Linearity of transthoracic conductance with respect to electrodeforce and area during high-voltage defibrillation shocks

Canine transthoracic conductance (G_T) was measured during high-voltage defibrillation shocks to test the hypothesis that (G _T) is a linear function of electrode force (F) and electrode area (A). Symmetric protocols were used to compensate for changes in (G _T) with respect to shock number (n). Stainless steel electrodes were employed with a force-control system for precise selection and control of both F and A at each shock. For a constant A=60 cm², G_T was linear (r=0.996, 0.995, 0.971, 0.992, 0.995) over five dogs for 30 N⩽F⩽70 N. For a constant F=50 N, G _T was linear (r=0.992, 0.998, 0.994, 0.992) over four dogs for 20 cm²⩽A⩽60 cm², and in one dog (r=0.996) for 40 cm²⩽A⩽90 cm². The quantitative relationship demonstrated for G_T and F and A can be used in the design of experiments and interpretation of results used for validation of numerical defibrillation models     

Modeling current density distributions during transcutaneouscardiac pacing

The authors developed a two-dimensional finite element model of a cross-section of the human thorax to study the current density distribution during transcutaneous cardiac pacing. The model comprises 964 nodes and 1,842 elements and accounted for the electrical properties of eight different tissues or organs and also simulated the anisotropies of the intercostal muscles. The finite element software employed was a version for electrokinetics problems of Finite Element for Heat Transfer (FEHT) and the authors assessed the effects upon the efficacy of transcutaneous cardiac pacing of several electrode placements and sizes. To minimize pain in the chest wall and still be able to capture the heart, the authors minimized the ratio, R, between the current density in the thoracic wall (which causes pain) and the current density in the heart wall (which captures the heart). The best placement of the negative electrode was over the cardiac apex. The best placement of the positive electrode was under the right scapula, although other placements mere nearly as good. The efficiency of pacing increased as electrode size increased up to 70 cm and showed little improvement for larger areas. Between different configurations of the precordial electrodes V1, V2, ···, V6 the most efficient configuration to pace with was V1 and V2 positive and V5 and V6 negative. A more efficient configuration uses an auxiliary electrode located at the right subscapular region     

A three-dimensional finite element model of human transthoracicdefibrillation: paddle placement and size

A detailed 3-D finite element model of the conductive anatomy of the human thorax has been constructed to quantitatively assess the current density distribution produced in the heart and thorax during transthoracic defibrillation. The model is based on a series of cross-sectional CT scans and incorporates isotropic conductivities for eight tissues and an approximation of the anisotropic conductivity of skeletal muscle. Current density distributions were determined and compared for four paddle pairs and two paddle sizes. The authors' results show that the myocardial current density distributions resulting from a defibrillation shock were fairly uniform for the paddle pairs and sizes examined in this study. Specific details of the spatial distribution of the current density magnitudes in the heart were found to depend on paddle placement and size. When the minimum current necessary to defibrillate was delivered, the maximum myocardial current density produced with any of the paddle sizes and positions examined was less than four times the minimum current density necessary to render a myocyte in a fibrillating heart inexcitable, and less than 40% of the damage threshold. These results suggest that common clinically used defibrillation paddle positions have a safety margin as large as 2.5 for current and ~6 for energy     

Finite element models of thoracic conductive anatomy: sensitivityto changes in inhomogeneity and anisotropy

A moderately detailed 3-D finite element model of the conductive anatomy of a canine thorax was used to examine the sensitivity of the results obtained during simulated transthoracic defibrillation to variations in skeletal muscle anisotropy and differing degrees of model inhomogeneity. The authors results suggest that the myocardial current density distribution is not particularly sensitive to the method used to model skeletal muscle anisotropy. However, anisotropy variations caused defibrillation parameters such as paddle to paddle impedance and threshold current to change by as much as 50%. The authors found a greater sensitivity in the myocardial current density and the defibrillation parameters to variations in model inhomogeneity. The changes observed in both depended substantially on paddle placement. This sensitivity to paddle placement highlights the difficulty in predicting how a reduction in anatomical detail will affect the myocardial current density distribution. In general, the authors found the defibrillation parameters to be more sensitive than the myocardial current density distribution to the variations in anatomical detail they examined     

