A comparison of the pulmonary effects of 0.5 PPM versus 1.0 PPM sulfur dioxide plus sodium chloride droplets in asthmatic adolescents

Abstract

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 (NaCI); (2) 0.5 ppm SO₂ + NaCI; or (3) 1.0 ppm SO₂ + NaCI. All exposures were at ≥75% relative humidity and ∼22°C. The following pulmonary functional measurements, with the subject seated in a body plethysmograph, were recorded: total respiratory resistance (R_T), functional residual capacity (FRC), maximal flow at 50% and 75% expired vital capacity (Vmax50 and Vmax 75), 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 NaCI 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 + NaCI 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.