Imposing movements in vocal folds via electrical stimulation

Objectives: According to the most of the previous studies inducing movements in internal laryngeal muscles by Transcutaneous Electrical Stimulation (TES) was impossible. However, the movements have been reported after using needle electrodes inserted in Internal Superior Laryngeal Nerve (ISLN). Herein, we aimed to apply an innovated TES protocol to cause movements in vocal folds.Methods: A short duration and high frequency electrical current was applied by two surface electrodes just above the entrance of ISLN to larynx. The subjects were 32 normal participants (mean age=23.87; SD=3.43). During TES application, the vocal folds movements were examined by flexible videonasolaryngoscopy. Statistical paired t-test was used to analyze the differences of vocal folds opening angle, in degrees, during rest and TES periods. Furthermore, the movements were judged by seven experienced speech pathologists via a nine point rate scale from -1 (any abduction) to 8 (complete adduction).Results: The mean vocal folds adduction increased by 35.68 degrees (t=9.35, p> 0.001) due to the TES application. The mean qualitative scores assigned by raters to each subject were between 6 and 7 point which indicates an acceptable adduction in vocal folds through the TES.Conclusion: Unlike previous studies, the applied TES protocol in this research induced significant vocal fold movements. This might be attributed to our different stimulation parameters which were designed to penetrate deeply and stimulate ISLN specifically. Worth to note, we introduced a novel TES protocol which should be confirmed and then examined as a complementary therapy for neurologic voice disorders in future studies.

Keywords:

vocal cords , electric stimulation , laryngeal