Analysis of the concentration–respiratory response among asthmatics following controlled short-term exposures to sulfur dioxide

Abstract

Some of the most compelling evidence of sulfur dioxide (SO₂)-induced respiratory morbidity is derived from a large body of studies involving controlled short-term exposures among groups of asthmatic volunteers. These studies were extensively cited in the recently completed review of the primary National Ambient Air Quality Standards for SO₂. Although it is clear from these investigations that exposure to SO₂ may result in a significant increase in bronchoconstriction, there is uncertainty regarding the range of concentrations over which this respiratory response occurs. The objective of this study was to better characterize the concentration–response relationship between SO₂ and measures of bronchoconstriction using individual subject lung function response data. In reviewing studies of asthmatics exposed to SO₂ during 5- to 10-min periods of elevated ventilation, we observed clear and consistent evidence of an increase in the bronchoconstrictive response to SO₂ with increasing exposure concentrations between 0.2 and 1.0 ppm. In a subsequent analysis of individual subject data, it was found that those asthmatics experiencing SO₂-induced respiratory effects at relatively high exposure concentrations are also more likely than nonresponders to experience similar effects after exposure to lower SO₂ concentrations (≤0.4 ppm). Although the clinical significance of these effects is unsettled, the findings provide additional support to epidemiologic evidence of an association between ambient SO₂ concentration and various measures of respiratory morbidity in the general population.