The effect of plunge electrodes during electrical stimulation of cardiac tissue

The mechanism for far-field stimulation of cardiac tissue is not known, although many hypotheses have been suggested. This paper explores a new hypothesis: the insulated plunge electrodes used in experiments to map the extracellular potential may affect the transmembrane potential when an electric field is applied to cardiac tissue. Our calculation simulates a 10-mm-diameter sheet of passive tissue with a circular insulated plunge electrode in the middle of it, ranging in diameter from 0.05 to 2 mm. We calculate the transmembrane potential induced by a 500-V/m electric field. Our results show that a transmembrane potential is induced around the electrode in alternating areas of depolarization and hyperpolarization. If the electric field is oriented parallel to the myocardial fibers, the maximum transmembrane potential is 89 mV. A layer of fluid around the electrode increases the transmembrane potential. We conclude that plunge electrodes may introduce artifacts during experiments designed to study the response of the heart to strong electric shocks.     

A closed-loop electrical stimulation system for cardiac cell cultures

An integrated electrical stimulation and recording system was designed for closed-loop control and analysis of cardiac cultures on planar microelectrode arrays. Stimulated action potentials from HL-1 clonal myocyte cultures were digitized, stimulation artifacts were removed using nulling and filtering methods, and analysis was performed to determine stimulation efficacy in real time. Results of this analysis were used to determine future stimulation waveform parameters such as polarity, amplitude, pulse duration, and rate or pattern. Algorithms were designed utilizing real-time analysis and control to maintain a desired electrophysiological response of the culture, such as an arbitrary capture fraction value. This paper presents the hardware and software design of the stimulus pulse circuitry, artifact extraction, analysis, and control components of the system. Applications of this technology include the study of cardiac cell physiology, improving the speed and accuracy of traditional open-loop stimulation protocols, pharmacological screening, and improving the performance of biosensors based on sensing electrical activity in cardiac cultures.     

Functional electrical stimulation of the latissimus dorsi musclefor use in cardiac assist

Direct and nondirect nerve stimulation modes of the thoraco-dorsal nerve (TDN) leading to the latissimus dorsi muscle (LDM) were evaluated by using nerve cuff electrodes (NCE) and intramuscular electrodes (IME), respectively. Following electrode implantation, the LDM was chronically stimulated for two months to induce muscle transformation to oxidative, fatigue-resistant type I muscle fibers. Threshold and impedance values were measured regularly to establish the stability of the implants. The LDM was then dissected, shaped into a ventricle, subjected to a hydraulic load and stimulated using a controlled-voltage pulse-train stimulator with adjustable parameters. Electrical input and hydraulic output variables were measured to obtain the recruitment characteristics and to compare the efficiency of the two types of electrodes. Results indicate a tradeoff between the NCE's lower threshold, higher recruitment, and lower energy consumption at saturation, and the IME's greater mechanical stability and better long-term reproducibility.     

High-frequency electrical stimulation of cardiac cells and application to artifact reduction

A novel modality for the electrical stimulation of cardiac cells is described. The technique is based on HF stimulation-burst of HF (1-25 kHz) biphasic square waves-to depolarize the cells and trigger action potentials (APs). HF stimulation was demonstrated in HL-1 cardiomyocyte cultures using microelectrode arrays, and the underlying mechanisms were investigated using single-cell model simulations. Current thresholds for HF stimulation increased at higher frequencies or shorter burst durations, and were typically higher than thresholds for single biphasic pulses. Nonetheless, owing to the decreasing impedance of metal electrodes with increasing frequencies, HF bursts resulted in reduced electrode voltages (up to four fold). Such lowered potentials might be beneficial in reducing the probability of irreversible electrochemical reactions and tissue damage, especially for long-term stimulation. More significantly, stimulation at frequencies higher than the upper limit of the AP power spectrum allows effective artifact reduction by low-pass filtering. Shaping of the burst envelope provides further reduction of the remaining artifact. This ability to decouple extracellular stimulation and recording in the frequency domain allowed detection of APs during stimulation-something previously not achievable to the best of our knowledge.     

Suppressing the surface field during transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is used commonly as both a diagnostic tool and as an alternative to electric shock therapy for the treatment of clinical depression. Among the clinical issues encountered in its use is the mitigation of accompanying pain. The objective becomes one of minimizing the induced surface field while still achieving the target field objective. Three techniques discussed for realizing this end are 1) placing a conducting shield over a portion of the central target region, 2) using supplementary coils of opposite polarity in tandem with the primary field, and 3) opening the core angle to distribute the field. Option (3) shows the greatest promise for reducing the ratio of the maximum surface field to the induced target field.     

The electrical stimulation of bone healing

A brief introduction to the structure and electrical properties of bone is followed by an account of investigations into bone growth stimulation using small electric currents. Clinical work using this method is then summarized. The effects of electric and magnetic fields on bone are introduced, and clinical applications of the relevant techniques are described. The review concludes with examples of investigations into the fundamental aspects of the effects of electrical phenomena on bone. It is concluded that although the clinical applications of electrical stimulation are of value in the treatment of nonunion, the fundamental processes occurring remain obscure.     

