Role of proximal electrode position in transvenous ventricular defibrillation

Transvenous defibrillation lead systems have been demonstrated to reduce operative morbidity and mortality associated with implantation of cardioverter-defibrillators. To determine the best position for the proximal electrode in transvenous systems, defibrillation thresholds were compared for three positions in a single-pathway, two-lead system. Two defibrillation lead electrodes were transvenously inserted into seven dogs. The distal electrode was positioned in the right ventricular apex. The proximal electrode was randomized to one of three positions: (1) the superior (cranial) vena cava (SVC) at he junction of the right atrium, (2) the left innominate vein at the junction of the SVC, or (3) the external jugular vein. Biphasic defibrillation thresholds for converting electrically induced ventricular fibrillation were determined for the three positions of the proximal electrode in each dog. The innominate vein position resulted in the lowest defibrillation threshold (555±123 V) as compared to the SVC (640±126 V;p=0.0612) and the jugular vein (709±117 V;p=0.0013). Lead impedance gradually increased with increasing dostamce between the two shocking electrodes: 58.4±11.4 Ω for SVC, 76.2±13.8 Ω for innominate vein, and 94.9±10.2 Ω for jugular vein proximal lead electrode position (p<0.05 for all pairwise comparisons). In two-electrode transvenous defibrillation lead systems, positioning the proximal electrode in the left innominate vein produced the lowest defibrillation threshold.     

Skin impedance measurements using simple and compound electrodes

We have studied the effect of the electrode configuration on the measurement of body impedance and found that the electrode configuration greatly affects the impedance measurement using the four-electrode method. We studied the characteristics of the compound electrode and found that the compound electrode provides the four-electrode method in a compact form. A new method of measuring the skin impedance using simple electrodes at low frequencies was developed. At high frequencies where the effect of internal tissue impedance is not negligible, we used the compensation method using compound electrodes, because they measure the voltage right under the skin. At 50 kHz, we measured the real part of the skin impedance of less than 80 Ω on the thorax. We propose a simple instrument which can measure accurate skin impedance at various frequencies.     

Effect of skin impedance on image quality and variability in electrical impedance tomography: a model study

A computer simulation is used to investigate the relationship between skin impedance and image artefacts in electrical impedance tomography. Sets of electrode impedance are generated with a pseudo-random distribution and used to introduce errors in boundary voltage measurements. To simplify the analysis, the non-idealities in the current injection circuit are replaced by a fixed common-mode error term. The boundary voltages are reconstructed into images and inspected. Where the simulated skin impedance remains constant between measurements, large impedances (>2kΩ) do not cause significant degradation of the image. Where the skin impedances ‘drift’ between measurements, a drift of 5% from a starting impedance of 100Ω is sufficient to cause significant image distortion. If the skin impedances vary randomly between measurements, they have to be less than 10 Ω to allow satisfactory images. Skin impedances are typically 100–200 Ω at 50 kHz on unprepared skin. These values are sufficient to cause image distortion if they drift over time. It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement.     

The Effects of Concentric Ring Electrode Electrical Stimulation on Rat Skin

Surface electrodes are commonly used electrodes clinically, in applications such as functional electrical stimulation for the restoration of motor functions, pain relief, transcutaneous electrical nerve stimulation, electrocardiographic monitoring, defibrillation, surface cardiac pacing, and advanced drug delivery systems. Common to these applications are occasional reports of pain, tissue damage, rash, or burns on the skin at the point where electrodes are placed. In this study, we quantitatively analyzed the effects of acute noninvasive electrical stimulation from concentric ring electrodes (CRE) to determine the maximum safe current limit. We developed a three-dimensional multi-layer model and calculated the temperature profile under the CRE and the corresponding energy density with electrical-thermal coupled field analysis. Infrared thermography was used to measure skin temperature during electrical stimulation to verify the computer simulations. We also performed histological analysis to study cell morphology and characterize any resulting tissue damage. The simulation results are accurate for low energy density distributions. It can also be concluded that as long as the specified energy density applied is kept below 0.92 (A²/cm⁴·s⁻¹), the maximum temperature will remain within the safe limits. Future work should focus on the effects of the electrode paste.     

