Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ELECTRODES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1988

Studies of the tissue reaction induced by transvenous pacemaker electrodes. I. Microscopic examination of the extent of connective tissue around the electrode tip in the human right ventricle.

The purpose of this study was to investigate the extent of connective tissue of the human right ventricle induced by cardiac pacing electrodes. Between January 1984 and July 1987, 34 consecutive patients with VVI-pacing systems were autopsied in the Department of Pathology at the University of Frankfurt/M. The surrounding tissue of these 34 electrodes (17 Siemens Elema 412 S, five Medtronic 6957, one Medtronic 6959, one Medtronic 4011, three Biotronik D2K, three Biotronik K 10, two Osypka FY 62, one Biotronik N, and one Siemens Elema 588) in the right ventricle were investigated histologically. The tissue was stained with Giemsa and the thickness of the connective tissue layer was measured. Stimulation threshold data at various times were known in four of eight screw-in electrodes, in seven of 17 vitreous carbon electrodes and in two of seven smooth surface electrodes. Electrode surface area, implantation time, age of the patient and cause of death were comparable for all three electrode groups. However, a significant difference was found in the extent of connective tissue between the porous surface and screw-in electrodes (128 +/- 55 vs 397 +/- 269 micron, P less than or equal to 0.01) and porous surface and smooth surface electrodes (128 +/- 55 vs 307 +/- 117 micron, P less than or equal to 0.01). No relation (r = 0.106) was found between the duration of implantation and the extent of connective tissue for the vitreous carbon electrodes (Siemens Elema 412 S).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2006

Radiofrequency ablation for small hepatocellular carcinoma: prospective comparison of internally cooled electrode and expandable electrode.

PURPOSE: To prospectively compare the effectiveness of radiofrequency (RF) ablation performed by using an internally cooled electrode and an expandable electrode for the treatment of small (< or = 3.0 cm) hepatocellular carcinomas (HCCs). MATERIALS AND METHODS: The human subjects research review board at the study institution approved the protocol, and each patient provided informed consent. Seventy-four patients (58 men and 16 women; age range, 41-83 years) with 83 HCC nodules 3 cm or smaller were randomly divided into an internally cooled electrode group (38 patients with 41 nodules) and an expandable electrode group (36 patients with 42 nodules). RF ablation was performed by one individual. Primary technique effectiveness and rates of major complications were evaluated between the two groups with the Fisher exact test. Rates of local tumor progression, overall survival, local progression-free survival, and event-free survival were evaluated by using the Kaplan-Meier method. RESULTS: The primary technique effectiveness was 95% in the internally cooled electrode group and 93% in the expandable electrode group (P = .51); rates of major complications were 0% and 2.1% per session (P = .50) and 0% and 2.8% per patient (P = .49), respectively. Rates at 1, 2, and 3 years in the internally cooled electrode group versus the expandable electrode group were as follows: local tumor progression, 12% versus 17%, 20% versus 22%, and 20% versus 22% (P = .72, log-rank test); overall survival, 100% versus 94%, 94% versus 92%, and 94% versus 77% (P = .29, log-rank test); local progression-free survival, 87% versus 78%, 73% versus 66%, and 73% versus 46% (P = .27, log-rank test); and event-free survival, 47% versus 44%, 34% versus 22%, and 34% versus 22% (P = .40, log-rank test). CONCLUSION: On the basis of the study findings, RF ablation with an internally cooled electrode needle and an expandable electrode needle has equivalent effectiveness for the treatment of small HCCs.

Adult↗
PubMed2004

Cellular basis for the monophasic action potential. Which electrode is the recording electrode?

BACKGROUND: The cellular basis for the monophasic action potential (MAP) has long been a matter of debate. At the center of the controversy is the issue as to which of the two electrodes is the recording electrode and which is the indifferent electrode. The present study is designed to address this issue. METHODS: Transmembrane action potentials (TAPs) and either intramural MAPs or contact (Franz-like) MAPs were recorded from adjacent sites in canine arterially perfused ventricular wedge preparations. Intramural MAPs were recorded using thin wire electrodes referenced to a KCl electrode. RESULTS: Local cooling or injection of ATX-II into the region subtending the inactivating (contact or KCl) electrode did not affect the MAP. Similar maneuvers at the site of the noninactivating electrode always prolonged the MAP. The intramural MAP always prolonged in proportion to the TAP, whereas the contact MAP did not, often displaying apparent early afterdepolarizations (EADs) or delayed afterdepolarizations (DADs) due to its much wider field of view, which captured activity from the region of prolonged repolarization as well as the remote normal regions. CONCLUSIONS: Our results suggest that (1) it is not the contact or MAP electrode that records the MAP, but rather the noninactivating "indifferent" electrode and (2) intramural MAPs provide more accurate recordings of local activity. The data provide compelling evidence in support of the hypothesis that the MAP represents the extracellular potential difference between active and inactive sites within the heart rather than injury currents flowing at the boundary of the active and inactive zone under the inactivating electrode.

