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.

SourceResearch connectionFrom yearThrough year

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

At least 865 records · Page 48Linked to original sources

PubMed1998

Two gamma-interferon-activation sites (GAS) on the promoter of the human intercellular adhesion molecule (ICAM-1) gene are required for induction of transcription by IFN-gamma.

We describe the molecular features of the interferon (IFN)-gamma-mediated transcription of the human intercellular adhesion molecule (ICAM-1) gene. We identified putative IFN-gamma-activated sites (GAS) distributed throughout a large segment of the ICAM-1 promoter (4.0 kb region). Using computer-assisted search, these sequences were similar to potential IFN-gamma responsive elements that have a core sequence 5'-TTNCNNNAA-3'. In this report we show that in the ICAM-1 promoter a GAS site is located at -115 from the translation initiation site, and binds with strong affinity to IFN-gamma-activated Signal Transducers and Activators of Transcription (STAT1) homodimers. The same sequence is responsible for the IFN-gamma-mediated transcription of the ICAM-1 gene. Moreover, we present evidence that a more distal GAS element that maps at -2787 from the translation initiation site, binds IFN-gamma-activated STAT1 dimers with lower affinity. Multimeric copies of such GAS sequence inserted into a tkCAT minimal promoter can drive transcription, demonstrating that the -2787 bp GAS element has an independent functional activity upon binding of IFN-gamma-activated STAT1 proteins as documented by in vitro binding assays. Furthermore, using recombinant ICAM-CAT mutants, we show that, in vivo, the -2787 GAS, but not a mutagenized -2787 GAS site, when coupled to the more proximal -115 GAS element, has an additive effect in enhancing the IFN-gamma-mediated transcription of ICAM-1 promoter. Nevertheless, using a recombinant construct bearing the wild type -2787 GAS element and a mutagenized -115 GAS element, we could not detect any transcription after transfection of U937 recipient cells, suggesting that the -2787 bp GAS element is not sufficient as such for gene activation, but can cooperate with its cognate proximal sequence to give full function to the ICAM-1 promoter during the IFN-gamma response. Taken together these data provide evidence that two GAS sites are required for the full potential activity in the mechanism of ICAM-1 gene activation by IFN-gamma.

5' Untranslated Regions↗

PubMed1994

Landfill gas effects on groundwater samples at a municipal solid waste facility.

A study was performed to determine the source of low concentrations of volatile organic compounds (VOCs) detected in groundwater samples at a solid waste management facility. The affected wells were identified as hydraulically upgradient of an old unlined facility, but downgradient of a new clay-lined landfill. These monitoring wells are close to both sites. Subsurface landfill gas migration was identified after a low permeability cap was installed on the older site. Subsurface gas pressure was monitored to identify horizontal landfill gas migration. Monitoring well headspace gases were evaluated to identify depressed oxygen concentrations and methane because of landfill gas migration into the well. Monitoring well headspace gas VOC concentrations were compared to groundwater VOC concentrations to determine the direction of phase transfer. A ratio above 1.0 of the observed well headspace gas concentration of a VOC to the concentration that would be in equilibrium with the groundwater concentration indicates gas-to-water phase transfer within the well. For the major gas-phase and aqueous-phase VOC, cis-1,2-dichloroethene, gas-to-water phase transfer is clearly indicated from the data for two of the four wells. Fifteen other VOCs were detected in monitoring well headspace gases but not in groundwater samples from the four wells studied. Only one compound in one well was detected in the groundwater sample but not in the headspace gases, and only one compound in one well was detected in both matrices at concentrations that suggested water-to-gas phase transfer. This study suggests that if landfill gas is suspected as the source of detected VOCs, monitoring well construction and stratigraphy are important considerations when attempting to differentiate between groundwater contamination by landfill gas and contamination from other sources.

Environmental Monitoring↗

PubMed1997

Monitoring gastric mucosal carbon dioxide pressure using gas tonometry: in vitro and in vivo validation studies.

