Exhaled ethane is elevated in cystic fibrosis and correlates with carbon monoxide levels and airway obstruction

Breath Testing in the Surgical Setting: Applications, Challenges, and Future Perspectives

BACKGROUND

The potential for exhaled breath to be a valuable diagnostic tool is often overlooked as it can be difficult to imagine how a barely visible sample of breath could hold such a rich source of information about the state of our health. However, technological advances over the last 50 years have enabled us to detect volatile organic compounds (VOCs) present in exhaled breath, and this provides the key to understanding the wealth of information contained within these readily available samples.

SUMMARY

VOCs are produced as a by-product of metabolism; hence, changes in the underlying physiological processes will be reflected in the exact composition of VOCs in exhaled breath. It has been shown that characteristic changes occur in the breath VOC profile associated with certain diseases including cancer, which may enable the non-invasive detection of cancer at primary care level for patients with vague symptoms. The use of breath testing as a diagnostic tool has many advantages. It is non-invasive and quick, and the test is widely accepted by patients and clinicians. However, breath samples provide a snapshot of the VOCs present in a particular patient at a given point in time, so this can be heavily influenced by external factors such as diet, smoking, and the environment. These must all be accounted for when attempting to draw conclusions about disease status. This review focuses on the current applications for breath testing in the field of surgery, as well as discussing the challenges encountered with developing a breath test in a clinical environment. The future of breath testing in the surgical setting is also discussed, including the translation of breath research into clinical practice.

KEY MESSAGES

Analysis of VOCs in exhaled breath can identify the presence of underlying disease including cancer as well as other infectious or inflammatory conditions. Despite the patient factors, environmental factors, storage, and transport considerations that must be accounted for, breath testing demonstrates ideal characteristics for a triage test, being non-invasive, simple, and universally acceptable to patients and clinicians. Many novel biomarkers and diagnostic tests fail to translate into clinical practice because their potential clinical application does not align with the requirements and unmet needs of the healthcare sector. Non-invasive breath testing, however, has the great potential to revolutionise the early detection of diseases, such as cancer, in the surgical setting for patients with vague symptoms.

Mitochondria-Targeted Antioxidants as a Therapeutic Strategy for Chronic Obstructive Pulmonary Disease

Oxidative stress is a major hallmark of COPD, contributing to inflammatory signaling, corticosteroid resistance, DNA damage, and accelerated lung aging and cellular senescence. Evidence suggests that oxidative damage is not solely due to exogenous exposure to inhaled irritants, but also endogenous sources of oxidants in the form of reactive oxygen species (ROS). Mitochondria, the major producers of ROS, exhibit impaired structure and function in COPD, resulting in reduced oxidative capacity and excessive ROS production. Antioxidants have been shown to protect against ROS-induced oxidative damage in COPD, by reducing ROS levels, reducing inflammation, and protecting against the development of emphysema. However, currently available antioxidants are not routinely used in the management of COPD, suggesting the need for more effective antioxidant agents. In recent years, a number of mitochondria-targeted antioxidant (MTA) compounds have been developed that are capable of crossing the mitochondria lipid bilayer, offering a more targeted approach to reducing ROS at its source. In particular, MTAs have been shown to illicit greater protective effects compared to non-targeted, cellular antioxidants by further reducing apoptosis and offering greater protection against mtDNA damage, suggesting they are promising therapeutic agents for the treatment of COPD. Here, we review evidence for the therapeutic potential of MTAs as a treatment for chronic lung disease and discuss current challenges and future directions.

Volatile compounds in human breath: critical review and meta-analysis

Volatile compounds contained in human breath reflect the inner workings of the body. A large number of studies have been published that link individual components of breath to disease, but diagnostic applications remain limited, in part due to inconsistent and conflicting identification of breath biomarkers. New approaches are therefore required to identify effective biomarker targets. Here, volatile organic compounds have been identified in the literature from four metabolically and physiologically distinct diseases and grouped into chemical functional groups (e.g. - methylated hydrocarbons or aldehydes; based on known metabolic and enzymatic pathways) to support biomarker discovery and provide new insight on existing data. Using this functional grouping approach, principal component analysis doubled explanatory capacity from 19.1% to 38% relative to single individual compound approaches. Random forest and linear discriminant analysis reveal 93% classification accuracy for cancer. This review and meta-analysis provides insight for future research design by identifying volatile functional groups associated with disease. By incorporating our understanding of the complexities of the human body, along with accounting for variability in methodological and analytical approaches, this work demonstrates that a suite of targeted, functional volatile biomarkers, rather than individual biomarker compounds, will improve accuracy and success in diagnostic research and application.

Mass Spectrometry-based Metabolomics in Translational Research

Metabolomics is the systematic study of metabolite profiles of complex biological systems, and involves the systematic identification and quantification of metabolites. Metabolism is integrated with all biochemical reactions in biological systems; thus metabolite profiles provide collective information on biochemical processes induced by genetic or environmental perturbations. Transcriptomes or proteomes may not be functionally active and not always reflect phenotypic variations. The metabolome, however, consists of the biomolecules closest to the phenotype of living organisms, and is often called the molecular phenotype of biological systems. Thus, metabolome alterations can easily result in disease states, providing important clues to understand pathophysiological mechanisms contributing to various biomedical symptoms. The metabolome and metabolomics have been emphasized in translational research related to biomarker discovery, drug target discovery, drug responses, and disease mechanisms. This review describes the basic concepts, workflows, and applications of mass spectrometry-based metabolomics in translational research.

Volatile organic compound breath signatures of children with cystic fibrosis by real-time SESI-HRMS

Early pulmonary infection and inflammation result in irreversible lung damage and are major contributors to cystic fibrosis (CF)-related morbidity. An easy to apply and noninvasive assessment for the timely detection of disease-associated complications would be of high value. We aimed to detect volatile organic compound (VOC) breath signatures of children with CF by real-time secondary electrospray ionisation high-resolution mass spectrometry (SESI-HRMS). A total of 101 children, aged 4-18 years (CF=52; healthy controls=49) and comparable for sex, body mass index and lung function were included in this prospective cross-sectional study. Exhaled air was analysed by a SESI-source linked to a high-resolution time-of-flight mass spectrometer. Mass spectra ranging from m/z 50 to 500 were recorded. Out of 3468 m/z features, 171 were significantly different in children with CF (false discovery rate adjusted p-value of 0.05). The predictive ability (CF versus healthy) was assessed by using a support-vector machine classifier and showed an average accuracy (repeated cross-validation) of 72.1% (sensitivity of 77.2% and specificity of 67.7%). This is the first study to assess entire breath profiles of children with SESI-HRMS and to extract sets of VOCs that are associated with CF. We have detected a large set of exhaled molecules that are potentially related to CF, indicating that the molecular breath of children with CF is diverse and informative.

