Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory disease with high prevalence worldwide and with relevant impact on patient-related quality of life, morbidity and mortality. There is evidence that airway inflammation correlates with the severity of the disease and that airway inflammation is further enhanced during exacerbation. However, it is unknown whether daily fluctuation of symptoms or changes in lung function is paralleled by changes in airway inflammation.

Patients will undergo a visit every 7 days during one month (5 visits in total). At each visit airway inflammation (exhaled NO, sputum inflammatory cell count) and lung function will be performed. At home patients will be asked to fill a daily diary for symptom assessment.

Inclusion Criteria:

• Post-bronchodilator FEV1/FVC ratio < 70%
• Post-bronchodilator FEV1 < 80%
• Smokers or ex-smoker with pack/years > 15

Exclusion Criteria:

• Atopy
• Asthma
• Concomitant lung diseases (e.g. lung cancer)
• Acute infections of the respiratory tree in the previous 2 months including COPD exacerbation.

Moderate to severe COPD patients (according to GOLD guidelines) will be enrolled in the study