Methodological aspects of exhaled breath condensate collection and analysis

The Role of Exhaled Breath Condensate in Chronic Inflammatory and Neoplastic Diseases of the Respiratory Tract

Asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic respiratory diseases. Chronic inflammation of the airways leads to an increased production of inflammatory markers by the effector cells of the respiratory tract and lung tissue. These biomarkers allow the assessment of physiological and pathological processes and responses to therapeutic interventions. Lung cancer, which is characterized by high mortality, is one of the most frequently diagnosed cancers worldwide. Current screening methods and tissue biopsies have limitations that highlight the need for rapid diagnosis, patient differentiation, and effective management and monitoring. One promising non-invasive diagnostic method for respiratory diseases is the assessment of exhaled breath condensate (EBC). EBC contains a mixture of volatile and non-volatile biomarkers such as cytokines, leukotrienes, oxidative stress markers, and molecular biomarkers, providing significant information about inflammatory and neoplastic states in the lungs. This article summarizes the research on the application and development of EBC assessment in diagnosing and monitoring respiratory diseases, focusing on asthma, COPD, and lung cancer. The process of collecting condensate, potential issues, and selected groups of markers for detailed disease assessment in the future are discussed. Further research may contribute to the development of more precise and personalized diagnostic and treatment methods.

Biomarkers in exhaled breath condensate as fingerprints of asthma, chronic obstructive pulmonary disease and asthma-chronic obstructive pulmonary disease overlap: a critical review

Asthma, chronic obstructive pulmonary disease (COPD) and asthma-COPD overlap are the third leading cause of mortality around the world. They share some common features, which can lead to misdiagnosis. To properly manage these conditions, reliable markers for early and accurate diagnosis are needed. Over the past 20 years, many molecules have been investigated in the exhaled breath condensate to better understand inflammation pathways and mechanisms related to these disorders. Recently, more advanced techniques, such as sensitive metabolomic and proteomic profiling, have been used to obtain a more comprehensive understanding. This article reviews the use of targeted and untargeted metabolomic methodology to study asthma, COPD and asthma-COPD overlap.

HBM4EU chromates study - the measurement of hexavalent and trivalent chromium in exhaled breath condensate samples from occupationally exposed workers across Europe

The aim of this study was to investigate the practicability of exhaled breath condensate (EBC) as a biological matrix to detect and measure hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) in workers occupationally exposed to Cr(VI). EBC samples were collected from workers in France, Finland, Italy, The Netherlands and the United Kingdom from three different target activities: chrome platers, stainless steel welders and surface treatment workers. Pre and post working week EBC samples were collected from 177 exposed workers and 98 unexposed workers (control group). Hyphenated chromatography systems with inductively coupled plasma - mass spectrometry (ICP-MS) were for the analysis. The results showed that the occupationally exposed workers had significantly higher levels of Cr(VI) and Cr(III) than the control group. Chrome platers exhibited the highest Cr(VI) levels in their EBC samples, with a significant increase from their pre to post samples for both Cr(VI) and Cr(III). A significant difference was also found between pre and post EBC samples for Cr(III) in welders. This study has shown that EBC has the potential to be a valid, non-invasive biological matrix to assess occupational exposure to Cr(VI) and Cr(III) for biological monitoring assessment, with the ability to detect low level inhalation exposures.

Towards Reference Values for Malondialdehyde on Exhaled Breath Condensate: A Systematic Literature Review and Meta-Analysis

Many pathological conditions and certain airway exposures are associated with oxidative stress (OS). Malondialdehyde (MDA) is an end-product of the oxidation of lipids in our cells and is present in all biological matrices including exhaled breath condensate (EBC). To use MDA as a biomarker of OS in EBC, a reference interval should be defined. Thus, we sought to summarize reference values reported in healthy adult populations by performing a systematic review and meta-analysis using a standardized protocol registered in PROSPERO (CRD42020146623). Articles were retrieved from four major databases and 25 studies with 28 subgroups were included. Defining the distribution of MDA measured in reference populations with a detection combined with a separation technique still represents a challenge due to the low number of studies available, different analytical methods used, and questionable methodological qualities of many studies. The most salient methodological drawbacks have been in data collection and reporting of methods and study results by the researchers. The lack of compliance with the recommendations of the European Respiratory Society and American Thoracic Society was the major limitation in the current research involving EBC. Consequently, we were unable to establish a reference interval for MDA in EBC.

Review of non-invasive detection of SARS-CoV-2 and other respiratory pathogens in exhaled breath condensate

In 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged to cause high viral infectivity and severe respiratory illness in humans (COVID-19). Worldwide, limited pandemic mitigation strategies, including lack of diagnostic test availability, resulted in COVID-19 overrunning health systems and spreading throughout the global population. Currently, proximal respiratory tract (PRT) specimens such as nasopharyngeal swabs are used to diagnose COVID-19 because of their relative ease of collection and applicability in large scale screening. However, localization of SARS-CoV-2 in the distal respiratory tract (DRT) is associated with more severe infection and symptoms. Exhaled breath condensate (EBC) is a sample matrix comprising aerosolized droplets originating from alveolar lining fluid that are further diluted in the DRT and then PRT and collected via condensation during tidal breathing. The COVID-19 pandemic has resulted in recent resurgence of interest in EBC collection as an alternative, non-invasive sampling method for the staging and accurate detection of SARS-CoV-2 infections. Herein, we review the potential utility of EBC collection for detection of SARS-CoV-2 and other respiratory infections. While much remains to be discovered in fundamental EBC physiology, pathogen-airway interactions, and optimal sampling protocols, EBC, combined with emerging detection methods, presents a promising non-invasive sample matrix for detection of SARS-CoV-2.

Recent Advances in Facemask Devices for In Vivo Sampling of Human Exhaled Breath Aerosols and Inhalable Environmental Exposures

Since the COVID-19 pandemic, the unprecedented use of facemasks has been requiring for wearing in daily life. By wearing facemask, human exhaled breath aerosols and inhaled environmental exposures can be efficiently filtered and thus various filtration residues can be deposited in facemask. Therefore, facemask could be a simple, wearable, in vivo, onsite and noninvasive sampler for collecting exhaled and inhalable compositions, and gain new insights into human health and environmental exposure. In this review, the recent advances in developments and applications of in vivo facemask sampling of human exhaled bacteria, viruses, proteins, and metabolites, and inhalable facemask contaminants and air pollutants, are reviewed. New features of facemask sampling are highlighted. The perspectives and challenges on further development and potential applications of facemask devices are also discussed.

