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PubMed1995

Electrical resistances of interstitial and microvascular space as determinants of the extracellular electrical field and velocity of propagation in ventricular myocardium.

BACKGROUND: In myocardial ventricular tissue, extracellular electrical resistance (ro) is an important determinant of propagation velocity (theta) and the magnitude of the extracellular bipolar electrogram (delta Vo). The extracellular space is composed of two compartments, the vascular space and the interstitial space. To assess the electrical equivalent of this compartmentation in the ventricular myocardium and its effect on ro, theta, and delta Vo, electrical cable analysis was performed in an arterially perfused rabbit papillary muscle. METHODS AND RESULTS: Vascular resistivity was changed from 75 to 86 to 143 and to 221 omega/cm by variation of hematocrit in the perfusate from 0% to 10% to 40% and to 60%. As a means to vary the volume of the interstitial space and with this as its resistivity, colloid osmotic pressure (COP) in the perfusate was changed from 9 to 36 and to 94 mm Hg by altering the dextran concentration in the perfusate from 10 to 40 to 80 g/L. Decreasing COP had a marked effect on ro (56% decrease), delta Vo (decrease from 61 to 42 mV), theta (increase from 48 to 59 cm/s), and the diameter of the muscle fiber (increase of 12%). If COP was increased from 36 to 94 mm Hg, ro (by 35%) and delta Vo (from 62 to 75 mV) increased; theta and diameter showed no significant changes. In contrast, alterations of intravascular electrical resistivity in a range from 75 to 221 omega/cm did not induce any significant changes in ro, delta Vo, theta, and diameter of the preparations. CONCLUSIONS: We conclude from our data that (1) the microvascular tree in ventricular myocardium is electrically insulated to a large degree from the interstitial space and that (2) electrical current flow in the extracellular space during excitation is confined to the narrow, anisotropic interstitial space.

Animals↗
PubMed1998

The electric image in weakly electric fish: physical images of resistive objects in Gnathonemus petersii.

The present study describes a measurement-based model of electric image generation in the weakly electric mormyrid fish Gnathonemus petersii. Measurements of skin impedance, internal resistivity and fish body dimensions have been used to generate an electrical-equivalent model of the fish and to calculate electrical images and equivalent dipole sources for elementary resistive objects. These calculations allow us to understand how exafferent and reafferent signals are sensed by electroreceptors. An object's electric image consists of the modulation of the transcutaneous voltage profile generated by the fish's own discharge. The results suggest a set of rules for electrolocation: (1) the side of the fish where modulation is larger indicates the side on which the object is situated; (2) the object's position in the electroreceptive field is indicated by the point of maximum modulation of the transcutaneous voltage; (3) the degree of focus of the image indicates the distance to the object. In addition, center-surround opposition originating at pre-receptor level is proposed. Both experimental measurements and modeling indicate that fish skin impedance is relatively low (400-11 000 cm 2 ) and mainly resistive. This low skin impedance appears to enhance the local electric organ discharge modulation, the center-surround effect, the signal-to-noise ratio for electrolocation and the active space for electrocommunication.

Animals↗
PubMed1975

Electrical sizing of liver cell nuclei by the particle beam method. Mean volume, volume distribution and electrical resistance.

Electrical sizing of liver cell nuclei gives similar results as histological techniques for the mean volume, the volume distribution and the proportions of the different nuclear volume populations. The electrical method has, compared to histological technics, however, the advantage of higher rapidity and accuracy. Due to the good volume resolution of the improved electrical sizing method two populations of nuclei with different mean volumes can be distinguished in rat liver tissue besides di-, tetra- and octoploid cell nuclei. In addition to the volume distribution curves, the mean electrical resistance of isolated liver nuclei can be determined by the electrical sizing method. A newly developed micromehod provides enough cell nuclei for electrical sizing from only 10 mg liver tissue in a few minutes. This should enable the measurement of nuclear volume distribution curves of human biopsy material from the liver and gastrointestinal tract for diagnostic purposes on a larger scale.

Animals↗
PubMed2005

Electric interactions through chirping behavior in the weakly electric fish, Apteronotus leptorhynchus.

