Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CATHODE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed2005

Enhanced electrokinetic extraction of heavy metals from soils assisted by ion exchange membranes.

The potential of electrokinetic remediation technology has been successfully demonstrated for the remediation of heavy metal contaminated fine-grained soils through laboratory scale and field application studies. Various enhancement techniques have been proposed and used in order to further improve the remediation process. However, it has been reported that such enhancement schemes can create other obstacles, such as the introduction of non-target ions into the system and thereby decrease the efficiency of the remediation process. Electrokinetic soil remediation technology enhanced by an ion exchange membrane (IEM), IEM-enhanced EK processing, was experimentally evaluated for the purpose of overcoming these obstacles. In particular, this study focused on observations of a fouling problem and its settlement using an auxiliary solution cell (ASC). In addition, the efficacies of two different types of electrode configurations, rectangular and cylindrical, were investigated. The experimental results indicate that the effectiveness of the technology was increased by an enhancement scheme using an IEM. This may be explained by the prevention of metal precipitation in the region near the cathode originating from hydroxide ions generated by the electrolysis of water in the cathode. The experimental results also imply that placement of the ASC can nullify the fouling problem within the cation exchange membranes used in IEM-enhanced EK processing, and thus improve the overall effectiveness of the process. The experimental results indicate that the cylindrical electrode configuration can be implemented in practical situations to improve the treatability of cathode effluent containing a high level of contaminants after processing.

Electrochemistry↗
PubMed2006

Simultaneous removal of organic contaminants and heavy metals from kaolin using an upward electrokinetic soil remediation process.

Kaolins contaminated with heavy metals, Cu and Pb, and organic compounds, p-xylene and phenanthrene, were treated with an upward electrokinetic soil remediation (UESR) process. The effects of current density, cathode chamber flushing fluid, treatment duration, reactor size, and the type of contaminants under the vertical non-uniform electric field of UESR on the simultaneous removal of the heavy metals and organic contaminants were studied. The removal efficiencies of p-xylene and phenanthrene were higher in the experiments with cells of smaller diameter or larger height, and with distilled water flow in the cathode chamber. The removal efficiency of Cu and Pb were higher in the experiments with smaller diameter or shorter height cells and 0.01M HNO(3) solution as cathode chamber flow. In spite of different conditions for removal of heavy metals and organics, it is possible to use the upward electrokinetic soil remediation process for their simultaneous removal. Thus, in the experiments with duration of 6 days removal efficiencies of phenanthrene, p-xylene, Cu and Pb were 67%, 93%, 62% and 35%, respectively. The experiment demonstrated the feasibility of simultaneous removal of organic contaminants and heavy metals from kaolin using the upward electrokinetic soil remediation process.

Copper↗
PubMed2004

Electrochemical behavior and determination of amiloride drug in bulk form and pharmaceutical formulation at mercury electrodes.

The polarographic behavior of amiloride hydrochloride has been studied in Britton-Robinson buffers of pH 1.9-11. In acidic medium at Ph< or =2, the dc-polarograms exhibited a single 4-electron cathodic irreversible wave, while at pH values >2, a second two-electron irreversible cathodic wave appeared at a more negative potential. The single or first wave may be attributed to the cleavage of the double bond of the -CH=NH of the imidino amide group with the release of NH(3). While the second wave may be due to the saturation of the C=O of the carboxamide moiety. A polarographic procedure of suffocate sensitivity for the determination of bulk amiloride drug in Britton-Robinson buffer at pH 2 is described. The calibration graph was obtained over the concentration range 2.5 x 10(-5) to 2.5 x 10(-4) M amiloride. The limits of detection (LOD) and quantitation (LOQ) of the procedure were 1 x 10(-5) and 3.3 x 10(-4) M bulk amiloride, respectively. Moreover, a differential-pulse adsorptive cathodic stripping voltammetric procedure has been described to assay of the drug at lower concentration levels. The optimal conditions were: E(acc) = -0.9V, t(acc)=30 s, scan rate=20mV, pulse-height=90 mV and Britton-Robinson buffer of pH 8. The calibration graph was obtained over the concentration range 2 x 10(-8) to 1 x 10(-6) M for bulk amiloride. Both procedures were successfully applied to the determination of amiloride in tablets without the necessity for sample pretreatment or any time-consuming extraction or evaporation steps prior to the drug analysis.

