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PubMed1999

A convenient electrode holder for glass pipettes to stabilize electrode potentials.

Electrophysiological techniques require stable, reversible electrodes for accurate recording. Ag/AgCl electrodes are commonly used in patch-clamp and intracellular recording pipettes, but when these electrodes are exposed to Cl--free media they are no longer reversible and may develop large, unstable offset potentials. We present here a simple electrode holder design that provides a liquid junction between the electrode solution and a KCl-filled reservoir containing the AgCl pellet. This allows an electrode solution of any composition to be used without affecting the reversibility of the electrode, and the liquid junction potentials that develop are small and well defined. Mechanical isolation of the AgCl pellet from the pipette improves long-term stability of the electrode because the AgCl coating is not scraped while changing pipettes. The response time of the holder and its wide-band noise levels are comparable to those of standard holders. For practical experiment durations, the diffusion for KCl from the reservoir down the pipette produces negligible contamination at the tip. Similarly, back diffusion of the pipette contents into the reservoir is also negligible.

Diffusion↗

PubMed2000

Comparison of electrode position in the human cochlea using various perimodiolar electrode arrays.

OBJECTIVE: This study was conducted to evaluate the insertion properties and intracochlear trajectories of three perimodiolar electrode array designs and to compare these designs with the standard Cochlear/Melbourne array. BACKGROUND: Advantages to be expected of a perimodiolar electrode array include both a reduction in stimulus thresholds and an increase in dynamic range, resulting in a more localized stimulation pattern of the spiral ganglion cells, reduced power consumption, and, therefore, longer speech processor battery life. METHODS: The test arrays were implanted into human temporal bones. Image analysis was performed on a radiograph taken after the insertion. The cochleas were then histologically processed with the electrode array in situ, and the resulting sections were subsequently assessed for position of the electrode array as well as insertion-related intracochlear damage. RESULTS: All perimodiolar electrode arrays were inserted deeper and showed trajectories that were generally closer to the modiolus compared with the standard electrode array. However, although the precurved array designs did not show significant insertion trauma, the method of insertion needed improvement. After insertion of the straight electrode array with positioner, signs of severe insertion trauma in the majority of implanted cochleas were found. CONCLUSIONS: Although it was possible to position the electrode arrays close to the modiolus, none of the three perimodiolar designs investigated fulfilled satisfactorily all three criteria of being easy, safe, and atraumatic to implant.

Cochlear Implantation↗

PubMed2000

Electrode impedance: an indicator of electrode-tissue contact and lesion dimensions during linear ablation.

Pre-ablation impedance was evaluated for its ability to detect electrode-tissue contact and allow creation of long uniform linear lesions with a multi-electrode ablation catheter. The study consisted of 2 parts, both of which used the in vivopig thigh muscle model. In part 1, a 7 Fr. multi-electrode catheter was held in 3 electrode-tissue contact conditions: (1) non-contact; (2) light contact with a 30g downward force; and (3) tight contact with a 90g downward force. Impedances were measured in unipolar, modified unipolar and bipolar configurations using a source with frequencies from 100Hz to 500kHz. Compared with non-contact, the impedance increased 35 +/- 22 % with 30g contact pressure and 68 +/- 40% when the contact pressure was increased to 90g across the range of frequencies studied. In part 2, the same catheter was held against the tissue with different forces. Pre-ablation impedance was measured using a 10kHz current. Phased radiofrequency energy was applied to the 5 electrodes simultaneously using 10W power at each electrode for 120s. A total of 32 linear lesions were created. The lesion dimensions correlated with pre-ablation impedance. A unipolar impedance > or = 190 Omega indicates 95% possibility to create a uniform linear lesion of at least 3mm depth with our ablation system. We conclude that pre-ablation impedance may be a useful indicator for predicting electrode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.

Analysis of Variance↗

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↗

PubMed2005

A model for cochlear implant electrode insertion and force evaluation: results with a new electrode design and insertion technique.

