Reflex effects of chemical irritation of the upper airways on the laryngeal lumen in cats

Abstract

Changes in airflow resistance of the larynx isolated in situ have been measured in spontaneously breathing cats, vagotomised in the chest, during chemical stimulation of the nose and larynx. Insufflation of ammonia vapour into the larynx inhibited breathing with a large increase in expiratory laryngeal resistance. These responses were abolished by cutting the superior laryngeal nerves, which established the afferent path for the reflex. Insufflation of ammonia into the nose caused sneezing or inhibition of breathing with expiratory increases in laryngeal resistance, which were smaller after sensory denervation of the larynx. The main afferent pathway for this reflex is probably in the trigeminal nerves. The laryngeal reflexes were generally more sensitive than those with the same stimuli affecting breathing.