Bioelectrochemistry and bioenergetics (Lausanne, Switzerland)最新文献

For unipolar electrocardiography, a zero reference electrode is necessary. The zero potential is usually considered as that at infinity but not well understood for a finite conductor. In practice, Wilson's central terminal has been utilized, as a zero equivalent, with remarkable clinical success. The grade of approximation has, however, not been established. In this paper, we discuss related topics including a review of older literature, the definition of zero potential and the method for obtaining the zero potential from the measurements on the body surface. With this method, the potential of Wilson's electrode with respect to that at infinity can be calculated. Our previous calculation in 60 clinical cases showed the time course of the absolute voltage of Wilson's electrode, which is nearly parallel with the body surface potential.

Radio frequency radiation (RFR) dosimetry is based on the rate of absorbed energy (specific absorption rate: SAR) per unit mass. It is most conveniently measured by acquiring changes in temperature per unit time and converting the results to joules per second (watts) per kilogram, based on the specific heat of the biological material interacting with the RFR. To date, SAR has been predicted by modeling based on the dielectric properties of tissues, or measured by infrared (IR) thermography or with macroscopic high-resistance thermistors or thermofluorescent macroscopic point probes. Thermochemiluminescence (TCL) was invented to provide a high degree of continuous spatial and temporal thermal resolution in phantoms. It is defined as the steady-state emission of visible light from a peroxidizing mixture based on the temperature of the mixture. The best material for this purpose, to date, is diazoluminomelanin (DALM). Unfortunately, standardization of the synthesis (chemical composition) of this polymer and its thermal response constant (thermal quantum efficiency) has been difficult. This paper presents a biosynthetic method for the large-scale production of the polymer and a computational method for directly determining the SAR from the luminescence.

The plasmid size can be an important factor in electrotransformations. We have examined bacterial electroporation with a specific interest in the transformation of plasmids with different sizes of their molecules. We used plasmids pUC19, pBR322 and pPP4. Transformation efficiency drops with increasing size of the DNA. We achieved with plasmid pUC19 a 81% frequency of transformation. The optimal field strength decreases with increasing size of the plasmid. Not only large sized plasmids but also large DNA concentrations lead to a reduced survival rate of the Escherichia coli JM109 cells.

Adherently growing mouse fibroblasts were cultivated for days in highly conductive culture media between micro-fabricated electrodes under strong ac-electric fields. Miniature electrodes have improved heat dissipation which allows the use of media with conductivity of more than 1 S/m at field strengths of up to 100 kV/m. Cell division rates, cell motility, cell viability and physiological parameters such as vesiculation were monitored and the actin and β-tubuline structures of cyto-skeleton were imaged by laser scanning fluorescence. The specific effects of polarisation could be differentiated from unspecific effects such as heating. We estimated the real field strength acting on cells. In the kHz-range, field application was clearly limited by membrane dielectric breakdown while temperature increases were less than 3°C. In the MHz-range, much stronger fields could be applied and heating became the limiting factor. Above an induced trans-membrane potential of 130–150 mV cells no longer proliferated under prolonged field application. In the MHz-range (above 5 MHz) cells could be exposed to surprisingly high field strengths (40 kV/m) for days. Therefore, there is a frequency window (up to several 100 MHz) which can be used for cell positioning, manipulation and characterisation techniques without significant loading of cells.

Fetal magnetocardiography is a non-invasive technique for studying the electrical activity of the fetal heart. Fetal magnetocardiograms (fMCG) can be used to diagnose and classify fetal cardiac arrhythmias reliably. An averaged fMCG shows a QRS-complex, a P-wave, and a T-wave. However, it is still unknown if the currents in the tissues surrounding the fetal heart disturb these features. Furthermore, the measuring technique is not yet optimised for fMCG registrations. Simulation studies may provide guidelines for the design of an appropriate magnetometer system. Therefore, finite-element and boundary-element models were constructed in order to study the possible influence of the volume conductor. Especially, the influence of the layer of vernix caseosa, a fatty layer that covers the fetus, was investigated. The computations showed that the layer of vernix caseosa will affect the waveform of the fMCG. The signal processing procedure used is also discussed. It turned out to be difficult to deduce the onset and offset of the T-wave from the resulting averaged signals. Possibly, the QRS-complex does not provide a correct trigger to obtain a distinguishable T-wave in the averaged signal, because the RT-interval may be variable.

