INTRODUCTION
In recent decades, there has been a significant reduction in mortality associated with premature birth, allowing for a greater number of survivors of extremely preterm birth1. Bronchopulmonary dysplasia (BPD; defined as a need for oxygen at or beyond 28 days of life, and characterized in severity by degree of support required at 36 weeks post-menstrual age)2 is a common comorbidity in preterm neonates, associated with long-term effects on respiratory function3,4. As the survival of extremely preterm children increases, there is a need to evaluate the outcomes of these children in all aspects of life and health, and how different clinical and behavioural factors might mitigate morbidity. Participation in physical activity can impact the health and well-being of school-aged children5, and engagement in physical activity in childhood increases the likelihood of ongoing physical activity in adulthood6. Evaluating and encouraging physical activity in preterm born children and youth is therefore important for improving long-term health outcomes.
Prior studies on the physical activity of children with BPD have demonstrated lower participation in physical activity through self-report5,7,8. Study findings have been mixed, showing both normal and reduced exercise tolerance9,10and similar aerobic capacity7 in children born preterm (with and without BPD) when compared to children born at term. Children with BPD have been shown to have pulmonary function abnormalities including reduced forced expiratory volume in one second (FEV1)7,8,11 and mid-expiratory flows (FEF25-75)8, moderate-to-severe airflow obstruction and hyperinflation9,11. They may also have an increased respiratory rate11, lower tidal volumes11, and decreased peak oxygen saturation9,11 during aerobic activity, compared to their full term peers without BPD. Furthermore, most adolescents and young adults who had BPD in infancy have some degree of pulmonary dysfunction (airway obstruction, hyper-reactivity, hyperinflation), even if they were clinically asymptomatic12. Given these findings of reduced lung function and exercise capacity in children with BPD, it is important to understand physical activity in this population and its relationship to measures of lung disease.
To date, studies evaluating degree of participation in physical activity have been through self-report assessment tools, rather than by objective means. There may be important differences between perceived and actual participation in physical activity in this population, and physical activity may be mitigated by other clinical or behavioural factors. This study therefore sought to compare perceived exercise tolerance and objective physical activity data in a home environment in children born extremely preterm (<28 weeks gestation), who are now school-aged (7-9 years), with and without history of BPD. We also examined associations of physical activity with pulmonary magnetic resonance imaging (MRI) and lung function. Our hypothesis was that children with a history of BPD would have decreased physical activity compared to those without a history of BPD.