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PubMed2000

Electrical stimulation of the preoptic area in Eigenmannia: evoked interruptions in the electric organ discharge.

The functional role of the basal forebrain and preoptic regions in modulating the normally regular electric organ discharge was determined by focal brain stimulation in the weakly electric fish, Eigenmannia. The rostral preoptic area, which is connected with the diencephalic prepacemaker nucleus, was examined physiologically by electrical stimulation in a curarized fish. Electrical stimulation of the most rostral region of the preoptic area with trains of relatively low intensity current elicits discrete bursts of electric organ discharge interruptions in contrast to other forebrain loci. These responses were observed primarily as after-responses following the termination of the stimulus train and were relatively immune to variations in the stimulus parameters. As the duration and rate of these preoptic-evoked bursts of electric organ discharge interruptions (approximately 100 ms at 2 per s) are similar to duration and rate of natural interruptions, it is proposed that these bursts might be precursors to natural interruptions. These data suggest that the preoptic area, consistent with its role in controlling reproductive behaviors in vertebrates, may be influencing the occurrence of electric organ discharge courtship signals by either direct actions on the prepacemaker nucleus or through other regions that are connected with the diencephalic pre-pacemaker nucleus.

Action Potentials↗
PubMed2003

Electric images of two low resistance objects in weakly electric fish.

Electroreceptive fish detect nearby objects by processing the information contained in the pattern of electric currents through their skin. In weakly electric fish, these currents arise from a self-generated field (the electric organ discharge), depending on the electrical properties of the surrounding medium. The electric image can be defined as the pattern of transepidermal voltage distributed over the receptive surface. To understand electrolocation it is necessary to know how electric image of objects are generated. In pulse mormyrids, the electric organ is localized at the tail, far from the receptors and fires a short biphasic pulse. Consequently, if all the elements in the environment are resistive, the stimulus at every point on the skin has the same waveform. Then, any measure of the amplitude (for example, the peak to peak amplitude) could be the unique parameter of the stimulus at any point of the skin. We have developed a model to calculate the image, corroborating that images are spread over the whole sensory surface and have an opposite center-surround, "Mexican-hat" shape. As a consequence, the images of different objects superimpose. We show theoretically and by simulation that the image of a pair of objects is not the simple addition of the individual images of these objects.

Animals↗
PubMed2000

Leukemia in electric utility workers: the evaluation of alternative indices of exposure to 60 Hz electric and magnetic fields.

BACKGROUND: Epidemiological studies have inconsistently demonstrated a positive relationship between magnetic and/or electric fields and leukemia. Although exposure to both 60 Hz electric and magnetic fields can be characterized in many ways, to date, risk assessment has been performed by using only a limited number of exposure indices. METHODS: The associations between adult leukemia and indices of electric and magnetic fields were explored within a nested case-control study of 31,453 Ontario electric utility workers. RESULTS: The percentage of time spent above electric field thresholds of 20 and 39 V/m was predictive of leukemia risk after adjusting for duration of employment and the arithmetic mean exposure to both electric and magnetic fields (P<0.05). Duration of employment was strongly associated with an increased risk of leukemia. Those who had worked for at least 20 years, and were in the highest tertiles of percentage of time spent above 10 and 20 V/m had odds ratios of 10.17 (95% CI = 1.58-65.30) and 8.23 (95% CI = 1. 24-54.43), respectively, when compared to those in the lowest tertile. Nonsignificant elevations in risk were observed between indices of magnetic fields and leukemia. CONCLUSIONS: Our results support the hypothesis that electric fields act as a promoting agent in the etiology of adult leukemia. Exposure assessment based on alternate indices of electric and magnetic fields should be incorporated into future occupational studies of cancer.

