Normal Atmospheric Levels Research Articles

Comparison of Oropharyngeal Oxygen Pooling and Suctioning During Intubated and Nonintubated Dental Office-Based Anesthesia.

The risk of a spontaneous surgical fire increases as oxygen concentrations surrounding the surgical site rise above the normal atmospheric level of 21%. Previously published in vitro findings imply this phenomenon (termed oxygen pooling) occurs during dental procedures under sedation and general anesthesia; however, it has not been clinically documented. Thirty-one children classified as American Society of Anesthesiologists I and II between 2 and 6 years of age undergoing office-based general anesthesia for complete dental rehabilitation were monitored for intraoral ambient oxygen concentration, end-tidal CO2, and respiratory rate changes immediately following nasotracheal intubation or insertion of nasopharyngeal airways, followed by high-speed suctioning of the oral cavity during simulated dental treatment. Mean ambient intraoral oxygen concentrations ranging from 46.9% to 72.1%, levels consistent with oxygen pooling, occurred in the nasopharyngeal airway group prior to the introduction of high-speed oral suctioning. However, 1 minute of suctioning reversed the oxygen pooling to 31.2%. Oropharyngeal ambient oxygen concentrations in patients with uncuffed endotracheal tubes ranged from 24.1% to 26.6% prior to high-speed suctioning, which reversed the pooling to 21.1% after 1 minute. This study demonstrated significant oxygen pooling with nasopharyngeal airway use before and after high-speed suctioning. Uncuffed endotracheal intubation showed minimal pooling, which was reversed to room air ambient oxygen concentrations after 1 minute of suctioning.

Overpressure Exposure From .50-Caliber Rifle Training Is Associated With Increased Amyloid Beta Peptides in Serum.

Background: Overpressure (OP) is an increase in air pressure above normal atmospheric levels. Military personnel are repeatedly exposed to low levels of OP caused by various weapon systems. Repeated OP may increase risk of neurological disease or psychological disorder diagnoses. A means to detect early phase effects that may be relevant to brain trauma remain elusive. Therefore, development of quantitative and objective OP-mediated effects during acute timeframes would vastly augment point-of-care or field-based decisions. This pilot study evaluated the amplitude of traumatic brain injury (TBI)–associated biomarkers in serum as a consequence of repeated OP exposure from .50-caliber rifle use over training multiple days.Objective: To determine the acute temporal profile of TBI-associated serum biomarkers and their relationship with neurocognitive decrements or self-reported symptoms among participants exposed to low-level, repeated OP from weapons used in a training environment.Methods: Study participants were enrolled in .50-caliber sniper rifle training and exposed to mild OP (peak pressure 3.8–4.5 psi, impulse 19.27–42.22 psi-ms per day) for three consecutive days (D1–D3). Defense automated neurobehavioral assessment (DANA) neurocognitive testing, symptom reporting, and blood collection were conducted 2–3 h before (pre-) and again 0.45–3 h after (post-) OP exposure. The TBI-associated serum biomarkers, glial fibrillary acidic protein (GFAP), ubiquitin C-terminal hydrolase-L1 (UCH-L1), neurofilament light (Nf-L), tau, and amyloid beta peptides (Aβ-40 and Aβ-42) were measured using digital ELISAs.Results: Serum GFAP decreased on D1 and D3 but not D2 after OP exposure. Nf-L was suppressed on D3 alone. Aβ-40 was elevated on D2 alone while Aβ-42 was elevated each day after OP exposure. Suppression of GFAP and elevation of Aβ-42 correlated to OP-mediated impulse levels measured on D3.Conclusions: Acute measurement of Aβ-peptides may have utility as biomarkers of subconcussive OP caused by rifle fire. Fluctuation of GFAP, Nf-L, and particularly Aβ peptide levels may have utility as acute, systemic responders of subconcussive OP exposure caused by rifle fire even in the absence of extreme operational deficits or clinically defined concussion.

