Objective To investigate the effect of high-frequency oscillatory ventilation (HFOV) on inflammatory responses in lung tissues of dogs with severe acute respiratory distress syndrome (ARDS).Methods Healthy mongrel dogs of both sexes,weighing 13.7-16.2 kg,in which severe ARDS was induced by intravenous infusion of the mixture of oleic acid 0.2 ml/kg and autologous blood (equal to the volume of oleic acid).Twenty-four dogs with severe ARDS were randomly divided into 4 groups (n=6 each) using a random number table:conventional mechanical ventilation with low tidal volume group (group CMV),HFOV-9 Hz group,HFOV-12 Hz group and HFOV-15 Hz group.In HFOV-9 Hz,HFOV-12 Hz and HFOV-15 Hz groups,the frequency was 9,12,and 15 Hz,respectively,mean airway pressure 20 cmH2O,oscillation pressure 70 cmH2O,and inspired oxygen fraction ratio 1.0.In group CMV,the animals were mechanically ventilated in volume-controlled mode,with positive end-expiratory pressure 5 cmH2O,tidal volume 6 ml/kg,respiratory rate 30 breaths/min,inspiratory/expiratory ratio 1:2,and inspired oxygen fraction ratio 1.0.At 4 h of ventilation,the animals were sacrificed,and lungs were removed for determination of wet/dry weight (W/D) ratio,contents of tumor necrosis factor-alpha (TNF-α),interleukin-6 (IL-6) and IL-10 (by enzyme-linked immunosorbent assay),and expression of vascular endothelial (VE)-Cadherin (by Western blot) and for microscopic examination.Lung injury scores were assessed.Results Compared with group CMV,the lung injury scores,W/D ratio,and contents of TNF-α and IL-6 were significantly decreased,the content of IL-10 was significantly increased,and the expression of VE-Cadherin was significantly up-regulated in the other three groups (P＜0.05).Compared with group HFOV-9Hz,the lung injury scores,W/D ratio and contents of TNF-α and IL-6 were significantly decreased,the content of IL-10 was significantly increased,and the expression of VE-Cadherin was significantly up-regulated in group HFOV-15 Hz,and the content of IL-6 was significantly decreased in group HFOV-12 Hz (P＜0.05).Conclusion HFOV can significantly inhibit inflammatory responses in lung tissues of dogs with severe ARDS as compared with mechanical ventilation with low tidal volume,which may be involved in the mechanism of lung-protective ventilation effect.