Action Potentials↗
PubMed2004

Evaluation of a skin reference electrode used for intraoral pH measurements in combination with a microtouch electrode.

The aim of this in vivo study was to evaluate a skin reference electrode used with the microtouch method for measurements of intraoral pH. Registrations of plaque pH were made in ten healthy subjects before and up to 30 min after a mouth rinse with 10% sucrose. A microtouch electrode (Beetrode) was used in combination with two different half-cell reference electrodes: a skin silver-silver chloride plate or a glass capillary reference electrode. The skin electrode was placed on the subject's forearm in combination with a conductive gel. The glass capillary electrode, together with one of the test subject's fingers, was placed in a beaker with a 3 M KCl solution. High agreement between the two reference systems resulted in almost identical plaque-pH curves (r=0.97). The mean differences between the two systems at the different time points varied between -0.15 and +0.01 pH units, with an overall mean pH difference of 0.03 pH units. It can be concluded that the use of the skin reference electrode may very well replace the traditional reference electrode used in combination with a microtouch electrode for intraoral use.

Adult↗
PubMed2004

Polyvinylferrocenium modified Pt electrode for the design of amperometric choline and acetylcholine enzyme electrodes.

A simple method of enzyme immobilization was investigated, which is useful for development of enzyme electrodes based on polyvinylferrocenium perchlorate coated Pt electrode surface. Enzymes were incorporated into the polymer matrix via ion exchange process by immersing polyvinylferrocenium perchlorate coated Pt electrode in enzyme solution for several times. Choline and acetylcholine enzyme electrodes were developed by co-immobilizing choline oxidase and acetylcholinesterase in polyvinylferrocenium perchlorate matrix coated on a Pt electrode surface. The amperometric responses of the enzyme electrodes were measured at +0.70 V versus SCE, which was due to the electrooxidation of enzymatically produced H2O2. The effects of the thickness of the polymeric film, pH, temperature, substrate and enzyme concentrations on the response of the enzyme electrode were investigated. The optimum pH was found to be pH 7.4 at 25 degrees C. The steady-state current of these enzyme electrodes were reproducible within +/-5.0% of the relative error. Response time was found to be 30-50s and upper limit of the linear working portions was found to be 1.2mM choline and acetylcholine concentrations in which produced detectable currents were 1.0 x 10(-6)M substrate concentrations. The apparent Michaelis-Menten constant and the activation energy of this immobilized enzyme system were found to be 1.74 mM acetylcholine and 14.9 kJ mol(-1), respectively. The effects of interferents and stability of the enzyme electrodes were also investigated.

Acetylcholine↗
PubMed2006

Micro-agar salt bridge in patch-clamp electrode holder stabilizes electrode potentials.

Maintaining a stable electrode potential is critical for patch-clamp measurements. The electrode potential of conventional patch electrode-holder assembly, where an Ag/AgCl wire is in direct contact with the patch pipette filling solution, is subject to drift if the pipette solution contains a low concentration of chloride ions (Cl-). We developed an agar bridge of 3 M KCl filled in a polyimide microtubing which forms an electrical connection between an Ag/AgCl wire and the pipette solution. We examined the offset potentials of the micro-agar salt bridge electrode assembly in parallel with a conventional electrode assembly in generic recording conditions (the pipette solution contained 5 mM NaCl). The junction potential between the Ag/AgCl wire and the pipette filling solution in the conventional electrode contributed to most of the offset potential drift observed during the course of 30 min recordings. The drift was up to 27.3 mV after several changes of the glass pipette. In contrast, the micro-agar salt bridge stabilized the electrode potential within typically 2 mV without affecting the patch electrode resistance, capacitance or noise level. Numerical simulations showed that Cl- diffusion from the agar bridge to the tip caused a negligible 0.4 microM Cl- concentration change at the pipette tip within 30 min. This method is easy to implement and provides long-term recording stability. The micro-agar salt bridge can fit in most commercial patch electrode holders and can be conveniently maintained.