Adult↗
PubMed1997

An Electrical Suspension Method for Measuring the Electric Charge on Small Silicone Oil Droplets Dispersed in Aqueous Solutions

The electric charge on small liquid droplets dispersed in another immiscible liquid is of fundamental interest in various colloidal and interfacial phenomena and industrial processes. In this paper, the authors present a new experimental method to measure the charge on small silicone oil droplets in aqueous solutions. Basically, an oil droplet was kept stationary inside a test cell between two electrode plates by application of an electric field of an appropriate polarity and strength. Thus, the electric charge on the oil droplet was determined from the force balance among the electrical force, the gravitational force, and the buoyancy force exerted on it. By using the electrical suspension method, the effects of two different silicone oils, pH values, valences, and concentrations of three different electrolytes on the measured electric charge were investigated. One of the two silicone oils is heavier (rho1 = 1050 kg m-3) and the other is lighter (rho2 = 963 kg m-3) than the aqueous solutions. There was an appreciable difference between the measured electric charges for the two silicone oils. The point of zero charge (pzc) for the heavier oil droplets was found to be pH approximately 5.0, which is essentially the same as the value for the mineral oil droplets in the oil-in-water (O/W) emulsions reported by other researchers. It was also observed that the electric charge depends strongly on not only the concentrations but also the ionic valences of electrolytes added to the solutions. More specifically, divalent and trivalent cations, such as Ca2+ and Al3+, were more readily adsorbed on the oil-water interface. Therefore, their effects were more pronounced than that of monovalent cations, Na+, on reducing the negative charge or even reversing the charge polarity as their ionic concentrations increase, in accordance with the valence difference. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2001

Volume conductor effects on the spatial resolution of magnetic fields and electric potentials from gastrointestinal electrical activity.

An analysis of the relative capabilities of methods for magnetic and electric detection of gastrointestinal electrical activity is presented. The model employed is the first volume conductor model for magnetic fields from GEA to appear in the literature. A mathematical model is introduced for the electric potential and magnetic field from intestinal electrical activity in terms of the spatial filters that relate the bioelectric sources with the external magnetic fields and potentials. The forward spatial filters are low-pass functions of spatial frequency, so more superficial external fields and potentials contain less spatial information than fields and potentials near the source. Inverse spatial filters, which are reciprocals of the forward filters, are high-pass functions and must be regularised by windowing. Because of the conductivity discontinuities introduced by low-conductivity fat layers in the abdomen, the electric potentials recorded outside these layers required more regularisation than the magnetic fields, and thus, the spatial resolution of the magnetic fields from intestinal electrical activity is higher than the spatial resolution of the external potentials. In this study, two smooth muscle sources separated by 5cm were adequately resolved magnetically, but not resolved electrically. Thus, sources are more accurately localized and imaged using magnetic measurements than using measurements of electric potential.

Digestive System↗
PubMed2006

Electrical excitation of the acoustically sensitive auditory nerve: single-fiber responses to electric pulse trains.

Nearly all studies on auditory-nerve responses to electric stimuli have been conducted using chemically deafened animals so as to more realistically model the implanted human ear that has typically been profoundly deaf. However, clinical criteria for implantation have recently been relaxed. Ears with "residual" acoustic sensitivity are now being implanted, calling for the systematic evaluation of auditory-nerve responses to electric stimuli as well as combined electric and acoustic stimuli in acoustically sensitive ears. This article presents a systematic investigation of single-fiber responses to electric stimuli in acoustically sensitive ears. Responses to 250 pulse/s electric pulse trains were collected from 18 cats. Properties such as threshold, dynamic range, and jitter were found to differ from those of deaf ears. Other types of fiber activity observed in acoustically sensitive ears (i.e., spontaneous activity and electrophonic responses) were found to alter the temporal coding of electric stimuli. The electrophonic response, which was shown to greatly change the information encoded by spike intervals, also exhibited fast adaptation relative to that observed in the "direct" response to electric stimuli. More complex responses, such as "buildup" (increased responsiveness to successive pulses) and "bursting" (alternating periods of responsiveness and unresponsiveness) were observed. Our findings suggest that bursting is a response unique to sustained electric stimulation in ears with functional hair cells.

Animals↗
PubMed1996

Exposure to 60-Hz magnetic and electric fields at a Canadian electric utility.