Breath Sensors for Health Monitoring

Breath sensors can revolutionize medical diagnostics by on-demand detection and monitoring of health parameters in a noninvasive and personalized fashion. Despite extensive research for more than two decades, however, only a few breath sensors have been translated into clinical practice. Actually, most never even left the scientific laboratories. Here, we describe key challenges that currently impede realization of breath sensors and highlight strategies to overcome them. Specifically, we start with breath marker selection (with emphasis on metabolic and inflammatory markers) and breath sampling. Next, the sensitivity, stability, and selectivity requirements for breath sensors are described. Concepts are elaborated to systematically address these requirements by material design (focusing on chemoresistive metal oxides), orthogonal arrays, and filters. Finally, aspects of portable device integration, user communication, and clinical applicability are discussed.

Breath analysis in respiratory diseases: state-of-the-art and future perspectives

INTRODUCTION

The vast majority of respiratory diseases are associated with the production of volatile organic compounds (VOCs), the analysis of which might improve our knowledge about these disorders and their clinical management. The aim of this narrative review is to provide a comprehensive summary of current evidence supporting the application of breath analysis in the field of respiratory diseases, as well as suggesting potential applications available in the near future. Areas covered: A computerized literature search was performed to identify relevant articles reporting original data on the clinical use of breath analysis in respiratory diseases. Papers focusing on diseases other than respiratory, technical issues of VOC sampling and analysis, in vitro experiments or exogenous compounds were excluded. Expert commentary: Currently available evidence on the application of breath analysis in respiratory diseases is encouraging; however, it is mostly based on single-center studies without external validation. The standardization of the technique, together with multicenter clinical trials with external validation, will ensure it is ready for clinical use. Current and new applications in respiratory diseases may represent a major breakthrough in the field, so much so as to deserve further efforts in outlining the most effective way to apply VOC analysis for clinical purposes.

Pancreatic ductal adenocarcinoma can be detected by analysis of volatile organic compounds (VOCs) in alveolar air

Background

In the last decade many studies showed that the exhaled breath of subjects suffering from several pathological conditions has a peculiar volatile organic compound (VOC) profile. The objective of the present work was to analyse the VOCs in alveolar air to build a diagnostic tool able to identify the presence of pancreatic ductal adenocarcinoma in patients with histologically confirmed disease.

Methods

The concentration of 92 compounds was measured in the end-tidal breath of 65 cases and 102 controls. VOCs were measured with an ion-molecule reaction mass spectrometry. To distinguish between subjects with pancreatic adenocarcinomas and controls, an iterated Least Absolute Shrinkage and Selection Operator multivariate Logistic Regression model was elaborated.

Results

The final predictive model, based on 10 VOCs, significantly and independently associated with the outcome had a sensitivity and specificity of 100 and 84% respectively, and an area under the ROC curve of 0.99. For further validation, the model was run on 50 other subjects: 24 cases and 26 controls; 23 patients with histological diagnosis of pancreatic adenocarcinomas and 25 controls were correctly identified by the model.

Conclusions

Pancreatic cancer is able to alter the concentration of some molecules in the blood and hence of VOCs in the alveolar air in equilibrium. The detection and statistical rendering of alveolar VOC composition can be useful for the clinical diagnostic approach of pancreatic neoplasms with excellent sensitivity and specificity.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4452-0) contains supplementary material, which is available to authorized users.

Development of breath test for pneumoconiosis: a case-control study

Background

Lipid peroxidation plays an important role in the pathogenesis of pneumoconiosis. Volatile organic compounds (VOCs) generated from lipid peroxidation might be used to detect pneumoconiosis. The objective of this study was to develop a breath test for pneumoconiosis.

Methods

A case-control study was designed. Breath and ambient air were analysed by gas chromatography/mass spectrometry. After blank correction to prevent contamination from ambient air, we used canonical discriminant analysis (CDA) to assess the discrimination accuracy and principal component analysis (PCA) to generate a prediction score. The prediction accuracy was calculated and validated using the International Classification of Radiographs of the Pneumoconiosis criteria combined with an abnormal pulmonary function test as a reference standard. We generated a receiver operator characteristic (ROC) curve and calculated the area under the ROC curve (AUC) to estimate the screening accuracy of the breath test.

Results

We enrolled 200 stone workers. After excluding 5 subjects with asthma and 16 subjects who took steroids or nonsteroidal anti-inflammatory drugs, a total of 179 subjects were used in the final analyses, which included 25 cases and 154 controls. By CDA, 88.8% of subjects were correctly discriminated by their exposure status and the presence of pneumoconiosis. After excluding the VOCs of automobile exhaust and cigarette smoking, pentane and C5-C7 methylated alkanes constituted the major VOCs in the breath of persons with pneumoconiosis. Using the prediction score generated from PCA, the ROC-AUC was 0.88 (95% CI = 0.80—0.95), and the mean ROC-AUC of 5-fold cross-validation was 0.90. The breath test had good accuracy for pneumoconiosis diagnosis.

Conclusion

The analysis of breath VOCs has potential in the screening of pneumoconiosis for its non-invasiveness and high accuracy. We suggest that a multi-centre study is warranted and that all procedures must be standardized before clinical application.

Oxidative Stress in the Lung - The Essential Paradox

As eukaryotic life evolved, so too did the need for a source of energy that meets the requirements of complex organisms. Oxygen provides this vast potential energy source, but the same chemical reactivity which provides this potential also can have detrimental effects. The lung evolved as an organ that can efficiently promote gas exchange for the entire organism but as such, the lung is highly susceptible to its external environment. Oxygen can be transformed through both enzymatic and non-enzymatic processes into reactive oxygen species (ROS) and reactive nitrogen species (RNS), which can lead to protein, lipid, and DNA damage. Under normal conditions ROS/RNS concentrations are minimized through the activity of antioxidants located both intracellularly and in the epithelial lining fluid of the lung. Oxidative stress in the lung results when the antioxidant capacity is overwhelmed or depleted through external exposures, such as altered oxygen tension or air pollution, or internally. Internal sources of oxidative stress include systemic disease and the activation of resident cells and inflammatory cells recruited in response to an exposure or systemic response. Pulmonary responses to oxidative stress include activation of oxidases, lipid peroxidation, increases in nitric oxide, and autophagy. These internal and external exposures with the subsequent pulmonary responses contribute to development of diseases directly linked to oxidative stress. These include asthma, COPD, and lung cancers. While the vulnerability of the lung to oxidative stress is acknowledged, few effective preventative strategies or therapeutics are currently available.

