Monopolar Electrode Configuration Research Articles

Performance of combined organic precipitation, electrocoagulation, and electrooxidation in treating anaerobically treated palm oil mill effluents

Palm oil mill effluent (POME), wastewater generated from palm oil production, is known for its extremely high chemical oxygen demand and brownish color. Anaerobic digestion is the primary treatment method for POME in the palm oil industry; however, anaerobically treated POME has high concentrations of residual contaminants and color intensity. This study proposes an approach to treat anaerobically-treated POME in recycled water for industrial applications by integrating preliminary organic precipitation, electrocoagulation, and electrooxidation (EO). The EO process was optimized in terms of the current density, electrolysis time, electrode arrangement, and feed flow rate. At a current density of 60 mA/cm2 and an electrolysis time of 9 min, the EO process with a graphite anode and stainless-steel cathode in the monopolar electrode configuration reduced the phenolic concentration and color in the preliminary-treated POME from 8.95 mg/L and 317.19 ADMI to 0.25 mg/L and 26.10 ADMI, respectively. Additionally, the EO process exhibited a 92.26% efficiency in lowering the ammonium-nitrogen content.

Gaussianity Evaluation of HD-sEMG Signals with Aging and Sex During Low and Moderate Isometric Contractions of the Biceps Brachii

IntroductionAging is associated with muscle decline, which alters both functional and anatomical properties of the neuromuscular system. These modifications can be reflected in high-density surface electromyography (HD-sEMG) signals. This study examines how age and sex impact the shape of the amplitude Probability Density Function (PDF) of HD-sEMG signals. Materials and MethodsMonopolar HD-sEMG signals were collected from the Biceps Brachii in a cohort of 17 individuals: 10 women (mean age: 22.9 ± 3.6 years) and 7 men (mean age: 24.4 ± 2.5 years) in the younger group, and 10 women (mean age: 69.8 ± 4.8 years) and 7 men (mean age: 72.8 ± 2.7 years) in the elderly group. The recordings were conducted during an elbow flexion at both 20% and 40% maximum voluntary contraction. The signal amplitude was evaluated using root means square amplitude (RMSA) and the PDF shape of each HD-sEMG signal was assessed through skewness, excess Kurtosis, and robust functional statistics. These shape distance metrics evaluate the departure from Gaussianity related to muscle aging. a) We conducted a comparison study of the HD-sEMG PDF shapes between younger and elderly individuals. b) Evaluating differences between men and women. c) Considering monopolar and Laplacian electrode configurations that are sensitive to different muscle regions. ResultsA) The HD-sEMG PDFs of elderly subjects demonstrated a lower departure from Gaussianity than their younger counterparts. B) Women exhibited lower RMSA values than men, and, on average, a lower departure from Gaussianity whatever the age and contraction level C) Trends of departure from Gaussianity with contraction level, seems to be influenced by the electrode configuration. In fact, a decrease in Gaussianity departure is observed with monopolar recordings where an increase is observed with Laplacian one, clearly indicating different muscle region assessment. DiscussionThe findings highlight the influence of factors such aging, sex, contraction level and electrode montage on the shape of the HD-sEMG PDF, emphasizing the significance of using this descriptor for monitoring and better assessment of muscle aging.

Computer Simulation of the Electrical Stimulation of the Human Vestibular System: Effects of the Reactive Component of Impedance on Voltage Waveform and Nerve Selectivity

The vestibular system is responsible for our sense of balance and spatial orientation. Recent studies have shown the possibility of partially restoring the function of this system using vestibular implants. Electrical modeling is a valuable tool in assisting the development of these implants by analyzing stimulation effects. However, previous modeling approaches of the vestibular system assumed quasi-static conditions. In this work, an extended modeling approach is presented that considers the reactive component of impedance and the electrode-tissue interface and their effects are investigated in a 3D human vestibular computer model. The Fourier finite element method was employed considering the frequency-dependent electrical properties of the different tissues. The electrode-tissue interface was integrated by an instrumental electrode model. A neuron model of myelinated fibers was employed to predict the nerve responses to the electrical stimulus. Morphological changes of the predicted voltage waveforms considering the dielectric tissue properties were found compared to quasi-static simulations, particularly during monopolar electrode configuration. Introducing the polarization capacitance and the scar tissue around the electrode in combination with a power limitation leads to a considerable current reduction applied through the active electrode and, consequently, to reduced voltage amplitudes of the stimulus waveforms. The reactive component of impedance resulted in better selectivity for the excitation of target nerves compared to the quasi-static simulation at the expense of slightly increased stimulus current amplitudes. We conclude that tissue permittivity and effects of the electrode-tissue interface should be considered to improve the accuracy of the simulations.

