The effects of emphysema on oxygen toxicity in rats

In order to determine if lungs with emphysema respond to oxygen toxicity in a different way from normal lungs, the effects of hyperoxia on pulmonary function, morphologic aspects, and survival were studied in rats with enzyme-induced emphysema. A hyperoxic pulmonary syndrome similar to adult respiratory distress syndrome (ARDS) was produced by a continuous 48-h exposure to 100% oxygen at 1 atm. An emphysematous condition was induced by intratracheal instillation of porcine pancreatic elastase. The 4 study groups consisted of (1) control, (2) oxygen-treated, (3) elastase-treated, and (4) combined oxygen-elastase-treated rats. The emphysematous rats exposed to 100% O2 had reductions in quasi-static compliance and CO diffusing capacity similar to those in oxygen-treated normal animals. They also had reductions in forced expiratory volumes and flow rates similar to those in rats treated with elastase alone. Histologically, there was no enhancement or attenuation of emphysematous or ARDS lesions in the combined oxygen-elastase lungs compared with that in lungs treated with only one agent. Emphysematous and normal rats were also exposed for 96 h to a similar hyperoxic atmosphere to evaluate survival. The survival curves for these 2 groups were not statistically different. These results indicate that the severity of ARDS alterations was not affected by the emphysematous condition, and hyperoxia did not enhance or attentuate preexisting emphysematous lesions. These findings suggest that emphysematous lungs respond to hyperoxia in a similar fashion to normal lungs, and that the functional and structural manifestations of oxygen toxicity are simply superimposed over preexisting emphysematous changes.