Reciprocal Impedance Research Articles

Post-iontophoresis recovery of human skin impedance in vivo

The objective of this study was to better understand the recovery of human skin impedance following iontophoresis in vivo. Volunteers were subjected to a 15-min period of iontophoresis in the presence of aqueous solutions of either NaCl, KCl, CaCl 2 or MgCl 2 at 133 mM. Subsequently, the low-frequency impedance (at 1 Hz) recovery was followed for a further 30 min. Assuming direct proportionality between the reciprocal impedance and the ion concentration in the membrane, the experimental data were fitted to the appropriate solutions of Fick's second law of diffusion to derive characteristic diffusion parameters ( D/ L 2), apparent diffusivities ( D), diffusion pathlengths ( L) and mobilities, and ion concentrations in the skin immediately post-iontophoresis. Ion fluxes out of the membrane after termination of current flow were also deduced. In general, recovery was relatively independent of the background electrolyte as previously reported, and the data were consistent with ion transport in predominantly aqueous pathways. Compared to its mobility in aqueous solution, however, the apparent Cl − mobility in the skin was smaller, presumably due to the fact that, under normal physiological conditions, the human skin barrier supports a net negative charge. In parallel, the initial ‘release’ of Na + and K + from the skin post-iontophoresis was faster than that of Ca 2+ and Mg 2+, the latter cations of higher charge density being able to associate more strongly, it seems, with the negatively-charged skin. The simple physicochemical analysis of the data presented serves to emphasize that a decrease in skin impedance is not a manifestation of damage to the barrier – rather, it is a natural response to the relevant electrical potential and ion concentration gradients involved.

Step-polarization impedance spectroscopy of implant alloys in physiologic solutions.

A novel test method is presented whereby the polarization behavior and impedance characteristics of an electrochemical interface can be determined simultaneously from potential-step current transient responses. In this test, small incremental steps in potential are applied to an electrochemical interface and the current transient response is collected digitally. Then, the data are subjected to a numerical Laplace transform technique to obtain the frequency-dependent admittance (reciprocal impedance) of the interface. From this analysis, several interesting and relevant parameters, including the high- and low-frequency resistances, interfacial capacitance, and polarization behavior, can be obtained. The mathematical basis for this technique is presented and the methodology is applied to three implant alloys (titanium, Co-Cr-Mo, and platinum). Electrochemical tests were performed in 0.9% NaCl at room temperature. Starting at an initial negative potential, the samples were stepped in 50-mV increments every 10 or 100 s up to a maximum potential and then reversed back to the starting potential. The impedances were calculated and used to evaluate the behavior. From these tests, one can determine the potential dependence of the oxide film thickness as well as the changes in the underlying electrochemical state of the interfaces with potential. This technique is inexpensive and easily applied to any electrochemical system, and yields significantly more electrochemical information than either anodic polarization or electrochemical impedance spectroscopy alone.

Investigations of the negative plate of lead/acid cells 3. Model calculations of the impedance of self-similar porous electrodes

In this paper a model for the calculation of the admittance (reciprocal impedance) of a porous metal electrode is derived, under anodic constant-current conditions, during precipitation of an insoluble salt at the metal/electrolyte interface. An example of the discharge, at low current density, of the negative plate in a lead/sulphuric acid battery during which lead sulphate is formed. The discussion is based on the assumption that porosity has a self-similar fractal character. The impedance of fractal electrodes will be discussed in terms of geometrical and physical parameters.

Role of vasopressin V2 receptors in modulation of the renal cortico-papillary NaCl gradient.

In order to examine if modulation by vasopressin of NaCl transport in Henle's loops (via V2 receptors) can significantly modify medullary ionic hypertonicity, the effects of stimulation or inhibition of these receptors were studied in anaesthetized Wistar rats. Total electrolyte concentration in the medullary interstitium was continuously measured as tissue admittance (reciprocal impedance), using needle electrodes recording from the inner and outer medulla of the in situ kidney. Deamino-[Cys1, D-Arg8]vasopressin (dDAVP], a V2 agonist, infused i.v. at 7.5 ng.min-1.kg-1, significantly increased admittance by 9% and 8% in the inner and outer medulla, respectively. A slightly pressor i.v. infusion of natural arginine vasopressin (AVP) induced pressure natriuresis and did not affect medullary electrolyte concentration. Inhibition of V2 receptors with [d(CH2)5, D-Phe2, Ile4]-AVP, infused i.v. at 133 micrograms.h-1 kg-1 in indomethacin-treated rats, decreased admittance (significant in the inner medulla). Neither of the three agents used caused significant changes in the renal blood flow (RBF) or clearance of inulin (Cin). The demonstration that changing activity of V2 receptors affects the corticopapillary NaCl gradient indicates that, at least in rodents, stimulation of loop salt transport by AVP may represent an additional mechanism enhancing urine concentration.

