Objective: To characterize the changes in the anteroposterior dimensions of both the retropalatal and retrolingual airway spaces of the pharynx and hyoid bone position during hypoglossal nerve stimulation under general anesthesia in subjects with obstructive sleep apnea.
Study design: Cross-sectional.
Setting: Academic center.
Subjects and methods: Cross-table fluoroscopic images obtained during hypoglossal nerve stimulation were studied in 26 subjects enrolled in the Apnex Medical Hypoglossal Nerve Stimulation (HGNS) system feasibility trials. Changes in the anteroposterior dimensions (2-dimensional) of the retropalatal and retrolingual airway spaces and hyoid bone position were recorded. Measurements were estimated in millimeters and standardized to each subject's C3 vertebral height. Opening of the pharyngeal airspace was examined relative to body mass index.
Results: During hypoglossal nerve stimulation, all subjects demonstrated anterior displacement of the tongue base on fluoroscopy. The average retrolingual airway opening was 0.71 ± 0.23 C3 vertebral body heights (9 ± 3 mm). Opening of the retropalatal airway with stimulation occurred in 65% (15/23) of subjects. When present, the average opening was 0.42 ± 0.14 vertebral heights (5 ± 3 mm). Anterior displacement of the hyoid occurred in 92% (23/25) of subjects. Retrolingual airway opening was independent of baseline body mass index.
Conclusion: Unilateral hypoglossal nerve stimulation results in anterior tongue base displacement and an increase in the anterior-posterior retrolingual airway dimensions of the pharynx, independent of body mass index. Opening of the retropalatal airway occurred in a majority of subjects and had a trend toward correlation with body mass index.