A differential bronchomotor response to cooling and drying the upper airway

The present study aimed to compare the reflex bronchoconstrictor effects of upper airway applications of dry airstreams with equivalent cooling produced by cold isotonic and hypertonic saline solutions in anaesthetized rabbits. A method of on-line, breath by breath analysis of lung mechanics was used. The changes in total lung resistance (RL) and dynamic lung compliance (Cdyn) produced by dry airstreams and by cold hypertonic saline were greater than those induced by cold isotonic saline. Warm isotonic saline and supersaturated airstreams were ineffective. These results implicate osmotic disturbances in the response to dry airstreams. The response to dry airflow was abolished by section of the superior laryngeal nerves, by vagotomy and by atropine, suggesting a central cholinergic reflex mechanism is involved. Phosphoramidon had no effect, indicating that tachykinins are unlikely to play a role in this particular reflex.