Magnetoelectric Nanoparticles: Evaluating Stimulation Feasibility of the Possible Next Generation Approach for Deep Brain Stimulation

The purpose of this study is to quantify the distributions of the electric field induced by CoFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> core - BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> shell magneto-electric nanoparticles (MENPs) when localized in deep brain structures. These fields can be used for deep brain stimulation (DBS), and their effect is compared to the fields induced by conventional DBS electrodes in monopolar and bipolar configuration. A computational approach based on finite element method was applied, along with the use of a highly detailed anatomical model of the brain structures. Different MENPs configurations were investigated and compared to conventional DBS electrode configuration. The activation of nervous fibers was quantified by calculating the Activation Function (AF) defined as the second derivative of the electric potential along the fiber. Electric field amplitudes obtained by MENPs were much lower than the ones obtained by the monopolar and bipolar electrode configurations. The AF values showed that MENPs were able to obtain very localized activation patterns along the fibers. In addition to the minimal invasiveness and proven biocompatibility of the MENPs, the results show that the proposed approach represents an important step towards a selective and minimally invasive strategy for DBS. All these findings are essential in identifying the unique characteristics that MENPs could provide for nervous system stimulation, and how the use of MENPs could improve the development of a new generation of DBS techniques.

Estimating health of the implanted cochlea using psychophysical strength-duration functions and electrode configuration

It is generally believed that the efficacy of cochlear implants is partly dependent on the condition of the stimulated neural population. Cochlear pathology is likely to affect the manner in which neurons respond to electrical stimulation, potentially resulting in differences in perception of electrical stimuli across cochlear implant recipients and across the electrode array in individual cochlear implant users. Several psychophysical and electrophysiological measures have been shown to predict cochlear health in animals and were used to assess conditions near individual stimulation sites in humans. In this study, we examined the relationship between psychophysical strength-duration functions and spiral ganglion neuron density in two groups of guinea pigs with cochlear implants who had minimally-overlapping cochlear health profiles. One group was implanted in a hearing ear (N = 10) and the other group was deafened by cochlear perfusion of neomycin, inoculated with an adeno-associated viral vector with an Ntf3-gene insert (AAV.Ntf3) and implanted (N = 14). Psychophysically measured strength-duration functions for both monopolar and tripolar electrode configurations were then compared for the two treatment groups. Results were also compared to their histological outcomes. Overall, there were considerable differences between the two treatment groups in terms of their psychophysical performance as well as the relation between their functional performance and histological data. Animals in the neomycin-deafened, neurotrophin-treated, and implanted group (NNI) exhibited steeper strength-duration function slopes; slopes were positively correlated with SGN density (steeper slopes in animals that had higher SGN densities). In comparison, the implanted hearing (IH) group had shallower slopes and there was no relation between slopes and spiral ganglion density. Across all animals, slopes were negatively correlated with ensemble spontaneous activity levels (shallower slopes with higher ensemble spontaneous activity levels). We hypothesize that differences in strength-duration function slopes between the two treatment groups were related to the condition of the inner hair cells, which generate spontaneous activity that could affect the across-fiber synchrony and/or the size of the population of neural elements responding to electrical stimulation. In addition, it is likely that spiral ganglion neuron peripheral processes were present in the IH group, which could affect membrane properties of the stimulated neurons. Results suggest that the two treatment groups exhibited distinct patterns of variation in conditions near the stimulating electrodes that altered detection thresholds. Overall, the results of this study suggest a complex relationship between psychophysical detection thresholds for cochlear implant stimulation and nerve survival in the implanted cochlea. This relationship seems to depend on the characteristics of the electrical stimulus, the electrode configuration, and other biological features of the implanted cochlea such as the condition of the inner hair cells and the peripheral processes.

