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PubMed2002

Electrical impedance scanning in breast cancer imaging: correlation with mammographic and histologic diagnosis.

This work was addressed to study correlations between histopathology of breast malignancy and variations in depth, intensity, multiplicity, and simultaneous capacitance-conductance features of electrical impedance scanning (EIS), in cases presenting mammographic findings. The EIS was performed in 74 patients. The entrance criterion was the presence of either suspicious or dubious mammography. The EIS evaluation was unblinded to mammographic data. The histologic findings of patients eligible for biopsy (Bi-rads 4, 5, and Bi-rads 0 after re-evaluation) were correlated to EIS and mammography. Depth localization of lesion, intensity, multiplicity, and capacitance-conductance features of the EIS signals were evaluated. There was association between histopathological diagnosis and EIS results. The presence of multiplicity of EIS signal, or simultaneous capacitance-conductance signals, was significantly ( p<0.05) more frequent in cases with either suspicious mammography or malignant biopsy than those dubious for mammography or with benign biopsy. There was no significant relationship between depth and intensity of EIS signal. In 15 (20%) cases there was discordance among mammography, EIS, and histology (controversial cases). Six of these 15 (40%) were perimenopausal women. Benign proliferating lesion was diagnosed in 6 of 15 (40%) controversial cases. It is concluded that the multiplicity of EIS spots and simultaneousness of capacitance and conductance signals were attributed to malignancy. Detection of false-positive EIS results was common in perimenopausal patients (40%). Patients with benign proliferating lesions presented also false positivity to EIS. Mammography and EIS had similar rates of false-positive findings in this study.

Adult↗
PubMed1980

The effect of temperature on capacitance changes in an oscillating model membrane.

The electrical properties of model membranes are altered during stretching or pressure pulses. We have used a mechanico-electric transduction model to interpret the temperature dependence of capacitance changes produced in oxidized cholesterol membranes during mechanical oscillation. The relative contribution of the torus and bilayor portions of the membrane to the capacitance change is identified. The difference in elasticity between the bilayer and torus decreases rapidly with decreasing temperature and ultimately the torus becomes as solid as the bilayer portion of the model membrane.

Calorimetry, Differential Scanning↗
PubMed1999

A tunable reentrant resonator with transverse orientation of electric field for in vivo EPR spectroscopy.

There has been a need for development of microwave resonator designs optimized to provide high sensitivity and high stability for EPR spectroscopy and imaging measurements of in vivo systems. The design and construction of a novel reentrant resonator with transversely oriented electric field (TERR) and rectangular sample opening cross section for EPR spectroscopy and imaging of in vivo biological samples, such as the whole body of mice and rats, is described. This design with its transversely oriented capacitive element enables wide and simple setting of the center frequency by trimming the dimensions of the capacitive plate over the range 100-900 MHz with unloaded Q values of approximately 1100 at 750 MHz, while the mechanical adjustment mechanism allows smooth continuous frequency tuning in the range +/-50 MHz. This orientation of the capacitive element limits the electric field based loss of resonator Q observed with large lossy samples, and it facilitates the use of capacitive coupling. Both microwave performance data and EPR measurements of aqueous samples demonstrate high sensitivity and stability of the design, which make it well suited for in vivo applications.

Animals↗
PubMed2001

Myelin as longitudinal conductor: a multi-layered model of the myelinated human motor nerve fibre.

The myelin sheath is normally regarded as an electrical insulator. Low values of radial conductance and capacitance have been measured, and in electrical models of myelinated axons the contribution of longitudinal conduction within the sheath has been ignored. According to X-ray diffraction studies, however, myelin sheaths comprise alternate lipid and aqueous layers, and the latter may be expected to have a low resistivity. We propose a new model of myelinated axons in which the aqueous layers within the myelin provide appreciable longitudinal and radial conductance, the latter via a spiral pathway. We have investigated the likely contribution of these conductive paths within the myelin to the electrical properties of a human motor nerve fibre by computer simulation, representing the myelin sheath as a series of interconnecting parallel lamellae. With this new model, action potential conduction has been simulated along a 20-node cable, and the electrotonic responses to 100-ms depolarizing and hyperpolarizing current pulses have been simulated for a uniformly polarized fibre. We have found that the hypothesis of a longitudinally conducting myelin sheath improves our previous model in two ways: it is no longer necessary to make implausible assumptions about the resistivity or width of the periaxonal space to simulate realistic electrotonus, and the conduction velocity is appreciably faster (by 8.6%).