Effects of surface preparation on the electrical and reliabilityproperties of ultrathin thermal oxide

A new wafer cleaning procedure has been developed for ultrathin thermal oxidation process (⩽50 Å). It consists of a conventional RCA clean and a two-dip step, first in diluted HF and then in a methanol/HF solution, with no final DI water rinse. The effectiveness of this cleaning process has been compared to other commonly used cleaning methods, based on the dielectric integrity of the ultrathin thermal oxide grown. It has been found that this two-dip method produces oxides with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxide. Furthermore, this new procedure increases dielectric breakdown field, E_bd and charge-to-breakdown, Q_bd (both intrinsic and defect-related values) of ultrathin oxides. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen and the reduced surface micro-roughness     

Information obtained from the surface profile of a cut single-modefiber

This paper investigated the fiber-end surface modulation by atomic force microscopy (AFM) and optical profilometry after a careful cross cleavage with a diamond. The image of the surface allows to see the different parts of the fiber. The cladding appears above the mean level whereas the core appears depressed. This profile is tightly connected to the stress profile, itself induced by the doping field and the drawing conditions. Magnification of the core shows fluctuations of the glass structure at the scale of 25 nm with some of ≈80 nm. This method seems to be suitable to study fiber defects but is still difficult to perform due to the small size of the sample (φ=125 μm) and the dependence of the surface profile with the care to cleave the fiber. However, due to the better spatial resolution of the AFM measurements compared to the optical profilometry, itself larger than the one of photoelasticity measurements, it was possible to conclude that the axial stress exhibits a discontinuity at the core cladding interface and not a peak at the center of the core     

The control of the electrical conductivity of copper phosphate glasses by the admixture of chlorine during preparation

The electrical conductivity of copper phosphate glasses depends on the relative concentrations of Cu⁺ and Cu²⁺ ions and it is found that by adding cupric chlorine to the melt when the glass is formed the added chlorine which acts as an oxidizing agent alters the ratio of the concentration of Cu⁺ and Cu²⁺ and thus the conductivity. The change in the concentration of Cu²⁺ ions in the glasses is determined by infrared spectroscopic measurements and by studies of electron spin resonance, and the change in the Cu⁺ ion concentration is inferred since the total copper content in the glasses is held constant. It is suggested that the principle of adding a component in the form of a strong oxidizing agent to the glass to alter the reduced valency ion ratio may be of general application in the control of electrical conductivity in transition metal ion glasses.     

Electric field stimulation of cardiac myocytes during postnatal development

Studies on cardiac cell response to electric field stimulation are important for understanding basic phenomena underlying cardiac defibrillation. In this work, we used a model of a prolate spheroidal cell in a uniform external field (Klee and Plonsey, 1976) to predict the threshold electric field (ET) for stimulation of isolated ventricular myocytes of rats at different ages. The model assumes that ET is primarily determined by cell shape and dimensions, which markedly change during postnatal development. Neonatal cells showed very high ET, which progressively decreased with maturation (experimental mean values were 29, 21, 13, and 5.9 and 6.3 V/cm for 3-6, 13-16, 20-21, 28-35, and 120-180 day-old rats, respectively, P < 0.001; theoretical values were 24, 18, 11, 9, and 6 V/cm, respectively). Estimated maximum membrane depolarization at threshold (deltaVT approximately equals 35 mV, under our experimental conditions) was reasonably constant during development, except for cells from 1-mo-old animals, in which deltaVT was lower than at other ages. We conclude that the model reasonably correlates ET with cell geometry and size in most cases. Our results might be relevant for the development of efficient procedures for defibrillation of pediatric patients.     

The effect of electrical anisotropy during magnetoacoustic tomography with magnetic induction

Magnetoacoustic tomography with magnetic induction (MAT-MI) is a technique for imaging electrical conductivity in tissue. A time-varying magnetic field induces currents that interact with a static magnetic field to produce a Lorentz force, initiating ultrasonic waves. The goal of this communication is to examine the effect of anisotropy during MAT-MI.     

Theoretical determination of the current density distributions inhuman vertebral bodies during electrical stimulation

Electrical stimulation with a 60 kHz sinewave input signal, supplied via external plate electrodes on the skin surface, is presently being studied as a treatment for human systemic osteoporosis. In this paper, Maxwell's equations were solved for voltage and current density values at nodal points in a three-dimensional, anatomically-based, finite element grid model of the human trunk constructed from T5 to L5. Based on the dose response results from Luessenhop's castrated Sprague Dawley breeder rat experiment and our theoretical determination, the magnitude of the input current to the electrodes necessary to induce a response in the human vertebral body was determined. Four different electrode systems in current clinical use were evaluated, and the optimal input current determined. In addition, the effect of subcutaneous fat was studied.     

