Ansa Cervicalis Stimulation Effects on Upper Airway Patency: A Structure-Based Analysis.

RATIONALE Ansa cervicalis stimulation (ACS) of the infrahyoid muscles has been proposed as a neurostimulation therapy for obstructive sleep apnea (OSA). ACS stabilizes the pharynx by pulling it caudally, but its specific effects on flow limitation caused by palatal, oropharyngeal lateral wall, tongue base, or epiglottis collapse remains unclear. OBJECTIVES To quantify the effect of ACS on collapsibility of different pharyngeal flow-limiting structures. METHODS Participants with OSA underwent bilateral ACS during drug-induced sleep endoscopy. Maximum inspiratory airflow was assessed over a range of positive airway pressures while ACS was applied. The flow-limiting structure for each breath was classified based on manometric and endoscopic findings and a linear mixed-effects model characterized their response to ACS. The influence of patient characteristics was explored with univariate models. MEASUREMENTS AND MAIN RESULTS Forty-one participants yielded 1761 breaths for analysis. On average, bilateral ACS decreased the observed pharyngeal critical closing (PCRIT) and opening (POPEN) pressures by -3.0 [95% confidence interval: [-3.6, -2.3] and -3.7 [-4.4, -3.0] cmH2O, respectively (p<0.001). During tongue base obstruction, modeled ACS effects for PCRIT and POPEN were -2.0 [-2.7, -1.4] and -3.1 [-3.8, -2.4] cmH2O, respectively (p<0.001). Greater reductions were generally observed for other flow-limiting structures. A lower apnea-hypopnea index was associated with a greater decrease in POPEN (p<0.01). Other patient characteristics, including body mass index, did not influence PCRIT or POPEN (p>0.05). CONCLUSIONS Bilateral ACS decreased collapsibility of all airway flow-limiting structures. ACS generally had greater effects on palatal, oropharyngeal lateral wall, and epiglottic collapse than the tongue base.