ACTIVATION OF INTRINSIC LARYNGEAL MUSCLES DURING COUGH

We studied the pattern of discharge of the posterior cricoarytenoid (P CA), cricothyroid (CT), thyroarytenoid (TA), and arytenoideus transver sus (AR) muscles during cough in 12 anesthetized dogs. Diaphragm elect romyographic (EMG) activity was also recorded, together with subglotti c and esophageal pressures. Trains of repetitive coughs were induced b y mechanically stimulating the tracheobronchial airway. Trials with th e upper airway isolated from and connected to the lower airway were pe rformed before and following bilateral sectioning of the internal bran ch of the superior laryngeal nerve (SLN). The immediate effect of trac heal stimulation was an ''apneic'' period at FRC, during which the PCA , a laryngeal abductor, showed a progressive increase in activity acco mpanied by small, variable increases in the activity of the CT and the laryngeal adductors, the TA and AR. The subsequent cough efforts were divided into three phases: inspiration, glottic narrowing, and forced expiration. PCA activity was greatest during the inspiratory phase an d CT activity was greatest during the expiratory phase. Peak subglotti c pressure occurred during glottic narrowing and coincided with the gr eatest activation of the TA and AR during the cough effort, and suppre ssion of the PCA and CT. The patterns of EMG activation were not affec ted by the route of breathing or SLN section. The results suggest the presence of a uniquely central process controlling laryngeal muscles d uring cough, independent of laryngeal sensory feedback.