Nitrous Dioxide Research Articles

Air quality improvement and the prevalence of frequent ear infections in children

Objective To determine whether air quality influences the prevalence of pediatric frequent ear infections and respiratory allergy. Study Design Case-control study. Setting Academic medical center. Subjects and Methods The National Health Interview Survey child sample for the calendar years 1997 through 2006 was analyzed, extracting 12-month prevalence data for the following three disease conditions: frequent (≥3 within 12 months) ear infections, respiratory allergy, and seizures (nonrespiratory control condition). Based on information from the Environmental Protection Agency, yearly historical data for the air quality criteria pollutants carbon monoxide, nitrous dioxide, sulfur dioxide, and particulate matter were tabulated. Graphical and linear regression analyses were conducted to determine the influence of air quality on each of the disease conditions. Results A total of 126,060 children were studied (51.4% male, mean age 8.6 yrs). Overall, the 12-month prevalence for three or more ear infections, respiratory allergy, and seizures was 6.6%, 11.7%, and 0.7%, respectively. Air quality steadily improved over the study period. Statistically significant positive regression coefficients were obtained for each of the criteria pollutants with ear infections (all P < 0.001), with regression coefficients ranging from 0.007 (particulate matter) to 11.2 (sulfur dioxide). For respiratory allergies, nonstatistically significant regression coefficients for the criteria pollutants were obtained (range <0.001-0.379, all P ≥ 0.409). For the nonrespiratory condition seizures, nonsignificant regression coefficients were again identified (all P ≥ 0.404). Conclusions Better air quality is significantly associated with lower prevalence of pediatric frequent ear infections but is not associated with the prevalence of pediatric respiratory allergy. Improvements in air quality may be implicated in the decreased rates of pediatric ear infections over time.

Children’s asthma hospitalizations and relative risk due to nitrogen dioxide (NO2): Effect modification by race, ethnicity, and insurance status

This study explores the role of race, ethnicity, and insurance status in modifying the effects of air pollution on children's asthma hospitalizations in Phoenix, Arizona (US) between 2001 and 2003. While controlling for weather, interactions between nitrous dioxide (NO(2)) and race, ethnicity, and insurance status are used to predict relative risk for subgroups of children. The generalized logit regression model for nominal categorical data within a multinomial likelihood framework was used. This model is specifically suited to small counts and the reporting of 95% confidence intervals for the odds ratio of hospital admission for one group as compared to another. The odds ratio is known to approximate relative risk for rare events. Several significant findings were found for race, ethnicity, and insurance status as modulators for the effect of NO(2) on children's risk for asthma hospitalization: (1) children without insurance have 1.4 (95% CI: 1.1-1.8) times higher risk of asthma admissions than those with private insurance at exceedances of 0.02 parts per million (ppm) of NO(2) above the seasonal mean; the same finding holds for children without insurance as compared to those with Medicaid; (2) black children have 2.1 (95% CI: 1.3-3.3) times higher risk of hospitalization than Hispanic children at seasonal mean NO(2) levels, but this disproportionate risk shrinks to 1.7 with exceedances of 0.02 ppm of NO(2) above the seasonal mean. Specific to finding (1) among those children without health insurance, Hispanic children have 2.1 (95% CI: 1.1-3.8) times higher risk of hospitalization than white children. Among all Hispanic children, those without health insurance have 1.9 (95% CI: 1.3-3.0) times greater risk than those with private insurance; the same finding holds for Hispanic children without insurance as compared to Hispanic children with Medicaid. Specific to finding (2), among children with private insurance, the disproportionate risk of black children as compared to Hispanic children is magnified by a factor of 1.3 (95% CI: 1.0-1.8) for exceedances of 0.02 ppm of NO(2) above the seasonal mean. Although we cannot confirm a cause-effect relationship, this analysis suggests that increasing insurance enrollment for all children, and specifically Hispanic children, may reduce their disproportionate risk from exceedances of air pollution. There are few black children in Phoenix, so further studies are needed to investigate the increasing risk of black children with private insurance as compared to Hispanics at exceedances of NO(2).

