Critical role of central facilitation in the glottic closure reflex

The sphincteric function of the larynx, essential to lower airway protectio n. is most efficiently achieved through strong reflex adduction by both voc al cords. We hypothesize that central facilitation is an essential componen t of a bilateral adductor reflex and that its disturbance could result in w eakened sphincteric closure. Six adult 50-kg pigs underwent evoked response laryngeal electromyography under 0.5 to 1.0 minimal alveolar concentration (MAC) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and reco rding electrodes were positioned in the ipsilateral and contralateral thyro arytenoid muscles. Consistent threshold responses were obtained ipsilateral ly from 0.5 to 1.0 MAC anesthesia. However, the contralateral reflex respon ses approached 0% in successive trials as anesthetic levels approached 1.0 MAC. Alteration of central facilitation by deepening anesthesia abolishes t he crossed adductor reflex. predisposing to a weakened glottic closure resp onse. A precise understanding of this effect may improve the prevention of aspiration in patients emerging from prolonged sedation or under heavy psyc hotropic control.