[Influence of 20 % sulfur hexafluoride (SF6) on human corneal endothelial cells : An in vitro study]. / Einfluss von 20 % Schwefelhexafluorid (SF6) auf humane korneale Endothelzellen : Eine In-vitro-Studie.

BACKGROUND: In posterior lamellar keratoplasties, such as Descemet membrane endothelial keratoplasty (DMEK) and Descemet's stripping automated endothelial keratoplasty (DSAEK) an air bubble is left inside the anterior chamber to promote graft attachment during the early postoperative period. In the case of insufficient graft adhesion a renewed intracameral air injection is often necessary. The use of sulfur hexafluoride diluted with air (SF6 20 %) as an alternative to pure air may further enhance graft attachment and reduce the rebubbling rate. The effect of SF6 20 % on corneal endothelium is currently unclear and was therefore examined in vitro. MATERIAL AND METHODS: For this study 12 human corneoscleral discs were mounted in artificial anterior chambers, the systems were continuously filled with culture medium and the anterior chambers with air (n = 5) or SF6 20 % (n = 7) as tamponade. After 6 days of storage in the incubator endothelial cell density, toxicity on endothelial cells and corneal thickness were evaluated. RESULTS: There were no significant differences in endothelial cell loss (p = 1.000), endothelial cell count (p = 0.648), toxicity on endothelial cells (p = 0.048) and central corneal thickness (p = 0.905) between the two groups after 1 week. The level of significance was defined as p ≤ 0.05 and adjusted to p ≤ 0.0056 according to the Bonferroni correction for multiple testing. CONCLUSION: The use of SF6 20 % as tamponade in the anterior chamber for posterior lamellar keratoplasty can be proposed as a safe alternative to pure air filling related to endothelial cell loss. Increased toxic effects on the corneal endothelium by SF6 20 % were not detected in this study; however, further prospective clinical trials are needed to examine the long-term effects in humans.

Corneal endothelial toxicity of air and SF6.

PURPOSE: The authors conducted in vivo assessment of corneal endothelial toxicity of air and SF6 in the feline model. This research was motivated by the increased use of air in anterior segment surgery in human subjects. METHODS: This was a prospective masked study. The eyes of 16 healthy adult cats were randomly assigned for the injection of 0.7 mL air into the anterior chamber of one eye and SF6 in the contralateral eye. Daily examination included slit lamp photographs, pachymetry, and tonometry. Specular microscopy was performed before, 7 days after, and 10 days after injection. The animals were euthanatized, and the corneas were processed for alizarin red-trypan blue staining and for light and electron microscopy. RESULTS: SF6 remained in the anterior chamber significantly longer than air. Both groups showed postinjection inflammation, which on average was maximal at day 2 and more severe with SF6. No difference in IOP was observed between the two groups. Specular microscopy showed significant endothelial cell loss in the SF6 group (mean postinjection cell loss, 132 ± 50 cells/mm(2)) but not in the group injected with air. Alizarin red staining revealed significant regional differences in cell density only in the SF6 group and more pronounced endothelial cell loss in the superior area. CONCLUSIONS: These results indicate that both air and SF6 injected into the anterior chamber of the eye can induce intraocular reaction in the feline model and that SF6 is more toxic than air in terms of endothelial cell loss and anterior chamber inflammation.

On the mechanisms of ultrasound contrast agents-induced arrhythmias.

Recent reports have shown that imaging hard-shelled ultrasound (US) contrast agents at high mechanical indices engenders premature ventricular contractions (PVCs). We have shown that the oscillations of microbubbles next to a cell induce a mechanical pressure on its membrane resulting in the activation of stretch activated channels (SAC). The aim of this study is to demonstrate, in vivo and in vitro, the relationship between PVCs and SAC opening. Five anesthetized rats were used. PVCs were created in vivo with (1) US and a diluted solution of contrast microbubbles injected intravenously through the tail vein at a rate of 0.5 mL per min and (2) a manually induced mechanical stimulus, which consisted of stimulations by a flexible catheter introduced into the rat aorta and pushed until the left ventricle. PVCs were quantified through ECG measurements. In vitro experiments consisted of patch Clamp measurements on HL-1 heart cell line. The stimulation was carried out either manually with a glass rod or with US and microbubbles. For both in vivo and in vitro experiments, US consisted of 40-cycle waveforms at 1 MHz and peak negative pressures up to 300 kPa and exposure time varied from 1 to 2 min. We should emphasize that these parameters are different from those used in diagnostic conditions. In vivo, microbubbles and US at 300 kPa induced modification of rat's ECG while pressures below 300 kPa did not induce any PVC. US alone did not modify the rat's ECG. Similar PVCs were also created when stimulation with a catheter was applied. Regular heart beat rate was recovered immediately after the stimulation was stopped. In vitro, the mechanical stretch induced a cell membrane depolarization due to SAC opening. Similar effect was observed with US and microbubbles. The cell potential returned to its initial value when the stimulation was released. In conclusion, we presume that PVCs are generated through a cascade of events characterized by a mechanical action of oscillating microbubbles, opening of stretch activated ion channels, membrane depolarization and triggering of action potentials.

