Tripolar Electrode Research Articles

Pudendal Nerve Stimulation and Block by a Wireless-Controlled Implantable Stimulator in Cats

The study aims to determine the functionality of a wireless-controlled implantable stimulator designed for stimulation and block of the pudendal nerve. In five cats under α-chloralose anesthesia, the stimulator was implanted underneath the skin on the left side in the lower back along the sacral spine. Two tripolar cuff electrodes were implanted bilaterally on the pudendal nerves in addition to one bipolar cuff electrode that was implanted on the left side central to the tripolar cuff electrode. The stimulator provided high-frequency (5-20 kHz) biphasic stimulation waveforms to the two tripolar electrodes and low-frequency (1-100 Hz) rectangular pulses to the bipolar electrode. Bladder and urethral pressures were measured to determine the effects of pudendal nerve stimulation (PNS) or block. The maximal (70-100 cmH2O) urethral pressure generated by 20-Hz PNS applied via the bipolar electrode was completely eliminated by the pudendal nerve block induced by the high-frequency stimulation (6-15 kHz, 6-10 V) applied via the two tripolar electrodes. In a partially filled bladder, 20-30 Hz PNS (2-8 V, 0.2 ms) but not 5 Hz stimulation applied via the bipolar electrode elicited a large sustained bladder contraction (45.9 ± 13.4 to 52.0 ± 22 cmH2O). During cystometry, the 5 Hz PNS significantly (p < 0.05) increased bladder capacity to 176.5 ± 27.1% of control capacity. The wireless-controlled implantable stimulator successfully generated the required waveforms for stimulation and block of pudendal nerve, which will be useful for restoring bladder functions after spinal cord injury.

An Integrated Amplifier With Passive Neutralization of Myoelectric Interference From Neural Recording Tripoles

This paper describes an integrated amplifier for neural recording from tripolar electrode books connected in the quasi-tripole arrangement. The same tripole is used in the implant for neural stimulation. To remove myoelectric interference from neural recordings, a resistor-capacitor network is used to balance the electrode impedances in the tripole. The amplifier is programmable (recording mode, passband, gain, and trimming impedance) via a serial peripheral interface. Its front-end instrumentation amplifier employs current feedback to achieve high common-mode rejection ratio. The circuit was implemented in 0.35- μm CMOS technology and occupies an area of ~1.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . In the very-low noise mode, the analog front-end features a maximum of 0.68 μVrms input-referred noise in the passband and consumes ~310 μA from a 3 V supply. The measured common-mode rejection ratio of the instrumentation amplifier (CMRRIA) approaches 100 dB. The effect of component mismatch on the CMRRIA and the noise performance of the instrumentation amplifier are examined. In addition, the recording tripole is analyzed to derive the overall common-mode rejection ratio that is shown to exceed 80 dB. The ability of the neural amplifier to reduce myoelectric interference is demonstrated. The amplifier is also tested with a tripole immersed in saline in the stimulate-record mode.

273 INVOLVEMENT OF 5-HT2 RECEPTOR IN PUDENDAL NERVE INHIBITION OF NOCICEPTIVE AND NON-NOCICEPTIVE BLADDER ACTIVITY IN CATS

