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Virtual electrode polarization leads to reentry in the far field.

INTRODUCTION: Our previous article examined cardiac vulnerability to reentry in the near field within the framework of the virtual electrode polarization (VEP) concept. The present study extends this examination to the far field and compares its predictions to the critical point hypothesis. METHODS AND RESULTS: We simulate the electrical behavior of a sheet of myocardium using a two-dimensional bidomain model. The fiber field is extrapolated from a set of rabbit heart fiber directions obtained experimentally. An S1 stimulus is applied along the top or left border. An extracellular line electrode on the top delivers a cathodal or anodal S2 stimulus. A VEP pattern matching that seen experimentally is observed and covers the entire sheet, thus constituting a far-field effect. Reentry arises from break excitation, make excitation, or a combination of both, and subsequent propagation through deexcited and recovered areas. Reentry occurs in cross-field, parallel-field, and uniform refractoriness protocols. For long coupling intervals (CIs) above CImake(min) (defined as the shortest CI at which make excitation can take place), rotors move away from the cathodal electrode and the S1 site for increases in S2 strength and CI, respectively. For cathodal S2 stimuli, findings are consistent with the critical point hypothesis. For CIs below CImake(min), reentry is initiated by break excitation only, and the resulting reentrant patterns are no longer consistent with those predicted by the critical point hypothesis. CONCLUSION: Shock-induced VEP can explain vulnerability in the far field. The VEP theory of vulnerability encompasses the critical point hypothesis for cathodal S2 shocks at long CIs.

Animals↗

Decolorization of Congo Red with three-dimensional flow-by packed-bed electrodes.

The electrochemical removal of the color of the dyestuff Congo Red was investigated experimentally by using packed graphite anodes as well as packed graphite or C-304 stainless steel cathodes in an undivided reactor. The effects of the applied apparent current density, the amount of chloride ion addition, the pH value of the solution, the cathode material, the operating temperature, the volumetric flow rate and the initial concentration of Congo Red on the removal efficiencies were investigated in this study. Experimental results showed that the main pathway of color removal was by the hypochlorite generated in-situ at the anodes. Compared with the indirect oxidation, the color removal due to direct oxidation was insignificant. Cathodic oxidation by using graphite cathodes had little influence on the removal rate in an undivided electrochemical cell.

Coloring Agents↗

A role of tyrosine phosphorylation in the formation of acetylcholine receptor clusters induced by electric fields in cultured Xenopus muscle cells.

During the development of the neuromuscular junction, acetylcholine receptors (AChRs) become clustered in the postsynaptic membrane in response to innervation. In vitro, several non-neuronal stimuli can also induce the formation of AChR clusters. DC electric field (E field) is one of them. When cultured Xenopus muscle cells are exposed to an E field of 5-10 V/cm, AChRs become clustered along the cathode-facing edge of the cells within 2 h. Recent studies have suggested the involvement of tyrosine kinase activation in the action of several AChR clustering stimuli, including nerve, polymer beads, and agrin. We thus examined the role of tyrosine phosphorylation in E field-induced AChR clustering. An antibody against phosphotyrosine (PY) was used to examine the localization of PY-containing proteins in E field-treated muscle cells. We found that anti-PY staining was colocalized with AChR clusters along the cathodal edge of the cells. In fact, cathodal PY staining could be detected before the first appearance of AChR clusters. When cultures were subjected to E fields in the presence of a tyrosine kinase inhibitor, tyrphostin RG-50864, cathodal AChR clustering was abolished with a half maximal inhibitory dosage of 50 microM. An inactive form of tyrphostin (RG-50862) had no effect on the field-induced clustering. These data suggest that the activation of tyrosine kinases is an essential step in E field-induced AChR clustering. Thus, the actions of several disparate stimuli for AChR clustering seem to converge to a common signal transduction mechanism based on tyrosine phosphorylation at the molecular level.

Animals↗

Galvanotaxis of slime mold.

