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PubMedDate not supplied

The position of the opposite flat applicator changes the SAR and thermal distributions of the RF capacitive intracavitary hyperthermia.

The variations of the specific absorption rate (SAR) and thermal distribution in the JSHO QA phantoms were investigated by radiofrequency (RF) capacitive intracavitary hyperthermia (ICHT) applicator (AP-T01, Omron Electric Co., Kyoto, Japan) with the changing position of the opposite flat applicator (15-cm in diameter). The thermal distribution was observed with the thermographic camera and the normalized SAR distribution was calculated with the thermal data that were measured with the thermocouple thermometers. The SAR and thermal distributions of AP-T01 significantly varied with the position of the opposite flat applicator. The slope of the normalized SAR became gradual towards the side of the flat applicator. During the operating of a high flow rate (1500 ml/min) cooling system, the region between AP-T01 and the flat applicator was widely and rather homogeneously heated, except the hot spot around the end of AP-T01. This hot spot may be due to the imbalance of cooling of AP-T01 and the warming-up of the electrode. These results suggest that the RF capacitive ICHT using AP-T01 may be clinically effective on the deep-seated tumours in the direction of either the end wall, such as cervical cancers, or the upper wall, such as prostatic cancers and the mediastinal metastatic lymph nodes, if an improvement of the cooling system is achieved.

Female↗
PubMed1975

Influence of activity on the passive electrical properties of denervated soleus muscle fibres in the rat.

The technique of direct electrical stimulation of denervated muscle was used to study the role of muscle activity per se in controlling the passive electrical properties of muscle fibres. 2. Specific membrane resistance and capacitance of the denervated and the denervated-stimulated muscle fibres were measured by a sinewave technique at frequencies between 5 and 240 Hz. The parameter values were constant at low frequencies up to a variable transition frequency and declined rapidly at higher frequencies. 3. Following denervation the low-frequency value of specific membrane resistance increased (2291 omega cm2 for 19-day denervated fibres vs. 766 omega cm2 for innervated fibres), the specific membrane capacitance declined (2-7 muF/cm2 vs. 3-6 muF/cm2) and the transition frequency shifted towards lower frequencies. The specific internal resistance was higher in denervated fibres (301 omega cm for 19-day denervated fibres vs. 240 omega cm in innervated fibres) apart from a transient decline after 5 days of denervation (164 omega cm). 4. Direct electrical stimulation for 2 weeks beginning on the 5th day after denervation restored all parameters listed above to their original values before denervation. 5. Stimulation arrested in most cases further atrophy from the time of stimulation but did not restore normal fibre size.

Animals↗
PubMed1999

Problems of weak electromagnetic field effects in cell biology.

Electrostimulations of cells by weak electric or electromagnetic LF and HF-fields are applied widely today; capacitively or inductively coupled, however, they are seldom applied for cell-free and membrane-free solutions of enzymes. First, the detection of a response of the cells ('electrical window') is a prerequisite for testing at least three parameters: frequency, amplitude and treatment time, besides reproducible biological conditions. The 'state-of-the-art' of this fast developing direction of bioelectrochemistry can be characterized in the following way: the results from several laboratories of (a) cell proliferation, (b) ion transport, (c) activation of several enzymes (Na,K-ATPase), (d) increase of certain protein concentrations (heat-shock protein hsp70) are more or less in agreement. Unfortunately, there are discrepancies between no less than 7 labs in the gene expression of c-myc, c-fos histone 2B, -actin, URA-3 and others, especially for low fields (< 0.05 mT), e.g., in HL60 cells! The reason why seems to be: (1) differences in the most suitable isolation procedure, (2) interferences in the case of too low magnetic flux and (3) too small ranges of parameters have been measured. Today, three open problems must be pointed out: (A) What is the physiological causality for specific 'electrical windows' and their positive or negative efficacy? (B) What are the biochemical targets for either magnetic or electric fields or both? (C) What is the influence of electrical and (or) thermal noise on field efficiency?

Animals↗
PubMed1995

Estimation of the junctional resistance between electrically coupled receptor cells in Necturus taste buds.

