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PubMedDate not supplied

Criteria for the selection of materials for implanted electrodes.

There are four criteria that must be considered when choosing material for an implanted electrode: (1) tissue response, (2) allergic response, (3) electrode-tissue impedance, and (4) radiographic visibility. This paper discusses these four criteria and identifies the materials that are the best candidates for such electrodes. For electrodes that make ohmic contact with tissues: gold, platinum, platinum-iridium, tungsten, and tantalum are good candidates. The preferred insulating materials are polyimide and glass. The characteristics of stimulator output circuits and the importance of the bidirectional waveform in relation to electrode decomposition are discussed. The paper concludes with an analysis, the design criteria, and the special properties and materials for capacitive recording and stimulating electrodes.

Biocompatible Materials↗
PubMed2002

Implanted electrode recordings from a praying mantis auditory interneuron during flying bat attacks.

Using an implanted electrode, we recorded the responses from the ultrasound-sensitive mantis interneuron 501-T3 during flying bat attacks in a large flight room where the mantis served as the target. 501-T3 responds to each vocalization emitted with multi-spike bursts when pulse repetition rates (PRRs) are below 55 pulses x s(-1). As PRR increases and pulse durations fall below 3 ms, 501-T3 ceases burst activity. On average, spike bursts cease 272 ms before contact (when the bat is 73 cm away from the preparation). The timing of cessation of activity in 501-T3 is similar to the latency for the diving portion of the response of the mantid (242 ms). Experiments using vocalizing stationary bats confirm that 501-T3 responds more reliably to longer pulse durations (> or =3 ms) when intensities are below 90 dB pe SPL. The cessation of 501-T3 activity is probably due both to the increasing PRR and to the decreasing pulse duration that occur in the terminal buzz phase of a bat attack. 501-T3 may be actively shut off at high PRRs and/or intensities to protect the interneuron from habituation while the mantis performs an escape response. The cessation of 501-T3 activity is consistent with the lack of a very late ultrasound-mediated evasive response by the mantis. However, cessation of 501-T3 activity may allow a true 'last-chance' response to be mediated by other neural systems.

Animals↗
PubMed1989

A complex case of cochlear implant electrode placement.

Cochlear implantation is becoming an increasingly accepted rehabilitative procedure for post lingually deafened adults. The testing, evaluation, and surgery have become standardized procedures. In this case results of two different promontory tests were contradictory. A constant voltage stimulation test was negative, while a later constant current stimulation test indicated good residual function. The CT scan accurately predicted the location of the round window remanent. In order to gain access to the cochlea, a partial labyrinthectomy was performed. Successful implantation was ultimately achieved. This implies that a previous labyrinthectomy may not be an absolute contraindication to cochlear implantation.

Adult↗
PubMed1985

Scanning electron microscopical analysis of the acute and chronic effects of intra-cochlear electrode implantation.

Scanning electron microscopy was used to study the acute histopathological effects immediately after surgical implantation of a 2-channel electrode, and the chronic effects after long-term placement of the perscalar implant. This study with cats shows that an atraumatic implantation can be achieved and that the peripheral neural structures were retained although the hair cells degenerated and the spatial organization of the supporting cells was slightly changed. The population of hair cells outside the region of the implanted electrode was not affected.

Animals↗
PubMed1983

Intracerebral electrode implantation system. Technical note.

A new technique for deep-brain electrode implantation is described. A very flexible nontraumatic electrode guided by a central stylet and a new electrode head-fixation screw are the two unique features of this system. Electrodes can be guided precisely and their watertight fixation to the bone by means of the special screw is reliable and totally reversible. The system has been designed to fit most of the stereotaxic frames currently in use.

Electrodes, Implanted↗
PubMed1976

The ultrastructure of the sheath around chronically implanted electrodes in brain.

