Exhaled breath condensate in COPD: application in clinical practice

Exhaled breath consists of a gaseous phase that contains volatile biomolecules (e.g., nitric oxide, carbon monoxide and volatile organic compounds) and a liquid phase, known as exhaled breath condensate (EBC), that is mainly formed by water vapour, but also contains aerosol particles in which non-volatile biomolecules have been detected. As it is completely non-invasive, EBC might also be suitable for longitudinal studies, and for monitoring the efficacy of pharmacotherapy in patients with COPD. Different profiles of biomarkers might reflect different aspects of lung inflammation or oxidative stress, that is an important component of inflammation. Identification of selective profiles of biomarkers in lung diseases might be of value for differential diagnosis in respiratory medicine. However, the possible application EBC analysis in the clinical setting requires the elucidation of several methodological aspects, including standardization this technique and validation of the analytical methods commonly used to measure biomolecules in EBC. This article summarizes the results of the EBC analysis in patients with COPD, discusses some methodological aspects, presents advantages and limitations of this technique, and proposes directions for future research.