Desaturation during exercise is not a sufficient mechanism for prediction of osteoporosis in non-cystic fibrosis bronchiectasis

BACKGROUND: Recent research has proposed an association between desaturation during a six minute walking test (6MWT) and osteoporosis in an elderly group of individuals with non-cystic fibrosis bronchiectasis. A causative pathway through activation of hypoxia-inducible factor 1-alpha (HIF-1alpha) has been proposed. COMMENTARY: Queries regarding the statistical approaches used are identified and discussed within this correspondence. These predominate around the use of linear regression models to predict osteoporosis in a group that is already osteoporotic, presenting with extreme values for bone mineral density (BMD). Further queries are raised regarding the HIF-1alpha pathway, and physical activity (PA) is proposed as an upstream mechanism for both reduced exercise tolerance and low BMD. CONCLUSIONS: It is suggested that osteoporosis cannot be predicted in a group that is already osteoporotic, and that PA is likely to be the causative mechanism between desaturation in the 6MWT and low BMD in non-cystic fibrosis bronchiectasis.