Exhaled Breath Condensate-A Non-Invasive Approach for Diagnostic Methods in Asthma

The pathophysiology of asthma has been intensively studied, but its underlying mechanisms such as airway inflammation, control of airway tone, and bronchial reactivity are still not completely explained. There is an urgent need to implement novel, non-invasive diagnostic tools that can help to investigate local airway inflammation and connect the molecular pathways with the broad spectrum of clinical manifestations of asthma. The new biomarkers of different asthma endotypes could be used to confirm diagnosis, predict asthma exacerbations, or evaluate treatment response. In this paper, we briefly describe the characteristics of exhaled breath condensate (EBC) that is considered to be an interesting source of biomarkers of lung disorders. We look at the composition of EBC, some aspects of the collection procedure, the proposed biomarkers for asthma, and its clinical implications. We also indicate the limitations of the method and potential strategies to standardize the procedure of EBC collection and analytical methods.

Detecting COVID-19 from Breath: A Game Changer for a Big Challenge

Coronavirus disease 2019 (COVID-19) is probably the most commonly heard word of the last 12 months. The outbreak of this virus (SARS-CoV-2) is strongly compromising worldwide healthcare systems, social behavior, and everyone's lives. The early diagnosis of COVID-19 and isolation of positive cases has proven to be fundamental in containing the spread of the infection. Even though the polymerase chain reaction (PCR) based methods remain the gold standard for SARS-CoV-2 detection, the urgent demand for rapid and wide-scale diagnosis precipitated the development of alternative diagnostic approaches. The millions of tests performed every day worldwide are still insufficient to achieve the desired goal, that of screening the population during daily life. Probably the most appealing approach to consistently monitor COVID-19 spread is the direct detection of SARS-CoV-2 from exhaled breath. For instance, the challenging incorporation of reliable, highly sensitive, and cost-efficient detection methods in masks could represent a breakthrough in the development of portable and noninvasive point-of-care diagnosis for COVID-19. In this perspective paper, we discuss the critical technical aspects related to the application of breath analysis in the diagnosis of viral infection. We believe that, if achieved, it could represent a game-changer in containing the pandemic spread.

Breathomics: Review of Sample Collection and Analysis, Data Modeling and Clinical Applications

Metabolomics research is rapidly gaining momentum in disease diagnosis, on top of other Omics technologies. Breathomics, as a branch of metabolomics is developing in various frontiers, for early and noninvasive monitoring of disease. This review starts with a brief introduction to metabolomics and breathomics. A number of important technical issues in exhaled breath collection and factors affecting the sampling procedures are presented. We review the recent progress in metabolomics approaches and a summary of their applications on the respiratory and non-respiratory diseases investigated by breath analysis. Recent reports on breathomics studies retrieved from Scopus and Pubmed were reviewed in this work. We conclude that analyzing breath metabolites (both volatile and nonvolatile) is valuable in disease diagnoses, and therefore believe that breathomics will turn into a promising noninvasive discipline in biomarker discovery and early disease detection in personalized medicine. The problem of wide variations in the reported metabolite concentrations from breathomics studies should be tackled by developing more accurate analytical methods and sophisticated numerical analytical alogorithms.

Exhaled Breath Condensate (EBC): Is It a Viable Source of Biomarkers for Lung Diseases?

The exhaled breath condensate is a source of biomarkers with many advantages and benefits compared to other traditional sampling techniques in respiratory medicine. It is a biological product that is formed by cooling the exhaled air via its guidance through a condenser. It is characterized as a cocktail of volatile and non-volatile compounds with water being the predominant constituent. Its composition presents a non-uniformed structure as the volatile and the non-volatile compounds vary in type and ratio. All these compounds originate from the whole respiratory tract. Some of them fulfil the criteria to be characterized as biomarkers since there is a similarity between the content of the exhaled breath condensate and the respiratory tract lining fluid. In addition, the potential biomarkers of the exhaled breath condensate and those from other biological fluids are equivalent.Advantages and Disadvantages Its place in the respiratory medicine as a matrix of biomarkers relies on its various strengths. Some of them are very important and make it exceptional regarding its application, such as its totally non-invasive character and its usage in all ages, while others present a more potential action regarding its purpose such as the categorization of respiratory diseases. However, there are limitations in its application due to the lack of standardization of its conduct which can be minimized by following the official recommendations. Additional studies are needed to develop said standardization.Aim The aim of this paper is to present a brief and comprehensive picture of the sampling technique of the exhaled breath condensate, as well as the criteria to make it a preferred choice as a source of biomarkers.

Reference Ranges of 8-Isoprostane Concentrations in Exhaled Breath Condensate (EBC): A Systematic Review and Meta-Analysis

Isoprostanes are physiopathologic mediators of oxidative stress, resulting in lipid peroxidation. 8-isoprostane seems particularly useful for measuring oxidative stress damage. However, no reference range values are available for 8-isoprosante in exhaled breath condensate (EBC) of healthy adults, enabling its meaningful interpretation as a biomarker. We conducted this systematic review and meta-analysis according to the protocol following PROSPERO (CRD42020146623). After searching and analyzing the literature, we included 86 studies. After their qualitative synthesis and risk of bias assessment, 52 studies were included in meta-analysis. The latter focused on studies using immunological analytical methods and investigated how the concentrations of 8-isoprostane differ based on gender. We found that gender had no significant effect in 8-isoprostane concentration. Among other studied factors, such as individual characteristics and factors related to EBC collection, only the device used for EBC collection significantly affected measured 8-isoprostane concentrations. However, adjustment for the factors related to EBC collection, yielded uncertainty whether this effect is due to the device itself or to the other factors. Given this uncertainty, we estimated the reference range values of 8-isoprostane stratified by gender and EBC collection device. A better standardization of EBC collection seems necessary; as well more studies using chemical analytical methods to extend this investigation.

Metabolomics of Exhaled Breath Condensate by Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry: A Methodological Approach

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Respiratory diseases present a very high prevalence in the general population, with an increase in morbidity, mortality and health-care expenses worldwide. They are complex and heterogeneous pathologies that may present different pathological facets in different subjects, often with personal evolution. Therefore, there is a need to identify patients with similar characteristics, prognosis or treatment, defining the so-called phenotype, but also to mark specific differences within each phenotype, defining the endotypes.

