Dual versus mono antiplatelet therapy for acute non- cardio embolic ischemic stroke or transient ischemic attack, an efficacy and safety analysis - updated meta-analysis.

BACKGROUND: New evidence on the efficacy and safety of dual antiplatelet therapy for secondary stroke prevention have been realized in the recent years. An updated meta analysis was done to determine the effect of the various dual antiplatelets vs aspirin alone on recurrence rate of ischemic stroke, cardiovascular morbidity and mortality, and its safety profile as reported through major bleeding. METHODS: PubMed, Cochrane and Science Direct data bases were utilized, RCTs evaluating dual antiplatelet vs mono antiplatelet therapy for acute ischemic stroke or transient ischemic attack within < 72 h from ictus were searched up to July 2019. Risk ratio at 95% confidence intervals were calculated to evaluate stroke recurrence, cardiac events and mortality, and major bleeding. RESULTS: Sixteen randomized controlled trials with a population of 28, 032 patients were pooled into a meta-analysis. Dual antiplatelet therapy was significantly superior over mono antiplatelet therapy in the reduction of stroke (RR 0.75, 95% CI:0.68-0.83, p value< 0.00001) and composite events namely cardiovascular morbidity and mortality (0.73 95% CI: 0.65-0.82, p value < 0.00001), while bleeding events were noted to be not significant (1.22 95% CI: 0.87-1.70, p value = 0.25). CONCLUSION: In acute non-cardioembolic ischemic strokes or those who have suffered a transient ischemic attack, dual antiplatelet therapy was associated with efficacy in stroke recurrence and composite cardiac events, with a non-significant risk of major bleeding.

Extending the study of mass transport across the gas-liquid interface by reversed-flow gas chromatography.

The transfer of dichlorodifluoromethane to water was utilized as model system to provide better insight on the determination of mass transport parameters across the gas-liquid interface. Weak signals by reversed-flow gas chromatography were recorded at various temperatures, from 320.7 to 344.3 K, by digitizing and smoothing the output of the flame ionization detector. A flexible uncertainty analysis distinguished the main sources of error in the determined parameters, suggesting improvements on the utilized experimental setup. Liquid diffusivities decreased with rising temperature (4.39 to 1.01 × 10-10 m2 s-1), approaching literature values at lower temperatures. The estimated liquid film thicknesses similarly decreased (1.8 to 1.0 × 10-4 m) and were one order of magnitude larger than previous findings, due to the larger extent of evaporation permitted by the current experimental setup. A mass transfer coefficient was estimated, corresponding to the endothermic contribution of the reverse (liquid-to-gas) process, whose activation energy (43.4 ±â€¯2.8 kJ mol-1) matched the vaporization enthalpy of water in the studied temperature range. Successful comparisons were made with literature distribution coefficients and Henry's law constants. The dissolution of CFC-12 in water was found to be exothermic, slightly spontaneous at lower temperatures and approaching equilibrium at higher ones (indicated by the small negative molar Gibbs free energy values), with negative entropy change values [average: -(190.7 ±â€¯6.9) J K-1 mol-1], as expected for a process of increased order.

An inverse gas chromatographic methodology for studying gas-liquid mass transfer.

A novel methodology of reversed flow inverse gas chromatography (RF-IGC) is presented. It permits the simultaneous determination of mass transfer coefficients across the gas liquid interface as well as the respective solubility parameters and thermodynamic functions of dissolution of gases into liquids. The standard deviation of the experimentally determined parameters is estimated for first time, which combined with the successful comparison of the values of the present parameters with other literature ones ascertain the reliability of the methodology. Another novelty of the present work is that the chromatographic sampling of the physicochemical phenomena is done without performing the usual flow reversals procedure. Vinyl chloride monomer's (VCM) interaction with various composition liquid foods: orange juice, milk and olive oil was used as model system. The present transfer rates are controlled by the gas film at lower temperatures, but at higher temperatures the resistances in both films tend to become equal. The found liquid diffusivity values express the total mass transfer from the gas phase into the liquid's bulk and they decrease with rising temperature, as the solubilities of gases in liquids do. Solubility, expressed by Henry's law constant and the mean values of interfacial thickness are of the same order of magnitude to literature ones. From the thermodynamic point of view, VCM dissolution in all liquids is accompanied by significant heat release and it is a slightly non-spontaneous process, near equilibrium, while the entropy change values are negative.