OBJECTIVES: The purpose of this study was to estimate exposure to extremely low frequency (ELF) magnetic and electric fields in the Québec electrical utility Hydro-Quebec. METHODS: Personal exposures to ELF magnetic and electric fields were measured for workers randomly selected from 32 job categories at Hydro-Québec. Weekly arithmetic and geometric means, and other indices of exposure were estimated from 465 worker-weeks of data. RESULTS: By job category, the arithmetic means of the ELF magnetic field ranged from 0.09 to 2.36 microT. Those of the ELF electric field exposures ranged from 2.5 to 400 V.m-1. Within each field, correlations of either the arithmetic or geometric means with alternative indices, including an index of the time rate of change, were generally high (r > or = 0.8). Exceptions were the 20th percentile of the electric means and the proportion of time above 12.4 and 100 microT. The day-to-day variation of exposure was greater than the variation between workers. The median between-day and between-worker components of variance (as geometric standard deviations) by job category were 2.13 and 1.71 for magnetic fields (2.24 and 1.81 for electric fields). CONCLUSIONS: Substation workers, hydroelectric generating station operators, and cable splicers showed the highest arithmetic means for 60-Hz magnetic fields above 1 microT. For 60-Hz electric fields, forestry workers, equipment electricians in 735 kV substations, and distribution linemen (contact method) had arithmetic mean exposures greater than 100 W.m-1. Of the total variance in the logarithms of the weekly magnetic and electric field means, job category explained 49.6% and 59.5%, respectively.

Analysis of Variance↗
PubMed2003

Electrical conductivity imaging by magnetic resonance electrical impedance tomography (MREIT).

Magnetic resonance electrical impedance tomography (MREIT) is a recently developed imaging technique that combines MRI and electrical impedance tomography (EIT). In MREIT, cross-sectional electrical conductivity images are reconstructed from the internal magnetic field density data produced inside an electrically conducting subject when an electrical current is injected into the subject. In this work the results of an electrical conductivity imaging experiment are presented, along with some practical considerations regarding MREIT. The MREIT experiment was performed with a 0.3 Tesla MRI system on a phantom made of two compartments with different electrical conductivities. The current density inside the phantom was measured by the MR current density imaging (MRCDI) technique. The measured current density was then used for conductivity image reconstruction by the J-substitution algorithm. The conductivity phantom images obtained with an injection current of 28mA showed conductivity errors of about 25.5%.

Algorithms↗
PubMed2006

Determinants of thoracic electrical impedance in external electrical cardioversion of atrial fibrillation.

The success of external cardioversion (ECV) of atrial fibrillation depends on generating sufficient transmyocardial current for defibrillation with minimal myocardial injury. Thoracic electrical impedance plays an important role in the relation between the delivered energy and transmyocardial current. This study assessed the determinants of thoracic electrical impedance in ECV of atrial fibrillation. ECV of atrial fibrillation was performed in 80 consecutive patients (mean age 73 +/- 9 years; men 69%; body mass index 26.0 +/- 3.6 kg/m(2)) within 12 months, using biphasic shocks (Multipulse Biowave) delivered through adhesive pads in an anteroposterior position. Thoracic electrical impedance was measured using the first shock. The mean thoracic electrical impedance was 57.7 +/- 12.3 Omega (energy 71 +/- 43 J, current intensity 33 +/- 12 A). Sinus rhythm was immediately restored in 75 patients (94%). Thoracic electrical impedance was greater (60.9 +/- 11.8 vs 51.7 +/- 11.0 Omega, p = 0.001) in patients requiring >1 shock (65%). At multivariate linear regression analysis (R = 0.761, p <0.001), female gender (+9.7 +/- 2.0 Omega, p <0.001), body mass index (+1.5 +/- 0.3 for a 1 kg/m(2) increase, p <0.001), hemoglobin concentration (+1.9 +/- 0.6 for a 1 g/dl increase, p = 0.004), and the presence of chronic heart failure (-5.3 +/- 2.0 Omega, p = 0.009) were independent predictors of thoracic electrical impedance. In conclusion, to increase ECV efficacy and minimize complications, the delivered energy should be adjusted in accordance with the clinical variables that independently affect thoracic electrical impedance and, hence, transmyocardial current.

Aged↗
PubMed1987

Electrical injury mechanisms: electrical breakdown of cell membranes.