OBJECTIVES AND HYPOTHESIS: This study has the specific aim of evaluating the insertion characteristics of a new cochlear implant electrode. Techniques for evaluation of fluoroscopic real time mechanical insertion dynamics, histologic electrode position and trauma results, hydraulic force, and mechanical insertion forces are presented. In addition, this study should serve to present a novel model for cochlear implant electrode insertion evaluations. STUDY DESIGN: Prospective analysis using a series of analytical techniques. METHODS: All studies are conducted in fixed cadaveric temporal bones. Real time fluoroscopic insertion evaluations, histologic evaluations for trauma and electrode position in embedded bones, hydraulic measures, and mechanical intracochlear force measurements are conducted with a current and new electrode. RESULTS: The Contour Advance electrode provides a more reliable and less traumatic insertion when deployed with the Advance Off Stylet technique. This is largely because of a reduction in intracochlear outer wall force generation. Fluoroscopic and histologic analysis reveal a smooth insertion without reliance on cochlear outer wall contact. No hydraulic forces were detected when measured from the superior semicircular canal ampulla. CONCLUSION: The model used for this study provides valuable information to cochlear implant surgeons and design engineers. The Contour Advance electrode, inserted with the Advance Off Stylet technique, represents an improvement over the Contour electrode inserted with the standard insertion technique.

Cadaver↗

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↗

PubMed1996

Adsorption behavior of serum albumin on electrode surfaces and the effects of electrode potential.

The adsorption behavior of serum albumin onto the surface of platinum, gold, and glassy carbon electrodes was studied in relation to the electrode potential, by using cyclic voltammetry and a quartz-crystal microbalance. The kinetics of adsorption was significantly dependent on the electrode potential. The adsorption was highly accelerated by the application of positive potential to the electrode, suggesting an electrostatic interaction between the negatively charged albumin molecules and the positively polarized electrode as the origin of the accelerated adsorption. The adsorption of albumin on the electrodes was irreversible with respect to dilution of the albumin solution, while the quartz-crystal microbalance data showed that albumin forms a monomolecular layer on the electrode surface. Protein adsorption on electrode surface in serum was also examined.

Adsorption↗

PubMed1982

Continuous intra-arterial PO2 monitoring with a surface heparinized catheter electrode. A study of conformity in conventional blood gas analysis and of long-term electrode function in the non-heparinized dog.

Surface-heparinized catheter PO2 electrodes were used for continuous intra-arterial monitoring in non-heparinized dogs. During one-day experiments the read-out of the electrode monitoring unit was compared with that of conventional blood gas analysis. Furthermore, the electrodes were studied after long-term implantation. The intra-arterial PO2 electrodes have previously been reported to be linear in the gas phase, water phase and in heparinized blood. The present study demonstrates that the catheter electrodes remain linear after surface heparinization. As compared with the conventional blood gas analysis it was found that the desk analyser in the range PaO2 greater than 18 kPa underestimated the actual PaO2 as compared to the invasively monitored PaO2, but in the range below 7 kPa the desk analyser overestimated the PaO2. Surface-heparinized PO2 catheter electrodes were studied after up to 23 days of implantation. No coagulation phenomenon was found around the catheters, neither macroscopically nor by scanning electron microscopy. The electrical function withstood 7 days of implantation. After more extended periods the electrical leads were broken without any damage to the catheter itself. When compared with acutely implanted surface-heparinized electrodes, there was no difference in monitoring characteristics between the acutely implanted and the long-term implanted PO2 electrodes.

Animals↗

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↗

PubMed1997

Comparison of surface EMG signals between electrode types, interelectrode distances and electrode orientations in isometric exercise of the erector spinae muscle.

The influence of electrode type, interelectrode distance (IED) and electrode orientation on EMG signals from the paraspinal muscles was investigated. Bipolar electrodes were placed at distances 2, 3, 4, 6 and 8 cm over the erector spinae in the cranio-caudal direction ("in series") as well as in the direction perpendicular to it ("in parallel"). Ten subjects performed 5 s isometric contractions of the erector spinae at 20, 40, 60, 80 and 100% MVC by pulling upward on a handlebar attached to the floor. RMS EMG signals were analyzed for mean average amplitude (AA). Mean total power (TP) and mean median frequency (MF) of the raw EMG signal were determined using fast Fourier transform. In addition to graded loading, sustained fatiguing contractions were performed from which TP and MF were obtained. With increasing IED the AA and TP increased while MF decreased. Although a trend towards higher AA, TP and MF was found for electrodes "in series", as compared to those "in parallel", the difference never reached significance. It is concluded that consistent information about muscle activity was obtained with Miniature Biopotential Skin Electrodes and 14445C Hewlett-Packard electrodes independently from IED or orientation. Orientation "in parallel" prevented the electrodes from sliding during muscle contraction. The third tested type, electrodes developed in the Neuromuscular Research Center, Boston, proved extremely sensitive to movement.

Adult↗

PubMed2000

Novel intracochlear electrode positioner: effects on electrode position.

