Abstract
Transcutaneous electrical stimulation can depolarize nerve or muscle cells applying impulses through electrodes attached on the skin. For these applications, the electrode-skin impedance is an important factor which influences effectiveness. Various models describe the interface using constant or current-depending resistive-capacitive equivalent circuit. Here, we develop a dynamic impedance model valid for a wide range stimulation intensities. The model considers electroporation and charge-dependent effects to describe the impedance variation, which allows to describe high-charge pulses. The parameters were adjusted based on rectangular, biphasic stimulation pulses generated by a stimulator, providing optionally current or voltage-controlled impulses, and applied through electrodes of different sizes. Both control methods deliver a different electrical field to the tissue, which is constant throughout the impulse duration for current-controlled mode or have a very current peak for voltage-controlled. The results show a predominant dependence in the current intensity in the case of both stimulation techniques that allows to keep a simple model. A verification simulation using the proposed dynamic model shows coefficient of determination of around 0.99 in both stimulation types. The presented method for fitting electrode-skin impedance can be simple extended to other stimulation waveforms and electrode configuration. Therefore, it can be embedded in optimization algorithms for designing electrical stimulation applications even for pulses with high charges and high current spikes.
Highlights
Electrical stimulation is a powerful tool for diagnosis, treatment and function restoration in the human body
The impedance of the skin-electrode interface should be carefully considered, since previous reports have shown that it has a non-negligible direct influence on the stimulation outcome [1]
The slight decreasing trend of Rs values suggests that the electrical field induced in an organism leads to electroporation in deeper lying tissue
Summary
The main aim of this work is to provide extended systematic experimental data on application of CC and VC biphasic rectangular stimuli via electrodes of various sizes and associated model calculations that allow to some extend general predictive calculations for other stimulus shapes and stimulation setups
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