Mobile measurement of methane emissions from natural gas developments in northeastern British Columbia, Canada

Abstract. North American leaders recently committed to reducing methane emissions from the oil and gas sector, but information on current emissions from upstream oil and gas developments in Canada are lacking. This study examined the occurrence of methane plumes in an area of unconventional natural gas development in northwestern Canada. In August to September 2015 we completed almost 8000 km of vehicle-based survey campaigns on public roads dissecting oil and gas infrastructure, such as well pads and processing facilities. We surveyed six routes 3–6 times each, which brought us past over 1600 unique well pads and facilities managed by more than 50 different operators. To attribute on-road plumes to oil- and gas-related sources we used gas signatures of residual excess concentrations (anomalies above background) less than 500 m downwind from potential oil and gas emission sources. All results represent emissions greater than our minimum detection limit of 0.59 g s−1 at our average detection distance (319 m). Unlike many other oil and gas developments in the US for which methane measurements have been reported recently, the methane concentrations we measured were close to normal atmospheric levels, except inside natural gas plumes. Roughly 47 % of active wells emitted methane-rich plumes above our minimum detection limit. Multiple sites that pre-date the recent unconventional natural gas development were found to be emitting, and we observed that the majority of these older wells were associated with emissions on all survey repeats. We also observed emissions from gas processing facilities that were highly repeatable. Emission patterns in this area were best explained by infrastructure age and type. Extrapolating our results across all oil and gas infrastructure in the Montney area, we estimate that the emission sources we located (emitting at a rate > 0.59 g s−1) contribute more than 111 800 t of methane annually to the atmosphere. This value exceeds reported bottom-up estimates of 78 000 t of methane for all oil and gas sector sources in British Columbia. Current bottom-up methods for estimating methane emissions do not normally calculate the fraction of emitting oil and gas infrastructure with thorough on-ground measurements. However, this study demonstrates that mobile surveys could provide a more accurate representation of the number of emission sources in an oil and gas development. This study presents the first mobile collection of methane emissions from oil and gas infrastructure in British Columbia, and these results can be used to inform policy development in an era of methane emission reduction efforts.

Stimulation of growth of the human gastric pathogen Helicobacter pylori by atmospheric level of oxygen under high carbon dioxide tension.

BackgroundHelicobacter pylori (Hp), a human pathogen that is associated with gastritis, peptic ulcer, and gastric cancer, has been considered a microaerophile, but there is no general consensus about its specific O2 requirements. A clear understanding of Hp physiology is needed to elucidate the pathogenic mechanism(s) of Hp infection.ResultsWe cultured Hp under a range of O2 levels with or without 10% CO2 and evaluated growth profiles, morphology, intracellular pH, and energy metabolism. We found that, in the presence of 10% CO2, the normal atmospheric level of O2 inhibited Hp growth at low density but stimulated growth at a higher density. Field emission scanning electron microscopy and fluorescence microscopy of Hp cells cultured under 20% O2 tension revealed live spiral-shaped bacteria with outer membrane vesicles on a rugged cell surface, which became smooth during the stationary phase. Fermentation products including acetate, lactate, and succinate were detected in cell culture media grown under microaerobic conditions, but not under the aerobic condition. CO2 deprivation for less than 24 h did not markedly change cytoplasmic or periplasmic pH, suggesting that cellular pH homeostasis alone cannot account for the capnophilic nature of Hp. Further, CO2 deprivation significantly increased intracellular levels of ppGpp and ATP but significantly decreased cellular mRNA levels, suggesting induction of the stringent response.ConclusionsWe conclude, unlike previous reports, that H. pylori may be a capnophilic aerobe whose growth is promoted by atmospheric oxygen levels in the presence of 10% CO2. Our data also suggest that buffering of intracellular pH alone cannot account for the CO2 requirement of H. pylori and that CO2 deprivation initiates the stringent response in H. pylori. Our findings may provide new insight into the physiology of this fastidious human pathogen.