Insulated, bipolar stainless steel electrodes were chronically implanted in various regions of the cat brain and the long-term structural changes in the tissue surrounding the electrodes were studied by light and electron microscopy. A sheath surrounded and separated the electrode from normal grey or white matter. A layer of foreign body giant cells of variable thickness was formed adjacent to the electrode. This layer was attenuated in some places so that it was unrecognizable by light microscopy. The bulk of the sheath structure consisted of collagen fibrils, leptomeningeal cells and hypertrophied astrocytes. Areas consisting of modified leptomeningeal cells with long thin processes we designated as spongy areas. These have not been previously reported using the electron microscope. Glycogen bodies were seen in leptomeningeal cells. Astrocytes became greatly enlarged and were more numerous in and around the sheath. Oligodendrocytes contained lamellar bodies, and direct continuity was shown between a lamellar body and an adjacent myelin sheath. Myelin was seen in abnormal sites (around oligodendrocytes and neurons) and in unusual configurations. Neuronal changes near the sheath included whorls and stacks of modified endoplasmic reticulum and the presence of cytoplasmic nucleolus-like bodies. Reactive, regenerative and degenerative axons were observed. Blood vessels were more numerous in the sheath and surrounding tissue than normal. Perivascular spaces were prominent even around capillaries and often plasma cells and monocytes were in these spaces. As compared to normal tissue the extracellular space is noticeably increased. Electrodes passing through ventricles were surrounded with a sheath covered with ependymal cells. This sheath was comparable in structure to the sheath present around the electrode in other locations.

Animals↗
PubMed1986

Heart rate response to shock delivered via different implanted electrodes.

The heart rate reaction elicited by electric shock was studied in rats stimulated via implanted electrodes that were placed entirely beneath the skin (subcutaneous electrodes) or were passed under and through the skin (cutaneous electrodes). Cutaneous shock elicited greater cardioaccelerations than subcutaneous shock except at very low intensities. This finding may help to explain differences in conditioned heart rate responses when these two types of electrodes are used to deliver shock stimuli.

Animals↗
PubMed2001

New method of deep brain stimulation therapy with two electrodes implanted in parallel and side by side.

Reversibility and adaptability are preferred features of long-term therapeutic deep brain stimulation (DBS). In such therapy, a permanent stimulating electrode with four contact points is placed at the stimulation site and, generally speaking, bipolar stimulation is induced by various pairs of adjacent contact points on one electrode. The stimulation sites are thus all located along the trajectory of the implanted electrode. In a patient with unilateral severe essential tremor, the authors implanted two electrodes side by side and parallel to each other in the unilateral thalamic ventralis intermedius nucleus. Using these electrodes, the authors were able to deliver current flow not only along the electrode trajectory, but also between the two electrodes in a direction parallel to the anterior commissure-posterior commissure line. Although individual stimulations, delivered by each of the two electrodes using all parameters and all stimulation points, were unable to stop the patient's tremor completely without adverse effects, the new stimulation method, in which electrical currents passed between the two electrodes, effected complete abolition of the tremor without adverse effects. With the aid of this method, one can use two electrodes, implanted in parallel and side by side, to achieve maximum efficacy and to reduce adverse effects in some instances of DBS therapy.

Aged↗
PubMed1977

[The management of urinary and fecal incontinence due to a neurinoma of the cauda equina with an electrode implanted in the pelvic muscles (Caldwell) (author's transl)].

A woman, aged 49, had a complete sensory and motor deficit of the S2-5 segments with urinary and fecal incontinence due to a neurinoma of the cauda. A Caldwell electrode was implanted surgically into the muscles of the pelvic floor in April 1974. The patient was observed for 2 years thereafter and had an excellent result. The medical and technical problems of treating urinary and fecal incontinence due to a lower motor neuron lesion of S2-5 can be handled satisfactorily with an implanted electrode.

Cauda Equina↗
PubMed2004

Subretinal electrical stimulation of the rabbit retina with acutely implanted electrode arrays.

BACKGROUND: Subretinal implants intend to replace photoreceptor function in patients suffering from degenerative retinal disease by topically applying electrical stimuli from the subretinal space. This study intended to prove the feasibility of a newly developed transchoroidal surgery and, furthermore, of a subretinal electrode array, which closely resembles envisioned human implants to electrically stimulate the visual system in rabbits. METHODS: Five rabbits (ten eyes) were implanted with a 4x2-electrode array via a transchoroidal access to the subretinal space. The electrodes were connected to an arbitrary stimulus generator to apply voltage pulses. Retinae were accessed by light microscopy after stimulation with various intensities. RESULTS: The stimulating foil could be introduced into the subretinal space in all eyes. In seven of ten eyes electrically evoked cortical potentials following subretinal electrical stimulation could be elicited. Threshold voltages ranged from less than 0.1 to 2.38 V with a corresponding threshold charge of approximately 1.0 nC per electrode or 10 micro C/cm(2). Histology revealed localized retinal damage over some of the electrodes succeeding stimulation strengths of 2 V and consistent damage over all electrodes succeeding voltages of 3 V. CONCLUSIONS: The study demonstrates the feasibility of the transchoroidal surgical access to place subretinal implants in rabbit eyes and provides proof of successful cortical activation following subretinal electrical stimulation by an electrode array envisioned for human implantations.