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Biomarkers are very useful to study respiratory phenotypes and endotypes. Metabolomics, one of the recently introduced “omics”, is becoming a leading technique for biomarker discovery. For the airways, metabolomics appears to be well suited as the respiratory tract offers a natural matrix, the Exhaled Breath Condensate (EBC), in which several biomarkers can be measured. In this review, we will discuss the main methodological issues related to the application of Nuclear Magnetic Resonance (NMR) spectroscopy and Mass Spectrometry (MS) to EBC metabolomics for investigating respiratory diseases.

Cytokines and Chemokines Are Detectable in Swivel-Derived Exhaled Breath Condensate (SEBC): A Pilot Study in Mechanically Ventilated Patients

Introduction

Exhaled breath condensate (EBC) is a noninvasive method to collect samples from the respiratory tract. Usually, a thermoelectric cooling module is required to collect sufficient EBC volume for analyses. In here, we assessed the feasibility of cytokine and chemokine detection in EBC collected directly from the ventilator circuit without the use of a cooling module: swivel-derived exhaled breath condensate (SEBC).

Methods

SEBC was prospectively collected from the swivel adapter and stored at -80°C. The objective of this study was to detect cytokines and chemokines in SEBC with a multiplex immunoassay. Secondary outcomes were to assess the correlation between cytokine and chemokine concentrations in SEBC and mechanical ventilation parameters, systemic inflammation parameters, and hemodynamic parameters.

Results

Twenty-nine SEBC samples were obtained from 13 ICU patients. IL-1β, IL-4, IL-8, and IL-17 were detected in more than 90% of SEBC samples, and significant correlations between multiple cytokines and chemokines were found. Several significant correlations were found between cytokines and chemokines in SEBC and mechanical ventilation parameters and serum lactate concentrations.

Conclusion

This pilot study showed that it is feasible to detect cytokines and chemokines in SEBC samples obtained without a cooling module. Despite small sample size, correlations were found between cytokines and chemokines in SEBC and mechanical ventilation parameters, as well as serum lactate concentrations. This simple SEBC collection method provides the opportunity to collect EBC samples in large prospective ICU cohorts.

cfDNA in exhaled breath condensate (EBC) and contamination by ambient air: toward volatile biopsies

Exhaled breath is a source of volatile and nonvolatile biomarkers in the body that can be accessed non-invasively and used for monitoring. The collection of lung secretions by conventional methods such as bronchoalveolar lavage, induced sputum collection, and core biopsies is limited by the invasive nature of these methods. Non-invasive collection of exhaled breath condensate (EBC) provides fluid samples that are representative of airway lining fluids. Various volatile and nonvolatile biomarkers can be detected in volatile condensates, such as H₂O₂, nitric oxide, lipid mediators, cytokines, chemokines, DNA, and microRNAs. Studies have examined cell-free DNA (cfDNA) in plasma samples from non-small-cell lung cancer patients, offering to new insights and fostering development of the liquid biopsy. However, few studies have examined cfDNA in EBC samples. This study examined whether EBC is an appropriate source of cfDNA using housekeeping-gene-specific primer probes and quantitative real-time polymerase chain reaction in healthy subjects. Ambient (room) air is contaminated with DNA, so caution is needed. Preliminary studies indicated that volatile biopsies are becoming an important diagnostic tool in lung cancer.

Expressions of MMP-12, TIMP-4, and Neutrophil Elastase in PBMCs and Exhaled Breath Condensate in Patients with COPD and Their Relationships with Disease Severity and Acute Exacerbations

OBJECTIVE

The purpose of this study was to compare matrix metalloproteinase-12 (MMP-12), neutrophil elastase (NE), and tissue inhibitor of metalloproteinase-4 (TIMP-4) in peripheral blood of patients with chronic obstructive pulmonary disease (COPD) and controls. At the same time, MMP-12, NE, and TIMP-4 in exhaled breath condensate (EBC) were also evaluated.

METHODS

Peripheral blood and EBC samples from COPD patients and healthy controls were collected. In serum and EBC, MMP-12, NE, and TIMP-4 proteins were detected by enzyme-linked immunoassays. The mRNA expression levels of MMP-12, NE, and TIMP-4 in peripheral blood mononuclear cells (PBMCs) were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

The concentration of TIMP-4 protein in EBC was lower in patients with COPD (P < 0.001). MMP-12 (P = 0.046), NE (P = 0.027), and TIMP-4 (P = 0.005) proteins in serum of patients with COPD showed higher levels of concentration. The mRNA of MMP-12 (P = 0.0067), NE (P = 0.0058), and TIMP-4 (P = 0.0006) in PBMCs of COPD patients showed higher expression levels. Compared with stable patients, mRNA expression level of NE (P = 0.033) in PBMCs of patients with acute exacerbation of COPD was increased. There were differences in the ratio of MMP-12/TIMP-4 in PBMC (P = 0.0055), serum (P = 0.0427), and EBC (P = 0.0035) samples between COPD patients and healthy controls. The mRNA expression of MMP-12 (r = -0.3958, P = 0.0186) and NE (r = -0.3694, P = 0.0290) in COPD patients was negatively correlated with pulmonary function. However, the mRNA expression of TIMP-4 (r = 0.2871, P = 0.0945) in PBMCs was not correlated with the FEV1 of the pulmonary function. Serum MMP-12 level was positively correlated with the MMP-12 level in EBC (P = 0.0387). The level of TIMP-4 in serum was not correlated with the level in the EBC sample (P = 0.4332).

CONCLUSION

The expression levels of MMP-12, NE, and TIMP-4 in PBMCs and serum were elevated in COPD patients. In PBMCs of COPD patients, the mRNA expression level of NE may predict acute exacerbation, and MMP-12 mRNA expression level may be used to reflect the severity of airflow limitation. However, to better assess their diagnostic or prognostic value, larger studies are necessary.

