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The fast development of analytical techniques in the field of gas analysis can be compared to that of computers during the last two decades. Not only speed but also sensitivity of analysis has been greatly improved, sometimes by a factor of 100 or more. This technological development has fostered the analysis of exhaled breath. Since this can be done in real-time, very fast biological processes can be monitored. Also simulation and modelling of haemodynamics and lung mechanics become possible. During the next decade we will see miniaturized equipment (of the size of a cigarette box) appear. Here we review and illustrate the rich diversity of compounds observed in exhaled breath with a particular focus on lung cancer patients. Each of the many volatile compounds has its own particular biochemical background, and cell types with different genetic background have been shown to have a different pattern of released and consumed volatile compounds. Nevertheless we still lack an understanding, if and how genetic alterations, which are seen as the underlying cause of the transformation process, control the VOC phenotype observed in patients or cancer cell lines. The concentration pattern of volatile compounds in exhaled breath may be used in the future for phenotyping individuals in large-scale screening approaches. Also changes in VOC patterns may provide disease-relevant information (e.g. on the activity of metabolizing enzymes). Future applications will also include the follow-up of exogenous compounds which are ingested or inhaled as drugs, food components or components in cigarette smoke and metabolic products of these compounds.

Non-invasive disease monitoring on the basis of volatile breath markers is a very attractive but challenging task. Several hundreds of compounds have been detected in exhaled air using modern analytical techniques (e.g. proton-transfer reaction mass spectrometry, gas chromatography-mass spectrometry) and have even been linked to various diseases. However,the biochemical background for most of compounds detected in breath samples has not been elucidated; therefore, the obtained results should be interpreted with care to avoid false correlations. The major aim of this study was to assess the effects of smoking on the composition of exhaled breath. Additionally, the potential origin of breath volatile organic compounds (VOCs) is discussed focusing on diet, environmental exposure and biological pathways based on other's studies. Profiles of VOCs detected in exhaled breath and inspired air samples of 115 subjects with addition of urine headspace derived from 50 volunteers are presented. Samples were analyzed with GC-MS after preconcentration on multibed sorption tubes in case of breath samples and solid phase micro-extraction (SPME) in the case of urine samples. Altogether 266 compounds were found in exhaled breath of at least 10% of the volunteers. From these, 162 compounds were identified by spectral library match and retention time (based on reference standards). It is shown that the composition of exhaled breath is considerably influenced by exposure to pollution and indoor-air contaminants and particularly by smoking. More than 80 organic compounds were found to be significantly related to smoking, the largest group comprising unsaturated hydrocarbons (29 dienes, 27 alkenes and 3 alkynes). On the basis of the presented results, we suggest that for the future understanding of breath data it will be necessary to carefully investigate the potential biological origin of volatiles, e.g., by means of analysis of tissues, isolated cell lines or other body fluids. In particular, VOCs linked to smoking habit or being the results of human exposure should be considered with care for clinical diagnosis since small changes in their concentration profiles(typically in the ppt(v)–ppb(v) range) revealing that the outbreak of certain disease might be hampered by already high background.

