Conduction mechanism in oxide films on ferrous alloys studied by impedance spectroscopy in symmetrical and asymmetrical configurations

The electrical and electrochemical properties of the oxide films formed on Fe–25%Cr–x%Mo (x=0, 5 and 10) alloys by polarisation at ?0.8–0.2 V vs. SHE in a 0.1 M Na₂B₄O₇ electrolyte at 200 and 300 °C are characterised by impedance measurements in both asymmetrical (alloy|oxide|electrolyte) and symmetrical (alloy|oxide|metal) configurations. The impedance magnitude at low frequencies in the symmetrical configuration has been found to be ca. more than one order of magnitude smaller than that in the asymmetrical configuration, indicating that the oxide films are mixed conductors with predominant electronic conductivity. The impedance spectra in both configurations comprised two time constants. The high-frequency time constant is ascribed to the electronic properties of the space-charge layer in the oxide, whereas the low-frequency time constant is associated with the solid-state transport of point defects. Kinetic parameters characterising the reactions of defect generation and consumption are estimated by fitting the equations of the Mixed-Conduction Model proposed earlier to the experimental impedance spectra in both configurations.     

Attenuation of ECG voltage in cirrhotic patients.

Two patients with cirrhosis (CIR), ascites (ASC), and peripheral oedema (PEROD) are presented. They were followed for many years, had multiple hospital admissions and clinic evaluations, had repeated laboratory testing, and many ECGs recorded. As their condition worsened, they developed attenuation of the ECG voltage (ATTECGV), which was more pronounced during intervals of increased fluid overload. Attenuation of the ECG voltage was decreased at times of successful diuresis and amelioration of PEROD, while abdominal paracenteses for ASC did not have any influence on the ATTECGV, suggesting that ATTECGV in patients with CIR is due to the associated PEROD, and not to ASC.     

Current Distribution in Skeletal Muscle Activated by Functional Electrical Stimulation: Image-Series Formulation and Isometric Recruitment Curve

The present work develops an analytical model that allows one to estimate the current distribution within the whole muscle and the resulting isometric recruitment curve (IRC). The quasistatic current distribution, expressed as an image series, i.e., a collection of properly weighted and shifted point-source responses, outlines an extension for more than three layers of the classical image theory in conductive plane-stratified media. Evaluation of the current distribution via the image series expansions requires substantially less computational time than the standard integral representation. The expansions use a unique recursive representation for Green's function, that is a generic characteristic of the stratification. This approach permits one to verify which of the tissue electrical properties are responsible for the current density distribution within the muscle, and how significant their combinations are. In addition, the model permits one to study the effect of different electrode placement on the shape and the magnitude of the potential distribution. A simple IRC model was used for parameter estimation and model verification by comparison with experimentally obtained isometric recruitment curves. Sensitivity of the model to different parameters such as conductivity of the tissues and activation threshold was verified. The resulting model demonstrated characteristic features that were similar to those of experimentally obtained data. The model also quantitatively confirmed the differences existing between surface (transcutaneous) and implanted (percutaneous) electrode stimulation. © 2000 Biomedical Engineering Society. PAC00: 8719Ff, 8754Dt, 8719Nn, 8717Nn     

Simulation of propagation along an isolated skeletal muscle fiber in an isotropic volume conductor

This paper describes a model of the frog skeletal muscle fiber that includes the effects of the transverse tubular system (T system) on propagation. Uniform propagation on an isolated fiber suspended in Ringer’s solution or in air is simulated by placing the cylindrical fiber model in a concentric three-dimensional isotropic volume conductor. The current through the T system outlets at the sarcolemmal surface is comparable in magnitude to the sarcolemmal current density, but is of opposite polarity. When it is added to the sarcolemmal current, the resulting triphasic waveform has a 100% increase in the leading positive peak, a 50% reduction in the negative peak, and more than 60% reduction in the trailing positive peak. As a result the tubular output current causes a reduction in the conduction, velocity, a decrease in the maximum rate of rise of the action potential, and an important modification of the extracellular potential. Compared to an isolated fiber in a large volume of Ringer’s solution, uniform propagation within a 2-μm-thick volume conductor annulus is slowed down from 1.92 to 0.72 m/s, and the extracellular potential is increased from 1 to 108 mV peak to peak, in agreement with published experimental measurements.     

