[Cerebrospinal fluid pressure instability in relation to variations in atmospheric pressure].
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Atmospheric Pressure↗
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Results for “ATMOSPHERIC PRESSURE”
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[Performance of hypoxic radiotherapy in malignant tumors taking atmospheric pressure into account].
Hypoxic mixtures, delivered during hypoxic radiotherapy, must contain different values of the volume portion of oxygen depending on atmospheric pressure variations. The authors give a formula of calculation of a necessary volume portion of oxygen and tables of atmospheric pressure variations in Moscow as well as rated values of the volume portion of oxygen, applied to possible atmospheric pressure variations.
Atmospheric Pressure↗
Dysbarism: the medical problems from high and low atmospheric pressure.
The most serious problems resulting from a change in ambient pressure are pulmonary barotrauma with air embolism and decompression sickness. The small differential pressures used in ventilators at atmospheric pressure may tear lung tissue and, in diving, deaths have occurred from the expansion of pulmonary gas on an ascent of less than two metres. The bubbles of respired gas that enter the systemic circulation often occlude cerebral arteries and may cause infarction. In decompression sickness, bubbles form in the tissues from supersaturation of the nitrogen or helium absorbed under pressure. Joint pain--the 'bends'--is associated with gas in particular connective tissue. Serious decompression sickness results from the entry of microbubbles into the systemic veins. Large numbers of bubbles trapped in the lung cause an acute respiratory syndrome known as 'chokes'. If the lung filter is overwhelmed, or microbubbles pass into the systemic arteries through an atrial septal defect, they may open the blood-brain barrier, affecting brain and spinal cord function. Untreated, demyelination with relative preservation of axons may occur, the pathological hallmarks of multiple sclerosis. Gas bubble disease requires urgent compression in a hyperbaric chamber and the use of high partial pressures of oxygen.
Atmospheric Pressure↗
Atmospheric-pressure Penning ionization of aliphatic hydrocarbons.
A study has been made of the atmospheric-pressure Penning ionization (APPeI) of aliphatic hydrocarbons (pentane, hexane, heptane, and octane) with long-lived rare gas atoms (Rg*). The metastable rare gas atoms (He*, Ne*, Ar* and Kr*) were generated by the negative-mode corona discharge of atmospheric-pressure rare gases. In the Rg*APPeI mass spectra for aliphatic hyrocarbons, the relative abundances of fragment ions were found to increase in the order of He* --> Ne* --> Ar* --> Kr*. The order is in the opposite direction to the internal energies of the Rg*. The less fragmentation observed for He* may be because the nascent molecular ions [M(+.)]* formed by Penning ionization have lifetimes long enough for them to be collisionally deactivated in the atmospheric-pressure ion source. It was found that the relative abundances of fragment ions in Ar*APPeI increased when the sample pressure in the ion source was reduced. This is attributed to the collision of Ar* with molecular ions followed by fragmentation.
Journal Article↗
Hypobaric biology: Arabidopsis gene expression at low atmospheric pressure.
As a step in developing an understanding of plant adaptation to low atmospheric pressures, we have identified genes central to the initial response of Arabidopsis to hypobaria. Exposure of plants to an atmosphere of 10 kPa compared with the sea-level pressure of 101 kPa resulted in the significant differential expression of more than 200 genes between the two treatments. Less than one-half of the genes induced by hypobaria are similarly affected by hypoxia, suggesting that response to hypobaria is unique and is more complex than an adaptation to the reduced partial pressure of oxygen inherent to hypobaric environments. In addition, the suites of genes induced by hypobaria confirm that water movement is a paramount issue at low atmospheric pressures, because many of gene products intersect abscisic acid-related, drought-induced pathways. A motivational constituent of these experiments is the need to address the National Aeronautics and Space Administration's plans to include plants as integral components of advanced life support systems. The design of bioregenerative life support systems seeks to maximize productivity within structures engineered to minimize mass and resource consumption. Currently, there are severe limitations to producing Earth-orbital, lunar, or Martian plant growth facilities that contain Earth-normal atmospheric pressures within light, transparent structures. However, some engineering limitations can be offset by growing plants in reduced atmospheric pressures. Characterization of the hypobaric response can therefore provide data to guide systems engineering development for bioregenerative life support, as well as lead to fundamental insights into aspects of desiccation metabolism and the means by which plants monitor water relations.