Spiral ganglion cells, located in the cochlear modiolus, are widely thought to be the neural elements stimulated by cochlear implants (CIs). Positioning CI electrodes adjacent to the modiolus may allow delivery of more focused, discrete fields of electrical stimulation, reducing both current requirements and the channel interaction associated with simultaneous stimulation. In order to provide greater consistency in positioning CI electrodes against the modiolus, Advanced Bionics Corporation has designed a silicone intracochlear positioner that is inserted alongside the electrode. Placed against the outer wall of the scala tympani, it directs the electrode array toward the modiolus. Five fresh-frozen temporal bones were studied to validate enhanced electrode placement. Electrode position was documented with image-enhanced digital fluoroscopy, and the distance to the modiolus was measured with computer-assisted morphometrics. The electrode positioner was highly effective in positioning the electrodes closer to the modiolus (p < .001).

Adult↗

PubMed2004

Ferrocene-containing polyelectrolyte multilayer film-covered electrodes: electrocatalytic determination of ascorbic acid and use of inner blocking layers to improve the upper detection limit of the electrodes.

A multilayer film composed of ferrocene(Fc)-appended poly(allylamine hydrochloride) (Fc-PAH) and poly(potassium vinylsulfate) (PVS) has been prepared on the surface of a gold(Au) electrode by using a layer-by-layer self-assembly technique. Fc-containing polyelectrolyte multilayer (PEM) film-modified electrodes can electrochemically catalyze the oxidation of ascorbic acid successfully. For a 2 (Fc-PAH/PVS) bilayer-covered electrode the catalytic current increased linearly with increasing concentration of ascorbic acid over the concentration range 6 micromol L(-1)-3 mmol L(-1). To extend the dynamic range for ascorbic acid, the surface of the Au electrode was first covered with a (PAH/PVS)(2) film on which an additional (Fc-PAH/PVS)(5) film was coated. This strategy successfully extended the dynamic range of the electrode up to 25 mmol L(-1) ascorbic acid, because the (PAH/PVS)(2) layer blocked access of ascorbic acid to the electrode surface. The upper detection limit of the (PAH/PVS)(2) (Fc-PAH/PVS)(5) film-modified electrode is much higher than those of Fc-based ascorbic acid sensors reported so far. Electron transfer is diffusion-controlled within the (PAH/PVS)(2)(Fc-PAH/PVS)(5) film.

Ascorbic Acid↗

PubMed1980

I. Novel capacitative electrode with a wide frequency range for measurements of flash-induced changes of interface potential at the oil-water interface. Mechanical construction and electrical characteristics of the electrode.

The mechanical construction and the electrical properties of a new type of capacitative electrode for the oil-water interface are described. The electrode is designed to detect changes of the interface potential induced by photochemical, photophysical, and photobiological reactions occurring at the interface. The construction is based on capacitative coupling of two aqueous compartments separated by a thin Teflon film. Thereby, the oil-water interface is in horizontal position and the electrode is placed with its planar bottom about 10 micrometer above the interface. A main feature of the electrode is the transparency to visible light which is achieved by having a clear electrolyte solution in the inner compartment of the capacitative electrode. The aqueous subphase and the inner electrolyte are connected with Ag/AgCl electrodes to voltage amplifiers. The capacitative electrode is best operated under open circuit conditions. The frequency range experimentally verified is 500 MHz larger than or equal to 0.03 Hz. The sensitivity is mainly determined by the noise of the electronic amplifiers, typical 50-100 muV.

Electric Conductivity↗

PubMed1983

Electrical stimulation with Pt electrodes. VII. Dissolution of Pt electrodes during electrical stimulation of the cat cerebral cortex.

Procedures are described for determining trace quantities of Pt released into brain tissue directly beneath cortical surface stimulation electrodes. Implanted electrodes (1.1 mm Pt discs) were stimulated for 4.5 h, 9 h and 36 h (4 X 9 h/day) with balanced biphasic pulses (20 micro C/cm2 or 100 micro C/cm2 per phase, 50 Hz), following which tissue 0-2 mm beneath stimulation electrodes and the encapsulating tissue adherent to electrodes was excised and analyzed for Pt. A time-dependent increase in Pt concentration was observed between 4.5 h (4-20 ng Pt/stimulation site) and 9 h (50-339 ng Pt/site) of stimulation at 100 micro C/cm2 with nearly all of the Pt located in the encapsulating tissue associated with the electrodes. Somewhat less Pt was observed in the 36 h samples, and it was almost equally distributed between the encapsulating tissue of the electrodes and the first millimeter depth of underlying brain tissue. Little or no Pt was found at electrode sites receiving 20 micro C/cm2 pulses. Control brain tissue samples as well as samples of blood, CSF and kidney were negative for Pt. The findings indicate that the rate of Pt dissolution gradually decreases during in vivo stimulation, and that dissolved Pt may slowly move away from stimulation sites, possibly by diffusion or fluid exchange.

