During bronchodilator tests, it's common to ask patients with asthma or chronic obstructive pulmonary disease (COPD) to take bronchodilator therapy by inhaling after a maximal exhalation, when the respiratory system volume equals the residual volume. The same maneuver is required for the chronic therapy.

Nevertheless, in patients with COPD the distribution of ventilation is more heterogeneous, especially when lung volumes are closer to residual volume . It is therefore predictable that the distribution of air volume containing bronchodilator that has been inhaled at residual volume is more heterogeneous than at higher volumes, such as at functional residual capacity. Accordingly, the bronchodilator can be preferentially distributed in more open airways than in less patent ones, with a heterogeneous distribution of the medication. Therefore, the overall bronchodilation should be greater when the drug inhalation is performed at functional residual capacity than at residual volume.

It is common knowledge that the effectiveness of bronchodilator therapy with pMDI in subjects with COPD is greatly affected by the inhalation technique, which can be difficult to perform for many patients. Therefore, in addition to the possibility that inhalation of bronchilation therapy at residual volume could lower the drug effectiveness, this maneuver complicates the sequence of actions required to the patient, enhancing the risk of errors and decreasing the aderence to treatment.

The aim of this study is to investigate whether the inhalation of a bronchodilator at different lung volumes can affect its effectiveness in terms of respiratory function, in patients with COPD.

Assuming that the bronchodilator effectiveness is equal or greater when inhaled at functional residual capacity rather than at residual volume, the inhalation maneuver can be simplified for patients with COPD.

Inclusion Criteria:

• age above 40 years old;
• history of smoking equal or above 10 PKYs;
• VEMS after bronchodilatation ≤ 70%,
• medical Necessity to perform a bronchodilatation test.

Exclusion Criteria:

• history of bronchial asthma or other chronic respiratory diseases such as pulmonary fibrosis;
• uncontrolled cardiovascular diseases at the time of the visit;
• current pregnancy;
• incapacity to execute lung function tests for cognitive impairment, substance abuse or claustrophobia;
• known hypersensitivity or intolerance to salbutamol.

Patients with COPD diagnosis (VEMS/FVC after bronchodilatation <0.7) will be enrolled in a stable state of disease, diagnosed from at least 12 months [GOLD].