Significance of Exhaled Breath Test in Clinical Diagnosis: A Special Focus on the Detection of Diabetes Mellitus

Analysis of volatile organic compounds (VOCs) emanating from human exhaled breath can provide deep insight into the status of various biochemical processes in the human body. VOCs can serve as potential biomarkers of physiological and pathophysiological conditions related to several diseases. Breath VOC analysis, a noninvasive and quick biomonitoring approach, also has potential for the early detection and progress monitoring of several diseases. This paper gives an overview of the major VOCs present in human exhaled breath, possible biochemical pathways of breath VOC generation, diagnostic importance of their analysis, and analytical techniques used in the breath test. Breath analysis relating to diabetes mellitus and its characteristic breath biomarkers is focused on. Finally, some challenges and limitations of the breath test are discussed.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

Advances in electronic-nose technologies for the detection of volatile biomarker metabolites in the human breath

Recent advancements in the use of electronic-nose (e-nose) devices to analyze human breath profiles for the presence of specific volatile metabolites, known as biomarkers or chemical bio-indicators of specific human diseases, metabolic disorders and the overall health status of individuals, are providing the potential for new noninvasive tools and techniques useful to point-of-care clinical disease diagnoses. This exciting new area of electronic disease detection and diagnosis promises to yield much faster and earlier detection of human diseases and disorders, allowing earlier, more effective treatments, resulting in more rapid patient recovery from various afflictions. E-nose devices are particularly suited for the field of disease diagnostics, because they are sensitive to a wide range of volatile organic compounds (VOCs) and can effectively distinguish between different complex gaseous mixtures via analysis of electronic aroma sensor-array output profiles of volatile metabolites present in the human breath. This review provides a summary of some recent developments of electronic-nose technologies, particularly involving breath analysis, with the potential for providing many new diagnostic applications for the detection of specific human diseases associated with different organs in the body, detectable from e-nose analyses of aberrant disease-associated VOCs present in air expired from the lungs.

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.

Inflammation, oxidative stress, and cardiovascular disease risk factors in adults with cystic fibrosis

Cystic fibrosis (CF) represents one of a number of localized lung and non-lung diseases with an intense chronic inflammatory component associated with evidence of systemic oxidative stress. Many of these chronic inflammatory diseases are accompanied by an array of atherosclerotic processes and cardiovascular disease (CVD), another condition strongly related to inflammation and oxidative stress. As a consequence of a dramatic increase in long-lived patients with CF in recent decades, the specter of CVD must be considered in these patients who are now reaching middle age and beyond. Buttressed by recent data documenting that CF patients exhibit evidence of endothelial dysfunction, a recognized precursor of atherosclerosis and CVD, the spectrum of risk factors for CVD in CF is reviewed here. Epidemiological data further characterizing the presence and extent of atherogenic processes in CF patients would seem important to obtain. Such studies should further inform and offer mechanistic insights into how other chronic inflammatory diseases potentiate the processes leading to CVDs.

Factors influencing the levels of exhaled carbon monoxide in asthmatic children

OBJECTIVE

Bronchial asthma is characterised by chronic airway inflammation commonly associated with increased oxidative stress. Exhaled carbon monoxide (eCO) levels could act as markers of both oxidative stress and allergic inflammation. We aimed to study eCO levels in asthmatics and detect the possible factors influencing them.

METHODS

We studied 241 asthmatic children and 75 healthy children. The differences in eCO levels among various asthmatic phenotypes and the correlations between eCO and other measured parameters (spirometric indices, Asthma Control Test score, exhaled nitric oxide, total IgE, blood eosinophils and marker of oxidative damage of proteins) were analysed.

RESULTS

Levels of eCO widely differed according to the selected characteristics of asthma. Asthmatics showed higher eCO concentrations than controls (1.44 ± 0.12 ppm vs. 0.91 ± 0.11 ppm, p < 0.001). Acute exacerbation of asthma was accompanied by a significant increase in eCO compared to the clinically controlled stage (2.17 ± 0.36 ppm vs. 1.33 ± 0.13 ppm, p < 0.001). Atopic, non-atopic asthma and asthma associated with allergic rhinitis (AR) showed elevated levels of eCO. The levels of eCO negatively correlated with the marker of protein oxidation in asthmatics, especially in atopic form and during acute exacerbation.

CONCLUSIONS

In a population of asthmatic children, eCO levels could be considered as a marker of both allergic inflammation and oxidative stress in the airways. Concomitant AR and asthma control were the most important factors affecting the levels of eCO in asthmatic children. However, our results do not support the use of routine eCO in the clinical practice.

A novel approach to partition central and peripheral airway nitric oxide

BACKGROUND

Determining the site of airways inflammation may lead to the targeting of therapy. Nitric oxide (NO) is a biomarker of airway inflammation and can be measured at multiple exhalation flow rates to allow partitioning into bronchial (large/central airway maximal nitric oxide flux [J'awno]) and peripheral (peripheral/small airway/alveolar nitric oxide concentration [Cano]) airway contributions by linear regression. This requires a minimum of three exhalations. We developed a simple and practical method to partition NO.

METHODS

In 29 healthy subjects (FEV1, 97% ± 3% predicted), 13 patients with asthma (FEV1, 90% ± 4% predicted), 14 patients with COPD (FEV1, 59% ± 3% predicted), and 12 patients with cystic fibrosis (CF) (FEV1, 60% ± 3% predicted), we measured the area under the curve of the NO concentration/exhalation time plot (AUC-NO) at exhalation flow rates of 50, 100, 200, and 300 mL/s. We determined the change of the total AUC-NO production (ΔAUC-NO) among the four different exhalation flow rates and compared these levels to Cano and J'awno indices measured conventionally by linear regression.

RESULTS

The change in AUC-NO between increasing exhalation flow rates of 50 to 200 mL/s (ΔAUC-NO50-200) was strongly correlated with J'awno in all patient groups as follows: healthy subjects (r = 0.94, P &lt; .001), patients with asthma (r = 0.98, P &lt; .001), patients with COPD (r = 0.93, P &lt; .001), and patients with CF (r = 0.74, P &lt; .05). In all subjects, AUC-NO at an exhalation flow rate of 200 mL/s (AUC-NO200) correlated with Cano (r = 0.69, P &lt; .01).

CONCLUSIONS

The bronchial production of NO can be determined by measuring ΔAUC-NO50-200, whereas AUC-NO200 measures its peripheral concentration. This approach is simple, quick, and does not require sophisticated equipment or mathematical models.

