Airway effects of low concentrations of sulfur dioxide: Dose-response characteristics

Abstract

The acute respiratory effects of exposure to low-level, short-term sulfur dioxide (SO2) were studied in ten asthmatic and ten healthy subjects. Subjects were exposed in an environmental chamber in a double-blind, random sequence to (SO2) levels of 0.00, 0.25, 0.50, 0.75, and 1.00 ppm for 40 min. During the first 10 min subjects exercised on a cydoergometer at a level of 450 kpm/min. On separate days, subjects were exposed to 0 and 1.0 ppm SO2 in the absence of exercise. In exercising asthmatic subjects, breathing 1 ppm SO2 resulted in significant changes from baseline in airway resistance (Raw), forced expiratory volume in 1 sec (FEV1), maximal expiratory flow at 60% of the vital capacity (VC) below total lung capacity on the partial flow volume curve [MEF40%(P)] as well as reductions in flows at 50% of VC (Vmax50%). None of these parameters showed significant changes for exposures to 0.5 ppm or less, with the exception of small decreases (i.e., < 0.2 L/sec) in Vmax50% at 0.25 and 0.5 ppm. Ten minutes after the end of exercise, there were no statistically significant differences from baseline, even though SO2 was still present in the chamber atmosphere. For asthmatic subjects, the average changes in Raw, FEV10, MEF40%(P), and Vmax50% increased as SO2 levels increased, suggestive of a dose-response relationship with a consistent effect first seen at 0.75 ppm. In individual exercising asthmatics, responses may occur at levels of S02 below 0.75 ppm. No changes were seen in healthy individuals on any day, or in asthmatic subjects at rest. These results indicate that asthmatic individuals engaged in moderate activity have transient bronchoconstriction following exercise in the presence of S02, with consistent changes first being noted for the group when ambient levels reach 0.75 ppm. © 1984 Taylor & Francis Group, LLC.