You have accessJournal of UrologyBladder and Urethra: Anatomy, Physiology and Pharmacology (I)1 Apr 2013273 INVOLVEMENT OF 5-HT2 RECEPTOR IN PUDENDAL NERVE INHIBITION OF NOCICEPTIVE AND NON-NOCICEPTIVE BLADDER ACTIVITY IN CATS Yosuke Matsuta, Zeyad Schwen, Abhijith Mally, Bing Shen, Jicheng Wang, James Roppolo, William de Groat, and Changfeng Tai Yosuke MatsutaYosuke Matsuta Pittsburgh, PA More articles by this author , Zeyad SchwenZeyad Schwen Pittsburgh, PA More articles by this author , Abhijith MallyAbhijith Mally Pittsburgh, PA More articles by this author , Bing ShenBing Shen Pittsburgh, PA More articles by this author , Jicheng WangJicheng Wang Pittsburgh, PA More articles by this author , James RoppoloJames Roppolo Pittsburgh, PA More articles by this author , William de GroatWilliam de Groat Pittsburgh, PA More articles by this author , and Changfeng TaiChangfeng Tai Pittsburgh, PA More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.1657AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Understanding the neurotransmitter mechanisms involved in pudendal nerve inhibition of bladder activity could lead to identify new pharmacological targets for overactive bladder (OAB). Currently little is known about the effect of 5-hydroxytryptamine (5-HT)2 receptor on micturition reflex. This study used methysergide, a 5-HT2 receptor antagonist, and naloxone, an opioid receptor antagonist, to examine the involvement of these receptors in the inhibition of micturition reflex induced by pudendal nerve stimulation (PNS). METHODS Experiments were conducted in 20 cats under α-chloralose anesthesia. A tripolar cuff electrode was applied around the right pudendal nerve and connected to a stimulator. Drugs were administered via the right cephalic vein. Pharmacological studies were performed in two experimental groups (i.e. AA and saline group). In both group, cumulative doses (0.01, 0.03, 0.1, 0.3, and 1 mg/kg) of methysergide and then naloxone (1 mg/kg) were given. RESULTS AA irritated the bladder, induced bladder overactivity and significantly (p < 0.0001) reduced bladder capacity (BC) to 27.0 ± 7.4 % of saline control capacity. PNS (5 Hz, 0.2 ms) at 1-2 and 3-4 times the threshold (T) intensity for inducing an observable twitching of anal sphincter suppressed AA-induced bladder overactivity and significantly increased BC to 60.1 ± 8.0 % at 1-2T (p < 0.0001) and 92.2 ± 14.1 % at 3-4T (p = 0.001) of the saline control capacity. Methysergide (0.03-1 mg/kg, i.v.) suppressed PNS inhibition of bladder overactivity at low intensity (1-2T) but not at high intensity (3-4T). During saline infusion PNS increased BC to 150.8 ± 9.9 % at 1-2T (p < 0.01) and 180.4 ± 16.6 % at 3-4T (p < 0.01) of the saline control capacity. Methysergide significantly increased BC at the doses of 0.1-1 mg/kg (p < 0.05) and suppressed pudendal inhibition. After 1 mg/kg dose of methysergide, naloxone significantly (p < 0.05) reduced BC in AA condition, however, PNS-induced inhibition at 3-4T was still observed. On the other hand, naloxone did not change BC and PNS-induced inhibition in saline condition. CONCLUSIONS These results suggest that 5-HT2 receptor antagonist plays an inhibitory role in both nociceptive and non-nociceptive bladder activity. 5-HT2 receptor interacts with opioid receptor in micturition reflex pathway. Our study indicates methysergide (a FDA-approved drug with few side effects) could be a new treatment for OAB. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e111 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yosuke Matsuta Pittsburgh, PA More articles by this author Zeyad Schwen Pittsburgh, PA More articles by this author Abhijith Mally Pittsburgh, PA More articles by this author Bing Shen Pittsburgh, PA More articles by this author Jicheng Wang Pittsburgh, PA More articles by this author James Roppolo Pittsburgh, PA More articles by this author William de Groat Pittsburgh, PA More articles by this author Changfeng Tai Pittsburgh, PA More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Can subject-specific single-fibre electrically evoked auditory brainstem response data be predicted from a model?

This article investigates whether prediction of subject-specific physiological data is viable through an individualised computational model of a cochlear implant. Subject-specific predictions could be particularly useful to assess and quantify the peripheral factors that cause inter-subject variations in perception. The results of such model predictions could potentially be translated to clinical application through optimisation of mapping parameters for individual users, since parameters that affect perception would be reflected in the model structure and parameters. A method to create a subject-specific computational model of a guinea pig with a cochlear implant is presented. The objectives of the study are to develop a method to construct subject-specific models considering translation of the method to in vivo human models and to assess the effectiveness of subject-specific models to predict peripheral neural excitation on subject level. Neural excitation patterns predicted by the model are compared with single-fibre electrically evoked auditory brainstem responses obtained from the inferior colliculus in the same animal. Results indicate that the model can predict threshold frequency location, spatial spread of bipolar and tripolar stimulation and electrode thresholds relative to one another where electrodes are located in different cochlear structures. Absolute thresholds and spatial spread using monopolar stimulation are not predicted accurately. Improvements to the model should address this.

