Sensitivity of bronchoprovocation and tracheal mucous velocity in detecting airway responses to O3

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Abstract
Whether measurements of tracheal mucous velocity or airway reactivity to inhaled carbachol more sensitively detect airway effects of inhaled O3 in conscious sheep was determined. Dose-response curves of mean pulmonary flow resistance (RL) to carbachol were obtained by measuring RL after 5 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 8 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, 6 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. In conscious sheep, airway hyperreactivity may be a more sensitive indicator of airway effects produced by short-term exposure to 0.5 ppm O3 than depression of tracheal mucous velocity.

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