Inflammatory mediators in exhaled breath condensate and peripheral blood of healthy donors and stable COPD patients

Objective: The aim of this work was to compare matrix metalloproteinase-9 and -12, tissue inhibitor of metalloproteinase-1 and -4, and neutrophil elastase in exhaled breath condensate (EBC) and peripheral blood of patients with COPD. Methods: Peripheral blood and EBC samples from COPD patients and healthy donors were collected. In serum and EBC, MMP-9, MMP-12, NE, TIMP-1, and TIMP-4 proteins were detected by ELISA. The mRNA expression levels of MMP-9, MMP-12, NE, TIMP-1, and TIMP-4 in peripheral blood mononuclear cells (PBMCs) were analyzed by qRT-PCR. Results: The protein levels of MMP-9 (p=.034) and MMP-12 (p=.041) in the EBC of COPD smokers were higher than those of COPD never-smokers. The concentrations of TIMP-1 (p=.072) and TIMP-4 (p=.084) in the EBC of COPD smokers were higher than those of COPD never-smokers; however, the difference was not statistically significant. MMP-9 (r=-0.78, p<.0001) and TIMP-1 (r=-0.71, p<.0001) levels in EBC were significantly negatively correlated with pulmonary function FEV1%pred. The protein levels of MMP-12 (r=-0.37, p=.034) and TIMP-4 (r=-0.34, p=.041) were also negatively correlated with FEV1%pred. The expression of MMP-9, MMP-12, NE, TIMP-1, and TIMP-4 in PBMCs and serum of COPD smokers were significantly higher than those of control never-smokers (p<.05). Conclusions: Exhaled MMP-9, MMP-12, TIMP-1, and TIMP-4 levels increased in stable COPD patients and were negatively correlated with FEV1%pred, which suggests the usefulness of their measurement in EBC for the monitoring of airway inflammation. However, to better assess their diagnostic or prognostic value, larger studies are necessary.

Exhaled Breath Condensate in Childhood Asthma: A Review and Current Perspective

Exhaled breath condensate (EBC) was introduced more than two decades ago as a novel, non-invasive tool to assess airway inflammation. This review summarizes the latest literature on the various markers in EBC to predict asthma in children. Despite many recommendations and two comprehensive Task Force reports, there is still large heterogeneity in published data. The biggest issue remains a lack of standardization regarding EBC collection, preservation, processing, and analysis. As a result, published studies show mixed or conflicting results, questioning the reproducibility of findings. A joint, multicenter research study is urgently needed to address the necessary methodological standardization.

Bronchoalveolar pH and inflammatory biomarkers in patients with acute exacerbation of chronic obstructive pulmonary disease

Objectives

This study aimed to directly measure pH in the lungs, determine lactate dehydrogenase (LDH), C-reactive protein (CRP), and glucose levels in serum and bronchoalveolar aspirate, and identify bacterial pathogens from bronchoalveolar fluid during acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

Methods

We performed an observational, analytical case–control study from February 2015 to March 2017. We included 84 patients with AECOPD and 42 with stable chronic obstructive pulmonary disease (COPD). All participants underwent detailed medical anamnesis, a clinical examination, chest radiography, spirometry, an arterial blood gas test, bronchoscopy, bacterial culture, and serum/bronchiolar aspirate laboratory testing.

Results

The mean pH of bronchoalveolar fluid was significantly higher in patients with AECOPD than in patients with stable COPD. The mean lung pH value, bronchoalveolar and serum LDH levels, and serum CRP levels in patients with isolated bacteria were higher than those in patients without isolated bacteria in the AECOPD patient group. Lung pH values in patients with AECOPD were significantly correlated with bronchoalveolar LDH and glucose levels.

Conclusions

AECOPD is associated with local cell and tissue injury in the lungs, especially in the presence of bacterial pathogens, which is accompanied by a low systemic inflammatory response.

A feasibility study into adenosine triphosphate measurement in exhaled breath condensate: a potential bedside method to monitor alveolar deformation

Recent research suggested an important role for pulmonary extracellular adenosine triphosphate (ATP) in the development of ventilation-induced lung injury. This injury is induced by mechanical deformation of alveolar epithelial cells, which in turn release ATP to the extracellular space. Measuring extracellular ATP in exhaled breath condensate (EBC) may be a non-invasive biomarker for alveolar deformation. Here, we study the feasibility of bedside ATP measurement in EBC. We measured ATP levels in EBC in ten subjects before and after an exercise test, which increases respiratory parameters and alveolar deformation. EBC lactate concentrations were measured as a dilution marker. We found a significant increase in ATP levels in EBC (before 73 RLU [IQR 50–209] versus after 112 RLU [IQR 86–203]; p value 0.047), and the EBC ATP-to-EBC lactate ratio increased as well (p value 0.037). We present evidence that bedside measurement of ATP in EBC is feasible and that ATP levels in EBC increase after exercise. Future research should measure ATP levels in EBC during mechanical ventilation as a potential biomarker for alveolar deformation.

Exhaled breath NOx levels in a middle-aged adults population-based study: reference values and association with the smoking status

BACKGROUND

Biomarkers in exhaled breath condensate (EBC) are potentially sensitive indicators of early biochemical changes in airways following exposure to pneumotoxic substances, particularly in susceptible subjects. NOx are the stable end products of the nitrite-nitrate-NO oxidative stress pathway and can be used to monitor airway inflammatory diseases, especially in asthma. Nevertheless, population-based surveys are needed to better interpret EBC NOx levels in clinical studies. The aim of this study was to establish reference values of EBC NOx in a large group of middle-aged, healthy adults of a sample of the general population with particular focus on the smoking status.

METHODS

The EBC NOx levels were analysed from 2872 subjects among the ELISABET population-based cross sectional study including a representative sample of men and women aged from 40 to 66 years olds conducted in northern France, which included comprehensive questionnaires by interview and spirometry data. Healthy participants were defined as participants with no self-reported respiratory disease.

RESULTS

For the healthy subjects (n = 1251), the median NOx concentration (IQR) was equal to 7.2  μM (3.12) and concentrations of NOx in EBC did not differ significantly according to smoking status. The upper fifth percentile (95%) (ULN) of NOx concentrations among healthy subjects was equal to 13.6  μM, ranging from 12.7  μM (smokers) to 14.4  μM (ex smokers). Among subjects with EBC NOx values higher than the ULN and compared with subjects that had EBC NOx values lower than the ULN, we found a significant higher proportion of subjects with current asthma (10.5% vs 6.5%) or with chronic bronchitis symptoms (7.6% vs 3.3%).

CONCLUSION

This population-based study has provided the distribution and the upper limit reference value of a nitrosative stress biomarker (NOx) in EBC of middle aged, healthy adults. EBC NOx levels were not associated with smoking status.