Quantitative analysis of the excitability of hypoglossal motoneurons during natural sleep in the rat

We describe a novel approach to assess the excitability of hypoglossal motoneurons in rats during naturally occurring states of sleep and wakefulness. Adult rats were surgically prepared with permanently placed electrodes to record the EEG, EOG and neck EMG. A stimulating/recording miniature tripolar cuff electrode was implanted around the intact hypoglossal nerve and a head-restraining device was bonded to the calvarium. After a period of adaptation to head-restraint, the animals did not exhibit any sign of discomfort and readily transitioned between the states of wakefulness, NREM and REM sleep. There was no spontaneous respiratory or tonic activity present in the hypoglossal nerve during sleep or wakefulness. Hypoglossal motoneurons were activated by electrical stimulation of the hypoglossal nerve (antidromically) or by microstimulation directly applied to the hypoglossal nucleus. Microstimulation of hypoglossal motoneurons evoked compound action potentials in the ipsilateral hypoglossal nerve. The magnitude of their integrals tended to be higher during wakefulness (112.6%±15; standard deviation) and were strongly depressed during REM sleep (24.7%±3.4), compared to the integral magnitude during NREM sleep. Lidocaine, which was delivered using pressure microinjection to the microstimulation site, verified that the responses evoked in hypoglossal nerve can be affected pharmacologically. We conclude that this animal model can be utilized to study the neurotransmitter mechanisms that control the excitability of hypoglossal motoneurons during naturally occurring states of sleep and wakefulness.

Selectivity for Specific Cardiovascular Effects of Vagal Nerve Stimulation With a Multi-Contact Electrode Cuff

The cardiovascular system can be influenced by electrically stimulating the vagal nerve. Selectivity for specific cardiac fibers may be limited when stimulating at the cervical level. Our objective was to increase effectiveness and selectivity for cardiovascular effects of vagal nerve stimulation by using local bipolar stimulation in one nerve cross section using a multi-contact cuff instead of less localized stimulation using a tripolar ring electrode. Both types of cuff electrodes were compared with respect to their relative effects on R-R interval (RRI), P-Q interval (PQI), left ventricular contractility (LVC), and left ventricular pressure (P(LV)) in seven pigs. Stimulation using the optimal bipolar configuration on the multi-contact cuff significantly affected RRI, PQI, LVC, and P(LV), whereas stimulation with the ring electrode only significantly affected RRI and PQI. The cardiovascular parameters that could be significantly influenced varied between the bipolar configurations. These novel findings may be relevant for optimizing electrode configurations for clinical cardiac applications of vagal nerve stimulation.

El cardiodesfibrilador totalmente subcutáneo

The implantable cardioverter-defibrillators (ICD) is a therapy for the prevention of sudden cardiac death. Complications with implant have been associated mainly with transvenous lead insertion. Difficulties in achieving venous access can occasionally result in failed ICD implantation. Lead failures remains a major limitation and often require removal. This procedure is associated with important morbidity and mortality. To eliminate the need for venous access, Bardy et al. designed an entirely subcutaneous ICD system. The subcutaneous ICD consists of a 3-mm tripolar parasternal electrode positioned parallel to the left of the sternal midline and guided exclusively by anatomical landmarks without fluoroscopy. The pulse generator is positioned over the sixth rib between the midaxillary line and the anterior axillary line. The device delivers a maximum of only 80-J shocks. Ventricular fibrillation was converted twice in 58 of 59 patients (98%) with the delivery of 65-J shocks in two tests to ensure a margin of safety. A demand pacing at 50 beats per minute is available for 30 seconds after a shock. These studies are preliminary but the system will need to be employ in a long-term, randomized, prospective, multicenter clinical trials.

Continuous intraoperative monitoring of autonomic nerves during low anterior rectal resection: an innovative approach for observation of functional nerve integrity in pelvic surgery

The aim of this study was to develop a methodological setup for continuous intraoperative neuromonitoring with intent to improve nerve-sparing pelvic surgery. Fourteen pigs underwent low anterior rectal resection. Continuous stimulation of pelvic autonomic nerves was carried out with a newly developed tripolar surface electrode during lateral, anterolateral, and anterior mesorectal dissection. Neuromonitoring was performed under electromyography of the autonomic innervated internal anal sphincter. Continuous neuromonitoring resulted in significantly increased electromyographic amplitudes of the internal anal sphincter, confirming intact innervation throughout the whole dissection in each animal (median 0.9 μV, interquartile range 0.5; 1.5 vs. median 3.4 μV, interquartile range 2.1; 4.7) (p < 0.001). The median dissection time in each animal was 10 min within a median number of ten (range 8-13) tripolar electric stimulations. The present study is the first to demonstrate that continuous intraoperative monitoring of pelvic autonomic nerves during low anterior rectal resection is feasible.

