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At least 19 recordsLinked to original sources
PubMed1992

[Temperature distribution and geometry of the electrodes in RF interstitial hyperthermia using circular and interstitial electrodes].

To evaluate the feasibility of clinical application of a newly developed interstitial hyperthermia system, which consists of an 8 MHz radiofrequency generator, interstitial needle electrodes, and a superficial circular electrode, we conducted preclinical experiments using an agar phantom and VX-2 carcinoma in the rabbit. In the experiment with an agar phantom, four 4 cm needle electrodes were placed in a square array at intervals of 1.0, 1.5, and 2.0 cm. Thermography demonstrated homogeneous temperature distribution at electrode intervals of 1.0 and 1.5 cm, but hot spots around the electrodes at an interval of 2.0 cm. When electrode deviation was less than 8 degrees from the parallel plane, no temperature deviation was observed. Using two 2 cm electrodes and two 4 cm electrodes in square array, thermography demonstrated a homogeneous temperature distribution in the area surrounded by the electrodes. Even if the electrodes were located at the periphery of the agar phantom, a homogeneous temperature distribution was obtained in the area surrounded by the electrodes. Using four 4 cm electrodes at intervals of 1.5 cm in VX-2 carcinoma in the rabbit, ideal heating was obtained: 42 degrees C at the periphery of the tumor and 43 degrees C at the center. These data suggest that the newly developed interstitial hyperthermia apparatus provides homogeneous heat distribution at electrode intervals of 1.5 cm or less and can be used in a Phase I study for deep-seated or superficial tumors.

Animals↗
PubMed1989

[Nonthoracotomy internal defibrillation in dogs using a body surface electrode with a transvenous catheter electrode].

The efficacy of truncated exponential waveform shocks using a cardioverter-defibrillator catheter (Medtronic 6880) and body surface electrodes was examined in comparison with using a RV epicardial patch electrode and a LV epicardial patch electrode in fifteen pentobarbital-anesthetized dogs. The defibrillation thresholds (DFT) for 5 lead configurations were measured by the total energy, peak voltage and peak current: A) a body surface electrode (positioned at the right lateral chest wall) as the anode and a body surface electrode (positioned at the left lateral chest wall) as the cathode; B) a superior vena cava catheter electrode as the anode and a RV apex catheter electrode as the cathode; C1) a body surface electrode (positioned at left anterior chest wall) as the anode and a RV apex catheter electrode as the cathode; C2) a body surface electrode (positioned at the left lateral chest wall) as the anode and a RV apex catheter electrode as the cathode; and D) a RV epicardial patch electrode as the anode and a LV epicardial patch electrode as the cathode. The total energy at DFT for configurations C2 and D was lower than for configurations A, B, and C1, respectively (7.2 +/- 3.1 and 4.7 +/- 2.0 less than 18.9 +/- 3.8, 12.0 +/- 3.8 and 11.2 +/- 2.2 joules; p less than 0.05). The peak voltage at DFT for configurations C2 and D was lower than for configurations A, B, and C1, respectively (463 +/- 70 and 377 +/- 73 less than 767 +/- 85, 585 +/- 117 and 600 +/- 62 volts; P less than 0.05).

Animals↗
PubMed1991

The importance of the orientation of the electrode plates in recording the external anal sphincter EMG by non-invasive anal plug electrodes.

Two non-invasive anal plug electrodes of similar size have been compared, one with the electrode plates orientated circularly in the anal canal and the other with the plates in the long axis of the anal canal. There was a significant increase in the amplitude in the EMG signals recorded at rest and during squeeze from the external anal sphincter with a longitudinally placed electrode in 117 patients. Inappropriate contraction of the external anal sphincter when straining at stool was more readily detected using the longitudinal electrode in 52 patients investigated for intractable constipation. The longitudinal electrode detected the amplitude of the response to the elicitation of a pudeno-anal reflex more readily than the circular electrode. When in 12 of the 117 the pudeno-anal reflex EMG signal was either absent or not detected with the circumferential plug electrode, the longitudinal electrode detected the presence of a low amplitude response in 11 of these. When the non-invasive longitudinal electrode was compared to invasive fine wire stainless steel electrodes, a correlation was found for external anal sphincter resting EMG (r = 0.99, p less than 0.01), voluntary squeeze EMG (r = 0.99, p less than 0.001) and strain EMG (r = 0.91, p less than 0.01). The longitudinal anal plug electrode thus facilitates surface acquisition of EMG activity.

Adult↗
PubMed1991

Impedance plethysmography in human limbs. Part 1. On electrodes and electrode geometry.

