 A more in depth qualitative assessment of the impact of ambulatory oxygen will be undertaken via a semi-structured interview, in a subset of 20 patients, to investigate patients and their carers personal perspective on how the ambulatory oxygen has affected their day to day life. The interview will be conducted within 2 weeks of the end of treatment visit. Patients from the Royal Brompton Hospital site will be approached by the researcher at the end of treatment visit and asked if they will participate in the qualitative assessment. If the patient agrees a date will be agreed for the patient to be interviewed at a venue convenient to them usually the patients home. 