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PubMedDate not supplied

Melanocytes do not migrate directionally in physiological DC electric fields.

Wounding skin generates an endogenous electric field of 100-200 mV/mm in the immediate vicinity of the wound. When keratinocytes are exposed to direct current electric fields of this magnitude, they exhibit galvanotaxis, or directional migration toward the cathode, suggesting that wound-generated electric fields provide migrational cues that contribute to wound healing. Because melanocytes must also migrate into the healing wound to repigment it, their motility in response to electric fields of physiologic magnitude was examined. Human skin-derived melanocytes, either exposed to 100 mV/mm direct current electric fields or nonexposed controls, both exhibited motility rates of 9 micro m/hour, significantly (three- to five-fold) lower than the motility rates of keratinocytes under identical conditions. However, in sharp contrast to keratinocytes, melanocytes exhibited no directional migration in the electric field. Additionally, neither the number of primary dendrites per cell, nor the orientation of the dendrites with respect to the field vector, nor the average length of the dendrites was significantly different in melanocytes exposed to the electric field as compared to nonexposed controls. Thus, in marked contrast to keratinocytes, human skin-derived melanocytes do not respond to direct current electric fields of physiologic magnitude with either directional migration or reorientation of dendrites. This may account for the delay in repigmentation that often accompanies wound reepithelialization.

Cell Movement↗
PubMed1997

Auditory cortex activation in deaf subjects during cochlear electrical stimulation. Evaluation by functional magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The authors detect activation in the auditory cortex during cochlear electrical stimulation in deaf patients using functional magnetic resonance (MR) imaging. METHODS: Stimulating electrode was inserted gently under local anesthesia close to the round window membrane of the cochlea in seven cochlear implant candidates. These patients suffered from postlingual-acquired deafness. Four patients were stimulated above the electrical perception threshold and three below the electrical discomfort threshold. Functional scans (fast low-angle shot 91 mseconds/60 mseconds) were acquired in an oblique axial plane running parallel to the sylvian fissure. Four consecutive series of six images were obtained in 6 minutes. The acquisition time of each image was 15 seconds. RESULTS: During electrical cochlear stimulation below the discomfort threshold, the three patients described "auditory" sensations with activation of the superior temporal regions. In two patients with electrical stimulation of the left ear, the maximum signal intensity increased by 8.42% in the right auditory cortex and 5.69% in the left. In one patient with a right electrical stimulation only the left cortex was activated. Electrical cochlear stimulation above the perception threshold induces no significant activation in the auditory cortex. CONCLUSION: Functioning MR imaging can detect activation in the auditory cortex during cochlear electrical stimulation in deaf patients using a conventional 1.5-tesla system in a routine hospital environment. Further studies are needed to investigate its usefulness in clinical practice.

Adult↗
PubMed2002

Synchronized electrical stimulation in treating pharyngeal dysphagia.

OBJECTIVE/HYPOTHESIS: The objectives were to test the hypothesis that synchronous contraction of the thyrohyoid muscle by electrical stimulation during swallowing would improve dysphagia resulting from reduced laryngeal elevation and to evaluate the effectiveness of the synchronous electrical stimulator. STUDY DESIGN: Prospective study. METHODS: Eleven male and 12 female patients (age range, 35-87 y) with moderate to severe degree of dysphagia resulting from reduced laryngeal elevation who did not respond to medical treatment were treated by stimulating synchronous contraction of the thyrohyoid muscle during swallowing with the synchronous electrical stimulator. Treatment was given daily for 4 hours until criteria for improved swallow were fulfilled or other intervention was deemed necessary. Follow-up was performed monthly (range, 3-33 mo). RESULTS: Of the 23 patients, 20 showed marked improvement at the first course of treatment. The duration of stimulation varied from 2 to 4 days (median duration, 2 d) in patients with moderate dysphagia and from 3 to 30 days (median duration, 6 d) in patients with severe dysphagia. Three patients showed failed synchronous electrical stimulator treatment, one owing to device failure and two requiring gastrostomy for feeding. Six patients who achieved improved swallow criteria relapsed at 2 to 9 months after the first treatment course and were successfully treated with an additional course of synchronous electrical stimulation. CONCLUSIONS: The study supports the hypothesis that stimulating synchronous contraction of the thyrohyoid muscle by synchronous electrical stimulator during swallowing improves dysphagia resulting from reduced laryngeal elevation. Synchronized electrical stimulation has the advantages of noninvasiveness and actively assisting swallowing and can be used as an alternative treatment. The synchronized feature of the synchronous electrical stimulator helps to restore normal swallowing mechanism and decreases the incidence of nasogastric tube insertion and gastrostomy.

