Measurements of cardiopulmonary response in awake rats during acute exposure to nearambient concentrations of ozone

Cardiopulmonary responses during acute exposure to near‐ambient (< 1.0 ppm) concentrations of ozone (O3) have not been reported for the unanesthetized rat. Such data on species sensitivity are crucial for the extrapolation of animal data to man. Therefore, this study was conducted to obtain functional measurements on awake rats using head‐out plethysmographs and intrapleural or carotid artery catheters during a 135‐min exposure to 0.0, 0.12, 0.25, 0.5 or 1.0 ppm O3. Carbon dioxide was added during alternate 15‐min periods of the exposure to increase ventilation, much like the use of exercise in human O3 exposure studies. The results established that frequency of breathing was increased and tidal volume was decreased as a function of both the concentration and the duration of exposure. Breathing mechanics and cardiopulmonary measures were only marginally affected. Differences in the response of individual rats revealed that as O3 concentration increased, the proportion of rats responding and the magnitude of the response was increased. These data indicate that, for similar functional responses, the rat's sensitivity to O3 is comparable to that observed in man.