Air quality influences the prevalence of hay fever and sinusitis

Determine associations between air quality and the prevalence of hay fever and sinusitis. Cross-sectional study. The National Health Interview Survey for the calendar years 1997-2006 adult sample was analyzed to determine for each calendar year the one-year period prevalence of the two respiratory conditions, hay fever and sinusitis and the nonrespiratory (control) condition, weak/failing kidneys. From the Environmental Protection Agency, yearly historical data for air quality criteria pollutants, carbon monoxide, nitrous dioxide, sulfur dioxide, and particulate matter, were tabulated. Graphical and linear regression analyses were conducted for each disease condition against each of the air quality variables to determine if higher pollutant concentrations predicted a higher prevalence for the disease condition. A total of 313,982 patients were studied over the 10 calendar years 1997-2006. Mean patient age increased very slightly from year to year (overall average, 45.2 years); the percentage of female patients remained the same. The air concentrations of each of the criteria pollutants decreased steadily over time with the exception of particular matter, which reached a plateau in the most recent 3 years. For each of the disease conditions a statistically significant relationship with air quality (all p < .001) was obtained. For the control condition of kidney failure/weakening, the standardized regression coefficient with air quality was very small (range-0.001-0.004). For hay fever and sinusitis, substantially larger coefficients were obtained ranging from 0.0120-.016 and 0.013-0.027, respectively. Prevalence of hay fever and sinusitis are correlated with air quality. Improvements in air quality are associated with decreased prevalence of both hay fever and sinusitis. Laryngoscope, 2009.

Soil–atmosphere exchange of N2O, CO2 and CH4 along a slope of an evergreen broad-leaved forest in southern China

At most sites the magnitude of soil-atmosphere exchange of nitrous dioxide (N2O), carbon dioxide (CO2) and methane (CH4) was estimated based on a few chambers located in a limited area. Topography has been demonstrated to influence the production and consumption of these gases in temperate ecosystems, but this aspect has often been ignored in tropical areas. In this study, we investigated spatial variability of the net fluxes of these gases along a 100 m long slope of a evergreen broadleaved forest in southern China over a whole year. We expected that the lower part of slope would release more N2O and CO2, but take up less atmospheric CH4 than the upper part due to different availability of water and nutrients. Our results showed that the soil moisture (Water Filled Pore Space, WFPS) decreased along the slope from bottom to top as we expected, but among the three gases only N2O emissions followed this pattern. Annual means of WFPS ranged from 27.7% to 52.7% within the slope, and annual emissions of N2O ranged from 2.0 to 4.4 kg N ha−1 year−1, respectively. These two variables were highly and positively correlated across the slope. Neither potential rates of net N mineralization and nitrification, nor N2O emissions in the laboratory incubated soils varied with slope positions. Soil CO2 release and CH4 uptake appeared to be independent on slope position in this study. Our results suggested that soil water content and associated N2O emissions are likely to be influenced by topography even in a short slope, which may need to be taken into account in field measurements and modelling.

Community Structure of Ammonia Oxidizing Bacteria and Their Potential to Produce Nitrous Oxide and Carbon Dioxide in Acid Tea Soils

The potentials of nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) production in acid tea soils from Indonesia and Japan were investigated in a laboratory incubation experiment, and the community structures of ammonia-oxidizing bacteria in these soils were characterized using PCR-DGGE approaches. The soils used were sampled from tea plantations in Shizuoka, Japan and in Bogor and Malino, Indonesia. All of the soils were acidic (pH 3.45 to 4.00). The N 2 O and CO 2 production in Shizuoka was almost 5 times higher than in Bogor and Malino. All of the amoA gene sequences defined belong to the genus Nitrosospira sp. with cluster 2 and cluster 3a.

Gaseous Products of Dinitromethane Decomposition Determined by DTA/FTIR

Gaseous products of the thermal decomposition of dinitromethane and potassium dinitromethanide were investigated by simultaneous DTA/FTIR analyses. Both isothermal and non-isothermal DTA regimes were applied. Nitrous oxide and carbon dioxide were detected by FTIR.