Electric fields are capable of damaging cells through both thermal and nonthermal mechanisms. While joule heating is generally recognized to mediate tissue injury in electrical trauma, the possible role of electrical breakdown of cell membranes has not been thoroughly considered. Evidence is presented suggestive that in many instances of electrical trauma the local electrical field is of sufficient magnitude to cause electrical breakdown of cell membranes and cell lysis. In theory, large cells such as muscle and nerve cells are more vulnerable to electrical breakdown. To illustrate the significance of cell size and orientation, a geometrically simple model of an elongated cell is analyzed.

Arm↗
PubMed1999

Electric organ discharges and electric images during electrolocation.

Weakly electric fish use active electrolocation - the generation and detection of electric currents - to explore their surroundings. Although electrosensory systems include some of the most extensively understood circuits in the vertebrate central nervous system, relatively little is known quantitatively about how fish electrolocate objects. We believe a prerequisite to understanding electrolocation and its underlying neural substrates is to quantify and visualize the peripheral electrosensory information measured by the electroreceptors. We have therefore focused on reconstructing both the electric organ discharges (EODs) and the electric images resulting from nearby objects and the fish's exploratory behaviors. Here, we review results from a combination of techniques, including field measurements, numerical and semi-analytical simulations, and video imaging of behaviors. EOD maps are presented and interpreted for six gymnotiform species. They reveal diverse electric field patterns that have significant implications for both the electrosensory and electromotor systems. Our simulations generated predictions of the electric images from nearby objects as well as sequences of electric images during exploratory behaviors. These methods are leading to the identification of image features and computational algorithms that could reliably encode electrosensory information and may help guide electrophysiological experiments exploring the neural basis of electrolocation.

Animals↗
PubMed2001

A split-mouth comparison of a three-dimensional-action electric toothbrush and a high-frequency electric toothbrush for reducing plaque and gingivitis.

PURPOSE: To compare the effectiveness in reducing plaque and gingivitis of an electric toothbrush with three-dimensional (oscillating/rotating/pulsating) brush head action, Braun Oral-B 3D Plaque Remover, and an electric toothbrush with high-frequency vibrating action, Sonicare Plus. MATERIALS AND METHODS: This was a randomised, split-mouth study of 33 adult subjects who used both electric toothbrushes for a total of 9 weeks. After a 2-week acclimation period of brushing with each device on alternating days, subjects received a prophylaxis, then refrained from any oral hygiene on the mandibular teeth for 21 days to induce gingivitis. However, they continued to brush the maxillary teeth on alternating days with each electric toothbrush. Then, for a period of 4 weeks they brushed each side of the mouth with different toothbrushes, randomly assigned to right or left. Plaque and gingivitis were assessed initially, after the 21-day no-oral-hygiene period, and after 2, 3 and 4 weeks of brushing twice daily. RESULTS: After 21 days without oral hygiene, mean mandibular plaque and gingivitis scores increased significantly for all subjects. Use of both electric toothbrushes during the treatment phase progressively reduced plaque and gingivitis scores at each successive examination. The Braun toothbrush was significantly more effective than the Sonicare toothbrush in reducing plaque at every examination and gingival bleeding after 4 weeks of brushing. It is concluded that the Braun electric toothbrush with three-dimensional brush head action offers advantages over the Sonicare electric toothbrush with high-frequency vibrating action in terms of plaque control and potential improvement of gingival health following induction of experimental gingivitis.

Adult↗
PubMed1990

Electric fields induced by low frequency magnetic fields in inhomogeneous biological structures that are surrounded by an electric insulator.

Electric fields induced by low-frequency magnetic fields into inhomogeneous structures, which have electric conductivities and dielectric permittivities of typical biological substances, are evaluated. Closed-form approximate and numerical solutions are obtained for nonconcentric cylinders with different electric properties (such as bone embedded in muscle), which are surrounded by a good electrical insulator (such as air). It is shown that even a single inhomogeneity in an otherwise homogenous cylinder, which is exposed to a uniform, axially directed magnetic field, can lead to substantial deviations from the direction and distribution of the induced electric field that would exist in the homogenous cylinder. Thus the induced field is not everywhere circumferential, nor does it magnitude at all angular positions increase linearly with the radial distance. Radially and circumferentially directed field components depend on size, electrical properties, and eccentricity of the inhomogeneities. Equations as well as graphical presentations are given that describe the induced fields when the enclosed inhomogeneities consist either of eccentrically located single cylinders or pairs of coaxial cylinders with different electrical conductivities or dielectric permittivities.