The plasmodium of Physarum polycephalum reacts to direct current by migration toward the cathode. Cathodal migration was obtained upon a variety of substrata such as baked clay, paper, cellophane, and agar with a current density in the substratum of 1.0 microa./mm.(2) Injury was produced by current densities of 8.0 to 12.0 microa./mm.(2) The negative galvanotactic response was not due to electrode products. Attempts to demonstrate that the response was due to gradients or orientation in the substratum, pH changes in the mold, cataphoresis, electroosmosis, or endosmosis were not successful. The addition of salts (CaCl(2), LiCl, NaCl, Na(2)SO(4), NaHCO(3), KCl, MgSO(4), sodium citrate, and sea water) to agar indicated that change of cations had more effect than anions upon galvanotaxis and that the effect was upon threshold values. K ion (0.01 M KCl) increased the lower threshold value to 8.0 microa./mm.(2) and the upper threshold value to 32.0 microa./mm.(2), whereas the Li ion (0.01 M LiCl) increased the lower threshold to only 4.0 microa./mm.(2) and the upper threshold to only 16.0 microa./mm.(2) The passage of electric current produced no increase in the rate of cathodal migration; neither was there a decrease until injurious current densities were reached. With increase of subthreshold current densities there was a progressive decrease in rate of migration toward the anode until complete anodal inhibition occurred. There was orientation at right angles to the electrodes in alternating current (60 cycle) with current density of 4.0 microa./mm.(2) and in direct current of 5.0 microa./mm.(2) when polarity of current was reversed every minute. It is concluded that the negative galvanotactic response of P. polycephalum is due to inhibition of migration on the anodal side of the plasmodium and that this inhibition results in the limitation of the normal migration of the mold to a cathodal direction. The mechanism of the anodal inhibition has not been elucidated.

Fungi↗

Anodal block V anodal stimulation. Fact or fiction.

Anodal block and stimulation are poorly documented electrophysiologic phenomenon. Median and superficial radial nerves are examined in a prospective study to explore the significance of anodal block in routine nerve conduction studies. In addition, the anode's ability to stimulate the peripheral nervous system is evaluated. A monopolar stimulation technique is employed to achieve pure anode-generated responses. Additionally, a similar monopolar cathode stimulation technique is utilized and found to be equivalent to the traditional bipolar cathode stimulation. Based on the findings in this investigation, anodal block does not appear to occur during routine nerve conduction studies; however, transposition of the anode and cathode is clinically significant because the increased distance between the cathode and recording electrode results in predictably prolonged latencies. With higher levels of stimulus intensity, sensory, motor and F wave responses are generated by anodal stimulation in all cases. The actual mechanism of anodal stimulation remains uncertain and requires further study. Predicated on the results of this investigation, it appears that anodal block is an unlikely occurrence during routine electrodiagnostic medicine evaluations.

Action Potentials↗

Interference of anesthetic gases at skin surface sensors for oxygen and carbon dioxide.

Several variables may account for the response of electrochemical skin surface PO2 sensors to anesthetic gases: cathode material and size, pH of the electrolyte and membrane material. These variables cannot be chosen arbitrarily and their influence has been tested with two types of sensors. In one type (LSC), a large size cathode (mm range) and a membrane with low permeability for oxygen such as mono-axially oriented polyethylene is used. The other type (MC) contains one or more microcathodes (micron range) and a membrane which is highly permeable for oxygen such as Teflon PTFE. With the LSC sensor, the N2O interference current is smaller than 5% of the air current when the sensor is polarized at --600 mV. The interference current with 2% halothane is smaller than 3% of the air current. With the MC sensor, the N2O interference may be up to 40% of the current in air when the sensor is polarized at --800 mV. The magnitude of this interference depends considerably on the silver deposition on the platinum cathode. At --600 mV the N2O interference is negligible. However, at this polarization voltage, the sensor is not operated within the limiting current plateau of oxygen. The interference current with 2% halothane may be up to 30% of the current in air. With both types of sensors there was no measurable interference by 2% enflurane. The authors conclude that to reduce the interference of anesthetic gases at skin surface sensors for oxygen to a reasonable level, it is necessary to use a membrane with low permeability for oxygen and a polarization voltage of approximately --600 mV. These two conditions can be fulfilled optimally only with a sensor design in which a large size cathode is used. At Stowe-Severinghaus type skin surface sensors for PCO2, there is no measurable interference by N2O, halothane or enflurane.

Anesthetics↗

Experimental investigation of battery-induced esophageal burn injury in rabbits.