BACKGROUND: Saline gastric tonometry of carbon dioxide has been proposed as a means to assess the adequacy of splanchnic perfusion. However, this technique has several disadvantages, including the long time interval needed for gases to reach equilibrium in saline milieu. Thus the authors evaluated a system that uses a gas-filled instead of a saline-filled gastric balloon. METHODS: In vitro, we simultaneously placed two tonometry catheters in an equilibration water bath maintained at a predetermined and constant pressure of carbon dioxide (P(CO2)). The first catheter's balloon was filled with air and the second with saline. The performance of gas tonometry was tested by comparing the P(CO2) measurements of the bath obtained via gas tonometry (PgCO2) to the P(CO2) measurements of direct bath samples (PbathCO2). These results were also compared with the P(CO2) measurements obtained simultaneously by saline tonometry (PsCO2). The response time of gas versus saline tonometry was also studied. In vivo, the performance of gas tonometry was tested comparing the measurements of gastric intramucosal P(CO2) obtained by gas tonometry (PgCO2) at different equilibration times with those obtained by saline tonometry (PsCO2) using an equilibration time of 30 min. Two nasogastric tonometry catheters were placed simultaneously in seven stable patients in the intensive care unit. The first balloon was filled with air and the second with saline. RESULTS: In vitro, there was a close correlation between PgCO2 and PbathCO2, for each level of PbathCO2, and for each different gas equilibration time. For an equilibration time of 10 min at a PbathCO2 level of approximately 40 mmHg, the bias of the gas device defined as the mean of the differences between PbathCO2 and PgCO2 and its precision defined as the standard deviation of the bias, were -0.3 mmHg and 0.7 mmHg, respectively. Using the same definitions, the bias and precision of saline tonometry were 11.2 mmHg and 1.4 mmHg, respectively. If the equilibration time-dependent correction factor provided by the catheter manufacturer for saline tonometry was applied, the bias and precision were -6.9 mmHg and 2.9 mmHg, respectively. In vivo, using an equilibration time of 10 min for gas and 30 min for saline tonometry, there was a close correlation between the two techniques (r2 = 0.986). A Bland and Altman analysis revealed a bias (+/- 2 SD) of 0.1 +/- 6.8 mmHg. The correlation between the two methods was not improved if we prolonged the equilibration time of the gas tonometer. CONCLUSIONS: Gas tonometry is comparable to saline tonometry for measuring gastric intramucosal P(CO2). Because gas tonometry is easier to automate, it may offer advantages over saline tonometry.

Adult↗

PubMed1999

Gas dynamics in CO2 angiography: in vitro evaluation in a circulatory system model.

RATIONALE AND OBJECTIVES: The use of carbon dioxide (CO2) as a vascular contrast agent has increased significantly since the introduction of digital subtraction angiography. To optimize the injection of CO2 for digital subtraction angiography, we evaluated the gas dispersion patterns from differing catheter designs, gas flow dynamics, and the influence of vessel size and inclination on luminal gas filling. METHODS: A circulatory system model was constructed and perfused with 36% glycerin solution at a rate of 1.08 to 1.13 liters per minutes (pulse rate 72 beats/minute, pressure 90-111 mm Hg). Fifty milliliters of CO2 was rapidly injected into the vascular tube of the model (diameter 6.4-15.9 mm) at an inclination of 0 degrees to 45 degrees via a catheter, and imaged digitally in a cross-table lateral projection. The dispersal patterns of gas bubbles from the halo, pigtail, and end-hole catheters were evaluated as well as the degree of luminal gas filling. RESULTS: The halo and end-hole catheters produced continuous gas flow with homogeneous density. The pigtail catheter produced smaller bubbles with inhomogeneous density. Luminal gas filling was incomplete, with a residual fluid level posteriorly regardless of the size and inclination of the tube. At 0 degrees inclination, gas filling was greater with the 6.4-mm tube than with the 15.9-mm tube. With an inclination of 0 degrees to 15 degrees, gas filling was significantly improved for the larger tubes. On dispersal, CO2 bubbles rapidly coalesced and moved forward along the anterior aspect of the tube. The frontal motion of the bubble was parabolic in configuration. CONCLUSIONS: The halo and end-hole catheters provide more homogeneous gas density than the pigtail catheter. Gas filling was incomplete regardless of catheter design, vessel size, or inclination. Inclination improves gas filling in vessels > 12.7 mm in diameter.

Angiography, Digital Subtraction↗

PubMed2006

Effects of endothelin receptor antagonism on acute lung injury induced by chlorine gas.

