Defensive reflexes of the respiratory tract in dogs

Intrapleural pressure, the tracheal air flow and tidal volume were recorded simultaneously in pentobarbital-anaesthetized dogs and changes occurring in them during defensive reflexes elicited by mechanical stimulation of the mucosa of different parts of the respiratory tract were evaluated quantitatively. The results show that, in addition to coughing and sneezing provoked by inserting a nylon fibre into the tracheobronchial region, the larynx and the nose, further respiratory reflexes described in other mammals also appear in these animals. Mechanical stimulation of the epipharynx with a fine polyvinylchloride catheter, for instance, also produces in dogs an aspiration reflex characterized by sniff-like inspiratory efforts without subsequent active expiration. Touching the vocal folds, however, produces an expiration reflex consisting of expiratory efforts without preceding inspiratory effort. The character of all these reflexes is typical and closely resembles their character in cats. Stimulation of the various parts of the respiratory tract sometimes evokes an apnoeic reaction instead of typical respiratory defensive reflexes.