Aged↗
PubMed2006

Anisotropic ion diffusivity in intervertebral disc: an electrical conductivity approach.

STUDY DESIGN: Investigation of the transport behavior of ions in intervertebral disc using an electrical conductivity method. OBJECTIVES: To determine the electrical conductivity and ion diffusivity of nucleus pulposus and anulus fibrosus in 3 major directions (axial, circumferential, and radial). SUMMARY OF BACKGROUND DATA: Knowledge of diffusivity of small molecules is important for understanding nutrition supply in intervertebral disc and disc degeneration. However, little is known on the anisotropic behaviors of ion diffusivity and of electrical conductivity in intervertebral disc. METHODS: Electrical conductivity measurement was performed on 24 axial, circumferential, and radial anulus fibrosus specimens and 24 axial nucleus pulposus specimens from bovine coccygeal discs. The diffusivity of Na and Cl were estimated by the analysis of conductivity data. RESULTS: The electrical conductivity (mean +/- standard deviation; n = 24) of the bovine anulus fibrosus was 4.70 +/- 1.08 mS/cm in the axial, 2.86 +/- 0.83 mS/cm in the radial, and 4.38 +/- 1.25 mS/cm in the circumferential direction. For nucleus pulposus, the electrical conductivity (mean +/- standard deviation; n = 24) was 8.95 +/- 0.89 mS/cm. The mean value for nucleus pulposus was significantly higher than that of anulus fibrosus (t test, P < 0.05). For anulus fibrosus, the conductivity in the radial direction was significantly lower than in axial or circumferential directions. Similar trends were found for both Na and Cl diffusivities. Both electrical conductivity and ion diffusivity were highly sensitive to water content. CONCLUSIONS: Electrical conductivity and ion diffusivity of anulus fibrosus are anisotropic.

Animals↗
PubMed2004

Effect of electrical modification of cardiomyocytes on transcriptional activity through 5'-AMP-activated protein kinase.

Endothelin-1 (ET-1) is known as an aggravating factor of the failing cardiomyocytes and, therefore, a therapeutic method is indispensable to decrease cardiac ET-1 expression. To study the mechanisms of how cardiac ET-1 gene expression can be modified, we investigated the effect of electrical stimulation against cardiomyocytes. Considering the physiology of cardiomyocytes, in vitro cultured cardiomyocytes demonstrate distinctive features from in vivo cardiomyocytes (i.e. the absence of a stretch along with electrical stimulation). In this study, we especially focused on the effect of electrical stimulation. The electrical stimulation reduced the gene expression of ET-1 mRNA in rat primary cultured cardiomyocytes. Furthermore, this effect on the transcriptional modification of ET-1 was also identified in H9c2 cells. Luciferase activity using H9c2 cells was decreased by electrical stimulation in the early phase, suggesting that the attenuation of the ET-1 gene transcription by electrical stimulation should be due to a transcriptional repression. To further investigate a trigger signal involved in the transcriptional repression, phosphorylation of 5'-AMP-activated protein kinase (AMPK) was evaluated. It was revealed that AMPK was phosphorylated in the early phase of electrical stimulation of H9c2 cells as well as in rat primary cultured cardiomyocytes, and that AMPK phosphorylation was followed by ET-1 transcriptional repression, suggesting that electrical stimulation directly regulates AMPK. This study suggests that AMPK activation in cardiomyocytes plays a crucial role in the transcriptional repression of ET-1.

AMP-Activated Protein Kinases↗
PubMed1999

Evaluation of the ability of thermal and electrical tests to register pulp vitality.