Thermal conductivity measurements of coarse-grained gravel materials using a hollow cylindrical sensor

We report on new results for the thermal conductivity of granular materials, in particular large-grained gravels. For these measurements, a cylindrical-shaped heated sensor was developed and used, which allows to include gravels with grain sizes in the several centimeter size range into the investigation. Such materials are, among else, important as construction materials for road and railway embankments. Measurements were done at different gas pressure levels (from normal atmospheric level down to the millibar range) and for dry and wet conditions. The results of the low pressure measurements may become relevant in view of possible applications on other planetary bodies, like at the surface of the planet Mars, which will be explored in the coming decade by in situ geotechnical methods.

Tracking Performance of a Recoverable Flight Control System in Neutron Environments

This paper analyzes the output tracking performance of a Boeing 737 aircraft in closed loop with a Recoverable Computer System (RCS) operating in a high intensity neutron environment at the Los Alamos National Laboratory. A stochastic hybrid model, validated by simulated-neutron experiments done at the NASA Langley Research Center, is used to theoretically predict the outcome of the experiment. In particular, this model predicts and the data confirms that the recoverable digital flight control system, when functioning as designed, will provide accurate output tracking performance in the presence of neutron-induced single-event upsets (SEUs) at normal atmospheric levels.

The other greenhouse effect

Rising carbon dioxide levels should increase crop yields. But what if their effect on the nutritional value of our food is less benign, asks Ned Stafford. Commercial growers often raise carbon dioxide levels in their greenhouses to twice the normal atmospheric level to boost crop yield. This provides an opportunity to test a theory put forward by a number of researchers: that the anticipated increase in atmospheric carbon dioxide might reduce the nutritional value of food crops.

The use of pleopods for shell water circulation and respiration by hermit crabs

The use of the pleopods was investigated in two species of Diogenid hermit crabs, Dardanus arrosor and D. calidus. A transparent glass shell was used to observe the movements of the pleopods in hermit crabs. The movements consisted of periodic, irregular beating, which generated an irregular flow of the water within the shell. A strong, regular beating movement was elicited when there was detritus or faeces in the shell, as was occupation of a new shell. Injection of water with a low oxygen concentration into the shell failed to induce any variation in the pleopod beating frequency (PBF), while the injection of water with a high CO2 concentration induced a sudden PBF increase. When pH was varied and CO2 concentration held at normal atmospheric level, there was a change in PBF. However, CO2 variation alone, at constant pH, did not trigger any visible reaction. This suggests that there is a receptor for pH, which acts independently of the CO2 concentration. The function of males hermit crabs pleopods has always been obscure. However, at least in Dardanus, they are actively involved in water circulation within the shell for shell-cleaning and probably for ventilation.

Humidity Response of Adult MaleOryzaephilus surinamensis(Coleoptera: Cucujidae) with Special Reference to the Effect of Carbon Dioxide

The behavioral response of the sawtoothed grain beetle, Oryzaephilus surinamensis (L.), to moisture gradients has been studied in some detail, but the effect of carbon dioxide (CO2), alone and in combination with low humidity, has never been reported. The effect of CO2 is of some interest because CO2 levels in stored grain are often elevated well above normal atmospheric levels by the metabolism of insects, fungi, and the grain itself. Also, CO2 is sometimes applied to bulk grain to control stored-product insects. The response of adult male O. surinamensis to humidity alternatives of 60 or 100% RH was determined in 2-way choice chambers after various treatments. Beetles removed from laboratory cultures and held at 60% RH with food for 4 h showed a strong avoidance of the higher humidity (hygronegative response). Beetles held without food in a dry atmosphere (<5% RH) with an elevated level of CO2 (39%) for 4 h showed a reversal of the response from hygronegative to hygropositive. The same period of exposure, again without food, to dry air (<5% RH), or to a moist atmosphere (80% RH) with an elevated level of CO2 did not produce a reversal. The failure of CO2 to produce a reversal when exposure occurred in a moist atmosphere suggests that the gas acts indirectly on the humidity response by increasing the rate of moisture loss. Elevated levels of CO2 are known to cause prolonged opening of the spiracular regulatory apparatus that controls moisture loss in insects.

