Detection of respiratory waveforms using non-contact electrodes during bathing.

The aim of this study is to develop a method for measuring the respiratory waveform using non-contact electrodes during bathing. To determine the most appropriate electrode arrangement, we modeled a composite system consisting of a body submerged in bath water. We calculated the frequency dependence of the impedance amplitude using a three-dimensional finite difference method (3D-FDM). The simulation results showed that an increase in chest size due to inspiration caused a decrease in the impedance amplitude in the frequency range of 0.1 Hz to 1 MHz. Next, bioelectric impedance (BEI) was measured in the frequency range of 4 kHz to 4 MHz at the maximum-end-expiration and maximum-end-inspiration stages. BEI results were consistent with those obtained from the model simulations. We found that 1 MHz was the appropriate frequency for measuring the respiratory waveform, and the time dependence of the impedance amplitude was measured at 1 MHz. The impedance amplitude agreed well with the respiratory waveform obtained from rubber strain gauge plethysmography, which was used as a reference.

Boundary-element calculations for amplification of effects of low-frequency electric fields in a doublet-shaped biological cell.

To examine the amplification of the effects of low-frequency electric fields due to the junction between the cells, the amplitude of transmembrane potential P(TMP0), the time-averaged normal stress sigma(n) and the outward force density sigma(out) on the shell-phase, and the squared intensity I(ee) of electric fields in the inner and the outer phases induced by uniform external ac fields were calculated with the boundary-element method for doublet-shaped cell models consisting of two spheres of the same size connected by the junction; the results were compared with those in a spherical model. When the external fields were parallel to the long axis of the doublet-shaped models, P(TMP0), sigma(n) and sigma(out) at the pole were greater than those in the spherical model, and sigma(out) and I(ee) at the junction increased with the decrease in the junction-radius. The external fields perpendicular to the long axis caused I(ee) greater than that at the center of the spherical model and negative sigma(out), at the junction. The amplification of P(TMP0), sigma(n), sigma(out) and I(ee) took place within restricted frequency-regions that could be specified by the characteristic frequencies for the frequency-dependence of the polarization factor of the models.

Effects of T-tubules on dielectric spectra of skeletal muscle simulated by boundary element method with two-dimensional models.

In order to investigate the origin of large intensity the alpha-relaxation in skeletal muscles observed in dielectric measurements with extracellular electrode methods, effects of the interfacial polarization in the T-tubules on dielectric spectra were evaluated with the boundary-element method using two-dimensional models in which the structure of the T-tubules were represented explicitly. Each model consisted of a circular inclusion surrounded by a thin shell corresponding to the sarcolemma. The T-tubules were represented by simplified two types of invagination of the shell: straight invagination along the radial directions, and branched one. Each of the models was subjected to two kinds of calculations relevant to experiments with the extracellular and the intracellular electrode methods. Electrical interactions between the cells were omitted in the calculations. Both calculations showed that the dielectric spectra of the models contained two relaxation terms. The low-frequency relaxation term assigned to the alpha-relaxation depended on the structure of the T-tubules. Values of the relaxation frequency of the alpha-relaxation obtained from the two types of calculations agreed with each other. At the low-frequency limit, the permittivity obtained from the extracellular-electrode-type calculations varied in proportion to the capacitance obtained from the intracellular-electrode-type ones. These results were consistent with conventional lumped and distributed circuit models for the T-tubules. This confirms that the interfacial polarization in the T-tubules in a single muscle cell is not sufficient to explain the experimental results in which the intensity of the alpha-relaxation in the extracellular-electrode-type experiments exceeded the intensity expected from the results of the intracellular-electrode-type experiments. The high-frequency relaxation term that was assigned to the beta-relaxation was also affected by the T-tubule structure in the calculations relevant to the extracellular-electrode-type experiments.

Boundary-element calculations for dielectric behavior of doublet-shaped cells.

In order to simulate dielectric relaxation spectra (DRS) of budding yeast cells (Saccharomyces cerevisiae) in suspension, the complex polarization factor (Clausius-Mossotti factor) beta for a single cell and the complex permittivity of a cell suspension epsilon(sus)* were calculated with a doublet-shaped model (model RD), in which two spheres were connected with a part of a ring torus, using the boundary element method. The beta values were represented by a diagonal tensor consisting of components beta(z) parallel to the rotation axis (z axis) and beta(h) in a plane (h plane) perpendicular to the axis. The epsilon(sus)* values were calculated from the complex permittivity of the suspending medium epsilon(a)* and the components of beta. The calculation was compared with that of a conventional prolate spheroid model (model CP). It was found that model CP could be used as a first approximation to model RD. However, differences existed in beta(z) between models RD and CP; beta(z) showed three relaxation terms in the case of model RD in contrast with two terms in model CP. Narrowing the junction between the two spheres in model RD markedly decreased the characteristic frequency of one of the relaxation terms in beta(z). This suggests that the structure of the junction can be estimated from DRS. Effects of the shape change from model RD to a two-sphere model (model RD without the junction) were also examined. The behavior of beta(z) in the two-sphere model, the relaxation intensity of which was much lower than model RD, was quite similar to that in a single-sphere model. These simulations were consistent with the experimental observations of the dielectric behavior of the yeast cells during cell cycle progression.

Calculation of dielectric spectra of suspensions of rod-shaped cells using boundary element method.

The boundary element method (BEM) has been applied to the calculation of dielectric spectra of suspensions of rod-shaped cells using two kinds of models: model-R consisting of a cylinder and two hemispheres and model-PU of prolate spheroid shape. Both models have an insulating shell phase of a uniform thickness. The calculations were compared with those using a conventional spheroidal model with a confocal shell (model-PC) and previous observations on rod-shaped yeast cells. The differences among the three models were not considerable and all the models succeeded in interpreting the observed data on yeast cells.