The aim of the present study was to evaluate the ability of thermal and electrical tests to register pulp vitality. Sensitivity, specificity, negative predictive value and positive predictive value were calculated by comparing the test results with a "gold standard". The thermal tests studied were a cold test (ethyl chloride) and a heat test (hot gutta-percha). For the electrical test, the Analytic Technology Pulp Tester was used. The examined teeth were 59 teeth with unknown pulpal status in need of endodontic treatment and 16 intact teeth, all with radiographically normal periapical bone structures. In total 46 teeth with vital pulps and 29 teeth with necrotic pulps were tested. This gave a disease prevalence of 39%. The gold standard was established by direct pulp inspection of the 59 teeth in need of endodontic treatment. In the 16 intact teeth the pulp was judged as vital. The number of true positive (TP), false positive (FP), true negative (TN) and false negative (FN) test results was calculated for each method as compared to the gold standard. Based on this, the sensitivity, specificity, positive predictive value and negative predictive value were calculated for each method. The sensitivity was 0.83 for the cold test, 0.86 for the heat test and 0.72 for the electrical test. The specificity was 0.93 for the cold test, 0.41 for the heat test and 0.93 for the electrical test. The positive predictive value was 0.89 for the cold test, 0.48 for the heat test and 0.88 for the electrical test, and the negative predictive value was 0.90 for the cold test, 0.83 for the heat test and 0.84 for the electrical test. This indicated that the probability of a non-sensitive reaction representing a necrotic pulp was 89% with the cold test, 48% with the heat test and 88% with the electrical test. It also indicated that the probability of a sensitive reaction representing a vital pulp was 90% with the cold test, 83% with the heat test and 84% with the electrical test.

Adult↗
PubMed1999

Thermoacoustic energy effects in electrical arcs.

Electrical arcs commonly occur in electrical injury incidents. Historically, safe work distances from an energized surface along with personal barrier protection have been employee safety strategies used to minimize electrical arc hazard exposures. Here, the two-dimensional computational simulation of an electrical arc explosion is reported using color graphics to depict the temperature and acoustic force propagation across the geometry of a hypothetical workroom during a time from 0 to 50 ms after the arc initiation. The theoretical results are compared to the experimental findings of staged tests involving a mannequin worker monitored for electrical current flow, temperature, and pressure, and reported data regarding neurologic injury thresholds. This report demonstrates a credible link between electrical explosions and the risk for pressure (acoustic) wave trauma. Our ultimate goal is to protect workers through the design and implementation of preventive strategies that properly account for all electrical arc-induced hazards, including electrical, thermal, and acoustic effects.

Accidents, Occupational↗
PubMed1999

Biological effects of electric shock and heat denaturation and oxidation of molecules, membranes, and cellular functions.

Direct exposure of cells in suspension to intense electric pulses is known to produce damages to cell membranes and supramolecular organizations of cells, and denaturation of macromolecules, much like injuries and tears seen in electric trauma patients. Thus, the system has been used as a laboratory model for investigating the biochemical basis of electric injury. An intense electric pulse can produce two major effects on cells--one caused by the field, or the electric potential, and the other by current, or the electric energy. The field-induced transmembrane potential can produce electro-conformational changes of ion channels and ion pumps and, when the potential exceeds the dielectric strength of the cell membrane (approximately 500 mV for a pulse width of a few ms), electro-conformational damages and electroporations of membrane proteins and lipid bilayers. These events lead to passage of electric current through the membrane-porated cells and to heating of cell membranes and cytoplasmic contents. The subsequent denaturation of cell membranes and cytoplasmic macromolecules brings about many complex biochemical reactions, including oxidation of proteins and lipids. The combined effects may cripple the cells beyond repair. This communication will focus on the thermal effects of electric shock. After a brief review of the current state of knowledge on thermal denaturation of soluble enzymes and muscle proteins, this paper will describe experiments on the thermal denaturation of cellular components and functions, such as nucleosomes, and the electron transport chain and ATP synthetic enzymes of the mitochondrial inner membranes. Data will show that lipid peroxidation and the subsequent loss of the energy-transducing ability of the cells may occur even at moderate temperatures between 40 degrees C and 45 degrees C. However, lipid peroxidation may be prevented with reducing reagents such as mercaptoethanol, dithiothreitol, and ascorbic acid. Reactivation of denatured cellular proteins and functions may also be possible and a strategy for doing so is discussed.