Optimal Electrode Configurations for External Cardiac Pacing and Defibrillation: An Inhomogeneous Study

We have developed an inhomogeneous two-dimensional finite element computer model of the human torso, and have used it to study electrode performance in defibrillation and external cardiac pacing. Gross individual organ effects were assessed first for different electrode configurations by creating models which included one organ at a time, and comparing the results to those obtained with a homogeneous body. Electrode placement on the body was varied in order to determine, within the limitations of the model, optimal electrode configurations for external cardiac pacing and defibrillation. Finally, the electrical and geometric parameters of a previously proposed plate electrode design were optimized for the selected external pacing position. It was found that organs of extreme resistivity, close to the body surface, and within the direct current path between two electrodes, tended to have dominant effects on the surface current density distributions. The optimum pacing position is to place the driven electrode directly over the heart and the receiving electrode on the left lateral chest wall. For defibrillation, the driven electrode is moved to the right of the sternum.     

Influence of electrical coupling on early after depolarizations inventricular myocytes

Computer modeling is used to study the effect of electrical coupling between a myocardial zone where early after-depolarizations (EADs) can develop and the normal neighboring tissue. The effects of such coupling on EAD development and on the likelihood of EAD propagation as an ectopic beat are studied. The influence on EAD formation is investigated by approximating two partially coupled myocardial zones modeled as two active elements coupled by a junctional resistance R. For R values lower than 800 Ω cm², the action potentials are transmitted to the coupled element, and for R values higher than 850 Ω cm² they are blocked. In both ranges of R, when the electrical coupling increases, the EADs appear at more negative takeoff potentials with higher amplitudes and upstrokes. The EADs are not elicited if the electrical coupling is too high. In a separate model of two one-dimensional cardiac fiber segments partially coupled by a resistance R, critical R values exist, between 42 and 54 Ω cm² that facilitate EAD propagation. These results demonstrate that in myocardial zones favorable to the formation of EAD, the electrical coupling dramatically affects initiation of EAD and its spread to the neighboring tissue     

Effects of low charge injection densities on corrosion responses ofpulsed 316LVM stainless steel electrodes [functional neuromuscularstimulation]

The safe charge injection density for pulsing of 316LVM electrodes has been reported to be 40 μC/cm². However, only 20 μC/cm² is available for nonfaradic charge transfer and double layer charge injection. Therefore, the authors evaluated long term pulsing at 20 μC/cm² with capacitor coupling     

Membrane polarization induced in the myocardium by defibrillationfields: an idealized 3-D finite element bidomain/monodomain torso model

This study develops a three-dimensional finite element torso model with bidomain myocardium to simulate the transmembrane potential (TMP) of the heart induced by defibrillation fields. The inhomogeneities of the torso are modeled as eccentric spherical volumes with both the curvature and the rotation features of cardiac fibers incorporated in the myocardial region. The numerical computation of the finite element bidomain myocardial model is validated by a semianalytic solution. The simulations show that rotation of fiber orientation through the depth of the myocardial wall changes the pattern of polarization and decreases the amount of cardiac tissue polarized compared to the idealized analytic model with no fiber rotation incorporated. The TMP induced by transthoracic and transvenous defibrillation fields are calculated and visualized. The TMP is quantified by a continuous measure of the percentage of myocardial mass above a potential gradient threshold. Using this measure, the root mean square differences in TMP distribution produced by reversing the electrode polarity for anterior-posterior and transvenous electrode configurations are 13.6 and 28.6%, respectively. These results support the claim that a bidomain model of the heart predicts a change of defibrillation threshold with reversed electrode polarity     