Cochlear implant channels with high thresholds degrade medial vowel perception.

There is considerable evidence that the functional interface between cochlear implant electrodes and the auditory nerve varies from channel to channel within individual patients. Recently a method was proposed to gauge the status of a channel’s interface on the basis of its threshold to focused stimulation using tripolar electrode configuration. This approach showed that channels with high tripolar thresholds have broader psychophysical tuning curves. In this study, the relationship between the number and distribution of high threshold channels with medial vowel identification in a bvt paradigm was examined. Tripolar thresholds were measured for all channels in seven listeners. Vowel identification was tested in the sound field with six repetitions. On the basis of each listener’s electrodogram (the sound processor output of current amplitude as a function of time and channel), the similarity of the vowels using a principle component analysis was examined. We then related the vowel confusions based on the electrodogram of different subsets of channels, based on basal to apical location or tripolar threshold. Preliminary results suggest that the channels with high tripolar thresholds, or in regions of high variability in tripolar threshold, can account for a significant amount of the variance in subject performance. [Work supported by NIH Grant No. DC8883.]

Electrical field imaging as a means to predict the loudness of monopolar and tripolar stimuli in cochlear implant patients

Tripolar and other electrode configurations that use simultaneous stimulation inside the cochlea have been tested to reduce channel interactions compared to the monopolar stimulation conventionally used in cochlear implant systems. However, these “focused” configurations require increased current levels to achieve sufficient loudness. In this study, we investigate whether highly accurate recordings of the intracochlear electrical field set up by monopolar and tripolar configurations correlate to their effect on loudness. We related the intra-scalar potential distribution to behavioral loudness, by introducing a free parameter ( α) which parameterizes the degree to which the potential field peak set up inside the scala tympani is still present at the location of the targeted neural tissue. Loudness balancing was performed on four levels between behavioral threshold and the most comfortable loudness level in a group of 10 experienced Advanced Bionics cochlear implant users. The effect of the amount of focusing on loudness was well explained by α per subject location along the basilar membrane. We found that α was unaffected by presentation level. Moreover, the ratios between the monopolar and tripolar currents, balanced for equal loudness, were approximately the same for all presentation levels. This suggests a linear loudness growth with increasing current level and that the equal peak hypothesis may predict the loudness of threshold as well as at supra-threshold levels. These results suggest that advanced electrical field imaging, complemented with limited psychophysical testing, more specifically at only one presentation level, enables estimation of the loudness growth of complex electrode configurations.

Partial tripolar cochlear implant stimulation: Spread of excitation and forward masking in the inferior colliculus

This study examines patterns of neural activity in response to single biphasic electrical pulses, presented alone or following a forward masking pulse train, delivered by a cochlear implant. Recordings were made along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) in ketamine/xylazine anesthetized guinea pigs. The partial tripolar electrode configuration was used, which provided a systematic way to vary the tonotopic extent of ICC activation between monopolar (broad) and tripolar (narrow) extremes while maintaining the same peak of activation. The forward masking paradigm consisted of a 200 ms masker pulse train (1017 pulses per second) followed 10 ms later by a single-pulse probe stimulus; the current fraction of the probe was set to 0 (monopolar), 1 (tripolar), or 0.5 (hybrid), and the fraction of the masker was fixed at 0.5. Forward masking tuning profiles were derived from the amount of masking current required to just suppress the activity produced by a fixed-level probe. These profiles were sharper for more focused probe configurations, approximating the pattern of neural activity elicited by single (non-masked) pulses. The result helps to bridge the gap between previous findings in animals and recent psychophysical data.