Junctional resistance between coupled receptor cells in Necturus taste buds was estimated by modeling the results from single patch pipette voltage clamp studies on lingual slices. The membrane capacitance and input resistance of coupled taste receptor cells were measured to monitor electrical coupling and the results compared with those calculated by a simple model of electrically coupled taste cells. Coupled receptor cells were modeled by two identical receptor cells connected via a junctional resistance. On average, the junctional resistance was approximately 200-300 M omega. This was consistent with the electrophysiological recordings. A junctional resistance of 200-300 M omega is close to the threshold for Lucifer yellow dye-coupling detection (approximately 500 M omega). Therefore, the true extent of coupling in taste buds might be somewhat greater than that predicted from Lucifer yellow dye coupling. Due to the high input resistance of single taste receptor cells (> 1 G omega), a junctional resistance of 200-300 M omega assures a substantial electrical communication between coupled taste cells, suggesting that the electrical activity of coupled cells might be synchronized.

Animals↗
PubMed2000

Perspectives on MEMS in bioengineering: a novel capacitive position microsensor.

We describe a novel capacitive position sensor using micromachining to achieve high sensitivity and large range of motion. These sensors require a new theoretical framework to describe and optimize their performance. Employing a complete description of the electrical fields, the sensor should deviate from the standard geometries used for capacitive sensors. By this optimization, the sensor gains a twofold increase in sensitivity. Results on a PC board 10x model imply that the micromachined sensor should achieve a sensitivity of less than 10 nm over 500-micron range of travel. Some bioengineering applications are addressed, including positioning of micromirrors for laser surgery and dose control for implantable drug delivery systems.

Drug Delivery Systems↗
PubMed1990

Electrical properties of canine subendocardial Purkinje fibers surviving in 1-day-old experimental myocardial infarction.

The passive electrical properties of subendocardial Purkinje fibers surviving in infarcted regions of canine ventricle 24 hours after coronary ligation were studied by using microelectrode techniques and cable theory. In normal hearts, cells within the subendocardial Purkinje fiber strands were found to be well coupled to each other but electrically isolated from neighboring myocardium. Voltage response to intracellular current injection was consistent with one-dimensional cable behavior and yielded estimates of passive electrical properties in general agreement with previous work on free-running Purkinje strands (membrane length constant, 1.2 +/- 0.1 mm; membrane time constant, 7.3 +/- 0.8 msec; input resistance, 67.4 +/- 7.4 K omega; membrane resistance, 8.2 +/- 0.7 K omega.cm; axial resistance, 0.52 +/- 0.06 M omega/cm; membrane capacitance, 960 +/- 102 nF/cm) (n = 21). On the day after coronary ligation, subendocardial Purkinje fiber action potentials were prolonged and slightly depolarized. Significant increases were measured in input resistance (+40.5%), membrane resistance (+43.9%), and axial resistance (+47.5%), whereas membrane capacitance was found to be significantly decreased (-24.3%) (n = 19). Conduction velocity, membrane length constant, membrane time constant, and the time constant and capacitance for the foot of the action potential remained unchanged. These results are consistent with electrical uncoupling between adjacent cells, which will increase internal resistivity, accompanied by changes in cellular phospholipid content, which can increase membrane resistance and alter membrane capacitance. Alternatively, the results can be explained by a simple model in which the apparent electrical structure is altered by changes in electrical coupling alone, with specific electrical properties remaining constant. Although the mechanisms underlying the observed changes remain uncertain, the present study indicates that myocardial infarction is associated with alterations in the passive electrical structure of surviving subendocardial Purkinje fibers, which, together with changes in action potential configuration, may provide a substrate for the generation of ventricular arrhythmias 24 hours after coronary ligation.

Action Potentials↗
PubMed1994

Mechanosensitive fibroblasts in the sino-atrial node region of rat heart: interaction with cardiomyocytes and possible role.