Background Lung cancer is one of the leading causes of death in Europe and the western world. At present, diagnosis of lung cancer very often happens late in the course of the disease since inexpensive, non-invasive and sufficiently sensitive and specific screening methods are not available. Even though the CT diagnostic methods are good, it must be assured that "screening benefit outweighs risk, across all individuals screened, not only those with lung cancer". An early non-invasive diagnosis of lung cancer would improve prognosis and enlarge treatment options. Analysis of exhaled breath would be an ideal diagnostic method, since it is non-invasive and totally painless. Methods Exhaled breath and inhaled room air samples were analyzed using proton transfer reaction mass spectrometry (PTR-MS) and solid phase microextraction with subsequent gas chromatography mass spectrometry (SPME-GCMS). For the PTR-MS measurements, 220 lung cancer patients and 441 healthy volunteers were recruited. For the GCMS measurements, we collected samples from 65 lung cancer patients and 31 healthy volunteers. Lung cancer patients were in different disease stages and under treatment with different regimes. Mixed expiratory and indoor air samples were collected in Tedlar bags, and either analyzed directly by PTR-MS or transferred to glass vials and analyzed by gas chromatography mass spectrometry (GCMS). Only those measurements of compounds were considered, which showed at least a 15% higher concentration in exhaled breath than in indoor air. Compounds related to smoking behavior such as acetonitrile and benzene were not used to differentiate between lung cancer patients and healthy volunteers. Results Isoprene, acetone and methanol are compounds appearing in everybody's exhaled breath. These three main compounds of exhaled breath show slightly lower concentrations in lung cancer patients as compared to healthy volunteers (p < 0.01 for isoprene and acetone, p = 0.011 for methanol; PTR-MS measurements). A comparison of the GCMS-results of 65 lung cancer patients with those of 31 healthy volunteers revealed differences in concentration for more than 50 compounds. Sensitivity for detection of lung cancer patients based on presence of (one of) 4 different compounds not arising in exhaled breath of healthy volunteers was 52% with a specificity of 100%. Using 15 (or 21) different compounds for distinction, sensitivity was 71% (80%) with a specificity of 100%. Potential marker compounds are alcohols, aldehydes, ketones and hydrocarbons. Conclusion GCMS-SPME is a relatively insensitive method. Hence compounds not appearing in exhaled breath of healthy volunteers may be below the limit of detection (LOD). PTR-MS, on the other hand, does not need preconcentration and gives much more reliable quantitative results then GCMS-SPME. The shortcoming of PTR-MS is that it cannot identify compounds with certainty. Hence SPME-GCMS and PTR-MS complement each other, each method having its particular advantages and disadvantages. Exhaled breath analysis is promising to become a future non-invasive lung cancer screening method. In order to proceed towards this goal, precise identification of compounds observed in exhaled breath of lung cancer patients is necessary. Comparison with compounds released from lung cancer cell cultures, and additional information on exhaled breath composition in other cancer forms will be important.

Background Analysis of exhaled breath is a promising diagnostic method. Sampling of exhaled breath is non-invasive and can be performed as often as considered desirable. There are indications that the concentration and presence of certain of volatile compounds in exhaled breath of lung cancer patients is different from concentrations in healthy volunteers. This might lead to a future diagnostic test for lung cancer. Methods Exhaled breath samples from 65 patients with different stages of lung cancer and undergoing different treatment regimes were analysed. Mixed expiratory and indoor air samples were collected. Solid phase microextraction (SPME) with carboxen/polydimethylsiloxane (CAR/PDMS) sorbent was applied. Compounds were analysed by means of gas chromatography (GC) and mass spectrometry (MS). Results The method we used allowed identification with the spectral library of 103 compounds showing at least 15% higher concentration in exhaled breath than in inhaled air. Among those 103 compounds, 84 were confirmed by determination of the retention time using standards based on the respective pure compound. Approximately, one third of the compounds detected were hydrocarbons. We found aromatic hydrocarbons, alcohols, aldehydes, ketones, esters, ethers, sulfur compounds, nitrogen-containing compounds and halogenated compounds. Acetonitrile and benzene were two of 10 compounds which correlated with smoking behaviour. A comparison of results from cancer patients with those of 31 healthy volunteers revealed differences in the concentration and presence of certain compounds. The sensitivity for detection of lung cancer patients based on eight different compounds not seen in exhaled breath of healthy volunteers was 51% and the specificity was 100%. These eight potential markers for detection of lung cancer are 1-propanol, 2-butanone, 3-butyn-2-ol, benzaldehyde, 2-methyl-pentane, 3-methyl-pentane, n-pentane and n-hexane. Conclusions SPME is a relatively insensitive method and compounds not observed in exhaled breath may be present at a concentration lower than LOD. The main achievement of the present work is the validated identification of compounds observed in exhaled breath of lung cancer patients. This identification is indispensible for future work on the biochemical sources of these compounds and their metabolic pathways.