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At least 145 records · Page 8Linked to original sources
PubMed1987

[A complication in gas surgery: injection of gas beneath the retina in a pseudophakic eye].

Report on an inadvertent injection of gas beneath the retina in a pseudophakic eye. The gas was injected through the pupil to tamponade a retinal break. Instead, however, it found its way under the retina, increasing the extent of the detachment. A thick, transparent membrane posterior to the intraocular lens prevented the gas from entering the vitreous space and diverted it laterally behind the iris to the ciliary body, where it penetrated between layers of the ciliary epithelium and entered the subretinal space. The gas became visible under the retina. The bullous redetachment had a mother-of-pearl-like opalescence characteristic of gas beneath the retina.

Aged↗
PubMed2005

Small gas-phase dianions produced by sputtering and gas flooding.

We have extended our previous experiment [Schauer et al., Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of C(n) (2-)(n > or =7) by means of sputtering a graphite surface by Cs(+) ion bombardment. Our detection sensitivity for small C(n) (2-) could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C(5) (2-) was not successful. As an upper limit, the sputtered flux of C(5) (2-) must be at least a factor of 5000 lower than that of C(7) (2-), provided that the lifetime of C(5) (2-) is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O(2) or with N(2)O) was supplied to the Cs(+)-bombarded graphite surface, small dianions of OC(n) (2-)(5< or =n < or =14) and O(2)C(7) (2-) were observed in addition to C(n) (2-)(n > or =7). Similarly, Cs(+) sputtering of graphite with simultaneous SF(6) gas flooding produced SC(n) (2-)(6< or =n< or =18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF(6) gas flooding of various Cs(+)-bombarded metal surfaces were successful for the case of Zr, where metastable ZrF(6) (2-) was observed. Cs(+) bombardment of a silicon carbide (SiC) wafer produced SiC(n) (2-) (n=6,8,10). When oxygen gas was supplied to the Cs(+)-bombarded SiC surface, small dianions of SiOC(n) (2-) (n=4,6,8) and of SiO(2)C(n) (2-) (n=4,6) as well as a heavier unidentified dianion (at mz=98.5) were observed. For toluene (C(7)H(8)) vapor flooding of a Cs(+)-bombarded graphite surface, several hydrocarbon dianion clusters of C(n)H(m) (2-)(n> or =7) were produced in addition to C(n) (2-)(n> or =7), while smaller C(n)H(m) (2-) with n< or =6 could not be observed. BeC(n) (2-) (n=4,6,8,10), Be(2)C(6) (2-), as well as BeC(8)H(m) (2-) (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs(+)-bombarded beryllium metal foil. The metastable pentamer (9)Be(12)C(4) (2-) at mz=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SC(n) (2-), OC(n) (2-), BeC(n) (2-), and SiO(m)C(n) (2-) (m=0,1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeC(n) (2-) and SiC(n) (2-), even though calculated molecular structures of BeC(6) (2-) and SiC(6) (2-) are different. The abundance pattern of SC(n) (2-) is fairly similar to that of C(n) (2-).

Journal Article↗
PubMed1987

Relationships among ventilation-perfusion distribution, multiple inert gas methodology and metabolic blood-gas tensions.

The retention equations upon which the Multiple Inert Gas Method is based are derived from basic principles using elementary algebra. It is shown that widely disparate distributions produce indistinguishable sets of retentions. The limits of resolution of perfused compartments in the VA/Q distribution obtainable by the use of the multiple inert gas method are explored mathematically, and determined to be at most shunt and two alveolar compartments ("tripartite" distribution). Every continuous distribution studied produced retentions indistinguishable from those of its unique "matching" tripartite distribution. When a distribution is minimally specified, it is unique. Any additional specification (increased resolution--more compartments) of the distribution results in the existence of an infinitude of possible distributions characterized by indistinguishable sets of retention values. No further increase in resolution results from the use of more tracers. When sets of retention values were extracted from published multiple inert gas method continuous distributions, and compared with the published "measured" retention sets, substantial differences were found. This illustrates the potential errors incurred in the practical, in vivo application of the multiple inert gas method. In preliminary studies, the tripartite distribution could be determined with at least comparable accuracy by blood-gas (oxygen, carbon dioxide) measurements.