Electric Conductivity↗
PubMed2005

Modification of polysulfone membranes with polyethylene glycol and lignosulfate: electrical characterization by impedance spectroscopy measurements.

Two sets of composite membranes having an asymmetric sulfonated polysulfone membrane as support layer have been obtained and electrically characterized (membranes SPS-PEG and PA-LIGS). The skin layer of the membrane SPS-PEG contains different percentages of polyethylene glycol in the casting solution (5, 25, 40, and 60 wt%), while lignosulfonate was used for manufacturing PA-LIGS membranes (5, 10, 20, and 40 wt%). Membrane electrical characterization was done by means of impedance spectroscopy (IS) measurements, which were carried out with the membranes in contact with NaCl solutions at different concentrations (10(-3) < or = c(M) < or = 5x10(-2)). Electrical resistance and equivalent capacitance of the different membrane samples were determined from IS plots by using equivalent circuits as models. Results show a clear decrease in the membrane electrical resistance as a result of both polysulfone sulfonation and the increase of the concentration of modifying substances, although a kind of limit concentration was obtained for both polyethylene glycol and lignosulfonate (40 and 20%, respectively). Results also show a decrease of around 90% in electrical resistance due to polysulfone sulfonation, while the value of the dielectric constant (hydrated state) clearly increases.

Electric Impedance↗
PubMedDate not supplied

Unipolar cardiac pacemakers in electromagnetic fields of high voltage overhead lines.

Experimental studies have shown that both electric and magnetic extremely low frequency fields are able to disturb a cardiac pacemaker (CPM) at certain field strengths. However, the simultaneous influence of multiphase electric and magnetic fields beneath high voltage overhead lines (HVOLs) has not yet been investigated. Therefore, the distribution of the electric and the magnetic field as well as the phase angle between both components for an exemplary HVOL was numerically calculated. The calculations show that the phase difference of the capacitive and the inductive induced voltage on the input of an implanted cardiac pacemaker is position-dependent. Based on these and our earlier results a worst-case-scenario for two virtual patients beneath an exemplary HVOL was derived. It turned out that although the interference of CPMs by the electromagnetic fields (EMFs) of HVOLs cannot be ruled out, the life-threatening interference condition 'inhibition by EMF' is unlikely. Due to various factors depending on technical parameters and the individual patient a definite answer about the disturbance of an implanted CPM beneath HVOLs can be given by studies with real CPM patients only.

Computer Simulation↗
PubMed2005

Electrical measurement of a high-frequency, high-capacitance piezoceramic resonator with resistive electrodes.

In a thin and large area PZT-ceramics piezoresonator (PR) with relatively low resonance impedance, caused by high-frequency resonance and high PR capacitance, the effect of electrode resistivity and parasitic resistive and inductive elements in the measurement fixture results in significant distortion of the measured thickness-mode (longitudinal TL, shear TS) resonance response-resonance frequency shifts and characteristics deformation. This distortion may not allow the precise measurement of the PR characteristic frequencies, quality factor, and electromechanical coupling coefficient so essential to a complete PR and material characterization. A theoretical description of the "energy-trap" phenomena in a thickness-vibrating PR with resistive electrodes is presented. To interpret electrical measurements, the electromechanical model, including for completeness both the PR with resistive electrodes (as a system with distributed parameters) and the measurement fixture, is developed. The method of two contact points on the electrode provides deep sharpening and exact determination of the PR resonance. For the optimal disposition of the contact fingers, the resonance bandwidth of a real PR with resistive electrodes is even more pointed than that for the ideal PR.