Estimation of the distribution of intramuscular current during electrical stimulation of the quadriceps muscle

Electrical stimulation is commonly used for strengthening muscle but little evidence exists as to the optimal electrode size, waveform, or frequency to apply. Three male and three female subjects (22–40 years old) were examined during electrical stimulation of the quadriceps muscle. Two self adhesive electrode sizes were examined, 2 cm × 2 cm and 2 cm × 4 cm. Electrical stimulation was applied with square and sine waveforms, currents of 5, 10 and 15 mA, and pulse widths of 100–500 μs above the quadriceps muscle. Frequencies of stimulation were 20, 30, and 50 Hz. Current on the skin above the quadriceps muscle was measured with surface electrodes at five positions and at three positions with needle electrodes in the same muscle. Altering pulse width in the range of 100–500 μs, the frequency over a range of 20–50 Hz, or current from 5 to 15 mA had no effect on current dispersion either in the skin or within muscle. In contrast, the distance separating the electrodes caused large changes in current dispersion on the skin or into muscle. The most significant finding in the present investigation was that, while on the surface of the skin current dispersion was not different between sine and square wave stimulation, significantly more current was transferred deep in the muscle with sine versus square wave stimulation. The use of sine wave stimulation with electrode separation distances of less then 15 cm is recommended for electrical stimulation with a sine wave to achieve deep muscle stimulation.     

Movement-induced potentials in surface electrodes

Movement-induced potentials of streaming potential type were studied in various electrode configurations. The geometric design of the electrode was important for the reduction of noise generated by the movements of gel. Potential and impedance variations were measured for electrode movements in electrolytes. The impedance variations were small and the streaming potentials were electrolyte-concentration dependent and in the order of 10μV. The same type of study was carried out for electrodes applied to the skin. The conclusion from this experiment is that skin deformation potentials dominate the disturbance pattern in this type of recordings.     

Electrode studies for the long-term ambulatory ECG

Noise and motion artefacts interfere with ambulatory ECG recording. In the paper the hypothesis that proper skin preparation and electrode design and placement could reduce the artefact levels is tested. The comparison of four commercial electrodes shows differences in adhesive strength and levels of skin irritation but does not indicate significant differences in the artefact levels produced by the electrodes. Four treatments are compared—no skin preparation, rubbing with alcohol, abrasion and puncturing—for their effectiveness in reducing motion artefact. Skin preparations do not reduce the motion artefact significantly but cause much discomfort. Therefore, skin preparation is not recommended. We recorded the signal (QRS complex) to-noise (artefact at the electrode site) ratio at 15 thoracic locations and recommend two pairs for ambulatory ECG recording. The statistical experimental design procedures used can also be adopted for comparison and testing for improvement of other electrode properties and designs.     

Characteristics of skin admittance for dry electrodes and the measurement of skin moisturisation

The properties of skin adminttance were investigated with the intention of applying them to skin moisturisation measurement. Skin admittance is determined by measuring relative permittivity and the resistivity of the stratum corneum, and by contact ratio between dry electrode and stratum corneum. It was found, however, that the contact ratio is the predominant factor producing the change of skin admittance induced by changes in the water content of skin. To measure skin admittance, the following conditions were found to be approriate: (a) frequency of about 100 kHz; (b) concentric electrodes, the diameter of the measuring (inner) electrode being about 5 mm, and (c) an electrode pressure of about 100 g cm⁻². Based on these optimal conditions, a system for measuring skin admittance was constructed. All measuring procedures were automated. Experimental observations made with this system have indicated its usefulness for the measurement of skin moisturisation.     

