contained 2100 ppm SO2 and 75 ppm NOx. Total Hg measured by the Hg analyzer was within 20% of the Ontario Hydro results.

Air Pollutants↗
PubMed1980

Rupture of the cell envelope by induced intracellular gas phase expansion in gas vacuolate bacteria.

Using a new approach, we estimated the physical strength of the cell envelopes of three species of gram-negative, gas vacuolate bacteria (Microcyclus aquaticus, Prosthecomicrobium pneumaticum, and Meniscus glaucopis). Populations of cells were slowly (0.5 to 2.9 h) saturated with argon, nitrogen, or helium to final pressures up to 100 atm (10, 132 kPa). The gas phases of the vesicles remained intact and, upon rapid (1 to 2 s) decompression to atmospheric pressure, expanded and ruptured the cells; loss of colony-forming units was used as an index of rupture. Because the cell envelope is the cellular component most likely to resist the expanding intracellular gas phase, its strength can be estimated from the minimum gas pressures that produce rupture. The viable counts indicated that these minimum pressures were between 25 and 50 atm; the majority of the cell envelopes were ruptured at pressures between 50 and 100 atm. Cells in which the gas vesicles were collapsed and the gas phases were effectively dissolved by rapid compression tolerated decompression from much higher gas saturations. Cells that do not normally possess gas vesicles (Escherichia coli) or that had been prevented from forming them by addition of L-lysine to the medium (M. aquaticus) were not harmed by decompression from gas saturation pressures up to 300 atm.

Atmospheric Pressure↗
PubMed1982

Midazolam determination by gas chromatography, liquid chromatography and gas chromatography--mass spectrometry.

Midazolam is determined in serum by gas chromatography with a nitrogen-selective detector, by liquid chromatography, and by gas chromatography--mass spectrometry. Comparable results are obtained with the three techniques with a within-run precision of 9% by gas chromatography and gas chromatography---mass spectrometry and 5% by liquid chromatography. Between-run precision is 13% by gas chromatography--mass spectrometry and 10% by liquid chromatography. Comparison of patient's sera by gas chromatography (x), liquid chromatography (y), and by gas chromatography (x), gas chromatography--mass spectrometry (y) gave correlations of 0.98 and 0.89, respectively. Interferences observed when using one technique, for example liquid chromatography, can be eliminated by analyzing the sample extract with one of the other techniques.

Anti-Anxiety Agents↗
PubMed1995

Tracheal gas exchange: perfusion-related differences in inert gas elimination.

Exchange of inert gases across the conducting airways has been demonstrated by using an isolated dog tracheal preparation and has been characterized by using a mathematical model (E. R. Swenson, H. T. Robertson, N. L. Polissar, M. E. Middaugh, and M. P. Hlastala, J. Appl. Physiol. 72: 1581-1588, 1992). Theory predicts that gas exchange is both diffusion and perfusion dependent, with gases with a higher blood-gas partition coefficient exchanging more efficiently. The present study evaluated the perfusion dependence of airway gas exchange in an in situ canine tracheal preparation. Eight dogs were studied under general anesthesia with the same isolated tracheal preparation. Tracheal perfusion (Q) was altered from control blood flow (Qo) by epinephrine or papaverine instilled into the trachea and was measured with fluorescent microspheres. Six inert gases of differing blood-gas partition coefficients were used to measure inert gas elimination. Gas exchange was quantified as excretion (E), equal to exhaled partial pressure divided by arterial partial pressure. Data were plotted as ln [E/(l-E)] vs. In (Q/Qo), and the slopes were determined by least squares. Excretion was a positive function of Q, and the magnitude of the response of each gas to changes in Q was similar and highly significant (P < or = 0.0002). These results confirm a substantial perfusion dependence of airway gas exchange.

Animals↗
PubMed2003

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.

Airway Obstruction↗
PubMed1987

Comparison between aqueous-phase and gas-phase exposure protocols for determining the mutagenic potential of nitrogen dioxide and the gas fraction of welding fumes.

Nitrogen dioxide and the gas fraction of welding fumes, a complex gas mixture which contains high concentrations of nitrogen dioxide, were tested for mutagenicity in Salmonella typhimurium tester strains, TA1535 and TA1538. A comparison between 2 exposure protocols, aqueous phase and gas phase, was made to evaluate the sensitivity of each in measuring the mutagenic potential of the gases. In the aqueous-phase exposure, a suspension of cells in an isotonic salt solution was exposed by bubbling the gas through the culture. In the gas-phase exposure, the plated cells were exposed to the gas in a chamber. For both gases tested, the gas-phase exposure resulted in a higher reversion frequency than the aqueous-phase exposure. Furthermore, we found that nitrogen dioxide accounted for only a fraction of the mutagenicity observed for the gas fraction of welding fumes.

Filtration↗
PubMed2004

Critically pressured free-gas reservoirs below gas-hydrate provinces.

Palaeoceanographic data have been used to suggest that methane hydrates play a significant role in global climate change. The mechanism by which methane is released during periods of global warming is, however, poorly understood. In particular, the size and role of the free-gas zone below gas-hydrate provinces remain relatively unconstrained, largely because the base of the free-gas zone is not a phase boundary and has thus defied systematic description. Here we evaluate the possibility that the maximum thickness of an interconnected free-gas zone is mechanically regulated by valving caused by fault slip in overlying sediments. Our results suggest that a critical gas column exists below most hydrate provinces in basin settings, implying that these provinces are poised for mechanical failure and are therefore highly sensitive to changes in ambient conditions. We estimate that the global free-gas reservoir may contain from one-sixth to two-thirds of the total methane trapped in hydrate. If gas accumulations are critically thick along passive continental slopes, we calculate that a 5 degrees C temperature increase at the sea floor could result in a release of approximately 2,000 Gt of methane from the free-gas zone, offering a mechanism for rapid methane release during global warming events.

Journal Article↗