OBJECTIVE: To test the hypothesis that the endothelin system is involved in chlorine gas-induced lung injury. DESIGN: Experimental study. SETTING: Academic research laboratory. SUBJECTS: Twenty-four domestic juvenile pigs. INTERVENTIONS: Anesthetized, ventilated pigs were exposed to chlorine gas (400 parts per million in air) for 20 mins and then randomly allocated to four groups (n=6 in each group). The tezosentan pretreatment group received the dual endothelin receptor antagonist tezosentan 20 mins before and hyperoxic gas (Fio2 0.6) after chlorine gas exposure. The tezosentan postinjury treatment group received hyperoxic gas after chlorine gas exposure and tezosentan 60 mins later. Animals in the oxygen group received hyperoxic gas after chlorine gas exposure. Pigs in the fourth group (air) were ventilated with room air (Fio2 0.21) throughout the experiment. MEASUREMENTS AND MAIN RESULTS: Hemodynamics, gas exchange, lung mechanics, and plasma endothelin-1 were evaluated for 6 hrs. Chlorine gas exposure induced an increase in circulating endothelin-1 by 90% (p<.05). The acute chlorine gas-induced rise in pulmonary vascular resistance was partly blocked by tezosentan pretreatment (p<.001). Tezosentan postinjury treatment also decreased pulmonary vascular resistance to levels significantly lower than in the air and oxygen groups (p<.001). Recovery of peak airway pressure was better in the tezosentan-treated groups than in the air group. There were significant linear relationships between circulating endothelin-1 and pulmonary vascular resistance (r=.47, p<.001) and endothelin-1 and peak airway pressure (r=.41, p<.001). These relationships were modified by tezosentan. CONCLUSIONS: Tezosentan modified chlorine gas-induced pulmonary dysfunction, indicating that the endothelin system is involved in this mode of acute lung injury.

Animals↗

PubMed1994

Gas vesicles.

The gas vesicle is a hollow structure made of protein. It usually has the form of a cylindrical tube closed by conical end caps. Gas vesicles occur in five phyla of the Bacteria and two groups of the Archaea, but they are mostly restricted to planktonic microorganisms, in which they provide buoyancy. By regulating their relative gas vesicle content aquatic microbes are able to perform vertical migrations. In slowly growing organisms such movements are made more efficiently than by swimming with flagella. The gas vesicle is impermeable to liquid water, but it is highly permeable to gases and is normally filled with air. It is a rigid structure of low compressibility, but it collapses flat under a certain critical pressure and buoyancy is then lost. Gas vesicles in different organisms vary in width, from 45 to > 200 nm; in accordance with engineering principles the narrower ones are stronger (have higher critical pressures) than wide ones, but they contain less gas space per wall volume and are therefore less efficient at providing buoyancy. A survey of gas-vacuolate cyanobacteria reveals that there has been natural selection for gas vesicles of the maximum width permitted by the pressure encountered in the natural environment, which is mainly determined by cell turgor pressure and water depth. Gas vesicle width is genetically determined, perhaps through the amino acid sequence of one of the constituent proteins. Up to 14 genes have been implicated in gas vesicle production, but so far the products of only two have been shown to be present in the gas vesicle: GvpA makes the ribs that form the structure, and GvpC binds to the outside of the ribs and stiffens the structure against collapse. The evolution of the gas vesicle is discussed in relation to the homologies of these proteins.

Amino Acid Sequence↗

PubMed1998

Ensiling effects of the ethanol fractionation of forages using gas production.

We studied the use of gas curve subtraction to distinguish between two fractions soluble in neutral detergent solution. Samples of unfractionated (whole) forage, residue insoluble in 90% ethanol, and isolated NDF were fermented in vitro, and gas production was monitored. The gas volume associated with the ethanol solubles (A fraction) was determined as the difference between the gas from the whole forage and from the ethanol residue. The gas yield associated with the fraction insoluble in 90% ethanol but soluble in neutral detergent solution (B fraction) was determined by subtracting the isolated NDF gas curve from the corresponding ethanol residue curve. This experiment included three forages (alfalfa, bromegrass, and orchardgrass) harvested at two maturities and preserved by freeze-drying or ensiling to form a 3 x 2 x 2 factorial arrangement. Ensiling reduced the rate of gas formation from the A fraction by approximately 30% (P < .01). Ensiling increased (P < .05) the size of the A fraction (2 to 10% of DM) but did not change the volume of gas produced (P > .05). The gas yield from the B1 fraction was reduced 40% (P < .05) by ensiling with no significant change in rate. Curve subtraction of gas production profiles may be used to obtain rate estimates for multiple neutral detergent soluble pools. The separation of the neutral detergent solubles into two pools clarified the effects caused by ensiling. Changes due to ensiling on the rate of gas produced were associated with the A fraction, and the effects on final gas volume were associated with the B1 fraction.