磺酸型聚氨酯离聚物的离子导电性能

本文以多种聚醚为软段，二异氰酸酯（ＭＤＩ和ＴＤＩ）为硬段，合成了多嵌段聚醚聚氨酯，以此聚氨酯为基材，与ＮａＨ及１，３－丙碳酸内酯反应，进一步合成了一系列不同离子化程度的阴离子型碳化聚氨酯离聚物，用交流阻抗谱仪测定了样品的阻抗谱，由此计算出样品的离子电导率。研究结果表明其他条件相同时，以聚乙二醇（ＰＥＧ）为软段的样品具有较高的离子电导率；以聚环氧丙烷（ＰＰＯ）为软段的样品次之，以聚四氢呋喃（ＰＴＭＯ）为软段的样品最低，对于离子化程度不同的聚氨酯离聚物以金属离子和烷氧单元之比为０．０５时导电性能最好。阳离子为Ｌｉ＋和Ｎａ＋的样品具有相近的离子电导率。     

自制心电图机导联线摆放装置

目的 解决心电图机导联线经常被接错、缠绕和污染等问题。方法 自制心电图机导联线摆放装置。本文描述了该装置的制作过程、使用方法和功能特点。结果 该装置完全解决了上述问题，同时，也延长了心电图机导联线寿命、减少了心电图机电极吸球和电极夹容易丢失的现象、提高了工作效率，又可起到一个心电图机防尘罩的作用。结论 该装置制作简单，成本低廉，使用方便，功能多，值得临床推广应用。     

Spatial relationship of source localizations in patients with focal epilepsy: Comparison of MEG and EEG with a three spherical shells and a boundary element volume conductor model

Epilepsy surgery is an option for patients with pharmacoresistant focal epilepsies, but it requires a precise focus localization procedure. Magnetoencephalography (MEG) and electroencephalography (EEG) can be used for analysis of interictal activity. The aim of this prospective study was to compare clusters of source localization results with MEG and EEG using a three spherical shells (3SS) and a boundary element method (BEM) volume conductor model. The study was closed when 100 patients met the inclusion criteria. Simultaneous MEG and EEG were recorded during presurgical evaluation. Epileptiform signals were analyzed using an equivalent current dipole model. Centroids of source localizations from MEG, EEG, 3SS, and BEM in their respective combinations were compared. In a 3SS model, MEG source localizations were 5.6 mm inferior to those obtained by EEG, while in a BEM model MEG source localizations were 6.3 mm anterior and 4.8 mm superior. The mean scattering of source localizations between both volume conductor models was 19.5 mm for EEG and 9.6 mm for MEG. For MEG no systematic difference between BEM and 3SS source localizations was found. For EEG, source localizations with BEM were 5.9 mm posterior and 11.7 mm inferior to those determined using 3SS. No differences were found between the 46 temporal and the 54 extratemporal lobe epilepsy patients. The observed systematic differences of source localizations of epileptic spikes due to the applied source signal modality and volume conductor model should be considered in presurgical evaluation when only one source signal and volume conductor model is available.     

Transparent indium-tin oxide electrode patterns for extracellular, multisite recording in neuronal cultures

Glass plates coated with transparent thin film conductors of indium-tin oxide (ITO), 100 nm thick and 10 microns wide, have been successfully used to record spike potentials from neuronal monolayer cultures. The material is non-toxic to mammalian spinal neurons and is stable under warm culture medium. Laser-deinsulated recording craters that expose 100 mu m2 of ITO yield impedances of 8-10 M omega at 1 kHz with noise levels of 40 muV. Conventional gold plating of the craters reduces these impedances to below 3 M omega. The material is easily etchable and sputtered glass plates of high quality are commercially available at relatively low cost. The high light transmittance of ITO makes the conductors essentially invisible and allows unobstructed observation of circuit components in monolayer cultures. The introduction of ITO as a thin film microelectrode material should accelerate the construction of high density recording patterns that could exceed 400 microelectrodes per mm2.     

On the magnetic field and the electrical potential generated by bioelectric sources in an anisotropic volume conductor

The electrical conductivity in biological tissue is often dependent on the direction of the fibres. In the paper the influence of this anisotropic nature on the electrical potential and magnetic field generated by a current dipole is studied analytically. Three different methods are discussed. The volume conductor is described by piecewise homogeneous compartments and the interfaces between compartments are either parallel or perpendicular to one of the principal axes. To illustrate the methods, the influence of the anisotropic nature is computed for a two-layered medium. It turns out that the influence on both the potential and the magnetic field cannot be ignored. However, for some commonly used models of the head and torso, a certain component of the magnetic field is not influenced by the anisotropy.