Carbon Dioxide↗
PubMed1996

A gas scintillation monitor for tritium gas in argon or in nitrogen.

For civilian purposes tritium is presently used in quantities of tens of PBq (MCi) in laboratories for the studies of tritium technology, at the Joint European Torus plant (Abingdon, Oxon, OX143A, UK) as fuel for the process of nuclear fusion, and in the manufacture of radio-luminescent items. Given the extreme mobility of tritium in most materials, it is necessary to use systems for double containment, such as glove boxes or spaces between primary and secondary containers, in which inert gas like argon or nitrogen flows. With these systems it is possible to recover tritium that escapes from the primary containment. Presently the gas flow is monitored continuously by means of ionization chambers which may present problems in particular applications ("memory effect" with high activity, strong dependence of the response on the presence of impurity, etc.). The aim of the work here presented is to determine the prospects for the realization of a new type of monitor mainly dedicated to the measurement of gas activity in isolation space of the containing systems of the high activity tritium plants. This monitor should have sufficient sensitivity, quick response, and should be easily decontaminated. As a detection technique we chose the scintillation produced in the inert gas by radioactive decay. With the first prototype, designed in cylindrical form, it was possible to observe gaseous scintillation events in mixture of tritium and argon or nitrogen. Following that, a spherical prototype was designed, of which we studied the performances and the dependence of the response varying the pressure, the concentration of tritium, the percentage of the impurity, and the gas flow rate. The results are satisfactory and suggest that the monitor could be used in glove boxes and double containment systems. The future research program will include tests involving large quantities of tritium and a study of the ideal dimensions and geometry of the detection chamber in order to optimize the detector response.

Argon↗
PubMed2006

Onsager-Casimir reciprocal relations based on the Boltzmann equation and gas-surface interaction: single gas.

The approach to the nonequilibrium thermodynamics based on the Boltzmann equation and gas-surface interaction law proposed in previous papers [F. Sharipov, Physica A 203, 457 (1994); 209, 457 (1994)] is generalized considering kinetic coefficients, which are neither odd nor even with respect to time reversal. It is proved that the reciprocity of the gas-gas and gas-surface interactions is a necessary and sufficient condition to derive the symmetry of the Onsager matrix. As an example of the generalized theory, the thermal slip coefficients are related to the heat flux vector appearing in the isothermal shear gas flow in a semi-infinite space, i.e., both viscous and thermal slip coefficients can be calculated simultaneously, solving a unique kinetic coefficient.

Journal Article↗
PubMed1975

Effects on breathing mechanics and gas exchange of different inspiratory gas flow patterns in patients undergoing respirator treatment.

In order to investigate the importance of different inspiratory gas flow patterns in respirator treatment, eight intensive care patients were studied with breathing mechanics and five patients also with gas exchange studies. Three different inspiratory gas flow patterns were tested in randomized sequences namely, accelerating, constant and decelerating flow. All three flow patterns were generated by the same respirator. No end-inspiratory pause was used. The results point to a favourable effect on breathing mechanics of a decelerating and a constant flow when compared with an accelerating flow type. However, when the total effects on gas distribution and lung perfusion were evaluated in the gas exchange studies, no significant differences were seen between the three flow patterns.

Aged↗
PubMed2002

The sequence of the major gas vesicle protein, GvpA, influences the width and strength of halobacterial gas vesicles.

Transformation experiments with Haloferax volcanii show that the amino acid sequence of the gas vesicle protein GvpA influences the morphology and strength of gas vesicles produced by halophilic archaea. A modified expression vector containing p-gvpA was used to complement a Vac(-) strain of Hfx. volcanii that harboured the entire p-vac region (from Halobacterium salinarum PHH1) except for p-gvpA. Replacement of p-gvpA with mc-gvpA (from Haloferax mediterranei) led to the synthesis of gas vesicles that were narrower and stronger. Other gene replacements (using c-gvpA from Hbt. salinarum or mutated p-gvpA sequences) led to a significant but smaller increase in gas vesicle strength, and less marked effects on gas vesicle morphology.

Amino Acid Sequence↗
PubMed2004

Theoretical gas body pulsation in relation to empirical gas-body destabilization and to cell membrane damage thresholds.