Electrode design and electrode positioning are important factors in blood flow measurements using impedance plethysmography. Optimal electrode type and accurate positioning will decrease measurement errors and improve the signal-to-noise-ratio. Disk electrodes were found to be superior to tape electrodes because of their better skin-electrode stability and because they prevent limb compression. The distance between current electrodes and potential electrodes should be greater than 2.3 R (disk electrodes) and 1.5 R (tape electrodes) to avoid the influence of the so-called diffusion resistance (R is the radius of the limb at the electrode site).

Adult↗
PubMed1992

Comparison of colloidal gold electrode fabrication methods: the preparation of a horseradish peroxidase enzyme electrode.

In order to prepare biosensing electrodes which respond to hydrogen peroxide, horseradish peroxidase has been adsorbed to colloidal gold sols and electrodes prepared by deposition of these enzyme-gold sols onto glassy carbon using three methods: evaporation, electrodeposition and electrolyte deposition. In the latter method the enzyme-gold sol is applied to the surface of a glassy carbon disk electrode followed by an equal volume of 2 mM CaCl2. The electrolyte causes the sol to precipitate on the electrode surface, producing an immobilized enzyme electrode. Satisfactory electrodes which gave an electrochemical response to hydrogen peroxide in the presence of the electron transfer mediator ferrocenecarboxylic acid were produced by all three methods. Evaporation of horseradish peroxidase-gold sols produced electrodes with the best reproducibility and the widest linear amperometric response range. These electrodes can also easily be stored in a dry state. Although not as good as evaporation, electrodeposition also produced satisfactory electrodes. Electro-deposition provides the added advantage that it lends itself to the preparation of multi-enzyme/multi-analyte electrodes by the adsorption of different enzymes to separate gold sols, followed by sequential electrodeposition onto discrete areas of a multichannel electrode.

Biosensing Techniques↗
PubMed1989

ERG electrode in pediatric patients: comparison of DTL fiber, PVA-gel, and non-corneal skin electrodes.

Hard contact lens electrodes have been the type most frequently used in pediatric electroretinography but they are not well-tolerated by patients. The Dawson Trick Litzkow fiber electrode is better tolerated but it is fragile and difficult to sterilize. A new electrode made from anomalous polyvinyl alcohol gel is inexpensive, has stable electrical recording properties, and can be discarded after use. Dermal electrodes have been used for electroretinogram recording for some time; however, there are few reports that directly compare their performance against standard contact lens assemblies. We compared the DTL and the polyvinyl gel electrodes in the same group of subjects and investigated their recording characteristics along with non corneal skin electrodes placed on the infraorbital ridge. Signal-averaged electroretinogram were obtained under both scotopic and photopic stimulation conditions and the implicit time and amplitudes of the a- and b-waves were determined. Overall, dermal recordings generally had shorter implicit times and lower amplitudes than with the fiber or gel electrodes. The dermal electrodes were best tolerated and outlasted the corneal in repeated use. Since amplitude characteristics of the dermal electrodes were generally about 50% of that obtained with corneal electrodes, we feel that under standardized conditions they are acceptable for most clinical recording situations in infants and young children.

Adolescent↗
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↗
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↗
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↗
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↗
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↗
PubMed1975

Studies with the "Severinghaus" PCO2 electrode I: electrode stability, memory and S plots.

A study of the Radiometer "Severinghaus" Pco2 electrode has been made in order to investigate its stability and reproducibility when exposed to a series of inknown gas samples of various carbon dioxide concentrations. Electrodes were found to exhibit a pronounced memory effect, which depended upon the Pco2 of the last sample to which they had been exposed if the exposure had been for more than a few minutes. When a number of electrodes were exposed to a single reference gas at all times, except for the few minutes required to measure the Pco2 of an unknown sample, the electrical output of the electrode was unexpectedly stable and reproducible. This implies a high degree of measurement accuracy. If the reference gas to which the electrode is usually exposed is of low carbon dioxide concentration, the electrode displays its highest degree of stability and reproducibiltiy. The use of low carbon dioxide content reference gases is not always convenient, however, because they increase the response time of the electrode. Reference gases of high carbon dioxide content induce unstable electrode behaviour, and so it is recommended that gases higher than 5% v/v Co2 are not chosen for this purpose.

Carbon Dioxide↗
PubMed1989

A comparison of platinized grooved electrode performance with ring-tip electrodes.

