The Expiration Reflex from the Trachea and Bronchi

The expiration reflex (ER) is a forced expiratory effort against a closed glottis that subsequently opens to eject laryngeal debris and prevent aspiration of material. It is distinct from the cough reflex. Its source is usually assumed to be restricted to the larynx and vocal folds, and its possible origin from the tracheobronchial (TB) tree has been suggested but never studied. The current authors re-analysed previous records with mechanical or chemical stimulation of the TB tree to see if an ER can consistently be elicited, and to see whether it has properties similar to that from the larynx and vocal folds. A random review was made of some of the extensive literature on TB "cough" to see if it confirmed the authors' conclusions. The TBER was consistently seen in cats and rabbits, either alone or followed by cough. These results are consistent with many studies in other species, including humans. It was enhanced, relative to cough, by inflation of the lungs and by general anaesthesia. Tracheobronchial expiration reflex occurs frequently with mechanical stimulation of the tracheobronchial tree. It differs fundamentally from many of the properties of "true" cough. Its features similar to the laryngeal expiration reflex suggest that both should be labelled "expiration reflexes" and not cough. Its existence should be taken into account in experimental, and possibly clinical, studies on tracheobronchial cough.