The Effect of Duration of Exposure on Sulfuric Acid-Induced Pulmonary Function Changes in Asthmatic Adolescent Subjects: A Dose-Response Study

Abstract

To evaluate the pulmonary effects of varying doses of sulfuric acid, adolescent subjects with asthma were exposed to 35 or 70 μg/m³ sulfuric acid for 45 or 90 min. Exposure was carried out during intermittent moderate exercise. The pulmonary functions measured before and after exposure were FEV₁, FVC, and total respiratory resistance. The 45 min exposures were associated with larger decreases in FEV₁ (-6% or -3%) than the 90 min exposures (-1% or +2%). Analysis of variance of the change in FEV₁ among the exposures revealed that the 45 min exposure to 35 μg/m³ was significant (p = 0.03). The p value for 45 min exposure to 70 μg/m³ was not significant (p = 0.08). Using analysis of variance, neither of the 90 min exposures was associated with a significant decrease in FEV₁ compared to air exposure. Also, none of the changes in FVC or R_T was significant. When baseline to post-exposure changes were compared for each of the five test atmospheres using paired t tests, both of the 45 min exposures were associated with statistical significance (p < 0.001 for 35 μg/m³ and p < 0.005 for 70 μg/m³). This baseline to post exposure change was not statistically significant for the 90 min exposures. The reason for the lesser effect on pulmonary function at increased exposure duration is not known; it may be due to changes in either varying deposition patterns or changes in buffering capacity of the cells lining the airways. With respect to individual sensitivities to H₂SO₄, the data showed a significant consistency across test atmospheres.