H(2) and CO(2) coadsorption effects in CO adsorption over nanosized Au/gamma-Al(2)O(3) catalysts.

The present study is focused on the kinetic investigation of the effects of H(2) and CO(2) on the rates related to the elementary steps of CO sorption over Au/gamma-Al(2)O(3). The kinetic study was carried out in a wide temperature range (50-300 degrees C) by the novel methodology of reversed flow gas chromatography (RF-GC). The findings of preliminary coadsorption studies of CO with H(2), O(2) and O(2)+H(2) indicate that a reductive pre-treatment of the Au catalyst with a mixture of CO in excess of H(2) can be more beneficial concerning CO oxidation activity at low temperatures, compared to the usual reduction in a diluted hydrogen atmosphere, most probably due to the easier activation of oxygen molecules. At high temperatures the rate of reversed water gas shift reaction becomes significant resulting in H(2) and CO(2) consumption. The kinetic findings indicate that hydrogen strongly influences the adsorption of CO over Au/gamma-Al(2)O(3), by enhancing CO adsorption at lower temperatures and weakening the strength CO binding. On the other hand, CO(2) adsorption competes that of CO under hydrogen-rich conditions. However, the strength of CO(2) bonding is higher compared to that of CO and it further increases at higher temperatures, in agreement with the observed deactivation of the selective CO oxidation in the presence of CO(2).

Gas chromatographic investigation of the effects of hydrogen and temperature on the nature of the active sites related to CO adsorption on nanosized Au/gamma-Al(2)O(3).

Nanometer-sized Au particles on oxide supports exhibit extraordinary activity for the selective oxidation of CO (SCO) under conditions compatible with the operation of polymer electrolyte membrane fuel cells (PEM-FCs). In the present work, the novel methodology of reversed flow inverse gas chromatography (RF-IGC) is further extended to the study of the nature of the active sites related to CO adsorption over Au/gamma-Al(2)O(3) catalyst both in the presence as well as in the absence of hydrogen in a wide temperature range. The main findings are as follows: (i) higher amounts of CO can be bound on the catalyst active sites, at conditions compatible with the operation of PEM-FCs. (ii) At rising temperatures, catalyst adsorptive capacity decreases while the degree of surface heterogeneity increases since new groups of active sites appear, both in the presence and in the absence of hydrogen. (iii) The experimentally observed high-activity of Au/gamma-Al(2)O(3) for SCO at ambient temperatures can be explained as the consequence of CO weaker bonding over metallic Au actives sites in comparison with stronger CO bonding taking place at active sites located on gamma-Al(2)O(3) support, which is related to deactivation.

Inverse gas chromatographic investigation of the active sites related to CO adsorption over Rh/SiO2 catalysts in excess of hydrogen.

In the present work, the novel methodology of reversed-flow gas chromatography (RF-GC) is extended in a topic of contemporary scientific and technological interest, such as the effect of hydrogen in the "topography" of the active sites related to CO adsorption. This study concerns CO adsorption on a silica-supported Rh catalyst, at 90 degrees C. The topography of the catalyst in the absence of hydrogen consists of both randomly and islands of CO bound over chemisorbed CO molecules. In contrast, under H2-rich conditions, the observed topography is almost entirely patchwise ascribed to long-range lateral attractions between adsorbate molecules. In excess of hydrogen, CO adsorption is shifted at higher lateral attractions values which correspond to weaker adsorbate-adsorbent interactions and lower surface coverage. This provides an indication of a H2-induced desorption, which can be attributed to the formation of an H-CO complex desorbing from the catalyst surface below the temperature required for CO desorption, in the absence of H2, and it may explain the well-known enhancement of the rate of selective CO oxidation in excess of hydrogen by H2.

Gas chromatographic investigation of the competition between mass transfer and kinetics on a solid catalyst.

The reversed-flow gas chromatography (RF-GC) method is used to investigate the competition between mass transfer and kinetics in heterogeneous catalysis. The well-studied dissociative adsorption of carbon monoxide over a silica supported rhodium catalyst at various temperatures is used as model system. The Thiele-type modulus phis, and the effectiveness factor eta are calculated for both adsorbate (CO) and product (CO2), from the experimental chromatographic peaks. The values experimentally found are similar to those predicted theoretically and give interesting information for the mechanism of the interaction of carbon monoxide with the catalyst studied.