Finite element analysis of cardiac defibrillation currentdistributions

We have developed a two-dimensional finite element model of the canine heart and thorax to examine different aspects of the distribution of current through cardiac tissue during defibrillation. This model allows us to compare various electrode configurations for the implantable cardioverter/defibrillator. Since we do not yet know the electrical criteria to apply for predicting defibrillation thresholds, such as the minimum current density required for defibrillation or the critical mass if indeed such quantities are applicable, we measured defibrillation energy in dogs to determine the voltages to apply to the model for calculating current distributions. By analyzing isopotential contours, current lines, power distributions, current density histograms, and cumulative current distributions, we estimated the critical fraction and threshold current density for defibrillation, compared various electrode configurations, and assessed the sensitivity of the defibrillation threshold to electrode position, patch size, and tissue conductivity. We found that blood can shunt defibrillation current away from the myocardium, particularly in configurations using a two-electrode catheter, that myocardial tissue conductivity strongly affects the current distributions, and that epicardial patch size is more important that subcutaneous patch size. Our results are consistent with successful defibrillation requiring that 80 +/- 5% of the heart must be rendered inexcitable by a current density of 35 +/- 5 mA/cm2 or greater. This two-dimensional, isotropic model has allowed us to analyze some of the determinants of defibrillation, but more detailed interpretation of experimental data may require the extension of the model to three dimensions.     

Three-dimensional computer model of electric fields in internaldefibrillation

The automatic internal defibrillator delivers a low-energy shock directly to the heart. Optimal strategies for these shock deliveries are determined by studying a three-dimensional computer model of the electric fields produced by initial defibillation electrodes. A finite-element analysis technique is used to calculate energy and current density distributions in three commonly used electrode configurations: (1) patch-patch (PP), (2) catheter-patch (CP), and (3) catheter-catheter (CC). analysis of these simulations indicates that : (1) the PP and CP configurations are more effective at channeling energy to the myocardium than the CC configuration; (2) small electrodes and the edges of the electrodes give rise to high local current densities which might cause damage to the myocardium: (3) energy delivered to the myocardium is not significantly altered for different electrode placements tested; (4) electrode size influences current density distribution, especially near the electrodes; and (5) energy distribution is sensitive to the relative conductances of the myocardial tissue and blood     

Micromachining technology for lateral field emission devices

We demonstrate a range of novel applications of micromachining and microelectromechanical systems (MEMS) for achieving efficient and tunable field emission devices (FEDs). Arrays of lateral field emission tips are fabricated with submicron spacing utilizing deep reactive ion etch (DRIE). Current densities above 150 A/cm² are achieved with over 150·10⁶ tips/cm². With sacrificial sidewall spacing, electrodes can be placed at arbitrarily close distances to reduce turn-on voltages. We further utilize MEMS actuators to laterally adjust electrode distances. To improve the integration capability of FEDs, we demonstrate batch bump-transfer of working lateral FEDs onto a quartz target substrate     

Pulsed laser damage thresholds in vitro for intraocular lenses and membranes

Energy and power density damage thresholds were determined in air, for plastic IOL's and membranes at the focal point of several solid-state laser systems: 1) 694 nm,Q-switched single pulse (30 ns), multimode, 2) 1064 nm,Q-switched single pulse (20 ns), TEM00, 3) 1060 nm, mode-locked single pulse, 15 ps, TEM11, 4) 530 nm, mode-locked single pulse, 15 ps, TEM11, and 5) 1064 nm, mode-locked pulse train (9-11 pulses, 30 ps), TEM00. Pulse energies bracketing damage thresholds as well as focal diameter and pulse duration for each system were determined. Energy density thresholds are lower, and power density thresholds higher, for shorter duration pulses-e.g., 23 J/cm²(1.15 GW/cm²) versus 6 J/cm²(400 GW/cm²) at the same wavelength as in systems 2) and 3) (p = 0.005). Damage thresholds for glass IOL's are 37 J/cm²(1.9 GW/cm²) and 37 J/cm²(1235 GW/cm²) as in systems 2) and 5). Damage threshold values for plastic membranes (Saran Wrap^®) exposed to nanosecond and picosecond pulse trains of Nd:YAG at 1064 nm are about half that of plastic IOL's. When laser pulses with a cone angle of 14° from systems 2) and 5) are focused on plastic membrane next to the IOL, damage thresholds are 30 J/cm²(1.5 GW/cm²) for 20 nsQ-switched pulses and 20 J/cm²(670 GW/cm²) for trains of 30 ps mode-locked pulses. Damage thresholds of IOL's immersed in 0.9 percent saline are approximately the same as those obtained in air.     

