Inhalation of SO2 (4–6 ppm) for 10 min decreased airway conductance (increased airway resistance) in seven healthy subjects. Subcutaneous injection of atropine prevented this effect. In anesthetized, paralyzed, artifically ventilated cats, SO2 increased pulmonary resistance, whether delivered to the upper or to the lower airways. This was prevented by complete cold block of the cervical vagosympathetic nerves or by injecting atropine intravenously before the SO2 was inhaled. These results establish the reflex nature of bronchoconstriction during inhalation of SO2. Note: With the Technical Assistance of Earl H. White reflex bronchoconstriction; airway resistance Submitted on February 18, 1964

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