Cardiopulmonary effects of short-term nitrogen dioxide exposure in conscious sheep

Abstract We used conscious sheep to (a) evaluate the airway effects of 2-hr exposures to 7.5 and 15 ppm NO 2 , and (b) to measure pulmonary hemodynamics after a 4-hr exposure to 15 ppm NO 2 . Bronchial reactivity to aerosolized carbachol (BR), tracheal mucous velocity (TMV), and mechanics of breathing were determined to assess whether NO 2 induced airway effects immediately and 24 hr after exposure. The hemodynamic measurements included arterial blood gases, estimates of diffusing capacity, combined capillary blood and tissue volume, cardiac output, and pulmonary vascular pressures. In 10 sheep 7.5 ppm NO 2 did not significantly alter mean pulmonary resistance prior to carbachol challenge (Rpul), BR, or TMV. However, in 5 of these 10 animals, enhanced BR was apparent immediately after the exposure. In 10 animals, 15 ppm NO 2 did not produce significant changes in mean Rpul or BR, although in 7 animals there was a mean increase of 113% in Rpul immediately after the exposure, while BR was evident in 2 other sheep. TMV was, however, significantly depressed immediately after this exposure. In six sheep, who breathed 15 ppm NO 2 for 4 hr, Rpul was significantly elevated immediately after the exposure. In the same animals, there were no changes in arterial blood gases, cardiac output, pulmonary vascular pressures, systemic pressure, diffusing capacity, and combined pulmonary tissue plus capillary blood volume. We conclude that in conscious sheep (a) exposures to 7.5 and 15 ppm NO 2 for 2 hr may induce BR or elevations in Rpul, (b) exposure to 15 ppm NO 2 for 2 hr depresses TMV, while exposure to 7.5 ppm NO 2 for 2 hr has no effect on TMV, and (c) 15 ppm NO 2 for 4 hr has no effects on pulmonary hemodynamics.