Animals↗
PubMed1981

An electrical tuning mechanism in turtle cochlear hair cells.

1. Intracellular recordings were made from single cochlear hair cells in the isolated half-head of the turtle. The electrical responses of the cells were recorded under two conditions: (a) when the ear was stimulated with low-intensity tones of different frequencies and (b) when current steps were injected through the intracellular electrode. The aim of the experiments was to evaluate the extent to which the cochlea's frequency selectivity could be accounted for by the electrical properties of the hair cells.2. At low levels of acoustic stimulation, the amplitude of the hair cell's receptor potential was proportional to sound pressure. The linear tuning curve, which is defined as the sensitivity of the cell as a function of frequency when the cell is operating in its linear range, was measured for a number of hair cells with characteristic frequencies from 86 Hz to 425 Hz.3. A rectangular current passed into a hair cell elicited a membrane potential change consisting of a damped oscillation superimposed on a step. Small currents produced symmetrical oscillations at the beginning and end of the pulse. Larger currents increased the initial ringing frequency if depolarizing and decreased it if hyperpolarizing.4. For small currents the frequency of the oscillations and the quality factor (Q) of the electrical resonance derived from the decay of the oscillations were close to the characteristic frequency and Q of the hair-cell linear tuning curve obtained from sound presentations.5. The hair cell's membrane potential change to small-current pulses or low-intensity tone bursts could be largely described by representing the hair cell as a simple electrical resonator consisting of an inductance, resistor and capacitor.6. When step displacements of 29-250 nm were applied to a micropipette, placed just outside a hair cell in the basilar papilla, an initial periodic firing of impulses could be recorded from single fibres in the auditory nerve. Currents of up to 1 nA, injected through the same micropipette, failed to produce any change in the auditory nerve discharge. The experiment demonstrates that current injection does not produce gross movements of the electrode tip.7. The contribution of the electrical resonance to hair-cell tuning was assessed by dividing the linear tuning curve by the cell's impedance as a function of frequency. The procedure assumes that the electrical resonance is independent of other filtering stages, and on this assumption the resonance can account for the tip of the acoustical tuning curve.8. The residual filter produced by the division was broad; it exhibited a high-frequency roll-off with a corner frequency at 500-600 Hz, similar in all cells, and a low-frequency roll-off, with a corner frequency from 30 to 350 Hz which varied from cell to cell but was uncorrelated with the characteristic frequency of the cell.9. The phase of the receptor potential relative to the sound pressure at the tympanum was measured in ten cells. For low intensities the phase characteristic was independent of the sound pressure. At low frequencies the receptor potential led the sound by 270-360 degrees , and in the region of the characteristic frequency there was an abrupt phase lag of 90-180 degrees ; the abruptness of the phase change depended upon the Q of the cell.10. The calculated phase shift of the electrical resonator as a function of frequency was subtracted from the phase characteristic of the receptor potential. The subtraction removed the sharp phase transition around the characteristic frequency, and in this frequency region the residual phase after subtraction was approximately constant at +180 degrees . This is consistent with the idea that the hair cells depolarize in response to displacements of the basilar membrane towards the scala vestibuli. The high-frequency region of the residual phase characteristic was similar in all cells.11. It is concluded that each hair cell contains its own electrical resonance mechanism which accounts for most of the frequency selectivity of the receptor potential. All cells also show evidence of a broad band-pass filter, the high frequency portion of which may be produced by the action of the middle ear.

Animals↗
PubMed1990

Mortality from brain cancer and leukaemia among electrical workers.

