Breath gas analysis

Breath gas analysis is a method for gaining non-invasive information on the clinical state of an individual by monitoring volatile organic compounds present in the exhaled breath. Breath gas concentration can then be related to blood concentrations via mathematical modeling as for example in blood alcohol testing.

The area of modern breath testing commenced in 1971, when Nobel Prize winner Linus Pauling demonstrated that human breath is a complex gas, containing more than 200 different volatile organic compounds. However, physicians have used breath analysis since the days of Hippocrates.

Endogenous volatile organic compounds (VOCs) are released within the human organism as a result of normal metabolic activity or due to pathological disorders. They enter the blood stream and are eventually metabolized or excreted via exhalation, skin emission, urine, etc.

Breath sampling is non-invasive and breath samples can be extracted as often as desired.

Identification and quantification of potential disease biomarkers can be seen as the driving force for the analysis of exhaled breath. Moreover, future applications for medical diagnosis and therapy control with dynamic assessments of normal physiological function or pharmacodynamics are intended.

Exogenous VOCs penetrating the body as a result of environmental exposure can be used to quantify body burden. Also breath tests are often based on the ingestion of isotopically labeled precursors, producing isotopically labeled carbon dioxide and potentially many other metabolites.

However, breath sampling is far from being a standardized procedure due to the numerous confounding factors biasing the concentrations of volatiles in breath. These factors are related to both the breath sampling protocols as well as the complex physiological mechanisms underlying pulmonary gas exchange. Even under resting conditions exhaled breath concentrations of VOCs can strongly be influenced by specific physiological parameters such as cardiac output and breathing patterns, depending on the physico-chemical properties of the compound under study.

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