OBJECTIVE: In recent years, small high-performance batteries have become very popular. With this increasing miniaturization of batteries, clinicians have noted an increasing frequency rate of esophageal injury due to battery ingestion by infants. The situation is associated with severe injury to the esophagus due to the electrical current produced, particularly in the case of high-performance batteries producing high currents. The pathophysiologic features and complications of esophageal battery burns have not been thoroughly investigated. Our study intended to investigate the pathophysiologic features and complications of esophageal battery burn. DESIGN: Open, randomized, controlled study. SETTING: Experimental animal laboratory in a university hospital. SUBJECTS: Male adult mixed-breed rabbits, 22 wks old and weighing 3 to 3.5 kg. INTERVENTIONS: The experimental rabbit model of esophageal injury due to battery ingestion described herein was designed to study not only the direct influence of contact with the battery but also damage to neighboring tissues and the biochemical and pathologic mechanisms of injury. We investigated the relationship between the direction of the inserted battery and the mechanism underlying these complications. Esophageal burn injury was created by placing a 3-V battery into the esophagus for 9 hrs. MEASUREMENTS AND MAIN RESULTS: The cathode side of the esophagus became increasingly alkaline, while the anode side was acidic. Low-voltage battery burns are likely to be due to secondary chemical reactions caused by the electric current because of acid generated at the anode and alkali at the cathode using a micro pH meter. Injury was significantly more severe on the alkaline side when a battery was placed with its cathode directed toward the trachea. Alkaline complications affecting neighboring tissues were more severe than acid complications. These results indicate that as well as the esophageal mucosa itself being injured, deleterious effects are exerted on surrounding tissues, the severity of which vary depending on the orientation and duration of the battery being lodged in the esophagus. CONCLUSIONS: The direction of the battery cathode, which produces alkali, is important in determining the severity of complications. Based on our investigation of the underlying mechanisms of these complications, we advocate the establishment of treatment guidelines for battery swallowing accidents.

Animals↗

The effects of pulse configuration on magnetic stimulation.

A study is presented in which the authors have examined the effects of pulse configuration, stimulation intensity, and coil current direction during magnetic stimulation. Using figure-8 and circular coils, the median nerve was stimulated at the cubital fossa and at the wrist of 10 healthy volunteers, and the response amplitude and site of stimulation were determined. The key findings of this study are in agreement with other researchers' findings and confirm that biphasic stimulating pulses produce significantly higher M-wave amplitudes than monophasic stimulating pulses for the same stimulus intensity. Mean response amplitudes for biphasic stimuli applied by both coils at the elbow and wrist are consistently higher for the normal current direction. Mean response amplitudes for monophasic pulses are almost always higher for reversed currents. The site for effective stimulation (the position of the virtual cathode) cannot be defined within a fixed distance from the center of the coil (3 to 4 cm), as has been suggested by other researchers, but was found to vary depending on the coil current amplitude and direction as well as the degree of inhomogeneity of the tissues surrounding the nerve. There is a statistically significant relationship between virtual cathode shift and stimulus intensity for biphasic and monophasic pulses. Reversing the coil current direction has no statistically significant effect on the virtual cathode position. Virtual cathode shifts can be measured for biphasic and monophasic stimulations using a figure-8 coil at the wrist and the elbow. However, such a shift is difficult to determine with a circular coil.

Action Potentials↗

The short-term effects of delayed application of electric fields in the damaged rodent spinal cord.

Previous studies have indicated that the application of electrical fields to the contused rat spinal cord could result in a partial return of function within 3 weeks after injury/treatment. Whether similar functional recovery could be established after a delay in the treatment was investigated. Rat spinal cords were contused and allowed to recover untreated for 10 days. At that time, a stimulator delivering 3 microA of direct current was applied to the dorsal portion of the cord such that the cathode was oriented either rostral or caudal to the lesion. Inactive stimulators were also used as controls. Rats were then assessed behaviorally and clinically at weekly intervals up to 3 weeks on an inclined plane and then killed for histological assessments. The results indicate that both the "cathode rostral" and "anode rostral" groups performed statistically significantly better on the inclined plane than the "no current" group. The cathode rostral and anode rostral group animals also demonstrated superior motor abilities. The number of axons in the dorsal funiculi rostral to the lesion in the actively treated groups were also statistically significantly greater than no current controls. The cathode rostral group animals demonstrated a greater number of viable neuronal cell bodies near the site of the lesion. These data suggest that electric fields may facilitate functional recovery and regeneration in the mammalian spinal cord, even after a delay in such treatment.