The effect of surface preparation on voltage threshold in liquid crystal phase-change cells

The threshold behaviour of cholesteric to nematic phase-change cells with homogeneous and homeotropic surface alignment is compared. The former raises, the latter lowers, the threshold voltage. Departures from predicted linearity are seen when the cholesteric pitch is comparable with the film thickness.     

Field distributions in the rat tibia with and without a porousimplant during electrical stimulation: a parameteric modeling

Expeditious post-operative ingrowth of bone is necessary for clinically successful fixation of porous joint prostheses. Electrical or electromagnetic fields to stimulate bone growth into porous implants have been used; however, they produced nonconvincing data. This was partially attributable to the lack of quantification of the localized electric fields produced in the pores of the implants. Therefore, this study set out: i) to quantify the local electric field values induced into the surface pores of nonconducting implants by "capacitive" coupling and to determine the magnitude of the macroscopically applied capacitively coupled electrical currents to induce specific electric field amplitudes in the pores, ii) to identify the important dielectric properties of the implant-tissue interface, and iii) to create the basis for successfully applying electrical fields in an animal model to stimulate bone ingrowth. A finite element method was used to calculate the electric field gradients and current densities present in a rat tibia modeled with a porous intramedullary implant when capacitively stimulated. Results indicated that while the current density in the pores are reduced in comparison to the region just outside the pore by about one order of magnitude, a significant current density still exists in the pore region. Furthermore, the presence of the implant increases the current densities in the trabecular bone while decreasing these values in the cortical bone. Replacing the trabecular bone in the pore by saline increases the current density in the pore by three-fold, but decreases the voltage gradient by a similar factor.     

The effect of surface treatment on the electrical properties ofmetal contacts to boron-doped homoepitaxial diamond film

Both doped and undoped homoepitaxial diamond films were fabricated using microwave plasma-enhanced chemical vapor deposition (CVD). The conductivity of the diamond film is strongly affected by the surface treatment. In particular, exposure of film surface to a hydrogen plasma results in the formation of a conductive layer which can be used to obtain linear (ohmic) I-V characteristics of the Au/diamond contacts, regardless of the doping level. It is shown how the proper chemical cleaning of the boron-doped homoepitaxial diamond surface allows the fabrication of Au-gate Schottky diodes with excellent rectifying characteristics at temperatures of at least 400°C     

制备过程中对VO2薄膜热致相变光电性能的控制

本文利用真空还原Ｖ２Ｏ５的方法制备出优质对ＶＯ２薄膜;研究了不同真空还原时间ＶＯ２薄膜热致相变过程中光电性能的影响;利用ＸＰＳ、ＸＲＤ对薄膜的化学状态和结晶状态进行了研究。制备的薄膜高／低 电阻变化最大达到三个数量级,９００ｎｍ处的光学透过率在相变前后改变了４０％左右,热致相变性能优良。讨论了不同的真空还原时间下ＶＯ２薄膜热滞回线的宽度、相变温度点以及高低温光透射性能。最后给出了最佳真空还原时间。     

制备过程中对VO_2薄膜热致相变光电性能的控制

本文利用真空还原V2 O5的方法制备出优质对VO2 薄膜 ;研究了不同真空还原时间VO2 薄膜热致相变过程中光电性能的影响 ;利用XPS、XRD对薄膜的化学状态和结晶状态进行了研究。制备的薄膜高 /低温电阻变化最大达到三个数量级 ,90 0nm处的光学透过率在相变前后改变了 40 %左右 ,热致相变性能优良。讨论了不同的真空还原时间下VO2 薄膜热滞回线的宽度、相变温度点以及高低温光透射性能。最后给出了最佳真空还原时间。     

Diffraction coefficient of a conducting wedge loaded with a dielectric slab on the illuminated surface

The asymptotic solution for the diffraction of anE-polarized plane incident electromagnetic wave by a conducting wedge, whose illuminated surface is loaded with a dielectric slab of small thickness and relative permittivity, is employed to derive a ray optical diffraction coefficient for the edge.     

Using electrical impedance to predict catheter-endocardial contact during RF cardiac ablation

During radio-frequency (RF) cardiac catheter ablation, there is little information to estimate the contact between the catheter tip electrode and endocardium because only the metal electrode shows up under fluoroscopy. We present a method that utilizes the electrical impedance between the catheter electrode and the dispersive electrode to predict the catheter tip electrode insertion depth into the endocardium. Since the resistivity of blood differs from the resistivity of the endocardium, the impedance increases as the catheter tip lodges deeper in the endocardium. In vitro measurements yielded the impedance-depth relations at 1, 10, 100, and 500 kHz. We predict the depth by spline curve interpolation using the obtained calibration curve. This impedance method gives reasonably accurate predicted depth. We also evaluated alternative methods, such as impedance difference and impedance ratio.