The weakly electric fish Apteronotus leptorhynchus produces wave-like electric organ discharges distinguished by a high degree of regularity. Transient amplitude and frequency modulations ("chirps") can be evoked in males by stimulation with the electric field of a conspecific. During these interactions, the males examined in this study produced six types of chirps, including two novel ones. Stimulation of a test fish with a conspecific at various distances showed that two electrically interacting fish must be within 10 cm of each other to evoke chirping behavior in the neighboring fish. The chirp rate of all but one chirp type elicited by the neighboring fish was found to be negatively correlated with the absolute value of the frequency difference between the two interacting fish, but independent of the sign of this difference. Correlation analysis of the instantaneous rates of chirp occurrence revealed two modes of interactions characterized by reciprocal stimulation and reciprocal inhibition. Further analysis of the temporal relationship between the chirps generated by the two fish during electric interactions showed that the chirps generated by one individual follow the chirps of the other with a short latency of approximately 500-1,000 ms. We hypothesize that this "echo response" serves a communicatory function.

Animal Communication↗
PubMed1987

Electric fish approach stationary signal sources by following electric current lines.

African electric fish of a pulse species, Brienomyrus brachyistius (Mormyridae), housed singly in a large, circular arena, were presented with electrical stimuli which mimicked a conspecific intruder. Stimuli were produced with either dipolar or bipolar electrodes in three different geometries. We tracked the unconditioned approach response paths taken by the fish and compared tracks for each of the geometries. The results suggest that B. brachyistius can determine neither the distance nor the direction of an electric dipole from afar, but that they do manage to find the source by maintaining a precise alignment of their body axis parallel to the direction of the local electric field vector (parallel to current lines) while swimming. This behaviour ultimately leads to the current source. We propose that this behaviour may be a simple mechanism mediating the approach response of one electric fish to another.

Animals↗
PubMed1998

Surface Electric Properties of the Na-Bentonite/Cetylpyridinium Chloride System as Studied by Reversing-Pulse Electric Birefringence

The adsorption of a cationic surfactant, cetylpyridinium chloride (CPC), on disklike Na-bentonite particles has been studied in very dilute suspensions by reversing-pulse electric birefringence (RPEB). The electric parameters of the particle/surfactant system were evaluated from signals taken at extremely low degrees of orientation by using the ion-fluctuation RPEB theory. The electric field orientation of the particles was found to result from the simultaneous action of the polarizability anisotropy Deltaalpha' and the ion-atmosphere polarizability alpha3 caused by ion fluctuation. Two different CPC concentration ([CPC]) ranges could be distinguished according to the magnitude of the induced dipole moment of the particles. When [CPC] was lower than 0.01 mM, the orientation of the particles was mainly due to the covalent polarizability anisotropy Deltaalpha'. When [CPC] was higher than 0.01 mM, the ionic polarizability alpha3 was predominant over Deltaalpha', the particles being oriented with the symmetric axis parallel to the direction of the electric field. Values of the electric parameters of the particles changed upon reversal of the sign of the applied reversing-pulse electric field. The change was probably due to the reordering and/or redistribution of the multilayer structure of adsorbed CPC molecules. Such effects were negligible below the critical [CPC] of 0.01 mM, where the adsorbed molecules may form a loose monolayer on the bentonite surface. Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗
PubMed2004

Electric field prediction for a human body-electric machine system.

A system consisting of an electric machine and a human body is studied and the resulting electric field is predicted. A 3-phase induction machine operating at full load is modeled considering its geometry, windings, and materials. A human model is also constructed approximating its geometry and the electric properties of tissues. Using the finite element technique the electric field distribution in the human body is determined for a distance of 1 and 5 m from the machine and its effects are studied. Particularly, electric field potential variations are determined at specific points inside the human body and for these points the electric field intensity is computed and compared to the limit values for exposure according to international standards.

Biomechanical Phenomena↗
PubMed1996

Leukemia following occupational exposure to 60-Hz electric and magnetic fields among Ontario electric utility workers.

