The effects of sulfur oxides on nasal and lung function in adolescents with extrinsic asthma

Ten adolescent subjects with extrinsic asthma were exposed during intermittent exercise to filtered air, 0.5 ppm of sulfur dioxide (SO2), or 100 μg/m3 of sulfuric acid (H2SO4) on 5 separate days. The purpose of the study was to compare changes in nasal power (the work of nose breathing) with pulmonary functional changes depending on the route of inhalation of the sulfur oxide pollutants, oral inhalation through a rubber mouthpiece or oronasal inhalation via a face mask. Nasal power was measured with a modified skin diving mask equipped with two differential pressure transducers. Statistically significant changes in total respiratory resistance, FEV1, and maximum flow calculated at 50% and 75% vital capacity were observed after all exposures to SO2 and H2SO4. The magnitude of change in FEV1 and maximum flow calculated at 50% vital capacity was higher after oral compared to oronasal inhalation of SO2. The nasal work of breathing increased 32% after SO2 exposure by mouthpiece and 30% after SO2 exposure via face mask (p < 0.05). The nasal power changes after the H2SO4 exposures were not different from the sham exposures. We conclude that oronasal inhalation of 0.5 ppm of SO2 produces a significant increase in the nasal work of breathing and that the route of exposure reduces but does not eliminate the lower airway reactions observed on oral exposure.