Total toxicity equivalents emissions of SF6, CHF3, and CCl2F2 decomposed in a RF plasma environment.

Sulfur hexafluorine compound (SF6), trifluoromethane (CHF3) and diclorodifluoromethane (CCl2F2) are extensively used in the semiconductor industry. They are global warming gases. Most studies have addressed the effective decomposition of fluorine compounds, rather than the toxicity of decomposed by-products. Hence, the concepts of toxicity equivalents (TEQs) were applied in this work. The results indicated that HF and SiF4 were the two greatest contributors of TEQ to the SF6/H2/Ar plasma system, while F2 and SiF4 were the two greatest contributors to the SF6/O2/Ar system. Additionally, SiF4 and HF were the two greatest contributors of TEQ to both the CHF3/H2/Ar and CHF3/O2/Ar plasma systems. HF and HCl were the two greatest contributors of TEQ to the CCl2F2/H2/Ar plasma system, and Cl2 and COCl2 were the two greatest contributors to the CCl2F2/O2/Ar system. HCl and HF can be recovered using wet scrubbing, which reduces the toxicity of these emission gases. Consequently, the hydrogen-based plasma system was a better alternative for treating gases that contained SF6, CHF3 and CCl2F2 from the TEQs point of view.

[Sulfur hexafluoride gas, perfluorocarbon liquid, air and balanced salt solution retinal toxicity in rabbit eyes]. / Toxicidade retiniana do gás hexafluoreto de enxofre, líquido perfluorocarbono, ar e solução salina balanceada em olhos de coelhos.

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.

Toxicidade retiniana do gás hexafluoreto de enxofre, líquido perfluorocarbono, ar e solução salina balanceada em olhos de coelhos / Sulfur hexafluoride gas, perfluorocarbon liquid, air and balanced salt solution retinal toxicity in rabbit eyes

OBJETIVOS: Determinar a toxicidade retiniana do gás hexafluoreto de enxofre, líquido perfluorocarbono e solução salina balanceada em olhos de coelhos. MÉTODOS: Foram analisados 22 olhos de 16 coelhos albinos da raça Nova Zelândia divididos em grupos: solução salina balanceada (7 olhos); hexafluoreto de enxofre (4 olhos), líquido perfluorocarbono (5 olhos) e controle (6 olhos). Após aspiração de 0,3 ml de humor vítreo, foi injetado a mesma quantidade de solução salina balanceada ou hexafluoreto de enxofre a 100 por cento ou líquido perfluorocarbono na cavidade vítrea. O grupo controle não foi submetido a nenhum procedimento. Três semanas depois o humor vítreo foi coletado para análise bioquímica e o olho enucleado para análise histológica. RESULTADOS: Os olhos dos animais que receberam injeção de hexafluoreto de enxofre e líquido perfluorocarbono mostraram significativo aumento da concentração vítrea de glutamato quando comparado aos grupos solução salina balanceada e controle (p<0,05). A análise histológica confirmou os achados bioquímicos mostrando alterações como disrupção do segmento externo dos fotorreceptores, afilamento das camadas plexiforme interna e externa, diminuição do número de núcleos na camada ganglionar e nuclear interna, edema e presença de macrófagos nas camadas superficiais. Estas alterações foram mais acentuadas no grupo líquido de perfluorocarbono em relação ao grupo hexafluoreto de enxofre. Não foram observadas alterações histológicas retinianas significativas nos grupos solução salina balanceada e controle. CONCLUSAO: A presença de gás hexafluoreto de enxofre e líquido perfluorocarbono na câmara vítrea se mostrou potencialmente tóxica para a retina de coelhos quando comparado ao grupo controle e solução salina balanceada.

