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At least 433 records · Page 24Linked to original sources
PubMed1997

Gases in ice cores.

Air trapped in glacial ice offers a means of reconstructing variations in the concentrations of atmospheric gases over time scales ranging from anthropogenic (last 200 yr) to glacial/interglacial (hundreds of thousands of years). In this paper, we review the glaciological processes by which air is trapped in the ice and discuss processes that fractionate gases in ice cores relative to the contemporaneous atmosphere. We then summarize concentration-time records for CO2 and CH4 over the last 200 yr. Finally, we summarize concentration-time records for CO2 and CH4 during the last two glacial-interglacial cycles, and their relation to records of global climate change.

Journal Article↗
PubMed2001

The heme-regulated eukaryotic initiation factor 2alpha kinase. A potential regulatory target for control of protein synthesis by diffusible gases.

Nitric oxide (NO) has been reported to inhibit protein synthesis in eukaryotic cells by increasing the phosphorylation of the alpha-subunit of eukaryotic initiation factor (eIF) 2. However, the mechanism through which this increase occurs has not been characterized. In this report, we examined the effect of the diffusible gases nitric oxide (NO) and carbon monoxide (CO) on the activation of the heme-regulated eIF2alpha kinase (HRI) in rabbit reticulocyte lysate. Spectral analysis indicated that both NO and CO bind to the N-terminal heme-binding domain of HRI. Although NO was a very potent activator of HRI, CO markedly suppressed NO-induced HRI activation. The NO-induced activation of HRI was transduced through the interaction of NO with the N-terminal heme-binding domain of HRI and not through S-nitrosylation of HRI. We postulate that the regulation of HRI activity by diffusible gases may be of wider physiological significance, as we further demonstrate that NO generators increase eIF2alpha phosphorylation levels in NT2 neuroepithelial and C2C12 myoblast cells and activate HRI immunoadsorbed from extracts of these non-erythroid cell lines.

Animals↗
PubMed1998

Exchange rates of gases across the tympanic membrane in rhesus monkeys.

The exchange rates of CO2 and He across the tympanic membrane were estimated in 5 monkeys. For these experiments, the monkey was anesthetized and one arm of a polyethylene "T" tube was introduced into the external canal of the test ear and sealed to the ambient environment with wax. One arm of the T tube was attached to a pressure transducer and the other to an argon gas source via a valve. Silica tubing sealed within the probe provided periodic gas samples for composition analysis by an online mass spectrometer. Prior to each experiment, the probe was washed with Argon. In 5 experiments the probe was sealed within the external canal of animals with physiological middle ear gas compositions, and in 5 experiments the probe was sealed within the external canal of animals whose middle ears were partially washed with He. The gas in the probe was sampled and analyzed at 10-min intervals for up to 4 h. The results documented a significant increase in the percentage composition of CO2 but not He in the experiments conducted with physiological middle ear gas compositions, and increases in both He and CO2 in the experiments conducted after the middle ear was washed with He. Estimated, average exchange constants for He and CO2 were 0.0005 microl/min/mmHg and 0.0103 microl/min/mmHg, respectively. Using data from previous experiments, the relative trans-mucosal to trans-tympanic membrane gas exchange rates in monkeys are estimated to be in the order of 10:1 for inert gases and 180:1 for chemically active gases.

Animals↗
PubMed2000

Functional MR imaging of pulmonary ventilation using hyperpolarized noble gases.

The current status of experimental and clinical applications for functional MR imaging of pulmonary ventilation using hyperpolarized noble gases are reviewed. 3-helium (3He) and 129-xenon (129Xe) can be hyperpolarized by optical pumping techniques such as spin exchange or metastability exchange in sufficient amounts. This process leads to an artificial, non-equilibrium increase of the density of excited nuclei which represents the source of the MR signal. Those hyperpolarized gases are administered mostly via inhalation, and will fill airways and airspaces allowing for ventilation imaging. Recent human studies concentrate on imaging the airways and airspaces with high spatial resolution. Normal ventilation is reflected by an almost complete and homogeneous distribution of the hyperpolarized gas represented by the signal detected. Loss of signal or inhomogeneous signal distribution represent mass effects and ventilatory abnormalities. Even healthy subjects with seasonal allergies without pulmonary symptoms have been observed to exhibit transient ventilation defects. Real-time imaging of ventilation has become feasible for 3He MR imaging and allows for assessment of ventilation-distribution. Furthermore, functional oxygen-sensitive 3He MR imaging opens the field of non-invasive assessment of regional intrapulmonary oxygen concentrations in vivo. Knowing that the diffusion of gas is affected by the geometry and nature of its environment, diffusion measurements are under investigation as a sensitive marker of diseases that involve structural changes of lung parenchyma, such as emphysema and fibrosis. Whereas 3He is not absorbed and is restricted to the airspaces, 129Xe is soluble in blood and lipid-rich tissue. This presents the opportunity for additional dissolved-phase imaging, providing a step towards simultaneous ventilation-perfusion studies.

