Does Positive Expiratory Pressure Mask Therapy Improve Recovery From Acute Exacerbations of Chronic Obstructive Pulmonary Disease?

Inclusion Criteria (all of the following criteria must be met): * The primary reason for hospital admission is an acute exacerbation of clinically diagnosed COPD * There is evidence of sputum expectoration or they are a chronic sputum producer ('regularly expectorates sputum on most days') * They are able and willing to provide written, informed consent * Recent (within the last 6 months) lung function data indicates obstructive lung disease (of any severity), according to the GOLD criteria: post-bronchodilator FEV1/FVC \< 0.7 (only if available) * They have a smoking history of ≥ 10 pack/years (only if diagnosis unclear) Exclusion Criteria (none of the following criteria must be present): * They are breathing via an artificial airway (e.g. endotracheal or tracheostomy tube) * They have a more significant respiratory disease other than COPD (e.g. primary diagnosis of bronchiectasis, cystic fibrosis, interstitial lung disease, asthma, lung cancer) * They have had recent (within the last 6 months) lung volume reduction procedure(s) (e.g. surgery, valve or stent insertion, or other), lung transplantation or pneumonectomy * The intervention is contraindicated (including but not limited to evidence of undrained pneumothorax, significant frank haemoptysis, recent facial, oral, oesophageal or skull surgery/trauma, altered conscious state or inability to co-operate) * They have poor oxygen saturation at rest (SpO2 \< 88%) despite supplemental oxygen delivered via nasal prongs * They intend to continue performing established ACT routines throughout the study period * It is more than 48 hours since being admitted as an inpatient to hospital.