Comparison of the closed-chamber and gas concentration gradient methods for measurement of CO2 and N2O fluxes in two upland field soils

We measured nitrous oxide (N2O) and carbon dioxide (CO2) fluxes from Gray Lowland soil (onion field) and Andosol soil (maize field) using the closed-chamber method and the concentration-gradient method based on Fick's law (gradient method). Measurements of gas concentration (at a depth of 0.05 m) and relative gas diffusion coefficients (D/D 0) (0–0.05 m depth) in the soil were carried out every week during the snow-free season (May–October) each year for 6 years in the Gray Lowland soil (1995–2000) and for 3 years in the Andosol soil (1998–2000). The seasonal pattern of N2O and CO2 fluxes using the chamber method was similar to those using the gradient method, and there were significant positive correlations between the fluxes using the chamber and gradient methods when extremely high N2O flux values were excluded (Smirnov–Grubbs’ outlier test, P < 0.01). There were no significant differences in N2O fluxes between the two methods, but CO2 flux using the chamber method was higher than that using the gradient method. As the gradient method could not measure the production, consumption and gas diffusion in the surface soil above the soil-air sampling tube (upper 0.05 m), differences in extremely high N2O and CO2 fluxes between the two methods resulted when the production and consumption of these gases were active in the soil above the installed location of the soil-air sampling tube. Measurements of gas concentration and D/D0 in the soil were required at every measurement during the investigation period because these values showed large seasonal variation. The measurement of CO2 flux was more influenced by plants than the N2O measurements. Therefore, it is necessary to consider the distance between the instruments (chambers and soil-air sampling tubes) and nearby plants. Our results suggest that the gradient method could lead to under or over estimation of CO2 flux and to extremely high N2O flux measurements. In contrast, the gradient method could be used for N2O flux measurement, excluding extremely high fluxes, and to understand seasonal patterns in CO2 flux. The gradient method is useful because it can estimate gas fluxes both in the soil and from soil to the atmosphere at the same time.

Gas concentration driven fluxes of nitrous oxide and carbon dioxide in boreal forest soil

Gas concentration driven fluxes of nitrous oxide and carbon dioxide in boreal forest soil

Gas-Phase Photocatalytic Oxidation of Dimethylamine: The Reaction Pathway and Kinetics

Gas-phase photocatalytic oxidation (PCO) and thermal catalytic oxidation (TCO) of dimethylamine (DMA) on titanium dioxide was studied in a continuous flow simple tubular reactor. Volatile PCO products of DMA included ammonia, formamide, carbon dioxide, and water. Ammonia was further oxidized in minor amounts to nitrous oxide and nitrogen dioxide. Effective at 573 K, TCO resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide, and water. The PCO kinetic data fit well to the monomolecular Langmuir-Hinshelwood model, whereas TCO kinetic behaviour matched the first-order process. No deactivation of the photocatalyst during the multiple long-run experiments was observed.

Single-Dose Intravenous Flurbiprofen Administration Increases Blood Pressure Under General Anesthesia In Normotensive Patients

We studied whether blood pressure elevation is influenced by intravenous single-dose administration of flurbiprofen during general anesthesia. Twenty female patients who underwent lower abdominal laparotomy under general anesthesia were divided into two groups. Both groups received anesthesia with nitrous dioxide, sevoflurane, and pentazocine. The flurbiprofen group (n=10) received 50 mg flurbiprofen intravenously 10 minutes after the start of the surgery. The control group (n=10) received 50 mg flurbiprofen at the end of the examination. Blood pressure was assessed before administration (0 minute as baseline) and after administration (15, 30 and 60 minutes). Systolic blood pressures inceased after 60 minutes in the flurbiprofen group (fluctuation ratio from baseline: 1.28±0.06, mean±SEM) compared with that in the control group (1.07±0.04, p <0.05) and with baseline at 15, 30, and 60 minutes (1.17±0.05, 1.17±0.05, and 1.28±0.06, respectively, p <0.05).

Income and Pollutant Emissions in the ObjECTS MiniCAM Model

This article examines the relationship between income and pollutant emissions in the Obj ECTS Mini Climate Assessment Model (MiniCAM) to determine how historical analysis can best guide modeling efforts. Future scenarios for energy-related emissions of nitrous oxide (NOx ) and sulfur dioxide (SO2 )are presented along with the methodology used. A pseudo-Kuznets approach is used where the level of emission control is assumed to vary with per capita income. Emission results depend on the assumptions for when emission controls are implemented and the stringency of those controls. Historical analysis of the relationship between income and emission controls might be particularly useful in informing the parameterization of when emission controls are implemented. However, historical analysis is likely to be less helpful in informing the selection of parameters for the future levels of control, particularly at future times when parameter values are well outside the range of historical experience.