Amiloride↗
PubMed2004

Behavior and quantification studies of amiloride drug using cyclic and square-wave adsorptive stripping voltammetry at a mercury electrode.

The cyclic voltammograms of amiloride at the hanging mercury drop electrode showed a single well-defined four-electron irreversible cathodic peak in Britton-Robinson (B-R) buffer of pH 2. At higher pH values (pH > or =3), two irreversible cathodic peaks corresponding to the transfer of four (first peak) and two (second peak) electrons, were obtained The peak potentials were shifted to more negative values on the increase of pH of the medium, implying the involvement of protons in the electrode reaction and that the proton-transfer reaction precedes the proper electrode process. The 4-electron single peak (pH 2) or the first peak (pH > or = 3) may be attributed to the cleavage of the -CH=NH double bond of the N-imidino amide group with the release of NH(3) molecule. While the second peak may be due to the saturation of the C?O double bond of the carboxamide moiety. Based on the interfacial adsorptive character of the drug onto the mercury electrode surface, a simple, sensitive and low cost square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was optimized for analysis of the drug. The optimal operational conditions of the proposed procedure were: accumulation potential E(acc)= -0.7 V, accumulation time t(acc)= 60-65s, scan increment= 10 mV, pulse-amplitude = 50-60 mV, frequency =120 Hz using a B-R buffer of pH 8 as a supporting electrolyte. The linear concentration range was found to be 2 x 10(-9) to 2 x 10(-7) M amiloride with limits of detection (LOD) and quantitation (LOQ) of 1.9 x 10(-10) and 6.3 x 10(-10) M, respectively. The procedure was successfully applied for determination of amiloride in pharmaceutical formulation and spiked in human serum. The LOD and LOQ of amiloride spiked in human serum were 5.7 x 10(-10) and 1.9 x 10(-9) M amiloride, respectively. The procedure did not require sample pretreatment or any time-consuming extraction or evaporation steps, other than deproteinization and then centrifugal separation of protein from serum sample prior to analysis of the drug.

Amiloride↗
PubMed2005

Assay of the anti-psychotic drug haloperidol in bulk form, pharmaceutical formulation and biological fluids using square-wave adsorptive stripping voltammetry at a mercury electrode.

The cyclic voltammetric behavior of haloperidol at a hanging mercury drop electrode was studied in Britton-Robinson buffer series of pH 2.5-11 containing 40% (v/v) ethanol. A single two-electron irreversible cathodic peak was obtained which attributed to reduction of the CO double bond. In addition, a small enhanced adsorptive pre-wave was observed at less negative potentials over the pH range 3.5-11. Controlled adsorptive accumulation of haloperidol onto the hanging mercury drop electrode provided the basis for its direct trace assay in bulk form, pharmaceutical formulation and human biological fluids using square-wave adsorptive cathodic stripping voltammetry. Following preconcentration of bulk haloperidol onto the HMDE a well-developed square-wave cathodic peak was generated in Britton-Robinson buffer especially at pH values 9-10; its peak current showed a linear dependence on the concentration of haloperidol over the range 1 x 10(-9)M to 1.5 x 10(-6)M depending on the preconcentration duration. The procedural parameters for assay of haloperidol were studied. The achieved limits of detection (LOD) and quantitation (LOQ) were 3.83 x 10(-10)M and 1.28 x 10(-9)M bulk haloperidol, respectively. The procedure was successfully applied to assay haloperidol in tablets (Safinace) and in spiked human serum and urine. LOD of 3.3 x 10(-9)M and 5.46 x 10(-9)M, and LOQ of 1.10 x 10(-8) and 1.82 x 10(-8)M haloperidol were achieved in spiked human serum and urine samples, respectively.