The positive chronotropic response of the heart to stretch of the right atrium is one of the major mechanisms adjusting the heart rate to variations in venous return on a beat-by-beat basis. The precise pathway of this mechano-electric feedback and its cellular basis are uncertain. In this study, a possible contribution of mechanosensitive fibroblasts, abundant in the sino-atrial node region, was investigated using a mathematical model of the electrical interaction of a mechanosensitive fibroblast and a sino-atrial pacemaker cell. Electrophysiological evidence for a bio-electrical interaction of mechanosensitive fibroblasts with surrounding cardiomyocytes has been studied in (i) the isolated spontaneously beating atrium of rat hearts, and (ii) cell cultures of the neonatal rat heart. These investigations were performed using (i) double-barrelled floating microelectrodes for intracellular potential registrations, and (ii) the double whole cell patch-clamp technique. It was shown that cardiac fibroblasts and surrounding cardiomyocytes can be either electrically well isolated from each other, or coupled both capacitively and electrotonically. The electrophysiological data obtained were incorporated into the OXSOFT HEART program. Assuming that equivalent coupling may occur between mechanosensitive fibroblasts and sino-atrial pacemaker cells, a heterologous cell pair consisting of one fibroblast and one sino-atrial node myocyte connected by ten to thirty single gap junctional channels with a conductance of 30 pS was modelled. The model of the electrotonic interaction of these cells showed that stretch of the fibroblast during atrial diastole, simulating increased atrial wall tension during atrial filling, can raise the spontaneous depolarization rate of the pacemaker cell in a stretch-dependent manner by up to 24%. These results show that cardiac mechanosensitive fibroblasts could form a cellular basis for the positive chronotropic response of the heart to stretch of the right atrium.

Animals↗
PubMed2006

Epithelial electrical resistance as a measure of permeability changes in pediatric duodenal biopsies.

OBJECTIVES: Intestinal permeability measured with medium-sized oral probes is increased in cystic fibrosis (CF) and celiac disease (CD), probably reflecting reduced tight junction resistance. The aim of this study was to evaluate whether square-pulse analysis of duodenal biopsies from children can be used to determine electrical tight junction resistance. METHODS: Intestinal biopsies from children with different stages of CD and from patients with CF were studied in a modified Ussing chamber. The epithelium was assumed to act as an electrical circuit consisting of a current generator parallel with a resistance and a capacitance. Subepithelial and epithelial resistances were determined by square-pulse analysis, and the generated current was calculated. RESULTS: Confirming data using permeability probes, reduced epithelial electrical resistance was found both in patients with CF and CD. Only the CF patients had reduced resting current as well. The secretagogues prostaglandin E2, cyclic adenosine monophosphate and acetylcholine increased the current in both control biopsies and biopsies with villous atrophy but had no significant effect on epithelial resistance. CONCLUSIONS: Measurement of electrical resistance in duodenal biopsies can be used as an alternative method of quantifying permeability in pediatric biopsies.

Adolescent↗
PubMed1988

Electrical properties of motoneurons in the spinal cord of rat embryos.

Electrical properties of immature motoneurons were studied in vitro using isolated segments of spinal cords of rat embryos aged 14-21 days of gestation. Stable resting potentials and evoked synaptic potentials were recorded for more than 9 hr, indicating that motoneurons remain viable for many hours. Motoneurons are electrically excitable at 14 days of gestation and from the onset of excitability the action potentials are Na+-dependent but slow rising long-duration Ca2+-dependent action potentials can be evoked if K+ conductance is reduced. Thus, during embryonic development the regenerative potential inward current is Na+-and Ca2+-dependent. During motoneurons' differentiation there are some changes in their electrical properties: resting membrane potential increases, input resistance decreases, input capacitance increases, threshold for action potential decreases, and maximum rate of rise of action potential increases. Afferent motoneuron contacts are formed at 16-18 days of gestation when excitatory synaptic potentials can first be evoked in response to dorsal root stimulation. The changes in input capacitance and threshold for action potential occur at the onset of functional afferent motoneuron contacts, but it is not known whether these changes are autonomous or are influenced by the newly formed sensory inputs.

Action Potentials↗
PubMed2001

Multi-frequency bioimpedance measurements of children in intensive care.