Helium↗
PubMed2001

Use of computational fluid dynamics models for dosimetry of inhaled gases in the nasal passages.

Computational fluid dynamics (CFD) models of the nasal passages of a rat, monkey, and human are being used (1) to determine important factors affecting nasal uptake, (2) to make interspecies dosimetric comparisons, (3) to provide detailed anatomical information for the rat, monkey, and human nasal passages, and (4) to provide estimates of regional air-phase mass transport coefficients (a measure of the resistance to gas transport from inhaled air to airway walls) in the nasal passages of all three species. For many inhaled materials, lesion location in the nose follows patterns that are both site and species specific. For reactive, water-soluble (Category 1) gases, regional uptake can be a major factor in determining lesion location. Since direct measurement of airflow and uptake is experimentally difficult, CFD models are used here to predict uptake patterns quantitatively in three-dimensional reconstructions of the F344 rat, rhesus monkey, and human nasal passages. In formaldehyde uptake simulations, absorption processes were assumed to be as rapid as possible, and regional flux (transport rate) of inhaled formaldehyde to airway walls was calculated for rats, primates, and humans. For uptake of gases like vinyl acetate and acrylic acid vapors, physiologically based pharmacokinetic uptake models incorporating anatomical and physical information from the CFD models were developed to estimate nasal tissue dose in animals and humans. The use of biologically based models in risk assessment makes sources of uncertainty explicit and, in doing so, allows quantification of uncertainty through sensitivity analyses. Limited resources can then be focused on reduction of important sources of uncertainty to make risk estimates more accurate.

Animals↗
PubMed2000

Effect of varying the combustion parameters on the emissions of carbon monoxide and nitrogen oxides in the exhaust gases from propane-fueled vehicles.

Propane-fueled forklifts are one source of carbon monoxide (CO) contamination of workplace air. The previous study carried out by the Quebec Occupational Health and Safety Research Institute dealt with worker exposure to CO during forklift use in buildings. It recommends that exhaust gas emissions be kept below a 1 percent concentration. However, this control has not produced a significant reduction in worker exposure to CO, when factors (ventilation, type of work tasks, and management of vehicle fleet) specific to companies are taken into account. Consequently, a reduction in CO emissions below the threshold of 0.3 percent should be considered. The experience acquired with propane-fueled ice resurfacers can be used to determine the effect of combustion parameters on exhaust gas emissions. It is known that a reduction in CO emissions from ice resurfacers resulted in the appearance of nitrogen oxides (NOx) and eventually in nitrogen dioxide (NO2) poisoning. Few publications present NOx results in relation to the CO measured in the exhaust gases of propane-fueled vehicles. The objective of this study is to define the level to which CO emissions can be reduced without increasing NOx concentrations. This real-situation study quantified the CO, NO, and NOx in the exhaust gases of a fleet of propane-fueled forklifts in relation to the mixture ratio. The results show the impact of the motor speed and mixture ratio on the CO, NO, and NO2 concentrations. They confirm an increase in NOx concentrations when CO concentrations are reduced. They also show that proper maintenance of forklifts combined with optimal adjustments can reduce CO and NOx emissions. The study proposes a compromise between CO and NOx emissions by taking into account worker health and safety as well as vehicle performance. Monitoring must be done to control air quality in work areas and worker exposure to CO and NO2. A forklift preventive maintenance program and general building ventilation are the favored and recommended means of control.

Air Pollution, Indoor↗
PubMed2005

Field enhancements of packed-bed performance for low-concentration acidic and basic-waste gases from semiconductor manufacturing process.