Modeling the electrode–neuron interface of cochlear implants: Effects of neural survival, electrode placement, and the partial tripolar configuration

The partial tripolar electrode configuration is a relatively novel stimulation strategy that can generate more spatially focused electric fields than the commonly used monopolar configuration. Focused stimulation strategies should improve spectral resolution in cochlear implant users, but may also be more sensitive to local irregularities in the electrode–neuron interface. In this study, we develop a practical computer model of cochlear implant stimulation that can simulate neural activation in a simplified cochlear geometry and we relate the resulting patterns of neural activity to basic psychophysical measures. We examine how two types of local irregularities in the electrode–neuron interface, variations in spiral ganglion nerve density and electrode position within the scala tympani, affect the simulated neural activation patterns and how these patterns change with electrode configuration. The model shows that higher partial tripolar fractions activate more spatially restricted populations of neurons at all current levels and require higher current levels to excite a given number of neurons. We find that threshold levels are more sensitive at high partial tripolar fractions to both types of irregularities, but these effects are not independent. In particular, at close electrode–neuron distances, activation is typically more spatially localized which leads to a greater influence of neural dead regions.

Identifying Cochlear Implant Channels with Poor Electrode-Neuron Interface: Partial Tripolar, Single-Channel Thresholds and Psychophysical Tuning Curves

The goal of this study was to evaluate the ability of a threshold measure, made with a restricted electrode configuration, to identify channels exhibiting relatively poor spatial selectivity. With a restricted electrode configuration, channel-to-channel variability in threshold may reflect variations in the interface between the electrodes and auditory neurons (i.e., nerve survival, electrode placement, and tissue impedance). These variations in the electrode-neuron interface should also be reflected in psychophysical tuning curve (PTC) measurements. Specifically, it is hypothesized that high single-channel thresholds obtained with the spatially focused partial tripolar (pTP) electrode configuration are predictive of wide or tip-shifted PTCs. Data were collected from five cochlear implant listeners implanted with the HiRes90k cochlear implant (Advanced Bionics Corp., Sylmar, CA). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the pTP configuration for which a fraction of current (sigma) from a center-active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. Forward-masked PTCs were obtained for channels with the highest, lowest, and median tripolar (sigma = 1 or 0.9) thresholds. The probe channel and level were fixed and presented with either the monopolar (sigma = 0) or a more focused pTP (sigma > or = 0.55) configuration. The masker channel and level were varied, whereas the configuration was fixed to sigma = 0.5. A standard, three-interval, two-alternative forced choice procedure was used for thresholds and masked levels. Single-channel threshold and variability in threshold across channels systematically increased as the compensating current, sigma, increased and the presumed electrical field became more focused. Across subjects, channels with the highest single-channel thresholds, when measured with a narrow, pTP stimulus, had significantly broader PTCs than the lowest threshold channels. In two subjects, the tips of the tuning curves were shifted away from the probe channel. Tuning curves were also wider for the monopolar probes than with pTP probes for both the highest and lowest threshold channels. These results suggest that single-channel thresholds measured with a restricted stimulus can be used to identify cochlear implant channels with poor spatial selectivity. Channels having wide or tip-shifted tuning characteristics would likely not deliver the appropriate spectral information to the intended auditory neurons, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.

Use of tripolar electrodes for minimization of current spread in uncut peripheral nerve stimulation

The electrical stimulation of an uncut peripheral nerve requires a countermeasure to avoid the spread of current through a loop pathway formed outside the electrode array. Here the use of tripolar electrodes (TE) is proposed. By binding the two end poles, current spread through the loop pathway can theoretically be eliminated since both end poles are held equipotential. Experimentally, we tested the validity of this approach. In chloralose–urethane anesthetized rats, the left cervical vagus (LCV) was placed on TE which could function as such or as bipolar electrodes (BE) by the use of a selector switch. The spread of current to the adjacent tissues (rectus capitis muscle underlying the LCV, and the right cervical vagus (RCV) incised and translocated beside the target, LCV) was compared between TE and BE. When the stimulus intensity was increased, contraction occurred in the capitis muscle with BE, but not TE. Compound spike potentials of A fiber origin were evoked in the non-target RCV on high-intensity stimulation with BE, but not TE. Constant voltage stimulation of the LCV with TE produced bradycardia of the same magnitude as that with BE. In conclusion, constant voltage stimulation using TE can minimize current spread without changing the stimulus's effects.

