Mucociliary clearance of inhaled particles measured at 2 h after ozone exposure in humans.

Acute exposure of humans to ozone is known to acutely cause pulmonary function decrements, inflammation, and increased permeability of pulmonary epithelium. A single study in humans has also shown that mucociliary transport increases during acute ozone exposure. Because different responses have shown a different time course of recovery after exposure, it was important to examine mucociliary transport at a different time after the cessation of ozone exposure. We exposed 15 healthy male and female nonsmoking subjects, on different occasions, to clean air and 0.4 ppm ozone for 1 h while they exercised continuously. Pulmonary function was measured immediately before and after exposure and 90 min and 24 h after exposure. Between 2 and 5 h after each exposure, retention of inhaled 5-microns mass median aerodynamic diameter 99mTc-labeled Fe2O3 particles was measured. Each subject returned the next day for a final particle retention measurement. Despite significant changes in pulmonary function, there was no difference in mean whole lung retention time of particles between clean air [77.9 +/- 0.8 (SE) min] and ozone (78.0 +/- 0.8 min) exposures, indicating that mucociliary transport is unaffected by ozone exposure when it is measured 2 h after exposure.