Effect of inhaled carbon dioxide on laryngeal abduction

Hypercapnia produces a profound effect on respiratory drive and upper airway function to maintain airway patency. Previous work has evaluated the effects of hypercapnia on the sole arytenoid abductor, the posterior cricoarytenoid (PCA), using indirect measures of func-tion, such as electromyography and direct nerve recording. Here we describe a novel method to evaluate PCA function in anesthetized animals and use this method to determine the effects of hypercapnia on PCA function. Eight dogs were anesthetized, and a laryngeal mask airway was used, in combination with high-speed videoendoscopy, to evaluate laryngeal function. A stepwise increase in inspired partial pressure of CO2 produced marked arytenoid abduction above 70-mmHg end-tidal CO2 (ETCO2) (P 0.001). Glottic length increased above 80-mmHg ETCO2 (P 0.02), and this lead to underrepresen-tation of changes in glottic area, if standard measures of glottic area (normalized glottic gap area) were used. Use of a known scale t