Agar↗
PubMed2001

Linear ablation using an irrigated electrode electrophysiologic and histologic lesion evolution comparison with ablation utilizing a non-irrigated electrode.

OBJECTIVES: To characterize the electrophysiologic and histologic sequelae of linear atrial ablation utilizing an irrigated electrode. To compare "irrigated" lesions with lesions deployed using the same electrode in a non-irrigated mode. BACKGROUND: Previous reports of radiofrequency catheter ablation using an irrigated electrode have emphasized its favorable effect on lesion depth. We hypothesized that electrode irrigation would also benefit linear ablation of smooth atrial myocardium, a relatively superficial target. METHODS: In healthy pigs, lesions were deployed in the right and left atria. Acutely, lesions resulting from ablation using an irrigated electrode, with radiofrequency energy titration guided by electrogram amplitude reduction, were compared to lesions using the same electrode without irrigation, with energy titration guided by electrode thermometry. Irrigated lesions were also assessed serially. RESULTS: Acutely, irrigated lesions formed complete conduction barriers and were uncomplicated. In contrast, non-irrigated lesions formed complete conduction barriers but were frequently complicated, exhibiting endocardial charring, barotrauma, and pericardial damage. The rate and pattern of histologic evolution of irrigated lesions were uniform throughout each lesion; right and left atrial lesions healed similarly. During healing, 90 % of lesions remained complete conduction barriers and 10 % manifested single discrete conduction gaps where viable appearing myocytes bridged the lesion. CONCLUSIONS: Complete, uncomplicated linear lesions could be reliably deployed in either atrium with an irrigated electrode. Not all lesions remained complete barriers to conduction during their histologic evolution. Lesions deployed with the same electrode in a non-irrigated mode were complete but frequently complicated.

Animals↗
PubMed2001

[Comparison of susceptibility artefacts of different radiofrequency electrodes at O.2 T. Influence of electrode positioning, pulse sequence and image reconstruction methods].

PURPOSE: Interventional MRI procedure monitoring requires small but accurate susceptibility artifacts of the instruments used. In this investigation, susceptibility artifacts of different RF-electrode designs were compared using a variety of pulse sequences and k-space acquisition methods. METHODS: 4 different 18-gauge RF-electrodes (with three single electrodes made of stainless steel, copper, inconal, and a triple-clustered electrode configuration made of inconal) were placed in a 0.2 T MR-scanner perpendicular to the main magnetic field. Pulse sequences used included: TSE T2, FISP, true-FISP, PSIF, and a temperature sensitive ES-GRE sequence. In addition to the 2D Cartesian k-space trajectory with Fourier transformation (2DFT), projection reconstruction (PR) was used with the FISP, true-FISP and PSIF sequences. RESULTS: The best tip accuracy was achieved with the combination of inconal electrodes and TSE T2. The usefulness of the tested sequences was found to be: TSE T2 > PSIF > FISP/true-FISP > ES-GRE. In general 2DFT provided better or equal tip accuracy than PR. The apparent shaft width was smaller using the copper electrode compared to the inconal electrode. However, the "match shaped" tip artifact of the copper probe led to a higher error in tip accuracy. CONCLUSIONS: TSE-T2 sequences and Cartesian 2DFT acquisitions should be used for accurate tip positioning at 0.2 T. Further, artifact size of the electrode shaft prevents the use of inconal for temperature sensitive sequences. Copper electrodes can be used for these purposes, although copper is not considered to be biocompatible at present.

Artifacts↗
PubMed1975

Ion-selective electrodes and enzyme electrodes in environmental and clinical studies.

Electrodes have been developed for the assay of glucose, urea, amino acids, uric acid, phosphate, nitrate and perchlorate. The electrodes for the organic compounds are enzyme electrodes which are prepared by chemically immobilizing an enzyme over the outside of a conventional ion-selective electrode. These electrodes will be discussed in depth. The progress and the development of the electrodes that show sensitivity and selectivity for phosphate, nitrate and perchlorate will be outlined. The basis of these sensors is a complex of a transition metal of either an analog of thiourea or an organic chelator, such as 1,10-phenanthraline. Such electrodes respond linearly to phosphate, nitrate or perchlorate, and show selectivity over sulphate, halides and acetate. The linear range of all these electrodes is approx. 10(-1)-10(-5) M with a near Nernstian slope and a reproducibility of 1%. The electrodes are stable and can be used continuously.