Journal Article↗
PubMed1992

Fusion of membranes during fertilization. Increases of the sea urchin egg's membrane capacitance and membrane conductance at the site of contact with the sperm.

The early events of fertilization that precede and cause activation of an egg have not been fully elucidated. The earliest electrophysiological change in the sea urchin egg is a sperm-evoked increase of the egg's membrane conductance. The resulting depolarization facilitates entry of the fertilizing sperm and precludes the entry of supernumerary sperm. The sequence of the increase in the egg's membrane conductance, gamete membrane fusion, egg activation, and sperm entry, including causal relationships between these events, are not known. This study reports the use of whole egg voltage clamp and loose patch clamp to monitor simultaneously changes of membrane conductance and capacitance at the site of sperm-egg contact. Measurements were made during sperm-egg interactions where sperm entry readily proceeded or was precluded by maintaining the egg's membrane potential either at large, negative values or at positive values. Whenever the sperm evoked an increase of the egg's membrane conductance, that increase initiated abruptly, was localized to the site of sperm attachment, and was accompanied by a simultaneous abrupt increase of the membrane capacitance. This increase of capacitance indicated the establishment of electrical continuity between gametes (possibly fusion of the gametes' plasma membranes). If sperm entry was blocked by large negative membrane potentials, the capacitance cut off rapidly and simultaneously with a decrease of the membrane conductance, indicating that electrical continuity between gametes was disrupted. When sperm entry was precluded by positive membrane potentials, neither conductance nor capacitance increased, indicating that sperm entry was halted before the fusion of membranes. A second, smooth increase of capacitance was associated with the exocytosis of cortical granules near the sperm in eggs that were activated. Electrical continuity between the gametes always preceded activation of the egg, but transient electrical continuity between the gametes alone was not always sufficient to induce activation.

Animals↗
PubMed2005

Modeling error and stability of endothelial cytoskeletal membrane parameters based on modeling transendothelial impedance as resistor and capacitor in series.

Transendothelial impedance across an endothelial monolayer grown on a microelectrode has previously been modeled as a repeating pattern of disks in which the electrical circuit consists of a resistor and capacitor in series. Although this numerical model breaks down barrier function into measurements of cell-cell adhesion, cell-matrix adhesion, and membrane capacitance, such solution parameters can be inaccurate without understanding model stability and error. In this study, we have evaluated modeling stability and error by using a chi(2) evaluation and Levenberg-Marquardt nonlinear least-squares (LM-NLS) method of the real and/or imaginary data in which the experimental measurement is compared with the calculated measurement derived by the model. Modeling stability and error were dependent on current frequency and the type of experimental data modeled. Solution parameters of cell-matrix adhesion were most susceptible to modeling instability. Furthermore, the LM-NLS method displayed frequency-dependent instability of the solution parameters, regardless of whether the real or imaginary data were analyzed. However, the LM-NLS method identified stable and reproducible solution parameters between all types of experimental data when a defined frequency spectrum of the entire data set was selected on the basis of a criterion of minimizing error. The frequency bandwidth that produced stable solution parameters varied greatly among different data types. Thus a numerical model based on characterizing transendothelial impedance as a resistor and capacitor in series and as a repeating pattern of disks is not sufficient to characterize the entire frequency spectrum of experimental transendothelial impedance.

Cells, Cultured↗
PubMed1985

Electrical stimulation of hard and soft tissues in animal models.

Studies in animals have clearly established that various forms of electrical stimulation positively affect the growth, repair, and remodeling of hard and soft tissue. Although the various electrical stimulation modalities (faradic, capacitive, and inductive) are different in their physics and biochemistry, each produces a variety of biological responses in a wide range of animal models. The level of interest in animal studies of electrical stimulation is rising rapidly, and new understanding, in parallel with studies in vitro and in the clinic, will continue to be gained. The future holds the promise of a wide range of hard and soft tissue conditions being routinely treated by electrical stimulation, based in part on progress in studies in animals.

