Exhaled breath condensate

Exhaled breath condensate reflects not only the composition of the airway lining fluid and alveoli. EBC may also mix with salivary and gastric droplets. In addition, volatile gases arising from the alveoli, lower and upper airway wall as well as oral cavity dissolve into the exhaled water vapour and influence its pH. The primary constituents of EBC include: As EBC reflects the composition of the airway lining fluid, it contains most molecules found in the airway, but these are probably diluted by water vapour. Thus, these can range from simple ions, e.g. H+ measured as pH, hydrogen peroxide, proteins, cytokines, eicosanoids, and macromolecules such as mucin, phospholipids and DNA. Dilution is an issue that is a problem with all methods of sampling the airway and lungs including sputum collection and bronchoalveolar lavage. Suggestions to allow for dilution include using a denominator such as protein, urea or conductivity, but no single method is universally accepted at present. Increasing evidence indicates that in disease states EBC contains molecules reflective of that disease or greater concentrations of particular markers. For example, patients with gastroesophageal reflux disease patients have been demonstrated to have pepsin (usually localised to the stomach) in their EBC. Patients with COPD and asthma have been demonstrated to have increased levels of reactive oxygen species and histamine after bronchial challenge (Ratnawatti 2008). The content of exhaled breath condensate, however, is also strongly affected by physiological factors, such as diet, physical exercise and even pregnancy may affect mediator concentrations.