Animals↗
PubMed1988

Conduction studies in peripheral cat nerve using implanted electrodes: II. The effects of prolonged constriction on regeneration of crushed nerve fibers.

Arrays of chronically implanted electrodes were used to examine the time course of elongation and maturation of peripheral nerve fibers in the cat after crush of the tibial nerve in the proximal calf. Regeneration after crush alone was compared with crush 5 mm proximal to a tight constriction of the nerve. Regeneration was monitored by the progression of excitability along the electrode arrays on the tibial and plantar nerves. The sensitivity was sufficient to record the averaged activity in single nerve fibers allowing detection of the earliest regeneration. The diameters of the fastest regenerating fibers were estimated from the conduction velocity proximal to the site of crush. Both after crush alone, and after crush constriction, small myelinated fibers regenerated in front of large fibers. The rate of elongation after crush alone was 3.2 mm/day, whereas it was slower (P less than 0.02) distal to crush + constriction (2.2 mm/day). In both lesions, the extrapolated delay to onset of regeneration was 8 days. In observations up to 300 days after crush, maturation was delayed or impaired by the constriction, and the compound nerve action potential had a smaller amplitude and a dispersed shape. Transverse sections of nerves after crush + constriction showed a diminished number of large and an increased number of small fibers compared with crush alone, possibly due to persistent branching of regenerated fibers. After both crush alone and crush + constriction, regenerated fibers had similar g ratios, suggesting that myelination developed fully in fibers of diminished diameters.

Action Potentials↗
PubMed2005

Stimulation through electrodes implanted near the subthalamic nucleus activates projections to motor areas of cerebral cortex in patients with Parkinson's disease.

High-frequency electrical stimulation through electrodes implanted in the subthalamic nucleus (STN) has been shown to reduce significantly the cardinal symptoms of Parkinson's disease (PD). Despite the success of this treatment, the mechanisms of action of stimulation are poorly understood. To elucidate further the mechanisms of action of deep brain stimulation and its effects on cortical activity, we recorded electroencephalographic potentials from 61 scalp-surface electrodes during low-frequency (5-10 Hz) bipolar stimulation in 11 patients with advanced PD (14 implanted electrodes were tested). In all electrodes tested, stimulation through at least one of the four contacts produced a medium-latency waveform with an average onset of 14 +/- 3 ms and peak at 23 +/- 4 ms. This potential typically increased in magnitude across contacts from ventral to dorsal. Within-subject comparisons of median nerve somatosensory evoked potentials demonstrated that the generator of the medium-latency potential was within the primary sensorimotor cortex or lateral premotor cortex ipsilateral to stimulation. The timing and topography of this potential were consistent with indirect activation of the cortex by excitation of pallido-thalamic axons that traverse the dorsal aspect of the STN. The potential evoked by stimulation through the contact used for optimal clinical effect was highly variable across electrodes and frequently different from the medium-latency potential described above, suggesting that the neuronal elements mediating the medium-latency potential were different from those that mediate the clinical effects.

Adult↗
PubMed1979

[Transvenous electrode implantation into the left heart auricle via vena saphena magna].

A new simple variant of the transvernous implantation of atrial electrodes for the pacemaker therapy is reported. It consist in the fact that via the V. saphena magna under fluorography a hook electrode is shifted into the right auricular appendix by means of a slightly bent conducting wire and is anchored by leading out the hooks.

Cardiac Pacing, Artificial↗
PubMedDate not supplied

[Classification of implantable electrodes intended for constant electrostimulation of the heart].

