Collection and analysis of exhaled breath condensate in humans

Traditional methods of sampling secretions from the lower respiratory tract include sputum collection, sputum induction, and bronchoscopy with bronchoalveolar lavage (BAL). By far, bronchoscopy with BAL has become the preferred method for sampling the lining fluid of the lower respiratory tract. The invasive nature of bronchoscopy has led to a constant search for less intrusive methods that are easier to implement in ambulant individuals, particularly children. Recently there has been an increasing interest in using exhaled breath as a simple, noninvasive means to sample the lower respiratory tract in humans. The lining fluid of the lower respiratory tract contains various nonvolatile and over 200 volatile substances (1, 2). Although initial attempts were aimed at identifying volatile substances, particularly nitric oxide (NO), studies are now being conducted to detect nonvolatile macromolecules present in exhaled breath, including proteins, lipids, oxidants, and nucleotides. Analysis of these nonvolatile substances requires cooling of the expired breath, which results in condensation. These macromolecules represent biomarkers of various pathological processes in the lungs. In this review, we present the current body of knowledge on exhaled breath condensate as published in peer-reviewed journals in the English language. We focus on the use of this modality in determining host inflammatory response to injury in the lung as well as possible future applications, particularly its potential use as a single, noninvasive sampling method for point-of-care real-time analysis.