The aim of this study is to investigate whether the intelligent oxygen therapy system can reduce intermittent hypoxia in patients on LTOT during simulated activities of daily living. Patients will be asked to a series of activities of daily living over a period of 1 hour including: washing, dressing, putting away shopping and cleaning. The patients will do these activities twice: once on their usual LTOT and once on the auto-titrating oxygen system in a cross-over design.