Pulmonary effects of sulfur dioxide exposure and ipratropium bromide pretreatment in adults with nonallergic asthma

Abstract

In this study we examined the potential short-term effect of sulfur dioxide (SO 2) on total respiratory resistance and forced expiratory volume in patients with nonallergic asthma. A group of nine adult subjects with nonallergic asthma, 55 years of age or older, were exposed to SO 2 at 0, 0.5, and 1.0 ppm for 20 minutes at rest followed by 10 minutes during light-moderate exercise. The measures of pulmonary function assessed were FEV 1, specific total respiratory resistance (SR T), and maximal expiratory flow rates at 50% (V̇ max50) and 75% (V̇ max75) of expired vital capacity. Measurements were made before exposure to SO 2 (baseline), postresting exposure, postexercising exposure, and at 30 minutes thereafter (recovery). Repeat measure analysis of variance revealed a statistically significant dose-response effect of SO 2 inhalation on FEV 1 ( p = 0.008), SR T ( p = 0.033), V̇ max50 ( p = 0.017), and V̇ max75 ( p = 0.048). Eight subjects had repeat exposure to SO 2 at 1.0 ppm after treatment with either placebo or ipratropium bromide, 60 μg by metered-dose inhaler. Inpratropium bromide treatment, compared to placebo treatment, resulted in a statistically significant improvement in all baseline measures of pulmonary function: FEV 1 ( p = 0.017), SR T ( p = 0.027), V̇ max50 ( p = 0.018), and V̇ max75 ( p = 0.035). However, this drug did not significantly alter the proportionate change in pulmonary function caused by SO 2 inhalation in these subjects. These findings indicate that adults with nonallergic asthma are sensitive to short-term low-level SO 2 exposure and that treatment with 60 μg of ipratropium bromide causes significant bronchodilation but does not protect, completely, these patients from the effect of SO 2 inhalation.