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PubMed1996

Bipolar electrode implantation for myoelectrical recordings of rat bowel.

This report describes a technique to implant bipolar electrodes into the rat bowel. We implanted a total of 129 pairs of bipolar electrodes into the bowel of rats. 124 pairs of electrodes (96.3%) have continuously functioned allowing repeated myoelectrical readings. Of these, 69 electrodes functioned over 8 weeks. Only 5 electrodes (3.7%) failed. The advantage of our technique includes: (1) high success rate in implantation, (2) long term durability, and (3) less technical difficulty.

Animals↗
PubMed1994

Endoscopic electrode implantation for enhanced stimulation of the hamstring branches of the sciatic nerve in paralyzed subjects.

Seven hamstring branches of the sciatic nerves in eight posterior thighs of four paraplegics were implanted with electrodes endoscopically. Strong initial responses were obtained in each case on continuous electrical stimulation. Three of the implants were removed immediately due to rapid decay in the response to stimulation; two had muscle power reduced to grade IV and two to grade III over 2-week period postoperatively. We believe the reduction in strength was partly due to hematoma surrounding the electrode and partly due to migration of the electrode away from the target nerves. Further work needs to be done to improve the technique and implant designs to improve results. Due to the excellent visual control it offers, this technique has the potential for accurate implantation of electrodes without massive exposures and its attendant morbidity.

Arthroscopy↗
PubMed1982

Enhanced rate of kindling after prolonged electrode implantation into the amygdala of rats.

A comparison was made between the rate of amygdaloid kindling in rats which had been implanted with electrodes either 6-8 days or 28-33 days before the start of a series of kindling stimulations. Using both stainless-steel and platinum/iridium electrodes the rate of kindling was significantly reduced after the longer implantation time. Possible mechanisms by which the presence of an electrode in the amygdala may influence the rate of subsequent kindling, and the implications for studies on kindling, are discussed.

Amygdala↗
PubMed2005

A temporal bone study of insertion trauma and intracochlear position of cochlear implant electrodes. I: Comparison of Nucleus banded and Nucleus Contour electrodes.

In recent years, new designs of cochlear implant electrodes have been introduced in an attempt to improve efficiency and performance by locating stimulation sites closer to spiral ganglion neurons and deeper into the scala tympani. The goal of this study was to document insertion depth, intracochlear position and insertion trauma with the Nucleus Contour electrode and to compare results to those observed with the earlier generation Nucleus banded electrode. For this comparison eight Nuclears banded electrodes and 18 Contour electrodes were implanted in cadaver temporal bones using a realistic surgical exposure. Two experienced cochlear implant surgeons and two otology fellows with specialized training in cochlear implant surgery were selected for the study to represent a range of surgical experience similar to that of surgeons currently performing the procedure throughout the world. Following insertion of the electrodes, specimens were imaged using plain film X-ray, embedded in acrylic resin, cut in radial sections with the electrodes in place, and each cut surface was polished. Insertion depth was measured in digitized X-ray images, and trauma was assessed in each cross-section. The Contour electrode inserted more deeply (mean depth=17.9 mm or 417 degrees ) than the banded electrode (mean depth=15.3 mm or 285 degrees ). The incidence and severity of trauma varied substantially among the temporal bones studied. However, the nature and frequency of injuries observed with the two devices were very similar. The Contour electrode was clearly positioned closer to the modiolus than the banded model, and also appeared easier to use. Based on this difference in position and data from previous studies we conclude that the Contour electrode may provide lower thresholds and improved channel selectivity, but the incidence of trauma remains a problem with the newer design. The relative influences of electrode positioning and neural degeneration that may result from trauma are as yet unclear.

Cadaver↗
PubMed2002

Modiolar proximity of three perimodiolar cochlear implant electrodes.

A new generation of cochlear implant electrodes has been designed to position the stimulating contacts close to the modiolus in order to reduce power consumption and increase stimulation selectivity. The purpose of this study was to assess electrode position in the cochlea for three recently designed electrodes. Fifteen cadaveric temporal bones were implanted with one of three perimodiolar electrode arrays: Nucleus Contour; Med-El Combi40+ PM (developmental version); and Clarion HiFocus II. Image-enhanced videofluoroscopy and computer morphometrics were used to assess stimulating contact position relative to the modiolus. The mean distance (+/- 1 standard deviation) to the modiolus for all electrode contacts was 0.33 (+/-0.24), 0.30 (+/-0.27) and 0.16 mm (+/-0.19) for the Contour, Combi40+ PM and HiFocus II arrays, respectively. In addition, dynamic videofluoroscopy was used to correlate device-specific insertion characteristics with contact-to-modiolus distance. All three devices were successful in terms of locating electrode contacts very close to the modiolar wall.