Electrochemistry↗
PubMed2005

Simple models of stimulation of neurones in the brain by electric fields.

The excitation of pyramidal cells in the motor cortex, produced by electric fields generated by distant electrodes or by electromagnetic induction, has been modelled. Linear, steady-state models of myelinated axons capture most of the geometrical aspects of neurone activation in electric fields. Some non-linear features can be approximated. Models with a proximal sealed-end and distal infinite axon, or of finite length, are both serviceable. Surface anodal stimulation produces hyperpolarisation of the proximal axon (closest to the anode) and depolarisation in the distal axon. The point of maximum depolarisation can be influenced by the location of the cathode (greater separation of anode and cathode causes more distal depolarisation). Axon bends can produce very localised depolarisation. Cathodal stimulation may be less effective than anodal as a result of anodal block of conduction of action potentials in the distal axon. The latencies of responses to anodal stimulation, recorded in the distal axon, will decrease as the stimulus strength is increased and the point of action potential initiation moves distally node by node. Larger jumps in latency will be produced when the point of action potential initiation moves from one axon bend to another.

Action Potentials↗
PubMed2005

Electricity generation from cysteine in a microbial fuel cell.

In a microbial fuel cell (MFC), power can be generated from the oxidation of organic matter by bacteria at the anode, with reduction of oxygen at the cathode. Proton exchange membranes used in MFCs are permeable to oxygen, resulting in the diffusion of oxygen into the anode chamber. This could either lower power generation by obligate anaerobes or result in the loss in electron donor from aerobic respiration by facultative or other aerobic bacteria. In order to maintain anaerobic conditions in conventional anaerobic laboratory cultures, chemical oxygen scavengers such as cysteine are commonly used. It is shown here that cysteine can serve as a substrate for electricity generation by bacteria in a MFC. A two-chamber MFC containing a proton exchange membrane was inoculated with an anaerobic marine sediment. Over a period of a few weeks, electricity generation gradually increased to a maximum power density of 19 mW/m(2) (700 or 1000 Omega resistor; 385 mg/L of cysteine). Power output increased to 39 mW/m(2) when cysteine concentrations were increased up to 770 mg/L (493 Omega resistor). The use of a more active cathode with Pt- or Pt-Ru, increased the maximum power from 19 to 33 mW/m(2) demonstrating that cathode efficiency limited power generation. Power was always immediately generated upon addition of fresh medium, but initial power levels consistently increased by ca. 30% during the first 24 h. Electron recovery as electricity was 14% based on complete cysteine oxidation, with an additional 14% (28% total) potentially lost to oxygen diffusion through the proton exchange membrane. 16S rRNA-based analysis of the biofilm on the anode of the MFC indicated that the predominant organisms were Shewanella spp. closely related to Shewanella affinis (37% of 16S rRNA gene sequences recovered in clone libraries).

Bacterial Physiological Phenomena↗
PubMed2005

Advanced oxidation effect of ozonation combined with electrolysis.

The advanced oxidation effect of ozonation combined with electrolysis (electrolysis-ozonation) was discussed through the treatment of 4-chlorobenzoic acid (4-CBA) as a hydroxyl radical probe. The mechanism of hydroxyl radical production by electrolysis-ozonation process was also estimated with a mathematical model. The experimental results revealed that the electrolysis-ozonation process had a synergistic effect on the degradation of 4-CBA. The advanced oxidation effect of electrolysis-ozonation was inferred from standard potentials of relevant electrochemical reactions and mathematical model analysis to be mainly attributed to ()O(3)(-) promotion of O(3) at the cathodes. An increase in electric current improved the degradation rate of 4-CBA. However, the pseudo-first order degradation rate constant reached a plateau at high electric current densities, as ()O(3)(-) promotion of O(3) at the cathodes was regulated by O(3) transport process from the bulk to the cathodes in the range exceeding an electric current density of 10 Am(-2). Accordingly, the balance of O(3) transport flux and electric current is important for the efficient operation of the electrolysis-ozonation reactor.

Chlorobenzoates↗
PubMed1998

Anodal block in F-wave studies.

