Comparison of electrode impedances of Pt, PtIr (10% Ir) and Ir-AIROF electrodes used in electrophysiological experiments

In tissue impedance measurements with the 4-electrode assembly, unexpected difficulties may occur because a combination of electrode impedance and stray capacitance in the array of four electrodes, can lead to serious measuring failures in the low-frequency range. An optimal solution to this problem can be obtained if the electrode impedances are frequency independent. A comparative study of the electrode impedances of Pt and PtIr electrodes and of a new electrode material (Ir-AIROF) is reported. It is shown that the impedance of Ir-AIROF electrodes is relatively low and almost frequency independent. Therefore the use of Ir-AIROF electrodes provides a solution to the problem mentioned above

Electrical conductivity of skeletal muscle tissue: Experimental results from different musclesin vivo

For a quantitative EMG analysis reliable and unique values of the electrical conductivities of skeletal muscle tissuein vivo are indispensable. Literature values do not satisfy these criteria. In the paper experimental results of conductivity measurements (four-electrode technique) on musclesin vivo on which quantitative EMG experiments are also carried out are reported. Depending on the interelectrode distance (IED) in the four-electrode technique the results appear to be either frequency dependent (IED=0·5 mm) or frequency independent (IED=3·0 mm). The anisotropy value obtained with an IED of 0·5 mm is frequency dependentin the frequency range of EMG signals. Experimental results of different muscle types (white muscle, EDL rat and red muscle, soleus rat) appear to be significantly different

Model of electrical conductivity of skeletal muscle based on tissue structure

Recent experiments carried out in our laboratory with the four-electrode method showed that the electrical conductivity of skeletal muscle tissue depends on the frequency of the injected current and the distance between the current electrodes. A model is proposed in order to study these effects. The model takes into account the structure of the tissue on the scale of individual fibres. It discerns three main components with respect to electrical properties: (a) extracellular medium with electrical conductivity σe; (b) intracellular medium with electrical conductivity σi; (c) muscle fibre membrane with impedance Zm. The model results show an apparent frequency dependence of the electrical conductivity of skeletal muscle tissue, as well as the way the conductivity is affected by the length the current is conducted