Airway Responses to Sulfate and Sulfuric Acid Aerosols in Asthmatics

Abstract

Epidemiologic studies support an association between elevated levels of sulfates and increased symptoms in asthmatics. To determine if these pollutants produce airway responses, 17 asthmatics inhaled the following sulfates: sodium bisulfate, ammonium sulfate, ammonium bisulfate (NH₄HSO₄), or sulfuric acid (H₂SO₄) aerosols with an aerodynamic diameter of 0.80 μm at concentrations of 100 μg/m³, 450 μg/m³, and 1,000 μg/m³. A sodium chloride (NaCl) aerosol of similar characteristics, administered by double-blind randomization, served as a control. Subjects breathed these aerosols for a 16-minute period via a mouthpiece. Deposition studies showed 54 to 65% retention of the inhaled aerosols. At the 1,000 μg/m³ concentration, the Threshold Limit Value for occupational exposure, H₂SO₄ and NH₄HSO₄ inhalation produced significant reductions in specific airway conductance (SGaw) (p < 0.05) and forced expiratory volume in one second (p < 0.01) compared with NaCl or pre-exposure values. At the 450 μg/m³ concentration, only H₂SO₄ inhalation produced a significant reduction in SGaw (p < 0.01). At 100 μg/m³, a level 3 to 5 times greater than peak urban levels, no significant change in airway function occurred after any sulfate exposure. These data indicate that asthmatics demonstrate bronchoconstriction after brief exposures to common acidic sulfate pollutants.