Bilateral Stylopharyngeus Transection Alters Respiratory Airflow in Conscious Rats

Background/Objectives: Upper airway patency is a key pathophysiological factor in obstructive sleep apnea (OSA). Research has primarily focused on the role of the genioglossus muscle in maintaining airway patency in OSA. However, hypoglossal nerve stimulation (HNS) therapy, which activates the genioglossus muscle, has been associated with poor outcomes in patients with lateral oropharyngeal collapse. The stylopharyngeus muscle is an upper airway dilator muscle that supports the lateral pharyngeal wall. Its role in maintaining upper airway patency and its effect on normal respiratory airflow is unclear. We hypothesize that bilateral transection of the stylopharyngeus muscles disrupts normal breathing. Currently, no animal model depicting lateral pharyngeal collapse has been reported. This study aims to introduce a novel rodent model with bilateral transection of the stylopharyngeus muscles to examine its effect on respiratory airflow and tracing. Methods: Adult male Sprague Dawley rats were divided into two groups: (1) bilateral stylopharyngeus muscle transection (n = 4) and (2) sham surgery (n = 2). Under anesthesia, the stylopharyngeus muscle was transected bilaterally in the transection group, while only exposure of the muscle was performed in the sham group. Respiratory airflow was measured using whole-body plethysmography before and after surgery, and airflow tracings were analyzed. Results: Significant alterations in respiratory airflow and tracings, particularly a flattening in inspiratory flow and sharp expiratory peaks, were observed on the first post-operative day in the transection group. The flattening of the inspiratory flow persisted over 3 days. No significant changes were noted in the sham group. Conclusions: Bilateral stylopharyngeus muscle transection alters normal airflow in a conscious rodent model, supporting the hypothesis that stylopharyngeus muscle plays a vital role in shaping respiratory airflow. The flattening of the inspiratory airflow is an indication of flow limitations through the upper airway patency due to the loss of stylopharyngeus function.