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 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.
Department of Physiology and Biophysics, University of Kentucky Medical Center, Lexington 40536.
L Y
LY
Lee
E R
ER
Beck
R F
RF
Morton
Y R
YR
Kou
D T
DT
Frazier
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001049:Apnea / Q000209:etiology*; D001794:Blood Pressure / Q000187:drug effects; D001980:Bronchi / Q000294:innervation*; D002211:Capsaicin / Q000494:pharmacology; D003080:Cold Temperature; D004285:Dogs; D006339:Heart Rate / Q000187:drug effects; D008168:Lung / Q000294:innervation*; D012906:Smoke / Q000009:adverse effects*; D014630:Vagus Nerve / Q000502:physiology
D012906:Smoke; D002211:Capsaicin