OBJECTIVE: To determine whether F-wave results differ with the anode proximal or distal to the cathode, ie, if clinical anodal block exists. DESIGN: Prospective study of 30 healthy volunteers undergoing nerve conduction and F-wave studies in one median nerve. A needle cathode electrode was used with a surface anode placed alternately proximal and distal to the cathode. The same electromyographer performed all studies with a Dantec Counterpoint machine. RESULTS: F-wave latencies were essentially unaffected by distal versus proximal positioning. Minimum, maximum, and mean F-wave latencies correlated extremely highly (r=.973 to .988). For both F-wave and M-response latencies and amplitudes, differences between mean values obtained using the two methods were extremely small and were neither clinically nor statistically significant. The frequency of elicitation of F-waves may (p < .05) have been slightly (3.5%) lower when the anode was in the distal position. CONCLUSION: Anodal block is not seen in F-wave studies when using needle electrode stimulations. Reversing the stimulator does not seem to be required. Further study with surface stimulating electrodes is underway to confirm results.

Adult↗
PubMed1994

Virtual electrode effects in myocardial fibers.

The changes in transmembrane potential during a stimulation pulse in the heart are not known. We have used transmembrane potential sensitive dye fluorescence to measure changes in transmembrane potential along fibers in an anisotropic arterially perfused rabbit epicardial layer. Cathodal or anodal extracellular point stimulation produced changes in transmembrane potential within 60 microns of the electrode that were positive or negative, respectively. The changes in transmembrane potential did not simply decrease to zero with increasing distance, as would occur with a theoretical fiber space constant, but instead became reversed beyond approximately 1 mm from the electrode consistent with a virtual electrode effect. Even stimulation from a line of terminals perpendicular to the fibers produced negative changes in transmembrane potential for cathodal stimulation with the largest negative changes during a 50-ms pulse at 3-4 mm from the electrode terminals. Negative changes as large as the amplitude of the action potential rising phase occurred during a 50-ms pulse for 20-volt cathodal stimulation. Switching to anodal stimulation reversed the directions of changes in transmembrane potential at most recording spots, however for stimulation during the refractory period negative changes in transmembrane potential were significantly larger than positive changes in transmembrane potential. Anodal stimulation during diastole with 3-ms pulses produced excitation in the region of depolarization that accelerated when the stimulation strength was increased to > 3 times the anodal threshold strength. Thus, virtual electrode effects of unipolar stimulation occur in myocardial fibers, and for sufficiently strong stimuli the virtual electrode effects may influence electrical behavior of the myocardium.

Animals↗
PubMed1997

Locus coeruleus lesions decrease norepinephrine input into the medial preoptic area and medial basal hypothalamus and block the LH, FSH and prolactin preovulatory surge.

The aim of this work was to study the role of the dorsal noradrenergic ascending pathway (DNAP), which originates in the locus coeruleus (LC) on the preovulatory surge of luteinizing hormone (LH) follicle-stimulating hormone (FSH) and prolactin (PRL) by producing bilateral electrolytic lesions (cathodal or anodal) in this nucleus. LC lesions were placed at 11.00 h on proestrus in female rats with regular 4-day estrous cycles. Intact rats, sham-operated as well as animals with missed lesions served as controls. In Experiment I, anodal current was applied and hourly blood samples were withdrawn (from 13.00 to 17.00 h) via a jugular catheter from conscious, freely moving rats for determination of plasma LH, FSH and PRL concentrations. In Expt. II, Expt. I was repeated using cathodal current and collecting blood samples hourly from 13.00 to 18.00 h. In both experiments the animals were sacrificed on the next morning when the occurrence of ovulation was checked. The medial septal area (MSA), medial preoptic area (MPOA), and medial basal hypothalamus (MBH) were dissected and assayed for norepinephrine (NE), dopamine (DA) and 5-hydroxyindoleacetic acid (5-HIAA) content. Experiment III was performed in order to test if a hormonal discharge occurred immediately after lesion placement. Blood samples were collected immediately before and 15, 30, 60 and 90 min postoperatively (from 11.00 to 12.30 h). Either anodal or cathodal lesions blocked the proestrous surge of LH, FSH and PRL. The hypothesis that the lesions advanced or delayed these hormonal surges was rejected since we found no increases in the hormonal levels from 11.00 to 12.30 or from 13.00 to 18.00 h, and ovulation was not observed on the following morning in the lesioned animals. Since control, sham-operated and missed-lesion groups exhibited LH, FSH and PRL surges and ovulation, this blockage appears to be caused by the destruction of the LC neurons. Also, this blockade was correlated with a decrease in the NA content in the MPOA and MBH, but not in the MSA, whereas the DA and 5-HIAA content were not changed in all groups examined. The results lead us to suggest that the integrity of noradrenergic afferent input from the LC to luteinizing hormone-releasing hormone neurons in the MPOA and MBH is essential for triggering the preovulatory surge mechanisms for gonadotrophins and PRL.