Breath tests in respiratory and critical care medicine: from research to practice in current perspectives

Today, exhaled nitric oxide has been studied the most, and most researches have now focused on asthma. More than a thousand different volatile organic compounds have been observed in low concentrations in normal human breath. Alkanes and methylalkanes, the majority of breath volatile organic compounds, have been increasingly used by physicians as a novel method to diagnose many diseases without discomforts of invasive procedures. None of the individual exhaled volatile organic compound alone is specific for disease. Exhaled breath analysis techniques may be available to diagnose and monitor the diseases in home setting when their sensitivity and specificity are improved in the future.

Carbon monoxide in exhaled breath testing and therapeutics

Carbon monoxide (CO), a low molecular weight gas, is a ubiquitous environmental product of organic combustion, which is also produced endogenously in the body, as the byproduct of heme metabolism. CO binds to hemoglobin, resulting in decreased oxygen delivery to bodily tissues at toxicological concentrations. At physiological concentrations, CO may have endogenous roles as a potential signaling mediator in vascular function and cellular homeostasis. Exhaled CO (eCO), similar to exhaled nitric oxide (eNO), has been evaluated as a candidate breath biomarker of pathophysiological states, including smoking status, and inflammatory diseases of the lung and other organs. eCO values have been evaluated as potential indicators of inflammation in asthma, stable COPD and exacerbations, cystic fibrosis, lung cancer, or during surgery or critical care. The utility of eCO as a marker of inflammation and its potential diagnostic value remain incompletely characterized. Among other candidate 'medicinal gases' with therapeutic potential, (e.g., NO and H2S), CO has been shown to act as an effective anti-inflammatory agent in preclinical animal models of inflammatory disease, acute lung injury, sepsis, ischemia/reperfusion injury and organ graft rejection. Current and future clinical trials will evaluate the clinical applicability of this gas as a biomarker and/or therapeutic in human disease.

Clinical use of exhaled volatile organic compounds in pulmonary diseases: a systematic review

There is an increasing interest in the potential of exhaled biomarkers, such as volatile organic compounds (VOCs), to improve accurate diagnoses and management decisions in pulmonary diseases. The objective of this manuscript is to systematically review the current knowledge on exhaled VOCs with respect to their potential clinical use in asthma, lung cancer, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), and respiratory tract infections. A systematic literature search was performed in PubMed, EMBASE, Cochrane database, and reference lists of retrieved studies. Controlled, clinical, English-language studies exploring the diagnostic and monitoring value of VOCs in asthma, COPD, CF, lung cancer and respiratory tract infections were included. Data on study design, setting, participant characteristics, VOCs techniques, and outcome measures were extracted. Seventy-three studies were included, counting in total 3,952 patients and 2,973 healthy controls. The collection and analysis of exhaled VOCs is non-invasive and could be easily applied in the broad range of patients, including subjects with severe disease and children. Various research groups demonstrated that VOCs profiles could accurately distinguish patients with a pulmonary disease from healthy controls. Pulmonary diseases seem to be characterized by a disease specific breath-print, as distinct profiles were found in patients with dissimilar diseases. The heterogeneity of studies challenged the inter-laboratory comparability. In conclusion, profiles of VOCs are potentially able to accurately diagnose various pulmonary diseases. Despite these promising findings, multiple challenges such as further standardization and validation of the diverse techniques need to be mastered before VOCs can be applied into clinical practice.

Breath biomarkers in diagnosis of pulmonary diseases

Breath analysis provides a convenient and simple alternative to traditional specimen testing in clinical laboratory diagnosis. As such, substantial research has been devoted to the analysis and identification of breath biomarkers. Development of new analytes enhances the desirability of breath analysis especially for patients who monitor daily biochemical parameters. Elucidating the physiologic significance of volatile substances in breath is essential for clinical use. This review describes the use of breath biomarkers in diagnosis of asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), lung cancer, as well as other pulmonary diseases. A number of breath biomarkers in lung pathophysiology will be described including nitric oxide (NO), carbon monoxide (CO), hydrogen peroxide (H₂O₂) and other hydrocarbons.

The application of exhaled breath gas and exhaled breath condensate analysis in the investigation of the lower respiratory tract in veterinary medicine: A review

The analysis of biomarkers in exhaled breath (EB) and exhaled breath condensate (EBC) may allow non-invasive and repeatable assessment of respiratory health and disease in mammals. Compared to human medicine, however, research data from EB and EBC analysis in veterinary medicine are limited and more patient variables influencing concentrations of EB/EBC analytes may be present. In addition, variations in methodologies between studies may influence results. A comparison of the approaches used in veterinary research by different groups may aid in the identification of potentially reliable and repeatable biomarkers suitable for further investigation. To date, changes in acid-base status and increased concentrations of inflammatory mediators have been the main findings in studies of pulmonary disease states in animals. Whilst these biomarkers are unlikely to represent specific and sensitive diagnostic parameters, they do have potential application in monitoring disease progression and treatment response.

Collection of biological samples in forensic toxicology

Forensic toxicology is the study and practice of the application of toxicology to the purposes of the law. The relevance of any finding is determined, in the first instance, by the nature and integrity of the specimen(s) submitted for analysis. This means that there are several specific challenges to select and collect specimens for ante-mortem and post-mortem toxicology investigation. Post-mortem specimens may be numerous and can endow some special difficulties compared to clinical specimens, namely those resulting from autolytic and putrefactive changes. Storage stability is also an important issue to be considered during the pre-analytic phase, since its consideration should facilitate the assessment of sample quality and the analytical result obtained from that sample. The knowledge on degradation mechanisms and methods to increase storage stability may enable the forensic toxicologist to circumvent possible difficulties. Therefore, advantages and limitations of specimen preservation procedures are thoroughfully discussed in this review. Presently, harmonized protocols for sampling in suspected intoxications would have obvious utility. In the present article an overview is given on sampling procedures for routinely collected specimens as well as on alternative specimens that may provide additional information on the route and timing of exposure to a specific xenobiotic. Last, but not least, a discussion on possible bias that can influence the interpretation of toxicological results is provided. This comprehensive review article is intented as a significant help for forensic toxicologists to accomplish their frequently overwhelming mission.

Breath analysis using laser spectroscopic techniques: breath biomarkers, spectral fingerprints, and detection limits

Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis.

Volatile organic compounds in exhaled breath as a diagnostic tool for asthma in children

BACKGROUND

The correct diagnosis of asthma in young children is often hard to achieve, resulting in undertreatment of asthmatic children and overtreatment in transient wheezers.