Low-concentration acidic and basic-waste gas pollutants contribute significantly in the total emission of a facility. Previous results show that the control of high volumetric flow rate (approximately 500 m3/min), low-concentration acidic (< 1 ppm by vol) and basic (< 3 ppm by vol) gases from semiconductor process vent, by conventional wet scrubbing technique is a challenging task. This work was targeted to enhance the performance of packed beds for high-volumetric flow rate, low-concentration acidic (HF, HCl), and basic (NH3)-waste gases from the semiconductor manufacturing process. The methodology used to meet the goal was the application of fine-water mist over the inlet stream before entering to the packed bed and use of the surfactant with mist/packed-bed liquid in low concentration. An experimental study was carried out in two acid-packed beds to optimize the operating conditions, such as pH of the liquid, circulating liquid flow rate, blow-down cycle, and so forth. The relationship among liquid pH, liquid ionic concentration, and the removal efficiency of the packed bed for the pollutants has been discussed considering chemical equilibrium, two-film theory, and Henry's law. For the potential utilization of scrubbing water, the dependency of the efficiency on blow-down cycle was studied, and a mechanism is suggested. The proposed water-mist surfactant system was installed in two acid-packed beds, and performance of the packed beds was compared. The background efficiencies of the acid-packed beds for HF, HCl, and NH3 were found max to be (n = 11) 53, 40, and 27%, whereas after installation of the system, they increased significantly and became 76 +/- 13% (n = 10), 76 +/- 8% (n = 7), and 78 +/- 7% (n = 7), respectively, for inlet concentrations of HF and HCl < 1 ppm and NH3 < 14 ppm. The mechanism by which the surfactants operate to enhance the removal in scrubbing process is suggested considering the hydrodynamic effect and the interfacial effect with the charge-generating characteristic of surfactants on water surface, when dissolved into water. The results show that a proposed rectification system can effectively reduce the emission rates below the regulatory level (0.6 kg/hr) at the present conditions of the facility.

Air Movements↗
PubMed1984

Respiratory function responses of animals and man to oxidant gases and to pulmonary emphysema.

Data on the respiratory functional responses of animals and humans to inhaled oxidant gases and to pulmonary emphysema were reviewed and compared. Comparisons included responses to short-term inhalation of ozone, nitrogen dioxide, and oxygen and the functional manifestations of chronic emphysema. The comparisons illustrated that animals and humans have qualitatively similar functional responses to the irritant, bronchoconstrictive, and sensitizing effects of acutely inhaled ozone and nitrogen dioxide. Animals and humans responded similarly to the inflammatory and edematous effects of inhaled oxygen. Similar changes in maximal expiratory flow-volume curves, pressure-volume curves, lung volumes, and alveolar-capillary gas exchange occurred in animals and humans with emphysema. These results suggest that similar respiratory functional changes occur in both animals and humans when similar morphological changes result from lung injury. This observation lends confidence to the use of laboratory animals in studies to predict the effects of long-term exposure of humans to inhaled oxidant gases.

Aged↗
PubMed1985

An in vitro system for exposure of lung cells to gases: effects of ozone on rat macrophages.

A test system was developed for the in vitro exposure of lung cells to gases. The exposure system was used to evaluate ozone (O3) injury to pulmonary alveolar macrophages (PAM) obtained from Sprague-Dawley rats by bronchopulmonary lavage. Ozone exposures were conducted within temperature-controlled stainless-steel and Plexiglas chambers that contained glass petri dishes affixed to a revolving, inclined platform. Cell exposures were accomplished by rotation of the platform at 1 rpm to alternately expose PAM monolayers to culture media and O3. The system provided stable, O3-containing atmospheres and permitted simultaneous in vitro exposures at three O3 concentrations. In vitro exposure of PAM monolayers for 2 h at chamber concentrations ranging from 0.2 to 6.1 ppm O3 was associated with a significant, concentration-related reduction of latex-bead phagocytosis in rotated PAM cultures. In contrast, PAM that were similarly exposed in nonrotated dishes placed horizontally and covered with a stationary layer of media (1.5 mm depth) were not affected. Other parameters of cell function, including PAM viability and adherence, were unchanged compared to unexposed or horizontal, nonrotated controls. The inability to observe adverse effects among the nonrotated cultures is consistent with the impaired diffusion of O3 through the comparatively thick media overlay in stationary cultures. The in vitro system provides a realistic simulation of lung cell exposure to O3 and represents a useful model to study the toxicity of gases on cultured cells.

Animals↗
PubMed1968

Growth of Streptococcus faecalis under high hydrostatic pressure and high partial pressures of inert gases.