Electric Conductivity↗
PubMed1998

Depressive effects of segmental and heterotopic application of transcutaneous electrical nerve stimulation and piezo-electric current on lower limb nociceptive flexion reflex in human subjects.

OBJECTIVES: To evaluate quantitatively the effectiveness and clinical relevance of various parameters of electrical stimulation used to relieve acute and chronic pain and to further knowledge of the mechanisms that may underlie the physiologic response produced by the transcutaneous application of each type of current. DESIGN: A nociceptive flexion reflex (RIII reflex) elicited in the lower limb by electrical stimulation of the sural nerve at the ankle was studied before, during, and after application of the following conditioning stimuli: (1) non-noxious transcutaneous electrical nerve stimulation (TENS)--low-intensity (2mA), short-duration (0.1 msec), and high-frequency (100Hz) rectangular pulses (TENS1); (2) noxious TENS--high-intensity (20mA), long-duration (2 msec), and low-frequency (3Hz) rectangular pulses (TENS2); (3) noxious piezo-electric current (PEC)--high-voltage, low-charge, low-intensity, and low-frequency rectangular pulses delivered by a piezo-electric ceramic device (PECs1); (4) a sham PEC situation in which the piezo-electric device did not produce any electric current (Sham PEC). Each conditioning stimulus (TENS1, TENS2, PECs1, Sham PEC) was applied for a 2-minute period either segmentally on the sural nerve itself or heterotopically on the skin overlying the first interosseous space of the contralateral hand. PARTICIPANTS: Twenty-four healthy volunteers (14 women, 10 men, 19 to 52 years of age), who were briefed and familiarized with the experimental procedure. During the experimental sessions, subjects were prone in bed to ensure muscular relaxation. MEASURES: Value of the nociceptive RIII reflex before, during, and after application of conditioning stimuli in the four procedures described above. This reflex was selected because it has been shown to be an objective and physiologic correlate of pain. RESULTS: Non-noxious TENS1 stimulation applied segmentally produced inhibitions of the RIII reflex only during the 2-minute conditioning period. When given segmentally, the noxious TENS2 stimulation produced a facilitatory effect during the 2 minutes of application, followed by significant inhibitory after-effects. The administration of TENS2 heterotopically resulted in inhibitions of the RIII reflex both during and after the 2-minute conditioning period. Application of PECs1, whether segmentally or heterotopically, produced powerful and long-lasting inhibitory after-effects, especially with the heterotopic paradigm. These effects were associated with long-lasting local changes to the skin of the neurogenic inflammation type, which were well tolerated by all subjects. Application of Sham PEC did not result in significant modification of either the RIII reflex or the skin. CONCLUSIONS: These data are discussed in terms of possible spinal and supraspinal mechanisms involving inhibitory descending controls and underline the potential clinical use of PECs1 in the treatment of pain.

Adult↗
PubMed2006

Electrical properties and defect chemistry of TiO2 single crystal. I. Electrical conductivity.

The present work reports the electrical properties of high-purity single-crystal TiO(2) from measurements of the electrical conductivity in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities in the range 10(-13) to 10(5) Pa. The effect of the oxygen activity on the electrical conductivity indicates that oxygen vacancies are the predominant defects in the studied ranges of temperature and oxygen activities. The electronic and ionic lattice charge compensations were revealed at low and high oxygen activities, respectively. The determined semiconducting quantities include: the activation energy of the electrical conductivity (E(sigma) = 125-205 kJ.mol(-1)), the activation energies of the electrical conductivity components associated with electrons (E(n) = 218 kJ.mol(-1)), electron holes (E(p) = 34 kJ.mol(-1)), and ions (E(i) = 227 kJ.mol(-1)), and the enthalpy of motion for electronic defects (DeltaH(m) = 4 kJ/mol). The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. The obtained data allow the determination of the n-p demarcation line in terms of temperature and oxygen activities. The band gap determined from the electronic component of the electrical conductivity is 3.1 eV.

