CONTRIBUTION OF VAGAL AFFERENTS TO RESPIRATORY REFLEXES EVOKED BY ACUTE INHALATION OF OZONE IN DOGS

Acute inhalation of ozone induces vagally mediated rapid shallow breat hing and bronchoconstriction. In spontaneously breathing anesthetized dogs, we attempted to determine whether afferent vagal C-fibers in the lower airways contributed to these responses. Dogs inhaled 3 ppm ozon e for 40-70 min into the lower trachea while cervical vagal temperatur e was maintained successively at 37, 7, and 0-degrees-C. At 37-degrees -C, addition of ozone to the inspired air decreased tidal volume and d ynamic lung compliance and increased breathing frequency, total lung r esistance, and tracheal smooth muscle tension. Ozone still evoked sign ificant effects when conduction in myelinated vagal axons was blocked selectively by cooling the nerves to 7-degrees-C. Ozone-induced effect s were largely abolished when nonmyelinated vagal axons were blocked b y cooling to 0-degrees-C, breathing during ozone inhalation at 0-degre es-C being generally similar to that during air breathing at 0-degrees -C, except that minute volume and inspiratory flow were higher. We con clude that afferent vagal C-fibers in the lower airways make a major c ontribution to the acute respiratory effects of ozone and that nonvaga l afferents contribute to the effects that survive vagal blockade.