Amidohydrolases↗
PubMed2005

Surface EMG of jaw elevator muscles: effect of electrode location and inter-electrode distance.

This study addresses methodological issues on surface electromyographic (EMG) signal recording from jaw elevator muscles. The aims were (i) to investigate the sensitivity to electrode displacements of amplitude and spectral surface EMG variables, (ii) to analyse if this sensitivity is affected by the inter-electrode distance of the bipolar recording, and (iii) to investigate the effect of inter-electrode distance on the estimated amplitude and spectral EMG variables. The superficial masseter and anterior temporalis muscles of 13 subjects were investigated by means of a linear electrode array. The percentage difference in EMG variable estimates from signals detected at different locations over the muscle was larger than 100% of the estimated value. Increasing the inter-electrode distance resulted in a significant reduction of the estimation variability because of electrode displacement. A criterion for electrode placement selection is suggested, with which the sensitivity of EMG variables to small electrode displacements was of the order of 2% for spectral and 6% for amplitude variables. Finally, spectral and, in particular, amplitude EMG variables were very sensitive to inter-electrode distance, which thus should be fixed when subjects or muscles are compared in the same or different experimental conditions.

Adult↗
PubMed2006

Electrophysiologic channel interaction, electrode pitch ranking, and behavioral threshold in straight versus perimodiolar cochlear implant electrode arrays.

The primary goal of this study was to examine electrophysiologic measures of channel interaction, electrode pitch discrimination ability using a pitch-ranking task, and behavioral threshold levels in individuals implanted with a straight electrode array versus a perimodiolar array. It was hypothesized that perimodiolar arrays should yield lower thresholds, less channel interaction as measured with the electrically evoked compound action potential (ECAP), and better electrode pitch-ranking ability. Results from ten adult Nucleus 24 recipients (N=5 straight array, N=5 perimodiolar Contour array) showed no significant difference in threshold between the two electrode designs; however, there was significantly better electrode pitch-ranking ability and less channel interaction as measured with the ECAP for perimodiolar electrodes. Additionally, there was a significant positive correlation between behavioral threshold and width of the ECAP interaction function for Contour group data. There was no significant correlation between behavioral threshold and electrode pitch-ranking ability. These data suggest that electrode design and/or perimodiolar position may reduce physiologic channel interaction in the cochlea and improve electrode pitch discrimination ability; however, this positive finding did not translate into significantly better speech perception ability for Contour subjects.

Action Potentials↗
PubMed1992

Local anesthetic-sensitive electrodes: preparation of coated-wire electrodes and their basic properties in vitro.

Coated-wire electrodes with local anesthetic (LA) cation-selective membranes were prepared, and their properties in vitro were investigated. Copper wires (0.8-mm diameter) were coated with gel membranes of 110 mg of poly(vinyl chloride), 5 mg of ion pairs of tetraphenylborate anion with LA cation, 100 mg of dioctylphtalate, and 1.5 mL of tetrahydrofuran. This was the composition determined to be most suitable. Their electromotive force relative to an Ag/AgCl electrode was measured in LA solutions. The lidocaine, dibucaine, and mepivacaine electrodes all showed good Nernstian response at 25 degrees C in aqueous solutions in the concentration ranges of 1 x 10(-4) to 1 x 10(-2) mol/L, 4 x 10(-5) to 1 x 10(-2) mol/L, and 5 x 10(-5) to 1 x 10(-2) mol/L, respectively. The response time was within 10 s. The electrode potential decreased as the pH in the solution increased, with a corresponding decrease of the protonated form of LA. The hydrophobic nature of the LA was closely related to the electromotive force and to the selectivity of the electrode toward various LA cations. Dibucaine, the most hydrophobic, had the highest electrode potential. The more hydrophobic the LA of the electrode, the less it is interfered with by other LA molecules. The more hydrophobic the interferent cation, the more it acts on the electrode potential. The electrode system could also measure LA in human plasma at 37 degrees C, although the responsiveness was depressed in the low concentration range owing to binding of LA to the serum protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics, Local↗
PubMed1981

The effect on responsivity of the PtcO2 electrode by an increased pressure on the electrode membrane.

