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At least 199 records · Page 11Linked to original sources
PubMed1997

Electrical and physiological changes during short-term and chronic electrical stimulation of the normal cochlea.

In the electrical stimulation (ES) of auditory pathways, the type of stimulus and the electrode/tissue interface are critical parameters for the safety and efficacy of the protocol. In this study the influence of alternate pulses, applied between round window and vertex electrodes in chronically implanted guinea pigs, and maintained during 1 and 25 daily periods of 2 h (short-term and long-term experiments, respectively), was investigated. ES consisted of monophasic current pulses of +/- 70 microA and 300 (micro)s in duration at a rate of 167/s, with alternate polarity. Compound Action Potential (CAP) audiograms, amplitudes and latencies of click-evoked CAPs, amplitudes and latencies of electrically-evoked auditory responses (EARs), and electrode impedances, were measured periodically outside or during the ES periods. Short-term ES induced no change in CAP thresholds, amplitude and latency in response to clicks at 80 dB above normal threshold, but induced a slight latency increase and amplitude decrease of the EAR, correlated with an exponential decay of the electrode impedance. On a long-term basis, CAP audiograms and latencies did not change significantly, whereas CAP amplitudes and electrode impedances increased, in correlation with each other. In control guinea pigs receiving no ES, the same CAP amplitude and impedance changes were observed over the same long-term period. The EAR and CAP changes can be explained by a variation of the electrical impedance of the electrode/tissue interface. This is possibly due to a change in electrolytes around the electrode under the influence of the ES for the short-term variation, and to an electrode encapsulation by fibrous tissue independent of the ES for the long-term change. In itself, and under the conditions of this experiment, the ES demonstrated no adverse effects on the auditory function and can be safely used for inner-ear exploration.

Acoustic Impedance Tests↗
PubMed1998

Early recurrences of atrial fibrillation after electrical cardioversion: a result of fibrillation-induced electrical remodeling of the atria?

OBJECTIVES: We sought to investigate whether, in humans, the timing and incidence of a relapse of atrial fibrillation (AF) during the first month after cardioversion indicates the presence of electrical remodeling and whether this could be influenced by prevention of intracellular calcium overload during AF. BACKGROUND: Animal experiments have shown that AF induces shortening of the atrial refractory period, resulting in an increased vulnerability for reinduction of AF. This electrical remodeling was completely reversible within 1 week after cardioversion of AF and was presumably related to intracellular calcium overload. METHODS: Using transtelephonic monitoring in 61 patients cardioverted for chronic AF, we evaluated the daily incidence of recurrence of AF and determined, by Cox regression analysis, the influence of patient characteristics and medication on relapse of AF. RESULTS: During 1 month of follow-up, 35 patients (57%) had a relapse of AF, with a peak incidence during the first 5 days after cardioversion. Furthermore, in patients with a recurrence of AF, there was a positive correlation between the duration of the shortest coupling interval of the premature atrial beats after cardioversion and the timing of the recurrence of AF (p = 0.0013). Multivariate analysis revealed that the use of intracellular calcium-lowering drugs during AF was the only significant variable related to maintenance of sinus rhythm after cardioversion (p = 0.03). CONCLUSIONS: The daily distribution of recurrences of AF suggests a temporary vulnerable electrophysiologic state of the atria. Use of intracellular calcium-lowering medications during AF appeared to reduce recurrences, possibly due to a reduction of electrical remodeling during AF.

Aged↗
PubMed2004

[Nonthermal levels of electric currents applied in capacitive electric transfer therapy provokes partial cytotoxic effects in human neuroblastoma cultures].

The present study investigates the cellular response to weak, sine wave, 0.5-MHz electric currents. The experimental exposure to identical signals at an intensity high enough as to significantly increase the temperature in target tissues, has provided positive responses in clinical treatments of tumors with capacitive electric transfer (CET) thermal therapy. The present results show that the in vitro exposure to CET signals at athermal doses causes cytotoxic effects in human neuroblastoma cells. Such a response seems to be due to signal-induced alterations in the cell cycle. As a whole, the results suggest that the potential therapeutic effects of the CET strategy could be due to the thermal response of the tissues to the currents, added to an athermal response of the cells to the electric current itself.

Cell Division↗
PubMed1991

System identification of electrically coupled smooth muscle cells: the passive electrical properties.

