Acute effects of cigarette smoke inhalation on peripheral airways in dogs

We studied the acute effects of the inhalation of cigarette smoke on the central and peripheral airways of 35 open-chested and tracheotomized dogs by the direct measurement of central (Rc) and peripheral (Rp) airway resistances. Rc was calculated by dividing the pressure difference between a tracheal catheter and a retrograde catheter by mouth flow, and Rp was obtained by dividing the pressure difference between the retrograde catheter and a pleural capsule by mouth flow. The pleural capsule was attached to the pleural surface for alveolar pressure measurement. Rc and Rp were measured by the 2-Hz forced oscillation method. With lung inhalation of the smoke of two-thirds of one cigarette in vagi intact dogs, Rp increased to 239% of the control value and Rc increased to 112%. After bilateral vagotomy, Rp increased to 143% and Rc increased to 104%. Propranolol did not influence the results. Hexamethonium and atropine both blocked these responses when vagi were intact. When the upper trachea, larynx, and nasopharynx, which were completely blocked by vagotomy, were exposed to the smoke of two-thirds of a cigarette, Rp increased to 155% and Rc increased to 144%. We thus conclude that cigarette smoke causes a major increase in Rp, mainly via the vagal reflex and partially via the stimulation of parasympathetic ganglia (probably nicotine), and a minor increase in Rc via vagal reflex.