Animals↗
PubMed1976

Dielectric increment of low molecular weight RNA in dioxane after application of static electric fields.

A soluble RNA with a molecular weight between 15 000 and 23 000 was extracted from calf thymus and chromatographically purified. The RNA was slightly soluble in doxane (approx. 2.5 mug/ml) and RNA-dioxane solutions were used to fill a cell (452.02 pF capacitance) to which static electric fields of variable strength were applied. The dielectric permittivity of the solutions was measured at a fixed time interval after the application of the electric field. The RNA solutions showed a dielectric increment proportional to the strength of the applied field and to the RNA concentration. The existence of a hystersis effect was proven and the effect of the electric field on the RNA molecule might be related to a dielectric saturation phenomenon parallel to long-term changes of the molecule.

Animals↗
PubMed1990

Recording and physical characteristics of disposable concentric needle EMG electrodes.

There is currently considerable interest in using disposable concentric needle (CN) electrodes for clinical electromyography (EMG). To determine how these electrodes compare with reusable CN electrodes, we have compared signals recorded by these two electrode types from the same muscle in normal subjects. We also made similar recordings with two groups of reusable electrodes. There was no difference in the features of motor unit action potentials (MUAPs) recorded by the two groups of reusable electrodes. Disposable electrodes performed satisfactorily in conventional EMG examination. However, compared to reusable electrodes, the disposable electrodes recorded MUAPs with smaller amplitude and area but with the same area:amplitude ratio and MUAP duration. The physical and electrical properties of the CNE groups were also investigated. Disposable electrodes had lower electrical resistance and greater capacitance than reusable electrodes when measurements were made in saline. Photomicrographs showed that the disposable electrodes had smaller recording surfaces and that the central wire was frequently eccentric in the cannula. The differences in electrical recording characteristics could be due to differences in the size of the recording surface, eccentric placement of the central wire in the cannula or differences in the metal used for the central wire. We conclude that electrical and physical testing may not predict the recording characteristics of needle electrodes. Electrophysiologic testing is necessary to determine how EMG signals recorded by new types of electrodes compare with those recorded by currently used electrodes.

Action Potentials↗
PubMed2005

Magnetic field influence on electrical properties of human blood measured by impedance spectroscopy.

The impedance spectroscopy technique (IST) was used for studying the effect of a 0.5 T magnetic field on the electrical properties of whole human blood. A Solartron SI 1260 spectrometer was used to measure the impedance spectra of magnetic field exposed blood samples compared to non-exposed samples. An equivalent electrical circuit model, consisting in a resistance Rs in series with a parallel circuit formed by a constant phase element (CPE) and another resistance Rp, is proposed to fit the data in both cases. The experiment used 3 ml human blood samples from 160 healthy donors. A Wilcoxon matched pairs statistical test was applied to the data. The data analysis seems to show a statistically significant increase of the values of resistance Rp (Z = 5.06, P < 0.001) and capacitance CT (Z = 3.32, P < 0.001) of the blood exposed to magnetic field, by approximately 10.4% and 1.9%, respectively.

Adolescent↗
PubMedDate not supplied

[Myocardial electrodynamics during electrical systole].

A dipole equivalent generator of heart is considered, which represents a circuit containing an active, capacitive and inductive resistance. The model makes it possible to solve a direct diagnostic task for the electric systole. A differential equation for the integral electrical vector of the heart in the dipole approximation was solved. A model vector electrocardiogram and a linear electrocardiogram for the electrical heart parameters are presented.

Algorithms↗
PubMed2001

Extracellular measurement of anisotropic bidomain myocardial conductivities. I. Theoretical analysis.

