Pleil, J. AND J. Sobus. Mathematical and statistical approaches for interpreting biomarker compounds in exhaled human breath. Chapter 1, Volatile Biomarkers. Elsevier, Shannon, Ireland, , 1-18, (2013).
The various instrumental techniques, human studies, and diagnostic tests that produce data from samples of exhaled breath have one thing in common: they all need to be put into a context wherein a posed question can actually be answered. Exhaled breath contains numerous compounds; just the volatile organic fraction alone has been estimated to represent in excess of 500 different chemical species. In addition, the aerosol fraction contains proteins, signaling molecules, dissolved inorganic compounds, and even bacteria and viruses adding to the complexity of the total sample. No single technique can detect everything in breath, in fact, even the most broadly designed breath measurements result in suites of compounds restricted by the methods used. For example, reactive oxygen species may be observed using real-time sensors or real-time mass spectrometry (MS), but not by gas chromatography-mS (GC-MS), whereas GC-MS can discriminate among a variety of hydrocarbons, alcohols, and ketones that may overlap completely in a real-time MS instrument without benefit of chromatographic separation. Furthermore, the fraction of the breath (gas-phase or aerosol phase) also determines what measurements can be made; for example protiens and signaling molecules could be detected in exhaled breath condensate via enzyme-linked immuno-sorbent assay (ELISA), nuclear magnetic resonance (NMR), or liquid chromatography (LC) MS, but not with any gas-phase instruments such as those based on optical spectroscopy or gas chromatography.
The National Exposure Research Laboratory′s (NERL′s) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA′s mission to protect human health and the environment. HEASD′s research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA′s strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.