Comparing energy use and environmental performance of land transport modes

Environmental impacts related to policy measures such as transport investments are relevant for ex ante evaluations like cost–benefit analyses (CBAs), environmental impact assessments (EIAs) and strategic environmental assessments (SEAs). However, the methodologies used in determining impacts are much less developed than those employed in estimating transport and economic impacts. The aim of the present paper is to show how rough methodologies used in current practice might lead to serious faults in estimating environmental impacts. This is followed by suggestions for improvements to these methodologies. The first suggestion is related to indicators. Since only a limited number of these are used presently, such as emissions of carbon dioxide and nitrous oxide, including more indicators might prove to be helpful. Second, changes in emissions (e.g. due to regulations) are often considered for only a limited time horizon, so extending the time horizon for emission factors is therefore an important improvement. Third, sometimes emission factors from the literature or from another country/area are used, while the circumstances are not comparable; this might lead to serious faults. Using country‐ or region‐specific data, however, will improve the quality of assessments. Fourth, one often ignores that the effects of a given emission volume depend on the distance between source and receptor. The effects due to traffic, such as particulate matter or nitrous dioxide emissions, might then have more health impacts than emissions from industrial or power plants, and be reason enough to include these aspects as well. Fifth, it is suggested that categories of goods are broken down to determine freight modes, since lorries currently transport goods with a lower specific gravity (kilograms/volume unit) than those transported by rail and barge. The sixth suggestion calls for inclusion of indirect energy use and emissions resulting from the construction of vehicle and infrastructure. While some recommendations can be implemented relatively easily in ex ante evaluations, others will need further research.

Semiempirical analysis of electron scattering cross sections in N2O and CO2

Results of swarm analysis of electron scattering cross sections in nitrous oxide and carbon dioxide are presented — experimental diffusion coefficients are compared with numerical solution of the Boltzmann equation. Total cross sections for both N2O and CO2 exhibit similar resonant, structure and diffusion and drift coefficients are also similar. However, our analysis shows that values of partial cross sections, in particular vibrational ones (important for greenhouse IR absorption) can be quite different for those gases at low energies — much higher that commonly used now.

Small Island States in the Face of Climatic Change: The End of the Line in International Environmental Responsibility

I. SMALL ISLAND DEVELOPING STATES IN INTERNATIONAL LAW Small island developing states (SIDS) are increasingly recognized as deserving of special consideration both in international law generally and in international environmental law in particular. This special recognition has grown since the 1992 Earth Summit and was clearly reflected in the 1994 Programme of Action for the Sustainable Development of Small Island Developing States (to be revisited in 2004) and within the 2002 Plan of Implementation from the World Summit on Sustainable Development. (1) These documents all reflect the same consideration: that most SIDS face an uphill battle in meeting the challenges of sustainable development irrespective of climate change. Accordingly, they already need specific assistance to meet the economic, social, and environmental problems which already affect them. Accordingly, as the Political Declaration of the 2002 World Summit on Sustainable Development concluded, the countries of the world will, inter alia, to pay special attention to the developmental needs of Small Island Developing States. (2) However, unfortunately for SIDS, the other dilemmas they face in achieving sustainable development are dwarfed by one environmental problem: climate change. II. CLIMATE CHANGE Climate refers to change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods. (3) This anthropogenic climate change is caused by The primary greenhouse gases are carbon dioxide, methane, and nitrous dioxide. These gases are increasing in concentration in the atmosphere. The evidence for this may be seen from the scientific data of the oscillations of historical greenhouse gas concentrations through to more specific contemporary measurements. These measurements show concentrations of greenhouse gases not found in the atmosphere for thousands of years. III. THE SOURCES OF THE POLLUTANTS Modern industrial society is the primary culprit in terms of the creation of greenhouse gases. Since the Industrial Revolution, industry, agriculture, and transport have all contributed vast amounts of emissions. Historically, the lion's share of these pollutants came from developed countries. This share may be seen in terms of sovereign output (i.e., the countries' overall emissions) and per-capita output (i.e., an average individual's emissions from one country compared to another). Both ways of measuring output involve a different emphasis as well as a different political point of view. (4) For example, in the mid-1990s, the global average for per-capita carbon dioxide emissions, in kilograms, was 4157. Despite the average, the differences in the global total ranged from 19,675 kgs for the United States through to 949 kgs for China, 652 kgs for India, all the way down to 2 kgs for Somalia. (5) Although there are some developing countries which are taking their per-capita outputs to comparable levels of those of developed countries, such as Turkey, Korea, and Mexico, (6) the broad disparity in emissions on a per-capita basis between the developed and developing world is expected to continue into the foreseeable future. Conversely, when viewed from a sovereign basis, the United States has 36.1% of the total emissions of developed countries, the Russian Federation has 17.4%, Japan has 8.5%, Germany has 7.4% and the UK has 4.3%. (7) However, unlike the remaining differences between developed and developing countries with regard to greenhouse gas emissions on a per-capita basis, a clear change is occurring with regard to sovereign emissions. The key change is that the aggregate emissions from developing countries are growing at a much higher rate than developed countries. (8) If such increases continue, it is expected that the developing world will be producing more carbon dioxide from the burning of fossil fuels by 2005 than all the industrialized countries were producing in 1988. …

