Author(s)
Eriko Shimazaki M.D.
Yoichiro Sugiyama M.D., Ph.D.
Tomoya Ishida M.D.
Yuki Sato M.D.
Hiroyuki Shuto M.D., Akimichi Minesaki M.D., Ph.D.
Affiliation(s)
Department of Otolaryngology-Head and Neck Surgery, Saga University Faculty of Medicine, Saga, Saga, Japan;
Abstract:
Objective: Prolonged stimulation of the larynx and trachea may diminish sensitivity in the airway, resulting in a decline in swallowing function. Adequate airflow through the airway is crucial for restoring this function. To investigate the impact of aeration and airway clearance in the larynx and trachea on the swallowing reflex, we recorded the likelihood of pharyngeal swallowing and neuronal activities in the dorsal medulla, including the swallowing center, in response to the expiratory airflow in perfused rats.
Methods: We measured the number of swallows triggered by electrical stimulation of the superior laryngeal nerve or oral water injection during continuous airflow from the trachea following long-time fluid retention in the lower airway in 15 animals. Subsequently, we sectioned the superior laryngeal and vagus nerves and observed the changes in the number of swallows. In 8 animals, we recorded changes in the neuronal activities in the dorsal medulla due to the airflow.
Results: The number of swallows showed significant increases following airflow; which was significantly reduced after the nerve sections. The activities of 177 neurons were recorded, with 44 neurons displaying swallowing-related activity. The spontaneous firing rates of 40.9% of the swallowing-related and 36.8% of the non-swallowing-related neurons exhibited changes more than 30% due to the airflow.
Conclusion: Laryngotracheal airflow is crucial for maintaining swallowing by serving optimal sensory information to the swallowing center through the larynx and trachea. These findings provide practical insights for patients with reduced reflexibility of swallowing after experiencing prolonged irritation of the airway, such as post-extubation dysphagia.