A system model approach based on a network model is used to investigate the passive electrical properties of coupled smooth muscle cells. This approach makes use of a gradient method of optimization to estimate the passive electrical parameters directly from the magnitude of the input impedance or voltage transfer function of the network model. The need for subjective measurements of parameters and many intermediate steps involved in the analysis using the conventional signal model approach are eliminated. The coupling resistance and capacitance are estimated with sound theoretical and mathematical grounds directly from experimental data. From the simulated results using SPICE, it is evident that the system model approach is accurate, flexible, and reproducible. These properties grant the new approach excellent potential for future studies of drug actions on smooth muscle cells and their associated electrical coupling. Also, sensitivities of the network model with respect to its parameters can readily be obtained. This may provide new insight into the coupling mechanisms of smooth muscle cells.

Electric Conductivity↗
PubMedDate not supplied

Electrically evoked auditory brainstem response by direct electrical stimulation to the cochlear nerve in acoustic neuroma patients.

The electrically evoked auditory brainstem response (EABR) was recorded by direct electrical stimulation of the cochlear nerve in 8 acoustic neuroma patients. The EABR by electrical stimulation of the cochlear nerve at the fundus of the internal auditory canal was almost similar to those previously reported from cochlear implant patients in waveform morphology and wave latencies. However, the wave corresponding to wave II in human auditory ABR was not recorded in the EABRs by stimulation of the distal part of the intracranial cochlear nerve. These results suggest that the cochlear nucleus does not contribute to the generation of wave II in ABR.

Adult↗
PubMed2004

Comparison of percutaneous electrical nerve stimulation with transcutaneous electrical nerve stimulation for long-term pain relief in patients with chronic low back pain.

UNLABELLED: The long-term effect of percutaneous electrical nerve stimulation (PENS) on chronic low back pain (LBP) is unclear. We evaluated the number of sessions for which PENS should be performed to alleviate chronic LBP and how long analgesia is sustained. Patients underwent treatment on a twice-weekly schedule for 8 wk. Group A (n = 18) received PENS for 8 wk, group B (n = 17) received PENS for the first 4 wk and transcutaneous electrical nerve stimulation (TENS) for the second 4 wk, and group C (n = 18) received TENS for 8 wk. Pain level, degree of physical impairment, and the daily intake of nonsteroidal antiinflammatory drugs (NSAIDs) were assessed before the first treatment, 3 days after Week 2, Week 4, and Week 8 treatments, and at 1 and 2 mo after the sessions. During PENS therapy, the pain level decreased significantly from Week 2 in Groups A and B (P < 0.05 or 0.01), and physical impairment and required NSAIDs decreased significantly from Week 4 (P < 0.05 or 0.01) in Group A but only at Week 4 in Group B (P < 0.05 or 0.01). These effects were sustained until 1-mo follow-up (P < 0.01) in Group A but not in Group B; these effects were not observed at 2-mo follow-up even in Group A. In Group C, pain level decreased significantly only at Week 8 (P < 0.05). Our results indicate that repeated PENS is more effective than TENS for chronic LBP but must be continued to sustain the analgesic effect. IMPLICATIONS: A cumulative analgesic effect was observed in patients with chronic low back pain (LBP) after repeated percutaneous electrical nerve stimulation (PENS), but this effect gradually faded after the treatment was terminated. Results indicate that although PENS is effective for chronic LBP, treatments need to be continued to sustain analgesia.

Adult↗
PubMed2003

Serotonin modulates the electric waveform of the gymnotiform electric fish Brachyhypopomus pinnicaudatus.

The gymnotiform electric fish Brachyhypopomus pinnicaudatus communicates with a sexually dimorphic electric waveform, the electric organ discharge (EOD). Males display pronounced circadian rhythms in the amplitude and duration of their EODs. Changes in the social environment influence the magnitudes of these circadian rhythms and also produce more transient responses in the EOD waveforms. Here we show that injections of serotonin produce quick, transient, dose-dependent enhancements of the male EOD characters similar to those induced by encounters with another male. The response to serotonin administered peripherally begins 5-10 min post injection and lasts approximately 3 h. The magnitude of the response to serotonin is tightly associated with the magnitude of the day-to-night swing of the circadian rhythm prior to injection. Taken together these findings suggest that the male's social environment influences his response to serotonin by altering the function of some part of the downstream chain between the serotonin receptors and the ion channels involved in control of the EOD waveform. Although chronic activation of serotonin circuitry is widely known to elicit subordinate behavior, we find that 5-HT initially increases a dominance signal in these fish. These findings are consistent with the emerging view that serotonin facilitates different adaptive responses to acute and chronic social challenge and stress.

