Current Sheaths Research Articles

Right-sided approach to left bundle branch area pacing combined with atrioventricular node ablation in a patient with persistent left superior vena cava and left bundle branch block: a case report

BackgroundLeft bundle branch area pacing (LBBAP) is an alternative to right ventricular (RV) and biventricular (BiV) pacing in patients scheduled for pace and ablate treatment strategy. However, current delivery sheaths are designed for left-sided implantation, making the right-sided LBBAP lead implantation challenging.Case presentationWe report a case of a right-sided LBBAP approach via right subclavian vein in a heart failure patient with a persistent left superior vena cava scheduled for pace and ablate treatment of refractory atrial flutter. To enable adequate lead positioning and support for transseptal screwing, the delivery sheath was manually modified with a 90-degree curve at the right subclavian vein and superior vena cava junction to allow right-sided implantation. The distance between the reshaping point and the presumed septal region was estimated by placing the sheath on the body surface under fluoroscopy. With the reshaping of the delivery sheath, we were able to achieve LBBAP with relatively minimal torque. Radiofrequency ablation of the atrioventricular node was performed the next day and the pacing parameters remained stable in short-term follow-up.ConclusionWith the modification of currently available tools, LBBAP can be performed with the right-sided approach.

His bundle pacing: Tips and tricks.

His bundle (HB) pacing is an established modality for achieving physiological pacing with a low risk of long-term lead-related complications. The development of specially designed lead and delivery tools has improved the feasibility and safety of HB pacing (HBP). Knowledge of the anatomy of HB region and the variations is essential for successful implantation. Newer delivery systems have further improved procedural outcomes. Challenging implant cases can be successfully performed by reshaping the current sheaths, using "sheath in sheath" technique or "two-lead implantation technique." Special attention to the lead parameters at implant, programming, and follow-up is necessary for successful long-term outcomes with HBP. Widespread use of HBP by electrophysiologists and further advances in dedicated delivery systems and leads are essential to further improve the effectiveness of the implantation.

Modelling of multistage plasma focus using Sing Lee’s model

A generalized model for the multistage sequential plasma focus (PF) has been developed and used. This model is derived from Lee model, where the phases are adapted to describe several plasma current sheaths (PCS) that produce the consequence focus events. The model simulates the performance of such devices by cyclic five phases to consider all the states of the formed current sheaths. Comparison shows a remarkable agreement of the measured current with that computed from the multistage model code in the case of dual stage pinch PF. Using the model, the sequential focus events could be optimized, and the effective parameters could be investigated.

About the equilibrium and stability of non-electroneutral current sheaths

In this paper, we prove the necessity of using the Cauchy problem, i.e., initial value problem, for solving the equilibrium (steady state) current sheet. In this connection, it appears that equilibrium current sheaths exhibit structural instability.It is emphasized that during examination of the stability of a current sheath, the kinetic equation solution uses the angle integration technique (unlike the method of paths applied earlier). Therefore, in contrast to previous procedures of examination, this method demonstrates the possibility of studying tearing instability and also all the remaining eigenmodes of instability of a current sheath. The growth rate of tearing instability exceeds the values adopted previously by an order of magnitude or more. At this stage, we realize examination shortwave eigenmodes only.

Initial experience with the glidesheath slender for transradial coronary angiography and intervention: A feasibility study with prospective radial ultrasound follow‐up

The aim of this study is to evaluate the feasibility and safety of the Glidesheath Slender in routine transradial (TR) coronary angiography and intervention. In recent years, The TR approach has gained in popularity because of several advantages such as reduced vascular access site complications and immediate patient mobilization. Procedural success has been further improved through technological innovations and the development of less invasive devices. The Glidesheath Slender (Terumo, Tokyo, Japan) is a new dedicated radial sheath with a thinner wall and hydrophilic coating. It combines an inner diameter compatible with 6Fr guiding catheter with an outer diameter close to current 5Fr sheaths. Its use has the potential to decrease invasiveness and access site complications during TR procedures. A total of 114 consecutive patients undergoing TR coronary angiography and/or PCI using the Gidesheath Slender were included in a prospective single-center feasibility and safety study. Procedural success was 99.1% with only one case requiring conversion to femoral access. There were six minor hematomas but none of the patients experienced major vascular complications. The rate of symptomatic radial spasm was 4.4%. No case of major sheath kinking was noted. Doppler ultrasound examination of the radial artery at 1 month follow-up was available in 113/114 patients with only one case of radial artery occlusion (RAO) (0.88%). Routine use of the Glidesheath Slender for TR coronary angiography and interventions is safe and feasible with a high rate of procedural success and a low rate of RAO. © 2013 Wiley Periodicals, Inc.

