Transthoracic impedance to direct current discharge: effect of repeated countershocks.

The effect of repeated countershocks on transthoracic apparent impedance to direct current (dc) defibrillator discharges was studied. Repeated dc countershocks result in a progressive decrease in transthoracic apparent impedance that is dependent upon the time interval between countershocks. This decrease was significantly greater in the group of animals shocked at 3-min intervals compared to the groups shocked at 15-sec intervals (P less than 0.001) or at 1-min intervals (P less than 0.005). Since lowered impedance results in higher delivered current for the same energy setting on a defibrillator, this observation may help to explain the enhanced effectiveness of repeated countershocks in defibrillation. Plots of simultaneous current against voltage during transthoracic dc discharge revealed that the current lagged slightly behind voltage during the rising phase of the recording, but that current and voltage were nearly simultaneous during the falling phase. This effect appears to be similar to an ionization phenomenon in that the effective impedance asymptotically approaches a lower value with increasingly applied voltage. This might explain why transthoracic impedance is highest at low energy countershocks and decreases with higher energy countershock.     

The prediction of the impedance of the thorax to defibrillating current.

In this paper a technique for predicting thoracic impedance to defibrillator pulses is described. The impedance to low-current (1.0 mA) high-frequency (10-500kHz) sinusoidal current is used as an indicator of the impedance of the thorax to high-current, damped sinusoidal waveform pulses. Results from 71 dogs to which defibrillator shocks of 4 to 220 A peak current were applied show that thoracic impedance can be predicted by this method. This information indicates that it is possible to design a defibrillator that can automatically measure chest impedance prior to a defibrillation shock and deliver a predetermined peak current to the subject.     

电容耦合非接触电极及心电信号获取

电极与皮肤间接触所导致的不适感,是穿戴式心电信号测量系统实际应用中的常见问题。设计了一种非接触心电信号测量系统。采用印刷电路板制作的测量电极,借助电容耦合测量位移电流的方式获取心电信号。采用反接二极管提供测量所需的高阻值偏置电阻,结合高输入阻抗仪表放大器,制作了测量电极信号提取电路。测量系统由两个测量电极与一个直接与测量电路地相连的参考电极组成。选择金属铝板、导电纤维和导电橡胶作为参考电极,实验研究了共模干扰抑制性能与参考电极接触阻抗之间的量化关系。将主元分析与奇异谱分析相结合,提出了一种心电信号处理算法。实验结果表明,该系统可在棉质线衣外侧有效获得满意的心电信号。     

Sequential pulse defibrillation for implantable defibrillators

A technique is described that reduces defibrillation threshold for automatic implantable defibrillators, permits either reducing the size of the pulse generator or increasing the effectiveness of the pulse generator, and provides an increased safety factor. Defibrillation threshold was compared in 12 anesthetized dogs with mean (+/- SD) body weight of 21.6 +/- 3.4 kg for two defibrillating modalities: 1) single pulse technique with current flowing from electrodes in the right ventricle to electrodes either in the superior vena cava or on the left ventricular epicardium, and 2) sequential pulse technique. The sequential pulse technique tested uses two pulses and three or four electrodes. Current of the first 5-ms pulse flows from the superior vena caval electrode to an electrode in the right ventricle, and after a 1-ms interval, current of the second pulse flows from electrodes on the left ventricular epicardium to the right ventricular electrode. Ventricular defibrillation threshold was reduced by 56% to 6.3 +/- 1.03 joules (mean +/- SEM) (P less than 0.01). Because defibrillation threshold is less for sequential pulse defibrillation than for conventional techniques, sequential pulse defibrillators can be smaller and more effective than previously available devices.     

Considerations in the development of the automatic implantable defibrillator.

A highly reliable ventricular fibrillation detector and a satisfactory electrode system for delivering defibrillating pulses to the heart play a central role in the development of an automatic implantable defibrillator suitable for clinical use. Among the four implanted electrode designs tested, the combination of an electrode placed in the superior vena cava with a conformal electrode on the apex of the heart provided satisfactory defibrillation thresholds with ease of implantation. A new sensing method is also described for which an electrogram derived from the defibrillating electrodes is used as input. A form of a density function is developed for a filtered version of the input, ventricular fibrillation being characterized by a density curve lacking a large peak occurring at a level corresponding to the baseline of the filtered signal. These ideas are being incorporated into the design of a prototype implantable defibrillator delivering pulses of 24 joules.     

