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 broncho alveolar lavage (BAL). By far, bronchoscopy with BAL has become the preferr ed method for sampling the lining fluid of the lower respiratory tract. The invasive nature of bronchoscopy has led to a constant search for less intr usive methods that are easier to implement in ambulant individuals, particu larly children. Recently there has been an increasing interest in using exh aled breath as a simple, noninvasive means to sample the lower respiratory tract in humans. The lining fluid of the lower respiratory tract contains various nonvolatil e and over 200 volatile substances (1, 2). Although initial attempts were a imed at identifying volatile substances, particularly nitric oxide (NO), st udies are now being conducted to detect nonvolatile macromolecules present in exhaled breath, including proteins, lipids, oxidants, and nucleotides. A nalysis of these nonvolatile substances requires cooling of the expired bre ath, which results in condensation. These macromolecules represent biomarke rs 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 respo nse to injury in the lung as well as possible future applications, particul arly its potential use as a single, noninvasive sampling method for point-o f-care real-time analysis.