LBM & Lung Function in Adolescents With CF

In patients with cystic fibrosis (CF) the commonest cause of death is respiratory failure. Respiratory failure can have many causes. However, in patients with CF a major contributor is the impairment of the muscles required for breathing (respiratory muscles). Respiratory muscle impairment can result from poor nutrition. Lung function declines particularly during adolescence whilst body composition also changes at the same time. Thus, the investigators plan to study the relationship of nutrition and body composition to respiratory muscle strength and lung function in children and young people with CF aged between 12-18 years. The body mass index (BMI) is currently used in the clinical setting to measure nutritional status in CF. At King's College Hospital (KCH) there are portable devices to assess both respiratory muscle function and lung function. The research team will use a Bioelectrical Impedance Analysis (BIA) device to assess body composition, including BMI and lean body mass (LBM). The aim of the study is primarily to assess whether measurements of LBM impairment may better relate to poor lung function compared to BMI and secondly to examine whether lung and respiratory muscle function correlates with exercise tolerance.