Involvement of hypoglossal and recurrent laryngeal nerves on swallowing pressure

Swallowing pressure generation is important to ensure safe transport of an ingested bolus without aspiration or leaving residue in the pharynx. To clarify the mechanism, we measured swallowing pressure at the oropharynx (OP), upper esophageal sphincter (UES), and cervical esophagus (CE) using a specially designed manometric catheter in anesthetized rats. A swallow-evoked by punctate mechanical stimulation to the larynx-was identified by recording activation of the suprahyoid and thyrohyoid muscles using electromyography (EMG). Areas under the curve of the swallowing pressure at the OP, UES, and CE from two trials indicated high intra-subject reproducibility. Effects of transecting the hypoglossal nerve (12N) and recurrent laryngeal nerve (RLN) on swallowing were investigated. Following bilateral hypoglossal nerve transection (Bi-12Nx), oropharyngeal pressure was significantly decreased, and time intervals between peaks of thyrohyoid EMG bursts and oropharyngeal pressure were significantly shorter. Decreased oropharyngeal pressure and shortened times between peaks of thyrohyoid EMG bursts and oropharyngeal pressure following Bi-12Nx were significantly increased and longer, respectively, after covering the hard and soft palates with acrylic material. UES pressure was significantly decreased after bilateral RLN transection compared with that before transection. These results suggest that the hypoglossal nerve and RLN play crucial roles in oropharyngeal and UES pressure during swallowing, respectively. We speculate that covering the palates with a palatal augmentation prosthesis may reverse the reduced swallowing pressure in patients with hypoglossal nerve or tongue damage by the changes of the sensory information and of the contact between the tongue and plates.