Contrast agent gas bodies attached to phagocytic monolayer cells pulsate in response to ultrasound exposure and damage the cells above thresholds, which increase in proportion to frequency. This study considered the physical basis for the thresholds and their frequency dependence. Theory for the pulsation was evaluated using empirical pulse waveforms acquired at thresholds for 1.0, 2.25, 3.5, 5.0, 7.5, and 10 MHz. For optimum-sized gas bodies, the amplitudes calculated at the thresholds were about 11% of the initial radii. At the cell membrane damage thresholds, theoretical negative shell stresses were approximately constant with frequency at about 50 MPa. This stress appears to be sufficient to induce failure of the shell, and gas body destabilization was confirmed by increases in transmission of ultrasound pulses through the monolayer and by microscopically-observed shrinkage of the gas bodies. A model of acoustic microstreaming was used to calculate the shear stress during the pulses. The maximum shear stress increased from about 1500 to 4500 Pa from 1 to 10 MHz, sufficient for the cell membrane damage. This theoretical analysis shows that both the gas body destabilization and the cell membrane damage could be expected at similar peak rarefactional pressure amplitudes, with thresholds having the observed proportionality to frequency.

Albumins↗
PubMed1979

Effects of gas density on the frequency response of gas-filled pressure transducers.

The effects of gas density on the frequency responses of four pressure transducers were determined at gas densities from 1.2 to 25.0 g/l. Transducers tested included three sensitive differential types used with pneumotachographs to measure respiratory flow (Validyne DP-45 and DP-103; Medistor P-11) and a transducer commonly used to measure esophageal pressure (Statham P23Dd). Three different responses were obtained. The Validyne DP-103 was overdamped and its response was essentially independent of gas density. The frequency response of this transducer is adequate for use with quiet breathing only. The Validyne DP-45 and Medistor P-11 responses were underdamped. The resonant peaks of these transducers decreased markedly in frequency as the gas density increased. The Statham P23Dd was also underdamped; however, its resonant frequency increased as gas density increased. An esophageal balloon did not alter the frequency response characteristics of this tubing-transducer system. Both increases in length and decreases in diameter of connecting tubing reduced the frequency of resonant peaks of underdamped pressure transducers.

Atmospheric Pressure↗
PubMed1997

[The development of a gas chromatograph used in gas analysis below atmospheric pressure].

During the process of setting up a carbon monoxide infrared laser generator, it's necessary to analyze the gaseous components produced in laser cavity under reduced pressure for understanding its charging regularity. In this paper a self-made gas chromatograph for analysis of some special gas mixtures is described. This instrument can analyze O2, N2, CO (with normal contents) and trace CO2 simultaneously below atmospheric pressure. The gas sample below atmospheric pressure was taken into a small piston cylinder and then compressed by pushing the piston for injection. The injected sample was carried by He into two parallel chromatographic columns and detected separately. The gases with normal contents were detected by a thermalconductivity detector (TCD) and the trace CO2 was detected by a He ionization detector (HeID). The detection sensitivity of CO2 is in the order of magnitude of 10(-6) V/V. The experimental results show that this instrument with advantages of simple design, easy operation and good stability is suitable for on-line analysis of gas samples below atmospheric pressure. We have successfully analyzed on-line the gaseous components produced in the laser cavity by using this equipment. The technique described here can be used for complete analysis of gas samples below atmospheric pressure in many other fields.

English Abstract↗
PubMed1985

[Accuracy of halothane vaporizers with respect to temperature, carrier gas composition and gas flow rate].

Since the precise measurement of halothane-concentration in the patients gas support during routine anesthesia still requires much effort, the accuracy of the vaporizers halothane output remains important for the safety of anesthesia and the education of younger anesthesiologists. In the present study 30 halothane vaporizers (14 Fluotec Mark 3/Cyprane Ltd., 12 Vapor 19/Dräger, 4 Abingdon/Penlon) were removed from the operating rooms in the University Hospital Göttingen to test their accuracy. The measurements were performed with a masspectrometer under standardized laboratory conditions with varied temperatures (10 degrees, 21 degrees, 35 degrees C), gasflows (3, 5, 8 l/min) and compositions of carrier gas (100% O2, N2O/O2 = 2/1). All vaporizers in this study showed a light tendency to higher halothane outputs for low concentration adjustments and to distinct lower outputs for higher concentration adjustments. The Vapor 19 vaporizers compensated well with changes of temperatures and gasflows but had a distinct dependency on carriers gas compositions. The Fluotec Mark 3 vaporizers output depended on the temperature and gasflow but was almost unaffected by the carrier gas composition. Tremendous deviations appeared with the Abingdon vaporizers, which seamed to be without any temperature compensation and which were highly gas flow dependent. It can be concluded from our results that vaporizers according to their construction tend to be imprecise.