Comparison of neural damage induced by electrical stimulation with faradaic and capacitor electrodes

Arrays of platinum (faradaic) and anodized, sintered tantalum pentoxide (capacitor) electrodes were implanted bilaterally in the subdural space of the parietal cortex of the cat. Two weeks after implantation both types of electrodes were pulsed for seven hours with identical waveforms consisting of controlled-current, chargebalanced, symmetric, anodic-first pulse pairs, 400 μsec/phase and a charge density of 80–100 μC/cm² (microcoulombs per square cm) at 50 pps (pulses per second). One group of animals was sacrificed immediately following stimulation and a second smaller group one week after stimulation. Tissues beneath both types of pulsed electrodes were damaged, but the difference in damage for the two electrode types was not statistically significant. Tissue beneath unpulsed electrodes was normal. At the ultrastructural level, in animals killed immediately after stimulation, shrunken and hyperchromic neurons were intermixed with neurons showing early intracellular edema. Glial cells appeared essentially normal. In animals killed one week after stimulation most of the damaged neurons had recovered, but the presence of shrunken, vacuolated and degenerating neurons showed that some of the cells were damaged irreversibly. It is concluded that most of the neural damage from stimulations of the brain surface at the level used in this study derives from processes associated with passage of the stimulus current through tissue, such as neuronal hyperactivity rather than electrochemical reactions associated with current injection across the electrode-tissue interface, since such reactions occur only with the faradaic electrodes.     

Radio frequency perforation of cardiac tissue: Modelling and experimental results

Radio frequency (RF) current delivered through a thin catheter can be used to perforate the pulmonary valve or the atrial septum to treat pulmonary atresia in newborns. To understand better the mechanisms of RF perforation, a numerical model is developed, and experiments are performed in isolated canine cardiac tissue. The model consists of a cylindrical domain with a tissue layer between two blood layers. The finite-difference method is used to compute both the potential and temperature distributions. When the tissue temperature exceeds 100°C in all points that are directly in front of the catheter, these points are considered to be instantly vaporised, and the catheter advances over these points. The computed temperature time course coincides with measured temperature at small voltages (<16 V). Simulated perforation occurs when the voltage exceeds a threshold of 70–80V for a catheter diameter of 0.30–0.44 mm, which coincides with experimental observations in the myocardium. A voltage exceeding this perforation threshold tends to decrease tissue damage. Shorter electrodes (0.7 mm as against 2.4 mm) with smaller diameters produce a more rapid perforation. In conclusion, numerical simulations provide insights into aspects of RF perforation, such as electrode size, current, speed of perforation and collateral damage.     

Noise of surface bio-potential electrodes based on NASICON ceramic and Ag−AgCl

The electrochemical noise from dry NASICON-based surface electrodes and pregelled Ag−AgCl electrodes is evaluated in saline solutions and on the skin. The electrochemical noise from the electrode/electrolyte interface is found to be negligible (less than 1 μV peak to peak). On the skin, the noise level is highly dependent on the patient. At high frequencies, the skin/electrode interface noise is equal to ‘thermal noise’ and can be related to the real part of the skin/electrode impedance. At low frequencies (f<100 Hz), excess noise is observed that varies as f⁻². It is tentatively ascribed to a non-stationary process or noise of electrochemical origin due to the ionic nature of the skin. The contribution of residual EMG signal of low amplitude (5 μV peak to peak) is suggested for electrodes with large surface area. Reprint requests and correspondence should be addressed to Frist     

An intrafascicular electrode for recording of action potentials in peripheral nerves

We are developing a new type of bipolar recording electrode intended for implantation within individual fascicles of mammalian peripheral nerves. In the experiments reported here we used electrodes fabricated from 25 μm diameter Pt wire, 50 μm 90% Pt-10% Ir wire and 7 μm carbon fibers. The electrodes were implanted in the sciatic nerves of rats and in the ulnar nerves of cats. The signal-to-noise ratio of recorded activity induced by nonnoxious mechanical stimulation of the skin and joints was studied as a function of the type of electrode material used, the amount of insulation removed from the recording zone, and the longitudinal separation of the recording zones of bipolar electrode pairs. Both acute and short term (two day) chronic experiments were performed. The results indicate that a bipolar electrode made from Teflon^™-insulated, 25 μm diameter, 90% Pt-10% Ir wire, having a 1–2 mm long recording zone, can be used for recording of peripheral nerve activity when implanted with one wire inside the fascicle and the other lead level with the first lead, but outside the fascicle. No insulating cuff needs to be placed around the nerve trunk.     

