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At least 19 recordsLinked to original sources
PubMed2006

Shape resonances in molecular clusters: the 2t(2g) shape resonances in S 2p-excited sulfur hexafluoride clusters.

Sulfur hexafluoride clusters are investigated in the S 2p excitation regime. For the first time special emphasis is put on high-energy resolution spectroscopy of shape resonances in free clusters. We have investigated the 2t(2g)-shape resonance occurring above the S 2p threshold as one typical example to study size effects that are related to shape resonances. A small redshift of this resonance of 30 +/- 5 meV occurs in clusters relative to the free molecule and changes in line shape are observed. A double-barrier optical potential model is applied for the analysis of intra- and intermolecular effects occurring in SF6 clusters, which is suitable for rationalizing the experimentally observed spectral changes. The experimental and theoretical results are briefly discussed in comparison to previous work on core-excited van der Waals clusters containing diatomic molecules.

Cluster Analysis↗
PubMed2005

Sulfur hexafluoride's liquid-vapor coexistence curve, interfacial properties, and diffusion coefficients as predicted by a simple rigid model.

We present here molecular-dynamics simulation results of the vapor-liquid coexistence curve, surface tension, and self-diffusion coefficients of sulfur hexafluoride. Sulfur hexafluoride is modeled as a rigid molecule, following the model proposed by Pawley [Mol. Phys. 43, 1321 (1981)]. Vapor-liquid coexistence curve and surface tension are obtained through direct molecular-dynamic simulations in the NVT ensemble. Simulation results are able to reproduce the qualitative shape of the vapor-liquid envelope. However, lower densities, a higher critical temperature, and an overestimated surface tension are obtained here. Those deviations are explained on the basis of the rigidity of the molecular model used. Self-diffusion coefficients are calculated from simulations in the NVE ensemble for different gas states at atmospheric pressure. The rigid model performs better for dynamical properties since simulation results provide very good agreement with available experimental data in this case.

Journal Article↗
PubMed1989

The rate of sulfur hexafluoride escape from a plastic syringe.

Sulfur hexafluoride (SF6) gas is widely used for internal tamponade during retinal reattachment surgery and is commonly injected into the eye from a 10-mL plastic syringe. The rate of diffusion of SF6 out of a plastic syringe has not bee studied. We measured the percentage of SF6 gas in a 10-mL plastic syringe by gas chromatography, confirmed by infrared spectrometry. Measurements were obtained immediately after aspiration, and at 30 s and 10, 15, 60, 90, and 120 minutes, and 18 hours. A marked decrease in SF6 concentration, from 97% at 30 s to 76% at 60 minutes and 2% at 18 hours, was noted. The results were highly reproducible. Sulfur hexafluoride gas should be injected into the patient's eye as soon as possible after aspiration from the tank to ensure accurate concentrations.

Chromatography, Gas↗
PubMed1975

Sulfur hexafluoride in owl monkey vitreous cavity.

Sulfur hexafluoride (SF6) gas, tested in the vitreous chamber of owl monkey eyes, remained in the vitreous cavity about twice as long as air (ten to 11 days vs. five to six days). Its volume expanded from the diffusion of other gases into the created gas pocket. Lens opacities developed when the lens was in continuous contact with SF6 or air. Sulfur hexafluoride appeared to be no more toxic to the retina than air, using electroretinographic, histologic, and electron microscopic criteria.

Air↗
PubMed2005

[Sulfur hexafluoride gas, perfluorocarbon liquid, air and balanced salt solution retinal toxicity in rabbit eyes].

