Design of a Multi-site Electrical Stimulation System for Transcutaneous Lumbar Posterior Roots Stimulation

Abstract

Lumbar posterior roots in humans can be activated by transcutaneous electrical spinal cord stimulation (tSCS). This method employs paravertebral stimulation and can be used to control spasticity and modify gait patterns in people with upper motor neuron dysfunctions. Furthermore, when single stimuli are applied reflexes are elicited in all lower limb muscle groups simultaneously, posterior root-muscle reflexes, which can be used for electrophysiological studies. It is important to control stimulation settings and site. Here, a novel multi-site stimulation system is presented. The stimulation module is based on a microcontroller and delivers biphasic, voltage-controlled pulses with amplitudes up to +/-45 V. The stimulator is controlled and powered by a computer using the Universal Serial Bus (USB) data link. Software-controlled stimulation allows flexible parameter settings. The stimulator integrates a measurement unit, which records pulse shape and electrode impedance. An electrode array, based on a flexible printed circuit board with 8 gold coated square electrode contacts (1x1cm²) in a row on a flexible polymer base foil. These foil strips provide access lines and mechanical fixation means to assemble 2-dimensional array configurations. A 3x8 contact configuration was tested for delivery of impulses to the skin surface above the rosto-caudal spinal cord in combination with an abdominally placed 200cm² reference electrode.

Selectivity in eliciting reflex activity in lower extremity muscle groups could be demonstrated with potential advantages in automated stimulation site adjustment and multi-site test procedures.