Histopathologic abnormalities in rabbit retina after intravitreous injection of expansive gases and air.

PURPOSE: To evaluate histopathologic retinal changes in rabbit eyes after injection of pure perfluoropropane (C3F8) gas, pure sulfur hexafluoride (SF6) gas, or air into the vitreous cavity. METHODS: Air, C3F8 gas, or SF6 gas (0.4 mL each) were injected into rabbit vitreous cavities. Two, 4, and 6 weeks later, light and electron microscopic examinations were conducted, and the immunohistochemical localization of glutamate in the retina was studied. Noninjected eyes served as controls. RESULTS: At all time points, thinning or disappearance of the outer plexiform layer in the superior retina in eyes that received C3F8 gas was found; the inferior retina was the same as in controls. In eyes that received SF6 gas or air, light and electron microscopy showed that the superior and inferior retina were the same as in controls at all time points. Immunohistochemical examination showed abnormal glutamate distribution of the superior retina in eyes injected with C3F8 gas, SF6 gas, or air. However, glutamate distribution was the same as in controls in the inferior retina in eyes injected with C3F8 gas, SF6 gas, or air. CONCLUSIONS: Retinal tamponade using intraocular gases induces histopathologic retinal changes in the superior retina of the rabbit eye, where the gases are in continuous contact with the eye.

Sulfur hexafluoride (SF6): global environmental effects and toxic byproduct formation.

This work provides information concerning possible global environmental implications and personnel safety aspects that should be considered during the commercial uses of sulfur hexafluoride (SF6). SF6 is an anthropogenically produced compound, mainly used as a gaseous dielectric in gas insulated switchgear power installations. It is a potent greenhouse gas with a high global warming potential, and its concentration in the earth atmosphere is rapidly increasing. During its working cycle, SF6 decomposes under electrical stress, forming toxic byproducts that are a health threat for working personnel in the event of exposure. Several precautions are recommended to avoid personnel exposure to toxic byproducts: oxyfluoride levels or other byproduct concentrations in the operating gas matrix should be traced to predetermine the overall gas toxicity; contaminants should be systematically considered during maintenance, chamber evacuation and system opening process; small SF6 quantities leaking into air or stagnated pollutant concentrations in the operating field should be analyzed and compared to the threshold limit values and permissible exposure levels. New system design rules (i.e., hermetically sealed gas compartments, gas recycling or disposal in the field area) and different handling policies--both during maintenance and final disposal--now should be considered globally to provide for environmental and personnel safety.

Changes in the structure and properties of corpus vitreous and the preservation of enzymatic composition of rabbit antioxidative system under the influence of sulphur hexafluoride gas.

PURPOSE: To evaluate clinical, physiochemical and biochemical changes in rabbit vitreous body caused by local injection of sulphur hexafluoride gas. MATERIAL AND METHODS: The volume of fluid vitreous fraction was measured with Na+, K+, Mg2+, Ca2+ levels and full proteins concentration in both vitreous fractions in 24 New Zealand rabbits at 2, 7 and 14 day after SF6 injection. The activity of superoxide dismutase, catalase and malonyl dialdehyde were used to evaluate the activity of antioxidative enzymatic system. Control group consisting of 6 New Zealand rabbits had no experimental procedures. RESULTS: In the investigated group, the fluid vitreous fraction volume was increased while gelatous one was diminished from 0.08 ml in control group to 0.32 ml in the study group (on day 14). The level of Na+, K+, Mg2+, Ca2+ in the fluid fraction was unchanged. On day 7, we noticed statistically significant increase in protein concentration in comparison with the control group and the study group on 14 day. The activity of superoxide dismutase and catalase as well as the level of malonyl dialdehyde were increased in the fluid vitreous fraction compared to the gelatous one in the control group. After the SF6 injection we did not observe any changes of superoxide dismutase and catalase activities in the gelatous part of vitreous body while in the fluid one there was statistically significant decrease in the enzymatic activity and the MDA level in the whole observation time. CONCLUSIONS: The injected sulphur hexafluoride gas caused the damage of the gelatous vitreous fraction with the increase in the fluid one. The oxygen free radicals might trigger these pathological processes.