One of the determinants of the capture threshold of an endocardial pacing lead is the configuration of the electrode tip. To evaluate whether micro- and macroporous electrodes have better initial and chronic thresholds than nonporous electrodes, acute and chronic capture thresholds, stimulation impedance and sensing thresholds were determined in 22 patients in whom a ventricular ring-tip electrode and a unipolar, dual chamber pacemaker with bidirectional telemetry had been implanted. These values were compared to those obtained from 25 patients receiving an electrode constructed with a platinized groove surface at the time of implant of an identical pulse generator. The ventricular capture threshold at implant was 0.7 V +/- 0.3 at 0.6 msec pulse width for both groups. The capture threshold was significantly greater in the ring tip electrode group at follow-up periods of 1 month (1.1 V +/- 0.5 vs 1.6 V +/- 0.6, P less than 0.008), 4 months (1.0 V +/- 0.2 vs 1.7 V +/- 0.8, P less than 0.002), and 10 months (1.2 V +/- 0.4 vs 1.7 V +/- 0.5, P less than 0.04) following implantation. The stimulation impedance at the time of implantation was lower in the ring-tip electrode group (530 ohms vs 603 ohms, P less than 0.03), but thereafter no significant difference was seen between the two groups. The acute and chronic sensing thresholds were similar in both groups. While the microporous electrode had significantly lower chronic capture thresholds, the magnitude of this difference is small, and probably clinically inconsequential.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Stimulation characteristics of a steroid-eluting electrode compared with three conventional electrodes.

Stimulation thresholds of a steroid-eluting electrode (Medtronic CapSure 4003, 9 patients) were compared with three conventional electrodes (carbon-tipped lead, Siemens-Elema 423 S/60, 10 patients; Elgiloy-tipped lead, Cordis Encor, 10 patients; platinum-tipped lead, Telectronix Laserdish 030-276, 9 patients). Voltage thresholds were determined during implantation, 1-3 days, 6 weeks, and 6 months postimplantation. No significant difference among the four electrodes was found in regard to stimulation and sensing behavior during implantation. Compared to intraoperative measurements, mean increase in voltage threshold and absolute voltage thresholds were substantially less for the steroid-eluting electrode than for the other tested electrodes 6 weeks and 6 months after implantation. The rheobasechronaxie product, a parameter of the stimulation performance of electrodes, underlined the superior pacing characteristics of the steroid-eluting electrode. To achieve low chronic stimulation threshold by pharmacological means is an attractive direction for future electrode technology.

Adult↗
PubMed1977

Low threshold endocaridal electrodes for permanent cardiac pacing. Comparison between one large and two small surface electrodes.

Three different electrodes, i.e. conventional large and small surface endocardial electrodes and a new large contact area-small active surface electrode, have been compared with respect to their stimulation thresholds for cardiac pacing in 94 patients with 96 electrodes. Both capacitor discharge and constant current pulses were used for the measurements. The average 2 msec impulse threshold for the 47 mm(2) electrode reached its maximum on the 14th postoperative day and was 3.6+/-1.4 V and 4.4+/-1.8 mA. One month after insertion, the threshold was 3.2+/-1.4 V and 3.9+/-1.7 mA. Corresponding values after one month for the 6 mm(2) electrode were 2.0+/-1.0 V and 1.7+/-0.9 mA and for the new electrode 1.7+/-0.9 V and 1.4+/-0.8 mA. Thresholds increased by about 20% when the impulse duration was diminished from 2 to 0.5 msec. The new large area-small active surface electrode offers advantages of significantly smaller increases in stimulation thresholds during the first month after insertion and good attachment to the endocardium.

Adult↗
PubMed1978

Complications with permanent endocardial electrode systems. A comparison between two types of electrodes.

The study comprises 375 patients who had received an endocardial pacemaker electrode primarily. A stylet electrode of the Medtronic type was used in 165 patients and of the Elema type in 79 patients. Elema's flexible electrode model 588 EMT was used in 131 patients. The total number of electrode complications was surprisingly high. In 92 out of the 375 patients, 141 serious episodes of pacing failure occurred during the observation period of from 6 to 42 months. The complication rate increased with pacemaker function time. The stylet electrodes gave the highest complication rate. The choice of vein for introducing the electrode into the heart seems not to affect the complication rate significantly. Nor did the initial threshold value of stimulation influence the complication rate to any marked degree. The pacemaker manufacturers have devoted much effort to producing long-life impulse generators but there is also a great need for well-functioning long-life electrodes.

Clinical Trials as Topic↗
PubMed1976

The sutureless electrode: comparison with transvenous and sutured epicardial electrode placement for permanent pacing.

Consecutive series of 50 transvenous and 50 sutureless pacemaker insertions were reviewed and compared with a nonsimultaneous series of 50 patients who received sutured epicardial pacemakers. It is concluded that: (1) the sutureless electrode has a lower initial stimulation threshold than the transvenous type; (2) complications from sutureless electrodes are greater than with transvenous electrodes and similar to the incidence with sutured epicardial pacemakers; (3) initial pacing is more satisfactory with the sutureless electrode compared with the transvenous model; and (4) late electrode failure due to threshold rise is greater with the sutureless electrode than with the transvenous or sutured epicardial type.

Action Potentials↗