Back Stimulation with Gaussian Frequency Biphasic Burst Stimulation for Swallowing Motor Activation

• Published in: Physiology (Bethesda, Md.) Md.), 2024-05, Vol.39 (S1)
• Main Authors: Morimoto, In, Frazure, Michael, Iceman, Kimberly, Koike, Takuji, Pitts, Teresa
• Format: Article
• Language: English
• ISSN: 1548-9213; 1548-9221
• DOI: 10.1152/physiol.2024.39.S1.764

Abstract only Aspiration of food containing bacteria or saliva into the trachea, leading to bacterial lung infection, is termed aspiration pneumonia. In the United States, aspiration pneumonia results in over 57,000 deaths annually, constituting 2.3% of the total mortality. Similarly, according to data from 2021 in Japan, more than 49,000 individuals succumbed to aspiration pneumonia, accounting for approximately 3.4% of the total mortality, making it the sixth leading cause of death in Japan. Notably, the risk of mortality due to aspiration pneumonia can be mitigated through early detection and prevention of swallowing disorders. Consequently, this research focuses on rehabilitation strategies for swallowing disorders. Swallowing is a coordinated motor function, orchestrated by a program involving multiple muscles under the directives of the Swallow Central Pattern Generator (CPG) located in the medulla. Thus, activation of the Swallowing CPG is pivotal for effective swallowing rehabilitation. To this end, we propose a novel method to activate the Swallow CPG by electrical stimulating of the back. The back has been recognized as a site that activates the expiratory phase of respiration, where the swallow reflex is often triggered. Moreover, given the adjacency of the Swallowing CPG and the Respiratory CPG, we postulate that stimulating the back to activate the expiratory phase can lead to enhanced activation of swallowing movements. Methods: Surface electrodes were placed on the back (T9~T10) and neck of adult rats. Initially, burst stimuli of two polarities were randomly generated at frequencies of either 30 Hz or 300 Hz in accordance with a Gaussian distribution at one of the two sites. The electric stimuli were applied for 120 seconds, three times at each location. To evaluate the impact of stimulus frequency and location on swallowing movements, we compared four groups (n=4 in each group). Following stimulation at one site, identical waveforms of stimulation were administered to both the back and neck for 120 seconds, three times. Swallowing was induced by water injection into the mouth after each stimulation. Electromyography (EMG) of three swallow-related muscles (mylohyoid, thyroarytenoid, and thyropharyngeus) was recorded and their amplitudes compared, both before stimulation (control) and after six consecutive stimulations. Results: It was observed that stimulation of both the back and neck resulted in larger maximum muscle potentials in all meas