OBJECTIVES

To develop a new diagnostic tool that better discriminates between asthma and transient wheezing and that leads to a more accurate diagnosis and hence less undertreatment and overtreatment. A first stage in the development of such a tool is the ability to discriminate between asthmatic children and healthy controls. The integrative analysis of large numbers of volatile organic compounds (VOC) in exhaled breath has the potential to discriminate between various inflammatory conditions of the respiratory tract.

METHODS

Breath samples were obtained and analysed for VOC by gas chromatography-mass spectrometry from asthmatic children (n=63) and healthy controls (n=57). A total of 945 determined compounds were subjected to discriminant analysis to find those that could discriminate diseased from healthy children. A set of samples from both asthmatic and healthy children was selected to construct a model that was subsequently used to predict the asthma or the healthy status of a test group. In this way, the predictive value of the model could be tested.

MEASUREMENTS AND MAIN RESULTS

The discriminant analyses demonstrated that asthma and healthy groups are distinct from one another. A total of eight components discriminated between asthmatic and healthy children with a 92% correct classification, achieving a sensitivity of 89% and a specificity of 95%. Conclusion The results show that a limited number of VOC in exhaled air can well be used to distinguish children with asthma from healthy children.

Exhaled pentane as a possible marker for survival and lipid peroxidation during radiotherapy for lung cancer--a pilot study

To examine lipid peroxidation during radiotherapy (RT), exhaled pentane samples were collected from 11 lung cancer patients before RT and 30 and 120 min after the start of RT on days 1, 4 and 5 and at 30 and 40 Grays, if possible. Exhaled pentane samples were collected once from 30 healthy controls. Serum thiobarbituric-acid-reactive substances (TBARS) and conjugated dienes (CD) were obtained from patients on each exhaled air collection day. Lung cancer patients had higher exhaled pentane levels than controls (1.73 ng/L vs 0.83 ng/L, p=0.017). Exhaled pentane levels tended to decrease during the first RT day (p=0.075) and levels of CD decreased during the first week of RT (p=0.014). Higher pre-treatment pentane levels predicted better survival (p=0.003). Elevated exhaled pentane levels before RT may be due to the lipid peroxidation burden associated with cancer. The decrease of lipid peroxidation markers during RT may be attributable to enhanced antioxidant defense mechanisms.

Propofol and in vivo oxidative stress: effects of preservative

Reactive oxygen species are associated with tissue inflammation and injury. Our laboratory has demonstrated that ethane, a stable product of lipid peroxidation, in exhaled breath can be used to measure total body oxidative stress. An ischemia-reperfusion model of lung injury in sheep has been studied in which pulmonary and bronchial lung perfusion could be interrupted and restored. The goal of this study was to investigate whether two commercial formulations of propofol and the individual components of the commercial formulations attenuated the oxidative stress produced in this model. Breath ethane and breath carbon monoxide were measured as biomarkers of oxidative stress that occur at reperfusion of ischemic tissue. Data were analyzed by a standard least-squares-fit model. One of the formulations for propofol, which contained the preservative ethylenediaminetetraacetic acid (EDTA), was found to decrease the overall level of oxidative stress in sheep. Furthermore, while several models of severe lung injury demonstrate additional production of reactive oxygen species, our model of ischemia/reperfusion of lung tissue did not.

CO and NO in medicine

The occurrence, role and consequences of CO and NO in biological systems are reviewed. This includes their syntheses by heme oxygenases and NO synthases, their biological targets and the physiological effects of their signals. The use of CO and NO gases in medicine are discussed and methods of delivery are illustrated with particular emphasis on the therapeutic properties of compounds that generate controlled amounts of NO and CO in vivo.

Exhaled carbon monoxide as a biomarker of inflammatory lung disease

Carbon monoxide (CO) can be detected on the exhaled breath of humans. Exhaled CO (E-CO) originates from the inspiration of ambient CO and from endogenous metabolic sources that include heme metabolism catalyzed by heme oxygenase (HO) enzymes. HO occurs in both constitutive (HO-2) and inducible (HO-1) forms; the latter responds to pro-inflammatory or pro-oxidative stimuli. E-CO may arise in the airways from inducible HO-1 activity in the bronchial epithelium, alveolar macrophages and other lung cell types, as a consequence of local inflammation, and from the alveolae in equilibrium with carboxyhemoglobin (Hb-CO) in the pulmonary circulation. Elevations in Hb-CO in turn may reflect increases in ambient CO, as well as increased HO activity in systemic tissues. E-CO increases dramatically in active smokers and can be used to monitor the smoking habit. Elevations in E-CO have been observed in critically ill or post-surgical patients and those with various pulmonary diseases associated with inflammation, including chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis and infections. Despite improvements in the standardization and sensitivity of methods to detect E-CO, the predictive value of this measurement as a diagnostic tool remains unclear.

Antioxidants in cystic fibrosis. Conclusions from the CF antioxidant workshop, Bethesda, Maryland, November 11-12, 2003

Although great strides are being made in the care of individuals with cystic fibrosis (CF), this condition remains the most common fatal hereditary disease in North America. Numerous links exist between progression of CF lung disease and oxidative stress. The defect in CF is the loss of function of the transmembrane conductance regulator (CFTR) protein; recent evidence that CFTR expression and function are modulated by oxidative stress suggests that the loss may result in a poor adaptive response to oxidants. Pancreatic insufficiency in CF also increases susceptibility to deficiencies in lipophilic antioxidants. Finally the airway infection and inflammatory processes in the CF lung are potential sources of oxidants that can affect normal airway physiology and contribute to the mechanisms causing characteristic changes associated with bronchiectasis and loss of lung function. These multiple abnormalities in the oxidant/antioxidant balance raise several possibilities for therapeutic interventions that must be carefully assessed.

Determination of ethane, pentane and isoprene in exhaled air--effects of breath-holding, flow rate and purified air

AIM

Exhaled ethane, pentane and isoprene have been proposed as biomarkers of oxidative stress. The objectives were to explore whether ethane, pentane and isoprene are produced within the airways and to explore the effect of different sampling parameters on analyte concentrations.

METHODS

The flow dependency of the analyte concentrations, the concentrations in dead-space and alveolar air after breath-holding and the influence of inhaling purified air on analyte concentrations were investigated. The analytical method involved thermal desorption from sorbent tubes and gas chromatography. The studied group comprised 13 subjects with clinically stable asthma and 14 healthy controls.

RESULTS

Ethane concentrations decreased slightly, but significantly, at higher flow rates in subjects with asthma (P = 0.0063) but not in healthy controls. Pentane levels were increased at higher flow rates both in healthy and asthmatic subjects (P = 0.022 and 0.0063 respectively). Isoprene levels were increased at higher flow rates, but only significantly in healthy subjects (P = 0.0034). After breath-holding, no significant changes in ethane levels were observed. Pentane and isoprene levels increased significantly after 20 s of breath-holding. Inhalation of purified air before exhalation resulted in a substantial decrease in ethane levels, a moderate decrease in pentane levels and an increase in isoprene levels.