Oxygen sensitivity of photosynthesis and photorespiration in different photosynthetic types in the genus Flaveria.

Two major indicators were used to access the degree of photorespiration in various photosynthetic types of Flaveria species (C3, C3-C4, C4-like, and C4): the O2 inhibition of photosynthesis measured above the O2 partial pressure which gives a maximum rate, and O2- and light-dependent whole-chain electron flow measured at the CO2 compensation point (Γ). The optimum level of O2 for maximum photosynthetic rates under atmospheric levels of CO2 (34 Pa) was lower in C3 and C3-C4 species (ca. 2 kPa) than in C4-like and C4 species (ca. 9 kPa). Increasing O2 partial pressures from the optimum for photosynthesis up to normal atmospheric levels (ca. 20 kPa) caused an inhibition of photosynthesis which was more severe under lower CO2. This inhibition was calculated as the O2 inhibition index (ΘA, the percentage inhibition of photosynthesis per kPa increase in O2). From measurements of 18 Flaveria species at atmospheric CO2, the ΘA values decreased from C3 (1.9-2.1) to C3-C4 (1.2-1.6), C4-like (0.6-0.8) and C4 species (0.3-0.4), indicating a progressive decrease in apparent photorespiration in this series. With increasing irradiance at Γ under atmospheric levels of O2, and increasing O2 partial pressure at 300 μmol quanta·m-2·s-1, there was a similar increase in the rate of O2 evolution associated with whole-chain electron flow (Jo2, calculated from chlorophyll fluorescence analysis) in the C3 and C3-C4 species compared to a much lower rate in the C4-like and C4 species. The results indicate that there is substantial O2-dependent electron flow in C3 and C3-C4 species, reflecting a high level of photorespiration compared to that in C4-like and C4 species. Consistent with these results, there was a significant decrease in Γ from C3 (6-6.2 Pa) to C3-C4 (1.0-3.0 Pa), to C4-like and C4 species (0.3-0.8 Pa), indicating a progressive decrease in apparent photorespiration. However, C3 and C3-C4 species examined had high intrinsic levels of photorespiration with the latter maintaining low apparent rates of photorespiration and lower Γ values, primarily by refixing photorespired CO2. The C4-like and C4 Flaveria species had low, but measurable, levels of photorespiration via selective localization of ribulose-1,5-bisphosphate carboxylase in bundle sheath cells and operation of a CO2 pump via the C4 pathway.

Investigation of the CO2 Dependence of Quantum Yield and Respiration in Eucalyptus pauciflora

In leaves of C(3) plants, the rate of nonphotorespiratory respiration appears to be higher in darkness than in the light. This change from a high to a low rate of carbon loss with increasing photon flux density leads to an increase in the apparent quantum yield of photosynthetic CO(2) assimilation at low photon flux densities (Kok effect). The mechanism of this suppression of nonphotorespiratory respiration is not understood, but biochemical evidence and the observation that a Kok effect is often not observed under low O(2), has led to the suggestion that photorespiration might be involved in some way. This hypothesis was tested with snowgum (Eucalyptus pauciflora Sieb. ex Spreng.) using gas exchange methods. The test was based on the assumption that if photorespiration were involved, then it would be expected that the intercellular partial pressure of CO(2) would also have an influence on the Kok effect. Under normal atmospheric levels of CO(2) and O(2), a Kok effect was found. Changing the intercellular partial pressure of CO(2), however, did not affect the estimate of nonphotorespiratory respiraton, and it was concluded that its decrease with increasing photon flux density did not involve photorespiration. Concurrent measurements showed that the quantum yield of net assimilation of CO(2) increased with increasing intercellular partial pressure of CO(2), and this increase agreed closely with predictions based on recent models of photosynthesis.

