Study of Long-term HFNC for COPD Patients with HOT

Inclusion Criteria: 1. Patients who are diagnosed with the global initiative on obstructive lung disease (GOLD) stage 2-4 COPD. 2. Patients who have received nocturnal HOT 16 hours or more per day for 1 month or more at the time of the informed consent. 3. Patients with PaCO2 \>= 45 Torr and pH \>= 7.35 at screening. 4. Patients with COPD exacerbation (Moderate or Severe; judged by the investigators) within the past 1 year prior to the informed consent. 5. Patients who are more than 40 years old at the time of the informed consent. 6. Patients who agree to participate in the study with the written informed consent. Exclusion Criteria: 1. Patients with severe kidney, liver or cardiovascular disease. 2. Patients with active malignant tumor. 3. Patients with acute disease. 4. Patients who are diagnosed with asthma. (Excluding COPD patients with history of asthma). 5. Patients who have any history of obstructive sleep apnea syndrome (OSAS) or are highly-suspected cases in the clinical. (Excluding patients who are denied the diagnosis of OSAS by the result of overnight polysomnography.) 6. Patients with diseases that affecting the efficacy endpoints (for example: active pulmonary infection, clinically significant pulmonary fibrosis and bronchiectasis, α-1-antitrypsin deficiency etc.,) and are regarded as inadequate for the study by the investigators. 7. Patients who have experienced a COPD exacerbation (any Severity: judged by the investigators) within the past 4 weeks prior to the informed consent. 8. Patients who are receiving nocturnal noninvasive positive pressure ventilation (NPPV), or who had been received it within 4 weeks prior to the informed consent. 9. Patients who have used HFNC at home within the past 1 year prior to the informed consent, or are using any HFNC. (Excluding patients who used HFNC during hospitalization due to acute respiratory failure within 1 year prior to the informed consent.) 10. Patients with history of tracheotomy, severe pharyngeal surgery or severe nasal cavity surgery within the past 6 months prior to the informed consent. 11. Patients who are pregnant. 12. Patients with cognitive impairment or mental disorder who are regarded as inadequate to evaluate for the study by the investigators. 13. Patients who are regarded as being unable to operate the myAIRVO2 adequately at home by the investigators. 14. Patients who have participated in the other study at the time of the informed consent, or will participate in the other study. 15. Any other cases who are regarded as inadequate for the study enrollment by the investigators.