Equivalent Circuit Model to Simulate the Neuromuscular Electrical Stimulation

In this study, an equivalent circuit model (ECM) to simulate the Neuromuscular Electrical Stimulation (NMES) has been developed. The ECM includes all regions from the transcutaneous electrodes to the neuron cell membrane to simulate the nerve stimulation with biphasic rectangular waveform. The model was developed as a series of ‘tissue subsystems’, hence these can be treated independently. The frequency and current density dependency of the electrodeelectrolyte and gel-skin interfaces and the frequency dependency of the tissues were considered. The ECM was used to simulate in PSpice 6 strength–duration curves obtained by experimental transcutaneous stimulation of the extensor muscles in the forearm of one subject using two fully gelled electrodes of size 45x80 mm². To monitor muscle contraction, a three axial accelerometer was placed on the proximal phalange of the middle finger. The mean voltage response in the stimulation experiments was compared with ECM simulations. The energy dissipation in the human tissue layers was investigated using the ECM. The correlation coefficient was used to evaluate quantitatively the agreement between simulations and experiments.