Anesthesia↗
PubMedDate not supplied

Determination of salicylic acid in plasma by gas chromatography using steam as carrier gas.

A gas chromatography method using steam as the carrier gas was established for the determination of salicylic acid in plasma. A 0.5 mL plasma sample was mixed with 0.5 mL of 6N HCl and then extracted with 2 mL of dichloromethane. The dichloromethane was evaporated to dryness and the residue was redissolved in 0.5 mL of water and then analysed by gas chromatography using steam as the carrying gas. The result was calculated by external standardization.

Chromatography, Gas↗
PubMed1994

Determination of (13C) urea enrichment by gas chromatography/mass spectrometry and gas chromatography/isotope ratio mass spectrometry.

We present gas chromatographic/mass spectrometric and gas chromatographic/isotope ratio mass spectrometric assays of the 13C enrichment of plasma urea converted to its dimethylaminomethylene derivative. The limits of sensitivity of the two techniques are 0.2% and 0.02%, respectively. The techniques were tested in rats and humans infused with (13C)urea or (3-13C)lactate. (13C)Urea enrichment during the infusion of (3-13 C)lactate in humans was not detectable by gas chromatography/mass spectrometry but was easily measured by gas chromatography/isotope ratio mass spectrometry. These assays should be useful for clinical investigations, in which the incorporation of a (13C)gluconeogenic substrate into glucose must be corrected for the incorporation of 13CO2 derived from the oxidation of the substrate. This correction involves measuring the low-level 13C enrichment of urea.

Adult↗
PubMed1988

Influence of gas physical properties on pulmonary gas exchange.

Overall, the exchange of gas by the lung is strongly dependent on the blood-gas partition coefficient of that gas and weakly dependent on the molecular weight of the gas. The exchange of very soluble inert gases is dependent on interaction with the airway surface during inspiration and expiration.

Animals↗
PubMed1998

[Preclinical blood gas analysis. 2. Experience with three blood gas analyzers in emergency care].

UNLABELLED: Within the last few years the use of Point-of-Care Analyzers increased. These testing is primarily performed in the emergency room, intensive care units, and in the operating room using small portable analyzers. The fact of being transportable and working with rechargeable or changable batteries and disposable cartridges caused us to use blood gas analysis in the prehospital setting. METHODS: We tested three available blood gas analyzers: AVL OPTI 1, IRMA Blood Analyzer and the i-Stat Portlab System. All analyzers work with single-use cartridges and the calibration procedure is automatic. The AVL OPTI 1 uses a calibration gas and sucks in the blood by itself. The IRMA and the i-Stat system use a containing calibration gel, which must be removed from the sensory by injecting the blood sample. In all analyzers the results appear within 2-4 min on the screen. The OPTI 1 and the IRMA are able to print out the results automatically, the i-Stat uses an additional printer connected over an infrared adapter. RESULTS: During the observation period of 2 years more than 320 prehospital blood gas analyses were performed (200 with the OPTI 1.70 with IRMA and 50 with the i-Stat). All devices served their purpose. The main problems appeared with the application of the blood samples at the IRMA and the i-Stat. Because of this intricate procedures 21.4% and 20% of all tries failed. The time spent on the measurement was 2 to 5 minutes. CONCLUSIONS: All tested devices worked satisfactorily. Relating to the safety, the performance and the use the AVL OPTI 1 has to become the best notes. But this system is much more bigger and heavier than the others, especially the i-Stat Blood analyzer.

Blood Gas Analysis↗
PubMed2006

Characterization of volatile organic compounds and odors by in-vivo sampling of beef cattle rumen gas, by solid-phase microextraction, and gas chromatography-mass spectrometry-olfactometry.