PURPOSE: To determine retinal toxicity after intravitreous balanced salt solution, sulfur hexafluoride gas, and perfluorocarbon liquid injection in rabbit eyes. METHODS: Twenty-two eyes of sixteen New Zealand albino rabbits were divided into groups: balanced salt solution (7 eyes); sulfur hexafluoride gas (4 eyes); and perfluorocarbon liquid (5 eyes). After the introduction of a needle through the sclera the vitreous was aspirated (0.3 ml), balanced salt solution, sulfur hexafluoride gas 100% and perfluorocarbon liquid (0.3 ml) were injected into rabbit vitreous cavity. The control group (6 eyes) was not submitted to any procedure. After three weeks the vitreous was aspirated and submitted to biochemical analysis and the eyes prepared for histological analysis. RESULTS: The eyes submitted to perfluorocarbon liquid and sulfur hexafluoride gas injection showed a greater L-glutamate increase in the vitreous compared to balanced salt solution and control groups (p<0.05). Histological results confirmed small changes in the sulfur hexafluoride group and important lesions in perfluorocarbon liquid group, such as external photoreceptor segment disruption, external and internal plexiform layer thinning, ganglionar and internal nuclear layer decrease of nucleus number, edema, and presence of macrophages in the superficial layers. No major histological changes were observed with balanced salt solution and in control groups. CONCLUSION: Liquid intravitreous injection of sulfur hexafluoride gas and perfluorocarbon are potentially toxic to rabbit retina, compared to control and balanced salt solution groups.

Air↗
PubMed1989

[Damage to the corneal endothelium following exposure to sulfur hexafluoride gas].

Damage to the corneal endothelium caused by sulfur hexafluoride was analyzed in 14 rabbits. Fourteen eyes were used for testing, while the other 14 served as controls. Three stages of endothelial reaction resulting from long-term contact with sulfur hexafluoride were established by morphologic and morphometric analyses. The first stage - acute necrosis of the endothelial cells - covers all stages of destruction up to total obliteration in the exposed area of the endothelium, which is clearly demarcated from the rest of the endothelium. The second, repair stage, begins as early as 24 hours after the operation and includes the diverse forms of endothelial cell spread, transformations of the hexagonal endothelial cells, and endothelial cell migration with polymorphia and formation of rosettes. The third, proliferative phase of the endothelial cell reaction follows directly after the second phase and is characterized by the production of more giant cells, the production of giant rosettes, compaction of cell membranes and filling of the intercellular space with amorphous substances. The results of this research are of major practical relevance, since they show that a 40/60% sulfur hexafluoride/air mixture cannot be regarded as inert.

Animals↗
PubMed1992

Vitrectomy with silicone oil or sulfur hexafluoride gas in eyes with severe proliferative vitreoretinopathy: results of a randomized clinical trial. Silicone Study Report 1.

Between September 1985 and September 1987, 101 eyes with rhegmatogenous retinal detachment and severe (with a classification of at least C-3) proliferative vitreoretinopathy but without prior vitrectomy were treated with vitrectomy and randomized to either a mixture of 20% sulfur hexafluoride gas and air or to 1000 centistokes of silicone oil. Between 50% and 60% of eyes that received silicone oil had visual acuity better than or equal to 5/200 compared with 30% to 40% of the eyes that received sulfur hexafluoride gas (P less than .05). Macula attachment was more frequent in eyes that received silicone oil than in those that received sulfur hexafluoride gas (80% vs 60%, P less than .05). Hypotony was more prevalent in eyes with a detached macula (40% to 50% for sulfur hexafluoride gas vs 25% to 30% for silicone oil) when compared with those with attached maculas (less than 5% for either modality). Keratopathy was more prevalent in eyes with detached maculas (about 55% to 60% for either modality) compared with eyes with attached maculas (25% to 30% for sulfur hexafluoride gas vs 10% to 15% for silicone oil). In a companion article, we show that these differences between a gas tamponade and silicone oil are not found for perfluoropropane gas.

Adult↗
PubMed1982

The results of sulfur hexafluoride gas in vitreous surgery.

