Other factors influencing breath
6.3 Concluding remarks and future perspectives
From this thesis, it can be concluded that HCN in exhaled breath is not an exclu- sive biomarker for P. aeruginosa infection, which is a significant drawback in the attempt to develop a non-invasive method to detect P. aeruginosa in patients with
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Table 6.1: Recommendations for further research.
1. Online or at least high resolution measurements to study VOC patterns in detail.
2. A standardized protocol for breath sampling.
3. In vitro vs. in vivo correlation studies to determine the potential of VOCs for detection of pathogens in breath.
4. Combination of off-line techniques such as GC-MS, for the identification of potential biomarkers, with online methods, to study those specific VOCs in a detailed manner.
5. Larger cohort studies to confirm and validate potential biomarkers.
CF. However, breath analysis has still potential to diagnose lung infections. Al- though, in vitro, the VOCs in co-microbial environment differ from those released in mono-culture, patients with S. aureus (present in a polymicrobial environment) can be successfully discriminated from CF patients without S. aureus. However, future studies are needed in order to investigate which biomarker(s) are most suit- able for this purpose. Recommendations for further research will be discussed in this paragraph and are summarized in table 6.1.
The ideal biomarker is constantly produced by the pathogen, at equal concen- trations, in different growth phases. However, current data suggest that this is not necessarily realistic. Therefore, online- or at least high resolution measurements, like performed in this thesis using laser-based photo-acoustic spectroscopy, are de- sirable to better understand the production pattern of VOCs by pathogens. This knowledge can then be used to determine whether a certain VOC has potential for early detection of pathogens in exhaled breath. Secondly, a more standardized protocol for breath sampling is really needed in order to compare data obtained in different studies. This protocol ideally includes exhalation at a controlled flow speed or normal free breathing, and excludes the dead space volume. Moreover, analysis of CO2 concentration of these samples is desirable. Thirdly, it would be very interesting to further explore the correlation between in vitro and in vivo VOC production by analysing breath, the headspace of sputum of CF patients obtained on the day of breath sampling, and the headspace of bacterial cultures isolated from that sputum. This will provide more insight in the suitability of in vitro identified biomarkers. Another future possibility is to combine different tech- niques in order to study specific VOCs in a detailed manner. Combining off-line techniques such as GC-MS, for the identification of potential biomarkers, with on- line methods (such as laser-based methods, PTR-MS or SIFT-MS) to study those compounds in further detail. Additionally, high sensitivity and high resolution accurate mass data, such as obtained with GC-TOF-MS, can further improve the
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Chapter 6. Summary and future perspectives
detection of VOCs in breath. Finally, large cohort studies are necessary in order to confirm and validate the compounds that are currently proposed as biomarkers for different respiratory infections. These studies should show whether early detection and even monitoring of respiratory infections in exhaled breath of CF patients is ready for clinical practise. If that is the case, this non-invasive technique has also great potential for application in the diagnosis of pneumonia and other infectious diseases, lung diseases, and even diseases in other medical fields. To successfully perform high quality breath analysis studies to investigate this, a multidisciplinary research team in which trace gas researchers, medical doctors, technical experts, and statisticians collaborate, is vital.
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