Adult↗
PubMed2000

[Intracochlear position of cochlear implant electrodes].

The insertion of cochlear implant electrodes in human temporal bones may be associated with the destruction of structures within the cochlea. The aim of this study was to measure such insertional trauma by means of histologic processing of implanted human temporal bones following implantation of a Combi 40/40+ electrode array (Med-El, Innsbruck). We implanted 6 human temporal bones with original electrodes (3 with Combi 40 and 3 with Combi 40+). In 4 bones Healon was used for electrode insertion. The histological investigation was performed after radiographic evaluation of the position of the electrode. For the histological procedure we used a technique which keeps the electrodes in position within the cochlea. In these slides we could clearly identify the electrodes in the tympanic scale. When inserted properly (point of first resistance) no trauma occurred in the basal portion of the cochlea and minimal trauma in the middle portion of the cochlea.

Cochlea↗
PubMed2005

Nitric oxide synthases II and III and vascular endothelial growth factor are up-regulated in sciatic nerve after spiral cuff electrode implantation.

Nerve cuff electrodes, commonly used in functional electrical stimulation systems, induce local morphological changes that can affect nerve functionality. Nitric oxide (NO) and vascular endothelial growth factor (VEGF) have both neural and vascular effects. We investigated the time-dependent regulation of nitric oxide synthases (NOS) and of VEGF after implantation of spiral cuff electrode around rat sciatic nerve. NOSIII as well as VEGF were up-regulated in both epineurial and endoneurial compartments in cuff-implanted animals along with microvascular changes. Our results suggest that VEGF and NO are implied in morphological and functional alterations occurring in the early time after cuff implantation.

Animals↗
PubMed2004

[Image examination of postoperative evaluation for the cochlear implanted electrode].

OBJECTIVE: To evaluate the image feature of the X-ray plain film, the spiral computed tomography (CT) scans and three dimension reconstruction of inner ear with implanted electrode. METHODS: Eighteen patients of cochlear implant (MEDEL Combi 40+) recipients were involved in this study. The implanted electrode of all patients were examined on the fifth to seventh postoperative day, by the use of X-ray plain film with either anteroposterior transorbital projection (nine cases) or lateral position with coronal 60 degrees away from the examine table (nine cases). Three of the cochlear implant recipients were examined by the way of spiral CT scans with axial 1 mm image slices. The data of the CT scans was transferred to workstation for three-dimensioned reconstruction (direct volume rendering) of the inner ear. RESULTS: The X-ray plain film from both of anteroposterior projection and lateral with coronal 60 degrees projection provide satisfactory image of implanted electrode including the shape and the position in the temporal bone. The insertion depth of the electrode can be evaluated indirectly. In contrast, the images from CT scans with 3D reconstruction of the inner ear demonstrate more accurately the shape, the position, and the insertion depth of the electrode. Moreover, each of the electrode pairs can be identified clearly. CONCLUSIONS: X-ray plain film can meet the routine needs of postoperative evaluation of the implanted electrode with several kinds of head position of projection. But CT scans with 3D reconstruction of inner ear provide more accurate image of the spacial relationship of the electrode in the cochlear canal with direct demonstration of electrode insertion depth in the cochlea.

Adolescent↗
PubMed2004

Basic fitting and evaluation parameters of a newly designed cochlear implant electrode.

OBJECTIVE: To validate a newly designed cochlear implant electrode (TRACE) in the standard monopolar mode and compare it to a patient group implanted with a standard Nucleus Contour cochlear implant electrode. The electrode contacts of the TRACE electrode have the same active surface area for stimulation, but the position in the scala tympani is different from that of the Nucleus Contour electrode. MATERIAL AND METHODS: The following parameters, used in cochlear implant fitting and evaluation procedures, were determined: the threshold and comfort stimulation current levels; the electrode impedances; and the phoneme discrimination and speech recognition scores using the ACE speech algorithm. CONCLUSION: The new electrode does not differ significantly from the standard Nucleus Contour electrode in terms of the investigated parameters within the test group.

Acoustic Impedance Tests↗
PubMed2006

[The application of 3D reconstruction of CT scans for the observation of the cochlear implanted electrode location].

OBJECTIVE: To discuss the different methods of computed tomography (CT) scans and three dimensional reconstruction of inner ear with implanted electrodes, and to evaluate the value and image features of these methods. METHOD: Six cochlear implant (MEDEL Combi 40+, Advanced Bionics) recipients were involved in this study. The implanted electrodes of all patients were examined on the seventh postoperative day. The data of the CT scans was transferred to workstation for three dimensional reconstruction by volume rendering (VR), average intensity projection (AIP) and surface shaded display (SSD). RESULT: The three methods of three dimensional reconstruction provided satisfactory image of implanted electrode including the shape and the special relationship of the electrode in the inner ear. The insertion depth of the electrode can be evaluated directly. Moreover, each of the electrode pairs can be identified clearly. CONCLUSION: Postoperative evaluation of the implanted electrode with three methods of CT scans with three dimensions reconstruction of inner ear provide more accurate image of the special relationship of the electrode in the cochlear canal with direct demonstration of electrode insertion depth in the cochlea.