CONCLUSION

The major fractions of exhaled ethane, pentane and isoprene seem to be of systemic origin. There was, however, a tendency for ethane to be flow rate dependent in asthmatic subjects, although to a very limited extent, suggesting that small amounts of ethane may be formed in the airways.

[Role of oxidative stress in respiratory diseases and its monitoring]

Together with inflammation and subsequent remodeling of airways, an imbalance between oxidative and anti-oxidative agents is generated during the development of numerous pulmonary diseases. This process seems to be involved in both the pathogenesis and chronification of asthma, chronic obstructive pulmonary disease (COPD), SOAS, interstitial lung diseases and cystic fibrosis. Reactive oxygen species including superoxide anion, hidroxyl radicals and hydrogen peroxide (H2O2) are synthetised as a response of inflammatory cells and are responsible of the oxidation of nucleic acids, proteins and membrane lipids, leading to cell damage and enhanced inflammation. Until recently, it was difficult to quantify the airway production of reactive oxidative species (ROS). In fact, it has been only in the last few years when it has been possible to determine indirectly the levels of ROS in expired air and in tissue of asthmatic patients. The analysis of exhaled air is a single, reproducible and non-invasive technique which is useful in the study of volatile and non-volatile gases generated in different conditions. The determination of exhaled nitric oxide and carbon monoxide (CO) has a great usefulness in the assessment of asthma. Nitric oxide seems to be closely related to the physiopathology of asthma and COPD. In fact, it is correlated with the levels of sputum eosinophils and with the response to the treatment with steroids. Yet a correlation with the degree of airflow obstruction and the seriousness of the process has not been found. Exhaled CO is another indirect marker of inflammation and it is increased in asthma, COPD, cystic fibrosis and bronchectases. Even though numerous studies have shown its usefulness as a marker of inflammation and in the response to corticosteroids, its clinical application has limitations. In particular, it is not a specific and exclusive marker of oxidative stress and its levels are highly influenced by tobacco smoke. On the other hand, the association between exhaled CO and FEV1 is not clear and no relationship has been proved so far with the improvement of pulmonary function after steroid therapy and with the decrease of maximum expiratory flow at relapses. In this Review, we describe the advances in the knowledge of oxidative stress as a decisive factor in the pathogenesis of prevalent pulmonary diseases, as well as the methods allowing its analysis and monitoring.

Increased Oxidative Stress in Exudative Pleural Effusions

STUDY OBJECTIVES

Oxidative stress has been associated with various respiratory disorders. We tested the hypothesis that exudates would present higher levels of oxidative stress compared to transudates, expressing the increased local oxidative burst in the former.

DESIGN

Prospective, cross-sectional study.

PATIENTS OR PARTICIPANTS

One hundred six consecutive patients who had undergone thoracentesis were studied. Ninety patients with a final diagnosis of pleural effusion were further analyzed.

SETTING

The respiratory department and a clinical laboratory of a tertiary hospital.

INTERVENTIONS

Subjects underwent diagnostic thoracentesis, and standard biochemical parameters (ie, total protein, lactate dehydrogenase, and albumin levels) were measured in pleural fluid and serum. Oxidative stress levels were assessed with a commercially available method (d-ROMs test; Diacron; Grosseto, Italy) that uses conventional Carratelli units (UCarr). In 14 patients, duplicate measurements of oxidative stress and a second thoracentesis were performed on the following day for the assessment of the repeatability of measurements. Receiver operating characteristic (ROC) analysis was performed in order to determine the optimal cutoff level for the differentiation between exudates and transudates.

MEASUREMENTS AND RESULTS

Oxidative stress levels were higher in exudates compared to transudates (mean [+/- SD] stress level, 274 +/- 72 vs 126 +/- 34 UCarr, respectively; p < 0.0001). No significant differences were found among the levels of oxidative stress in exudative effusions of different etiologies. The area under the ROC curve was 0.992 (95% confidence interval, 0.945 to 0.997), and the method provided high sensitivity (96.8%), high specificity (96.3%), and high accuracy (96.7%) for the diagnosis of exudates at a cutoff level for oxidative stress of 186 UCarr. Consecutive measurements of oxidative stress in the same samples and on fluid from two different thoracenteses performed on 2 consecutive days presented excellent repeatability.

CONCLUSIONS

Oxidative stress levels are higher in exudative pleural effusions compared to transudative effusions, probably due to reactive oxygen species produced in the former.

Application of laser spectroscopy for measurement of exhaled ethane in patients with lung cancer

There is increasing interest in ethane (C(2)H(6)) in exhaled breath as a non-invasive marker of oxidative stress (OS) and thereby a potential indicator of disease. However, the lack of real-time measurement techniques has limited progress in the field. Here we report on a novel Tunable Diode Laser Spectrometer (TDLS) applied to the analysis of exhaled ethane in patients with lung cancer. The patient group (n=52) comprised randomly selected patients presenting at a respiratory clinic. Of these, a sub-group (n=12) was subsequently diagnosed with lung cancer. An age-matched group (n=12) corresponding to the lung cancer group was taken from a larger control group of healthy adults (n=58). The concentration of ethane in a single exhaled breath sample collected from all subjects was later measured using the TDLS. This technique is capable of real-time analysis of samples with accuracy 0.1 parts per billion (ppb), over 10 times less than typical ambient levels in the northern hemisphere. After correcting for ambient background, ethane in the control group (26% smokers) ranged from 0 to 10.54 ppb (median of 1.9 ppb) while ethane in the lung cancer patients (42% smokers) ranged from 0 to 7.6 ppb (median of 0.7 ppb). Ethane among the non-lung cancer patients presenting for investigation of respiratory disease ranged from 0 to 25 ppb (median 1.45 ppb). We conclude that, while the TDLS proved effective for accurate and rapid sample analysis, there was no significant difference in exhaled ethane among any of the subject groups. Comments are made on the suitability of the technique for monitoring applications.