Of 101 vitrectomies that used sulfur hexafluoride gas, 42 of 87 eyes followed up for six months had attached retinas and 28 had visual acuities of 6/240 (20/800) or better. Ocular hypertension occurred after 45 of the 101 operations and the incidence of ocular hypertension was significantly higher in eyes that received 100% sulfur hexafluoride than in eyes given lesser concentrations of gas (P less than .05). Twenty-six of 101 eyes developed transient fibrinous exudation. Ocular hypertension was significantly more common in eyes with fibrin than in eyes without fibrin (P = .001). After complicated vitrectomies, 11 eyes developed presumed central retinal artery occlusions and lost light perception on the first postoperative day. Ten of these eyes had increased intraocular pressures. Eyes with severe hemorrhagic complications from vitrectomy were most likely to develop presumed central retinal artery occlusions.

Cataract↗
PubMed1986

[Expansion behavior of intravitreous sulfur hexafluoride in exposure to nitrous oxide].

In experiments with 19 rabbits the changes in volume and concentration of intravitreously instilled sulfur hexafluoride were investigated under normal air conditions (10 rabbits in group A) and with application of laughing, gas to the inspiration system for 3 hours (9 rabbits in group B). Under normal air conditions the SF6 gas bubble attained its greatest volume after 24 hours (twice its initial volume). With the addition of 67% laughing gas to the inspiration system the largest expansion in volume (260%) was found after 3 hours, i.e., at the end of application of laughing gas, and was followed by another peak after 24 hours. With regard to the sulfur hexafluoride concentration in the gas bubble, the results in the two groups were similar. The authors conclude that in retinal surgery with application of sulfur hexafluoride general anesthesia should not include laughing gas.

Animals↗
PubMed2004

The role of recombinant lysine-plasminogen and recombinant urokinase and sulfur hexafluoride combination in inducing posterior vitreous detachment.

PURPOSE: To determine the optimal method of generating plasmin in vitreous using recombinant lysine-plasminogen and recombinant urokinase and to determine its efficacy in inducing posterior vitreous detachment when combined with sulfur hexafluoride. METHODS: Plasmin concentration of the rabbit vitreous after separate and combined intravitreal administrations of recombinant lysine-plasminogen and recombinant urokinase was tested in 78 rabbits to determine the optimal method of administration. The safety and efficacy of these agents and sulfur hexafluoride in inducing complete posterior vitreous detachment (total separation of the vitreous apart from vitreous base) were also evaluated. RESULTS: The highest plasmin concentration in vitreous was measured 10 minutes after injection. Intravitreal administration of recombinant lysine-plasminogen and recombinant urokinase did not cause any toxicity findings up to concentrations of 100 microg and 200 IU, respectively, on funduscopy, electroretinography, and histopathologic studies. When combined with sulfur hexafluoride injection, separate intravitreal administrations of 75 microg/0.1 mL of recombinant lysine-plasminogen and 15 IU/0.1 mL of recombinant urokinase induced complete posterior vitreous detachment in 75% of the eyes compared with 13% in eyes that received sulfur hexafluoride injection combined with balanced salt solution, recombinant lysine-plasminogen, or recombinant urokinase. CONCLUSIONS: Plasmin was effectively generated in the vitreous after separate intravitreal administrations of recombinant lysine-plasminogen and recombinant urokinase. When combined with intravitreal gas injection, this method of plasmin production induced complete posterior vitreous detachment in 75% of the eyes.

Animals↗
PubMed2005

Perforated corneal hydrops treated with sulfur hexafluoride (SF6) gas and tissue adhesive.

PURPOSE: To report a case of a perforated acute hydrops in a mentally retarded patient that was successfully managed with intracameral sulfur hexafluoride gas and cyanoacrylate tissue adhesive. METHODS: Interventional case report. RESULTS: A 14-year-old mentally retarded male patient with keratoconus presented with a perforated acute hydrops. A bandage contact lens was applied. However, following a large emesis 2 days later, the aqueous leak worsened with shallowing of the anterior chamber. Under general anesthesia, sulfur hexafluoride was injected to reform the anterior chamber and cyanoacrylate tissue adhesive was applied to the perforated site and covered by a bandage contact lens and temporary tarsorrhaphy. A follow-up examination at 1 month showed a formed anterior chamber with tissue adhesive in situ and no aqueous leak. CONCLUSIONS: The successful use of intracameral sulfur hexafluoride and tissue adhesive in the management of perforated acute hydrops may avoid emergency tectonic penetrating keratoplasty and reduce potential complications in the poorly cooperative patient.

