Bronchopulmonary dysplasia and expiratory airflow at 8 years in children born extremely preterm in the post-surfactant era

Background It is unclear if bronchopulmonary dysplasia (BPD) is independently associated with reduced expiratory airflow at school age. Objective To determine the independent associations of moderate-severe BPD, mild BPD, gestational age and birth weight z-score with expiratory airflow in children born extremely preterm (EP; <28 weeks' gestation). Methods All EP survivors born in Victoria, Australia, in three eras (1991-1992, n=225; 1997, n=151; and 2005, n=170) were recruited at birth and 418/546 (77%) had valid spirometry data at 8 years. BPD was classified as moderate-severe (oxygen requirement at 36 weeks' postmenstrual age), or mild (oxygen >28 days but not at 36 weeks' postmenstrual age). Expiratory airflow variables, including the forced expired volume in 1 s (FEV1), were measured and values converted to z-scores. Results Compared with no BPD (n=94), moderate-severe BPD (n=193) was associated with a substantial reduction in expiratory airflow (eg, zFEV(1) mean difference -0.69, 95% CI -0.97 to -0.41; p<0.001), but mild BPD (n=131) was not (zFEV(1) mean difference 0.01, 95% CI -0.28 to 0.31; p=0.93). On multivariable analysis, moderate-severe BPD remained strongly associated with reduced airflow (zFEV(1) mean difference -0.63, 95% CI -0.92 to -0.33; p<0.001), but mild BPD (zFEV(1) mean difference 0.04, 95% CI -0.26 to 0.34; p=0.27), gestational age (zFEV(1) 0.06 mean increase per week, 95% CI -0.05 to 0.17; p=0.29) and birth weight z-score (zFEV(1) 0.07 mean increase per SD, 95% CI -0.06 to 0.20; p=0.28) were not. Conclusions In children born EP, moderate-severe BPD, but not mild BPD was independently associated with reduced expiratory airflow at 8 years.