Growth of Streptococcus faecalis in a complex medium was inhibited by xenon, nitrous oxide, argon, and nitrogen at gas pressures of 41 atm or less. The order of inhibitory potency was: xenon and nitrous oxide > argon > nitrogen. Helium appeared to be impotent. Oxygen also inhibited streptococcal growth and it acted synergistically with narcotic gases. Growth was slowed somewhat by 41 atm hydrostatic pressure in the absence of narcotic gases, but the gas effects were greater than those due to pressure. In relation to the sensitivity of this bacterium to pressure, we found that the volume of cultures increased during growth in a volumeter or dilatometer, and that this dilatation was due mainly to glycolysis. A volume increase of 20.3 +/- 3.6 ml/mole of lactic acid produced was measured, and this value was close to one of 24 ml/mole lactic acid given for muscle glycolysis, and interestingly, close to the theoretic volume increase of activation calculated from the depression of growth rate by pressure.

Argon↗
PubMed1994

The evaluation of interactions between anaesthetic agent vapours and carrier gases by laser refractometry.

A measurement system and technique have been developed for the evaluation of interactions between anaesthetic agent vapours and carrier gases. The refractivities of mixtures of anaesthetic agent and carrier gas have been compared to values derived from the addition of the absolute refractivities of the individual components. These results show that there is no significant interaction between the anaesthetic agent and the carrier gas at the +/- 0.06% level of uncertainty. Results for the anaesthetic agents isoflurane, sevoflurane, enflurane, halothane, chloroform and desflurane and the carrier gases nitrogen, oxygen and dry air will be presented.

Anesthetics, Inhalation↗
PubMed2003

Chicxulub and climate: radiative perturbations of impact-produced S-bearing gases.

We use one-dimensional (1D) atmospheric models coupled to a sulfate aerosol model to investigate climate forcing and short-term response to stratospheric sulfate aerosols produced by the reaction of S-bearing gases and water vapor released in the Chicxulub impact event. A 1D radiation model is used to assess the climate forcing due to the impact-related loading of S-bearing gases. The model suggests that a climate forcing 100 times larger than that from the Pinatubo volcanic eruption is associated with the Chicxulub impact event for at least 2 years after the impact. In particular, we find a saturation effect in the forcing, that is, there is no significant difference in the maximum forcing between the highest (approximately 300 Gt) and lowest (approximately 30 Gt) estimated stratospheric S-loading from the Chicxulub impact. However, higher S-loads increase the overall duration of the forcing by several months. We use a single column model for a preliminary investigation of the short-term climate response to the impact-related production of sulfate aerosols (the lack of horizontal feedbacks limits the usefulness of the single column model to the first few days after the impact). Compared with the present steady-state climate, the introduction of large amounts of sulfate aerosols in the stratosphere results in a significant cooling of the Earth's surface. A long-term climate response can only be investigated with the use of a three-dimensional atmospheric model, which allows for the atmospheric circulation to adjust to the perturbation. Overall, although the climate perturbation to the forcing appears to be relatively large, the geologic record shows no sign of a significant long-term climatic shift across the K/T boundary, which is indicative of a fast post-impact climatic recovery.

Climate↗
PubMed2004

Effects of intraperitoneal and extraperitoneal carbon dioxide insufflation on blood gases during the perioperative period.

The aim of this study was to evaluate the effects of intraperitoneal and extraperitoneal CO2 insufflation on blood gases during and after laparoscopic surgery. Forty patients were included in this study. Twenty patients underwent elective laparoscopic cholecystectomy with intraperitoneal insufflation (intraperitoneal group) and 20 patients underwent laparoscopic inguinal hernia repair with extraperitoneal insufflation (extraperitoneal group). Arterial blood gases were analyzed at four points: 10 minutes after induction, 10 minutes after insufflation, 10 minutes after desufflation, and 30 minutes after the operation in the recovery room. PaCO2 values in the intraperitoneal group at the four points were 36.8 +/- 4, 39.6 +/- 5.9, 40.7 +/- 4.4, and 42.3 +/- 4.8 mm Hg; in the extraperitoneal group, 35.8 +/- 3.9, 37.4 +/- 4, 42.8 +/- 6.6, and 46.2 +/- 5.9 mm Hg. In the extraperitoneal group, there was a significant increase in postoperative PaCO2 compared to the desufflation PaCO2. In our study, extraperitoneal CO2 insufflation caused increases in PaCO2 values that started perioperatively and continued in the postoperative period.

Adult↗
PubMed1989

Hygiene aspects of occupational exposure to waste anaesthetic gases in Ontario hospitals.