High performance poly-Si TFTs fabricated using pulsed laserannealing and remote plasma CVD with low temperature processing

Key technologies for fabricating polycrystalline silicon thin film transistors (poly-Si TFTs) at a low temperature are discussed. Hydrogenated amorphous silicon films were crystallized by irradiation of a 30 ns-pulsed XeCl excimer laser. Crystalline grains were smaller than 100 nm. The density of localized trap states in poly-Si films was reduced to 4×10¹⁶ cm^-3 by plasma hydrogenation only for 30 seconds. Remote plasma chemical vapor deposition (CVD) using mesh electrodes realized a good interface of SiO ₂/Si with the interface trap density of 2.0×10¹⁰ cm^-2 eV^-1 at 270°C. Poly-Si TFTs were fabricated at 270°C using laser crystallization, plasma hydrogenation and remote plasma CVD. The carrier mobility was 640 cm²/Vs for n-channel TFTs and 400 cm²/Vs for p-channel TFTs. The threshold voltage was 0.8 V for n-channel TFTs and -1.5 V for p-channel TFTs. The leakage current of n-channel poly-Si TFTs was reduced from 2×10^-10 A/μm to 3×10^-13 A/μm at the gate voltage of -5 V using an offset gate electrode with an offset length of 1 μm     

Effect of bottom electrode materials on the electrical andreliability characteristics of (Ba, Sr)TiO3 capacitors

The dielectric constant and the leakage current density of (Ba, Sr)TiO₃ (BST) thin films deposited on various bottom electrode materials (Pt, Ir, IrO₂/Ir, Ru, RuO₂/Ru) before and after annealing in O₂ ambient were investigated. The improvement of crystallinity of BST films deposited on various bottom electrodes was observed after the postannealing process. The dielectric constant and leakage current of the films mere also strongly dependent on the postannealing conditions. BST thin film deposited on Ir bottom electrode at 500°C, after 700°C annealing in O₂ for 20 min, has the dielectric constant of 593, a loss tangent of 0.019 at 100 kHz, a leakage current density of 1.9×10 ^-8 A/cm² at an electric field of 200 kV/cm with a delay time of 30 s, and a charge storage density of 53 fC/μm² at an applied field of 100 kV/cm. The BST films deposited on Ir with post-annealing can obtain better dielectric properties than on other bottom electrodes in our experiments. And Ru electrode is unstable because the interdiffusion of Ru and Ti occurs at the interface between the BST and Ru after postannealing. The ten year lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir, IrO₂/Ir, Ru, and RuO₂/Ru have long lifetimes over ten gears on operation at the voltage bias of 2 V     

Measurement of defibrillation shock potential distributions andactivation sequences of the heart in three dimensions

The authors note that knowledge of the extracellular potential gradient field of the defibrillation shock and the cardiac-tissue response to the shock should lead to better understanding of the mechanism of defibrillation and stimulate improvement of defibrillation techniques. By measuring the potential distribution of the defibrillation shock throughout the heart and the location of the recording electrodes, the potential gradient field may be calculated. By recording local electrograms throughout the heart immediately before and after the shock, the tissue response to the shock can be evaluated     

基于石墨烯的肖特基结辐射伏特同位素电池

从传统肖特基结辐射伏特同位素电池金属电极存在的对放射源衰变粒子的阻挡及导电性不理想的问题出发,借鉴石墨烯肖特基结太阳电池结构,将石墨烯/硅肖特基结引入辐射伏特同位素电池中,在63Ni放射源的照射下验证石墨烯/硅肖特基结换能单元在辐射伏特同位素电池中应用的可行性.研究结果发现,基于硝酸掺杂,当少层(3?5层)石墨烯经过4...     