In a nested case-control study of 1,484 cancer cases and 2,179 matched controls from a cohort of 31,543 Ontario Hydro male employees, the authors evaluated associations of cancer risk with electric field exposure and reevaluated the previously reported findings for magnetic fields. Pensioners were followed from January 1, 1970, and active workers (including those who left the corporation) from January 1, 1973, with both groups followed through December 31, 1988. Exposures to electric and magnetic fields and to potential occupational confounders were estimated through job exposure matrices. Odds ratios were elevated for hematopoietic malignancies with cumulative electric field exposure. After adjustment, the odds ratio for leukemia in the upper tertile was 4.45 (95% confidence interval (CI) 1.01-19.7). Odds ratios were also elevated for acute nonlymphoid leukemia, acute myeloid leukemia, and chronic lymphoid leukemia. For cumulative magnetic field exposure, there were similar elevations that fell with adjustment. Evaluation of the combined effect of electric and magnetic fields for leukemia showed significant elevations of risk for high exposure to both, with a dose-response relation for increasing exposure to electric fields and an inconsistent effect for magnetic fields. There was some evidence of a nonsignificant association for brain cancer and benign brain tumors with magnetic fields. For lung cancer, the odds ratio for high exposure to electric and magnetic fields was 1.84 (95% CI 0.69-4.94).

Adult↗
PubMed1988

Electrical alternans and cardiac electrical instability.

We investigated the relationship between electrical alternans and cardiac electrical stability in a series of 20 dog experiments and in a pilot clinical study. Electrical alternans was detected in both the QRS complex and the ST-T wave by use of a novel multidimensional spectral technique. The magnitude of the alteration was expressed as the alternating electrocardiographic morphology index (AEMI), expressed as parts per million of waveform energy. Electrical stability in the dog preparations was assessed via the ventricular fibrillation threshold measurement, and in the clinical studies via programmed stimulation. In 10 dog experiments, systemic hypothermia resulted in a 60% decrease in ventricular fibrillation threshold (VFT) (p less than .0001) and a significant increase in both AEMI(QRS) form 3.7 +/- 3.0 to 1448 +/- 548 (p less than .0001) and AEMI(ST-T) from 43.9 +/- 18.4 to 19,178 +/- 5579 (p less than .0001). In 10 dog experiments, transient coronary artery ligation also resulted in a 60% decrease in VFT (p less than .0001), an increase from 76.3 +/- 46.5 to 245 +/- 11 in AEMI(QRS) (p less than .05), and an increase from 842 +/- 505 to 1365 +/- 392 in AEMI(ST-T) (p less than .002). In 119 observations in 20 animal experiments, the rank correlation between VFT and AEMI(QRS) was -.30 (p less than .001), with that between VFT and AEMI(ST-T) being -.55 (p less than .0001). In a double-blind pilot clinical trial consisting of 23 studies in 19 patients, the result of electrophysiologic testing was used as an independent measure of cardiac electrical stability. Alternation in waveform morphology identified the inducible patient population with a sensitivity of 92%, a positive predictivity of 70%, and a specificity of 50% (p less than .05). We conclude that analysis of subtle beat-to-beat variability in electrocardiographic morphology may provide a noninvasive measure of cardiac electrical stability.

Adult↗
PubMed1992

Electric organ morphology of Sternopygus macrurus, a wave-type, weakly electric fish with a sexually dimorphic EOD.

In several species of electric fish with a sex difference in their pulse-type electric organ discharge (EOD), the action potential-generating cells of the electric organ (electrocytes) of males are larger and more invaginated compared to females. Androgen treatment of females and juveniles produces a longer-duration EOD pulse that mimics the mature male EOD, with a concurrent increase in electrocyte size and/or membrane infolding. In Sternopygus macrurus, which generates a wave-type EOD, androgen also increases EOD pulse duration. To investigate possible morphological correlates of hormone-dependent changes in EOD in Sternopygus, we examined electric organs from both fish collected in the field, and untreated and androgen-treated specimens in the laboratory. The electrocytes are cigar shaped, with prominent papillae on the posterior, innervated end. Electrocytes of field-caught specimens were significantly larger in all parameters than were electrocytes of specimens maintained in the laboratory. EOD pulse duration and frequency were highly correlated, and were significantly different between the sexes in sexually mature fish. Nevertheless, no sex difference in electrocyte morphology was observed, nor did any parameters of electrocyte morphology correlate with EOD pulse duration or frequency. Further, whereas androgen treatment significantly lowered EOD frequency and broadened EOD pulse duration, there was no difference in electrocyte morphology between hormone-treated and control groups. Thus, in contrast to results from studies on both mormyrid and gymnotiform pulse fish, electrocyte morphology is not correlated with EOD waveform characteristics in the gymnotiform wave-type fish Sternopygus. The data, therefore, suggest that sex differences in EOD are dependent on changes in active electrical properties of electrocyte membranes.