Animal Communication↗
PubMed2005

Contextual effects of small environments on the electric images of objects and their brain evoked responses in weakly electric fish.

This article reports some contextual effects of fish hovering in small environments on active imaging. Foveal electrosensory images of objects and their corresponding evoked responses in the electrosensory lobe are altered in amplitude and waveform when the fish are inside tubes. The article describes: (i) the physical basis of the changes imposed by small environments on electric images, (ii) the field potential responses at the electrosensory lobe of chronically implanted animals when entering and leaving tubes, and (iii) the effect of context on object discrimination. Biophysical analysis indicates that tubes cause a change in the efficiency of a previously described pre-receptor/post-effector mechanism responsible for the electric 'illumination' of nearby objects (as mirrors change the illumination of visual scenes). Field potential responses at the electrosensory lobe showed two components corresponding to the fast- and slow-electrosensory pathways respectively: (a) an early spike following the input without adaptation; (b) a series of waves lasting the rest of the cycle and exhibiting different degrees of adaptation. Discrimination experiments showed that fish react to changes in image rather than to changes in object resistance. The amplitude of the novelty responses evoked by similar changes in the total energy of electric images was constant despite the large change in basal stimulus amplitude and waveform caused by hovering in the tubes. These facts may be explained by the presence of adaptive responses observed at the slow pathway in the electrosensory lobe.

Animals↗
PubMed2002

Electrically enhanced percutaneous delivery of delta-aminolevulinic acid using electric pulses and a DC potential.

Selectivity of photodynamic therapy can be improved with localized photosensitizer delivery, but topical administration is restricted by poor diffusion across the stratum corneum. We used electric pulses to increase transdermal transport of delta-aminolevulinic acid (ALA), a precursor to the photosensitizer protoporphyrin IX (PpIX). ALA-filled electrodes were attached to the surface of excised porcine skin or the dorsal surface of mice. Pulses were administered and, in some in vivo cases, a continuous DC potential (6 V) was concomitantly applied. For in vitro 14C ALA penetration, 10 microm layers parallel to the stratum corneum were assayed by liquid scintillation analysis, and 10 microm cross sections were examined autoradiographically. As the electrical dose (voltage x frequency x pulse width x treatment duration) increased, there was an increase in penetration depth. In vivo delivery was assayed by measuring the fluorescence of PpIX in skin samples. A greater than two-fold enhancement of PpIX production with electroporative delivery was seen versus that obtained with passive delivery. Superimposition of a DC potential resulted in a nearly three-fold enhancement of PpIX production versus passive delivery. Levels were higher than the sum of PpIX detected after pulse-alone and DC-alone delivery. Electroporation and electrophoresis are likely factors in electrically enhanced delivery.

Administration, Cutaneous↗
PubMed1981

Electrical phenomena associated with bones and fractures and the therapeutic use of electricity in fracture healing.

Living bones have small electrical potentials on their surfaces, the magnitudes of which change only slightly with the reaching of adulthood. When using a limb stresses are put on the bones inside, and these create piezo-electric potentials which may themselves cause bone growth along the lines of stress, hence making the bone stronger. Voltages also appear at fracture sites and may be important in causing the bone to heal its wound. Fractures that have not healed properly can be stimulated into repair by the passage of small electric currents through them. The factors involved in these processes are discussed.

Biomechanical Phenomena↗
PubMed1985

Electrical parameters for safe and effective electro-acupuncture and transcutaneous electrical stimulation: threshold potentials for tingling, muscle contraction and pain; and how to prevent adverse effects of electro-therapy. Part 1.

10 Essential electrical parameters for safe and effective electrical stimulation was discussed. Among them, especially importance of rise and fall time which influence capacitive current (Ic = C X dv/dt), pulse duration and output impedance for (+) and (-) polarities was emphasized. When comparing one pulse component with high amplitude with the other pulse component with low amplitude in the same stimulation pulse complex of the same electrical stimulator, effective stimulation voltage delivered to the body can be larger with the low amplitude pulse component if it has much lower output impedance than the other. When pulse repetition rate is higher than several pulses/sec., in spite of increase in pain threshold, microcirculation is often interfered with and as a result the effect will not last long after each treatment. Our studies indicate that optimal pulse repetition rate is about the same as heart rate synchronized with local circulation. Tingling threshold is a more reproducible reliable parameter than pain threshold in study of pain. Measurement of threshold potentials for tingling sensation, muscle contraction, along with pain threshold is extremely important in the same patient. Phenomena of short circuits between the nerve fibers responsible for tingling sensation and nerve fibers responsible for pain sensation is described.

