Abstract
Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.
Highlights
Humans exhale hundreds of gases, including inorganic compounds and volatile organic compounds (VOCs), arising10 Section of Anaesthetics, Pain Medicine and Intensive Care, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, UK11 Centre of Anaesthesia and Intensive Care, Semmelweis University, Budapest, Hungary1 3 Vol.:(0123456789)161 Page 2 of 21 from normal body metabolism [1,2,3,4]
This work presents an update of the current status of the optical methods for breath analysis over the last decade and reviews the clinical applications of promising laser spectroscopic methods: tunable diode laser absorption spectroscopy (TDLAS), cavity ring-down spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS)/ cavity-enhanced absorption spectroscopy (CEAS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb (OFC) spectroscopy
Mid-infrared optical parametric oscillators (OPOs) are considered amongst the most useful tools for sensitive laser photoacoustic spectroscopy (LPAS) gas sensing, due to their high power (Watt level), wide tuning range, and ease of tunability. Such a light source was successfully applied for the detection of hydrogen cyanide (HCN) in exhaled breath of cystic fibrosis (CF) patients being infected with various bacteria, namely Pseudomonas aeruginosa, Staphylococcus aureus, etc. [69, 70]
Summary
Humans exhale hundreds of gases, including inorganic compounds (e.g., ammonia, nitric oxide, and hydrogen sulfide) and volatile organic compounds (VOCs), arising. This work presents an update of the current status of the optical methods for breath analysis over the last decade and reviews the clinical applications of promising laser spectroscopic methods: tunable diode laser absorption spectroscopy (TDLAS), cavity ring-down spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS)/ cavity-enhanced absorption spectroscopy (CEAS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb (OFC) spectroscopy The selection of these techniques was based on their maturity and high potential for clinical applications, as well as the frequency in which they have been applied in breath research. By recognizing and utilizing its specific strengths, laser spectroscopy could provide a strong contribution to this rapidly evolving field
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