Content area
Full Text
Abstract
Breath analysis is a relatively recent field of research with much promise in scientific and clinical studies. Breath contains endogenously produced volatile organic components (VOCs) resulting from metabolites of ingested precursors, gut and air-passage bacteria, environmental contacts, etc. Numerous recent studies have suggested changes in breath composition during the course of many diseases, and breath analysis may lead to the diagnosis of such diseases. Therefore, it is important to identify the disease-specific variations in the concentration of breath to diagnose the diseases. In this review, we explore methods that are used to detect VOCs in laboratory settings, VOC constituents in exhaled air and other body fluids (e.g., sweat, saliva, skin, urine, blood, fecal matter, vaginal secretions, etc.), VOC identification in various diseases, and recently developed electronic (E)-nose-based sensors to detect VOCs. Identifying such VOCs and applying them as disease-specific biomarkers to obtain accurate, reproducible, and fast disease diagnosis could serve as an alternative to traditional invasive diagnosis methods. However, the success of VOC-based identification of diseases is limited to laboratory settings. Large-scale clinical data are warranted for establishing the robustness of disease diagnosis. Also, to identify specific VOCs associated with illness states, extensive clinical trials must be performed using both analytical instruments and electronic noses equipped with stable and precise sensors.
1Introduction
Breath analysis is a young field of research with much promise in scientific and clinical studies.
During breathing, the inhaled gas molecules diffuse from the alveolar region and are dissolved into the bloodstream. Gas molecules are then taken up by tissues through a simple physical dissolution process, which allows them to be partitioned between the air and blood during absorption and between the blood and other tissues during distribution. A chemical remains long enough in the alveoli to attain equilibrium with the blood [1], i.e., equilibrium wherein the ratio of chemical concentration in the blood to that in the gas phase remains constant. This relatively fast equilibrium between alveolar air and pulmonary capillary blood is the basis for breath analysis [2]. The number of volatile organic compounds (VOCs) exhaled through the lungs varies in direct proportion to their blood concentrations and vapor pressure and is indirectly proportional to their absorption by the lungs [3]. Hence, a single breath contains hundreds of...