Involvement of hypoglossal and recurrent laryngeal nerves on swallowing pressure

Abstract

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.

Involvement of the epithelial sodium channel in initiation of mechanically evoked swallows in anaesthetized rats

“…We found that the SH and TH durations and the onset and offset lag times between these muscles showed high intraindividual reproducibility. Consistent with these results, we previously reported that the swallowing pressure at the oropharynx, upper oesophageal sphincter and cervical oesophagus exhibited high intraindividual reproducibility (Tsujimura et al 2018). Jafari et al (2003) suggested that the afferent signals from the internal branch of the SLN, which contains afferents from the supraglottic larynx and epiglottis, play an important role in normal swallowing, particularly in facilitating laryngeal closure during swallowing.…”

“…Consistent with these results, we previously reported that the swallowing pressure at the oropharynx, upper oesophageal sphincter and cervical oesophagus exhibited high intraindividual reproducibility (Tsujimura et al . ). Jafari et al .…”

“…With the rat in the supine position, a midline incision was made along the ventral aspect from the pogonion to the caudal portion of the neck. To monitor respiratory efforts, the trachea was cannulated at its caudal-most end with a luer stub adaptor, and a pressure transducer was attached to a side port of the tracheal cannula (Tsujimura et al 2017(Tsujimura et al , 2018. Bipolar enamel-coated copper wire electrodes (0.23 mm diameter and 2 mm interpolar distance) were inserted into the left suprahyoid (SH) and thyrohyoid (TH) muscles for electromyographic (EMG) recording.…”

Recurrent laryngeal nerve transection in mice results in translational upper airway dysfunction

“…Yet, while murine laryngeal anatomy limits the assessment of aspiration (Lever, Braun, et al, ; Lever, Brooks, et al, ), other outcome metrics, especially those related to esophageal dysphagia, may be affected by RLN injury in this model. As the RLN also provides innervation to the esophagus in addition to the intrinsic laryngeal muscles, the trend for increased esophageal transit time following RLN transection observed in this study is consistent with pharyngoesophageal dysfunction documented in other RLN injury models (Fukushima et al, ; Gould et al, ; Tsujimura et al, ) and human unilateral VF paralysis patients (Aneas, Ricz, Mello‐Filho, & Dantas, ; Wilson, Pryde, White, Maher, & Maran, ). As such, future studies may benefit by utilizing a higher speed camera to better capture the start and end points of esophageal bolus transit or alternative methods, such as manometry, to accurately determine if significant pharyngeal or esophageal dysphagia exists in this small, fast‐drinking species.…”

Specific Vagus Nerve Lesion Have Distinctive Physiologic Mechanisms of Dysphagia

“…Although insult to either SLN or RLN results in increased aspiration (16,17), these two lesions impact the size and shape of the bolus in infant animal models differently (13,18,19). After surgical transection of the right SLN, the volume of the bolus was greater (13), although bolus size was not associated with increased aspiration.…”