Role of bronchopulmonary C-fiber afferents in the apneic response to cigarette smoke

The role of vagal bronchopulmonary C-fiber afferents in eliciting the immediate changes in breathing pattern after acute inhalation of cigarette smoke was assessed with a selective blockade of myelinated vagal afferents (innervating both stretch and irritant receptors) utilizing the method of differential cooling. In 15 of 17 choralose-anesthetized dogs tested, spontaneous inhalation of cigarette smoke (19.7% avg conc, 500-700 ml vol) reproducibly caused the following immediate responses: apnea, bradycardia, and hypotension. These responses occurred with 1 to 2 breaths of smoke inhalation and were followed by a delayed hyperpnea. The apneic duration reached 326 ± 33% (SE) (n = 15) of the mean base-line expiratory duration. Differential cold block of both vagi (coolant temperature 8.4 ± 0.3°C) abolished the reflex apnea induced by a positive-pressure (7-10 cm H₂O) lung inflation but did not affect the apneic response to smoke inhalation (345 ± 35%). The smoke-induced apnea was completely abolished by lowering the coolant temperature to -1.3 ± 0.2°C (n = 10) or by bilateral vagotomy (n = 5) and returned to the control level after both vagi were rewarmed. Based on these results, we suggest that the immediate apneic response to inhaled cigarette smoke is elicited by a stimulation of vagal C-fiber afferents in the lungs and airways.