Children born pre-term at less than 28 weeks' gestation, currently aged 7-9 years, with and without BPD will be included. BPD will be defined as need for oxygen at 36 weeks' postmenstrual age,2 which includes those with moderate-severe disease.47 Children 7-9 years of age were selected in order to include the youngest age at which pulmonary function, including lung volumes and single breath pulmonary diffusing capacity for carbon monoxide, can routinely be reliably measured using methods that require subject cooperation.