Animals↗

Origins and conducting pathways of motor evoked potentials elicited by transcranial (vertex-hard palate) stimulation in cats.

Spinal cord evoked potentials were elicited in cats by transcranial electrical stimulation with electrodes on the vertex and hard palate. Vertex motor evoked potentials (V-MEP) were also recorded. An extracellular microelectrode recording technique was then used to analyze the results by isopotential mapping. The relationship between the distribution of field potentials and the stimulation polarity was studied using the field potential distribution of the V-MEP in the lower thoracic spinal cord that had been represented on the isopotential maps. The first negative wave of the V-MEP showed maximal amplitude distribution in the anterior funiculus, which corresponds to the extrapyramidal tracts. This pattern was seen with both stimulation polarity arrangements: 1) stimulation with the cathode at the vertex and the anode at the hard palate, and 2) stimulation with the anode at the vertex and the cathode at the hard palate. When the cathode was at the vertex, the stimulation threshold was lower, and the response had higher amplitude than when the anode was at the vertex. Recording V-MEPs elicited by vertex cathode stimulation could provide an excellent method of monitoring the extrapyramidal tracts in cats.

Animals↗

Immunoreactive trypsin(ogen) in the sera of children with recent-onset insulin-dependent diabetes and matched controls. The Swedish Childhood Diabetes Group.

To evaluate the exocrine pancreatic function at the time of diagnosis of insulin-dependent diabetes mellitus, we determined immunoreactive anodal and cathodal trypsin(ogen) levels in sera from almost all children (n = 375) 0-14 years of age in Sweden in whom diabetes developed during 1 year, and in sex-, age-, and geographically matched control subjects (n = 312). The median level of anodal trypsin(ogen) was 5 (quartile range, 3-7) micrograms/L in children with newly diagnosed diabetes, compared with a median level of 7 (quartile range, 4-8) micrograms/L in control subjects (p less than 0.0001). Similarly, the median level of cathodal trypsin(ogen) was 8 (quartile range, 4-10) micrograms/L in children with diabetes, compared with a median level of 11 (quartile range, 7-15) micrograms/L in control subjects (p less than 0.0001). The median of the individual ratios between cathodal and anodal trypsin(ogen) was 1.4 in the diabetic patients and 1.7 in the control children (p less than 0.001). In a multivariate test, however, only the decrease in cathodal trypsin(ogen) concentration was associated with diabetes. The levels of trypsin(ogen)s did not correlate with levels of islet cell antibodies, present in 81% of the diabetic children. Several mechanisms may explain our findings, for example, similar pathogenetic factors may affect both the endocrine and exocrine pancreas simultaneously, a failing local trophic stimulation by insulin on the exocrine cells may decrease the trypsinogen production, and there may be an increased elimination of trypsin(ogen) because of higher filtration through the kidneys in the hyperglycemic state.

Adolescent↗

Soluble and cell wall peroxidases in reed canarygrass in relation to disease resistance and localized lignin formation.

The relationship of peroxidases to an inducible disease-resistance mechanism involving lignification of leaf epidermal cell walls was studied. Reed canarygrass (Phalaris arundinacea L.) leaf discs were inoculated with Helminthosporium avenae Eidam and floated on water. In inoculated discs, the activity of soluble, ionic wall-bound and covalent wall-bound peroxidases was about twice the level of activity in noninoculated discs. The increase was attributable to increases in activity of three cathodic isoperoxidases and to the appearance of a new cathodic isoperoxidase. Peroxidase activity in cryostat microtome sections of inoculated discs was histochemically localized in the wall near the site of attempted penetration. When inoculated discs were floated on solutions of cycloheximide (25 mug/ml), increases in peroxidase activity were inhibited, and the fungus penetrated the tissue. The inhibition of peroxidase activity was related to inhibition of cathodic isoperoxidase activity. Anodic isoperoxidase activity did not show changes in response to inoculation or cycloheximide treatment.It was suggested that the resistance mechanism in P. arundinacea involves an induction of cathodic isoperoxidases in challenged tissue. These peroxidases may function in the biosynthesis of lignin at the site of attempted penetration.

