Effect of microaerosol inhalation on the pattern of breathing

Microaerosol stimulation of the trachea and bronchi appears to have no effect on the pattern of breathing. However, laryngeal stimulation with microaerosol produces consistent changes characterized by slowing of the inspiratory effort. The reflex response can be abolished by either bilateral superior laryngeal nerve section or topical anesthesia of the laryngeal mucous membranes. Nasal stiumulation with saline microaerosol results in marked slowing of inspiration. This response can also be blocked by topical anesthesia of the nasal mucosa. The decreased breathing rate results from both increased t insp. and t exp. During inspiration the build-up phrenic discharge activity, the phrenic slope, decreases. The phrenic peak, however, remains unchanged. The nose and larynx, therefore, appear to play significant roles in the modification of the breathing pattern in response to a nonirritating solution delivered as a microaersol. Slower breathing, relexly produced in the human being by such a method, might benefit partial airway obstruction by reducing turbulence and therefore the work of breathing. It is speculated that in a marginally competent upper airway, this benefit might be a critical factor in survival.