The feasibility of bench tests for disposable ECG electrode adhesiveness

The feasibility of recommending one standard bench test that adequately qualifies electrode adhesives for clinical use was examined by UBTL. Small strips, cut from whole, commercially available disposable ECG electrodes, were attached to three types of surfaces, and samples of each type of electrode were peel tested at 15 minutes, 8 hours, and 48 hours after attachment. A program was developed to average, display, and calculate peel strength parameters. Analysis of the data showed that (a) the peel strength of electrodes varied by more than a factor of 10 when measured on human skin, and by more than a factor of 3 when measured on bench test surfaces, and (b) the peel strength of the electrode adhesive strips did not correlate with intact electrode loss on ambulatory subjects. Therefore, UBTL could not recommend one bench test that would measure adhesion performance for all electrode types appropriate for inclusion in an AAMI ECG electrode standard.     

新型EEG检测干电极设计制备和测试研究

设计制作了一款新型的脑电干电极,用于实现对EEG信号的检测。相较于传统的湿电极,该新型电极在测试过程中不需要导电介质,有效降低了实验准备过程的复杂度,可以大大缩短实验准备时间。而且,其接触电阻可以和湿电极在同一数量级,从而可实现长时间实时稳定测量EEG。利用聚吡咯石墨烯纳米复合物对电极探头进行修饰,对干电极与头皮的接触阻抗进行了阻抗谱测试,可以有效降低接触电阻,提高信号的稳定性和可靠性。采用自制干电极与碗状湿电极,在不同脑区进行了脑电信号检测的对比实验,信号线性相关度均在90%以上,将干电极检测的脑电信号分解,分解波段波形符合脑电信号特征波特征,证明该新型干电极可用于无发区和有发区脑电信号的检测。搭建了基于新型干电极的无线脑电采集分析系统,实现了简单的脑机接口设计,进一步证明了干电极的实用性。     

Analysis of the current-density distribution from a tapered, gelled-pad external cardiac pacing electrode

We have designed a high-impedance (5000 omega-cm), tapered, gelled-pad, external cardiac pacing electrode that limits the migration of charges to the perimeter of a circular electrode and produces a more uniform current-density distribution than external cardiac pacing electrodes in clinical use. A computer simulation was developed that uses cylindrical coordinates to analyze the current-density distribution at the interface between the electrode and human tissue. Our computer simulation analyzed 32 different electrodes, and the results showed that the gelled-pad thickness, the gelled-pad taper, and the radius of the conducting disk were not significant parameters in determining the current-density distributions for low-resistivity electrodes. Those parameters were, however, significant for high-resistivity electrodes. We defined the optimum resistivity as that at which the tapered, gelled-pad electrode produces the most uniform current-density distribution and delivers the most current to human tissue. When evaluating electrodes at the optimum resistivity, we determined that the peak current density of the tapered, gelled-pad electrode was 50% lower than that of the clinically available electrodes, while delivering 58% more current to the human tissue.     

Alternating current impedance spectroscopy measurement under high pressure

A microcircuit was designed and fabricated on a diamond anvil cell for alternating current impedance spectroscopy measurement under high pressure. Sputtered molybdenum film on a diamond anvil was used as an electrode, maintained the contact between the sample and the electrode stable, and reduced the electrode effect on the impedance measurement. By the empty cell and short circuit tests, the parasitic capacitive impedance from the sample chamber wall was observed to be larger than 10(5) Ω at a frequency lower than 1.0 MHz and could be ignored for samples with higher conductivity. The wire inductance was only 1.0 μH and just appeared at frequency higher than 20 kHz, which could be subtracted from measured impedance for the samples with higher impedance than several hundred ohms. Using this apparatus, the impedances of the II-VI group cadmium sulfide were measured. The pressure dependence of the grain interior conductance of CdS crystal was obtained, which reflected that the phase transitions of CdS under high pressure are the same as the single crystal measurement results.     

Note: electrode polarization of Galinstan electrodes for liquid impedance spectroscopy

Electrode polarization is a significant obstacle in the impedance measurements of ionic liquids. An atomically smooth electrode surface could potentially reduce unwanted impedance contributions from electrode polarization. Liquid metal electrodes were formed by adhering Galinstan to acrylic plates in a parallel-plate capacitor arrangement. Electrode polarization was compared to a similar cell with stainless steel electrodes. The impedance of salt and protein solutions (β-lactoglobulin) was measured from 40 Hz to 110 MHz. Because of oxide layer formation, the performance of the Galinstan electrode is significantly different than the theoretical ideal.     