Adaptation, Physiological↗
Direct quantitative analysis of organic compounds in the gas and particle phase using a modified atmospheric pressure chemical ionization source in combination with ion trap mass spectrometry.
A slightly modified atmospheric pressure chemical ionization source is employed for direct quantitative analysis of volatile or semivolatile organic compounds in air. The method described here is based on the direct introduction of an analyte in the gas or particle phase, or both, into the ion source of a commercial ion trap mass spectrometer. For quantitation, a standard solution is directly transferred into the vaporizer unit of the ion source via a deactivated fused-silica capillary by using the sheath liquid syringe pump, which is part of the mass spectrometer. The standard addition procedure is conducted by varying the pump rate of a diluted solution of the standard compound in methanol/water. A N2 sheath gas flow is applied for optimal vaporization and mixing with the analyte gas stream. By performing detailed reagent ion monitoring experiments, it is shown that the relative signal intensity of [M + H]+ ions is dependent on the relative humidity of the analyte gas stream as well as the composition and concentration of CI reagent ions. The method is validated by a comparison of the standard addition results with a calibration test gas of known concentration. To demonstrate the potential of atmospheric pressure chemical ionization mass spectrometry as a quantitative analytical technique for on-line investigations, a tropospherically relevant reaction is carried out in a 493-L reaction chamber at atmospheric pressure and 296 K in synthetic air at 50% relative humidity. Finally, the applicability of the technique to rapidly differentiate between analytes in the gas and particle phase is demonstrated.
Journal Article↗
Effect of increased atmospheric pressure on radial keratotomy.
PURPOSE: To evaluate the effect of increased atmospheric pressure on visual acuity in patients who have had radial keratotomy (RK). SETTING: Long Beach Memorial Medical Center, Long Beach, California, USA. METHODS: This controlled clinical study comprised 4 eyes that had RK and 4 control eyes that were age and sex matched. All patients had prehyperbaric chamber examinations consisting of manifest and cycloplegic refractions, intraocular pressure (IOP), keratometry, and corneal pachymetry. They were then placed into the hyperbaric chamber for 1 hour. Immediately after the patients were removed from the chamber, the examinations were performed again. RESULTS: No statistically significant changes in visual acuity, refractive error, IOP, keratometry, or pachymetry occurred in the 2 groups. CONCLUSION: The results of this study indicate that, unlike at high altitudes, RK is stable at increased atmospheric pressure. This suggests that RK patients can engage in recreational scuba diving without encountering deleterious visual changes.
Adult↗
Atmospheric-pressure Penning ionization mass spectrometry.
A preliminary study on the atmospheric-pressure Penning ionization (APP(e)I) of gaseous organic compounds with Ar* has been made. The metastable argon atoms (Ar*: 11.55 eV for (3)P(2) and 11.72 eV for (3)P(0)) were generated by the negative-mode corona discharge of atmospheric-pressure argon gas. By applying a high positive voltage (+500 to +1000 V) to the stainless steel capillary for the sample introduction (0.1 mm i.d., 0.3 mm o.d.), strong ion signals could be obtained. The ions formed were sampled through an orifice into the vacuum and mass-analyzed by an orthogonal time-of-flight mass spectrometer. The major ions formed by APP(e)I are found to be molecular-related ions for alkanes, aromatics, and oxygen-containing compounds. Because only the molecules with ionization energies less than the internal energy of Ar* are ionized, the present method will be a selective and highly sensitive interface for gas chromatography/mass spectrometry.