Transition and post-transition metals in exhaled breath condensate

Water vapor in expired air, as well as dispersed non-volatile components, condense onto a cooler surface after exiting the respiratory tract. This exhaled breath condensate (EBC) provides a dilute sampling of the epithelial lining fluid. Accordingly, the collection of EBC imparts a capacity to provide biomarkers of injury preceding clinical disease. Concentrations of transition and post-transition metals in EBC are included among these endpoints. Iron and zinc are the metals with the highest concentration and are measurable in all EBC samples from healthy subjects; other metals are most frequently either at or below the level of detection in this group. Gender, age, and smoking can impact EBC metal concentrations in healthy subjects. EBC metal concentrations among patients diagnosed with particular lung diseases (e.g. asthma, chronic obstructive disease, and interstitial lung disease) have been of research interest but no definite pattern of involvement has been delineated. Studies of occupationally exposed workers confirm significant exposure to specific metals, but such EBC metal measurements frequently provide evidence redundant with environmental sampling. Measurements of metal concentrations in EBC remain a research tool into metal homeostasis in the respiratory tract and participation of metals in disease pathogenesis. The quantification of metal concentrations in EBC is currently not reliable for clinical use in either supporting or determining any diagnosis. Issues that must be addressed prior to the use of EBC metal measurements include the establishment of both standardized collection and measurement techniques.

A European Respiratory Society technical standard: exhaled biomarkers in lung disease

Breath tests cover the fraction of nitric oxide in expired gas (F_eNO), volatile organic compounds (VOCs), variables in exhaled breath condensate (EBC) and other measurements. For EBC and for F_eNO, official recommendations for standardised procedures are more than 10 years old and there is none for exhaled VOCs and particles. The aim of this document is to provide technical standards and recommendations for sample collection and analytic approaches and to highlight future research priorities in the field. For EBC and F_eNO, new developments and advances in technology have been evaluated in the current document. This report is not intended to provide clinical guidance on disease diagnosis and management.Clinicians and researchers with expertise in exhaled biomarkers were invited to participate. Published studies regarding methodology of breath tests were selected, discussed and evaluated in a consensus-based manner by the Task Force members.Recommendations for standardisation of sampling, analysing and reporting of data and suggestions for research to cover gaps in the evidence have been created and summarised.Application of breath biomarker measurement in a standardised manner will provide comparable results, thereby facilitating the potential use of these biomarkers in clinical practice.

The simultaneous detection of trivalent & hexavalent chromium in exhaled breath condensate: A feasibility study comparing workers and controls

The analytical method outlined in this feasibility study has been used to show that trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) can be detected and measured in exhaled breath condensate (EBC) samples. EBC samples and urine samples were collected from a cohort of 58 workers occupationally exposed to hexavalent chromium compounds and 22 unexposed volunteers (control group). Levels of Cr(III) and Cr(VI) were determined in EBC samples and total chromium levels were determined in urine samples. Pre and post working week samples for both EBC and urine were collected in tandem. Total chromium in urine samples was analysed by inductively coupled plasma mass spectrometry (ICP-MS). Analysis of Cr(III) and Cr(VI) in EBC samples used a hyphenated micro liquid chromatography (μLC) system coupled to an ICP-MS. Separation was achieved using an anion exchange micro-sized column. The results showed that the occupationally exposed workers had significantly higher levels of Cr(III) and Cr(VI) in their EBC samples than the control group, as well as higher levels of total chromium in their urine samples. However, for the exposed workers no significant difference was found between pre and post working week EBC samples for either Cr(III) or Cr(VI). This study has established that Cr(III) and Cr(VI) can simultaneously be detected and measured in 'real' EBC samples and will help in understanding inhalation exposure.

MMP-8, MMP-9 and Neutrophil Elastase in Peripheral Blood and Exhaled Breath Condensate in COPD

Chronic obstructive pulmonary disease (COPD) is characterised by progressive and irreversible airflow limitation associated with chronic inflammation involving cytokines and metalloproteinases (MMPs). MMP-8, MMP-9 and neutrophil elastase (NE) are known to be implicated in COPD but the factors influencing activation and suppression remain unclear. This study aimed to compare MMP-8, MMP-9 and NE in the peripheral blood of COPD patients and controls and to likewise assess exhaled breath condensate (EBC) for these MMPs. Peripheral blood micro(mi)RNA139-5p levels, which may regulate MMPs in COPD, were also measured. Blood and EBC were collected from COPD patients (stable and during exacerbations) and healthy controls. Expression of mRNA for MMP-8, MMP-9, NE and miRNA-139-5p expression in peripheral blood mononuclear cells (PBMCs) was measured using qRT-PCR. MMP-8, MMP-9 and NE protein in plasma as well as MMP-8 and MMP-9 protein in EBC were analysed by enzyme-linked immunoassays. PBMCs from COPD patients showed greater expression of mRNA for MMP-8 (p = 0.0004), MMP-9 (p = 0.0023) and NE (p = 0.0019). PBMC expression of mRNA for NE was significantly higher in COPD exacerbations compared to stable cases (p < 0.05). Expression of mRNA for MMP-9 and NE correlated negatively with spirometry in patients (p < 0.05). Plasma from COPD patients showed greater levels of protein for MMP-8 (p = 0.003), MMP-9 (p = 0.046) and NE (p = 0.018). MMP-8 protein levels were lower in the EBC of COPD patients (p < 0.0001). In PBMCs, enhanced expression of mRNA for MMP-9 and NE is associated with COPD and may correlate with disease severity and exacerbations.

Exhaled breath condensate for lung cancer protein analysis: a review of methods and biomarkers

Lung cancer is a leading cause of cancer-related deaths worldwide, and is considered one of the most aggressive human cancers, with a 5 year overall survival of 10-15%. Early diagnosis of lung cancer is ideal; however, it is still uncertain as to what technique will prove successful in the systematic screening of high-risk populations, with the strongest evidence currently supporting low dose computed tomography (LDCT). Analysis of exhaled breath condensate (EBC) has recently been proposed as an alternative low risk and non-invasive screening method to investigate early-stage neoplastic processes in the airways. However, there still remains a relative paucity of lung cancer research involving EBC, particularly in the measurement of lung proteins that are centrally linked to pathogenesis. Considering the ease and safety associated with EBC collection, and advances in the area of mass spectrometry based profiling, this technology has potential for use in screening for the early diagnosis of lung cancer. This review will examine proteomics as a method of detecting markers of neoplasia in patient EBC with a particular emphasis on LC, as well as discussing methodological challenges involving in proteomic analysis of EBC specimens.