Optimization of epicardial electrode size and implant site for reduced sequential pulse defibrillation thresholds

The influence of epicardial electrode surface area and implant site on sequential pulse defibrillation threshold was investigated in four isolated heart preparations. Electrodes with surface areas of 2.5, 5.0, and 10.0 cm2 were each sutured, in random order, to the epicardial surface of the isolated heart at each of four sites: mid-ventral left ventricle (LV); mid-dorsal LV; lateral-apical LV; and lateral-basal LV. The epicardial electrode is one of the electrodes in a three-electrode, two-current pathway, sequential pulse system. The first two electrodes, which are catheter-mounted, are located in the right ventricular apex (RVA) and superior vena cava (SVC). In sequential pulse defibrillation, one shock is delivered from the SVC to the RVA, followed 1 msec later by a second shock delivered from the third electrode to the RVA. Sequential pulse defibrillation threshold was obtained with each epicardial electrode used at each site. A single-pulse (SVC to RVA) catheter threshold was also obtained in each heart. The overall mean sequential pulse threshold was 47 per cent less than the mean single-pulse threshold (P less than 0.001). Increasing patch size reduced sequential pulse threshold (P less than 0.03), but no significant effect of patch location could be demonstrated. It is concluded that sequential pulse defibrillation is superior to single-pulse catheter defibrillation and that increasing epicardial patch size is advantageous, although patch location does not influence thresholds in the isolated heart.     

Synergistic effects of fluid flow and sand particles on erosion–corrosion of aluminum in ethylene glycol–water solutions

The synergistic effects of fluid flow and sand particles on erosion–corrosion of 3003 aluminum (Al) alloy in ethylene glycol–water solution that simulates the automotive engine coolant were studied through a rotating disk electrode by electrochemical measurements. It was found that, in the absence of sand particles, the anodic current density of Al electrode decreases with the increase in electrode rotating speed, which is attributed to the enhanced electrode oxidation accompanying with accelerated oxygen diffusion and reduction. Mass-transport plays an important role in electrode process, as indicated by the presence of diffusive impedance. With the addition of sand particles, the de-stabilization of electrode is predominant and the anodic current density increases with the electrode rotation speed, which is attributed to the enhanced impact damage to electrode by sand particles. The electrode roughening effect due to sand impact is indicated by the presence of inductive loop in impedance plots. The variation of sand particle size does not have apparent effect on polarization behaviour of Al electrode, while an elevated temperature increases significantly the anodic current density of the electrode. There exists a synergism of fluid flow and sand impact on electrochemical corrosion behaviour of Al electrode.     

Electrode wear and material removal rate during EDM of aluminum and mild steel using copper and brass electrodes

In the present study an analysis has been done to evaluate the electrode wear along the cross-section of an electrode compared to the same along its length during EDM of aluminum and mild steel using copper and brass electrodes. In an overall performance comparison of copper and brass electrodes, we found that electrode wear increases with an increase in both current and voltage, but wear along the cross-section of the electrode is more compared to the same along its length. This is due to easier heat transfer along the length compared to the same along the cross-section of the electrode. It was also found that the wear ratio increases with an increase in current. That means, though a higher current causes more removal of work material and the electrode, comparatively more material is removed from the electrode. The highest wear ratio was found during machining of steel using a brass electrode. The low thermal conductivity of brass electrodes causes less heat loss, and its low melting point results in fast melting of the electrode material. At the same time, low thermal conductivity of steel results in poor heat absorption, and its high melting temperature causes poor removal of work material. These factors result in the highest wear ratio during machining of steel using a brass electrode. The highest material removal rate was observed during machining of aluminum using brass electrodes. Comparatively low thermal conductivity of brass as an electrode material does not allow the absorption of much heat energy, and most of the heat is utilized in the removal of material from aluminum workpiece at a low melting point. But during machining of steel using copper electrodes, a comparatively smaller quantity of heat is absorbed by the work material due to its low thermal conductivity. As a result material removal rate becomes very low.     

