Impairment of tracheal mucociliary clearance but not ciliary beat frequency by a combination of low level ozone and sulfur dioxide in sheep.

We used conscious sheep to determine the effect of a combined exposure to ozone (O3) and sulfur dioxide (SO2) on tracheal mucus velocity (TMV) and ciliary beat frequency (CBF). TMV was measured in vivo by tracking the movement of radiopaque particles which had been deposited on the tracheal mucosa. CBF of tracheal epithelial cells, obtained by brushing, was measured in vitro with phase contrast microscopy. On two separate occasions, six sheep were exposed by mask to either a combination of 0.3 ppm O3 and 3 ppm SO2 or air (control) for 5 h on each of three consecutive days. TMV and CBF were measured prior to the first exposure, and immediately and 24 h after the last exposure. The combination of O3 and SO2 depressed mean TMV by 40% immediately after and by 25%, 24 h after exposure. Both values were different from the corresponding values after air exposure (p less than 0.05). However, this depression in TMV was not associated with an impairment in CBF. We conclude that in conscious sheep, exposure to a combination of low level O3 and SO2 causes a depression in TMV, and changes in CBF are probably not a primary cause of this mucociliary dysfunction.