Methods: A total of 49 rats were used in this study. Seven rats were used as controls. Unilateral PC was induced in 42 rats and the rats were divided into two main groups, including contusion (n=21) and HBO group (n=21). Each group was divided into three subgroups (n=7). The first HBO subgroup received a single dose of HBO therapy, while the second HBO subgroup received two doses and the third HBO subgroup received three doses. The first subgroups of each main group were sacrificed 24 hours after the contusion, the second subgroups were after 48 hours and the third subgroups were sacrificed after 72 hours. Tissue samples obtained from the right lung were considered for tumor necrosis factor-alpha (TNF-a), malondialdehyde (MDA), myeloperoxidase (MPO) and, histopathological study and apoptosis analysis.

Results: When compared controls with the contusion group, a statistically siginificant increase in MPO and TNF-a levels was observed. In the HBO treated group, these parameters were decreased, however the decrease was not statistically significant. Histopathological examination revealed significant increases in alveolar hemorrhage, edema/congestion, alveolar distruption and leukocytic sequestration scores. HBO treatment resulted in a statistically nonsignificant, however dramatic improvement in these scores. Apoptosis analysis showed that contusion resulted in an apoptotic cell induction and this effect was significantly inhibited with HBO treatment.

Conclusion: Pulmonary contusion results in a serious local injury, as well as tissue injury via indirect effect of activated inflammatory response mechanisms and exposed free oxygen radicals. Statistically nonsignificance between the TNF-a, MDA and MPO levels in rats receiving a single dose of HBO, compared to others receiving two or three doses suggested that its effect was independent from dosage and the time, at least. We believe that HBO treatment decreases apoptotic cell death and further long-term observations should be carried out to assess the exact mechanism of HBO.