Time-resolved determination of surface diffusion coefficients for physically adsorbed or chemisorbed species on heterogeneous surfaces, by inverse gas chromatography.

A new simple method is developed for measuring surface diffusion coefficients Ds of gases adsorbed on heterogeneous surfaces, using the reversed-flow version of inverse gas chromatography. The Ds values are found in a time-resolved way, together with the corresponding adsorption energy values, the local adsorbed concentrations, and the local adsorption isotherm values. A relative dynamic adsorption rate constant, an adsorption/desorption rate constant, and a surface reaction rate constant are also found in the same experiment, together with the total diffusion coefficient of the gas in the solid bed. The method has been applied for carbon monoxide, oxygen gas, and carbon dioxide as adsorbates on 75% Pt+25% Rh catalyst supported on SiO2, at 593.8 K.

Study of the mechanism of the interaction of vinyl chloride with water by reversed-flow gas chromatography.

The investigation of the mechanism for the interaction of vinyl chloride (VC) with liquid foods is of great significance in food science. In the present work the model system VC-water was studied by using the relatively new technique of reversed-flow gas chromatography. Using suitable mathematical analysis the following physicochemical quantities were determined: (a) diffusion coefficients of VC into water, (b) overall mass transfer coefficients of VC in the water, and in the carrier gas nitrogen, (c) partition coefficients of VC between water and nitrogen, and (d) constants of Henry's law for the adsorption of VC by water. From the variation of the above parameters with temperature, and the stirring rate of the water, useful conclusions concerning the mechanism for the VC-water interaction were extracted. The experimental results for the transfer of VC into the bulk water suggest (i) a mechanism consisted of a fast equilibrium step between the VC in the gas phase and in the interface, followed by a slow adsorption of VC into the bulk of water, which is the rate-determining step, when the water is quiescent, and (ii) a mechanism consisted of a slow diffusion of VC from the gas phase to the interface, which is the rate-determining step, followed by a fast equilibrium step between the VC in the interface and in the water bulk, when the water is stirred.

Flux of gases across the air-water interface studied by reversed-flow gas chromatography.

In the present work the reversed-flow gas chromatographic technique was applied for the study of flux of gases across the air-water interface. The model system was vinyl chloride-water, which is of great significance in food and environmental chemistry. Using suitable mathematical analysis, equations were derived by means of which the following physicochemical quantities were calculated: diffusion coefficient of vinyl chloride (VC) into water, partition coefficient of VC between the water (at the interface and the bulk) and the carrier gas nitrogen, overall mass transfer coefficients of VC in the gas (nitrogen) and the liquid (water), gas and liquid film transfer coefficients of VC, gas and liquid phase resistances for the transfer of VC into the water, and finally the thickness of the stagnant film in the liquid phase, according to the two-film theory of Whitman. From the variation of the above parameters with temperature, as well as the volume and the free surface area of the water, useful conclusions concerning the mechanism for the transfer of VC into water were extracted. These are discussed in comparison with the same parameters calculated from empirical equations or determined experimentally by other techniques.

Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium alloy catalysts.

The kinetics for the oxidation of carbon monoxide in the presence of excess oxygen over Pt-Rh alloy catalysts were studied by using the reversed-flow gas chromatography technique. Suitable mathematical analysis equations were derived by means of which the rate constants for the oxidation reaction of carbon monoxide, as well as for the adsorption and desorption of the reactant CO on the catalysts pure Pt, 75 atom% Pt+25 atom% Rh, 50 atom% Pt+50 atom% Rh, 25 atom% Pt+75 atom% Rh and pure Rh supported on SiO2 were determined. All the catalysts show a maximum rate constant for the production of CO2 at a characteristic temperature close to that found in the literature. The rate constants for the adsorption of CO increase generally with increasing temperature, while those for the desorption decrease with increasing temperature. From the variation of the rate constants with temperature activation energies for the oxidation reaction and adsorption of CO were determined, which are sensitive to the composition of the catalytic surface. The appearance of CO2 and carbon, when introducing pure CO into the column with the catalysts, verified a partial dissociative adsorption (e.g., disproportionation) of CO on the catalysts used. The latter indicates a mechanism for the CO oxidation through a partial dissociative adsorption of CO followed by the reaction of adsorbed CO molecules with adsorbed O atoms.