Chronic obstructive pulmonary disease (COPD) is characterised by airflow limitation that is not fully reversible, and is usually progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases, most commonly cigarette smoking. The disease affects not only the large central airways but also the small, more peripheral airways deeper into the lung, defined as less than 2 mm in diameter.

Besides medical treatment, physiotherapy plays a major role in treatment and various methods have been suggested to remove airway of secretions. The flutter is a simple and small device shaped like a pipe that creates a positive expiratory pressure (PEP) and high frequency oscillation when the expired air passes through it. These vibrations are thought to mobilise airway secretions facilitating their clearance and improving breathing.

Standard blowing tests, like spirometry, where patients blow forcedly into a machine, have previously been used to investigate the efficacy of flutter devices. However, spirometry assesses the damage of larger airways but not small airways, also known as the "silent zone" which, crucially, are specifically damaged in COPD.

In this study the investigators hypothesise that because the flutter helps clear the airways from the excessive thick mucus produced by COPD patients, these patients may find it easier to breathe and have lower resistance to moving air in and out of their lungs.

The main objective of this study is to compare the effect of a flutter or a sham device on small airways damage using impulse oscillometry (IOS), a non-invasive method that, contrary to other common blowing tests, measures small airway resistance during normal breathing.

In addition, because COPD is characterised by inflammation, the investigators would also like to measure a gas the patients blow out, nitric oxide (NO) the levels of which reflect airway inflammation. This will give to investigators an insight into the relationship between airway inflammation and small airway function.

Chronic obstructive pulmonary disease (COPD) is characterised by airflow limitation that is not fully reversible. This limitation is usually progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases.

Patients suffering from COPD may show pathologic changes not only in the large but also in the small airways, which are defined as less than 2mm in diameter. Airway inflammation may cause increased thick mucus secretions which can narrow the airways increasing the resistance to the airflow.

Physiotherapy to remove secretions is indicated for patients with COPD who have regular sputum or those with thick secretions and various techniques and physiotherapy devices can be applied for the removal of secretions. The flutter is a simple and small device shaped like a pipe that creates a positive expiratory pressure (PEP) and high frequency oscillation as expired air passes through it. These vibrations and PEP are thought to mobilise airway secretions facilitating their clearance and improving airflow.

The effects of the flutter device have been studied in different patient groups, but especially in lung diseases characterised by mucus hypersecretion such as COPD, cystic fibrosis and bronchiectasis. In COPD, even though the flutter device increases the volume of expectorated secretions, its beneficial effects on pulmonary function as assessed by spirometry and plethysmography are inconclusive. However, these standard lung function tests (such as spirometry) asses the large airways, but do not provide an accurate estimate of the small airways which have been described by some authors as "the silent zone".

The investigators hypothesise that the use of impulse oscillometry (IOS), a non-invasive technique that provides information on small airway resistance during normal breathing, may reveal the effect of the flutter device which may have not been accurately measured by spirometry in previous studies.

In addition, the investigators would like to measure exhaled nitric oxide (NO) levels which reflect airway inflammation and may therefore be useful to determine the association between small airway disease and inflammation.

In summary, the symptoms of patients with COPD improve following breathing exercises with a flutter device, however, the effect of this device on lung function is unclear. The investigators hypothesise that the combined use IOS and NO, would help understand and quantify the effects of the flutter device on the small airways disease in COPD.

The main objective of this study is to measure the effect of a 30 minutes breathing exercise with a flutter device on airway resistance as assessed by impulse oscillometry in patients with COPD.

The secondary objective is to investigate the association between inflammation, airway resistance and volume of secretions in COPD patients.

Inclusion Criteria:

- patients with COPD meeting the Global Initiative for Obstructive Lung Disease (GOLD) guidelines, with forced expiratory volume in the first second of expiration (FEV1) <80% predicted, FEV1/FVC ratio <70% predicted (FVC= forced vital capacity), and total lung capacity (TLC) >80% predicted), with or without sputum, will be included.

The severity of COPD will be classified according to GOLD criteria:

Stage I: mild FEV1/FVC<0.70 and FEV1>80% predicted; Stage II: moderate FEV1/FVC<0.70 and 50\

9 months

Absence of some objective measurement of dyspnea, well being or satisfaction scales.