Combined Effect of Sulfur Dioxide and Cold in Exercising Asthmatics

ABSTRACT

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°, 7°, and — 6°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 SO; 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.