Bacterial volatiles and diagnosis of respiratory infections

Breath testing has enormous potential in the medical diagnostic field. The underlying complexity and perceived availability of adequate specimens, combined with a lack of knowledge of the metabolic pathways that give rise to compounds that are sources of analytes detectable in breath, has greatly slowed development. These real obstacles have recently been largely overcome in the use of breath testing to identify patients with cystic fibrosis associated Pseudomonas aeruginosa infection and tuberculosis. This review summarizes progress made in the characterization of microbial volatiles produced by major lower respiratory tract bacterial pathogens, and their potential use as diagnostic markers in patient breath testing.

Study of exhaled breath condensate sample preparation for metabolomics analysis by LC-MS/MS in high resolution mode

Metabolomic analysis of exhaled breath condensate (EBC) requires an unavoidable sample preparation step because of the low concentration of its components, and potential cleanup for possible interferents. Sample preparation based on protein precipitation (PP), solid-phase extraction (SPE) by hydrophilic and lipophilic sorbents or lyophilization has demonstrated that the analytical sample from the last is largely the best because lyophilization allows reconstitution in a volume as small as required (preconcentration factors up to 80-times with respect to the original sample), thus doubling the number of detected compounds as compared with the other alternatives (47 versus 25). In addition, PP and/or SPE cleanup are unnecessary as no effect from the EBC components removed by these steps appears in the chromatograms. The total 49 EBC compounds tentatively identified and confirmed by MS/MS in this research include amino acids, fatty acids, fatty amides, fatty aldehydes, sphingoid bases, oxoanionic compounds, imidazoles, hydroxy acids and aliphatic acyclic acids.

Noninvasive effects measurements for air pollution human studies: methods, analysis, and implications

Human exposure studies, compared with cell and animal models, are heavily relied upon to study the associations between health effects in humans and air pollutant inhalation. Human studies vary in exposure methodology, with some work conducted in controlled settings, whereas other studies are conducted in ambient environments. Human studies can also vary in the health metrics explored, as there exists a myriad of health effect end points commonly measured. In this review, we compiled mini reviews of the most commonly used noninvasive health effect end points that are suitable for panel studies of air pollution, broken into cardiovascular end points, respiratory end points, and biomarkers of effect from biological specimens. Pertinent information regarding each health end point and the suggested methods for mobile collection in the field are assessed. In addition, the clinical implications for each health end point are summarized, along with the factors identified that can modify each measurement. Finally, the important research findings regarding each health end point and air pollutant exposures were reviewed. It appeared that most of the adverse health effects end points explored were found to positively correlate with pollutant levels, although differences in study design, pollutants measured, and study population were found to influence the magnitude of these effects. Thus, this review is intended to act as a guide for researchers interested in conducting human exposure studies of air pollutants while in the field, although there can be a wider application for using these end points in many epidemiological study designs.

Exhaled Breath Condensate: Technical and Diagnostic Aspects

Purpose. The aim of this study was to evaluate the 30-year progress of research on exhaled breath condensate in a disease-based approach. Methods. We searched PubMed/Medline, ScienceDirect, and Google Scholar using the following keywords: exhaled breath condensate (EBC), biomarkers, pH, asthma, gastroesophageal reflux (GERD), smoking, COPD, lung cancer, NSCLC, mechanical ventilation, cystic fibrosis, pulmonary arterial hypertension (PAH), idiopathic pulmonary fibrosis, interstitial lung diseases, obstructive sleep apnea (OSA), and drugs. Results. We found 12600 related articles in total in Google Scholar, 1807 in ScienceDirect, and 1081 in PubMed/Medline, published from 1980 to October 2014. 228 original investigation and review articles were eligible. Conclusions. There is rapidly increasing number of innovative articles, covering all the areas of modern respiratory medicine and expanding EBC potential clinical applications to other fields of internal medicine. However, the majority of published papers represent the results of small-scale studies and thus current knowledge must be further evaluated in large cohorts. In regard to the potential clinical use of EBC-analysis, several limitations must be pointed out, including poor reproducibility of biomarkers and absence of large surveys towards determination of reference-normal values. In conclusion, contemporary EBC-analysis is an intriguing achievement, but still in early stage when it comes to its application in clinical practice.

Monitoring the ionic content of exhaled breath condensate in various respiratory diseases by capillary electrophoresis with contactless conductivity detection

The analysis of an ionic profile of exhaled breath condensate (EBC) by capillary electrophoresis with contactless conductivity detection and double opposite end injection, is demonstrated. A miniature sampler made from a 2 ml syringe and an aluminium cooling cylinder was used for the fast collection of EBC (under one minute). Analysis of the collected EBC was performed in a 60 mM 2-(N-morpholino)ethanesulfonic acid, 60 mM L-histidine background electrolyte with 30 µM cetyltrimethylammonium bromide and 2 mM 18-crown-6 at pH 6, and excellent repeatability of migration times (RSD  <1.3% (n = 7)) and peak areas (RSD  <  7% (n = 7)) of 14 ions (inorganic anions, cations and organic acids) was obtained. It is demonstrated that the analysis of EBC samples obtained from patients with various respiratory diseases (chronic obstructive pulmonary disease, asthma, pulmonary fibrosis, sarcoidosis, cystic fibrosis) is possible in less than five minutes and the ionic profile can be compared with the group of healthy individuals. The analysis of the ionic profile of EBC samples provides a set of data in which statistically significant differences among the groups of patients could be observed for several clinically relevant anions (nitrite, nitrate, acetate, lactate). The developed collection system and method provides a highly reproducible and fast way of collecting and analyzing EBC, with future applicability in point-of-care diagnostics.

Single-breath analysis using a novel simple sampler and capillary electrophoresis with contactless conductometric detection

The analysis of ionic content of exhaled breath condensate (EBC) from one single breath by CE with C(4) D is demonstrated for the first time. A miniature sampler made from a 2-mL syringe and an aluminum cooling cylinder for collection of EBC was developed. Various parameters of the sampler that influence its collection efficiency, repeatability, and effect of respiratory patterns were studied in detail. Efficient procedures for the cleanup of the miniature sampler were also developed and resulted in significant improvement of sampling repeatability. Analysis of EBC was performed by CE-C(4) D in a 60 mM MES/l-histidine BGE with 30 μM CTAB and 2 mM 18-crown-6 at pH 6 and excellent repeatability of migration times (RSD < 1.3% (n = 7)) and peak areas (RSD < 7% (n = 7)) of 12 inorganic anions, cations, and organic acids was obtained. It has been shown that the breathing pattern has a significant impact on the concentration of the analytes in the collected EBC. As the ventilatory pattern can be easily controlled during single exhalation, the developed collection system and method provides a highly reproducible and fast way of collecting EBC with applicability in point-of-care diagnostics.

