This study was undertaken to determine whether measurements of tracheal mucous velocity or airway reactivity to inhaled carbachol more sensitively detect airway effects of inhaled ozone (O3) in conscious sheep. Dose-response curves of mean pulmonary flow resistance (RL) to carbachol were obtained by measuring RL after five breaths of carbachol aerosol with stepwise increases in drug concentration. The animals then breathed 0.5 ppm O3 through an endotracheal tube for 2 h. The dose-response curves were repeated immediately after the 0.5 ppm O3 exposure and 24 h later. In the eight sheep studied, there were no significant alterations in base-line RL immediately after or 24 h after 0.5 ppm O3. Airway hyperreactivity was not apparent immediately after the sheep breathed 0.5 ppm O3, but it was evident 24 h later. In contrast, six sheep that breathed 0.5 ppm O3 in the same manner for 2 h did not show a significant depression in tracheal mucous velocity the same day or 24 h later. Exposure to 1 ppm O3 for 2 h resulted in airway hyperreactivity immediately after the exposure and elevated base-line RL 24 h later; 2 ppm O3 produced an increase in base-line RL immediately after exposure. We conclude that, in conscious sheep, airway hyperreactivity appears to be a more sensitive indicator of airway effects produced by short-term exposure to 0.5 ppm O3 than depression of tracheal mucous velocity.
This study was undertaken to determine the effects of an acute low-level exposure to diesel exhaust particulate material on pulmonary function in conscious sheep. This was accomplished by measuring pulmonary mechanics, airway reactivity to increasing doses of aerosolized carbachol, and tracheal mucous velocity both prior to and immediately after exposure to the diesel exhaust particulates. The diesel exhaust particulate material was aerosolized by a fluidized-bed dust generator. The mass concentration of the dust ranged between 400 to 500 micrograms/m3 and a mass median aerodynamic diameter of 2.8 micrometers. The sheep breathed the diesel exhaust particulates for 30 min by means of a Plexiglas helmet. The particulates caused no material alteration in pulmonary resistance, airway reactivity to aerosolized carbachol, or static lung compliance when compared to pre-exposure values. Tracheal mucous velocity was likewise unaffected. In conscious sheep under the present exposure conditions, the diesel exhaust material administered as a respirable aerosol does not materially affect the function of the large airways, the elastic properties of the lung, nor tracheal mucous transport.
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