Current halo structures in high-current plasma experiments: θ-pinch

Experimental data elucidating mechanisms for halo formation in θ-pinch discharges are presented and discussed. The experiments were performed with different gases (H2, D2, He, and Ar) in a theta-pinch device with a porcelain vacuum chamber and an excitation coil 15 cm in diameter and 30 cm in length. The stored energy, the current in the excitation coil, and the current half-period were W = 10 kJ, I = 400 kA, and T/2 = 14 μs, respectively. It is found that the plasma rings (halos) surrounding the pinch core arise as a result of coaxial pinch stratification due to both the excitation of closed currents (inductons) inside the pinch and the radial convergence of the plasma current sheaths produced after the explosion of T-layers formed near the wall in the initial stage of the discharge. It is concluded that halo structures observed in pinches, tokamaks, and other high-current devices used in controlled fusion research have the same nature.

Advances in device lead extraction.

The removal of chronically implanted pacemaker and defibrillator leads has evolved over the past 20 years into an integral part of the medical and surgical practice of electrophysiology. It is the basis for management of device-related complications. Lead removal has progressed from just pulling, to a sophisticated procedure based on telescoping sheaths, counterpressure, and countertraction. Current telescoping sheaths have a powered tip (laser or electrosurgical) for more efficient extirpation of leads from encapsulating fibrous tissue. The management of a device infection exemplifies the spectrum of procedures ranging from debridement of inflammatory tissue to transvenous, transatrial, or epicardial lead reimplantation (care must be given to the consequences of chronic implant complications such as superior vein occlusion). The magnitude of these lead removal procedures ranges from a transvenous procedure to cardiopulmonary bypass removing a pannus of infected material. Current procedure related mortality is less than 0.2% at experienced centers.

The physics of fastZpinches

The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizing the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 36 figures and more than 300 references.

Plasma focus characteristics using stainless steel anode

In a low energy (2.3 kJ) Mather-type plasma focus with stainless steel anode, neutron and x-ray emission is investigated by employing time-integrated and time resolved detectors. A neutron yield of 3.5 × 108 is observed, which is almost double the yield when a copper anode is used. It is speculated that a low sputtering yield of the anode material lowers the impurity concentration in the plasma and thus enhances the neutron yield. One may therefore conclude that a proper choice of electrode material is essential to achieve enhanced radiation yield from plasma focus devices. At a pressure of 2.0 mbar, the neutron yield is found to be the highest and almost isotropic. Further, multiple foci are also observed. The neutron fluence isotropy and the high yield are attributed to trapping of magnetic flux lines and of energetic deuterons between the two current sheaths.

Magnetic probe measurements of the initial phase in a plasma focus device

Measurements with magnetic probes performed in the initial phase of a plasma focus device (30 kV, ) in the pressure range 0.5 - 5 mbar deuterium are presented, and an interpretation of the obtained signals is given, which includes a procedure for disentangling the effect of variations in the discharge current from the signals. Thick current sheaths, essentially filling all the space between the electrodes, are shown to form at all pressures, travelling radially outwards at constant speeds of between 2.5 and 3.4 . Experimental confirmation of a theoretical prediction of distortions in the registered signals due to current exclusions by the probe's body is given, and evidence confirming the `inverse skin' effect is presented.

On the process of resistive heating instability and the formation of coronal loop structures

view Abstract Citations (8) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Process of Resistive Heating Instability and the Formation of Coronal Loop Structures Lou, Yu-Qing Abstract A cylindrical electric current sheath embedded in a coaxial magnetic flux rope is in an inductive, thermal, and mechanical equilibrium. The transport processes involved are assumed to be anomalous. Such a system is subject to a class of macroscopic resistive heating instabilities in addition to the known MHD mechanical, thermal, and tearing instabilities. The onset of the resistive heating instability within the sheath gives rise to various large-scale helical patterns of thermal perturbation winding along the background magnetic flux rope. These helical thermal structures roughly map out the general direction of the magnetic field lines within the sheath. In an idealized scenario, a solar coronal magnetic flux rope may consist of many coaxial current sheaths of different radii. The coupled development of the MHD resistive heating, mechanical, thermal, and tearing instabilities within such an ensemble of current sheaths may result in the appearance of compact X-ray loop patterns on virtually all spatial scales with various collective morphologies. We propose the resistive heating instability as an important elemental mechanism leading to the formation of compact X-ray loops in solar active regions. Publication: The Astrophysical Journal Pub Date: August 1992 DOI: 10.1086/171688 Bibcode: 1992ApJ...395..682L Keywords: Gamma Ray Astronomy; Magnetohydrodynamic Stability; Plasma Sheaths; Solar Corona; Solar X-Rays; Electric Current; Perturbation Theory; Solar Activity; Solar Magnetic Field; Solar Physics; MAGNETOHYDRODYNAMICS: MHD; SUN: CORONA; SUN: X-RAYS; GAMMA RAYS full text sources ADS | Related Materials (1) Erratum: 1993ApJ...404..418L

Coronal loops - Current-based heating processes

Based on new observations, a theoretical model of magnetic-field related heating processes in the solar corona is given. In this model, field-aligned currents are induced along coronal loops in thin current sheaths. Excitation of instabilities involving magnetic reconnection converts the energy associated with the current-related magnetic field directly into particle energy, where the heating process proceeds via short bursts corresponding to an intermittent disruption of the current sheath configuration. Because of the relatively low transverse thermal conduction, only a small fraction of the loop volume is heated to a much higher temperature than the average value. This is consistent with experimental observations of low filling factors of hot plasmas in coronal loops. Thus the model involves a repeated sequence of dynamic events taking into account the observed loop topology, the differential emission measure distribution in the 10 exp 6 - 10 exp 7 K range, the energy balance requirements in the loop, and the probable duty cycles involved in the heating processes.