Effect of some physiologically important drugs on the skin impedance

The impedance of rabbit skin has been measured in the frequency range 1–60 kHz using a simple a.c. bridge method and stainless steel electrodes. The effect of four important drugs, namely, adrenaline, noradrenaline, atropine and histamine, has been examined. It was found that all these drugs produced a decrease in the skin impedance in varying degrees, suggesting a penetration of the ions through the underlying layers of the skin. For the purpose of analysis, all these data are compared with their own controls. The order of applying the two drugs adrenaline and noradrenaline at the same site on the skin of an animal does not produce a change in the nature of the relative impedance variation. It was observed that the effect produced by noradrenaline is more pronounced than that by adrenaline. The effect produced by these drugs was compared with that produced by pure hydration of the skin. It was found that the change produced in the latter case is much less than that produced by drugs, thus showing a clear difference between the two effects.     

Microtube-based electrode arrays for low invasive extracellular recording with a high signal-to-noise ratio

We report on the development of a microtube electrode array as a neural interface device. To combine the desired properties for the neural interface device, such as low invasiveness with a small needle and a good signal-to-noise ratio in neural recordings, we applied the structure of a glass pipette electrode to each microtube electrode. The device was fabricated as sub-5-μm-diameter out-of-plane silicon dioxide microtube arrays using silicon microneedle templates, which are grown by the selective vapor–liquid–solid method. The microtubes had inner diameters of 1.9–6.4 μm and a length of 25 μm. Impedances ranged from 220 kΩ to 1.55 MΩ, which are less than those for conventional microneedles. In addition, the microtube electrodes had less signal attenuation than conventional microneedle electrodes. We confirmed that the effects of parasitic capacitances between neighboring microtubes and channels were sufficiently small using a test signal. Finally, neural responses evoked from a rat peripheral nerve were recorded in vivo using a microtube electrode to confirm that this type of electrode can be used for both electrophysiological measurements and as a neural interface device.     

Spinal cord direct current stimulation: finite element analysis of the electric field and current density

Applied low-intensity direct current (DC) stimulates and directs axonal growth in models of spinal cord injury (SCI) and may have therapeutic value in humans. Using higher electric strengths will probably increase the beneficial effects, but this faces the risk of tissue damage by electricity or toxic reactions at the electrode–tissue interface. To inform the optimisation of DC-based therapeutics, we developed a finite element model (FEM) of the human cervical spine and calculated the electric fields (EFs) and current densities produced by electrodes of different size, geometry and location. The presence of SCI was also considered. Three disc electrodes placed outside the spine produced low-intensity, uneven EFs, whereas the EFs generated by the same electrodes located epidurally were about three times more intense. Changes in electrical conductivity after SCI had little effect on the EF magnitudes. Uniformly distributed EFs were obtained with five disc electrodes placed around the dura mater, but not with a paddle-type electrode placed in the dorsal epidural space. Replacing the five disc electrodes by a single, large band electrode yielded EFs > 5 mV/mm with relatively low current density (2.5 μA/mm²) applied. With further optimisation, epidural, single-band electrodes might enhance the effectiveness of spinal cord DC stimulation.     

Analysis of temperature measurement for monitoring radio-frequency brain lesioning

During ablative neurosurgery of movement disorders, for instance therapy of Parkinson's disease, temperature monitoring is crucial. This study aims at a quantitative comparison of measurement deviations between the maximum temperature located outside the lesioning electrode and two possible thermocouple locations inside the electrode. In order to obtain the detailed temperature field necessary for the analysis, four finite element models associated with different surroundings and with different power supplies are studied. The results from the simulations show that both the power level and the power density as well as the surrounding medium affect the temperature measurement and the temperature field in general. Since the maximum temperature is located outside the electrode there will always be a deviation in time and level between the measured and the maximum temperature. The deviation is usually 2–7 s and 3–12°C, depending on, for example, the thermocouple location and surrounding medium. Therefore, not only the measured temperature but also the relation between measured and maximum temperature must be accounted for during therapy and device design.     