Circulating markers to assess nutritional therapy in cystic fibrosis

Cystic fibrosis (CF) is the most commonly occurring lethal autosomal recessive disorder. The gene defect causes defective sodium and chloride transport across epithelial cells of the respiratory, hepatobiliary, gastrointestinal and reproductive tracts, resulting in thick mucus secretions. In the respiratory tract, mucus traps bacteria, causing repeated lung infections, progressive bronchiectasis and eventual death due to respiratory failure. In the gastrointestinal tract, mucus prevents pancreatic enzymes reaching the gut, leading to nutrient malabsorption. Careful nutritional management has a dramatic effect on growth and survival rates in CF. Appropriate nutritional support includes pancreatic enzyme replacement therapy, a high-fat/high-energy diet and essential nutrient supplementation, specifically fat-soluble vitamins and essential fatty acids (EFA). Long-term studies are required to examine the effects of nutritional interventions on key clinical outcomes in CF, such as the rate of decline of lung function. The use of circulating markers to assess the influence of nutritional therapy allows short-term intervention studies to predict the potential for clinical improvements. This article provides an overview of the biomarkers useful in the prediction of the efficacy of nutritional therapy on improvements in quality and quantity of life in CF.

Breath ethanol and acetone as indicators of serum glucose levels: an initial report

BACKGROUND

Many volatile organic compounds are present in exhaled breath and may represent by-products of endogenous biological processes. Ethanol is produced via alcoholic fermentation of glucose by gut bacteria and yeast, while acetone derives from oxidations of free fatty acids, influenced by glucose metabolism. We hypothesized that the integrated analysis of breath ethanol and acetone would provide a good approximation of the blood glucose profile during a glucose load.

METHODS

We collected simultaneous exhaled breath gas, ambient air, and serum glucose and insulin samples from 10 healthy volunteers at baseline and during an oral glucose tolerance test (OGTT) (ingestion of 75 g of glucose followed by 120 min of sampling). Gas samples were analyzed by gas chromatography/mass spectrometry.

RESULTS

Mean glucose values displayed a typical OGTT pattern (rapid increase, peak values at 30-60 min, and gradual return to near baseline by 120 min). Breath ethanol displayed a similar pattern early in the test, with peak values at 30 min; this was followed by a fast return to basal levels by 60 min. Breath acetone decreased progressively below basal levels, with lowest readings obtained at 120 min. A multiple regression analysis of glucose, ethanol, and acetone was used to estimate glucose profiles that correlated with measured glucose values with an average individual correlation coefficient of 0.70, and not lower than 0.41 in any subject.

CONCLUSION

The integrated analysis of multiple exhaled gases may serve as a marker of blood glucose levels. Further studies are needed to assess the usefulness of this method in different populations.

Diagnostic potential of breath analysis--focus on volatile organic compounds

Breath analysis has attracted a considerable amount of scientific and clinical interest during the last decade. In contrast to NO, which is predominantly generated in the bronchial system, volatile organic compounds (VOCs) are mainly blood borne and therefore enable monitoring of different processes in the body. Exhaled ethane and pentane concentrations were elevated in inflammatory diseases. Acetone was linked to dextrose metabolism and lipolysis. Exhaled isoprene concentrations showed correlations with cholesterol biosynthesis. Exhaled levels of sulphur-containing compounds were elevated in liver failure and allograft rejection. Looking at a set of volatile markers may enable recognition and diagnosis of complex diseases such as lung or breast cancer. Due to technical problems of sampling and analysis and a lack of normalization and standardization, huge variations exist between results of different studies. This is among the main reasons why breath analysis could not yet been introduced into clinical practice. This review addresses the basic principles of breath analysis and the diagnostic potential of different volatile breath markers. Analytical procedures, issues concerning biochemistry and exhalation mechanisms of volatile substances, and future developments will be discussed.

Heme Oxygenase-1 Expression in Human Lungs with Cystic Fibrosis and Cytoprotective Effects againstPseudomonas Aeruginosa In Vitro

Inflammation and oxidative stress play important roles in cystic fibrosis (CF) lung disease. Inflammatory/oxidant-mediated induction of heme oxygenase-1 (HO-1) is believed to be a cytoprotective response. This study examined HO-1 expression in lung samples from patients with CF using immunohistochemistry and quantitative reverse transcription-polymerase chain reaction. In addition, we evaluated myeloperoxidase staining as a marker of acute inflammation and potentially an increase in oxidant stress and Prussian blue and ferritin staining to assess iron status of the lung. Macrophage HO-1 staining was increased in diseased lungs as compared with normal control subjects and correlated with myeloperoxidase staining. Quantitative reverse transcription-polymerase chain reaction further supported an increase in HO-1 expression in CF lung disease. Although iron staining was minimal, ferritin staining was increased in diseased lungs in concert with HO-1 staining. To determine whether HO-1 induction was cytoprotective, we evaluated a CF airway epithelial cell line, IB3.1, in response to Pseudomonas aeruginosa-induced injury/apoptosis in cells overexpressing HO-1 by either transient or stable transfection of pcDNA3.1/HO-1 construct. Overexpression of HO-1 resulted in protection against P. aeruginosa-induced injury/apoptosis. This suggests that the induction of HO-1 in patients with CF is a cytoprotective event and that augmenting its expression is a potential therapy against bacterial injury.

NO pathway in CF and non-CF children

Controversy exists concerning abnormalities of the nitric oxide (NO) pathway in cystic fibrosis (CF) lung disease. Although some studies suggested that NO activity is impaired in CF, changes in NO production in young children have not been studied. We hypothesized that nitric oxide synthase (NOS II) expression is decreased in young children with CF, leading to decreased production of lower airway NO, and that decreased NOS II expression is related to airway inflammation. Accordingly, we measured lower airway exhaled NO, nitrate, and NOS II expression in airway epithelium and macrophages by bronchoscopy, bronchoalveolar lavage (BAL), and bronchial brushing in 13 children with CF, 4 adolescent patients with CF, and 14 disease control children. Lower airway NO and nitrate were not different between CF and disease controls. Immunostaining studies of NOS II expression in airway epithelial cells and macrophages were similar in CF and control patients. Within the CF group, however, expression of NOS II was inversely related to BAL neutrophil counts and IL-8, two markers of airway inflammation. We conclude that lower airway NO, nitrate levels, and NOS II expression are not different in young children with CF and disease control patients, but that NOS II expression decreases in CF as airway inflammation increases.

Current and future uses of breath analysis as a diagnostic tool

The analysis of exhaled breath is a potentially useful method for application in veterinary diagnostics. Breath samples can be easily collected from animals by means of a face mask or collection chamber with minimal disturbance to the animal. After the administration of a 13C-labelled compound the recovery of 13C in breath can be used to investigate gastrointestinal and digestive functions. Exhaled hydrogen can be used to assess orocaecal transit time and malabsorption, and exhaled nitric oxide, carbon monoxide and pentane can be used to assess oxidative stress and inflammation. The analysis of compounds dissolved in the aqueous phase of breath (the exhaled breath condensate) can be used to assess airway inflammation. This review summarises the current status of breath analysis in veterinary medicine, and analyses its potential for assessing animal health and disease.