Adolescent↗
PubMed1993

Intractable chest pain in a patient whose postpneumonectomy space was managed with sulfur hexafluoride.

A 50-year-old man who had undergone right pneumonectomy 1 year previously was referred to our department following the sudden onset of severe chest pain. Since the operation, his postpneumonectomy space had been managed with sulfur hexafluoride. On admission, the pressure in the postpneumonectomy space was found to be more than +60 cmH2O. The chest pain was relieved after the sulfur hexafluoride had been drained and the pressure released. Thus, it is advisable to inject sulfur hexafluoride stepwise into the postpneumonectomy space of patients with long-standing fluid accumulation.

Diagnosis, Differential↗
PubMed1987

Automated measurement of functional residual capacity by sulfur hexafluoride washout.

We have constructed a computerized, totally automated system for measuring functional residual capacity (FRC) during mechanical ventilation, at any positive end-expiratory pressure (PEEP) and fraction of inspired oxygen. This system uses washout of a small amount (0.5 to 1.0%) of an insoluble, nontoxic tracer gas, sulfur hexafluoride, to measure FRC. It requires no modification of the ventilator and only minimal changes in the breathing circuit; it can be programmed to make measurements routinely without manual intervention. The system was evaluated with three tests. The prototype sulfur hexafluoride analyzer characteristic curve was determined, and the analyzer was evaluated to determine carbon dioxide interference. A comparison with nitrogen washout FRC measurements was made in an extensive bench test with a Plexiglas lung model. The bench test was designed to determine the effects of changing gas composition and minute volume. A study was done in six healthy dogs to determine reproducibility of the FRC measurements at four PEEP levels (0, 5, 10, and 15 cm H2O: two repetitions in each animal). The sulfur hexafluoride analyzer was well characterized by an exponential equation with a multiple r2 = 0.996. The analyzer was not affected by the presence of carbon dioxide (paired t test, t19 = 1.23, P greater than 0.10). The bench test indicated that FRC (measured) = 0.969 X FRC (true) - 5.3 ml. (Multiple r2 = 0.979.) This was significantly better than the nitrogen washout system, whose regression equation was also a function of minute volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

An analyzer for in-line measurement of expiratory sulfur hexafluoride concentration.

An infrared analyzer for the inert tracer gas sulfur hexafluoride (SF6) is described and evaluated. The analyzer consists of a transducer and a processor unit. It is designed to operate in a nonrebreathing system with a ventilator and a computer. The transducer, which is placed over a cuvette with windows in the ventilator tubings, reads the SF6 concentration in the airway during the expiratory phase. At the end of the inspiratory phase, the zero level of the instrument is automatically reset. The response time and linearity of the analyzer were tested, and interference by other gases was assessed. Full response was reached within 20 ms after a sudden introduction of 0.5% SF6 into the cuvette. The analyzer-computer system had adequate linearity below 0.5% of SF6. Oxygen, nitrogen, and humid air had no influence on the analyzer signal. One hundred per cent nitrous oxide, 4% enflurane, 4% isoflurane, and 4% halothane caused signals corresponding to 0.010, 0.023, 0.022, and 0.043% SF6, respectively. Due to the method for zero reset, the importance of interference from these gases is greatly reduced when inspired and expired concentration approach each other. The disturbance from CO2 (10% CO2 gave a signal corresponding to 0.020% SF6) can be compensated for by including a CO2 analyzer in the set-up. The rapid response and the high sensitivity of the analyzer may make it useful for studies of pulmonary gas mixing and for measurements of lung volume during mechanical ventilation.

Equipment Design↗
PubMed1989

Kinetics of intraocular gases. Disappearance of air, sulfur hexafluoride, and perfluoropropane after pars plana vitrectomy.

