Development of an electrical stimulator for swallow facilitation through action on spinal circuits

This paper studies a rehabilitation method to centrally facilitate swallowing by stimulating the peripheral sensory nervous system. We developed an electrical device using surface electrodes to promote swallowing through activation of spinal afferent pathways by effectively stimulating the sensory nerves of the back using a Gaussian frequency biphasic burst waveform, which differs from the conventional electrical stimulation method targeting the neck muscles. To validate its effectiveness, the Gaussian frequency biphasic burst waveform was generated in a Gaussian distribution with a mean of 30 Hz, and randomly applied as a burst to either the back or neck of adult rats. Experiments using a Gaussian frequency monophasic pulse waveform were conducted as a comparative reference. Swallow related electromyographic (EMG) activity from three upper airway muscles before and after a series of three electrical stimulation trials were compared. The current increased with the Gaussian biphasic waveform at 2V compared to the Gaussian monophasic waveform at 5V, suggesting the potential to reduce impedance between the skin and electrodes. Both the Gaussian frequency monophasic and biphasic burst waveforms increased the EMG amplitude of swallow related muscles, suggesting effective activation of the swallow reflex circuit. Furthermore, stimulation near the T9-T10 region of the back resulted in increased amplitude of the thyropharyngeus muscle early in the stimulation protocol for both waveform types, demonstrating the potential for improvement in swallowing dysfunction by electrical stimulation of the T9-T10 region of the back using surface electrodes.