Animals↗
PubMed2001

Experimental investigation on moving chemical reaction boundary theory for weak-acid-strong-base system with background electrolyte KCl in large concentration.

In this report, the moving chemical reaction boundary (MCRB) was formed with the weak acid of acetic acid (HAc) and the strong alkali of NaOH, coupled with the excess of background electrolyte KCl. The experiments were compared with the predictions by the moving chemical reaction boundary equation (MCRBE). It is very interesting that (1) the experimental results are in good agreement with the predictions with the original MCRBE if the MCRB is an anodic moving boundary, (2) however, the experiments are extremely far away from the predictions with the original MCRBE if a cathodic moving boundary. Hence, the original MCRBE must be corrected under the later situation of cathodic moving MCRB. The corrected MCRBE was well quantitatively proved to be valid for the cathodic moving MNRB formed with the same electrolytes of HAc, NaOH and KCl.

Acids↗
PubMed2000

Chiral anion exchangers applied to capillary electrochromatography enantioseparation of oppositely charged chiral analytes: investigation of stationary and mobile phase parameters.

Weak anion-exchange (WAX) type chiral stationary phases (CSPs) based on tert.-butyl carbamoyl quinine as chiral selector (SO) and different types of silica particles (porous and non-porous) as chromatographic support are evaluated in packed capillary electrochromatography (CEC). Their ability to resolve the enantiomers of negatively charged chiral analytes, e.g., N-derivatized amino acids, in the anion-exchange mode and their electrochromatographic characteristics are described in dependence of several mobile phase parameters (pH, buffer type and concentration, organic modifier type and concentration) and other experimental variables (electric field strength, capillary temperature). The inherent "zwitterionic" surface character of such silica-based WAX type CSPs (positively charged SO and negatively charged residual silanols) allows the reversal of the electroosmotic flow (EOF) towards the anode at pH values below the isoelectric point (pI) of the modified surface, whereas a cathodic EOF results at pH values above the pI. Since for negatively charged analytes also an electrophoretic transport increment has to be considered, which can be either in or against the EOF direction, several distinct modes of elution have been observed under different stationary phase and mobile phase conditions: (i) co-electrophoretic elution of the negatively charged solutes with the anodic EOF in the negative polarity mode, (ii) counter-electrophoretic elution with the cathodic EOF in the positive polarity mode, and (iii) electrophoretically dominated elution in the negative polarity mode with a cathodic EOF directed to the injection end of the capillary. Useful enantioseparations of chiral acids have been obtained with all three modes. Enantioselectivity values as high as under pressure-driven conditions and theoretical plate numbers up to 120000 per meter could be achieved under electrically driven conditions. A repeatability study yielded RSD values below 2% for retention times and RSD values in the range of 5-10% for theoretical plate numbers and resolution, thus clearly establishing the reliability of the investigated anion-exchange type CEC enantioseparation methods.

Anion Exchange Resins↗
PubMed2001

Denitrification and neutralization treatment by direct feeding of an acidic wastewater containing copper ion and high-strength nitrate to a bio-electrochemical reactor process.

