The primary purpose of this study is to compare and assess the immediate and long-term effects on pulmonary rehabilitation training with the usage of HFNC or conventional oxygen therapy device.

The hypotheses was, with high flow nasal cannula usage while exercising, the physiological outcome measurements would be better than conventional oxygen therapy device. Also, the usage of HFNC can immediately increase patient's exercising endurance and decrease dyspnea caused by exercising.

Pulmonary Rehabilitation is one of the most recommended methods to improve the muscle function of COPD patients. By exercise training, even patients with severe COPD can increase muscle strength, improve skeletal muscle function and enhance exercise endurance. Due to improvements in exercise endurance, when exercising at a higher intensity, ventilation support and dynamic hyperinflation would slightly decrease which leads to less dyspnea during exercise. Continuously exercising can also increase the motivation to exercise, reduce mood irritability and psychological burden caused by symptoms. By exercising, patient's health status can be both improved physically and mentally.

High Flow Nasal Cannula (HFNC) is a non-invasive ventilatory device that provides stable oxygen concentration, temperature (37℃) and humidity (Relative Humidity: 100%). Humidity provided by the HFNC reduces irritation caused by the high flow, which leads to the increase of user's tolerance with the device. With the half-closed system formed by a nasal prong, when the high flow enters the upper airway, continue positive airway pressure would be formed.

Subjects enrolled into this study are required to join a 6-week pulmonary rehabilitation program. Before starting the program, subjects were randomly assigned to high flow nasal cannula group and conventional oxygen therapy group. When exercising, the nasal cannula group would receive an oxygen flow of 3 - 5L to maintain SpO2>90% and the HFNC group with high flow setting of 45-50Lpm along with oxygen flow of 3-5L also to maintain SpO2>90%. When joining the pulmonary rehabilitation program, patients are required to exercise for approximately 45 minutes per session. When exercising, changes in the degree of dyspnea, quadriceps blood flow and hemodynamics are assessed. After 6-week of the exercise training, all the parameters will again be assessed and compared to the primary data that was collected from the beginning of the program.

Inclusion Criteria:

• Age > 55 years
• COPD patients with confirmed pulmonary function test results of FEV1<70%
• Regular follow-up at the pulmonary medicine clinic
• Stable condition without acute exacerbation
• No pulmonary rehabilitation training within a year
• None oxygen usage at home
• No smoking history or quit smoking
• Inform consent signed

Exclusion Criteria:

• Fever (Body Temperature >37.5°C)
• Acute infection symptoms
• Unstable cardiovascular status (Eg: Blood pressure >150/100 mmHg after medication usage, angina pectoris, or abnormal ECG)
• Activity restrictions due to orthopedic or neuromuscular disease