Efficacy of Transverse Tripolar Spinal Cord Stimulator for the Relief of Chronic Low Back Pain from Failed Back Surgery

Failed back surgery syndrome is a common clinical entity for which spinal cord stimulation has been found to be an effective mode of analgesia, but with variable success rates. To determine if focal stimulation of the dorsal columns with a transverse tripolar lead might achieve deeper penetration of the electrical stimulus into the spinal cord and therefore provide greater analgesia to the back. Case report. We describe a 42-year-old female with failed back surgery syndrome that had greater back pain than leg pain. The tripolar lead configuration was achieved by placing percutaneously an octapolar lead in the spinal midline followed by 2 adjacent quadripolar leads, advanced to the T7-T10 vertebral bodies. Tripolar stimulation pattern resulted in more than 70% pain relief in this patient during the screening trial, while stimulation of one or 2 electrodes only provided 20% pain relief. After implantation of a permanent tripolar electrode system with a single rechargeable battery, the pain relief was maintained for one year. This is case report describing a case of a patient with chronic low back pain with a diagnosis of failed back surgery syndrome in which transverse tripolar stimulation using an octapolar and 2 quadripolar leads appeared to be beneficial. The transverse tripolar system consists of a central cathode surrounded by anodes, using 3 leads. This arrangement may contribute to maximum dorsal column stimulation with minimal dorsal root stimulation and provide analgesia to the lower back.

The Role of Piriform Cortex Adenosine A1 Receptors on Hippocampal Kindling

The hippocampus and piriform cortex have a critical role in seizure propagation. In this study, the role of adenosine A1 receptors of piriform cortex on CA1 hippocampal kindled seizures was studied in rats. Animals were implanted with a tripolar electrode in the right hippocampal CA1 region and two guide cannulae in the left and right piriform cortex. They were kindled by daily electrical stimulation of hippocampus. In fully kindled rats, N6- cyclohexyladenosine (CHA; a selective adenosine A1 receptors agonist) and 1,3-dimethyl-8-cyclopenthylxanthine (CPT a selective adenosine A1 receptor antagonist) were microinfused into the piriform cortex. The animals were stimulated at 5, 15 and 90 minutes (min) after drug injection. Obtained data showed that CHA (10 and 100 microM) reduced afterdischarge duration, stage 5 seizure duration, and total seizure duration at 5 and 15 min after drug injection. There was no significant change in latency to stage 4 seizure. CPT at concentration of 20 microM increased afterdischarge duration, stage 5 seizure duration, and total seizure duration and decreased latency to stage 4 seizure at 5 and 15 min post injection. Pretreatment of rats with CPT (10 microM), 5 min before CHA (100 microM), reduced the effect of CHA on seizure parameters. These results suggested that activity of adenosine A1 receptors in the piriform cortex has an anticonvulsant effect on kindled seizures resulting from electrical stimulation of the CA1 region of the hippocampus.

Application of Tripolar Concentric Electrodes and Prefeature Selection Algorithm for Brain–Computer Interface

For persons with severe disabilities, a brain-computer interface (BCI) may be a viable means of communication. Lapalacian electroencephalogram (EEG) has been shown to improve classification in EEG recognition. In this work, the effectiveness of signals from tripolar concentric electrodes and disc electrodes were compared for use as a BCI. Two sets of left/right hand motor imagery EEG signals were acquired. An autoregressive (AR) model was developed for feature extraction with a Mahalanobis distance based linear classifier for classification. An exhaust selection algorithm was employed to analyze three factors before feature extraction. The factors analyzed were 1) length of data in each trial to be used, 2) start position of data, and 3) the order of the AR model. The results showed that tripolar concentric electrodes generated significantly higher classification accuracy than disc electrodes.