[Changes in the antioxidant system of the vitreous in rabbits after administration of sulfur hexafluoride]. / Zmiany w ukladzie antyoksydacyjnym ciala szklistego królików po podaniu szesciofluorku siarki.

PURPOSE: To evaluate the enzymatic activity of antioxidant system of rabbit's vitreous after sulfur hexafluoride (SF6) application. MATERIAL AND METHODS: Activity of CuZn-SOD, catalase and concentration of MDA in fluid and gel fraction of vitreous were determined in 24 rabbits of New Zealand race on the 2nd, 7th and 14th day after SF6 application. Control group consisted of 6 animals which did not undergo any operations. RESULTS: Dismutase and catalase activity as well as MDA concentration were higher in fluid fraction than in gel fraction in animals of control group. After SF6 application the activity of enzymes and MDA concentration did not change, whereas in fluid fraction all these values were statistically significantly reduced in all time intervals. CONCLUSIONS: SF6 leads to disintegration of vitreous structure especially just after its application. Damage to hyalocytes causes dysfunction of enzymatic system. Specific fluid fraction structure and insufficient number of substrates for peroxidation processes are the reasons for simultaneous reduction of MDA concentration.

[Changes in the antioxidant system of the aqueous humor, lens and erythrocytes after sulfur hexafluoride application to the vitreous of rabbits]. / Zmiany w ukladzie antyoksydacyjnym cieczy wodnistej, soczewce i krwinkach czerwonych krwi obwodowej po podaniu szesciofluorku siarki do ciala szklistego królików.

AIM: To determine the activity of superoxide dismutase, catalase and the concentration of malondialdehyde (MDA) in aqueous humor, lens and red blood cells after application of sulfur hexafluoride (SF6) into vitreous of rabbits. MATERIAL AND METHODS: 0.5 ml of 100% SF6 was injected into the vitreous of 24 rabbits of New Zealand race. The animals were randomly divided into 3 groups (of 8 rabbits each) depending on the observation day: group 1-2nd day of experiment, group 2-7th day and group 3-14th observation day. The control group (gr. 0) consisted of 6 rabbits that did not undergo any operations. Activity of superoxide dismutase, catalase and MDA concentration were determined in aqueous humor, lens and systemic blood erythrocytes. RESULTS: On the 7th day of observation an increased activity of dismutase and catalase as well as simultaneous increased MDA concentration were observed. In the lens on the 7th day the increased activity of dismutase was significant in relation to the results in the next time interval, whereas MDA concentration was significantly lower in all time intervals of the experiment in comparison with control group. In erythrocytes an increased activity of catalase was noticed on the 2nd and 14th day. CONCLUSIONS: Increased occurrence of active oxygen species in aqueous humor leads to insufficiency of the antioxidant system and intensification of peroxidation processes, which is reflected by increased MDA concentration. However, in the lens of this experimental model a slight stimulation of antioxidant system by a small number of free radicals is observed, which provokes a reaction of sweeping them away. Efficiency of lens antioxidant system is secured by weakening of peroxidation processes, which is expressed in minimal drop of MDA concentration.

Histological study of intraocular changes in rabbits after intravitreal gas injection.

To study the effects of different intravitreal gases on intraocular tissues, adult pigmented rabbits were given 0.4 mL intravitreal injections of air, 50% sulfur hexafluoride (SF6) and air, 100% SF6, 50% perfluoropropane (C3F8), or 100% C3F8. On postinjection days 1, 4, 7, and 14, the eyes were removed and the iris, ciliary body and retina processed for light and electron microscopy. Histopathological examination found no abnormalities in eyes that received air and none in the irises of gas-injected eyes. Eyes that received 50% or 100% SF6, or 50% C3F8 had vacuolar changes in the ciliary body and retina after maximum gas expansion; these changes were transient, returning to normal as the gas was absorbed. Eyes that received 100% C3F8 suffered irreversible damage to the ciliary body and retina, in both the superior and inferior portions. These observations indicate that expansion of some intravitreal gases can cause both reversible and irreversible changes in intraocular tissues. The degree of damage is affected by the duration of exposure and the gas concentration. Highly concentrated, long-lasting gases can cause irreversible changes resulting in breakdown of the blood-ocular barrier and impaired retinal function.

[Damage to the corneal endothelium following exposure to sulfur hexafluoride gas]. / Hornhaut-Endothelschädigungen nach Schwefelhexafluoridgaseinwirkung.

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.