The relation of brain cancer and mortality from leukaemia to electrical occupations was investigated in a case-control study based on all deaths in 1985 and 1986 in the 16 states in the United States that report occupational data from death certificates to the national vital statistics registry. The case series comprised all 2173 men who died of primary brain cancer (International Classification of Diseases-9 ((ICD-9) code 191) and all 3400 who died of leukaemia (ICD-9 codes 204-208). Each was matched with 10 controls who died of other causes in the same year. Men employed in any electrical occupation had age race adjusted odds ratios (ORs) of 1.4 (95% confidence interval (CI) 1.1-1.7) for brain cancer and 1.0 (95% CI 0.8-1.2) for leukaemia, compared with men in all other occupations. Brain cancer odds ratios were larger for electrical engineers and technicians (OR 2.7, 95% CI 2.1-3.4), telephone workers (OR 1.6, 95% CI 1.1-2.4), electric power workers (OR 1.7, 95% CI 1.1-2.7), and electrical workers in manufacturing industries (OR 2.1, 95% CI 1.3-3.4). There was some evidence of excess leukaemia among the same groups (ORs of 1.1-1.5) despite absence of an association for all electrical workers. The excess of deaths from brain cancer was concentrated among men aged 65 or older, whereas leukaemia was associated with electrical work only among younger decedents and those with acute lymphocytic leukaemia. These results from a large and geographically diverse population corroborate reports of increased mortality from brain cancer among electrical workers, but gives only limited support to suggestions of excess deaths from leukaemia.

Age Factors↗
PubMed1996

Comparison of magnetic and electrical phrenic nerve stimulation in assessment of diaphragmatic contractility.

Unlike the standard electrical approach, cervical magnetic stimulation of the phrenic nerves is less painful and achieves a constant degree of diaphragmatic recruitment, features that should enhance its applicability in a clinical setting. An unexplained phenomenon is the greater transdiaphragmatic twitch pressure (Pditw) with magnetic vs. electrical stimulation. We hypothesized that this greater Pditw is due to coactivation of extradiaphragmatic muscles. Because impedance to rib cage expansion is increased at high lung volumes and efficiency of extradiaphragmatic muscles is less than that of the diaphragm, we reasoned that the difference between electrical Pditw and magnetic Pditw would be less evident at high volumes than at end-expiratory lung volume. In human volunteers, magnetic Pditw and electrical Pditw were 37.7 +/- 1.9 (SE) and 32.3 +/- 2.2 cmH2O, respectively, at end-expiratory lung volume (P < 0.005) and 24.0 +/- 2.9 and 27.2 +/- 2.8 cmH2O, respectively, at one-half inspiratory capacity (not significant); at total lung capacity, magnetic Pditw was less than electrical Pditw (10.6 +/- 0.8 and 16.2 +/- 2.9 cmH2O, respectively; P < 0.05). Magnetic stimulation caused significant extradiaphragmatic muscle depolarization and rib cage expansion, whereas electrical stimulation caused virtually no extradiaphragmatic muscle depolarization and rib cage deflation. Despite these differences, the induction of respiratory muscle fatigue produced reductions in both electrical and magnetic Pditw values (P < 0.01), which were of similar magnitude and closely correlated (r = 0.96). In conclusion, magnetic stimulation recruits both extradiaphragmatic and diaphragmatic muscles, and it is equally as effective as electrical stimulation in detecting diaphragmatic fatigue.

Adult↗
PubMed1978

Functional characteristics of cochlear nucleus in behaving cat examined by acoustic masking of electrical stimuli.

1. Cats were trained, using an operant procedure, to detect and respond to electrical stimulation delivered in the vicinity of the cochlear nucleus. The electrical stimuli were presented both in silence and in synchrony with repeated noise bursts to determine whether detection thresholds for the electrical stimuli were elevated by the acoustic masking noise. 2. For stimulation sites centered within auditory structures (cochlear nucleus or acoustic nerve root), the acoustic maskers caused a consistent elevation of the electrical detection thresholds. For stimulation sites that were in or bordered on nonacoustic neural structures (e.g., vestibular), the acoustic maskers caused little or no elevation of electrical detection thresholds. 3. The magnitude of the acoustic masking effect was monotonically related to the intensity of the acoustic masker across the range of intensities tested. 4. The magnitude of the masking effect was strongly dependent on the relative timing of the stimulus pulse and the masker noise burst. Maximum masking occurred when the pulse just followed the onset of the neural activity in cochlear nucleus evoked by the masker burst. Less masking occurred when the electrical pulse occurred at the middle or end of the masker burst, and still less when the pulse occurred just prior to the onset (backward masking) or just after the offset (forward masking) of the masker burst. 5. The magnitude of the masking effect also depended on the frequency of the acoustic masker. For tone bursts, masking was maximal for each electrode at a particular frequency and declined monotonically for masker frequencies above or below the optimal frequency. 6. It is concluded that the masking of an electrical stimulus by an acoustic stimulus depends on a direct interaction between the neural responses evoked by the two stimuli, and that similar central, neural interactions may contribute to acoustic masking of acoustic stimuli. It is also concluded that the technique of masking an electrical stimulus by an acoustical stimulus is a precise and useful tool for the study of sensory-neural organization in intact behaving animals.

