Disease stage Main characteristics 1: Mild COPD FEV1/FVC < 70% FEV1 ≥ 80% predicted With or without symptoms 2: Moderate COPD FEV1/FVC < 70% 50% ≤ FEV1 < 80% predicted With or without symptoms 3: Severe COPD FEV1/FVC < 70% 30% ≤ FEV1 < 50% predicted With or without symptoms 4: Very severe COPD FEV1/FVC < 70% FEV1 < 30% predicted or < 50% predicted plus presence of chronic respiratory failure (PaO2 < 60 mm Hg while breathing room air at sea level)

Table 1: Classification of COPD stages based on spirometry [9]. FEV1 = Forced Expiratory Volume in 1 sec; FVC = Forced Vital Capacity; PaO2 = Arterial Partial Pressure of Oxygen.

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