Animals↗

PubMed1997

Lumbar nerve root compression caused by lumbar intraspinal gas. Report of three cases.

STUDY DESIGN: Three cases of lumbar nerve root compression associated with intradiscal gas formation and its migration are reported. OBJECTIVES: To establish the pathogenic mechanism by which gas is formed in the spinal canal. SUMMARY OF BACKGROUND DATA: Few such cases have been reported of patients with clinical symptoms of lumbar radiculopathy resulting from gas in the spinal canal. METHODS: Surgery with needle aspiration of the gas was performed in all cases. RESULTS: The presence of the gas was detected in the extradural space in one patient and within the nerve sheath in two patients. After surgery, all patients recovered well, and there were no obvious remnant neurologic abnormalities. One year later, all patients were completely free of symptoms. CONCLUSIONS: Surgery with needle aspiration of the gas resulted in clinical improvement in all cases, confirming that intraspinal gas is an important cause of lumbar radiculopathy. The composition of the gas in one patient was analyzed by gas chromatography, which revealed an overwhelming preponderance of nitrogen. A relationship between a gas-containing pseudocyst in the spinal canal and a degenerated intervertebral disc was identified, a key finding for understanding the precise nature of this disorder. Intradiscal gas formation and its outward migration as a sequel of intervertebral disc degeneration also has been addressed in this report.

Aged↗

PubMed1995

Preliminary evaluation of a new continuous intra-arterial blood gas monitoring device.

Continuous intra-arterial blood gas monitoring is a new technique, possibly offering therapeutic advantages through improved monitoring in patients prone to hypoxaemia, hypercapnia and/or respiratory acidosis. Therefore, we studied the clinical applicability, reliability, precision and side effect of long-term continuous intra-arterial blood gas monitoring in patients suffering from severe acute respiratory distress syndrome. In 10 patients continuous intra-arterial blood gas monitoring based on fluorescent optodes technique was performed. At 4 h intervals, arterial blood samples for in vitro blood gas analyses were drawn, stored in ice, and analysed within 3 min. Evaluation of data retrieved from the continuous intra-arterial blood gas monitoring and in vitro blood gas analysis was based on 596 data points using 10 catheters. Average length of insertion was 281 +/- 215 h, max. lengths of stay was 750 h. Arterial blood gas data obtained in vivo were compared to the mean of in vivo and in vitro arterial blood gases. Inter-catheter bias, expressed as percent difference between continuous intra-arterial blood gas and mean in vitro blood gas analysis was 0.19 +/- 0.23% for pH. 1.1 +/- 5.2% for PaCO2 and 1.6 +/- 5.7% for PaO2. No significant gas partial pressure dependent change in precision was demonstrable. There was no significant time dependent drift in sensor precision over the study period. No negative side-effects related to IABG monitoring were observed. We conclude that long-term use of this new device is possible in patients and represents a reliable alternative to conventional in vitro arterial blood gas analysis, when continuous monitoring of blood gases and/or acid-base balance is critical.

Acid-Base Equilibrium↗

PubMedDate not supplied

A method for increasing confidence in respiratory gas exchange measurements in mechanically ventilated patients.

Measurement of O2 uptake (VO2) and CO2 output (VCO2) with automated instruments can be used to optimize nutritional management of critically ill patients. However, these measurements may be made infrequently because of calibration problems or suspected inaccuracies, especially when the patient is given supplemental oxygen. A simple method is described for periodic testing of automated gas exchange measurements. While a test lung is mechanically ventilated an accurately known mixture of CO2 and nitrogen is introduced into the inspired gas, simulating VO2 by dilution and VCO2 by addition of CO2. The ratio of VCO2:VO2 (respiratory gas exchange ratio, R) in the "expired gas" should be [FGCO2/(1-FGCO2)] x [(1-FIO2)/FIO2], where FGCO2 is the fraction of CO2 in the diluting gas and FIO2 is the fraction of O2 in the inspired gas. R is independent of the flow rate of the diluting gas or the rate of ventilation of the test lung. Using a mixing chamber-mass spectrometer, we found that R calculated from measurement of CO2 and O2 concentrations in the simulated mixed expired gas closely matched the predicted R for FIO2 = 0.21-0.50. On the other hand, when an automated gas exchange measurement device was tested, R was sometimes excessively high, especially for FIO2 greater than 0.35. This method, using a single diluting gas and without precision flowmeters, may be useful for periodic testing of respiratory gas exchange instruments in the intensive care unit. If a discrepancy is found between measured and predicted R, measurements should not be relied upon until further calibration or repairs can be effected.