Journal Article↗

Focal magnetic stimulation of an axon.

The induced electric field produced by a circular coil during magnetic stimulation of an axon is derived from Maxwell's equations. The foci and virtual cathodal and anodal regions are predicted as a function of coil radius and orientation. Two virtual anode and cathode pairs are predicted, one lying outside the coil's perimeter and predominant in the far field, and one lying within the perimeter of the coil which may stimulate the axon when the coil and nerve are in close proximity. When the coil is positioned tangent to the nerve, an orientation commonly used in clinical magnetic stimulation, the foci of the predominant cathode and anode pair are extremely sensitive to changes in coil placement. In addition, the radius of curvature of the activating function, a measure of the size of the virtual cathode at threshold, is predicted to decrease with decreasing coil diameter and distance to the nerve. These predictions may help explain observed variability in measurements of conduction velocity and latency during magnetic stimulation of peripheral axons.

Axons↗

Potential-biased, asymmetric waveforms for charge-injection with activated iridium oxide (AIROF) neural stimulation electrodes.

The use of potential biasing and biphasic, asymmetric current pulse waveforms to maximize the charge-injection capacity of activated iridium oxide (AIROF) microelectrodes used for neural stimulation is described. The waveforms retain overall zero net charge for the biphasic pulse, but employ an asymmetry in the current and pulse widths of each phase, with the second phase delivered at a lower current density for a longer period of time than the leading phase. This strategy minimizes polarization of the AIROF by the charge-balancing second phase and permits the use of a more positive anodic bias for cathodal-first pulsing or a more negative cathodic bias for anodal-first pulsing to maximize charge injection. Using 0.4-ms cathodal-first pulses, a maximum charge-injection capacity of 3.3 mC/cm2 was obtained with an 0.6-V bias (versus Ag/AgCl) and a pulse asymmetry of 1:8 in the cathodal and anodal pulse widths. For anodal-first pulsing, a maximum charge capacity of 9.6 mC/cm2 was obtained with an asymmetry of 1:3 at an 0.1-V bias. These measurements were made in vitro in carbonate-buffered saline using microelectrodes with a 2000 microm2 surface area.

Animals↗

Structure/function relationships in the hemoglobin components from moray (Muraena helena).

Concerning the number and type of the hemoglobin components, the moray Muraena helena is characterized by three different phenotypes whose frequencies are nearly identical. Thus, the cathodal component is present in all individuals, whereas one or both of two anodal components may be present in the same phenotype. These components have been separated by chromatography. The oxygen binding properties of the purified hemoglobin components have been studied in the absence and presence of saturating concentrations of ATP or GTP and as a function of pH. The cathodal component shows an intrinsic O2 affinity four times higher than that of both anodal components, a very small Bohr effect and a significant decrease in O2 affinity upon addition of ATP and GTP (three and four times respectively with respect to stripped conditions), the latter being more effective than the former over the entire pH range examined. The anodal components do not appear functionally distinguishable and show the presence of an enhanced Bohr effect (Root effect) that is under the strict control of nucleotide triphosphates ATP, GTP, which, unlike in the cathodic component, exert the same effect on oxygen affinity. The complete sequence of the beta chains of the cathodal and of one of the anodal components have been determined. The possible molecular basis of these different functional characteristics are discussed in the light of the globin sequence and of those amino acid residues which are known to be responsible of hemoglobin functional behaviour.

Amino Acid Sequence↗

How does transcranial DC stimulation of the primary motor cortex alter regional neuronal activity in the human brain?

