Journal of Applied Physiology, Vol 63, Issue 4 1366-1373, Copyright © 1987 by American Physiological Society
Role of bronchopulmonary C-fiber afferents in the apneic response to cigarette smoke
L. Y. Lee, E. R. Beck, R. F. Morton, Y. R. Kou and D. T. Frazier
Department of Physiology and Biophysics, University of Kentucky Medical Center, Lexington 40536.
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 chloralose-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 within 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 degrees C) abolished the reflex apnea induced by a positive-pressure
(7-10 cmH2O) 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 degrees 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.