Acupuncture Therapy↗
PubMed1976

[Intracerebral measurement of electric tensions following peripheral electric injury].

The present research has originated from observing a 25-year-old man who - after an electrotrauma-- showed a hydrocephalus internus in the pneumoencephalogram. The review of the literature available at that time resulted in obtaining only one information concerning this nexus of related problems; thus the search of patients suffering from this trauma began, but as well experiments on animals. Most of the cats being injured by A.C. actually showed a dilatation of the lateral ventricles. Further experiments on dogs have shown that not only in case of transcerebral but also of peripheral injuries by electric currents of certain strength, distinct states of paling on the brain surface could be observed occurring in consequences of the extreme vasosoconstriction of the meningeal vessels. By a further series of experiments on dogs, there was finally demonstrated that also after peripheral electric irritations resp. injuries of different variations, electric tensions in the brain can be measured by intracerebrally installed electrodes at varying irritatnt voltages; up to now, this possibility has been in contest. Neuropathological investigations showed intracerebral and subarachnoid haemorrhages of different size in all injured animals.

Animals↗
PubMed1975

Electrical stimulation of small intestinal electrical control activity.

The small intestinal electrical control activity (ECA) was driven by an electrical stimulus and the resultant effects on the frequency and the phase relationships of control waves recorded. The small intestinal ECA can be driven from all sites from which it could be recorded. The mean maximum driven frequency (MDF) was the highest near the pylorus and it decreased distally, but at any given site it was the same before and after dividing the small intestine into small segments. The length of the frequency plateau decreased and phase lag per cm increased with an increase in plateau frequency. The direction of phase lag was orad proximal to a stimulation site and aborad distal to it. Intravenous atropine (up to 100 mug per kg) or reserpinization of dogs before an experiment had no effect on the MDF in the frequency plateau region. The study confirms the validity of an array of bidirectionally coupled relaxation oscillators as a model of small intestinal ECA and shows that the frequency and the phase relationship of small intestinal control waves can be altered by electrical stimulation. The study also points out some differences between the small intestinal and gastric ECA's at the cellular level.

Animals↗
PubMed2002

Comparison of electrically evoked whole-nerve action potential and electrically evoked auditory brainstem response thresholds in nucleus CI24R cochlear implant recipients.

In this study, differences between electrically evoked whole-nerve action potential (EAP) and electrically evoked auditory brainstem response (EABR) measurements within Nucleus CI24R cochlear implant recipients were evaluated. Precurved modiolus-hugging internal electrode arrays, such as the CI24R, are designed to provide more direct stimulation of neural elements of the modiolus. If the electrode array is closer to the modiolus, electrically evoked and behavioral levels might be lower than were previously recorded for the straight electrode array, the CI24M. EAP and EABR growth functions and behavioral levels were obtained for 10 postlingually deafened adults. Results revealed no significant differences between EAP and EABR threshold levels, and these levels were not significantly lower than those obtained using the CI24M.

Acoustic Stimulation↗
PubMed1975

Electrical and mechanical activities of longitudinal muscle contraction elicited by transmural electric stimulation.

Intracellular electrical and mechanical activities were simultaneously recorded from the longitudinal muscle of isolated guinea-pig jejunum when the preparation was stimulated transmurally by square pulses of 1 msec, 10 Hz, 10-40 V. Transmural stimulation of more than 30 V induced co-ordinated peristaltic waves under intraluminal pressure at levels subthreshold for the peristaltic reflex. Transmural stimulation of less than 30 V induced various types of mechanical responses. After termination of stimulation, rebound excitation was observed. Electrical activities of the longitudinal muscle were compared with various mechanical responses. Slow depolarization without spike potential was recorded when the longitudinal muscle contracted without circular muscle contraction. However, spike potential was recorded from the longitudinal muscle when circular muscle contraction was present as a response. Hyperpolarization was observed soon after the beginning of stimulation. This hyperpolarization was persistent to atropine at 10(-6) g/ml. These electrical and mechanical responses to transmural stimulation disappeared when the preparation was treated with tetrodotoxin at 2 X 10(-7) g/ml.

Animals↗
PubMed2004

Cardiac contractility modulation by non-excitatory electrical currents. The new frontier for electrical therapy of heart failure.

