Thirty to 50% of COPD patients have airway colonization with potentially pathogenic bacteria. This is associated with worse prognosis. Currently, diagnosis of bacterial colonization relies mainly upon quantitative sputum culture. However, this method lacks good sensitivity. The electronic nose is a novel device made up of nanosensors capable of detecting specific volatile organic compounds (VOCs). OBJECTIVES: Main 1) To assess the usefulness of the electronic nose in the diagnosis of bacterial colonization in COPD. Secondary 1) To define the VOCs pattern associated with bacterial colonization. 2) To study the pattern of pulmonary and systemic inflammation associated with bacterial colonization as well its relationship with the aforementioned VOCs patterns.