The feasibility of the direct denitrification treatment of copper metal pickling wastewater by using a bio-electrochemical reactor process was investigated experimentally. Carbon electrodes were installed in the reactor as the anode and cathode and denitrifying microorganisms were fixed on the surface of the cathode. The reactor was continuously operated by applying an electric current and feeding acetate. In this reactor, copper ion removal and denitrification proceeded simultaneously and the pH value of the treated water was increased almost to neutral. The electric current that passed through the cathode contributed to the removal of the copper ion and the generation of hydrogen gas. The generated hydrogen gas as well as the added acetate was effectively utilized for denitrification. A theoretical evaluation of pH in the effluent suggested that the pH increase was mainly caused by the generation of hydroxyl ion during denitrification. In addition, the inorganic carbon species generated during denitrification with acetate and by the electrochemical oxidation of anodic carbon acted as a buffer to minimize a further increase of pH at higher nitrate removal efficiencies. These results demonstrated that copper ion removal, denitrification and neutralization could be achieved simultaneously by using a single bioelectrochemical reactor.

Bioreactors↗
PubMed2000

Apolipoprotein E varepsilon4 allele has an impact on vascular reactivity in Alzheimer's disease.

Seventeen otherwise healthy, non-smoking patients with probable Alzheimer's disease (AD) and 11 healthy, non-smoking, age-matched controls participated in a study of vascular reactivity. Three substances were iontophoresed into the skin: sodium nitroprusside (SNP) delivered at the cathode, and acetylcholine chloride and isoprenaline sulphate delivered at the anode. The resultant vasodilation was mapped through a laser Doppler perfusion imager. The patients harbouring the Apolipoprotein E varepsilon4 allele (ApoE4) (n=9) showed significantly greater vasodilation compared both with patients without the ApoE4 and with controls (one control possessed the ApoE4) when SNP was delivered at the cathode. An additional study of ten of the AD patients and ten controls suggested that the enhanced reactivity in the patients with the ApoE4 depended on a greater sensitivity to the iontophoretic current itself at the cathode rather than to SNP. The quotient between total cholesterol and high-density lipoprotein-cholesterol was higher in the patients with the ApoE4 compared both with patients without the ApoE4 and with controls. A dysfunction of voltage-dependent ion channels and/or other membrane abnormalities in AD patients possessing the ApoE4 is suggested.

Journal Article↗
PubMedDate not supplied

Skin vessel reactivity tests in healthy middle-aged and elderly subjects: the influence of depolarizating current and serum lipids.

Ten healthy, non-smoking subjects without atopic constitution, (eight males and two females, mean age 67.3 +/- 2.5 years), participated in a study of vascular reactivity. The subjects were tested with respect to apolipoprotein E alleles. Three vasodilating substances were iontophoresed into the skin, acetylcholine chloride (ACh); isoprenaline sulfate (isoprenaline); and sodium nitroprusside (SNP). ACh and isoprenaline were delivered to the anode, while SNP was delivered to the cathode. Also, 0.9% sodium chloride (NaCl) was delivered to the cathode in order to assess the effect of the iontophoretic current itself. The resultant vasodilation was mapped by a newly developed laser Doppler perfusion imager (LDPI) and correlated with fasting concentrations of serum lipids and lipoproteins. Skin vessel reactivity test to ACh, isoprenaline and SNP, but not NaCl, showed statistically significant negative correlations to the ratio LDL cholesterol/HDL cholesterol (P<0.05). The skin vessel responses to endothelium-dependent and possibly also to endothelium-independent substances are correlated with serum lipids and lipoproteins. It might be feasible to follow the effect of lipid-lowering strategies non-invasively with the aid of iontophoresis and laser Doppler perfusion imaging. The response to NaCl at the cathode might be due to a direct depolarizating effect on perivascular nerves and might thus be of interest when evaluating small nerve fiber dysfunction, for instance in diabetes mellitus.

Journal Article↗
PubMed2001

The role of electroosmotic flow in transdermal iontophoresis.