Cysteine enhances in vivo natriuretic potency of ethacrynic acid in the rat

Total renal blood flow, glomerular filtration rate, and renal excretory function were determined in anesthetized rats treated with intravenous infusion of ethacrynic acid, 0.36 mg.min-1.kg-1, alone or in combination with cysteine. Simultaneously, the corticomedullary electrolyte gradient was evaluated in vivo from measurement of tissue electrical admittance (reciprocal impedance). Renal hemodynamics was not altered by drug infusion. Sodium excretion increased 1.7-fold with ethacrynic acid alone and 5-fold after the addition of cysteine. Tissue electrolytes of inner medulla decreased much more in rats given ethacrynic acid plus cysteine. We conclude that the addition of cysteine to intravenous infusion of ethacrynic acid greatly enhances its in vivo natriuretic potency in the rat.

Atrial peptide natriuresis in the rat without genuine rise in filtration rate or wash‐out of medullary electrolytes.

1. Effects of synthetic atrial natriuretic peptide (ANP) on renal excretion, total renal blood flow (RBF), glomerular filtration rate (GFR) and tissue electrical admittance (reciprocal impedance, an estimate of tissue electrolytes) were determined in pentobarbitone-anaesthetized rats. GFR was measured both as inulin clearance (Cin) and as a product of renal plasma flow (RPF) and inulin extraction ratio (Ein). 2. With the lowest dose of ANP (0.35 micrograms/(kg min) I.V.) a 5-fold increase in sodium excretion occurred without measurable change in Cin, RPF x Ein nor medullary electrolyte concentration estimated from tissue electrical admittance. 3. With medium and high dosage (2 and 6 micrograms/(kg min), respectively), major and rapid increases in sodium excretion and urine flow were associated with an acute increase in Cin but not RPF x Ein. 4. The RBF increase observed in all groups of rats was not dose-related and did not parallel the natriuresis. Electrolyte concentration in the medullary tissue showed a modest transient decrease in rats given medium and high ANP doses. 5. We conclude that pronounced ANP natriuresis can develop in the absence of a measurable increase of GFR, estimated by a method not subject to urinary dead space error (RPF x Ein). The small transient decrease in medullary tissue electrolytes observed with higher peptide doses does not support solute wash-out as an important mechanism of increased sodium excretion.

Tissue electrical admittance (electrolyte concentration) in rat renal medulla: Effects of furosemide and acetazolamide

Fluctuations of total electrolyte concentration in the renal medulla were estimated from continuous measurement of tissue electrical admittance (reciprocal impedance) by means of needle electrodes placed in the kidney of anaesthetized rats. To compare effects of two diuretic agents with different sites of action, rats received either furosemide, 0.3 mg/kg i.v. followed by an infusion at 0.3 mg/kg.h, or acetazolamide, a single injection of 10 mg/kg. At this dosage similar increases in renal excretion were obtained with either drug. After furosemide (a loop diuretic) admittance fell sharp within first 10 min, then partly recovered and reached a plateau 35 min after injection. Acetazolamide (inhibitor of proximal reabsorption) caused no changes in admittance compared to the pattern observed in untreated control animals. We conclude that dissipation of tissue electrolytes from the renal medulla is not simply a consequence of diuresis and natriuresis but depends critically on the site of transport inhibition in the nephron.

Magnetotelluric response on vertically inhomogeneous Earth

Magnetotelluric response in an inhomogeneous earth having resistivity varying linearly with depth is investigated. Horizontal electric and magnetic fields in such a medium are given in terms of modified Bessel functions. Impedance and apparent resistivity are computed for (1) an inhomogeneous half‐space, (2) an inhomogeneous half‐space overlain by a homogeneous layer, and (3) an inhomogeneous layer as a transition zone sandwiched between two homogeneous layers. Results are presented graphically and are compared with those of Cagniard models and with homogeneous multilayer models. In the case of resistivity decreasing with depth, the results of the above inhomogeneous models are similar to that of Cagniard two‐layer models, with the equivalence of h1c = h1, + ρ1/α. In the case of resistivity increasing with depth the results of the above inhomogeneous models can not usually be fitted with Cagniard two‐layer models but can be fitted with homogeneous multilayer models if the parameters of the layers are favorably chosen. The reciprocal impedance as a function of frequency is more useful than the apparent resistivity for determining the rate of increase α and the thickness h1 of an overlying homogeneous layer.