Histologic and physiologic evaluation of electrically stimulated peripheral nerve: Considerations for the selection of parameters

Helical electrodes were implanted around the left and right common peroneal nerves of cats. Three weeks after implantation one nerve was stimulated for 4–16 hours using charge-balanced, biphasic, constant current pulses. Compound action potentials (CAP) evoked by the stimulus were recorded from over the cauda equina before, during and after the stimulation. Light and electron microscopy evaluations were conducted at various times following the stimulation. The mere presence of the electrode invariably resulted in thickened epineurium and in some cases increased peripheral endoneurial connective tissue beneath the electrodes. Physiologic changes during stimulation included elevation of the electrical threshold of the large axons in the nerve. This was reversed within one week after stimulation at a frequency of 20 Hz, but often was not reversed following stimulation at 50–100 Hz. Continuous stimulation at 50 Hz for 8–16 hours at 400 μA or more resulted in neural damage characterized by endoneurial edema beginning within 48 hours after stimulation, and early axonal degeneration (EAD) of the large myelinated fibers, beginning by 1 week after stimulation. Neural damage due to electrical stimulation was decreased or abolished by reduction of the duration of stimulation, by stimulating at 20 Hz (vs. 50 Hz) or by use of an intermittent duty cycle. These results demonstrate that axons in peripheral nerves can be irreversely damaged by 8–16 hours of continuous stimulation at 50 Hz. However, the extent to which these axons may subsequently regenerate is uncertain. Therefore, protocols for functional electrical stimulation in human patients probably should be evaluated individually in animal studies.     

Noise characteristics of stainless-steel surface electrodes

Bioelectric events measured with surface electrodes are subject to noise components which may be significant in comparison with low-level biological signals such as evoked neuroelectric potentials, and myoelectric potentials. In an effort to better understand noise arising from these electrodes, electrode and measurement system noise is modelled. The effect of electrode surface area on electrode impedance and noise is studied using circular stainless-steel electrodes of varying diameters. The main contributions of the work are the development of a model for stainless-steel electrode noise as a function of electrode area, and demonstrating that, for the band-width of interest to evoked neuroelectric and myoelectric signals (8–10 000 Hz), the primary noise components are thermal and amplifier current generated. The magnitudes of both of these depend on the electrode impedance magnitude. Electrode impedance is shown to be a power function of both electrode diameter and frequency, consistent with a capacitive electrode model.     

Cutaneous vasomotor adjustments during arm-cranking in individuals with paraplegia

Skin blood flow (SKBF) was evaluated during arm-cranking exercise in able-bodied control subjects (AB; n=6) and in individuals with low- (LP; T10–T12 lesions; n=6) and high-level paraplegia (HP; T5–T9 lesions; n=6), using laser Doppler flowmetry (LDF). During moderate exercise SKBF decreased to [mean (SD)] 82 (15)% of the pre-exercise resting level in AB, whereas it increased to 158 (52)% in LP and to 112 (51)% in HP (the LP:AB difference, P < 0.05). During intense exercise SKBF increased to 366 (180)% of the resting level in AB, whereas it increased only moderately [147 (68)%] in both paraplegic groups (the paraplegic:AB difference, P < 0.05). The paraplegics developed a higher esophageal and leg skin temperature, which was attributed to the lack of active vasodilation and evaporative cooling over the legs. The results indicate that individuals with paraplegia suffer from impaired cutaneous vasoconstriction at the onset of arm exercise, and possess only a limited vasodilatory capability in the paralyzed regions. During intense exercise, thermoregulation depends critically on active cutaneous vasodilation and skin cooling. Accepted: 25 August 2000     

Electric current density distribution over the electrode surface of an autonomous electric stimulator of the gastrointestinal tract

Conclusion Thus, maximum density of electrical current is observed in the cylindrical part of the AES electrodes closer to the counter electrode. The inhomogeneity of the electrical current density distribution over the electrode surface is due to the specific shape and mutual orientation of the electrodes. Within the working range of electric stimulation currents, the inhomogeneity is substantially levelled because of nonlinearity of polarization characteristics of electrode material (12Kh18N9 stainless steel) in 1% solution of hydrochloric acid. The developed distributed model adequately describes the experimental data and it can be used for assessing functional performance and optimizing AES electrodes coated with various materials. Further development of the model could provide dynamic monitoring of the electrode-electrolyte system. Tomsk State Academy of Management Systems and Radioelectronics. Tomsk Polytechnical University. Translated from Meditsinskaya Tekhnika, No. 5, pp. 28–31, September–October, 1996.