Compared with the corresponding expression levels in the control group, two days after the cessation of hyperoxia stimulation, the expression levels of Nrf2 and HO-1 in the lung tissue of the BPD group at P7 increased (all P < 0.05) (Fig. 2a, b), and the feedback of antioxidant factors was upregulated. This evidence concerns the gene HMOX1 and bronchopulmonary dysplasia.