Modeling and optimization of a continuous electrocoagulation process using an artificial intelligence approach

Abstract An artificial neural network (ANN) with the topology 8-94-85-2 (input – hidden layer 1 - hidden layer 2 - output) was used to model the operation of the continuous electrocoagulation (CEC) process for the removal of fluoride from water. After the ANN training, the sum of the squared errors (MSE) and the determination coefficient (R2) of the testing set model predictions were 0.0088 and 0.999, respectively, showing a good generalization and the model's predictive capacity. The optimization of the process cost using the genetic algorithm (GA) showed that the optimal conditions are highly dependent on the feed concentration and the fluoride removal requirements. For 5 L of water containing 10 mg/L of fluoride, the optimal conditions to reduce the fluoride concentration below the permissible limit (1.5 mg/L) are 88.3 mA of current intensity, a flow rate of 73.6 mL/min, and the use of a series monopolar (SM) electrode configuration, corresponding to a fluoride removal of 85% and an operating cost of 0.05 €/L.

Pulse Shaping Strategies for Electroceuticals: A Comprehensive Survey of the Use of Interphase Gaps in Miniature Stimulation Systems.

Interphase gaps (IPGs) are among the most commonly suggested pulse shape variations to try to enhance neural stimulation efficiency by reducing the action potential (AP) suppressing effect of an early anodic hyperpolarization. The majority of published literature on the effect of IPGs is based on investigations of monopolar stimulation configurations. However, many contemporary neuromodulation applications including the emerging field of electroceutical devices operate in a bipolar electrode configuration. We investigated the effect of IPGs and asymmetric biphasic current controlled pulses with reduced anodic amplitude on neural activation in both principal electrode configurations in a rodent in-vivo nerve muscle preparation. In the monopolar electrode configuration, our findings of 10.9 ± 1.5% decreased stimulation amplitude with 200 μs IPGs in biphasic pulses of 40 μs phase width are in agreement with published literature in this configuration. Surprisingly, using the bipolar configuration, opposite effects of IPGs were observed and neural activation required up to 18.6 ± 3.1% (phase width 100 μs, IPG = 1000 μs) higher amplitudes. Electroneurogram recordings of the stimulated nerve revealed temporal differences in AP generation between the monopolar and bipolar configuration. In the bipolar configuration excitation first occurred in response to the middle field transition of biphasic pulses. This is the first study to report consistently increased amplitude requirements with IPGs in bipolar stimulation configurations. Our findings must be taken into consideration when designing stimulation waveforms for neuromodulation devices that operate in a bipolar mode to avoid increased amplitude requirements that result in increased energy consumption.

Image-based biophysical modeling predicts cortical potentials evoked with subthalamic deep brain stimulation

BackgroundSubthalamic deep brain stimulation (DBS) is an effective surgical treatment for Parkinson’s disease and continues to advance technologically with an enormous parameter space. As such, in-silico DBS modeling systems have become common tools for research and development, but their underlying methods have yet to be standardized and validated. ObjectiveEvaluate the accuracy of patient-specific estimates of neural pathway activations in the subthalamic region against intracranial, cortical evoked potential (EP) recordings. MethodsPathway activations were modeled in eleven patients using the latest advances in connectomic modeling of subthalamic DBS, focusing on the hyperdirect pathway (HDP) and corticospinal/bulbar tract (CSBT) for their relevance in human research studies. Correlations between pathway activations and respective EP amplitudes were quantified. ResultsGood model performance required accurate lead localization and image fusions, as well as appropriate selection of fiber diameter in the biophysical model. While optimal model parameters varied across patients, good performance could be achieved using a global set of parameters that explained 60% and 73% of electrophysiologic activations of CSBT and HDP, respectively. Moreover, restricted models fit to only EP amplitudes of eight standard (monopolar and bipolar) electrode configurations were able to extrapolate variation in EP amplitudes across other directional electrode configurations and stimulation parameters, with no significant reduction in model performance across the cohort. ConclusionsOur findings demonstrate that connectomic models of DBS with sufficient anatomical and electrical details can predict recruitment dynamics of white matter. These results will help to define connectomic modeling standards for preoperative surgical targeting and postoperative patient programming applications.

