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The effects of inhaled sulfur dioxide (SO2) on pulmonary function in nine adolescent subjects with extrinsic asthma were studied. The exposure modes, inhaled via a mouthpiece, were (1) 1 mg/m3 sodium chloride solution droplet aerosol (NaCl); (2) 0.5 ppm SO2 + NaCl; or (3) 1.0 ppm SO2 + NaCl. All exposures were at greater than or equal to 75% relative humidity and approximately 22 degrees C. The following pulmonary functional measurements, with the subject seated in a body plethysmograph, were recorded: total respiratory resistance (RT), functional residual capacity (FRC), maximal flow at 50% and 75% expired vital capacity (Vmax50 and Vmax75), and forced expiratory volume in one second (FEV1). Following 10 min of exposure to either SO2 mode during moderate exercise on a treadmill, statistically significant changes in all pulmonary functional measurements except FRC were seen. There were no statistically significant changes following 10 min of exposure during moderate exercise to the NaCl droplet aerosol alone. Since the average pulmonary changes following exposure to 0.5 ppm SO2 mixture during moderate exercise ranged from 8 to 47%, we conclude that this dose of SO2 is above the response threshold for these subjects. To explore the effects of nasal (or oronasal) inhalation on the SO2-induced pulmonary functional changes, 7 of the 9 subjects inhaled 0.5 ppm SO2 + NaCl via a face mask with no nose clips. The average percentage changes in pulmonary functional values seen after exposure via face mask were similar to those seen after exposure via mouthpiece. However, the changes seen after exposure via face mask were not as consistent as following inhalation via mouthpiece and not statistically different from baseline. We conclude that oral, and to a lesser degree oronasal, inhalation of 0.5 ppm of SO2 elicits SO2-induced changes in pulmonary function in these subjects.

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