Ratiometric fluorescence imaging and marker-free motion tracking of Langendorff perfused beating rabbit hearts

Optical mapping is a fluorescence based imaging technique used extensively in cardiac research to study the electrophysiological properties of isolated hearts kept at physiological conditions. The major limitation of optical mapping studies are the distortions of electrophysiological signals due to the contractile motion of the hearts. To reduce electrophysiological signal distortions due to the contractile motion artifacts, the mechanical motion has been suppressed in optical mapping experiments using electromechanical uncouplers such as Blebbistatin. Recent studies used marker-free numerical motion tracking and motion stabilization techniques to record electrophysiological parameters in the absence of electromechanical uncouplers and showed that contractile motion of the cardiac tissue is no longer a limitation in optical mapping studies. However, despite these developments, accurate measurements of quantities such as action potential duration (APD) and cardiac restitution are still challenging due to the residual motion artifacts present in the electrophysiological signals even after numerical motion tracking. A combination of marker-free motion tracking and ratiometric optical mapping technique is used in this thesis to minimize motion-related artifacts from contracting hearts. This combined experimental and numerical technique reduced motion artifacts significantly and hence, the combination is used to precisely measure APD, cardiac restitution and ventricular fibrillation frequencies from Langendorff perfused contracting and deforming rabbit hearts. A systematic comparison of these electrophysiological parameters in contracting and Blebbistatin-uncoupled conditions showed, on average, 27 ± 5% (N=5 hearts) shortening of APD in contracting hearts as compared to Blebbistatin-uncoupled hearts. Ventricular fibrillation frequency significantly increased in contracting hearts (13 ± 3.5 Hz) in comparison with Blebbistatin-uncoupled hearts (8 ± 1.5 Hz)

Optical mapping of contracting hearts

Optical mapping is a widely used tool to record and visualize the electrophysiological properties in a variety of myocardial preparations such as Langendorff-perfused isolated hearts, coronary-perfused wedge preparations, and cell culture monolayers. Motion artifact originating from the mechanical contraction of the myocardium creates a significant challenge to performing optical mapping of contracting hearts. Hence, to minimize the motion artifact, cardiac optical mapping studies are mostly performed on non-contracting hearts, where the mechanical contraction is removed using pharmacological excitation–contraction uncouplers. However, such experimental preparations eliminate the possibility of electromechanical interaction, and effects such as mechano-electric feedback cannot be studied. Recent developments in computer vision algorithms and ratiometric techniques have opened the possibility of performing optical mapping studies on isolated contracting hearts. In this review, we discuss the existing techniques and challenges of optical mapping of contracting hearts

Enhanced photocatalytic degradation of acetaminophen from wastewater using WO3/TiO2/SiO2 composite under UV–VIS irradiation

peer-reviewedThe full text of this article will not be available in ULIR until the embargo expires on the 26/8/2019This study investigates the photocatalytic degradation of acetaminophen (Ace) from synthetic wastewater by individual TiO2, TiO2/SiO2 and/or WO3/TiO2/SiO2 composite under UV-VIS illumination. To characterize changes in their morphology and crystal structures before and after treatment, Χ-ray diffraction (ΧRD), Fourier transform infrared spectroscopy (FTIR) , DRS UV-VIS absorption spectra, Brunaer-Emmer-Teller (BET) and scanning electron microscopy (SEM) techniques were used. The effects of varying loading ratios of the WO3 on the TiO2/SiO2 composite for Ace degradation were studied. Operating parameters such as initial concentration, reaction time, dose of photocatalyst and pH were tested. Degradation by-products were also presented. It is found that the photodegradation performance of the WO3/TiO2/SiO2 composite as a photocatalyst in this study could be enhanced by optimizing the loading ratio of the WO3. About 3% (w/w) of WO3/TiO2/SiO2 was found to improve the degradation of Ace from 33% to 95% at the same initial concentration of 5 mg/L. The resulting oxidation by-products included hydroquinone and 1,4-benzoquinone. Under the same conditions, the result of photocatalytic degradation by the 3% (w/w) of WO3/TiO2/SiO2 composite was significantly higher (95%) than that by the individual TiO2/SiO2 (42%) and/or by the TiO2 alone (33%). Under optimized conditions (1.5 g/L; 3% (w/w) of WO3/TiO2/SiO2 composite; pH 9; 4 h of reaction time), 95% of Ace removal with an initial concentration of 5 mg/L could be attained. However, the treated effluents still could not meet the discharge standard of less than 0.2 mg/L set by China’s and US legislation. This indicates that further subsequent treatment like biological processes is still necessary for completing the removal of target pollutant from the wastewater samples

Discharge mechanism in CO2: A study on possible occurrence of secondary discharges caused by field distortion during streamer or leader propagation