Argon↗
Effect of abnormal atmospheric pressure conditions upon mouse liver delta-aminolevulinic acid synthetase activity.
Liver delta-aminolevulinic acid synthetase activity was measured in mice living under abnormal atmospheric pressure conditions for 15 h. In the group living under low atmospheric pressure (51 kPa) the enzymic activity, either basal or induced by starvation and/or allylisopropylacetamide, was significantly (p less than 0.001) lower than that of the control group. In the group living under high atmospheric pressure (153 kPa) the enzymic activity was significantly (p less than 0.001) higher than the one of the controls. Our results might possibly be explained by changes in the cellular redox state, the heme oxygenase activity or the serum erythropoietin levels.
5-Aminolevulinate Synthetase↗
Liquid chromatography/electron capture atmospheric pressure chemical ionization/mass spectrometry: analysis of pentafluorobenzyl derivatives of biomolecules and drugs in the attomole range.
The corona discharge used to generate positive and negative ions under conventional atmospheric pressure chemical ionization conditions also provides a source of gas-phase electrons. This is thought to occur by displacement of electrons from the nitrogen sheath gas. Therefore, suitable analytes can undergo electron capture in the gas phase in a manner similar to that observed for gas chromatography/electron capture negative chemical ionization/mass spectrometry. This technique, which has been named electron capture atmospheric pressure chemical ionization/mass spectrometry, provided an increase in sensitivity of 2 orders of magnitude when compared with conventional atmospheric pressure chemical ionization methodology. It is a simple procedure to tag many biomolecules and drugs with an electron-capturing group such as the pentafluorobenzyl moiety before analysis. Pentafluorobenzyl derivatives have previously been used as electron capturing derivatives because they undergo dissociative electron capture in the gas phase to generate negative ions through the loss of a pentafluorobenzyl radical. A similar process was found to occur under electron capture atmospheric pressure chemical ionization conditions. By monitoring the negative ions that were formed, it was possible to obtain attomole sensitivity for pentafluorobenzyl derivatives of a representative steroid, steroid metabolite, prostaglandin, thromboxane, amino acid, and DNA-adduct.
Chromatography, Liquid↗
Positive and negative ion chemistry of the anesthetic halothane (1-bromo-1-chloro-2,2,2-trifluoroethane) in air plasma at atmospheric pressure.
The ion chemistry of 1-bromo-1-chloro-2,2,2-trifluoroethane (the common anesthetic halothane) in air plasma at atmospheric pressure was investigated by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The major positive ion observed at low declustering (API interface) energies is the ionized dimer, M(+.)M, an unexpectedly abundant species which possibly is stabilized by two H-bonding interactions. At higher energies [M--HF](+.) and [M--Br](+) prevail; the former, corresponding to ionized olefin [ClBrC=CF(2)](+.), appears to originate from M(+.)M and is quite stable towards fragmentation. The latter fragment ion ([M--Br](+)) and its analogue, [M--Cl](+), which is also observed though at much lower abundance, are originally ethyl cations (+)CHX--CF(3) (X = Br, Cl) which, upon collisional activation, rearrange and fragment to CHFX(+) via elimination of CF(2). All of the above described ions are also observed in humid air: in addition, the oxygenated ion [ClBrC=CFOH](+.) also forms in humid air via water addition to [ClBrC=CF(2)](+.) and HF elimination, as observed earlier for ionized trichloroethene. In contrast with similar chloro- and fluoro-substituted ethanes, halothane does not react with H(3)O(+) in the APCI plasma, a result confirmed by selected ion APCI triple-quadrupole (TQ) experiments. Major negative ions formed from halothane in the air plasma are Br(-) and, to a lesser extent, Cl(-), and their complexes with neutral halothane. APCI-TQ experiments indicated that Br(-) and Cl(-) are formed via reaction of halothane with O(2) (-.), O(2) (-.)(H(2)O) and O(3) (-.), possibly via dissociative electron transfer or nucleophilic substitution. Competing proton transfer was also observed in the reaction with O(2) (-.) and, at high halothane pressure, also with O(2) (-.)(H(2)O); at lower pressures the molecular anion M(-.) was observed instead. The other minor anions of the air plasma, NO(2) (-), N(2)O(2) (-.) and NO(3) (-), were found to be unreactive towards halothane.
