0333 Stylopharyngeus and Pharyngeal Nerve Transections Exhibit Flatness Airflow Pattern in Conscious Rats

Abstract Introduction The Guilleminault “tent hypothesis” (1978) proposed the coordinated action of stylopharyngeus and pharyngeal constrictor muscles in humans maintain upper airway patency. We previously demonstrated that bilateral transection of the stylopharyngeus muscles (upper airway dilator muscles) caused flattening of the inspiratory waveform flow in conscious rats consistent with inspiratory flow limitation. Here, we quantify the duration of the inspiratory flattening after bilateral stylopharyngeus transection and test the resilience of the system by additionally transecting the pharyngeal branch of the vagus nerve (Ph-X), innervating the pharyngeal constrictor muscles. Methods Adult male Sprague-Dawley rats underwent one of three procedures: 1) Bilateral stylopharyngeus transection (BST, n = 10), 2) Bilateral transection of stylopharyngeus and Ph-X (BST+BTPB, n = 3), 3) Sham surgery (n = 3). Respiratory flow was acquired using whole-body plethysmography (3-5 hours/session). Fifty stable breaths were analyzed at baseline and postoperative days (PD) 1, 3, 5, and 7. Median of inspiratory time (TI), duration of flatness (Flat), and the Flat/TI ratio were calculated. Statistical analysis used the Wilcoxon signed-rank test and Mann-Whitney U test. Results BST group vs sham group showed significant differences compared to baseline on PD1 in TI (sham -0.02s, BST 0.08s, p = 0.049), Flat (sham 0s, BST 0.09s, p = 0.014), and Flat/TI (sham 0s, BST 0.29s, p = 0.014). Compared to baseline, the BST group showed significant differences in TI (Baseline 0.23s, PD1 0.29s, p = 0.002), PD5 (0.25s, p = 0.037), and PD7 (0.25s, p = 0.002), Flat on PD7 (Baseline 0.03 s, PD7 0.20s, p = 0.002) and Flat/TI on PD1 (Baseline 0.15s, PD1 0.44s, p = 0.002). BST group vs BST+BTPB group showed significant differences in Flat (BST 0.01s, BST+BTPB 0.09s, p = 0.014) and Flat/TI on PD7 (0.26s, p = 0.014). Conclusion Bi-Stylopharyngeus transections alone increased Flat/TI recovered by PD7. Combined BST+BTPB group persisted the effect to PD7. Sham control did not show difference. In this model system, both dilator and constrictor pathways are needed to preserve inspiratory flow. Support (if any) Divisional funds. E.H. is supported by JRS, JSSR, Marubun Research Promotion Foundation, and Nara Medical University.