Effects of vagal afferents on laryngeal responses to hypercapnia and Hypoxia

Abstract

The effects of hypercapnia and isocapnic hypoxia on the respiratory movements of the vocal cords were assessed in anesthetized cats before and after bilateral vagotomy. In vagally intact animals, these stimuli lowered laryngeal airflow resistance by increasing both inspiratory and expiratory vocal cord abduction through activation of the posterior crioarytenod (PCA) muscle. Vagotomy had little effect on the laryngeal response to hypercapnia, but led to an increase in experatory laryngeal resistance during hypoxia owing to a decrease in expiratory PCA activity. Caroterial NaCN injection caused a similar increase in expiratory laryngeal resistance vagotomy, suggesting that the response to hypoxia was due to carotid chemoreceptor stimulation. The laryngeal responses to both hypoxia and NaCN were abolished by carotid sinus nerve section. The results indicate that afferent from central and peripheral chemoreceptors has different effects on the activity of motoneurons governing vocal cord movements during expiration. Vagal afferent serves to maintain the patency of the laryngeal airway during hypoxia.