Search

A funder is missing from the manuscript’s Funding section. The correct funding statement is as follows: JLVL was supported by the Mexican Council of Research and Technology (CONACYT) grant: 236850 (www.conacyt.mx). This work was also supported by the Vienna Science and Technology Fund (WWTF), Proj.Nr. LS11-057 (www.wwtf.at), and the Wings for Life Spinal Cord Research Foundation (WfL), Proj.Nr. WFL-AT-007/11 (http://www.wingsforlife.com). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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. © 2015 Vargas Luna et al.