Bioimpedance spectroscopy is used to monitor the condition of the tissues of children staying in intensive care for the treatment of meningitis. The results are significant, with the angular frequency at maximum reactance lying between 1500 and 6400 x 10(3) rads(-1), whereas in a control group, this value does not exceed 900 x 10(3) rads(-1). The ratio between the specific conductance at zero and that at infinite frequency (this ratio is proportional to total body volume/volume of extracellular space) remains constant at 1.4 and equal to the ratio in the control group, despite infusions with physiological saline. The electrical parameters are associated with physiological ones and indicate that the membrane 'capacitance' decreases, as a result of the illness, from approximately 0.4 in the control group to 0.05 in the patient group. However, there is a time-delay between the onset of illness and the change in membrane capacitance. It is also found that the ratio between extracellular and intracellular specific conductivity in the group of patients and controls remains constant at approximately 4.3. The changes in the physiological and electrical parameters were compared with chemical parameters that were measured during the stay in intensive care.

Child↗
PubMed1997

Impedance of a goat eye lens.

The complex electrical impedance of a goat eye lens is studied in the frequency range 10 mHz-10 Hz at room temperature, using a computer-controlled AC impedance system. AC impedance software (model 368, version 2.2) is employed to determine the total impedance and capacitance of the eye lens at various frequencies. A Cole-Cole plot of the eye lens material is drawn between the real component of impedance Z' and the imaginary component Z" for each excitation frequency that shows a perfect arc of a-semicircle, with its centre lying below the abscissa at an angle of 35 degrees. The half-angle phi between R(0) and R infinity is found to be 55 degrees, which mathematically demonstrates the selective permeability of the eye lens. Using graphical analysis of the Cole-Cole plot, characteristic frequency fc and distribution factor alpha are observed to be 1 Hz and 0.77, respectively. At characteristic frequency, capacitance and total impedance are found to be 1.14 microF and 9.08 k omega. The effect of electrode polarisation on capacitance is corrected, based on Fricke's power function. The observed electrical parameters are then used to explain the multiple current path through various tissue compartments. Further, an attempt is made to explain the results on the basis of a possible dipolar model.

Animals↗
PubMed2000

Magnetic stimulation coil and circuit design.

A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation [1]. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.

Biomedical Engineering↗
PubMed1996

White noise approach for estimating the passive electrical properties of neurons.

1. The passive electrical properties of whole cell patched dentate granule cells were studied with the use of zero-mean Gaussian white noise current stimuli. Transmembrane voltage responses were used to compute the first-order Wiener kernels describing the current-voltage relationship at the soma for six cells. Frequency domain optimization techniques using a gradient method for function minimization were then employed to identify the optimal electrical parameter values. Low-power white noise stimuli are presented as a favorable alternative to the use of short-pulse current inputs for investigating neuronal passive electrical properties. 2. The optimization results demonstrated that the lumped resistive and capacitive properties of the recording electrode must be included in the analytic input impedance expression to optimally fit the measured cellular responses. The addition of the electrode resistance (Re) and capacitance (Ce) to the original parameters (somatic conductance, somatic capacitance, axial resistance, dendritic conductance, and dendritic capacitance) results in a seven-parameter model. The mean Ce value from the six cells was 5.4 +/- 0.3 (SE) pF, whereas Re following formation of the patch was found to be 20 +/- 2 M omega. 3. The six dentate granule cells were found to have an input resistance of 600 +/- 20 M omega and a dendritic to somatic conductance ratio of 6.3 +/- 1.1. The electronic length of the equivalent dendritic cylinder was found to be 0.42 +/- 0.03. The membrane time constant in the soma was found to be 13 +/- 3 ms, whereas the membrane time constant of the dendrites was 58 +/- 5 ms. Incorporation of morphological estimations led to the following distributed electrical parameters: somatic membrane resistance = 25 +/- 4 k omega cm2, somatic membrane capacitance = 0.48 +/- 0.05 microF/cm2, Ri (input resistance) = 72 +/- 5 omega cm, dendritic membrane resistance = 59 +/- 4 k omega cm2, and dendritic membrane capacitance = 0.97 +/- 0.06 microF/cm2. On the basis of capacitive measurements, the ratio of dendritic surface area to somatic surface area was found to be 34 +/- 2. 4. For comparative purposes, hyperpolarizing short pulses were also injected into each cell. The short-pulse input impedance measurements were found to underestimate the input resistance of the cell and to overestimate both the somatic conductance and the membrane time constants relative to the white noise input impedance measurements.