Animals↗
PubMed2005

The combined effects of inhibitory and electrical synapses in synchrony.

Recent experimental results have shown that GABAergic interneurons in the central nervous system are frequently connected via electrical synapses. Hence, depending on the area or the subpopulation, interneurons interact via inhibitory synapses or electrical synapses alone or via both types of interactions. The theoretical work presented here addresses the significance of these different modes of interactions for the interneuron networks dynamics. We consider the simplest system in which this issue can be investigated in models or in experiments: a pair of neurons, interacting via electrical synapses, inhibitory synapses, or both, and activated by the injection of a noisy external current. Assuming that the couplings and the noise are weak, we derive an analytical expression relating the cross-correlation (CC) of the activity of the two neurons to the phase response function of the neurons. When electrical and inhibitory interactions are not too strong, they combine their effect in a linear manner. In this regime, the effect of electrical and inhibitory interactions when combined can be deduced knowing the effects of each of the interactions separately. As a consequence, depending on intrinsic neuronal properties, electrical and inhibitory synapses may cooperate, both promoting synchrony, or may compete, with one promoting synchrony while the other impedes it. In contrast, for sufficiently strong couplings, the two types of synapses combine in a nonlinear fashion. Remarkably, we find that in this regime, combining electrical synapses with inhibition amplifies synchrony, whereas electrical synapses alone would desynchronize the activity of the neurons. We apply our theory to predict how the shape of the CC of two neurons changes as a function of ionic channel conductances, focusing on the effect of persistent sodium conductance, of the firing rate of the neurons and the nature and the strength of their interactions. These predictions may be tested using dynamic clamp techniques.

Action Potentials↗
PubMed2006

P19 progenitor cells progress to organized contracting myocytes after chemical and electrical stimulation: implications for vascular tissue engineering.

PURPOSE: To test the hypothesis that a level of chemical and electrical stimulation exists that allows differentiation of progenitor cells into organized contracting myocytes. METHODS: A custom-made bioreactor with the capability of delivering electrical pulses of varying field strengths, widths, and frequencies was constructed. Individual chambers of the bioreactor allowed continuous electrical stimulation of cultured cells under microscopic observation. On day 0, 1% dimethylsulfoxide (DMSO), known to differentiate cells into myocytes, was added to P19 progenitor cells. Additionally, for the next 22 days, electrical pulses of varying field strengths (0-3 V/cm), widths (2-40 ms), and frequencies (10-25 Hz) were continuously applied. On day 5, the medium containing DMSO was exchanged with regular medium, and the electrical stimulation was continued. From days 6-22, the cells were visually assessed for signs of viability, contractility, and organization. RESULTS: P19 cells remained viable with pulsed electrical fields <3 V/cm, pulse widths <40 ms, and pulse frequencies from 10 to 25 Hz. On day 12, the first spontaneous contractions were observed. For individual colonies, local synchronization and organization occurred; multiple colonies were synchronized with externally applied electrical fields. CONCLUSION: P19 progenitor cells progress to organized contracting myocytes after chemical and electrical stimulation. Incorporation of such cells into existing methods of producing endothelial cells, fibroblasts, and scaffolds may allow production of improved tissue-engineered vascular grafts.

Animals↗
PubMed2000

The cytoskeleton of the electric tissue of Electrophorus electricus, L.

The electric eel Electrophorus electricus is a fresh water teleost showing an electrogenic tissue that produces electric discharges. This electrogenic tissue is distributed in three well-defined electric organs which may be found symmetrically along both sides of the eel. These electric organs develop from muscle and exhibit several biochemical properties and morphological features of the muscle sarcolema. This review examines the contribution of the cytoskeletal meshwork to the maintenance of the polarized organization of the electrocyte, the cell that contains all electric properties of each electric organ. The cytoskeletal filaments display an important role in the establishment and maintenance of the highly specialized membrane model system of the electrocyte. As a muscular tissue, these electric organs expresses actin and desmin. The studies that characterized these cytoskeletal proteins and their implications on the electrophysiology of the electric tissues are revisited.

