From the relationship between pathophysiology of chronic obstructive pulmonary disease (COPD), dyspnea, and dynamic hyperinflation during ventilatory increasing, the investigators hypothesize that

1. Positive expiratory pressure (PEP) breathing will reduce dyspnea more than normal breathing during exercise in mild to moderate COPD patients.
2. PEP breathing will improve dynamic hyperinflation during exercise more than normal breathing in mild to moderate COPD patients.
3. PEP breathing will improve cardiorespiratory function during exercise than normal breathing in mild to moderate COPD patients.

Expiratory airflow limitation is the pathophysiological hallmark of chronic obstructive pulmonary disease (COPD) that leads to air trapping and increases in dynamic hyperinflation (DH) and consequently causes dyspnea during exercise. Although pursed lips breathing is a simple technique that provides a positive back pressure may retard the airway collapsed, but previous studies showed an unsuccessful reduction of DH which might cause by insufficient back pressure. And thereby a conical positive expiratory pressure (C-PEP) has been developed in our laboratory to generate back pressure higher than pursed lips breathing. Moreover, an effect of PEP on DH has not carried out in patient with COPD. Therefore, the objective of the present study was to examine effects of a C-PEP on DH and respiratory response during exercise in patient with COPD.

Inclusion Criteria:

• Patients with stable mild-to-moderate COPD (Both stages: FEV1/FVC < 70%. Mild stage: FEV1 ≥ 80% predicted; Moderate stage: 50% ≤ FEV1 < 80% predicted according to Global Initiative Obstructive Lung Disease (GOLD) guideline).
• Free of exacerbations for more than 4 weeks (as defined by a change to pharmacological therapy, admission to hospital or ER or unscheduled clinic visit).
• Good communication

Exclusion Criteria:

• Older than 70 years old
• Musculoskeletal problems that limit mobility
• Cardiovascular disease
• Neurological or psychiatric illness
• Patient on long term oxygen or domiciliary noninvasive positive pressure ventilation
• Any other comorbidities which would affect ability to undertake exercise test