Intraocular gas bubbles are an important source of internal tamponade for the treatment of retinal breaks in eyes requiring vitrectomy. The kinetics of disappearance of air, 20% sulfur hexafluoride, and 10% perfluoropropane were prospectively evaluated in 76 eyes undergoing pars plana vitrectomy. The absorption of each gas approximated a first-order kinetic equation with respect to bubble volume. The half-life of air was 1.6 days in phakic and 0.9 days in aphakic eyes. The half-life of 20% sulfur hexafluoride was 2.8 days in phakic and 2.4 days in aphakic eyes. The half-life of 10% perfluoropropane was 5.7 days in phakic, 4.5 days in aphakic, and 4.3 days in pseudophakic eyes. The difference in half-life among the three gases was significant. Intraocular gases had a shorter half-life in aphakic than in phakic eyes.

Absorption↗
PubMed2004

Abatement of sulfur hexafluoride emissions from the semiconductor manufacturing process by atmospheric-pressure plasmas.

Sulfur hexafluoride (SF6) is an important gas for plasma etching processes in the semiconductor industry. SF6 intensely absorbs infrared radiation and, consequently, aggravates global warming. This study investigates SF6 abatement by nonthermal plasma technologies under atmospheric pressure. Two kinds of nonthermal plasma processes--dielectric barrier discharge (DBD) and combined plasma catalysis (CPC)--were employed and evaluated. Experimental results indicated that as much as 91% of SF6 was removed with DBDs at 20 kV of applied voltage and 150 Hz of discharge frequency for the gas stream containing 300 ppm SF6, 12% oxygen (O2), and 40% argon (Ar), with nitrogen (N2) as the carrier gas. Four additives, including Ar, O2, ethylene (C2H4), and H2O(g), are effective in enhancing SF6 abatement in the range of conditions studied. DBD achieves a higher SF6 removal efficiency than does CPC at the same operation condition. But CPC achieves a higher electrical energy utilization compared with DBD. However, poisoning of catalysts by sulfur (S)-containing species needs further investigation. SF6 is mainly converted to SOF2, SO2F4, sulfur dioxide (SO2), oxygen difluoride (OF2), and fluoride (F2). They do not cause global warming and can be captured by either wet scrubbing or adsorption. This study indicates that DBD and CPC are feasible control technologies for reducing SF6 emissions.

Air Pollutants↗
PubMed1998

Minimum alveolar concentrations of noble gases, nitrogen, and sulfur hexafluoride in rats: helium and neon as nonimmobilizers (nonanesthetics)

UNLABELLED: We assessed the anesthetic properties of helium and neon at hyperbaric pressures by testing their capacity to decrease anesthetic requirement for desflurane using electrical stimulation of the tail as the anesthetic endpoint (i.e., the minimum alveolar anesthetic concentration [MAC]) in rats. Partial pressures of helium or neon near those predicted to produce anesthesia by the Meyer-Overton hypothesis (approximately 80-90 atm), tended to increase desflurane MAC, and these partial pressures of helium and neon produced convulsions when administered alone. In contrast, the noble gases argon, krypton, and xenon were anesthetic with mean MAC values of (+/- SD) of 27.0 +/- 2.6, 7.31 +/- 0.54, and 1.61 +/- 0.17 atm, respectively. Because the lethal partial pressures of nitrogen and sulfur hexafluoride overlapped their anesthetic partial pressures, MAC values were determined for these gases by additivity studies with desflurane. Nitrogen and sulfur hexafluoride MAC values were estimated to be 110 and 14.6 atm, respectively. Of the gases with anesthetic properties, nitrogen deviated the most from the Meyer-Overton hypothesis. IMPLICATIONS: It has been thought that the high pressures of helium and neon that might be needed to produce anesthesia antagonize their anesthetic properties (pressure reversal of anesthesia). We propose an alternative explanation: like other compounds with a low affinity to water, helium and neon are intrinsically without anesthetic effect.

Anesthetics↗