Author(s)
Joshua J. Sturm MD PhD
Oleg Modik PhD
Maria V. Suurna MD FACS
Affiliation(s)
Weill Cornell Medicine
Abstract:
Educational Objective: At the conclusion of this presentation, the participants should be able to explain the nature of tongue muscle activation by hypoglossal nerve stimulation, and discuss how intraoperative neurophysiological monitoring of tongue muscle activation may provide essential data for stimulus optimization in the treatment of obstructive sleep apnea. Objectives: Upper airway stimulation for obstructive sleep apnea (OSA) via hypoglossal nerve (HGN) implantation reduces airway obstruction by selectively stimulating nerve fibers that innervate tongue protrusor muscles, while avoiding fibers that innervate retractor muscles. This selective stimulation likely depends upon the location, intensity and type (bipolar vs. unipolar) of electrical stimulation delivered, yet the nature of muscle activation has not been fully elucidated. This study investigates tongue muscle activation by HGN stimulation using intraoperative nerve integrity monitoring (NIM) in conjunction with electromyography (EMG). Study Design: Case series. Methods: Case series of 10 patients undergoing unilateral hypoglossal nerve stimulator implantation for OSA. Data included EMG responses in tongue protrusor (genioglossus), retractor (styloglossus and hyoglossus) and intrinsic (transverse and vertical) muscles in response to intraoperative bipolar probe electrical stimulation of lateral and medial branches of HGN and to implantable pulse generator (IPG) unipolar and bipolar settings after placement of the stimulation cuff. Statistical analyses performed using GraphPad Prism (La Jolla, CA). Results: Stimulation of medial HGN branches resulted in EMG responses in protrusor muscles but not in retractors, whereas stimulation of lateral HGN branches drove responses in retractor muscles. Variable intrinsic muscle responses were observed with stimulation of lateral and medial branches. Unipolar and bipolar HGN stimulation configurations resulted in unique patterns of muscle activation. After electrode cuff placement, only included HGN branches robustly activated protrusor muscle responses. Conclusions: The relative activation of tongue protrusor, retractor and intrinsic musculature by HGN stimulation is determined by stimulus location, intensity and type. Intraoperative neurophysiological monitoring of tongue muscle activation enables proper electrode cuff placement and may provide essential data for stimulus optimization.