Transcranial direct current stimulation (tDCS) of the primary motor hand area (M1) can produce lasting polarity-specific effects on corticospinal excitability and motor learning in humans. In 16 healthy volunteers, O positron emission tomography (PET) of regional cerebral blood flow (rCBF) at rest and during finger movements was used to map lasting changes in regional synaptic activity following 10 min of tDCS (+/-1 mA). Bipolar tDCS was given through electrodes placed over the left M1 and right frontopolar cortex. Eight subjects received anodal or cathodal tDCS of the left M1, respectively. When compared to sham tDCS, anodal and cathodal tDCS induced widespread increases and decreases in rCBF in cortical and subcortical areas. These changes in rCBF were of the same magnitude as task-related rCBF changes during finger movements and remained stable throughout the 50-min period of PET scanning. Relative increases in rCBF after real tDCS compared to sham tDCS were found in the left M1, right frontal pole, right primary sensorimotor cortex and posterior brain regions irrespective of polarity. With the exception of some posterior and ventral areas, anodal tDCS increased rCBF in many cortical and subcortical regions compared to cathodal tDCS. Only the left dorsal premotor cortex demonstrated an increase in movement related activity after cathodal tDCS, however, modest compared with the relatively strong movement-independent effects of tDCS. Otherwise, movement related activity was unaffected by tDCS. Our results indicate that tDCS is an effective means of provoking sustained and widespread changes in regional neuronal activity. The extensive spatial and temporal effects of tDCS need to be taken into account when tDCS is used to modify brain function.

Adult↗

Vestibulocollic reflexes evoked by short-duration galvanic stimulation in man.

1. Vestibular-dependent responses in leg muscles following transmastoid galvanic stimulation have been well characterized. Here we describe the properties of vestibulocollic responses evoked by transmastoid galvanic stimulation. 2. In twelve healthy human subjects we examined the averaged responses in unrectified sternocleidomastoid (SCM) EMG evoked by transmastoid stimulation using current pulses of 4 mA intensity and 2 ms duration. In ten subjects we also examined the effects of unilateral vestibular stimulation with the indifferent electrode at the vertex. In further experiments we studied the effects of different levels of background muscle activation, head position, current intensity and current duration. We compared these responses with click-evoked vestibulocollic responses in SCM. 3. A clearly defined biphasic response, beginning with a surface positivity, was recorded in the SCM ipsilateral to the side of cathode placement in all subjects. We refer to this as the p13/n23 [g] (galvanic) response, given the close similarity, in terms of waveform and latencies, to the previously described click-evoked p13/n23 vestibulocollic response. The amplitude of this response was linearly related to background muscle activation, current intensity and current duration, but independent of head position. Unilateral galvanic stimulation revealed the p13/n23 [g] response to be solely generated by the cathode. 4. A biphasic response beginning with a surface negativity (n12/p20 [g]) contralateral to the cathode was seen in all subjects and was generated by both the cathode contralaterally and the anode ipsilaterally. 5. Both the p13/n23 [g] and n12/p20 [g] potentials were abolished by selective vestibular nerve section and unaffected by severe sensorineural deafness. 6. We conclude that galvanic stimulation evokes short-latency vestibulocollic reflexes. These vestibulocollic reflexes have properties that are distinct from those described for galvanic-evoked vestibular reflexes in leg muscles, and which may be related to their differing physiological roles.

Acoustic Stimulation↗

Present understanding of shock polarity for internal defibrillation: the obvious and non-obvious clinical implications.

BACKGROUND: Uncertainty about the best electrode configuration has combined with the programming flexibility in modern implantable cardioverter-defibrillators (ICDs) to result in routine polarity reversal during an implant to deal with a high defibrillation threshold (DFT). We feel that this practice is not always supported by the clinical data and the present scientific understanding of defibrillation. METHOD: A meta-analysis of the clinical studies on ICD shock polarity was performed. Subgroup analyses were also performed to test the impact of high DFTs, various tilts, and the use of the hot can electrode. A review of the basic research surrounding the effects of polarity in defibrillation is also presented. RESULTS: A total of 224 patients were studied. The use of an anodal right ventricular (RV) coil lowers the mean DFT by 14.8% (P = 0.00001). It provides thresholds equal to or lower than cathodal defibrillation in 83% of patients. The fraction of patients with lower anodal DFTs was 94/224 versus 38/224 for cathodal polarity. This phenomenon may be explained by virtual electrode effects. In particular, anodal electrodes tend to produce collapsing wavefronts while cathodal electrodes tend to produce expanding proarrhythmic wavefronts. CONCLUSION: In an ICD implant, the RV coil should be the anode. Furthermore, DFT testing beginning with cathodal defibrillation is most likely unnecessary and needlessly extends the procedure's duration and increases the risks for the patient.

Clinical Trials as Topic↗