Heart failure (HF) may complicate ischemic heart disease in both its acute and chronic manifestations, representing a prevalent health problem throughout the world. Development of therapies to improve heart function, relieve symptoms, reduce hospitalizations and improve survival is a high priority in cardiovascular medicine. The available pharmacological strategies, including angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, beta-blockers, and aldosterone receptor antagonists have recently been complemented by new electrical therapy, including implantable cardioverter-defibrillators for "MADIT II" patients and cardiac resynchronization for the 30% of HF patients with concomitant intraventricular conduction delay. The wide variety of available HF medications provides ample evidence that we have not yet succeeded in this effort. Safe and effective inotropic electrical therapy could be a useful addition to our therapeutic armamentarium in an attempt to correct Ca2+ fluxes abnormalities during the cardiac action potential. Cardiac contractility modulation (CCM) by means of non-excitatory electrical currents delivered during the action potential plateau has been shown to acutely enhance systolic function in humans with HF. Herewith, we report on our preliminary experience with CCM therapy for patients with HF, providing fundamental notions to characterize the rationale of this novel form of therapy. Briefly, CCM therapy appears to be safe and feasible. Proarrhythmic effects of this novel therapy seem unlikely. Preliminary data indicate that CCM gradually and significantly improves systolic performance, symptoms and functional status. The technique would appear to be attractive as an additive treatment for severe HF. Controlled randomized studies are needed to validate this novel concept.

Action Potentials↗
PubMed1991

[Effects of electrical or chemical stimulation of the prefrontal cortex on arrhythmias induced in cats by electrical stimulation of the anteromedial hypothalamus].

When the anteromedial hypothalamus is stimulated with a chronically implanted electrode in conscious cats, negative emotional behaviors such as restlessness and escape occur during stimulation and ventricular extrasystoles occur in rapid succession immediately after the end of stimulation. It has been shown in the lightly anesthetized cat that the activity of the sympathetic nervous system becomes predominant during stimulation of the anteromedial hypothalamus thereby causing the rises in blood pressure and heart rate. However, immediately after the cessation of the stimulation, this 'sympathetic dominant' state was observed to be switched to the 'parasympathetic dominant' state with falls in blood pressure and heart rate which was very frequently followed by the appearance of the ventricular extrasystoles (Poststimulus Arrhythmia: PSA). The purpose of this experiment was to examine how the electric and pharmacological stimulation of the prefrontal cortex modulate the rise in the blood pressure and heart rate and PSA caused by electric stimulation of the anteromedial hypothalamus. When the prefrontal cortex was electrically stimulated simultaneously with stimulation of the anteromedial hypothalamus in 24 lightly anesthetized cats, PSA was inhibited or facilitated or remained unchanged depending on the site of stimulation in the prefrontal cortex. When dopamine or noradrenaline was microinjected into the site of prefrontal cortex where PSA was inhibited, PSA was suppressed and this effect was blocked by microinjection of haloperidol or phenoxybenzamine, respectively. Dopamine was ineffective when injected in the site where PSA was facilitated; PSA was facilitated by microinjection of noradrenaline and this effect was inhibited by microinjection of propranolol. Although changes in blood pressure and heart rate were observed when the inhibition or facilitation of PSA was elicited by prefrontal injection of noradrenaline, no changes in cardiovascular parameters occurred when dopamine injection caused the inhibition of PSA. These results suggest (1) that activation of the dopamine receptor or alpha adrenoceptor in the prefrontal cortex is involved in the inhibition of PSA, and activation of beta adrenoceptor is concerned with facilitation of PSA and (2) that the mechanisms of dopamine receptor mediated inhibition of PSA appear to be different from those of inhibition of PSA by activation of the alpha adrenoceptor in the prefrontal cortex.

Animals↗
PubMed1993

Biological, physical, and electrical parameters for in vitro studies with ELF magnetic and electric fields: a primer.

This paper presents material which is intended to assist researchers in identifying and controlling a range of biological, electrical, and other physical parameters that can affect the outcome of in vitro studies with extremely low frequency (ELF) magnetic and electric fields. Brief descriptions of power line magnetic and electric fields are provided and methods for the generation of 60 Hz as well as other ELF fields in the laboratory are surveyed. Methods for calculating and measuring exposure parameters in culture medium are also described. Relating in vitro and internal in vivo exposure conditions across different animal species is discussed to aid researchers in selecting levels of field exposure. The text is purposely elementary, and sometimes brief, with references provided to aid the interested reader in obtaining a fuller understanding of the many topics. Because the range of experimental parameters that can influence the outcome of in vitro studies with ELF fields is so broad, a multidisciplinary approach is normally required to carry out the research.

Animals↗