Changes in inert gas rebreathing parameters after ozone exposure in dogs

The acute (30 min postexposure) and delayed (24 and 48 h postexposure) effects of a 4-h exposure to 1.0 ppm O3 (n = 10), 0.3 ppm O3 (n = 9) were evaluated using an inert multiple gas rebreathing method as well as arterial blood gas determinations in anesthetized dogs. Rebreathing parameters included pulmonary capillary blood flow (Qc), diffusing capacity, functional residual capacity, pulmonary tissue plus capillary blood volume (VTPC), and oxygen consumption. The Qc and PaO2 were significantly decreased 30 min after exposure to O3 and remained decreased 24 and 48 h after exposure only in the 1.0 ppm O3 group. After exposure to 1.0 ppm O3 only, a 33% increase in VTPC was found at 24 but not at 48 h and was confirmed by autopsy lung water determinations. No changes in rebreathing parameters or arterial blood gas measurements occurred in the air exposure control group. Therefore, an acute exposure to O3 resulted in adverse cardiopulmonary effects in dogs. Five additional dogs were exposed to 1.0 ppm O3 for 4 h while breathing spontaneously rather than with ventilation being assisted by electrophrenic stimulation (as done in the other exposures), and no changes in VTPC occurred. Thus, the ventilatory pattern used during O3 exposure is also an important factor in causing critical degrees of parenchymal lung injury.