Abstract Rationale Upper airway patency depends on the coordination of multiple pharyngeal muscles. We previously demonstrated that bilateral transection of stylopharyngeus (an upper airway dilator) in conscious rats produced a flattening of the inspiratory waveform flow consistent with inspiratory flow limitations. This study aimed to assess whether the impairment persists or whether the network of pharyngeal muscles can adapt and restore the normal inspiratory waveform. Furthermore, we examined the system’s resilience with an additional transection of the pharyngeal nerve of the vagus (Ph-X) which innervates the pharyngeal constrictor muscles. Methods Adult male Sprague-Dawley rats underwent one of four interventions: 1) Bilateral stylopharyngeus transection (BST, n = 10), 2) Bilateral transection of Ph-X (BTPB, n = 5), 3) Bilateral transection of both (BST+BTPB,n = 5), and 4) Sham (n = 5). Respiratory airflow was obtained using whole-body plethysmography (3-5 h/session). 50 stable breaths were identified and inspiratory time (TI), expiratory time (TE), total breath duration (TTOT), and respiratory frequency (fR) were measured at prior to surgery (baseline) and postoperative days (PD) 1, 3, 5, and 7. Inspiratory airflow waveforms were captured by cycle-triggered averaging. Statistical analysis included Friedman with Wilcoxon post-hoc tests and Kruskal-Wallis with Mann-Whitney U tests. Results BST and BTPB groups exhibited significant difference in the percentage change from baseline in TI, TTOT, and fR compared to sham group (Table (1) and (2)). The BST+BTPB group only exhibited significant percentage changes in TI compared to sham group (Table (3)). Cycle trigger averages showed initial flattening of the inspiratory waveform exhibited by BST and BTPB group on PD1 diminished by PD3-5. The BST+BTPB group exhibited the same recovery PD3-5, however, the flattened inspiratory waveform presented on PD7. Conclusions Bilateral stylopharyngeus transection induced a transient prolongation of inspiratory time and a flattening of inspiratory waveform that resolved within days, indicating short-term adaption possibly mediated by the brainstem. Bilateral transection of Ph-X caused minimal changes, whereas combined bilateral transection of stylopharyngeus muscle and Ph-X produced flattening and timing instability that transiently resolved but began to present again 7 days later. These findings suggest CN IX and CN X branches play distinct roles and the system can adapt to the acute loss of one effector on pharyngeal muscles, however the combined loss of both effectors disrupt the system’s inherent resilience. This abstract is funded by: divisional funds from the Department of Pulmonary, Critical Care, and Sleep Medicine, Case Western Reserve University. E.H. is supported by The Japanese Respiratory Society Fellowship Grant, Research Promotion Foundation the International Exchange Grant, Support for Sleep Research by the Japanese Society of Sleep Research and Marubun Research Promotion Foundation the International Exchange Grant.
Hamada et al. (Fri,) studied this question.