Volatile organic compounds (VOCs) and odors in cattle rumen gas have been characterized by in-vivo headspace sampling by solid-phase microextraction (SPME) and analysis by gas chromatography-mass spectrometry-olfactometry (GC-MS-O). A novel device enabling headspace SPME (HS-SPME) sampling through a cannula was designed, refined, and used to collect rumen gas samples from steers. A Carboxen-polydimethylsiloxane (PDMS) fiber (85 microm) was used for SPME sampling. Fifty VOCs from ten chemical groups were identified in the rumen headspace. The VOCs identified had a wide range of molecular weight (MW) (34 to 184), boiling point (-63.3 to 292 degrees C), vapor pressure (1.05x10(-5) to 1.17x10(2) Pa), and water solubility (0.66 to 1x10(6) mg L-1). Twenty-two of the compounds have a published odor detection thresholds (ODT) of less than 1 ppm. More than half of the compounds identified are reactive and have an estimated atmospheric lifetime of <24 h. The amounts of VFAs, sulfide compounds, phenolic compounds, and skatole, and the odor intensity of VFAs and sulfide compounds in the rumen gas were all higher after feeding than before feeding. These results indicate that rumen gases can be an important potential source of aerial emissions of reactive VOCs and odor. In-vivo sampling by SPME then GC-MS-O analysis can be a useful tool for qualitative characterization of rumen gases, digestion, and its relationship to odor and VOC formation.

Animal Feed↗
PubMed1994

Method of expired gas collection during cardiopulmonary exercise testing does not affect respiratory gas exchange measurements in patients with heart failure.

Cardiopulmonary exercise testing is commonly used to assess patients with heart failure. Analysis of expired gases during exercise requires the use of either a facemask or mouthpiece with nose clip. The authors sought to determine if the method of expired gas collection during exercise testing (facemask or mouthpiece) influences gas exchange measurements in patients with heart failure. Nine patients with heart failure performed two maximal treadmill tests. Expired gases were collected with a facemask in one exercise test and a mouthpiece in the other. There were no significant differences in exercise test duration, peak oxygen uptake, heart rate, respiratory exchange ratio, or perceived exertion during maximal exercise performed with the facemask when compared to the mouthpiece. Test subjects reported that the overall comfort of the facemask was significantly greater than that of the mouthpiece (P < .02). The method of expired gas collection during cardiopulmonary exercise testing does not significantly affect measures of gas exchange or exercise performance in patients with heart failure. Heart failure patients find the overall comfort of the facemask superior to that of the mouthpiece, but this comfort preference does not affect exercise performance.

Exercise Test↗
PubMed1995

Evaluation of the Paratrend 7 intravascular blood gas monitor during cardiac surgery: comparison with the C4000 in-line blood gas monitor during cardiopulmonary bypass.

OBJECTIVE: To evaluate the performance of the Paratrend 7 intravascular blood gas monitor (Biomedical Sensors, High Wycombe, UK, Ltd) during cardiac surgery and compare it with that of an in-line blood gas monitor placed in the arterial limb of an extracorporeal circuit during cardiopulmonary bypass. DESIGN: A prospective study. Consecutive patient enrolment. SETTING: In the cardiac surgical intensive care units at a tertiary referral center. INTERVENTION: Insertion of the Paratrend 7 intravascular sensor through the radial arterial catheter after induction of anesthesia. MEASUREMENTS AND MAIN RESULTS: Simultaneous measurements of pH, PCO2, and PO2 were made from the sensor and the blood gas analyzer, and the bias and precision were calculated on all the measured parameters. The bias and precision of the intravascular sensor during bypass for pH, PCO2, and PO2 were 0.01 and 0.06 pH units, 0.5 and 2.5 mmHg (2% and 8%), and 3 and 45 torr (0.5% and 14%), respectively. The bias and precision for the prebypass and the postbypass phases were comparable. The bias and precision of the extracorporeal monitor for pH, PCO2, and PO2 were 0.04 and 0.1 pH units, -0.3 and 4 mmHg (-1% and 15%) and 8 and 48 mmHg (4 and 18%), respectively. There were no instances of any complications attributable to the intravascular sensor. CONCLUSIONS: The intravascular sensor used in this study functioned well during cardiopulmonary bypass and the postbypass phase. The performance of the intravascular sensor was better than the in-line blood gas monitor during cardiopulmonary bypass.

Adult↗