The Magnetic Properties of Electrical Pulses Delivered by Deep-Brain Stimulation Systems

The aim of this article is to analyze the magnetic field properties for both the monopolar and bipolar electrode configurations of deep-brain stimulation electrodes using 3-D magnetic field measurements and to investigate if the magnetic measurements enable a localization of the electrode as a proof of concept. Therefore, a simplified head phantom with an integrated deep-brain stimulation electrode was created to measure the magnetic flux densities in all the three dimensions with a fluxgate magnetometer over a sensor trajectory of measuring points inside the magnetically shielded chamber. The magnitude of the magnetic flux density for monopolar stimulation and bipolar stimulation is in the nT and pT ranges for the frequency 160 Hz, depending on the stimulation amplitude and on the distance between the sensor and the electrode. The field distributions show a linear decline in the magnetic field for the monopolar and a quadratic decline for the bipolar stimulation. We were able to reconstruct the magnetic field using multiple recording sites. As the magnetic field of deep-brain stimulation can be measured and its field strength can be reconstructed, it is feasible to estimate the strength of the field within the limits of programmable stimulation parameters and distance between the sensor and the electrode. The presented results are intended as preliminary work for the further development of electrode localization methods using magnetic measurements. As an example of the feasibility of electrode localization, this article presents a bipolar measurement that creates a more focused spatial field distribution and results in an accurate localization.

Pulse-rate discrimination deficit in cochlear implant users: is the upper limit of pitch peripheral or central?

Cochlear implant (CI) users do not reliably associate an increase in pulse rate above 300 pulses per second (pps) with an increase in pitch. The locus of this upper limit of pitch remains unknown. The present study tested the hypothesis that this deficit resides at least initially at the auditory nerve. The hypothesis was tested by comparing pulse rate discrimination in different neural excitation patterns, in which a large versus small population of auditory nerve fibers was activated. If poorer pulse rate discrimination was found under conditions where narrower spread of neural excitation (SOE) was anticipated where a relatively small neural population was activated, then it would support the hypothesis that the rate processing deficit found in CI users is related to peripheral neural degeneration. Nine listeners (12 ears) implanted with the Cochlear Americas Nucleus® devices participated in the study. Different SOE conditions were created by (1) selecting electrodes that showed narrow versus broad forward-masked psychophysical spatial tuning curves, and (2) by measuring these electrodes in monopolar (MP) and narrow bipolar (BP0) electrode configurations. Rate discrimination difference limen (DL) was measured at the selected electrodes in two electrode configurations at three base rates (200, 300 and 500 pps). Consistent with the prediction, group mean DL was better (1) at stimulation sites measured with broader tuning, and (2) in MP relative to BP stimulation. These effects were more salient at the more challenging base rates. There was a weak relationship between rate discrimination (above thresholds) and the effect of rate on detection thresholds. Finally, rate discrimination at rates above the known upper limit (i.e., 500 pps) was correlated with duration of deafness and highly predicted the subjects’ speech recognition performance in noise. These findings support that pulse rate discrimination depends, at least partially, on neural conditions at the auditory periphery and this peripheral limit predicts speech recognition outcomes with a CI.

A Dynamically Focusing Cochlear Implant Strategy Can Improve Vowel Identification in Noise.

The standard, monopolar (MP) electrode configuration used in commercially available cochlear implants (CI) creates a broad electrical field, which can lead to unwanted channel interactions. Use of more focused configurations, such as tripolar and phased array, has led to mixed results for improving speech understanding. The purpose of the present study was to assess the efficacy of a physiologically inspired configuration called dynamic focusing, using focused tripolar stimulation at low levels and less focused stimulation at high levels. Dynamic focusing may better mimic cochlear excitation patterns in normal acoustic hearing, while reducing the current levels necessary to achieve sufficient loudness at high levels. Twenty postlingually deafened adult CI users participated in the study. Speech perception was assessed in quiet and in a four-talker babble background noise. Speech stimuli were closed-set spondees in noise, and medial vowels at 50 and 60 dB SPL in quiet and in noise. The signal to noise ratio was adjusted individually such that performance was between 40 and 60% correct with the MP strategy. Subjects were fitted with three experimental strategies matched for pulse duration, pulse rate, filter settings, and loudness on a channel-by-channel basis. The strategies included 14 channels programmed in MP, fixed partial tripolar (σ = 0.8), and dynamic partial tripolar (σ at 0.8 at threshold and 0.5 at the most comfortable level). Fifteen minutes of listening experience was provided with each strategy before testing. Sound quality ratings were also obtained. Speech perception performance for vowel identification in quiet at 50 and 60 dB SPL and for spondees in noise was similar for the three tested strategies. However, performance on vowel identification in noise was significantly better for listeners using the dynamic focusing strategy. Sound quality ratings were similar for the three strategies. Some subjects obtained more benefit than others, with some individual differences explained by the relation between loudness growth and the rate of change from focused to broader stimulation. These initial results suggest that further exploration of dynamic focusing is warranted. Specifically, optimizing such strategies on an individual basis may lead to improvements in speech perception for more adult listeners and improve how CIs are tailored. Some listeners may also need a longer period of time to acclimate to a new program.