Child, Preschool↗
PubMed2005

Histopathological study of tissue reaction to pacemaker electrodes implanted in the endocardium.

Limited information is available about histopathological reactions to the implanted endocardial electrodes of pacemakers (PM). Gross anatomic and histologic studies of tissue reactions to PM electrodes were made in thirteen autopsy cases (nine men and four women, ages 25 approximately 89 years, mean age 71.8) who died two months to twenty-one years after PM implantation. Nine of them had complete atrioventricular (AV) block, three had sick sinus syndrome, and one had bradycardia-tachycardia syndrome. The direct causes of death were not related to their PM. The tip with projecting tines was implanted in the right ventricle in all patients. At the contact area between the electrode and the endocardium, no tissue reaction was observed in one patient with a history of over sixteen years of PM implantation. However, cardiomyocytes under the tip had been replaced by fibrotic tissue in many other patients. In two patients in particular where the electrode had been implanted at the apex of each right ventricle, all cardiomyocytes had disappeared and only fibrotic tissue and adipose tissue were observed under the tip. These findings suggest that mechanical stress caused by attaching the tip tightly damages cardiomyocytes and brings about changes in the pacing thresholds. In three patients, a space was seen between the tip and the endocardium. A fibrous sheath covering the electrode extended to the tip and formed a thick fibrous cap. This non-excitable fibrous cap acted as a virtual electrode and possibly affected the elevation of the threshold in these patients. In four patients, extensive myocardial fibrosis due to disease, e. g. previous myocardial infarction, dilated cardiomyopathy, amyloidosis, or sarcoidosis, was found in the area surrounding the tip and also might affect the elevation of the threshold. We concluded that elevation of pacing thresholds after PM implantation is not due to reactive endocardial thickening. The space between the tip and the endocardium is occupied by a fibrous sheath, and an overly tight attachment damages cardiomyocytes causing replacement fibrosis. Thus, it is not desirable in some patients to insert the electrodes into the apex, where the myocardium is thin. To avoid the elevation of thresholds, development of further devices is necessary to allow electrode fixation to the endocardium with a more suitable pressure level.

Adult↗
PubMed2005

Somatosensory evoked potential and clinical changes after electrode implant in basal ganglia of parkinsonian patients.

Median nerve somatosensory evoked potentials (SEPs) were recorded in three parkinsonian patients who underwent electrode implant in the subthalamic nucleus and/or globus pallidus for chronic deep brain stimulation (DBS). SEPs were evoked before surgery, in a medication-free condition, and after the functional stereotactic procedure, before beginning DBS. In order to evaluate the timing of the SEP changes after the electrode implant, in three further patients SEPs were recorded within the operating theater, before and immediately after the implantation. Patients' symptoms improved immediately after the electrode implant, and both N20 and N30 amplitudes increased in the postsurgical SEP recording. The clinical and neurophysiological effects observed after surgery, before commencing DBS, can be explained by microdamage in the target nucleus following the electrode implant. They occurred also in the patients studied in the operating theater, thus suggesting that they occur immediately after the stereotactic procedure. Our results suggest that the circuitries between the basal ganglia and the primary sensorimotor cortex may be modified not only by DBS but also by microdamage due to surgery and that they exert an important influence on SEP amplitude.

Basal Ganglia↗
PubMed2004

Three-dimensional localization of cochlear implant electrodes using epipolar stereophotogrammetry.

Three-dimensional (3-D) localization of individual cochlear implant electrodes within the inner ear is of importance for modeling the electrical field of the cochlea, designing the electrode array, and programming the associated speech processor. A 3-D reconstruction method of cochlear implant electrodes is proposed to localize individual electrodes from two X-ray views in combination with the spiral computed tomography technique. By adapting epipolar geometry to the configuration of an X-ray imaging system, we estimate individual electrode locations in the least square sense without using a patient attachment required by an existing stereophotogrammetry technique. Furthermore, our method does not require any knowledge of the intrinsic and extrinsic parameters of the imaging system. The performance of our method is studied in numerical simulation and with patient data and is found to be sufficiently accurate for clinical use. The maximum root mean-square errors measured are 0.0445 and 0.214 mm for numerical simulation and patient data, respectively.