Air↗
Atmospheric-pressure laser ionization: a novel ionization method for liquid chromatography/mass spectrometry.
We report on the development of a new laser-ionization (LI) source operating at atmospheric pressure (AP) for liquid chromatography/mass spectrometry (LC/MS) applications. APLI is introduced as a powerful addition to existing AP ionization techniques, in particular atmospheric-pressure chemical ionization (APCI), electrospray ionization (ESI), and atmospheric pressure photoionization (APPI). Replacing the one-step VUV approach in APPI with step-wise two-photon ionization strongly enhances the selectivity of the ionization process. Furthermore, the photon flux during an ionization event is drastically increased over that of APPI, leading to very low detection limits. In addition, the APLI mechanism generally operates primarily directly on the analyte. This allows for very efficient ionization even of non-polar compounds such as polycyclic aromatic hydrocarbons (PAHs). The APLI source was characterized with a MicroMass Q-Tof Ultima II analyzer. Both the effluent of an HPLC column containing a number of PAHs (benzo[a]pyrene, fluoranthene, anthracene, fluorene) and samples from direct syringe injection were analyzed with respect to selectivity and sensitivity of the overall system. The liquid phase was vaporized by a conventional APCI inlet (AP probe) with the corona needle removed. Ionization was performed through selective resonance-enhanced multi-photon ionization schemes using a high-repetition-rate fixed-frequency excimer laser operating at 248 nm. Detection limits well within the low-fmol regime are readily obtained for various aromatic hydrocarbons that exhibit long-lived electronic states at the energy level of the first photon. Only molecular ions are generated at the low laser fluxes employed ( approximately 1 MW/cm(2)). The design and performance of the laser-ionization source are presented along with results of the analysis of aromatic hydrocarbons.
Atmospheric Pressure↗
Highly sensitive screening method for nitroaromatic, nitramine and nitrate ester explosives by high performance liquid chromatography-atmospheric pressure ionization-mass spectrometry (HPLC-API-MS) in forensic applications.
A highly sensitive screening method based on high performance liquid chromatography atmospheric pressure ionization mass spectrometry (HPLC-API-MS) has been developed for the analysis of 21 nitroaromatic, nitramine and nitrate ester explosives, which include the explosives most commonly encountered in forensic science. Two atmospheric pressure ionization (API) methods, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), and various experimental conditions have been applied to allow for the detection of all 21 explosive compounds. The limit of detection (LOD) in the full-scan mode has been found to be 0.012-1.2 ng on column for the screening of most explosives investigated. For nitrobenzene, an LOD of 10 ng was found with the APCI method in the negative mode. Although the detection of nitrobenzene, 2-, 3-, and 4-nitrotoluene is hindered by the difficult ionization of these compounds, we have found that by forming an adduct with glycine, LOD values in the range of 3-16 ng on column can be achieved. Compared with previous screening methods with thermospray ionization, the API method has distinct advantages, including simplicity and stability of the method applied, an extended screening range and a low detection limit for the explosives studied.
Journal Article↗
[Explosive compression. Sudden elevation of atmospheric pressure from negative pressure to normal pressure].
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Atmospheric Pressure↗
Fragmentation induced in atmospheric pressure photoionization of peptides.