Humans↗

PubMed2004

The role of discontinuous gas exchange in insects: the chthonic hypothesis does not hold water.

Insects breathe through valved openings (spiracles) in their cuticle. Many insects open and close their spiracles in a cyclic pattern (discontinuous gas-exchange cycles, or DGC). These cycles were observed over half a century ago, their hypothesized function being to minimize loss of water from the tracheal system. However, numerous recent studies have found that respiration accounts for a small fraction of total water loss, and that insects stop performing DGC at times when this pattern would be most useful. Thus, the importance of cyclic gas exchange for water conservation has been challenged. The leading alternative is the chthonic hypothesis, which proposes that DGC originated in insects from hypercapnic (high CO2) environments (e.g. burrows) to aid in release of carbon dioxide. By keeping the spiracles closed, insects would concentrate CO2 and increase the gradient for outward diffusion of CO2. CO2 would be released rapidly when the spiracles opened, and respiratory water loss would be reduced. The chthonic hypothesis therefore predicts that DGC minimizes the ratio of respiratory water loss to CO2 release relative to other modes of gas exchange. We tested the chthonic hypothesis by simultaneously measuring water loss and CO2 release in reproductive females (queens) of the seed-harvester ant Pogonomyrmex barbatus, a burrowing species from North American deserts. Queens used one of three patterns of gas exchange, discontinuous, cyclic and continuous. We resolved the problem of separating cuticular transpiration and respiratory water loss for individuals that used continuous gas exchange by developing a regression method that can be used across all patterns of gas exchange. The ratio of respiratory water loss to CO2 release did not differ among ants using different patterns of gas exchange, in contrast to the expectation of the chthonic hypothesis. Metabolic rate, however, varied with gas-exchange pattern, and was lowest for individuals that used discontinuous gas exchange, intermediate for individuals using cyclic gas exchange, and highest for individuals using continuous gas exchange.

Analysis of Variance↗

PubMed1996

Non-destructive evaluation of membrane lung gas exchange performance.

This paper describes a method of evaluating the gas exchange effectiveness of hollow fiber oxygenators utilizing gas on both sides of the membrane. The goal of the study was to develop an evaluation technique which was accurate, reliable, and did not harm or contaminate a new, sterile oxygenator. Three pediatric oxygenators were tested and compared: the Medtronic Minimax Plus, the Terumo Capiox 320, and the Sorin Masterflo 34 (all with rated blood flows of 2-2.5 L/min). Gas entering the "blood" side was a mixture of CO2, O2, and N2 in a mixture matching typical venous blood partial pressures. The "blood" flows used were 0.5, 1, 1.5, or 2 L/min. Gas entering the gas port had an FiO2 of 0.4 flowing at 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 L/min. Fractional contents of CO2 and O2 at all inlets and outlets were determined using a gas analyzer and converted to partial pressures. Efficacy indices and gas transfer rates were calculated and compared. Of the devices studied, the Masterflo 34 had the highest gas transport rates and effectiveness followed by the Minimax-Plus and the Capiox 320. Reversing the direction of the flow through the "blood" phase of the Minimax-Plus greatly changed its gas exchange effectiveness. The techniques described in this study should allow for a more uniform and consistent evaluation of gas exchange by membrane lungs which can be made inexpensively and relatively quickly. In addition, these methods should allow manufactures to evaluate gas exchange effectiveness and transfer rates of individual units during production as well as reduce the complexity involved when evaluating newly developed oxygenators.

Materials Testing↗

PubMed1989

Effects of periodic administration of Nocardia rubra cell-wall skeleton on immunoglobulin production and B-cell-stimulatory factor activity in vitro in workers at a poison gas factory.

