Effect of TLV Levels of SO2and H2SO4on Bronchial Clearance in Exercising Man
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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.
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