Two-dimensional current density and temperature development in the return rail of an EM launcher with temperature-dependent properties

A method used to model the two-dimensional current and temperature development in the return rail of an electromagnetic launcher (EML) during launch, incorporating temperature-dependent electrical and thermal material properties, is presented. Due to these temperature dependencies and the nonlinearities they introduce, the derived equations must be solved numerically. Comparisons of the current and temperature responses are made with the results of a previously published constant-property model. This two-dimensional model duplicates the breech responses of one-dimensional analyses and, in addition, provides the detailed structure of the current and temperature sheaths. In particular, application of this model shows that the most severe gradients occur away from the breech, and that they are much in excess of those predicted by one-dimensional analyses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Current distribution during the breakdown in a coaxial electrode system

The breakdown stage in a coaxial electrode system (similar to Mather-type plasma focus) was studied in hydrogen for a wide range of pressures through the fast discharge of the energy stored in a parallel plate capacitor. A peak current Iep of 18.5 kA was reached in 60 ns for a 20 kV capacitor charge voltage, giving the typical initial current rise time obtained in normal plasma focus discharges. Thin current sheaths (≲2 mm thick) in the insulator region with current density ≳10 kA/cm2 were measured. These current sheaths always showed a well-defined filamentary structure with the number of filaments depending linearly on Iep , with an observed current limit per filament If depending on the pressure P as I2f∼1/P.

On the structure of plasma focus imploding current sheaths

An interpretation of the plasma density profiles of Plasma Focus radially imploding current sheaths is given in terms of strongly preionizing shocks. It is suggested that the preionizing process is essentially radiative in nature.

Self-similar motions in Z-pinch dynamics

New self-similar solutions of the equations of ideal magnetohydrodynamics for a cylindrically symmetric plasma carrying an axial current are presented. They describe the collapse of shock waves and cavities (hollow plasma liners) on the axis, the outward propagation of shock waves reflected from the axis, inverse Z-pinch flows and related phenomena. The current sheaths at the outer plasma boundary can (and, in fact, should) be included explicitly in these solutions. A comparison of the self-similar solutions with calculations based on the snowplow model show the limits of validity of the latter.

On the Boil-Off Time of Probe Surfaces in Plasmas

The time required for the melting of the surface of a glass-insulated probe inserted in a plasma is computed including the influence of plasma mass motion. This effect is relevant for probe measurements in moving current sheaths of electrical gas discharges. For dense plasma focus experiments, it is shown that the time of formation of a transition layer of evaporated material is shorter than the ion relaxation time in the plasma and the transit time of the current sheath by the probe position.

Electric current flow inside perineurial sheaths of mouse motor nerves.

Micro-electrodes were inserted inside the perineurial space to record external currents along the superficial nerve bundles of the triangularis sterni muscle of the mouse upon motor nerve stimulation. Two kinds of external currents were distinguished, the first circulating between neighbouring nodes of Ranvier in each fibre and the second circulating between the nodes and the motor endings. Ending-node current was caused by differences in the time course and the amplitude of the potential change at the endings and at the nodes, which depended in turn, on differences between their respective membrane conductances. The stretch of nerve over which ending-node current extended served to estimate that about eight to ten nodes of Ranvier supply the motor endings with depolarizing current.

Fine structure in current sheaths

The general, exact theory of a collisionless planar current sheath is developed with the constants of integration method. Every quantity depends on a single space variable x alone; electric field, current, and magnetic field are mutually orthogonal. Appropriate approximation methods can be developed to investigate the structure of the deviations from charge neutrality when the Debye distance d is much smaller than the sheath thickness; they appear either as local spatial electrostatic oscillations, whose wavelength is proportional to d as d → 0; or as space-charge regions whose size is comparable to the scale of the magnetic transition itself. The general criterion for the presence of such oscillations is given and the investigation of their structure is reduced to quadratures. In the simple case of two mono-energetic beams turned around by a magnetic field they are discussed in detail. If their amplitude vanishes where the field is nil, we recover Rosenbluth's profile ( 1); but the solution deviates slightly from neutrality near the turning points of the particle motions which, in general, are separated. The problem of confinement by an external magnetic field is treated in detail in the case where in the plasma the particles all move only in the x-direction with a Maxwellian distribution; there are no oscillations and the potential jump across the sheath diverges logarithmically as d → 0.

Fine structure in current sheaths: Bruno Bertotti, Laboratorio Gas Ionizzati, Laboratori Nazionali di Frascati del C. N. E. N., Frascati, Rome, Italy

Fine structure in current sheaths: Bruno Bertotti, Laboratorio Gas Ionizzati, Laboratori Nazionali di Frascati del C. N. E. N., Frascati, Rome, Italy