The purpose of this work was to estimate whether a considerable thermal absorption appears in the human body during standardized 1.5 T magnetic resonance imaging (MRI) system procedures applied in medical diagnostics. Therefore, based on magnetic resonance (MR) scans of a male volunteer, a human body heterogeneous tissue model has been simulated by a finite element method using isoparametric formulation, verified before with measurements. Numerical calculation has been performed for two radiofrequency (RF) exposure systems: saddle-shaped coils and bird-cage coil. Energy deposition in terms of specific absorption, specific absorption rate (SAR) and temperature elevation in the model has been calculated for the `worst-case' imaging sequence, i.e., multislice turbo spin echo sequence. Comparison to existing recommendations shows that there is no thermal hazard at 64 MHz, corresponding to 1.5 T MRI systems. However, new simulations should be performed for MR systems operating at higher frequencies.

Mechanisms of electrical injury may involve electrical and thermal phenomena. These factors affect cell membranes and membrane proteins. Results of the stress of these factors include permeabilization of the cell membranes and dysfunctions of the membrane proteins, especially the voltage-sensitive membrane proteins. In this paper, we discussed mechanisms involved in damaging the K⁺ channel proteins. We show that the level of channel damage is not directly correlated to the shock field-induced huge channel currents, therefore not to the thermal damages in the proteins. Instead, the channel damages are dependent on the field-induced supramembrane potential (magnitude and polarity). Moreover, the number of limiting charge particles which function as the voltage-sensor in the channel gating system was reduced after a supramembrane potential shock. These results indicate that a supramembrane potential shock may cause electroconformational changes in the membrane proteins, which may reveal a new mechanism involved in electrical injury. Moreover, these studies also provide evidence that external electric fields can be used to modify functions of the voltage-sensitive membrane proteins by electrical coupled conformational changes in the proteins.

The effect of low-level amplitude modulated radiofrequency radiation were studied on Na⁺–K⁺-ATPase activity in the brain of developing male Wistar rats of age 23 days (body weight 55–60 g). They were exposed to carrier wave (CW) frequency 147 MHz and its sub-harmonic frequencies 73.5 and 36.75 MHz amplitude modulated (AM) at 16 and 76 Hz for 30–35 days (3 h day⁻¹, Power density 1.47 mW cm⁻²,average specific absorption rate 9.65–6.11 W kg⁻¹). We observed a statistically significant increase in Na⁺–K⁺-ATPase activity in chronically exposed rats compared to the control ones. The increase in Na⁺–K⁺-ATPase activity was around 19–20% in the rats exposed to CW frequencies AM at 16 Hz compared to the controls, whereas the increase in Na⁺–K⁺-ATPase activity was around 15–16% in rats exposed to the same set of CW frequencies but AM at 76 Hz. Though there was a difference in Na⁺–K⁺-ATPase activities (3–4%) in the two groups but the difference was found to be statistically insignificant. Within the group of rats exposed to CW frequencies amplitude modulated at 16 and 76 Hz, respectively, the effect on Na⁺–K⁺-ATPase activity was found to be independent of the magnitude of CW frequencies. An additional single short duration (20–60 min) exposure of membranes in vitro from different exposed group to the above field did not show any significant alteration on Na⁺–K⁺-ATPase activity. It is concluded that a low level effect of amplitude modulated radiation produces statistically significant effect on Na⁺–K⁺-ATPase activity but is insensitive to the carrier wave frequencies under investigation.

A model for the detection of weak electric and magnetic fields is developed by analogy to a phased array antenna and receiver. Pyramidal cells from the cortex of the brain are shown to have elements which can be modeled as an antenna, a mixer amplifier, and a neural network narrow band filter with summing junctions output which could, in turn, modulate the firing rate of a pacemaker cell or ongoing brain oscillations. The signal-to-noise ratio is shown to increase for signals which are coherent in time and space with the square root of the number of elements involved. Additionally, the signal-to-noise ratio may be enhanced by increasing the power spectral density of the ongoing chaotic oscillation at the applied signal frequency.

Advantages of surface electromagnetic waves application in medicine, including increased efficiency and depth of energy penetration are shown. Two types of the electrodes for physiotherapy, based on slow-wave structures (applicators and radiators) are described. It is shown that varying deceleration and frequency can control electric and magnetic field penetration into body tissue. The new method of electromagnetic energy radiation into tissue is implemented. Other examples of surface waves application are demonstrated, including coagulation scalpel and artificial ear. The main parameters of slow-wave structures that are used for the deceleration of electromagnetic waves are also described.