ACUTE EXPOSURE TO ACID FOG - EFFECTS ON MUCOCILIARY CLEARANCE

Submicrometric sulfuric acid (H2SO4) aerosol can affect mucociliary cl earance without eliciting irritative symptoms or changes in pulmonary function. The effect of larger fog droplets containing H2SO4 on mucoci liary clearance is unknown. We quantified mucociliary clearance from t he trachea (n = 4) and small airways (n = 7) of young healthy male adu lts after an acute exposure to H2SO4 fog (MMAD = 10.3 mum; pH = 2.0; l iquid water content = 481 +/- 65 mg/m3; osmolarity = 30 mOsm). Acid fo g (AF) or saline fog (SF) (10.9 mum; 492 +/- 116 Mg/M3; 30 mOsm) was a dministered for 40 min of unencumbered breathing (no mouth-piece) at r est and for 20 min of exercise sufficient to produce oronasal breathin g. Fog exposures were followed by a methacholine (MCh) challenge (a me asure of airway reactivity) or inhalation of technetium-99M radioaeros ol (MMAD = 3.4 mum) on 2 study days each. Changes in symptoms and forc ed ventilatory function were also assessed. Clearance was quantified f rom computer-assisted analyses of gamma camera images of the lower res piratory tract in terms of %removal/min of the radiolabel from the tra chea 25 min after inhalation and from the outer zone of the right lung after 1.9 to 3 h. Symptoms, forced ventilatory function, and MCh resp onse were unaffected by either fog. Tracheal clearance was more rapid in four of four subjects after AF (0.83 +/- 1.58% removal/min) compare d with that after SF (-0.54 +/- 0.85% removal/min). Outer zone clearan ce was more rapid in six of seven subjects after AF (0.22 +/- 0.15% re moval/min) compared with that after SF (0.01 +/- 0.09% removal/min). T he association between outer zone clearance rate and the estimated amo unt of hydrogen ion inhaled orally was significant (rs = 0.79, p = 0.0 5). The mechanism(s) underlying these changes in regional clearance is unknown.