Influence of composts and liquid pig manure on CO2 and N2O emissions from a clay loam soil

Application of raw animal manure to agricultural land has resulted in environmental and health problems. Alternatives, such as composting, are now being developed to alleviate this situation. However, very little information is available regarding the fate of composts when added to fine-textured and poorly drained soils, especially with respect to the initial decomposition of composts and their effects on soil-derived CO2 and N2O emissions. We evaluated food waste compost (FW), yard waste compost (YW), liquid pig manure (LPM), LPM + yard waste compost (PMY) and LPM + wheat straw compost (PMS). Red clover (Trifolium pratense L.) (RC) and an unamended control soil were also tested. The solid amendments were divided into ground and unground treatments. Carbon dioxide emissions were increased relative to the control soil for all treatments except PMY. Total CO2 emissions over the 144-h incubation from unground material followed the pattern (P &lt; 0.05): YW (849 mg CO2-C kg-1 soil) &gt; RC (554 mg CO2-C kg-1 soil) &gt; LPM (444 mg CO2-C kg-1 soil) &gt; FW (203 mg CO2-C kg-1 soil) ≈ PMS (194 mg CO2-C kg-1 soil) ≈ PMY (157 mg CO2-C kg-1 soil). The RC, YW and PMS significantly increased N2O emissions compared to all other treatments and the control. Total N2O emissions from unground material over the 144-h incubation followed the pattern (P &lt; 0.05): RC ≈ YW ≈ PMS (1230–1490 μg N2O-N kg-1 soil) &gt; LPM ≈ FW ≈ PMY ≈ Control (44-404 μg N2O-N kg-1 soil). Grinding was found to increase CO2 emissions from YW, PMY, PMS, and N2O emissions from RC. The CO2 emissions were due primarily to amendment composition and not particle size, as the relative differences in CO2 emission among ground and unground treatments remained nearly constant. Carbon dioxide emissions from LPM were reduced substantially by composting the manure with yard waste (PMY). Key words: Compost, pig manure, carbon dioxide, nitrous dioxide, available N, incubation

Traffic related air pollution and acute hospital admission for respiratory diseases in Drammen, Norway 1995-2000.

The aim of this study was to estimate the associations between seven ambient air pollutants [particulate matter (PM10), nitrous dioxide (NO2), sulfur dioxide (SO2), ozone (O3), benzene, formaldehyde and toluene] and acute hospital admissions for respiratory diseases in Drammen, Norway 1995-2000. Time-series analysis of counts was performed by means of generalized additive models with log link and Poisson distribution. The results showed that benzene was the pollutant having the strongest association with respiratory diseases for the total study period, the relative risk of an interquartile increase of benzene was 1.095 with 95% confidence interval: 1.031-1.163. The corresponding results were 1.049 (0.990-1.112) for formaldehyde, 1.044 (1.000-1.090) for toluene, 1.064 (1.019-1.111) for NO2, 1.043 (1.011-1.075) for SO2, 0.990 (0.936-1.049) for O3 and 1.022 (0.990-1.055) for PM10. Dividing the total study period into two 3-year periods, there was a substantial reduction in the exposure levels of the volatile organic compounds (benzene, formaldehyde and toluene) from the first to the second period. Separate analyses for the second time period showed weaker association between these pollutants and the health outcome. This study provides further evidence for short-term respiratory health effects of traffic related air pollution.

Cryotherapy gas--to use nitrous oxide or carbon dioxide?