Model-Based Vestibular Afferent Stimulation: Evaluating Selective Electrode Locations and Stimulation Waveform Shapes.

A dysfunctional vestibular system can be a severe detriment to the quality of life of a patient. Recent studies have shown the feasibility for a vestibular implant to restore rotational sensation via electrical stimulation of vestibular ampullary nerves. However, the optimal stimulation site for selective elicitation of the desired nerve is still unknown. We realized a finite element model on the basis of μCT scans of a human inner ear and incorporated naturally distributed, artificial neural trajectories. A well-validated neuron model of myelinated fibers was incorporated to predict nerve responses to electrical stimulation. Several virtual electrodes were placed in locations of interest inside the bony labyrinth (intra-labyrinthine) and inside the temporal bone, near the target nerves (extra-labyrinthine), to determine preferred stimulation sites and electrode insertion depths. We investigated various monopolar and bipolar electrode configurations as well as different pulse waveform shapes for their ability to selectively stimulate the target nerve and for their energy consumption. The selectivity was evaluated with an objective measure of the fiber recruitment. Considerable differences of required energy and achievable selectivity between the configurations were observed. Bipolar, intra-labyrinthine electrodes provided the best selectivities but also consumed the highest amount of energy. Bipolar, extra-labyrinthine configurations did not offer any advantages compared to the monopolar approach. No selective stimulation could be performed with the monopolar, intra-labyrinthine approach. The monopolar, extra-labyrinthine electrodes required the least energy for satisfactory selectivities, making it the most promising approach for functional vestibular implants. Different pulse waveform shapes did not affect the achieved selectivity considerably but shorter pulse durations showed consistently a more selective activation of the target nerves. A cathodic, centered triangular waveform shape was identified as the most energy-efficient of the tested shapes. Based on these simulations we are able to recommend the monopolar, extra-labyrinthine stimulation approach with cathodic, centered triangular pulses as good trade-off between selectivity and energy consumption. Future implant designs could benefit from the findings presented here.

Screening of electrocoagulation process parameters for treated palm oil mill effluent using minimum-runs resolution IV design

The present study aimed at the screening of parameters for electrocoagulation treatment of treated palm oil mill effluent using minimum-runs resolution IV design. The responses examined include: chemical oxygen demand removal (%), total suspended solids removal (%) and turbidity reduction (%), and the varied dependent factors comprise: electrical current density (mA/cm2), time (min), pH, electrolyte concentration (g/L), stirring speed (rpm), electrode spacing (mm) and electrode configuration (monopolar or dipolar). The statistical results revealed that the current density has a significant influence on the treatment performance at two-level interactions with pH, electrode spacing and electrode concentration and at three-level correlations with time and pH. Thus, the most important factors affecting the removal efficiency of the organic compounds were found to be pH, time, electrode spacing, electrolyte concentration and electrode configuration at a P value less than 0.05, respectively, in the descending order of significance. Therefore, the optimized electrocoagulation process could be reached with current density equal to 5 mA/cm2, electrolysis time of 5 min, electrode spacing of 5 mm and using monopolar electrode configuration. This combination provided the maximum ability of the process for chemical oxygen demand (68.84%), total suspended solids (93.27%) and turbidity reduction (92.88%) predictions, with the corresponding experimental values of 69.27, 97.59 and 96.91%, respectively.

Intermuscular Coherence Between Surface EMG Signals Is Higher for Monopolar Compared to Bipolar Electrode Configurations.