The former workers at the Okunojima poison gas factory (poison gas workers) are a high-risk group for malignant neoplasms and show abnormalities in cellular immunity. At the same time, poison gas workers often have chronic respiratory diseases, such as chronic bronchitis, and are highly susceptible to respiratory infections. To explore the possibility of immunological cancer prevention, we have periodically administered 200 micrograms Nocardia rubra cell-wall skeleton (N-CWS) to poison gas workers once every 3 months since December 1978. During this period, we noted a significantly lower incidence of influenza among poison gas workers receiving N-CWS than in those not receiving the drug during the influenza epidemic. This finding suggested that the administration of N-CWS enhanced the resistance of these workers to infections. Therefore, periodical administration of N-CWS to poison gas workers was considered to enhance the reduced T-cell function of normalizing antibody production by stimulating the production of B-cell-stimulatory factor (BSF). In the present study, to clarify the mechanism of immunosuppression in the poison gas workers and to examine the effects of continual administration of N-CWS on this condition, we compared the immunoglobulin production and the proliferative and differentiative activities of B-cell-stimulatory factor (BSF) of peripheral blood mononuclear cells (PBMC), in poison gas workers treated or not treated with N-CWS. Comparisons were also made with age-matched healthy controls. In the untreated poison gas workers, immunoglobulin and BSF production of PBMC were reduced as compared with the control group. On the other hand, in the poison gas workers receiving N-CWS, immunoglobulin and BSF production of PBMC were restored nearly to the control level. These results show that in vitro antibody production in the poison gas workers was reduced and that a reduction in BSF production of T cells was one of its causes.

Adjuvants, Immunologic↗

PubMed2003

Better success of retinal reattachment with long-standing gas tamponade in highly myopic eyes.

BACKGROUND: To evaluate the efficacy of long-term gas tamponade after pars plana vitrectomy (PPV) for retinal detachment (RD) due to a macular hole (MH) in highly myopic eyes. METHODS: A retrospective study was conducted at two institutions. The study included 25 highly myopic eyes with RD resulting from a MH. C3F8 gas tamponade was used in 13 eyes (C3F8 gas group), and SF6 gas tamponade was used in 12 eyes (SF6 gas group) following PPV. C3F8 gas has a longer half-life time in the vitreous cavity than SF6 gas. The main outcome measures were the anatomic reattachment rate and the visual acuity (VA). Follow-up periods were at least 24 months. RESULTS: The anatomic reattachment rate and MH closure following the initial surgery were significantly higher in the C3F8 gas group (100%) than in the SF6 gas group (66.7%; P=0.039). The differences in the postoperative VAs were not significant both for all eyes and only for eyes with initial anatomic success. (P=0.42 and P=0.54, respectively). In addition, no significant difference was found in the improvement of VA both for all eyes and for the initial success eyes (P=0.66 and P=0.56, respectively). CONCLUSION: We conclude that the longer duration of tamponade with C3F8 gas results in a higher rate of successful closure and that C3F8 gas tamponade is an effective treatment for MH with RD in highly myopic eyes.

Aged↗

PubMed2005

Environmental sensitivity of gas exchange in different-sized trees.

The carbon isotope signature (delta13C) of foliar cellulose from sunlit tops of trees typically becomes enriched as trees of the same species in similar environments grow taller, indicative of size-related changes in leaf gas exchange. However, direct measurements of gas exchange in common environmental conditions do not always reveal size-related differences, even when there is a distinct size-related trend in delta13C of the very foliage used for the gas exchange measurements. Since delta13C of foliage predominately reflects gas exchange during spring when carbon is incorporated into leaf cellulose, this implies that gas exchange differences in different-sized trees are most likely to occur in favorable environmental conditions during spring. If gas exchange differs with tree size during wet but not dry conditions, then this further implies that environmental sensitivity of leaf gas exchange varies as a function of tree size. These implications are consistent with theoretical relationships among height, hydraulic conductance and gas exchange. We investigated the environmental sensitivity of gas exchange in different-sized Douglas-fir (Pseudotsuga menziesii) via a detailed process model that specifically incorporates size-related hydraulic conductance [soil-plant-atmosphere (SPA)], and empirical measurements from both wet and dry periods. SPA predicted, and the empirical measurements verified, that differences in gas exchange associated with tree size are greatest in wet and mild environmental conditions and minimal during drought. The results support the hypothesis that annual net carbon assimilation and transpiration of trees are limited by hydraulic capacity as tree size increases, even though at particular points in time there may be no difference in gas exchange between different-sized trees. Maximum net ecosystem exchange occurs in spring in Pacific Northwest forests; therefore, the presence of hydraulic limitations during this period may play a large role in carbon uptake differences with stand-age. The results also imply that the impacts of climate change on the growth and physiology of forest trees will vary depending on the age and size of the forest.

Carbon Dioxide↗

PubMed2006

Passive drainage and biofiltration of landfill gas: Australian field trial.