Exposure of workers to waste anaesthetic gases in the operating and recovery rooms of hospitals is an ongoing concern because a number of epidemiological and mortality studies have reported significant adverse effects. To evaluate the health risks if any, and to assist in the development of guidelines or regulations for the hospital sector in Ontario, the Health and Safety Support Services Branch of the Ontario Ministry of Labour conducted this extensive study. The results of the hygiene study show that exposure to waste anaesthetic occurs because of leaks in the anesthetic equipment. The three major sources of leaks (i.e. exhalation valves, masks and high-pressure fittings) produced concentrations above the limit of detection of nitrous oxide (1000 ppm of N2O) in a significant number of samples. Of the samples taken at leak sources those taken at the exhalation valve had the highest percentage of samples above 1000 ppm, which suggested that scavenging systems were not receiving proper service and maintenance. Only 23% of the operating rooms surveyed met the Ontario Ministry of Health Criterion of 24 air changes per hour. Dilution ventilation was less effective than scavenging in keeping down concentrations of air contaminants. The sampling data show that the anaesthetists have the highest time-weighted average exposure (median value range 56-79 ppm) of the major group of occupations surveyed and that the general surgeons' TWA is much lower (28 ppm). It was concluded that the dilution ventilation rate of 24 air changes per hour should be maintained in all operating rooms and that there should be no recirculation of exhaust air when operations are in progress. To keep down concentrations of anaesthetic gases scavenging systems should be provided in all operating rooms. In each hospital maintenance should be the responsibility of a qualified staff member who has been adequately trained in the repair and maintenance of anaesthetic delivery systems. Finally, a qualified staff member should be responsible for conducting periodic personal monitoring in operating rooms (ORs) and recovery rooms (RRs) and the sampling strategy should include individuals and the exhaust grilles.

Air Pollutants, Occupational↗
PubMed1977

Investigations of some aspects of atmospheric pollution by anaesthetic gases. I: Diffusion of halothane across plastic and rubber tubes.

Plastic and rubber tubing, of the types used frequently to convey anaesthetic gases to and from the patient, or anaesthetic waste gases out of the operating theatre, were assessed for their capacity to allow diffusion of halothane through the tube wall. The magnitude of this effect has been calculated in relation to pollution of the operating theatre atmosphere under different circumstances.

Air Pollution↗
PubMed1978

Bacterial contamination of anaesthetic gases.

The bacterial content of oxygen and nitrous oxide immediately before and after passing through clean and used breathing systems (circuits) was measured using a specially constructed agar chamber (Bourdillon's slit sampler). The content per litre of oxygen from the outlet of the anaesthetic machine was 4.0 X 10-2, and 2.9 X 10-2 for nitrous oxide, corresponding to 3.5 X 10-2 for a 50% mixture of the gases. After passing through cleaned circuits, the bacterial pollution of the gas mixture had increased by 30%, but more than elevenfold after passing through used circuits. The content from cleaned circuits was less than that measured previously in the air of hospital wards and operating theatres, whereas gases from used circuits were polluted to approximately the same extent. It is concluded that used circuits may increase the risk of cross-infection. The cleaning method employed by us (dish-washer--hot airy drying) appeared to be acceptable.

Anesthesia, Inhalation↗
PubMed2004

Contamination of anaesthetic gases with nitric oxide and its influence on oxygenation: study in patients undergoing open heart surgery.

BACKGROUND: Nitric oxide is important in vasomotor regulation. Contamination of anaesthetic gases with nitric oxide could affect gas exchange. METHODS: We measured oxygenation and nitric oxide concentrations in the inspiratory and expiratory limb of the ventilator circuit in patients about to have cardiac surgery. Measurements were made before surgery when the circulation and respiratory conditions were stable. Fi(o(2)) was set at 0.35. The breathing circuit was supplied with a fresh gas flow greater than the minute volume so that exhaled gas was not re-used. Three gas mixtures were given in sequence to each patient: oxygen and compressed air (AIRc), oxygen and nitrous oxide, and oxygen and synthetic air (AIRs) that was free from nitric oxide. All patients were given AIRs as the second gas and the other two gas mixtures (AIRc and nitrous oxide) were given randomly as the first and third gases. RESULTS: During ventilation with oxygen-AIRc, the median nitric oxide concentration was 5.6 ppb, during ventilation with oxygen-nitrous oxide it was 5.0 ppb and using oxygen-AIRs it was 1.5 ppb. When AIRc and nitrous oxide were used, Pa(o(2)) was greater and venous admixture was less than when AIRs was used. The different gas mixtures did not affect pulmonary vascular pressures or cardiac output. CONCLUSIONS: Compressed air and nitrous oxide contain very low concentrations of nitric oxide (<10 ppb). This can affect pulmonary oxygen transfer during anaesthesia.

Adult↗