Introduction: The vasti muscles have to work in concert to control knee joint motion during movements like walking, running, or squatting. Coherence analysis between surface electromyography (EMG) signals is a common technique to study muscle synchronization during such movements and gain insight into strategies of the central nervous system to optimize neuromuscular performance. However, different assessment methods related to EMG data acquisition, e.g., different electrode configurations or amplifier technologies, have produced inconsistent observations. Therefore, the aim of this study was to elucidate the effect of different EMG acquisition techniques (monopolar vs. bipolar electrode configuration, potential vs. current amplifier) on the magnitude, reliability, and sensitivity of intermuscular coherence between two vasti muscles during stable and unstable squatting exercises.Methods: Surface EMG signals from vastus lateralis (VL) and medialis (VM) were obtained from eighteen adults while performing series of stable und unstable bipedal squats. The EMG signals were acquired using three different recording techniques: (1) Bipolar with a potential amplifier, (2) monopolar with a potential amplifier, and (3) monopolar electrodes with a current amplifier. VL-VM coherence between the respective raw EMG signals was determined during two trials of stable squatting and one trial of unstable squatting to compare the coherence magnitude, reliability, and sensitivity between EMG recording techniques.Results: VL-VM coherence was about twice as high for monopolar recordings compared to bipolar recordings for all squatting exercises while coherence was similar between monopolar potential and current recordings. Reliability measures were comparable between recording systems while the sensitivity to an increase in intermuscular coherence during unstable vs. stable squatting was lowest for the monopolar potential system.Discussion and Conclusion: The choice of electrode configuration can have a significant effect on the magnitude of EMG-EMG coherence, which may explain previous inconsistencies in the literature. A simple simulation of cross-talk could not explain the large differences in intermuscular coherence. It is speculated that inevitable errors in the alignment of the bipolar electrodes with the muscle fiber direction leads to a reduction of information content in the differential EMG signals and subsequently to a lower resolution for the detection of intermuscular coherence.

Avoiding neuromuscular stimulation in liver irreversible electroporation using radiofrequency electric fields

Electroporation-based treatments typically consist of the application of high-voltage dc pulses. As an undesired side effect, these dc pulses cause electrical stimulation of excitable tissues such as motor nerves. The present in vivo study explores the use of bursts of sinusoidal voltage in a frequency range from 50 kHz to 2 MHz, to induce irreversible electroporation (IRE) whilst avoiding neuromuscular stimulation. A series of 100 dc pulses or sinusoidal bursts, both with an individual duration of 100 µs, were delivered to rabbit liver through thin needles in a monopolar electrode configuration, and thoracic movements were recorded with an accelerometer. Tissue samples were harvested three hours after treatment and later post-processed to determine the dimensions of the IRE lesions. Thermal damage due to Joule heating was ruled out via computer simulations. Sinusoidal bursts with a frequency equal to or above 100 kHz did not cause thoracic movements and induced lesions equivalent to those obtained with conventional dc pulses when the applied voltage amplitude was sufficiently high. IRE efficacy dropped with increasing frequency. For 100 kHz bursts, it was estimated that the electric field threshold for IRE is about 1.4 kV cm−1 whereas that of dc pulses is about 0.5 kV cm−1.

Assessment of effective operational parameters on dyeing wastewater treatment by electrocoagulation process

A wide range of chemicals and dyes are being used in textile industry, and are often found in the wastewater produced. This study attempts to investigate the reduction of COD, TSS, and dye in effluents from the dyeing and washing unit of textile industry, using electrocoagulation process. The reactor is equipped with 10 iron electrodes, connected to a direct current (DC) source in a monopolar electrode configuration. In each stage of the experiment, 2.5 l of the effluent enters the reactor and the effects of a number of important operational parameters such as voltage, pH, and reaction time is studied on the removal of COD, TSS, and dye parameters. Results show that the optimum operational conditions are reaction time of 120 min, voltage of 30 V, and pH of 7, which reduces COD, TSS, and dye by 87%, 91%, and 98%, respectively. Therefore, it has been concluded that the efficiency of pollutants removal from the wastewater improves as voltage and reaction time are increased.