The role of oxidative stress in chronic obstructive pulmonary disease

Tobacco smoke is the number one risk factor for chronic obstructive pulmonary disease (COPD) and contains a high concentration of oxidants. The lung has a high concentration of antioxidants and antioxidant enzymes; however, COPD patients show evidence of increased oxidative stress suggesting that endogenous antioxidants may be insufficient to prevent oxidative damage from cigarette smoke. The consequences of increased oxidative stress in the lung include increased transcription of inflammatory genes, increased protease activity, and increased mucus secretion. Oxidative stress is often associated with impaired skeletal muscle function and may be one of the causes of glucocorticoid resistance. While current pharmacologic approaches to the treatment of chronic obstructive pulmonary disease do not commonly include antioxidants, preclinical studies involving animal models suggest that antioxidant superoxide dismutase mimetics offer a potential new therapeutic approach to the prevention and treatment of chronic obstructive pulmonary disease.

Online recording of ethane traces in human breath via infrared laser spectroscopy

A method is described for rapidly measuring the ethane concentration in exhaled human breath. Ethane is considered a volatile marker for lipid peroxidation. The breath samples are analyzed in real time during single exhalations by means of infrared cavity leak-out spectroscopy. This is an ultrasensitive laser-based method for the analysis of trace gases on the sub-parts per billion level. We demonstrate that this technique is capable of online quantifying of ethane traces in exhaled human breath down to 500 parts per trillion with a time resolution of better than 800 ms. This study includes what we believe to be the first measured expirograms for trace fractions of ethane. The expirograms were recorded after a controlled inhalation exposure to 1 part per million of ethane. The normalized slope of the alveolar plateau was determined, which shows a linear increase over the first breathing cycles and ends in a mean value between 0.21 and 0.39 liter-1. The washout process was observed for a time period of 30 min and was modelled by a threefold exponential decay function, with decay times ranging from 12 to 24, 341 to 481, and 370 to 1770 s. Our analyzer provides a promising noninvasive tool for online monitoring of the oxidative stress status.

End-tidal carbon monoxide corrected for lung volume is elevated in patients with cystic fibrosis

Several factors influence levels of end-tidal carbon monoxide (ETCO). We studied determinants of ETCO corrected for inhaled CO (ETCOc) levels in healthy control subjects and compared ETCOc levels and determinants between healthy control subjects and patients with cystic fibrosis (CF). Thirty healthy control subjects (mean +/- SD age, 23 +/- 6 years) and twenty clinically stable patients with CF, aged 13.5 +/- 3.5 years were included. ETCO was measured with the CO-STAT End-Tidal Breath Analyzer (Natus Medical, Inc., San Carlos, CA), and determinants included lung volume (measured with the multiple-breath helium wash-in method), CO-diffusion capacity, and different expiratory flow rates. In healthy control subjects we found a significant correlation between ETCOc and lung volume (r = 0.64, p < 0.05) and with CO-diffusion capacity uncorrected for VA (r = 0.48, p = 0.02). There was no expiratory flow rate dependency in either group. Patients with CF showed no difference in ETCOc levels compared with control subjects (mean 1.2 +/- 0.4 ppm vs. 1.3 +/- 0.4 ppm, p = 0.32), but patients with CF had lower total lung capacity-helium than healthy control subjects. ETCOc corrected for lung volume was significantly higher in patients with CF compared with control subjects (p < 0.001). We hypothesize that a possible increase in breath CO caused by airway inflammation might be masked by differences in lung volumes between control subjects and patients with CF.

Increased leukotriene B4 and interleukin-6 in exhaled breath condensate in cystic fibrosis

Chronic neutrophilic airway inflammation is an important feature of cystic fibrosis (CF). Noninvasive inflammatory markers may be useful in monitoring CF. Leukotriene B4 (LTB4) and interleukin (IL)-6 are inflammatory mediators that are increased in chronic neutrophilic inflammation. The aim of this study was to assess whether LTB4 and IL-6 were increased in exhaled breath condensate of CF patients and whether they could be used to monitor inflammation. Twenty patients with CF (13 males, age of 28 +/- 9 years) were recruited together with 15 age-matched healthy subjects (8 males, age 35 +/- 7 years). LTB4 and IL-6 levels were markedly elevated in patients with acute exacerbations (28.8 +/- 4.3 and 8.7 +/- 0.4 pg/ml) compared with control subjects (6.8 +/- 0.7 and 2.6 +/- 0.1 pg/ml, p < 0.0001). We also observed a decrease of exhaled LTB4 and IL-6 concentrations after antibiotic treatment in six patients who were followed until clinically stable (31.1 +/- 4.4 and 9.5 +/- 0.4 pg/ml vs. 18.8 +/- 0.8 and 6.4 +/- 0.2 pg/ml, respectively) and an increase in 15 CF patients infected with Pseudomonas aeruginosa (34.3 +/- 5.0 and 9.3 +/- 0.3 pg/m) compared with those infected with other bacteria (18.3 +/- 0.7 and 6.9 +/- 0.5 pg/ml). These findings suggest that LTB4 and IL-6 levels are increased in exhaled breath condensate of patients with CF during exacerbation and could be used to monitor airway inflammation in these patients.

Heme oxygenase-1 and carbon monoxide in pulmonary medicine

Heme oxygenase-1 (HO-1), an inducible stress protein, confers cytoprotection against oxidative stress in vitro and in vivo. In addition to its physiological role in heme degradation, HO-1 may influence a number of cellular processes, including growth, inflammation, and apoptosis. By virtue of anti-inflammatory effects, HO-1 limits tissue damage in response to proinflammatory stimuli and prevents allograft rejection after transplantation. The transcriptional upregulation of HO-1 responds to many agents, such as hypoxia, bacterial lipopolysaccharide, and reactive oxygen/nitrogen species. HO-1 and its constitutively expressed isozyme, heme oxygenase-2, catalyze the rate-limiting step in the conversion of heme to its metabolites, bilirubin IXalpha, ferrous iron, and carbon monoxide (CO). The mechanisms by which HO-1 provides protection most likely involve its enzymatic reaction products. Remarkably, administration of CO at low concentrations can substitute for HO-1 with respect to anti-inflammatory and anti-apoptotic effects, suggesting a role for CO as a key mediator of HO-1 function. Chronic, low-level, exogenous exposure to CO from cigarette smoking contributes to the importance of CO in pulmonary medicine. The implications of the HO-1/CO system in pulmonary diseases will be discussed in this review, with an emphasis on inflammatory states.