Kim YH, Kim KW, Eun HS, et al. - According to bronchopulmonary dysplasia (BPD) severity, researchers determined significant indices for evaluating the pulmonary function of infants and ascertained if small for gestational age (SGA) could influence pulmonary function in BPD. One hundred seventeen preterm infants were assessed who had undergone tidal breathing flow-volume loop and multiple-breath washout analyses within 7 months after birth. In addition, nine healthy term infants as controls were evaluated. In infants with severe BPD compared with those with mild/moderate BPD, the tidal breathing ratio (time to peak expiratory flow/expiratory time [t_PEF/t_E]) was significantly lower. Based on BPD severity, lung clearance index was not different. According to findings, t_PEF/t_E could be a useful pulmonary index which exhibits lower values in severe BPD in infants with BPD. SGA results in infants with BPD may be associated with poor pulmonary function consistent with the values of t_PEF/t_E.