A new method for the localization of the innervation zone based on monopolar surface-detected potentials

In monopolar electrode configuration, the shape of the motor unit potential (MUP) undergoes essential morphologic changes with increasing distance from the innervation zone. In particular, the rising phase of the MUP slows down and becomes longer as the electrode is moved further from the innervation zone. Based on this, it is hypothesized that the maximum slope of the rising phase of a monopolar MUP (SlopeMAX) would reach its highest value at the innervation zone. Herein, we sought to determine whether the location of the innervation zone coincides with the position in the muscle of the monopolar MUP with highest SlopeMAX and whether new criteria for the localization of the innervation region can be proposed based on the SlopeMAX of monopolar potentials. Multichannel surface (13×5 electrode array) and intramuscular (wire electrodes inserted with needles of lengths 15 and 25mm) EMG signals were concurrently recorded in monopolar configuration from the biceps brachii muscle of 10 healthy subjects. The spatial distribution of monopolar and bipolar MUPs along the fibers’ direction were obtained by spike-triggered averaging of the surface EMG. We found that the monopolar MUP with steepest rising phase (i.e., highest SlopeMAX) was located either just above or at half of the inter-electrode distance from the innervation zone. High levels of agreement (94–98%) were found between the position of the innervation zone assessed with the SlopeMAX criteria of monopolar potentials and the position identified using the phase reversal criteria of bipolar potentials. The present results legitimize the use of compound muscle action potentials (M waves) to localize the innervation zone: this location would correspond to the electrode position which yielded the monopolar M wave with highest SlopeMAX.

The Spatial Extent of Epiretinal Electrical Stimulation in the Healthy Mouse Retina

Background/Aims: Retinal prostheses use electrical stimulation to restore functional vision to patients blinded by retinitis pigmentosa. A key detail is the spatial pattern of ganglion cells activated by stimulation. Therefore, we characterized the spatial extent of network-mediated electrical activation of retinal ganglion cells (RGCs) in the epiretinal monopolar electrode configuration. Methods: Healthy mouse RGC activities were recorded with a micro-electrode array (MEA). The stimuli consisted of monophasic rectangular cathodic voltage pulses and cycling full-field light flashes. Results: Voltage tuning curves exhibited significant hysteresis, reflecting adaptation to electrical stimulation on the time scale of seconds. Responses decreased from 0 to 300 µm, and were also dependent on the strength of stimulation. Applying the Rayleigh criterion to the half-width at half-maximum of the electrical point spread function suggests a visual acuity limit of no better than 20/946. Threshold voltage showed only a modest increase across these distances. Conclusion: The existence of significant hysteresis requires that future investigations of electrical retinal stimulation control for such long-memory adaptation. The spread of electrical activation beyond 200 µm suggests that neighbouring electrodes in epiretinal implants based on indirect stimulation of RGCs may be indiscriminable at interelectrode spacings as large as 400 µm.

Comparing auditory perceptual thresholds in pediatric and adult cochlear implant populations

It is well known that cochlear implant listeners show enormous variability in speech recognition performance, but the individual differences that affect outcomes are still poorly understood. The overall level and variability of psychophysical thresholds obtained with a focused electrode configuration may account for some of the variability in outcomes, as these measures might reflect the quality of the electrode-neuron interface. To date, psychophysical thresholds using direct stimulation have not been assessed in children. In this work, we compare such thresholds between pediatric and adult cochlear implant listeners. Thresholds were collected from 12 pediatric and 34 adult ears using a fast threshold sweeping method with both focused (partial quadrupolar) and broad (monopolar) electrode configurations. On average, both focused and broad thresholds were 4 dB lower in the pediatric population compared to the adult population. Intra-array variability in thresholds was found to be smaller in pediatric than adult populations for broad but not focused stimulation. Increased threshold observed for focused stimulation compared with broad, quantified as the ratio of focused to broad thresholds, did not differ significantly across populations. These results suggest that there may be differences in the quality of the electrode-neuron interfaces observed in pediatric and adult cochlear implant listeners.

Energy Dissipation in Ex Vivo Porcine Liver During Electrosurgery.

This paper explores energy dissipation in ex vivo liver tissue during radiofrequency current excitation with application in electrosurgery. Tissue surface temperature for monopolar electrode configuration is measured using infrared thermometry. The experimental results are fitted to a finite-element model for transient heat transfer taking into account energy storage and conduction in order to extract information about "apparent" specific heat, which encompasses storage and phase change. The average apparent specific heat determined for low temperatures is in agreement with published data. However, at temperatures approaching the boiling point of water, apparent specific heat increases by a factor of five, indicating that vaporization plays an important role in the energy dissipation through latent heat loss.