Crystallization↗
PubMed1984

Phosphorylation states of the (Na+ + K+)-transporting ATPase in preparations from lamb kidney and electric-eel (Electophorus electricus) electric organ.

Phosphorylation states of the (Na+ + K+)-transporting ATPase were studied in highly purified preparations isolated from electric-eel electric organ and from lamb kidney. The steady-state level of phosphorylated lamb kidney enzyme, obtained by reaction with [gamma-32P]ATP, was not appreciably reduced in the presence of ADP unless oligomycin was present. The phosphorylated form of the electric-eel electric-organ enzyme was reduced by at least 95% under the same conditions, suggesting that the E1P state in the kidney enzyme is more transitory than that in electric organ. The level of phosphorylation from [32P]Pi was higher in the lamb kidney preparation than in the electric-organ preparation, and the difference in stimulation of phosphorylation by ouabain in the two preparations was striking. Ouabain increased the level of phosphorylation by 35% in the kidney preparation and 734% in the electric-organ preparation. The E2P state seems to be stabilized by ouabain in the latter preparation. These findings, as well as the different reactivities of the thiol groups to blocking reagents in these preparations, suggest that the tertiary structure in the enzyme isolated from these two sources is different.

Adenosine Triphosphate↗
PubMed2005

Neuroprotective effect of epidural electrical stimulation against ischemic spinal cord injury in rats: electrical preconditioning.

BACKGROUND: Electroconvulsion therapy is likely to serve as an effective preconditioning stimulus for inducing tolerance to ischemic brain injury. The current study examines whether electrical stimuli on the spinal cord is also capable of inducing tolerance to ischemic spinal cord injury by transient aortic occlusion. METHODS: Spinal cord ischemia was induced by occlusion of the descending thoracic aorta in combination with maintaining systemic hypotension (40 mmHg) during the procedure. Animals implanted with epidural electrodes were divided into four groups according to electrical stimulation and sham. Two groups consisted of rapid preconditioning (RE group, n = 8) and sham procedure (RC group, n = 8) 30 min before 9 min of spinal cord ischemia. In the two groups that underwent delayed preconditioning, rats were exposed to 9 min of aortic occlusion 24 h after either pretreatment with epidural electrical stimulation (DE group, n = 8) or sham (DC group, n = 8). In addition, rats were exposed to 6-11 min of spinal cord ischemia at 30 min or 24 h after epidural electrical stimulation or sham stimulation. The group P50 represents the duration of spinal cord ischemia associated with 50% probability of resultant paraplegia. RESULTS: Pretreatment with electrical stimulation in the DE group but not the RE group protected the spinal cord against ischemia, and this stimulation prolonged the P50 by approximately 15.0% in the DE group compared with the DC group. CONCLUSIONS: Although the optimal setting for this electrical preconditioning should be determined in future studies, the results suggest that epidural electrical stimulation will be a useful approach to provide spinal protection against ischemia.

Animals↗
PubMed1991

A simple electrical-mechanical model of the heart applied to the study of electrical-mechanical alternans.

Recent evidence has shown that a subtle alternation in the surface ECG (electrical alternans) may be correlated with the susceptibility to ventricular fibrillation. This paper presents evidence that a mechanical alternation in the heart beat (mechanical alternans) generally accompanies electrical alternans. A simple finite-element computer model, which emulates both the electrical and mechanical activity of the heart, is presented. A pilot animal study is also reported. The computer model and the animal study both found that 1) there exists a regime of combined electrical-mechanical alternans during the transition from a normal rhythm towards a fibrillatory rhythm, 2) the detected degree of alternation is correlated with the relative instability of the rhythm, and 3) the electrical and mechanical alternans may result from a dispersion in local electrical properties leading to a spatial-temporal alternation in the electrical conduction process.

Animals↗