Abstract： Objective To explore the effect of methylprednisolone combined with HBO on acute lung injury (ALI) induced by rush decompression.Methods Twenty-six male healthy rabbits were randomly divided into the normal control group (n =6),the model group and the combined therapy group.Four animals in the model group and the combined therapy group died,following development of the ALI model by rush decompression by using vacuum pumps.Then,the remaining 24 animals were randomly divided into the model group and the combined therapy group,each consisting of 12 animals.The moment after the animals were surfaced from the chamber,4 animals in each group were sacrificed for the detection of wet/dry ratio of the lung tissue.The remaining animals in the model and control groups were given normal feeding for 3 days,without any treatment.Following injection of methylprednisolone (1 mg/kg),the animals in the combined therapy group were exposed to HBO (0.1 MPa gauge pressure,breathing oxygen for 2 hours),one session a day for a succession of 3 days.Three days later,observations were made on the wet/dry ratio of the lung tissue,pathologic morphology,concentrations of TNF-α and IL-1β,and the expressions of NF-κB p65 mRNA.Results The moment and 3 days after rush decompression,the wet/dry values of the animals in the model group were (5.29 ±0.26,3.20 ±0.21),which were higher than those of the animals in the control group (2.32 ±0.54,2.15 ±0.40) (P ＜0.01).Significant pulmonary exudation and inflammatory infiltration could obviously been seen.Three days after treatment with methylprednisolone combined with HBO therapy,the wet/dry value of the animals in the treatment group decreased significantly (2.34 ± 0.49),without statistical significance,when compared with that of the control group.However,statistical significance could be noted,when compared with that of the model group.Three days later,concentrations of TNF-α and IL-1β of the model group increased [(9.53 ± 1.28),(20.34 ± 1.87) ng/L)],which were significantly higher than those of the control group [(6.42 ±0.95),(15.63 ± 1.85) ng/L)] (P ＜ 0.05 or P ＜ 0.01).The expressions of NF-κB p65 mRNA (1.32 ± 0.48) also increased,when compared with those of the control group (0.35 ± 0.07) (P ＜ 0.05).After 3 days of combined treatment with methylprednisolone and HBO,acute lung injury score of the treatment group was(4.43 ± 0.93),which showed a significant improvement,when compared with that of the model group (8.56 ± 1.73) (P ＜ 0.01).Nevertheless,it was still rather high,when compared with that of the control group(0.97 ± 0.17)(P ＜ 0.01).The concentrations of TNF-α and IL-1β in the homogenates decreased [(7.17 ±0.65),(16.63 ± 0.57)ng/L],which were significantly lower than those of the model group [(9.53 ± 1.28),(20.34 ± 1.84) ng/L) (P ＜ 0.05).In the meantime,the expression of N F-κB p65 mRNA also declined markedly (0.43 ±0.15),when compared with that of the model group(1.32 ±0.48) (P ＜ 0.05).Conclusions The combined treatment of methylprednisolone and HBO could produce positive effects on acute lung injury induced by rush decompression,the inhibition in the expression of NF-κB p65 might be one of the mechanisms involved.