At application of the electrode for continuous transcutaneous oxygen monitoring, a superatmospheric pressure may be produced between the skin and the electrode membrane. Such a pressure may change the electrode characteristics resulting in a slower reacting electrode. A superatmospheric pressure may also influence on the subepidermal capillaries and on the oxygen diffusion through the skin. The results in the current in vitro study show that an increase of the pressure between the electrode membrane and the skin results in a slower reacting electrode, only when the pressure also produces an increased diffusion distance from the capillaries to the electrode membrane. Thus, the PtcO2 electrode seems rather rough and different PtcO2 levels recorded among patients or in the same patient at two applications are not produced by the application procedure per se but by physiological differences in the skin at the electrode application site.

Electrodes↗
PubMed1990

Catheter-type defibrillation electrode using glassy carbon: results of electrode implantation.

The implantable defibrillator, developed by Dr Michel Mirowski, is a remarkable electric therapeutic device which has been in clinical use since 1980 in the treatment of life-threatening arrhythmia. However, as the present life span of this device is only 3 years, research is being carried on to extend the lifetime with improved stimulation methods, circuits and electrodes. In particular, the electrode system which is inserted into the right ventricle has more than 50 times the electrode area of a pacing electrode and is prone to degradation. What is needed is biocompatibility and electrical stability, similar to that of cardiac pacemaker electrodes, which can be used for more than 10 years. For this purpose, we focused on a conductive ceramic as a new material for the defibrillation electrode instead of the previously-used metal. We selected glassy carbon as our electrode material and tested the surface condition through acute and chronic animal experiments. No clots formed around the electrodes after a 3-month implantation, nor were there surface disorders after the defibrillation stimulations. We concluded that glassy carbon is a promising material for future defibrillation electrodes.

Animals↗
PubMed2000

Electrode discrimination by early-deafened subjects using the cochlear limited multiple-electrode cochlear implant.

OBJECTIVE: The aims of this study were to determine whether electrode discrimination by early-deafened subjects using the Cochlear Limited prosthesis varied at different locations on the electrode array, was influenced by the effects of auditory deprivation and experience with electric stimulation, and was related to speech perception. DESIGN: Difference limens for electrode discrimination were measured in 16 early-deafened subjects at three positions on the array: electrodes 18 (apical), 14 (mid), and 8 (basal). Electrodes were stimulated using random variations in current level to minimize the influence of loudness cues. Assessed were correlations between the difference limens, subject variables related to auditory deprivation (age at onset of deafness, duration of deafness, and age at implantation) and auditory experience (duration of implant use and the total time period of auditory experience), and speech perception scores from two closed-set and two open-set tests. RESULTS: The average difference limens across the three positions were less than two electrodes for 75% of subjects, with average limens between 2 and 6.5 electrodes for the remaining 25% of subjects. Significant differences across the three positions were found for 69% of subjects. The average limens and those at the basal position positively correlated with variables related to auditory deprivation, with larger limens for subjects implanted at a later age and with a longer duration of deafness. The average limens and those at the apical position negatively correlated with closed-set speech perception scores, with lower scores for subjects with larger limens, but not with open-set scores. Speech scores also negatively correlated with variables related to auditory deprivation. CONCLUSIONS: These findings showed that early-deafened subjects were generally successful in electrode discrimination although performance varied across the array for over half the subjects. Discrimination performance was influenced by the effects of auditory deprivation, and both electrode discrimination and variables related to auditory deprivation influenced closed-set speech perception.

Age Factors↗
PubMed1992

Anterior "cheek" electrodes are comparable to sphenoidal electrodes for the identification of ictal activity.

Sphenoidal electrodes are used to localize epileptiform activity originating in the temporal lobe during complex partial seizures. Sphenoidal electrodes, however, are semi-invasive and uncomfortable to the patient. We compared skin electrodes placed on the cheek ("cheek electrodes") with sphenoidal electrodes for the detection of the side and site of complex partial seizure onset. In a masked, randomized comparison of single ictal recordings in 22 patients, there were no significant differences between sphenoidal and cheek electrode montages in detecting the side or site of ictal onset (P < 0.01). Signal/noise ratios for interictal spikes were a mean 16.5% greater at sphenoidal sites compared to cheek sites (paired t test, t = 2.4, P < 0.05). This difference, however, did not influence the detection of rhythmical ictal activity in cheek and sphenoidal montages in our study, nor the assignment of side, site or time of seizure onset by unbiased readers. Recordings from cheek electrodes are comparable to those from sphenoidal electrodes and are useful for localizing ictal activity.

Cheek↗