In this work, the fragmentation of peptides under atmospheric pressure photoionization conditions is investigated. Intensive fragmentations into b/y- and c-sequence ions are reported. Abundance of these c-ions appeared to be related to the quantity of dopant infused and to the disappearance of the doubly protonated peptide ion. A careful analysis of the role of the dopant indicates that the fragmentations are not dependent on the nature of the dopant but on their ionization efficiencies. This result shows that the fragmentation arises from the reaction of the protonated peptide with photoelectrons released upon ionization of the dopant in an electron capture dissociation/electron transfer dissociation (ECD/ETD) type mechanism. Experiments with peptides bearing a single proton indicate that additional mechanisms are involved. H-atom transfer reactions are suggested to be responsible for the fragmentations as well. Those atoms could arise either from the dopant ions or from negatively charged solvent nanodroplets. This is the first report of an ECD/ETD mechanism in a dense medium and at atmospheric pressure.
Acetylation↗
Anisole, a new dopant for atmospheric pressure photoionization mass spectrometry of low proton affinity, low ionization energy compounds.
Atmospheric pressure photoionization (APPI) is a novel method of ionization in liquid chromatography/mass spectrometry (LC/MS). It was originally developed in order to broaden the range of LC/MS ionizable compounds towards less polar compounds that cannot be analyzed by electrospray (ESI) and atmospheric pressure chemical ionization (APCI). Studies done thus far have shown that non-polar compounds that earlier were not ionizable in LC/MS can indeed be ionized by the use of APPI. However, the best ionization efficiency for low polarity samples has been achieved with low proton affinity (PA) solvents that are not suitable in reversed-phase LC (RP-LC). Here it is demonstrated that the signals for analytes with low proton affinities in acetonitrile can be increased 100-fold by using anisole as the dopant for APPI, which takes the sensitivity to the same level achieved in the analysis of high PA analytes.
Acetonitriles↗
Atmospheric pressure ion/molecule reactions for the selective detection of nitroaromatic explosives using acetonitrile and air as reagents.
Acetonitrile vapor and air are useful reagents for the selective detection of nitroaromatic compounds using atmospheric pressure ion/molecule reactions. Reagent ions CH2CN- and CN- generated from acetonitrile, and O-*, OH- and OOH- produced from the oxygen in air, react with vapor-phase and condensed-phase nitroaromatics in the course of atmospheric pressure chemical ionization (APCI) and desorption atmospheric pressure chemical ionization (DAPCI), respectively. The homogeneous and the heterogeneous phase reactions both lead to the formation of the same anionic adducts. These adducts have characteristic fragmentation patterns upon collisional activation, which makes these two reagents valuable for the selective detection of particular nitroaromatics, including explosives present as components of complex mixtures. Complementary information is available from the two reagents because their different chemistry facilitates analyte identification. DAPCI is demonstrated to be a useful ambient detection method for nitroaromatic explosives absorbed on surfaces.
Acetonitriles↗
Germination and growth of lettuce (Lactuca sativa) at low atmospheric pressure.
The response of lettuce (Lactuca sativa L. cv. Waldmann's Green) to low atmospheric pressure was examined during the initial 5 days of germination and emergence, and also during subsequent growth to vegetative maturity at 30 days. Growth took place inside a 66-l-volume low pressure chamber maintained at 70 kPa, and plant response was compared to that of plants in a second, matching chamber that was at ambient pressure (approximately 101 kPa) as a control. In other experiments, to determine short-term effects of low pressure transients, plants were grown at ambient pressure until maturity and then subjected to alternating periods of 24 h of low and ambient atmospheric pressures. In all treatments the partial pressure of O2 was maintained at 21 kPa (approximately the partial pressure in air at normal pressure), and the partial pressure of CO2 was in the range 66.5-73.5 Pa (about twice that in normal air) in both chambers, with the addition of CO2 during the light phase. With continuous exposure to low pressure, shoot and root growth was at least as rapid as at ambient pressure, with an overall trend towards slightly greater performance at the lower pressure. Dark respiration rates were greater at low pressure. Transient periods at low pressure decreased transpiration and increased dark respiration but only during the period of exposure to low pressure. We conclude that long-term or short-term exposure to subambient pressure (70 kPa) was without detectable detriment to vegetative growth and development.
Atmosphere Exposure Chambers↗