Actin Cytoskeleton↗
PubMed2002

Advances in gastrointestinal electrical stimulation.

Electrical stimulation of the gastrointestinal (GI) tract, analogous to pacing the human heart, is an attractive idea. This is because these organs, like the heart, have their own natural pacemakers, and the electrical signals they generate can be altered by externally delivering certain types of electric currents via intraluminal or serosal electrodes to certain areas of the GI tract. A number of studies on animals have been accomplished successfully to treat a variety of disease models, including gastroparesis, dumping, and short bowel syndrome. Over the past 10 years or so, electrical stimulation of the GI tract has received increasing attention among researchers and clinicians because of new techniques, such as implantable devices, and promising results achieved in treatment of gastroparesis and morbid obesity. The objective of this article is to review the advances in electrical stimulation of the gastrointestinal tract. First the electrophysiology of the GI tract and history of GI electrical stimulation are introduced. Then various methods of electrical stimulation of the stomach and small bowel in healthy animals and models of GI diseases are reviewed. Finally clinical applications of electrical stimulation to GI disorders and their possible mechanisms are discussed.

Anastomosis, Roux-en-Y↗
PubMed2005

Comparison of thermal dilution and electrical impedance dilution methods for measurement of cardiac output in standing and exercising horses.

OBJECTIVE: To compare cardiac output measured in the pulmonary artery and a carotid artery by use of thermal and electrical impedance dilution. Animals-7 fit, clinically normal Standardbreds between 2 and 5 years of age. PROCEDURE: Transient changes in electrical impedance and temperature of blood were induced by bolus injections of ice-cold saline hypertonic (6% and 9% NaCl) solutions. Cardiac output was calculated by applying Stewart-Hamilton principles to the indicator dilution transients. Measurements were made during sequential exercise episodes on a level treadmill over approximately an 8-fold range of cardiac output values. RESULTS: We detected agreement between cardiac output determined by use of electrical impedance dilution at the pulmonary artery and carotid artery. Cardiac output from thermal dilution measured at the carotid artery exceeded that measured at the pulmonary artery. Cardiac output from the thermal dilution technique exceeded cardiac output from the electrical impedance dilution technique at both locations. CONCLUSIONS AND CLINICAL RELEVANCE: The electrical impedance indicator is conserved on first transit; therefore cardiac output measured by electrical impedance dilution at the carotid artery is reliable over a large range of values. Thermal dilution provides a larger estimate of cardiac output, compared with the electrical impedance dilution technique, probably because of a loss of indicator. The transpulmonary electrical impedance dilution technique may have potential for clinical application, particularly in animals in which catheterization of the pulmonary artery is not appropriate or blood loss must be minimized.

Animals↗
PubMed2001

Neuronal population codes and the perception of object distance in weakly electric fish.

Weakly electric fish use an electric sense to navigate and capture prey in the dark. Objects in the surroundings of the fish produce distortions in their self-generated electric field; these distortions form a two-dimensional Gaussian-like electric image on the skin surface. To determine the distance of an object, the peak amplitude and width of its electric image must be estimated. These sensory features are encoded by a neuronal population in the early stages of the electrosensory pathway, but are not represented with classic bell-shaped neuronal tuning curves. In contrast, bell-shaped tuning curves do characterize the neuronal responses to the location of the electric image on the body surface, such that parallel two-dimensional maps of this feature are formed. In the case of such two-dimensional maps, theoretical results suggest that the width of neural tuning should have no effect on the accuracy of a population code. Here we show that although the spatial scale of the electrosensory maps does not affect the accuracy of encoding the body surface location of the electric image, maps with narrower tuning are better for estimating image width and those with wider tuning are better for estimating image amplitude. We quantitatively evaluate a two-step algorithm for distance perception involving the sequential estimation of peak amplitude and width of the electric image. This algorithm is best implemented by two neural maps with different tuning widths. These results suggest that multiple maps of sensory features may be specialized with different tuning widths, for encoding additional sensory features that are not explicitly mapped.

Algorithms↗