Breath analysis as a potential and non-invasive frontier in disease diagnosis: an overview

Currently, a small number of diseases, particularly cardiovascular (CVDs), oncologic (ODs), neurodegenerative (NDDs), chronic respiratory diseases, as well as diabetes, form a severe burden to most of the countries worldwide. Hence, there is an urgent need for development of efficient diagnostic tools, particularly those enabling reliable detection of diseases, at their early stages, preferably using non-invasive approaches. Breath analysis is a non-invasive approach relying only on the characterisation of volatile composition of the exhaled breath (EB) that in turn reflects the volatile composition of the bloodstream and airways and therefore the status and condition of the whole organism metabolism. Advanced sampling procedures (solid-phase and needle traps microextraction) coupled with modern analytical technologies (proton transfer reaction mass spectrometry, selected ion flow tube mass spectrometry, ion mobility spectrometry, e-noses, etc.) allow the characterisation of EB composition to an unprecedented level. However, a key challenge in EB analysis is the proper statistical analysis and interpretation of the large and heterogeneous datasets obtained from EB research. There is no standard statistical framework/protocol yet available in literature that can be used for EB data analysis towards discovery of biomarkers for use in a typical clinical setup. Nevertheless, EB analysis has immense potential towards development of biomarkers for the early disease diagnosis of diseases.

NMR metabolomic analysis of exhaled breath condensate of asthmatic patients at two different temperatures

Exhaled breath condensate (EBC) collection is a noninvasive method to investigate lung diseases. EBC is usually collected with commercial/custom-made condensers, but the optimal condensing temperature is often unknown. As such, the physical and chemical properties of exhaled metabolites should be considered when setting the temperature, therefore requiring validation and standardization of the collecting procedure. EBC is frequently used in nuclear magnetic resonance (NMR)-based metabolomics, which unambiguously recognizes different pulmonary pathological states. Here we applied NMR-based metabolomics to asthmatic and healthy EBC samples collected with two commercial condensers operating at -27.3 and -4.8 °C. Thirty-five mild asthmatic patients and 35 healthy subjects were included in the study, while blind validation was obtained from 20 asthmatic and 20 healthy different subjects not included in the primary analysis. We initially analyzed the samples separately and assessed the within-day, between-day, and technical repeatabilities. Next, samples were interchanged, and, finally, all samples were analyzed together, disregarding the condensing temperature. Partial least-squares discriminant analysis of NMR spectra correctly classified samples, without any influence from the temperature. Input variables were either integral bucket areas (spectral bucketing) or metabolite concentrations (targeted profiling). We always obtained strong regression models (95%), with high average-quality parameters for spectral profiling (R(2) = 0.84 and Q(2) = 0.78) and targeted profiling (R(2) = 0.91 and Q(2) = 0.87). In particular, although targeted profiling clustering is better than spectral profiling, all models reproduced the relative metabolite variations responsible for class differentiation. This warrants that cross comparisons are reliable and that NMR-based metabolomics could attenuate some specific problems linked to standardization of EBC collection.

Exhaled breath condensate in intubated neonates--a window into the lung's glutathione status

BACKGROUND

Analysis of exhaled breath condensates (EBC) is a non-invasive technique to evaluate biomarkers such as antioxidants in the pediatric population, but limited data exists of its use in intubated patients, particularly newborns. Currently, tracheal aspirate (TA) serves as the gold standard collection modality in critically ill newborns, but this method remains invasive. We tested the hypothesis that glutathione status would positively correlate between EBC and TA collections in intubated newborns in the Newborn Intensive Care Unit (NICU). We also hypothesized that these measurements would be associated with alveolar macrophage (AM) glutathione status in the newborn lung.

METHODS

Reduced glutathione (rGSH), glutathione disulfide (GSSG), and total GSH (rGSH + (2 X GSSG)) were measured in sequential EBC and TA samples from 26 intubated newborns via high performance liquid chromatography (HPLC). Additionally, AM glutathione was evaluated via immunofluorescence. Pearson's correlation coefficient and associated 95% confidence intervals were used to quantify the associations between raw and urea-corrected concentrations in EBC and TA samples and AM staining. Statistical significance was defined as p ≤ 0.05 using two-tailed tests. The sample size was projected to allow for a correlation coefficient of 0.5, with 0.8 power and alpha of 0.05.

RESULTS

EBC was obtainable from intubated newborns without adverse clinical events. EBC samples demonstrated moderate to strong positive correlations with TA samples in terms of rGSH, GSSG and total GSH. Positive correlations between the two sampling sites were observed in both raw and urea-corrected concentrations of rGSH, GSSG and total GSH. AM glutathione staining moderately correlated with GSSG and total GSH status in both the TA and EBC.

CONCLUSIONS

GSH status in EBC samples of intubated newborns significantly correlated with the GSH status of the TA sample and was reflective of cellular GSH status in this cohort of neonatal patients. Non-invasive EBC sampling of intubated newborns holds promise for monitoring antioxidant status such as GSH in the premature lung. Further studies are necessary to evaluate the potential relationships between EBC biomarkers in the intubated premature newborn and respiratory morbidities.

Exhaled breath condensate--from an analytical point of view

Over the past three decades, the goal of many researchers is analysis of exhaled breath condensate (EBC) as noninvasively obtained sample. A total quality in laboratory diagnostic processes in EBC analysis was investigated: pre-analytical (formation, collection, storage of EBC), analytical (sensitivity of applied methods, standardization) and post-analytical (interpretation of results) phases. EBC analysis is still used as a research tool. Limitations referred to pre-analytical, analytical, and post-analytical phases of EBC analysis are numerous, e.g. low concentrations of EBC constituents, single-analyte methods lack in sensitivity, and multi-analyte has not been fully explored, and reference values are not established. When all, pre-analytical, analytical and post-analytical requirements are met, EBC biomarkers as well as biomarker patterns can be selected and EBC analysis can hopefully be used in clinical practice, in both, the diagnosis and in the longitudinal follow-up of patients, resulting in better outcome of disease.