The passive electrical properties of cardiac tissue, such as the intracellular and interstitial conductivities along the longitudinal and transverse axes, have not been often measured because intracellular electrodes are usually needed for these measurements. In this paper, we present a theoretical analysis of two myocardial models developed to estimate these properties by analyzing potentials recorded with a pair of extracellular electrodes while injecting alternating current between another pair of electrodes. First, the cardiac tissue is represented by a standard bidomain model which includes a membrane capacitance; second, this model is modified by adding an intracellular capacitance representing the intercalated disks. Numerical solutions are computed with a fast Fourier transform algorithm without constraining the anisotropy ratios of the interstitial and intracellular domains. We systematically investigate the effects of changes in the bidomain parameters on the voltage-to-current ratio curves. We also demonstrate how the bidomain parameters can be theoretically estimated by fitting, with a modified Shor's r algorithm, the simulated potentials along the longitudinal and transverse axes for different frequencies between 10 and 10,000 Hz. An important finding is that the interelectrode distance must be similar to the myocardial space constant so as to obtain frequency dependent measurements.

Algorithms↗
PubMed2006

Micro-agar salt bridge in patch-clamp electrode holder stabilizes electrode potentials.

Maintaining a stable electrode potential is critical for patch-clamp measurements. The electrode potential of conventional patch electrode-holder assembly, where an Ag/AgCl wire is in direct contact with the patch pipette filling solution, is subject to drift if the pipette solution contains a low concentration of chloride ions (Cl-). We developed an agar bridge of 3 M KCl filled in a polyimide microtubing which forms an electrical connection between an Ag/AgCl wire and the pipette solution. We examined the offset potentials of the micro-agar salt bridge electrode assembly in parallel with a conventional electrode assembly in generic recording conditions (the pipette solution contained 5 mM NaCl). The junction potential between the Ag/AgCl wire and the pipette filling solution in the conventional electrode contributed to most of the offset potential drift observed during the course of 30 min recordings. The drift was up to 27.3 mV after several changes of the glass pipette. In contrast, the micro-agar salt bridge stabilized the electrode potential within typically 2 mV without affecting the patch electrode resistance, capacitance or noise level. Numerical simulations showed that Cl- diffusion from the agar bridge to the tip caused a negligible 0.4 microM Cl- concentration change at the pipette tip within 30 min. This method is easy to implement and provides long-term recording stability. The micro-agar salt bridge can fit in most commercial patch electrode holders and can be conveniently maintained.

Agar↗
PubMed2002

Contact flexible microstrip applicators (CFMA) in a range from microwaves up to short waves.

Contact flexible microstrip applicator (CFMA) is a new light-weight microstrip applicator type for superficial and deep local hyperthermia. Typical specimens are developed for operation at frequencies of 434, 70, 40, and 27 MHz. The main common features of CFMA, namely, their flexibility and light weight, as well as their aperture dimensions slightly depend on the operating frequency. Two antenna types are used in CFMAs: inductive antennas with a radiating plane electrical dipole at microwaves, and coplanar capacitive antennas, providing depression of the normal component of the electrical field in the very high-frequency (VHF) and high-frequency (HF) range. The flexibility of the applicators enables one to conform them with curved surfaces. In a bent state of the applicators there arises a focusing effect of energy deposition in deeper located tissues due to linear polarization of the irradiated electromagnetic (EM) field, inherent in CFMA. All CFMA are integrated with silicon water boluses which serve as a matching element, so as a skin cooling agent. Due to this and to the predominance of the tangential electrical component in the radiated EM field, no fat overheating effects are noticed, as a rule. The aperture of the developed applicators overlap the range 160-630 cm2 providing effective heating field sizes (EFSs) 64-400 cm2, respectively. The most bulky CFMAs with an aperture of (21 x 29) cm2 operating at the frequency of 434 MHz weigh 0.8 kg and 2.5 kg at 27 MHz. Phenomenological analysis of the radiating systems, as well as experimental evaluation of the applicators are presented. CFMAs operating at frequencies of 434 and 40 MHz are used in clinical practice. CFMA at 70 and 27 MHz are subjected to laboratory clinical investigations.

Electric Impedance↗