Iontophoresis enhances transdermal drug delivery by three mechanisms: (a) the ion-electric field interaction provides an additional force which drives ions through the skin; (b) flow of electric current increases permeability of skin; and (c) electroosmosis produces bulk motion of the solvent itself that carries ions or neutral species, with the solvent 'stream'. The relative importance of electroosmotic flow is the subject of this review. Experimental observations and theoretical concepts are reviewed to clarify the nature of electroosmotic flow and to define the conditions under which electroosmotic flow is an important effect in transdermal iontophoresis. Electroosmotic flow is bulk fluid flow which occurs when a voltage difference is imposed across a charged membrane. Electroosmotic flow occurs in a wide variety of membranes, is always in the same direction as flow of counterions and may either assist or hinder drug transport. Since both human skin and hairless mouse skin are negatively charged above about pH 4, counterions are positive ions and electroosmotic flow occurs from anode to cathode. Thus, anodic delivery is assisted by electroosmosis, but cathodic delivery is retarded. Water carried by ions as 'hydration water' does not contribute significantly to electroosmotic flow. Rather electroosmotic flow is caused by an electrical volume force acting on the mobile counterions. The simple 'limiting law' theory commonly given in textbooks and some research articles is a very poor approximation for transdermal systems. However, several extensions of the limiting law are compatible with each other and with the available experimental data. One of these theories, the Manning theory, has been incorporated into a theory for the effect of electroosmotic flow on iontophoresis, the latter theory being in good agreement with experiment. Both theory and experimental data indicate that electroosmotic flow increases in importance as the size of the drug ion increases. The 'ionic' or Nernst-Planck effect is the largest contributor to flux enhancement for small ions. Increased skin permeability or the skin 'damage effect', is a significant factor for both large and small ions, particularly for experiments at high current density. For monovalent ions with Stokes radii larger than about 1 nm, electroosmotic flow is the dominant flow mechanism. Because of electroosmotic flow, transdermal delivery of a large anion (or negatively charged protein) from the anode compartment can be more effective than delivery from the cathode compartment.

Administration, Cutaneous↗
PubMed2001

Auditory nerve responses to monophasic and biphasic electric stimuli.

Charge-balanced, biphasic stimulus pulses are commonly used in implantable cochlear prostheses as they can be safely delivered to living tissue. However, monophasic stimuli are more efficient (i.e. producing lower thresholds) and likely provide more spatially selective excitation of nerve fibers. We examined the neural responses to monophasic, 'pseudomonophasic', and biphasic stimuli to better understand the inherent tradeoffs of these stimuli. Using guinea pig and cat animal models, we compared the auditory nerve responses to both 40 micros monophasic and 40 micros/phase biphasic stimuli using both electrically evoked compound action potential and single-fiber recordings. We also made comparisons using a computational model of the feline auditory nerve fiber. In all cases, our stimuli were cathodic monophasic and cathodic-first biphasic pulses. As expected, monophasic stimuli provided lower thresholds relative to biphasic stimuli. They also evoked responses with relatively longer latencies. We also examined responses to charge-balanced biphasic pulses composed of two phases of differing duration (i.e. pseudomonophasic stimuli). The first phase was fixed at 40 micros, while the second phase was systematically varied from 40 to 4000 micros. With a relatively long second phase, we hypothesized that these stimuli would provide some of the beneficial features of monophasic stimuli. Both the gross-potential and single-fiber data confirmed this and indicate that the largest incremental effects of changing the second-phase duration occur for durations less than 500 micros. Consideration of single-fiber data and computer simulations suggest that these results are consistent with the neural membrane acting as a leaky integrator. The computer simulations also suggest that the integrative properties at least partially account for the difference between our monophasic-biphasic results and previously published data. Our results apply to cathodic-leading stimuli; due to differing patterns of membrane depolarization, they may not be applicable to situations using anodic-leading stimuli. Finally, we observed differences between the guinea pig and cat response patterns. Compared to cats, guinea pigs produced smaller monophasic vs. biphasic threshold differences. This interspecies disparity may be due to differences in cochlear anatomy.

Animals↗