Analysis of Variance↗
PubMed2001

Androgens alter electric organ discharge pulse duration despite stability in electric organ discharge frequency.

Weakly electric fish in the genus Sternopygus emit a sinusoidal, individually distinct, and sexually dimorphic electric organ discharge (EOD) that is used in electrolocation and communication. Systemically applied androgens decrease EOD frequency, which is set by a medullary pacemaker nucleus, and increase pulse duration, which is determined by the cells of the electric organ (the electrocytes), in a coordinated fashion. One possibility is that androgens broaden the EOD pulse duration by acting on the pacemaker neurons, thereby effecting a change in pacemaker firing frequency, and that the change in EOD pulse duration is due to an activity-dependent process. To determine whether androgens can alter pulse duration despite a stable pacemaker nucleus firing frequency, we implanted small doses of dihydrotestosterone in the electric organ. We found that androgen implants increased EOD pulse duration, but did not influence EOD frequency. In addition, using immunocytochemistry, we found that electrocytes label positively with an androgen receptor antibody. While it is not known on which cells androgens act directly, together these experiments suggest that they likely act on the electrocytes to increase EOD pulse duration. Since pulse duration is determined by electrocyte action potential duration and ionic current kinetics, androgens may therefore play a causative role in influencing individual variation and sexual dimorphism in electrocyte electrical excitability, an important component of electrocommunicatory behavior.

Androgens↗
PubMed1983

Influence of electrical stimulation and deprivation on the electric organ discharge behaviour and metabolism of neuronal gangliosides of the tapirfish (Gnathonemus petersi, Mormyridae, Teleostei).

The influence of electrical stimulation ("attack"-frequency of 40 Hz, 2 V, 2 days) and of social and electrical deprivation on the metabolism of gangliosides of various brain structures and the electric organ of the weakly electric tapirfish (Gnathonemus petersi, Mormyridae) was investigated. After stimulation the daily average discharges of the electric organ increased from 9.4 to 11.1 Hz, whereas after deprivation they decreased to 7.9 Hz as compared with controls. There were significant and structure specific differences in some ganglioside-fractions (GM1, GD3, GD1a, GD1b and GP1) in concentration and in specific radioactive NeuAc-labelling between stimulated and deprived animals respectively, compared with controls.

Animals↗
PubMed1992

Magnetic and electric characteristics of the electric fish Gymnotus carapó.

The fresh water fish Gymnotus carapó produces a continuous series of weak pulsed electric fields in its surroundings and senses disturbances of this field as part of its sensory system. The electric and magnetic properties of the electric organ of this fish were studied. Magnetic fields close to the fish on the order of nT are produced by currents on the order of 10(-4) A in the electric organ of the fish. The electromotive force, the internal resistance, the current, and the electric power of the equivalent circuit were determined noninvasively.

Animals↗
PubMed2001

Electric accidents in the production, transmission, and distribution of electric energy: a review of the literature.

Many work related electric accidents occurred in electric energy industries and they were very often fatal. The situation of electric accidents in electric companies worldwide is investigated by reviewing the scientific literature, to offer perspectives on the types and kinds of statistics available, the factors regarded as influencing their occurrence, their consequences, and also methodological shortcomings. Worldwide, reliable comparable data exist and indicate a downward trend in fatal electric accidents. Difficulties were encountered in compiling international statistics because of differences in how accident data were defined and recorded, variations in mandatory practices, lack of suitable data and indices, accident insurance systems, and lack of correlation between technical, financial, and medical aspects.

Accidents, Occupational↗