Laryngeal Regulation Of Respiratory Airflow.

Abstract We measured laryngeal resistance in spontaneously breathing anesthetized cats and upper airway resistance in unanesthetized, unrestrained cats. In anesthetized cats breathing air, the vocal cords were abducted during inspiration and moved toward the midline during expiration, thus increasing laryngeal resistance. With CO2 administration the inspiratory abduction of the cords was more pronounced, and the cords remained open throughout most of expiration as well. Thus hypercapnia decreased laryngeal resistance, especially during expiration. Electromyographic (EMG) studies indicated that the respiratory movements of the cords are caused by phasic contractions of the posterior cricoarytenoid (PCA) muscles. The responses to hypercapnia and lung inflation suggested that PCA motoneurones have central connections with both inspiratory and expiratory neurones. In unanesthetized cats, upper airway resistance was higher during expiration than during inspiration. CO2 administration reduced upper airway resistance, especially during expiration. These findings, together with those reported in the accompanying paper, indicate that the larynx is a significant respiratory effector organ, which provides fine regulation of respiratory airflow, particularly during expiration.