Cochlea↗
PubMed2004

Electrophysiologic effects of placing cochlear implant electrodes in a perimodiolar position in young children.

OBJECTIVE: The purpose of this study was to intraoperatively record the electrically evoked auditory brainstem response (EABR) before and after placement of the electrode positioning system (EPS) (CII Bionic Ear with HiFocus I cochlear implant electrode array) as well as before and after stylet removal (Nucleus Contour cochlear implant electrode array). It was hypothesized that physiologic changes would occur after perimodiolar positioning of the electrode array and these changes would be evident from the EABR recordings. STUDY DESIGN: Consecutive young (11-36 month old) pediatric cochlear implant recipients (n = 17) had intraoperative EABRs recorded from three intracochlear electrodes that represented apical, medial, and basal locations. Wave V amplitudes and thresholds were studied relative to electrode location and pre- versus postperimodiolar positioning. These evoked potential measures were analyzed for statistical significance. SETTING: Tertiary referral children's hospital/medical college. RESULTS: Wave V thresholds of the EABR were lower, and amplitudes were larger after perimodiolar positioning, although the changes were dependent on electrode location and implant design. Statistically significant decreases in EABR wave V threshold and increases in suprathreshold wave V amplitude were found for the basal electrode for the CII Bionic Ear HiFocus I and for the apical electrode for the Nucleus Contour. CONCLUSIONS: Placement of either the CII Bionic Ear HiFocus I or Nucleus Contour cochlear implant electrode array in the perimodiolar position in young children resulted in less electrical current necessary to stimulate the auditory system. Changes in electrophysiologic thresholds and amplitudes, measured with EABR, indicate that the electrode array is placed closer to the modiolus with both electrode designs.

Child, Preschool↗
PubMed2000

Localization of cochlear implant electrodes in radiographs.

Multielectrode cochlear implantation is the most effective treatment for profound sensorineural hearing loss. In vivo three-dimensional 3-D localization of cochlear implant electrodes is important for modeling of the electrical field in the cochlea, design of electrode arrays, and may improve speech processor programming for better speech recognition. The prerequisite for 3-D localization of the electrodes is their 2-D localization in x-ray radiographs. In this paper, we develop a practical method to localize the electrodes with high efficiency, accuracy, and reproducibility. In this method, a priori knowledge of the electrodes and their approximate positions are utilized, an intelligent thresholding and segmentation mechanism is embedded, and the electrode center is computed as the weighted geometric center of segmented electrode pixels. Experiments with physical phantoms and human data demonstrate the feasibility and utility of this method. The PC-based program developed for this project is disseminated on the Web.

Cochlear Implants↗
PubMed1991

Properties of implanted electrodes for functional electrical stimulation.

Implanted wire electrodes are increasingly being used for the functional electrical stimulation of muscles in partially paralysed patients, yet many of their basic characteristics are poorly understood. In this study we investigated the selectivity, recruitment characteristics and range of control of several types of electrode in triceps surae and plantaris muscles of anaesthetized cats. We found that nerve cuffs are more efficient and selective (i.e., cause less stimulus spread to surrounding muscles) than intramuscular electrodes. Bipolar intramuscular stimulation was more efficient and selective than monopolar stimulation, but only if the nerve entry point was between the electrodes. Monopolar electrodes are efficient and selective if located close to the nerve entry point, but their performance declines with distance from it. Nonetheless, for a variety of reasons monopolar stimulation provides the best compromise in many current applications. Short duration pulses offer the best efficiency (least charge per pulse to elicit force) but high peak currents, increasing the risk of electrode corrosion and tissue damage. Electrode size has little effect on recruitment and should therefore be maximised because this minimises current density.

Action Potentials↗
PubMed1995

Endoscopic electrode implantation. A new technique in an animal model.

The purpose of this study was 2-fold: (1) to describe a technique of creating an endoscopic interstitial working space; and (2) to describe the technique of implanting the modified double helix and the Huntington cuff electrode in the space created. Two cannulated balloons were inserted on either side of a standard arthroscope, which had been inserted to identify the target branch of the sciatic nerve. Traction was applied on each cannula after inflating the balloons with 3 to 5 cc of saline, to create a cylindrical operating space between them. After mobilizing a segment of the nerve, either of the 2 electrodes was implanted with the aid of special instruments. The results indicate that (a) it is possible to create interstitial operating spaces reliably and consistently; (b) satisfactory hemostasis can be achieved through the tamponade effect of the balloons and endoscopic cautery units; (c) excellent visualization is achievable; and (d) it is possible to implant electrodes in a reproducible manner. The interstitial spaces are portable and can be used for various procedures in most anatomic locations. Modification of the cuff electrode will be necessary to make it easier for endoscopic implantation.

Animals↗