Ansa Cervicalis Stimulation Increases Pharyngeal Patency in Patients with Obstructive Sleep Apnea
Rationale: Hypoglossal nerve stimulation (HNS) is an alternative treatment option for obstructive sleep apnea (OSA) that reduces pharyngeal collapsibility, but HNS non-responders often demonstrate continued retropalatal and lateral pharyngeal wall collapse. Recent evidence suggests that caudal pharyngeal traction with sternothyroid muscle contraction via ansa cervicalis stimulation (ACS) can also stabilize the pharynx, but the underlying mechanisms have not been elucidated. Objectives: To evaluate the effect of ACS on pharyngeal patency during expiration when the airway is most hypotonic. Methods: Eight participants with OSA underwent sustained ultrasound-guided fine-wire stimulation of the medial branch of the right hypoglossal nerve with and without transient stimulation of the branch of the ansa cervicalis nerve plexus innervating the right sternothyroid muscle during drug-induced sleep endoscopy. Airway cross-sectional area and expiratory airflow (VE) were measured from endoscopy video with ImageJ and pneumotachometry, respectively. Measurements and Main Results: ACS significantly increased retropalatal cross-sectional area (CSArp) to 211% [159-263] of unstimulated CSArp (p<0.05). Adding ACS to HNS increased CSArp from baseline by 341% [244-439] (p<0.05), a 180% [133-227] increase over isolated HNS (p<0.05). ACS increased VE from baseline by 177% [138-217] (p < 0.05). Adding ACS to HNS increased VE by 254% [207-301], reflecting decreases in pharyngeal collapsibility. Conclusions: Combining ACS with HNS increased retropalatal cross-sectional area and increased expiratory airflow, suggesting decreases in pharyngeal collapsibility. Our findings suggest that ACS exerts caudal traction on the upper airway through sternothyroid muscle contraction, and that it may augment HNS efficacy in patients with OSA.