Animals↗
PubMed1975

Electrical properties of squid axon membrane. II. Effect of partial degradation by phospholipase A and pronase on electrical characteristics.

Passive electrical characteristics of perfused squid axon membrane are investigated. In a previous publication, we reported that the capacitance of intact squid axon membrane is partly frequency dependent. We extended the same measurement to perfused axons. We found that the electrical characteristics of perfused axon membrane are essentially the same as those of intact axons. In this work, we investigated the effects of phospholipase A and pronase on the membrane capacitance. Phospholipase A is known to block the sodium activation and pronase to eliminate the sodium inactivation. Phospholipase A is found to increase the frequency dependent as well as the frequency independent capacitances. Our tentative conclusion is that this enzyme perturbs the lipid structure and decreases its thickness. Pronase is found to increase the frequency dependent capacitance slightly while the capacitance of the lipid layer remains unaltered. Although voltage clamp data indicate that the pronase disrupts the excitatory mechanism extensively, this enzyme has relatively little effect on the overall membrane capacitance.

Animals↗
PubMed1988

A low cost high intensity flash device for photolysis experiments.

Novel techniques of flash photolysis experiments require high intensity light sources in the near UV. We describe here a simple and inexpensive flash device which may complete with bulky and expensive laser systems if the experiments do not necessitate very short light pulses. Using a particular optical arrangement and stored electrical energy, a variation of the parameters voltage and capacitance led to a difference in light output by a factor of more than two. The system is used to relax both skeletal and smooth muscle fibres in the rigor state by releasing up to 2 mM ATP from 12.5 mM caged-ATP.

Adenosine Triphosphate↗
PubMed1999

Hypothetical model for monitoring microbial growth by using capacitance measurements--a minireview.

Microbiological impedance devices are used routinely by food and manufacturing industries, and public health agencies to measure microbial growth and metabolism. In this paper a hypothetical model explaining the effects of microbial growth and metabolism on capacitance at electrode-medium interfaces, that can be supported by fundamental theories and principles of electrochemistry, is presented. This model provides a framework to interpret changes in capacitance during microbial growth and metabolism and can be used to generate and test hypotheses on factors (i.e., temperature, microbial cell density, microbial growth and medium conductivity) contributing to increases or decreases in capacitance.

Culture Media↗
PubMedDate not supplied

The size and distance of the opposite flat applicator change the SAR and thermal distributions of RF capacitive intracavitary hyperthermia.

The variations of the specific absorption rate (SAR) and thermal distributions in the JSHO QA phantom were investigated by using the radiofrequency (RF) capacitive intracavitary hyperthermia (ICHT) applicator (AP-T01, Omron Electric Co., Kyoto, Japan) and the opposite flat applicators of different sizes (AP-75E: 7.5 cm in diameter, AP-100E: 10 cm in diameter, and AP-150E: 15 cm in diameter). The influences of the distance between both applicators were also investigated. Heating of the region between both applicators became weaker with the increase in size of the opposite flat applicator, and it became stronger with the decrease of the distance between both applicators. Heating near the flat applicator became weaker with the increase in size of the flat applicators, and it showed no apparent difference with the increase of the distance between both applicators. The normalized SAR values between AP-T01 and the opposite flat applicator became smaller and its slope became steeper with the increase in size of the opposite flat applicator and in the distance between both applicators. These results suggest that the variability of the specific absorption rate (SAR) and thermal distributions of the region between both applicators may show the potentiality of usefulness for heating the tumours of various sizes, shapes and location.

Humans↗