Effect of metaproterenol sulfate on mild asthmatics' response to sulfur dioxide exposure and exercise

Twenty asthmatic volunteers, most with mild disease, underwent dose-response studies with sulfur dioxide (SO2) under three pretreatment conditions: (1) drug (metaproterenol sulfate in aerosolized saline solution), (2) placebo (aerosolized saline only), and (3) no pretreatment. Sulfur dioxide exposure concentrations were 0.0, 0.3, and 0.6 ppm. Experimental conditions were presented in random order at 1-wk intervals. Exposures lasted 10 min with heavy continuous exercise. Lung function was measured at baseline, after pretreatment (immediately pre-exposure), immediately post-exposure, and during a 2-hr follow-up. Subjects could elect to take bronchodilators during follow-up. Symptoms were monitored before, during, and for 1 wk after exposure. With no pretreatment, subjects exhibited typical exercise-induced bronchospasm at 0.0 ppm, slightly increased responses at 0.3 ppm, and more marked increases at 0.6 ppm. Seven subjects took bronchodilator after 0.6-ppm exposures, compared to 2 at lower concentrations. Within 30 min post-exposure, most subjects' symptoms and lung function had returned to near pre-exposure levels. A similar sequence was observed when subjects received placebo. Drug pretreatment improved lung function relative to baseline, prevented bronchoconstrictive responses at 0.0 and 0.3 ppm, and greatly mitigated responses at 0.6 ppm. Thus, typical bronchodilator usage by asthmatics is likely to reduce their response to ambient SO2 pollution.