Properties of hyoid muscle contraction during tongue lift measurement.

BACKGROUND: Tongue lift movement (TLM) task is considered a treatment strategy in dysphagic patients. However, there is no evidence of effect of sustained tongue movements on the related muscle contraction. OBJECTIVES: The present study aimed to characterise the properties and time-dependent changes of the electromyographic (EMG) features of suprahyoid muscles during TLM. METHODS: Twenty young healthy volunteers were instructed to perform TLM at maximum effort in either the anterior or the posterior position, during measurement of tongue pressure for 7 s. Supra- (S-hyo) and infra-hyoid (I-hyo) EMGs were recorded. The area and power frequency of EMG burst and the area under the curve of tongue pressure were compared among the conditions: trials (1st, 2nd vs 3rd trials); anterior vs posterior TLM; and early vs late 3 s of each trial. RESULTS: There was no difference in the tongue pressure among trials or between the early and late 3 s. Anterior tongue pressure was significantly higher than posterior tongue pressure (P < .001). The area of I-hyo EMG burst was significantly larger (P = .044), and the power frequency of I-hyo EMG burst was significantly smaller (P = .042) during posterior TLM than anterior TLM. A significant difference in the power frequency of both EMG bursts was observed between early and late stages during both anterior (P < .05) and posterior (P < .01) TLM. CONCLUSION: Hyoid muscles may compensate for rapid fatigue of the tongue muscle to maintain tongue pressure by changing their activity pattern during tongue pressure generation.

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 intrasubject reproducibility. Effects of transecting the hypoglossal nerve (12N) and recurrent laryngeal nerve (RLN) on swallowing were investigated. Following bilateral hypoglossal nerve transection (Bi-12Nx), OP pressure was significantly decreased, and time intervals between peaks of thyrohyoid EMG bursts and OP pressure were significantly shorter. Decreased OP pressure and shortened times between peaks of thyrohyoid EMG bursts and OP 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 12N and RLN play crucial roles in OP 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 12N or tongue damage by the changes of the sensory information and of the contact between the tongue and a palates. NEW & NOTEWORTHY Hypoglossal nerve transection reduced swallowing pressure at the oropharynx. Covering the hard and soft palates with acrylic material may reverse the reduced swallowing function caused by hypoglossal nerve damage. Recurrent laryngeal nerve transection reduced upper esophageal sphincter negative pressure during swallowing.