Combined effect of sulfur dioxide and cold in exercising asthmatics

Twenty-four asthmatic volunteers were exposed to 0, 0.3, and 0.6 ppm sulfur dioxide (SO2) in purified background air at each of three temperatures--21 degrees, 7 degrees, and -6 degrees C--in a controlled-environment chamber. Relative humidity was approximately 80%. Exposures consisted of 5 min heavy exercise periods plus brief warmup and cooldown periods. Airway resistance, thoracic gas volume, and symptoms were measured immediately before and after exposure. For the group, increasing SO2 concentration and decreasing temperature were associated with statistically significant unfavorable effects on airway resistance and respiratory symptoms, as expected from previous findings. Effects of SO2 and cold usually appeared to combine in an additive or less-than-additive fashion; there was little evidence of synergism. Individuals' response patterns were variable: a few suggested synergism, but others suggested a mitigating effect of cold on the bronchoconstrictive response to SO2.