Effect of TLV levels of SO2 and H2 SO4 on bronchial clearance in exercising man.

Pulmonary mucociliary function was assessed following exposure to industrial threshold limit values (TLV) of sulfur dioxide (5 ppm) SO2) and sulphuric acid mist (1 mg/m3 H2SO4). Bronchial clearance was measured in two sets of ten healthy exercising non-smoking adults under control and exposure conditions. A 99mTc-albumen saline aerosol (MMD 3 micrometer) was inhaled as a bolus in late inspiration under controlled conditions to produce reproducible deposition in large airways. Lung retention of radioactivity was quantified using a gamma camera and computer analysis. Clearance was significantly faster (P less than .05) on exposure to both SO2 and H2SO4 compared to control values. Maximum mid-expiratory flow rates (MMFR) were significantly reduced (P less than .01) on exposure to SO2 (mean decrease 8.5%), but only slightly reduced for H2SO4 (1.4%). The speeding in clearance was probably an irritant response in both cases. For SO2 the response appeared predominantly reflex, while H2SO4 showed evidence of a direct effect.