Monitoring the effect of exercise during the Nijmegen Four Days Marches using exhaled breath
Volatile organic compounds (VOCs) in exhaled breath reflect many metabolic processes in the body. Due to the non-invasive nature of breath sampling, it is an excellent way of studying interventions in human cohorts. During the Nijmegen Four Days Marches, we used a proton transfer reaction – time-of-flight – mass spectrometry (PTR-ToF-MS) system to directly analyse the chemical composition of the participants’ exhalations (Figure 1). With this PTR-ToF-MS setup, analysis of a breath sample takes less than a minute, making it ideal for high throughput. During exercise as the Four Days Marches, many processes in the body are affected. These effects were clearly reflected in the exhaled breath profile of the participants (Figure 2) .
Figure 1: Sampling station for on-site direct analysis of exhaled breath samples from Nijmegen Four Days Marches participants
Figure 2: Representation of the effect of exercise on the exhaled breath profile of Nijmegen Four Days Marches participants 
Real-time analysis of short-chain fatty acids (SCFAs) in exhaled breath
SCFAs are important metabolites mainly produced by the gut microbiome through digestion of dietary fibre. The most abundant SCFAs in the human body are acetic acid, propionic acid and butyric acid. Disbalance in SCFA levels can indicate e.g. poor dietary quality or metabolic disorders. Current analysis focuses on measuring SCFA levels in either breath or fecal matter. However, we developed and validated a method to detect SCFAs in exhaled breath in real-time using proton transfer reaction – time-of-flight – mass spectrometry (PTR-ToF-MS) . All investigated SCFAs (acetic acid, propionic acid and butyric acid) had detection limits below 1 part-per-billion volume (ppbV) and showed a linear response in a biologically relevant range (0-100 ppbV). This method can now be implemented to e.g. study dietary interventions in children.
Figure 3: Exhalation profile for five consecutive exhalations showing the SCFA levels and acetone (breath tracer)
More about this research?
 Henderson, B. et al. Exhaled Breath Reflects Prolonged Exercise and Statin Use during a Field Campaign. Metabolites vol. 11 192 (2021).
DOI:10.3390/metabo11040192 [Radboud Repository]
 Meurs, J., Sakkoula, E. & Cristescu, S. M. Real-Time Non-Invasive Monitoring of Short-Chain Fatty Acids in Exhaled Breath. Front. Chem. vol. 10 853541 (2022).
DOI:10.3389/fchem.2022.853541. [Radboud Repository]