CO2‐Enrichment Effects on Soybean Physiology. II. Effects of Stage‐Specific CO2 Exposure1

Soybeans [Glycine max (L.) Merr ‘Wye’] were exposed to CO2‐enriched atmospheres during specific stages of development Carbon dioxide enrichment from early pod development until plant maturity and from emergence to maturity increased seed yield 27 and 36%, respectively, compared with plants exposed to the normal atmospheric level of CO2. Plants receiving supplemental CO2 from either emergence to anthesis or from anthesis through early pod development did not exhibit an increase in grain yield. During each period of exposure, CO2‐enriched plants had higher rates of photosynthesis and accumulated significantly more starch, sucrose, and glucose in the leaves compared with nonenriched controls. After exposure to CO2 was terminated, rates of photosynthesis declined to control values and the accumulated leaf carbohydrates were rapidly depleted. Accumulation and subsequent utilization of stored photosynthate did not appear to influence seed yield except when these stored reserves were available at the onset of the grain‐filling period. Seed yield increases attributable to CO2 enrichment were the result of more pods per plant rather than increases in seed size. From the analysis of photosynthetic data and the trends in carbon accumulation and utilization, it appears that soybeans could support a higher degree of reproductive growth.

Limiting Factors in Photosynthesis

Using iron stress to reduce the total amount of light-harvesting and electron transport components per unit leaf area, the influence of light-harvesting and electron transport capacity on photosynthesis in sugar beet (Beta vulgaris L. cv F58-554H1) leaves was explored by monitoring net CO(2) exchange rate (P) in relation to changes in the content of Chl.In most light/CO(2) environments, and especially those with high light (>/=1000 microeinsteins photosynthetically active radiation per square meter per second) and high CO(2) (>/=300 microliters CO(2) per liter air), P per area was positively correlated with changes in Chl (a + b) content (used here as an index of the total amount of light-harvesting and electron transport components). This positive correlation of P per area with Chl per area was obtained not only with Fe-deficient plants, but also over the normal range of variation in Chl contents found in healthy, Fe-sufficient plants. For example, light-saturated P per area at an ambient CO(2) concentration close to normal atmospheric levels (300 microliters CO(2) per liter air) increased by 36% with increase in Chl over the normal range, i.e. from 40 to 65 micrograms Chl per square centimeter. Iron deficiency-mediated changes in Chl content did not affect dark respiration rate or the CO(2) compensation point. The results suggest that P per area of sugar beet may be colimited by light-harvesting and electron transport capacity (per leaf area) even when CO(2) is limiting photosynthesis as occurs under field conditions.

Inert gas narcosis: Avoidance behavior in rats breathing elevated pressures of nitrogen and helium

Avoidance response rates generated by a free-operant avoidance schedule with a response-shock interval of 20 sec and a shock-shock interval of 2 sec increased when rats breathed raised pressures of nitrogen up to 19 times normal atmospheric pressure. Further, nitrogen pressure increases to over 30 times normal pressure produced decreases in avoidance rates and disruption of temporal discrimination reflected by changes in conditional probabilities of interresponse times. Changes in avoidance response rates and shock frequencies were related to increases in nitrogen partial pressures rather than total absolute pressure as oxygen and carbon dioxide partial pressures were kept at normal atmospheric levels, and similar avoidance performance changes did not occur at identical pressures breathing helium. Increased helium pressures produced increases in avoidance responding at 25 to 30 times normal atmospheric pressure that were similar to effects of nitrogen at lower pressures, indicating that nitrogen is about four times as potent as helium in terms of narcotic effects on avoidance behavior.

PLANTS UNDER CLIMATIC STRESS

SummaryThe composition of the atmosphere influenced the apparent photosynthetic rate of Sorghum bicolor and the degree of permanent damage to the photosynthetic capacity of the leaves when plants were transferred to low‐temperature, high‐light (10° C; 170 W m‐2) environmental stress. High CO2 (1000 μl/l) or low O2 (3%) both partially protect the plants compared to normal atmospheric levels, while low CO2 (30 μl/l) or O2 (50%) enhanced the damaging effects of stress. Oxygen levels are the more significant in control of permanent photosynthetic damage.