Breath gas analysis of volatile organic compounds (VOCs) has become a growing field of research in recent years. It is a non-invasive approach with many potential applications such as screening for diseases biomarkers, monitoring of metabolic processes, studying pharmacokinetics, and drug testing. IONICON PTR-MS systems are particularly well suited for breath gas analysis: Their detection limits and linearity range match the concentrations typically found in breath. In addition to offline analysis, where breath is collected in a container and then analyzed, the high sensitivity and fast response time of IONICON PTR-MS systems allows to analyze breath online and in real-time.
Real-Time Breath Analysis with PTR-MS
In real-time breath analysis, the exhaled breath is directly analyzed without sample preparation. Recording a complete breathing cycles, see figure, yields the concentrations for the end-tidal (alveolar) fraction and also the inspired (room-air) concentrations, which can be extracted by software. This provides immediate results and avoids any complications often arising from sample collection and storage. Also, the measurement of unstable compounds that undergo rapid degradation may only be possible by real-time analysis.
IONICON has actively participated in several medical research projects. Our customers can benefit from this expertise which allows us to develop optimized products and to consult our clients for their medical application and scientific study design. IONICON has developed a BET breath-sampling inlet for real-time breath analysis with IONICON PTR-MS systems, which is certified for clinical use.
The classical application of breath analysis is the search for biomarkers. In such studies, the breath spectra of healthy volunteers are compared to subjects/patients with a certain condition. IONICON PTR-TOFMS instruments are particularly well suited, since the complete spectrum is analyzed at once. In combination with our BET breath sampling inlet, it is possible to analyze all detectable breath compounds down to pptv-levels from a single exhalation.
Breath-Markers for Smoking
The most prominent biomarkers typically found in breath are those for the smoking status of the test subject. These markers should always be identified, since they can easily act as confounding factors for more interesting correlations.
The figure shows a box-plot for the most prominent smoking marker acetonitrile. The data represents over 200 subjects measured. To assess the quality of the resulting breath test, the Area Under the Receiver-Operator-Characteristic curve (AUROC), which, with 99%, represents the best value published so far and shows the potential of the employed method.
Biomarkers for Lung-Cancer
The search for cancer biomarkers in breath is one of the most pursued but also the most challenging endeavor. The high quality and reproducibility offered by breath analysis with IONICON PTR-MS, together with the simplicity in the interpretation of the PTR-MS data, is a great advantage.
In the figure, we display results of a PTR-MS breath study conducted in the Center of Excellence in Medicine and IT (CEMIT). With data-mining tools, biomarkers for lung cancer can be identified. Due to the vast number of compounds that can be measured by IONICON’s PTR-MS instruments, it is recommended to apply (cross-)validation methods in the data analysis, see Miekisch et al.. By combining only two markers we reach a cross-validated AUROC value of > 83% for the detection of bronchial adeno-carcinoma.
Real-time breath analysis has also facilitated new types of studies, where the breath of a subject is monitored to follow the variation of one or several marker compounds in time.
Pharmacokinetics is the study of distribution and elimination of drugs in the body. With breath analysis, the blood concentrations of a drug can be monitored non-invasively and can be updated with every exhalation.
In the figure we show full exhalations, recorded every 15 minutes, which depicts the concentration of a drug in the exhaled breath after ingestion (t=0) of a capsule that dissolves in the intestinal tract after a few hours. The concentration shows a sharp increase and a slow decay from which pharmacokinetic models can be derived. An accurate model is not possible with a slower sampling frequency, which makes such studies tedious with offline breath sampling methods and renders it next to impossible with invasive blood analysis (Beauchamp et al.).
Monitoring metabolic processes
The human volatile metabolome can be monitored in exhaled breath. However, most volatile metabolites, such as acetone, isoprene, methanol, etc. play a role in several metabolic processes. A direct interpretation is rarely possible.
By administering isotopically labelled educts, the metabolic products will also be labelled and can clearly be distinguished from the metabolic background in the spectrum.
In the figure we show two isotopically labelled metabolites with individual variations over time, which arise as a result of the ingestion of a labelled compound. This allows to probe and study specific metabolic processes and deficiencies, and opens the door to personalized medicine. Metabolic monitoring with PTR-MS has recently been demonstrated by Winkler et al..