In Australia a significant number of landfill waste disposal sites do not incorporate measures for the collection and treatment of landfill gas. This includes many old/former landfill sites, rural landfill sites, non-putrescible solid waste and inert waste landfill sites, where landfill gas generation is low and it is not commercially viable to extract and beneficially utilize the landfill gas. Previous research has demonstrated that biofiltration has the potential to degrade methane in landfill gas, however, the microbial processes can be affected by many local conditions and factors including moisture content, temperature, nutrient supply, including the availability of oxygen and methane, and the movement of gas (oxygen and methane) to/from the micro-organisms. A field scale trial is being undertaken at a landfill site in Sydney, Australia, to investigate passive drainage and biofiltration of landfill gas as a means of managing landfill gas emissions at low to moderate gas generation landfill sites. The design and construction of the trial is described and the experimental results will provide in-depth knowledge on the application of passive gas drainage and landfill gas biofiltration under Sydney (Australian) conditions, including the performance of recycled materials for the management of landfill gas emissions.

Air Pollutants↗

PubMed1996

Association of respiratory symptoms and lung function in young adults with use of domestic gas appliances.

BACKGROUND: There is evidence from some studies that people living in homes with gas stoves and other unvented gas appliances experience more respiratory symptoms than those who use other fuels for cooking and heating, but other studies have found no such association. We have investigated whether the use of gas appliances is associated with an increased risk of respiratory symptoms and whether sensitisation to common environmental allergens modifies any such association. METHODS: A stratified random sample of 15,000 adults aged 20-44 years, living in three towns in East Anglia, UK, were sent a questionnaire on asthma and hayfever. From those who responded, a random sample of 1864 were invited to complete an extended questionnaire that included questions on use of gas appliances, to give blood samples for measurements of total IgE and specific IgE to common allergens, and to undergo tests of respiratory function, 659 women and 500 men agreed to an interview. The association of the use of gas appliances with respiratory symptoms, total IgE, specific IgE, and respiratory function was assessed by logistic and multiple regression models. FINDINGS: Women who reported they mainly used gas for cooking had an increased risk of several asthma-like symptoms during the past 12 months including wheeze (odds ratio 2.07 [95% CI 1.41-3.05]), waking with shortness of breath (2.32 [1.25-4.34]), and asthma attacks (2.60 [1.20 -5.6]). Gas cooking increased the risk of symptoms more in women who were atopic than in non-atopic women but the difference did not reach significance (p . 0.05). Women who used a gas stove or had an open gas fire had reduced lung function (forced expiratory volume in 1 s [FEV1]) and increased airways obstruction (FEV1 as a percentage of forced vital capacity) compared with women who did not. These associations were not observed in men. INTERPRETATION: In East Anglia, the use of gas cooking is significantly associated with subjective and objective markers of respiratory morbidity in women but not in men. Women may be more susceptible than men to the products of gas combustion or they may have greater exposure to high concentrations of these products because they cook more frequently than men.

Adult↗

PubMed2002

Gas production and transport in artificial sludge depots.

This paper presents a study to determine the impact of gas production in dredging sludge on the storage capacity of artificial sludge depots. Gas is produced as a result of the decomposition of organic material present in dredging spoil. This process, in which methane and carbon dioxide are formed, may lead to expansion of sludge layers, partly or even completely counterbalancing consolidation. The study shows that, even with a very conservative estimation of the rate of gas production, accumulation of gas occurs as convective and diffusive transport proceed very slowly. Nucleation of gas bubbles occurs already at a limited oversaturation of pore water. During their growth, bubbles push aside the surrounding grain matrix. Resulting stresses may initiate cracks around bubbles. If these cracks join, they may form channels stretching out to the depot surface and along which gas may escape. However, channels are only stable to a limited depth below which bubble accumulation may continue. The gas content at which sufficient cracks and channels are formed to balance the rate of gas production with the rate of outflow strongly depends on the constitutive properties of the dredging sludge considered. In sludge with a high shear strength (> 10 kPa), stable channels are created already at low deformations. However, a large expansion may occur in sludge with a low strength. The present study shows that accumulation of gas may continue until a bulk density less than that of water is attained. This is equivalent to a gas fraction of about 25-37%, depending on the initial water content of the sludge. Only then can gas escape as a result of instabilities in the sediment matrix. This should be well taken into account during the design and management of artificial depots.

Air Movements↗