Effect of 0.3 and 0.9 micron sulfuric acid aerosols on tracheal mucous clearance in beagle dogs.

Tracheal mucous clearance was measured in eight Beagle dogs after 1-h exposures to sulfuric acid mist with particle sizes of 0.3 micron and 0.9 micron mass median aerodynamic diameter (MMAD). The method used was to anesthetize the dogs with halothane, insert a fiberoptic bronchoscope into the trachea, turn off the anesthetic, and then deposit a 10-microliter droplet containing approximately 50 muCi of [99mTc]macroaggregated albumin as the dog started to regain consciousness. Subsequently, gamma camera scintiphotos were taken every minute for 25 min in the awake dogs to measure velocities of the labeled material moving up the trachea. For the 1.0 mg/m3, 0.9 micron MMAD exposures, tracheal mucous velocities were significantly depressed after 30 min (26% reduction, p = 0.05), 1 day (40%, p less than 0.01), and even after 1 wk (30%, p = 0.05). Velocities had returned to the control range 5 wk after exposure. For the 0.5 mg/m3 exposure nonsignificant increases in clearance were seen after 30 min (35%) and 1 day (8%). However, 1 wk after exposure, there was a significant depression in clearance (34%, p less than 0.01). There were no significant changes after exposures to the 0.3 micron MMAD aerosols at concentrations of 1.0 or even 5.0 mg/m3.