Effects of sulfuric acid aerosol on respiratory mechanics and mucociliary particle clearance in healthy nonsmoking adults.

Abstract

Ten healthy nonsmokers inhaled 0.5 µm (αg=1.9) H2SO4 at 0 (control), 110,330, and 980 µg/m3 for one hour via nasal mask in random sequence on four separate days. Respiratory mechanical function was assessed before and 1 /2, 2 and 4 hrs after the H2SO4 exposure. A 99mTc tagged Fe2O3 aerosol (7.5 µm aerodynamic diameter, αg≤1.1) was inhaled ∼10 min before each H2SO4 exposure, with flow rate=1.0 L/s, tidal volume=1.0 L and respiratory rate=15/min. Thoracic retention of the deposited radioactivity was monitored using collimated scintillation detectors. A tracheal probe was used to determine the tracheal mucociliary transport rates (TMTR's) of local concentrations of activity. Bronchial mucociliary clearance was markedly altered in a dose dependent pattern in six of the individuals and in the group as a whole. Exposures to 110 µg/m3 resulted in a significant acceleration in mucociliary clearance (group mean tracheobronchial clearance half-time, , decreased from 80 to 50 min). Exposures to 980 µg/m3 caused a significant transient slowing of clearance, with the increased to 118 min. In contrast, there were no significant changes in TMTR, or in indices of ventilatory mechanics ( 25, Raw and distribution of ventilation by N2 washout). The four individuals whose clearance times were not significantly affected by these H2SO4 exposures had the fastest bronchial clearance among the ten, and they were each given an additional test with a 1000 µg/m3 H2SO4 exposure preceding the tagged Fe2O3 aerosol. Three of them responded with threefold or greater increases in - Thus, 9 of 10 subjects had substantial changes in bronchial clearance times following H2SO4 exposures.