The analysis is given of the currently used classifications for implantable electrodes with special reference to their disadvantages. Since manufacturers produce a great variety of electrode models with the intrinsic codes, certain difficulties are involved when decoding. So, the new, unique seven-alphabetic coding is proposed that may find extensive application. The coding was approved at the Second All-Union school-seminar held in Kaunas in September, 1983. Foreign specialists present there appreciated the proposed coding.

Electrodes, Implanted↗
PubMed1995

A simple CT method for location of auditory brain stem implant electrodes.

A method for locating auditory brain stem implant electrodes that have been placed in the lateral recess of the fourth ventricle is described. CT bone window images are "inverted" to black on white, then manually superimposed onto soft-tissue window images to enable identification of electrodes in relation to soft-tissue structures.

Brain Stem↗
PubMed2004

Histologic evaluation of the tissue seal and biologic response around cochlear implant electrodes in the human.

HYPOTHESIS: Histopathologic study of the tissue seal and biologic response around cochlear implant electrodes in patients who had received a cochlear implant during life could provide clues concerning the pathogenesis of meningitis after cochlear implantation. BACKGROUND: Bacterial meningitis has been reported as an infrequent complication of cochlear implantation using a variety of electrode designs. The cause of meningitis in cochlear implant recipients has not been firmly established. In an analogous surgical situation, namely stapedectomy, delayed meningitis could occur as a complication of ipsilateral acute suppurative otitis media in which there was open communication between the middle ear and perilymph. METHODS: Twenty-one temporal bones from 20 individuals who had undergone cochlear implantation during life were studied by light microscopy. All sections passing through the cochleostomy site and electrode track were examined to evaluate the tissue seal at the cochleostomy, the presence or absence of an extracochlear electrode sheath, and finally, to seek evidence of a cellular inflammatory response near the electrode. These data were compared with clinical data, including electrode system used, the number of years between implantation and death, type of tissue used at surgery, and the age and sex of the patients. RESULTS: The 21 specimens included cases implanted with the Symbion Ineraid, Cochlear Corporation Nucleus 22-channel, Cochlear Corporation Nucleus 24-channel, a Cochlear Corporation Nucleus single channel, and Advanced Bionics Clarion C1 devices. At the cochleostomy site, and just within the cochlea, there was a robust fibrous and bony tissue response in all 21 ears and in most cases, there was a fibrous sheath surrounding the electrode in the middle ear. No recognizable open communication or potential communication between the middle ear and the inner ear was seen in any of the 21 ears. An inflammatory cellular response, including mononuclear leukocytes, histiocytes, and foreign body giant cells, were present in 12 of the 21 temporal bones (57%) and was most intense at the cochleostomy site. No statistically significant relationship was found between the presence or absence of inflammatory cells and the type of tissue graft used at surgery. CONCLUSIONS: The histologic evidence presented in this study does not support open communication between the middle and the inner ear as part of the pathogenesis of bacterial meningitis as a late complication after cochlear implantation. Rather, the finding of a cellular inflammatory response in 12 of 21 temporal bones suggests that late hematogenous contamination and colonization of the implant is a much more likely pathogenic mechanism. This putative mechanism has implications for possible strategies to prevent meningitis after cochlear implantation.

Aged↗
PubMed1994

Electrical pelvic floor stimulation by percutaneous implantable electrode.

OBJECTIVE: To describe a clinical experience of chronic pelvic floor stimulation using a percutaneous implantable electrode for the treatment of urinary incontinence. PATIENTS AND METHODS: Pelvic floor stimulation using a percutaneous procedure was performed in 10 patients who were suffering from urinary incontinence due to overactive detrusor function. After implantation of the electrode chronic stimulation was instituted with a portable external electrical stimulator. RESULTS: Four to 16 weeks of maximal electrical stimulation improved urinary incontinence in eight of 10 patients. In two of these eight patients incontinence disappeared as measured subjectively. Urodynamic investigations demonstrated a significantly increased volume at the first unstable contraction (P < 0.01) in all patients. One of 30 electrodes migrated during the follow-up period. CONCLUSION: Inhibition of detrusor overactivity was obtained using this procedure. Response appeared to be constant during chronic stimulation. This procedure appears to provide stable and reliable stimulation for chronic treatment of urinary incontinence and may be an alternative to electrical pelvic floor stimulation.

Adult↗