Airway responses during and directly after single-time exposure to ozone

Breathing pattern and lung mechanical parameters were measured in 7 female Wistar rats (ca. 200 g) during exposure to 1.0 (n = 5) or 1.3 (n = 2) ppm ozone in air for 2 h and during a 2-h post-exposure observation period. Changes in breathing pattern showed a gradual decrease from 3 to 2 Hz at constant minute ventilation during the first hour of exposure. During the second hour of exposure 6 out of 7 animals developed post-expiratory apnoea (resulting from interstitial oedema), which took about half the breathing cycle concomitant with a decrease of ca. 50% of the minute volume. The breathing pattern returned to normal at the end of the post-exposure observation period. Lung mechanical properties were determined by the forced oscillation method in the restrained, unanaesthetized, spontaneously breathing rats. Airway resistance, inertia and compliance were calculated at regular time intervals during exposure and during the observation period. Overall resistance increased significantly by a factor of 1.76 (P < 0.05); compliance decreased significantly by a factor of 3 (P < 0.05). Airway inertia showed individual increases or decreases. The mean increase (1.23) did not reach the level of significance. At the end of the exposure period the stable changes were interrupted by short-lasting periods of bronchospasms during which the airway resistance increased by a factor of 8 or more.