Exposure of humans to 4 to 6 ppM SO/sub 2/ decreased ratio of airway resistance to thoracic gas volume an average of 39% usually within 10 sec to 4 min. Atropine effectively blocked this change but did not decrease irritation or coughing during breathing. SO/sub 2/ delivered via tracheal cannula increased total pulmonary resistance in cats a mean of 246%. SO/sub 2/ delivered to upper airways only increased R/sub L/ a mean of 331%. Atropine or cooling of cervical vagosympathetic nerves negated this response. Rapidity of response and subsequent reversal suggests that changes in smooth muscle tone cause bronchoconstriction. Sensory receptors are in upper and lower airways, as lower airway constriction occurred with upper airway exposure. SO/sub 2/ acts like other stimuli producing bronchoconstriction.
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Nadel et al. (1965) studied this question.
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