Cryotherapy is regularly used in our clinic for treating genital warts. Nitrous oxide was used as the cryogenic gas. Following a health and safety review it was decided to monitor the nitrous oxide levels in the treatment room under different conditions. The Occupational Exposure Standard for nitrous oxide is 100 parts per million (PPM) (8-h time weighted average) and an indicative short-term exposure limit of 300 PPM (15-min reference period). High levels of gas were detected, especially when the exhaust was not vented to the outside. Venting of the gas to the outside could also present a hazard to adjacent areas. The situation was considered to be unacceptable and carbon dioxide was proposed as an alternative. The Occupational Exposure Standard for carbon dioxide is 5000 PPM (8-h time weighted average) and a short-term limit of 15,000 PPM (15-min reference period). Carbon dioxide levels were found to be within the Occupational Exposure Standard. There is no noticeable difference in the cryogenic efficacy of the 2 gases. Carbon dioxide is, therefore, a safer alternative. It also offers significant savings when compared with nitrous oxide.

Relationships between nitrous acid and other nitrogen oxides in urban air

Abstract Nitrous acid (HNO2), nitric acid (HNO3), nitric oxide (NO) and nitrogen dioxide (NO2) were measured over a four day period in Clairmont, CA. Concentrations of each nitrogen oxide (NOx) compound varied diurnally during the study period HNO3, NO2, and NO generally reached maxima during daylight hours. Conversely, HNO2 concentrations were highest at night. HNO3 and HNO2 concentrations increased with increasing NO and NO2. HNO3 dependance became limited at high NO2 and NO. HNO2 concentrations declined when high NO and NO2 concentrations were present. The decline in HNO2 is postulated to result from direct photolysis during the time periods of NO and NO2 maxima or from reactions to form HNO3.

亜硝酸前処理を用いるクラフトパルプ酸素漂白法とその漂白機構

A pretreatment method with nitrite, nitric acid and oxygen for oxygen bleaching of kraft pulp is proposed as one of the possible methods for the reduction of organic chlorine compounds from bleaching process. The effects of nitrous acid pretreatment is compared with those of nitrogen dioxide pretreatment, and its bleaching mechanism is discussed.(1) Pulp at medium consistency is pretreated with nitrite (as NO2- 0.3% on pulp) and nitric acid (4% on pulp) at 90°C for 3 hours in the atmosphere of oxygen, and then is oxygen bleached.Kappa number of oxygen-bleached pulps can decrease to 34 for both beech and ezo spruce pulp pretreated.(2) The relationship between kappa number and viscosity of oxygen-bleached pulp after the nitrous acid pretreatment is similar to that after the nitrogen dioxide pretreatment which is correspond to Samuelson's S 3 process. Although Samuelson's S 3 process improves oxygen bleaching, it requires the two-stages pretreatment and gas-phase nitrogen dioxide. The nitrous acid pretreatment is free from these defects.(3) In the Samuelson's S 3 process, nitrous acid which is a reasonable by-product from the first-stage treatment with nitrogen dioxide is thought to be a key compound in decreasing kappa number of pulp in the second-stage treatment.(4) Coexistence of oxygen shows more effective kappa number reduction during the nitrous acid pretreatment. Veratryl alcohol, a non-phenolic lignin model compound, gives methanol under the nitrous acid pretreatment conditions with oxygen. It also gives more veratraldehyde in the presence of oxygen. These results indicate that oxygen in this pretreatment should play an important role in degradation and modification of lignin.(5) Four-stages (NODP) bleaching of beech pulp with nitrous acid pretreatment (N), oxygen (O), chlorine dioxide (D), and hydrogen peroxide (P) gives pulps with the same brightness (87%) and viscosity (20 cP) level as a conventional bleaching (OCEHD).

The Effect of Nitrous Oxide on Laryngeal Mask Cuff Pressure

Summary We have studied the effect of nitrous oxide on the cuff pressure of a laryngeal mask both in vitro and in vivo. In laboratory tests, we showed that nitrous oxide and carbon dioxide diffuse across the cuff wall much more rapidly than nitrogen and oxygen. Differing partial pressures of these gases across the cuff wall therefore give rise to changes in volume and pressure within the cuff. We then studied 18 patients undergoing general anaesthesia with nitrous oxide, and found a consistent and linear increase in cuff pressure in all patients. After 30 min, the mean pressure had increased by 30 mmHg, and there was approximately 10% nitrous oxide in the cuff. It is difficult to relate these findings to pressure on pharyngeal structures, but methods of limiting the rise in intracuff pressure are discussed.