Current Steering and Current Focusing in Cochlear Implants: Comparison of Monopolar, Tripolar, and Virtual Channel Electrode Configurations

To compare the effects of Monopole (Mono), Tripole (Tri), and "Virtual channel" (Vchan) electrode configurations on spectral resolution and speech perception in a crossover design. Nine experienced adults who received an Advanced Bionics CII/90K cochlear implant participated in a crossover design using three experimental strategies for 2 wk each. Three strategies were compared: (1) Mono; (2) Tri with current partly returning to adjacent electrodes and partly (25 or 75%) to the extracochlear reference; and (3) a monopolar "Vchan" strategy creating seven intermediate channels between two contacts. Each strategy was a variant of the standard "HiRes" processing strategy using 14 channels and 1105 pulses/sec/ channel, and a pulse duration of 32 microsec/phase. Spectral resolution was measured using broadband noise with a sinusoidally rippled spectral envelope with peaks evenly spaced on a logarithmic frequency scale. Speech perception was measured for monosyllables in quiet and in steady-state and fluctuating noises. Subjective comments on music experience and preferences in everyday use were assessed through questionnaires. Thresholds and most comfortable levels with Mono and Vchan were both significantly lower than levels with Tri. Spectral resolution was significantly higher with Tri than with Mono; spectral resolution with Vchan did not differ significantly from the other configurations. Moderate but significant correlations between word recognition and spectral resolution were found in speech in quiet and fluctuating noise. For speech in quiet, word recognition was best with Mono and worst with Vchan; Tri did not significantly differ from the other configurations. Pooled across the noise conditions, word recognition was best with Tri and worst with Vchan (Mono did not significantly differ from the other configurations). These differences were small and insufficient to result in a clear increase in performance across subjects if the result from the best configuration per subject was compared with the result from Mono. Across all subjects, music appreciation and satisfaction in everyday use did not clearly differ between configurations. (1) Although spectral resolution was improved with the tripolar configuration, differences in speech performance were too small in this limited group of subjects to justify clinical introduction. (2) Overall spectral resolution remained extremely poor compared with normal hearing; it remains to be seen whether further manipulations of the electrical field will be more effective.

Detection of the bladder volume from the neural afferent activities in dogs: experimental results

Objective: We evaluate the bladder volume and pressure through recording the bladder afferent activity in the sacral nerve roots in acute experiments of paraplegic dogs. These measurements are intended to report the status of the bladder and to adjust the stimulation parameters of an implantable electric stimulator.Methods: The extraction of neural information for feedback in functional electrical stimulation is limited by the poor signal to noise ratio (SNR) in the sacral nerve recordings. We propose to inject a very low amplitude sinusoidal current with high SNR to the bladder through the nerve using a tripolar cuff electrode wrapped around the S2 nerve root. The application of this current (0.4 μA peak to peak, 30 Hz) allows detecting bladder afferent activity in its amplitude and the tissues impedance of the nerve. Acute experiments in dogs were performed to evaluate the proposed method. In each dog, the bladder infusion with saline was carried out at both slow and high filling rates. At the same time, the changes in the amplitude of the sinusoidal output voltage VOUT were recorded through the cuff nerve electrode.Results: The data obtained from 26 acute experiments using eight dogs demonstrate that the amplitude of the recorded sinusoidal voltage VOUT varies proportionally with the bladder pressure during the bladder filling with saline solution. It also demonstrates that the bladder volume can be estimated from the increasing amplitude of the recorded VOUT.Conclusion: This study shows that the increase in the VOUT is proportionally related to the increase in bladder pressure. The difference between the recorded VOUT during the bladder filling and the baseline VOUT can be a useful indicator of the changes in the bladder volume.

Matrix-addressable, active electrode arrays for neural stimulation using organic semiconductors—cytotoxicity and pilot experiments in vivo

Organic field effect transistors can be integrated into micromachined polyimide-based neural stimulation electrode arrays in order to build active switching matrices. With this approach, a matrix of N × M electrode contacts requires only N + M interconnects to a stimulator when active switching elements are used instead of N × M interconnects. In this paper, we demonstrated that pentacene-based organic field effect transistors (OFETs) can be used to drive stimulation currents through neural electrodes in a physiological-like environment. In order to prove the general applicability as an implant material, the cytotoxicity of pentacene was evaluated with respect to potential effects on cell viability. The results of these tests indicate that extracts from pentacene inhibit neither proliferation nor metabolism of the tested mouse fibroblasts. However, some effect on cell spreading was observed when cells were in direct contact to pentacene for 48 h. In pilot experiments it was demonstrated for the very first time that pentacene transistors can be used as switching elements, acting as voltage-controlled current sources, capable of driving currents suitable for electrical stimulation of a peripheral nerve via a tripolar cuff electrode.