Biomarkers for gastroesophageal reflux in respiratory diseases

Gastroesophageal reflux (GER) is commonly associated with respiratory symptoms, either through a vagal bronchoconstrictive reflex or through microaspiration of gastric contents. No diagnostic test is available, however, to diagnose when respiratory illnesses are caused by GER and when not, but research in this field has been moving forward. Various biomarkers in different types of biosamples have been studied in this context. The aim of this review is to summarize the present knowledge in this field. GER patients with respiratory diseases seem to have a different biochemical profile from similar patients without GER. Inflammatory biomarkers differ in asthmatics based on GER status, tachykinins are elevated in patients with GER-related cough, and bile acids are elevated in lung transplant patients with GER. However, studies on these biomarkers are often limited by their small size, methods of analysis, and case selections. The two pathogenesis mechanisms are associated with different respiratory illnesses and biochemical profiles. A reliable test to identify GER-induced respiratory disorders needs to be developed. Bronchoalveolar lavage is too invasive to be of use in most patients. Exhaled breath condensate samples need further evaluation and standardization. The newly developed particles in exhaled air measurements remain to be studied further.

Characterization of a portable method for the collection of exhaled breath condensate and subsequent analysis of metal content

Using exhaled breath condensate (EBC) as a biological media for analysis of biomarkers of exposure may facilitate the understanding of inhalation exposures. In this study, we present method validation for the collection of EBC and analysis of metals in EBC. The collection method was designed for use in a small scale longitudinal study with the goal of improving reproducibility while maintaining economic feasibility. We incorporated the use of an Rtube with additional components as an assembly, and trained subjects to breathe into the apparatus. EBC was collected from 8 healthy adult subjects with no known elevated exposures to Mn, Cr, Ni, and Cd repeatedly (10 times) within 7 days and analyzed for these metals via ICP-MS. Method detection limits were obtained by mimicking the process of EBC collection with ultrapure water, and resulted in 46-62% of samples falling in a range less than the method detection limit. EBC metal concentrations were found to be statistically significantly associated (p < 0.05) with room temperature and relative humidity during collection, as well as with the gender of the subject. The geometric mean EBC metal concentrations in our unexposed subjects were 0.57 μg Mn per L, 0.25 μg Cr per L, 0.87 μg Ni per L, and 0.14 μg Cd per L. The overall standard deviation was greater than the mean estimate, and the major source in EBC metals concentrations was due to fluctuations in subjects' measurements over time rather than to the differences between separate subjects. These results suggest that measurement and control of EBC collection and analytical parameters are critical to the interpretation of EBC metals measurements. In particular, rigorous estimation of method detection limits of metals in EBC provides a more thorough evaluation of accuracy.

Concentration of exhaled breath condensate biomarkers after fractionated collection based on exhaled CO2 signal

A standard procedure for exhaled breath condensate (EBC) collection is still lacking. The aim of this study was to compare the concentration of several biomarkers in whole (W-EBC) and fractionated EBC (A-EBC), the latter collected starting from CO2 ≥ 50% increase during exhalation. Forty-five healthy non-smokers or asymptomatic light smokers were enrolled. Total protein concentrations in W-EBC and A-EBC were overlapping (median: 0.7 mg l(-1) in both cases), whereas mitochondrial DNA was higher in A-EBC (0.021 versus 0.011 ng ml(-1)), indicating a concentration rather than a dilution of lining fluid droplets in the last portion of exhaled air. H2O2 (0.13 versus 0.08 µM), 8-isoprostane (4.9 versus 4.4 pg ml(-1)), malondialdehyde (MDA) (4.2 versus 3.2 nM) and 4-hydroxy-2-nonhenal (HNE) (0.78 versus 0.66 nM) were all higher in W-EBC, suggesting a contribution from the upper airways to oxidative stress biomarkers in apparently healthy subjects. NH4(+) was also higher in W-EBC (median: 590 versus 370 µM), with an estimated increase over alveolar and bronchial air by a factor 1.5. pH was marginally, but significantly higher in W-EBC (8.05 versus 8.01). In conclusion, the fractionation of exhaled air may be promising in clinical and occupational medicine.

Exhaled breath condensate: a promising source for biomarkers of lung disease

Exhaled breath condensate (EBC) has been increasingly studied as a noninvasive research method for sampling the alveolar and airway space and is recognized as a promising source of biomarkers of lung diseases. Substances measured in EBC include oxidative stress and inflammatory mediators, such as arachidonic acid derivatives, reactive oxygen/nitrogen species, reduced and oxidized glutathione, and inflammatory cytokines. Although EBC has great potential as a source of biomarkers in many lung diseases, the low concentrations of compounds within the EBC present challenges in sample collection and analysis. Although EBC is viewed as a noninvasive method for sampling airway lining fluid (ALF), validation is necessary to confirm that EBC truly represents the ALF. Likewise, a dilution factor for the EBC is needed in order to compare across subjects and determine changes in the ALF. The aims of this paper are to address the characteristics of EBC; strategies to standardize EBC sample collection and review available analytical techniques for EBC analysis.

Impact of bacterial colonization on exhaled inflammatory markers in wheezing preschool children

Wheeze is a common symptom in preschool children. The role of bacteria, regulatory T (T(reg)) cells and their association with airway inflammation in preschool wheeze is largely unknown. We evaluated inflammatory markers in exhaled breath condensate (EBC), bacterial colonization and circulating T(reg) cells in preschool children with and without recurrent wheeze. We recruited 252 children (aged two to four years) with (N = 202) and without (N = 50) recurrent wheeze. EBC was collected using an efficient closed glass condenser. Inflammatory markers in EBC (Interleukin(IL)-2, IL-4, IL-8, IL-10, IL-13) were assessed using multiplex immunoassay. Nasal and throat swabs were analysed for presence of Streptococcus pneumoniae, Haemophilus (para)influenzae and Staphylococcus aureus. Proportions of T(reg) cells (CD4(+)CD25(high)CD127(-)) were quantified by flow cytometry. Recurrent wheezing children had elevated EBC levels of IL-2, IL-4, IL-10 and IL-13 compared to non-wheezers (odds ratio (95% confidence interval): 1.67 (1.23-2.27): 1.58 (1.15-2.18): 1.47 (1.14-1.90): 1.55 (1.16-2.06), p <0.05, respectively). Bacteria were frequently present in children with and without wheeze, with no difference in prevalence (16-52% versus 16-50%, respectively). Moreover, the proportion of T(reg) cells did not differ between both groups. Wheezing children with bacterial colonization did not significantly differ in exhaled levels of inflammatory markers or proportion of T(reg) cells compared to wheezing children without colonization. The analysis of EBC might serve as a helpful non-invasive tool to early assess airway inflammation in wheezing children. The various elevated exhaled inflammatory markers indicate increased airway inflammation in wheezing preschool children. In the presence of wheeze, we found no evidence for bacterial induced airway inflammation.