平面叉指电极溶液阻抗的低频三角波测量*

针对低浓度电解质溶液中生物细胞阻抗微弱变化过程的测量问题,研究了一种三角波电压激励结合主元分析(PCA)的测量方法。用三角波电压信号作为激励,采集单周期响应电流信号构成测量向量,由不同时刻所得测量向量组成测量矩阵,PCA处理后的载荷向量中即包含有溶液阻抗的变化信息。这种信号处理方式对阻抗变化过程的测量结果不依赖于等效阻抗模型的计算,同时可有效避免等效阻抗计算过程中的噪声问题。对低浓度氯化钾溶液中硅基底金电极、PCB基底铜电极和PCB基底镀金电极3种平面叉指电极进行了实验分析。实验结果表明,三角波激励结合PCA处理的方法可实现对溶液电导率微弱变化过程的有效检测。     

A comparison of gel-to-gel and skin measurements of electrode impedance

Utilizing an automated test system, measurements of the 10-Hz impedance were made with electrode pairs joined gel-to-gel and electrode quartets on the skin of the backs of human volunteers. Two skin preparation procedures were examined. As a minimum skin preparation, the electrodes were applied to clean, dry skin from which body hair had been shaved if necessary. As a maximal preparation, the electrodes were applied after mild abrasion of the skin with fine emery cloth. Although the impedances measured for electrodes applied to mildly abraded skin correlated well with measurements made with electrodes of the same brand joined gel-to-gel, virtually no correlation was found if the electrodes were affixed to clean, dry skin.     

Studies on thin film based flexible gold electrode arrays for resistivity imaging in electrical impedance tomography

Practical phantoms are essential to assess the electrical impedance tomography (EIT) systems for their validation, calibration and comparison purposes. Metal surface electrodes are generally used in practical phantoms which reduce the SNR of the boundary data due to their design and development errors. Novel flexible and biocompatible gold electrode arrays of high geometric precision are proposed to improve the boundary data quality in EIT. The flexible gold electrode arrays are developed on flexible FR4 sheets using thin film technology and practical gold electrode phantoms are developed with different configurations. Injecting a constant current to the phantom boundary the surface potentials are measured by a LabVIEW based data acquisition system and the resistivity images are reconstructed in EIDORS. Boundary data profile and the resistivity images obtained from the gold electrode phantoms are compared with identical phantoms developed with stainless steel electrodes. Surface profilometry, microscopy and the impedance spectroscopy show that the gold electrode arrays are smooth, geometrically precised and less resistive. Results show that the boundary data accuracy and image quality are improved with gold electrode arrays. Results show that the diametric resistivity plot (DRP), contrast to noise ratio (CNR), percentage of contrast recovery (PCR) and coefficient of contrast (COC) of reconstructed images are improved in gold electrode phantoms.     

一种新型的基于四电极结构的生物电阻测量方法

提出了一种成本低而且精度高的人体阻抗测量系统。测量电路采用四电极结构,使每个电极模拟人体皮肤电阻,分别与人体的赤足接触,利用单片机产生50kHz的正弦波信号,经过四电极以及与其接触的人体后形成电压降,再经过信号放大电路处理,最终实现人体阻抗的测量。系统有效降低了产品的成本,克服了接触阻抗以及空间电磁波的干扰,试验结果与理论值证明了测量方法具有高精度、高稳定性和准确性。     

Coping with electrode polarization for development of DC-Driven electrical impedance tomography

An electrical impedance tomography (EIT) system design is proposed for imaging of phase distribution in gas-water two-phase flow from boundary measurement of electrical potentials in response to direct current (DC) injection. DC injection simplifies substantially the system design, but introduces problems due to polarization of injection electrodes. Electrode polarization means charge accumulation on the electrode-water interface causing a drift in the interfacial potential difference. The polarization problems are coped with by using dedicated electrodes for injection and potential measurement, and using a current source unaffected by the polarization of current-carrying electrodes (CCEs). Furthermore, the polarization of CCEs is controlled, to lessen the possible influence on the sensing electrodes (SEs), by using a short (milliseconds in width) pulse for injection with a charge balanced injection strategy. The impact of electrode polarization and the effectiveness of countermeasures introduced in the present design are discussed through comparisons of measured boundary potentials and of images reconstructed for a simple object simulating large bubbles in water.     

The skin-effect in ferromagnetic electrodes for wire-EDM

In wire electrical discharge machining (wire-EDM) material is removed by the thermal energy of an electric spark that has been initiated between two electrodes (the wire and the workpiece), submerged in demineralised water. The use of high frequency current pulses for sparking leads to excellent machining performance, in terms of the work piece roughness, the material integrity of the cut and the material removal rate. To reach the highest frequencies, the wire-EDM generator mostly consists of a voltage source with an as low as possible internal inductance. The working current delivered to the spark and, hence, the material removal rate of the process depends on the total impedance of the electrical circuit. In this article the importance of the wire’s impedance will be shown. Due to the skin-effect, this impedance depends on the frequency of the current signal, especially for ferromagnetic wires, such as steel wire. Coatings will prove to be primordial to prevent the machining speed from dropping significantly.