REFLEX CHANGES IN BREATHING PATTERN EVOKED BY INHALATION OF WOOD SMOKE IN RATS

The acute ventilatory response to inhalation of wood smoke was studied in 58 anesthetized Sprague-Dawley rats. Wood smoke (similar to 6 mi) was inhaled spontaneously via a tracheal cannula. Within the first two breaths of smoke inhalation, either a slowing of respiration (SR) (n = 39) or an augmented inspiration (AI) (n = 19) was elicited consisten tly in each rat. The SR was primarily due to a prolongation of expirat ory duration, whereas the AI was characterized by a two-step inspirato ry flow leading to an exceedingly large tidal volume. Both initial res ponses, usually accompanied by bradycardia and hypotension, were reduc ed by inhaling smoke at a decreased concentration. After these initial responses, a delayed tachypnea developed and reached its peak 6-10 br eaths after inhalation of smoke. Both the SR and AI were completely ab olished by bilateral cervical vagotomy. In contrast, the delayed tachy pneic response was not prevented by vagotomy but was significantly att enuated by denervation of peripheral chemoreceptors. We conclude that the initial responses to inhalation of several tidal breaths of wood s moke are mediated through vagal bronchopulmonary afferents, whereas th e delayed tachypnea may involve nonvagal mechanisms that include a sti mulation of peripheral chemoreceptors.