Since the introduction of SF6 in the 1950s, gas-insulated high voltage circuit breakers and Gas-insulated switchgear (GIS) have improved considerably, in particular concerning required drive energy for operation, compactness, and reliability. Nevertheless, high voltage insulation design has become increasingly challenging in recent years. Customer demands for reducing the physical footprint of HV equipment has led to an increase in operational field stress and therefore, much higher pressure on tolerances and increased susceptibility to defects. Dielectric design is based on how electrostatic fields are distributed and how much stress they can generate. In the course of conducting the intensive theoretical and experimental investigations on the dielectric design of insulation systems applied to high voltage power and pulsed power applications, it is becoming necessary to consider the influence of phenomena that have not been considered before. On top of that, as SF6 is one of the greenhouse gases listed in the Kyoto Protocol, SF6 usage regulations have been implemented in many industries. In Europe, SF6 is regulated under the F-Gas directive, which bansor restricts its use for several purposes. Several studies have indicated that CO2 is a viable alternative to SF6 for the transmission and distribution of electricity.In this context, this project aims to investigate a potential new phenomenon, theoccurrence of secondary discharges caused by propagating streamer or leader discharges in HV gas insulation. Learning more about such phenomena can help us improve the dielectric design or perhaps explain the occurrence of breakdowns reported in high voltage equipment for which no obvious cause could be found. Specifically, CO2/O2 mixtures will be studied, and its results compared to SF6. Breakdown in gaseous insulation is caused by propagating discharges that are external in ambient air, e.g. on a bushing, or inside high-pressure insulation, e.g. across the surface of a GIS insulator. During the propagation of such discharges and flashovers (streamer or leader), transient electric field enhancement may occur, leading the local fields to exceed the inception fields at other locations. This can result in secondary discharges.Dielectric experiments using Image Intensifier and Photomultiplier tubes (PMT)have been conducted at three different pressure ranges; SF6 and CO2/O2 were selected as the insulation mediums. A negative polarity electric field is expected to trigger the secondary discharge. An analysis of images obtained from optical investigations and time lag records obtained from PMT signals suggested that secondary discharges can occur at low pressures (0.2MPa) in both SF6 and CO2/O2. At higher pressures (0.4 to 0.6MPa), no secondary discharges were detected. The reason for this is that, at higher pressures, the breakdown field is higher leading to a faster propagation of discharge across that gap. Hence, the formative time lag of the discharge is very short (some 100푛푠 or less) and this short time is not sufficient for secondary discharge inception.Electrical Engineering | Electrical Power Engineerin

High-Resolution Optical Measurement of Cardiac Restitution, Contraction and Fibrillation Dynamics in Beating versus Blebbistatin-uncoupled Isolated Rabbit Hearts

Optical mapping is a high-resolution fluorescence imaging technique, that uses voltage- or calcium-sensitive dyes to visualize electrical excitation waves on the heart surface. However, optical mapping is very susceptible to the motion of cardiac tissue, which results in so-called motion artifacts in the fluorescence signal. To avoid motion artifacts, contractions of the heart muscle are typically suppressed using pharmacological excitation-contraction uncoupling agents, such as Blebbistatin. The use of pharmacological agents, however, may influence cardiac electrophysiology. Recently, it has been shown that numerical motion tracking can significantly reduce motion-related artifacts in optical mapping, enabling the simultaneous optical measurement of cardiac electrophysiology and mechanics. Here, we combine ratiometric optical mapping with numerical motion tracking to further enhance the robustness and accuracy of these measurements. We evaluate the method's performance by imaging and comparing cardiac restitution and ventricular fibrillation (VF) dynamics in contracting, non-working versus Blebbistatin-arrested Langendorff-perfused rabbit hearts ($N=10$). We found action potential durations (APD) to be, on average, $25 \pm 5 \%$ shorter in contracting hearts compared to hearts uncoupled with Blebbistatin. The relative shortening of the APD was found to be larger at higher frequencies. VF was found to be significantly accelerated in contracting hearts, i.e., $9 \pm 2 Hz$ with Blebbistatin and $15 \pm 4 Hz$ without Blebbistatin ($N=10$ hearts), and maintained a broader frequency spectrum. In contracting hearts, the average number of phase singularities was $N_{PS} = 11 \pm 4$ compared to $N_{PS} = 6 \pm 3$ with Blebbistatin during VF on the anterior left ventricular surface. VF inducibility was reduced with Blebbistatin. We found the effect of Blebbistatin to be concentration-dependent and reversible by washout. Aside from the electrophysiological characterization, we also measured and analyzed cardiac motion. Our findings may have implications for the interpretation of optical mapping data, and highlight that physiological conditions, such as oxygenation and metabolic demand, must be carefully considered in ex vivo imaging experiments

Optical mapping of contracting hearts.

Optical mapping is a widely used tool to record and visualize the electrophysiological properties in a variety of myocardial preparations such as Langendorff-perfused isolated hearts, coronary-perfused wedge preparations, and cell culture monolayers. Motion artifact originating from the mechanical contraction of the myocardium creates a significant challenge to performing optical mapping of contracting hearts. Hence, to minimize the motion artifact, cardiac optical mapping studies are mostly performed on non-contracting hearts, where the mechanical contraction is removed using pharmacological excitation-contraction uncouplers. However, such experimental preparations eliminate the possibility of electromechanical interaction, and effects such as mechano-electric feedback cannot be studied. Recent developments in computer vision algorithms and ratiometric techniques have opened the possibility of performing optical mapping studies on isolated contracting hearts. In this review, we discuss the existing techniques and challenges of optical mapping of contracting hearts