Sulfur dioxide-induced bronchoconstriction in freely breathing, exercising, asthmatic subjects

The purpose of this study was to determine whether 0.50 ppm sulfur dioxide (SO2) in filtered air causes bronchoconstriction in freely breathing asthmatic subjects exercising at a moderately heavy work rate. Ten volunteers who had mild asthma breathed air containing no SO2 or containing 0.50 ppm SO2 In an exposure chamber as they exercised for 5 min on a cycle ergometer at a work rate of 750 kilopond meters/min (about 125 watts). We determined their specific airway resistance by body plethysmography before and after exercise. Specific airway resistance increased by 13.55 +/- 9.18 cm H2O X s (mean +/- SD) when subjects exercised and breathed 0.50 ppm SO2 but only by 2.24 +/- 2.34 when they exercised and breathed air without SO2 (p less than 0.005). Thus, 0.50 ppm SO2 causes significant bronchoconstriction in freely breathing asthmatics during moderately heavy exercise.