Utility of exhaled breath condensates in chronic obstructive pulmonary disease: a critical review

Purpose of review Evaluation of the utility of exhaled breath condensates in chronic obstructive pulmonary disease. Recent findings Exhaled breath condensates have recently been introduced as a simple, noninvasive method of sampling respiratory fluid in inflammatory lung disorders, including chronic obstructive pulmonary disease. Increases in condensate concentrations of at least 12 markers of inflammation have been reported in these disorders. Furthermore, condensate pH appears to be decreased in both chronic obstructive lung disease and bronchial asthma. This has been referred to as acidopnea and could reflect airway acidification by inflammatory cells. Although safer and more convenient than bronchoalveolar lavage, interpretation of condensate data is complicated by uncertainty regarding the source of condensate solutes and by variable dilution of respiratory droplets from condensed water vapor, which represents more than 99.9% of condensate volumes. This dilution can be estimated from the dilution of plasma constituents such as urea or electrolytes. Because the principal buffer in condensate is NH4+, much of which is derived from bacterial degradation of urea in the mouth, condensate pH measurements may not provide accurate estimates of airway pH. Nevertheless, acidification of condensate may be indicative of gastroesophageal reflux, which frequently occurs in obstructive lung diseases and may contribute to cough and bronchospasm. Summary It is too early to tell how useful condensate studies will be to pulmonary investigators and clinicians. Realization of the enormous potential of this approach will require a thorough understanding of the manner in which these solutions are generated and how they should be analyzed.