Effect of paddle placement and size on defibrillation currentdistribution: a three-dimensional finite element model

A realistic three-dimensional finite-element model (FEM) of the conductive anatomy of a canine thorax was constructed for use in the study of transthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional computed tomography (CT) scans of a 14.5 kg beagle, each separated by 0.82 cm. The electrical conductive properties of eight distinct tissues were incorporated, including the anisotropic properties of skeletal muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. The results suggest that placing one or both of the paddles near the heart delivers a higher fraction of current to the heart. However, such placements also produce a less uniform myocardial current density distribution and thus have a higher potential for causing damage. Some paddle positions produced myocardial current densities close to the threshold for damage in successful defibrillations. The results indicate that 12 cm paddles may offer modest advantages over 8 cm paddles in clinical defibrillation     

Analysis of defibrillation efficacy from myocardial voltagegradients with finite element modeling

Increasing defibrillation efficacy by lowering the defibrillation threshold (DFT) is an important goal in positioning implantable cardioverter-defibrillator electrodes. Clinically, the DFT is difficult to estimate noninvasively. It has been suggested that the DFT relates to the myocardial voltage gradient distribution, but this relation has not been quantitatively demonstrated. We analyzed the relation between the experimentally measured DFT's and the simulated myocardial voltage gradients provided by finite element modeling. We performed a series of experiments in 11 pigs to measure the DFT's, and created and solved three-dimensional subject-specific finite element models to assess the correlation between the computed myocardial voltage gradient histograms and the DFT's. Our data show a statistically significant correlation between the DFT and the left ventricular voltage gradient distribution, with the septal region being more significant (correlation coefficient of 0.74) than other myocardial regions. The correlation between the DFT and the right ventricular and the atrial voltage gradient, on the other hand, is not significant.     

Efficiency of the a-Si:H solar cell and grain size of SnO2transparent conductive film

The relationship between average grain size on the surface of SnO2transparent conductive film and conversion efficiency of the a-Si:H solar cell was investigated. a-Si:H solar cells were fabricated on SnO2/glass substrates with various grain sizes. The cell structure was glass/p(SiC)-i-n/Al and the effective cell area was 4 × 10^-2cm². The reflectivity from the glass substrate was reduced to about 7 percent with increasing the grain size from 0.1 to 0.8µm, and the short-circuit current was inceased from 12 to 14mA/cm². A 7.9 percent of conversion efficiency was achieved using milky SnO2film of 0.4-µm average grain size at AM-100mW/cm².     

Computational studies of transthoracic and transvenousdefibrillation in a detailed 3-D human thorax model

A method for constructing and solving detailed patient-specific 3D finite element models of the human thorax is presented for use in defibrillation studies. The method utilizes the patient's own X-ray CT scan and a simplified meshing scheme to quickly and efficiently generate a model typically composed of approximately 400,000 elements. A parameter sensitivity study on one human thorax model to examine the effects of variation in assigned tissue resistivity values, level of anatomical detail included in the model, and number of CT slices used to produce the model is presented. Of the seven tissue types examined, the average left ventricular (LV) myocardial voltage gradient was most sensitive to the values of myocardial and blood resistivity. Incorrectly simplifying the model, for example modeling the heart as a homogeneous structure by ignoring the blood in the chambers, caused the average LV myocardial voltage gradient to increase by 12%. The sensitivity of the model to variations in electrode size and position was also examined. Small changes (<2.0 cm) in electrode position caused average LV myocardial voltage gradient values to increase by up to 12%. It is concluded that patient-specific 3D finite element modeling of human thoracic electric fields is feasible and may reduce the empiric approach to insertion of implantable defibrillators and improve transthoracic defibrillation techniques