Animals↗

PubMed2004

An investigation of the effect of electrode size and electrode location on comfort during stimulation of the gastrocnemius muscle.

The use of surface neuromuscular electrical stimulation (SNMES) in medicine is well established. However, discomfort has been identified as limiting the use of SNMES in these applications. This pilot study investigated the influence of various electrode sizes and their positioning on perceived pain and discomfort during neuromuscular electrical stimulation (NMES) of the gastrocnemius muscle using surface electrodes. This study formed part of a research project to develop a therapeutic device for calf muscle blood flow assist applications. Twelve healthy subjects (n=12) participated in this pilot study. Each participant attended the trial centre for testing which consisted of SNMES to four different electrode stimulation sites using two electrode sizes (round with areas 19.63 and 38.48 cm2). Comfort was assessed by asking the subjects to indicate the stimulation amplitude corresponding to the onset of discomfort (pain threshold) and the amplitude at which the discomfort became unbearable (pain tolerance). Of the four stimulation sites tested, two were deemed unsuccessful as it was very difficult to obtain a muscle contraction using these sites, while the remaining two sites elicited good muscle contraction. The most comfortable stimulation was achieved by placing the cathode electrode high on the calf, below the proximal end of the muscle heads and the anode electrode towards the end of the muscle belly and when the 19.63 cm2 electrodes were used at these sites (p=<0.001).

Adult↗

PubMed1995

A long thin electrode is equivalent to a short thick electrode for defibrillation in the right ventricle.

We hypothesized that a long thin right ventricular (RV) electrode would have equivalent defibrillation threshold (DFT) performance to a short thick electrode with approximately the same surface area. This could lead to thinner transvenous lead systems, which would be easier to implant. A thin (5.1 French) lead was compared to a standard control (10.7 French). The thin lead had an 8-cm RV electrode length with a surface area of 4.26 cm2. The standard lead had a RV electrode length of 3.7 cm and a surface area of 4.12 cm2. A 140-mu French capacitor 65%/65% tilt biphasic defibrillation shock was delivered between the RV electrode and a 14-cm2 subcutaneous patch. DFTs were determined following 10 seconds of fibrillation in 11 dogs by a triple determination averaging technique. The thin lead had a lower resistance (77.1 +/- 27.4 omega vs 88.9 +/- 30.3 omega, P < 0.001) than did the thick lead. There was no significant difference in stored energy DFTs (9.9 +/- 2.5 vs 10.3 +/- 2.7, P = 0.098 2-sided, P = 0.049 1- sided). This was in spite of the fact that the long thin lead had a portion of its RV coil extending above the tricuspid valve and, thus, not contributing efficiently to the ventricular gradients in the small dog heart. We conclude that a long thin right ventricular electrode and a standard short thick electrode had equivalent defibrillation performance. This preliminary result should be confirmed in clinical studies as it could lead to significantly thinner transvenous lead systems.

Animals↗

PubMed2001

Transdermal drug delivery by electroporation applied on the stratum corneum of rat using stamp-type electrode and frog-type electrode in vitro.

Transdermal enhancement effects of electroporation applied only on the stratum corneum by two electrode types, the stamp-type electrode and the frog-type electrode, were investigated in vitro using excised rat skin. Carboxyfluorescein (CF) was selected as a model compound. The excised skin was set in a Franz type diffusion cell and a square wave electric pulse was applied to the stratum corneum under various electric pulse conditions. We determined the permeability of CF to the receptor compartment under these conditions. Voltage, electric pulse length, and number of electric pulses, were varied from 10 to 1000 V, 50 micros to 15 ms and 5 to 30 pulses, respectively. Flux rate was enhanced as the electric pulse condition strengthened. However, the maximum value was attained in the flux rate, above which no increase was observed despite strengthening of the electric pulse. Although at low electric pulses, the enhancement effect of the frog-type electrode was superior to that of the stamp-type electrode, the maximum flux rates were the same. These results indicate that electroporation on the stratum corneum using the stamp-type electrode or frog-type electrode, is useful for transdermal drug delivery.

Administration, Cutaneous↗