Effect of HIgh-flow Therapy in Long-term Oxygen Therapy

Inclusion Criteria: * Age 40 years or older * Ongoing LTOT: prescribed for at least 15 hours per day; and since at least 28 days as registered in Swedevox * COPD or ILD as main underlying reason for LTOT * Oxygen concentrator as stationary oxygen source in the home including night-time * Body mass index (BMI) \< 35 kg/m2 Exclusion Criteria: * Current or previous treatment with home HFOT * Current treatment with home mechanical ventilation * Current treatment with home CPAP * Hospitalized during the last 2 weeks * Current smoking or contact with flames * Self-reported average use of the LTOT \< 15h per day (24 hours) * PaCO2 (breathing air at rest) \> 8 kPa * Strong clinical suspicion of obstructive sleep apnea (OSA) or obesity-related hypoventilation syndrome (OHS) (as judged by the responsible staff) * Inability to participate in the study procedures (as judged by the staff) * Not eligible for continuing LTOT due to other reason (as judged by the staff) * Expected survival less than 3 months (as judged by the staff)