Determinants of exhaled breath condensate pH in a large population with asthma

Inflammation-induced loss of CFTR-expressing airway ionocytes in non-eosinophilic asthma

BACKGROUND AND OBJECTIVE

Severe asthma is a heterogeneous disease with subtype classification according to dominant airway infiltrates, including eosinophilic (Type 2 high), or non-eosinophilic asthma. Non-eosinophilic asthma is further divided into paucigranulocytic or neutrophilic asthma characterized by elevated neutrophils, and mixed Type 1 and Type 17 cytokines in the airways. Severe non-eosinophilic asthma has few effective treatments and many patients do not qualify for biologic therapies. The cystic fibrosis transmembrane conductance regulator (CFTR) is dysregulated in multiple respiratory diseases including cystic fibrosis and chronic obstructive pulmonary disease and has proven a valuable therapeutic target. We hypothesized that the CFTR may also play a role in non-eosinophilic asthma.

METHODS

Patient-derived human bronchial epithelial cells (hBECs) were isolated and differentiated at the air-liquid interface. Single cell RNA-sequencing (scRNAseq) was used to identify epithelial cell subtypes and transcriptional activity. Ion transport was investigated with Ussing chambers and immunofluorescent quantification of ionocyte abundance in human airway epithelial cells and murine models of asthma.

RESULTS

We identified that hBECs from patients with non-eosinophilic asthma had reduced CFTR function, and did not differentiate into CFTR-expressing ionocytes compared to those from eosinophilic asthma or healthy donors. Similarly, ionocytes were also diminished in the airways of a murine model of neutrophilic-dominant but not eosinophilic asthma. Treatment of hBECs from healthy donors with a neutrophilic asthma-like inflammatory cytokine mixture led to a reduction in ionocytes.

CONCLUSION

Inflammation-induced loss of CFTR-expressing ionocytes in airway cells from non-eosinophilic asthma may represent a key feature of disease pathogenesis and a novel drug target.

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.

Diet Quality and Exhaled Breath Condensate Markers in a Sample of School-Aged Children

Exhaled breath condensate (EBC) analysis is a recently developed, non-invasive method used to identify and quantify biomarkers, mainly those coming from the lower respiratory tract. It seems that diet can influence the airway's inflammation and change the exhaled breath composition. This study aimed to assess the association between diet quality intake and markers in EBC among school-aged children. A cross-sectional analysis included 150 children (48.3% females, aged 7-12 years, mean age: 8.7 ± 0.8 years) from 20 schools across Porto, Portugal. We assessed diet quality through the Healthy Eating Index (HEI)-2015, which was estimated based on a single 24 h food recall questionnaire. EBC samples were collected, and we assessed their ionic content (Na⁺, K⁺) and conductivity. The association between diet quality and Na⁺, K⁺, Na⁺/K⁺ ratio and conductivity was estimated using logistic regression models adjusted for potential confounders. After adjustment, a higher quality diet score increases the odds of higher conductivity values of the EBC (aOR = 1.04, 95%CI 1.00; 1.08). Our findings suggest that a higher diet quality in school-aged children is associated with higher conductivity levels of the EBC.

Recent insights in the role of biomarkers in severe asthma management

Contemporary asthma management requires a proactive and individualized approach, combining precision diagnosis and personalized treatment. The introduction of biologic therapies for severe asthma to everyday clinical practice, increases the need for specific patient selection, prediction of outcomes and monitoring of these costly and long-lasting therapies. Several biomarkers have been used in asthma in disease identification, prediction of asthma severity and prognosis, and response to treatment. Novel advances in the area of personalized medicine regarding disease phenotyping and endotyping, encompass the development and application of reliable biomarkers, accurately quantified using robust and reproducible methods. The availability of powerful omics technologies, together with integrated and network-based genome data analysis, and microbiota changes quantified in serum, body fluids and exhaled air, will lead to a better classification of distinct phenotypes or endotypes. Herein, in this review we discuss on currently used and novel biomarkers for the diagnosis and treatment of asthma.

Neutrophils and Asthma

Although eosinophilic inflammation is characteristic of asthma pathogenesis, neutrophilic inflammation is also marked, and eosinophils and neutrophils can coexist in some cases. Based on the proportion of sputum cell differentiation, asthma is classified into eosinophilic asthma, neutrophilic asthma, neutrophilic and eosinophilic asthma, and paucigranulocytic asthma. Classification by bronchoalveolar lavage is also performed. Eosinophilic asthma accounts for most severe asthma cases, but neutrophilic asthma or a mixture of the two types can also present a severe phenotype. Biomarkers for the diagnosis of neutrophilic asthma include sputum neutrophils, blood neutrophils, chitinase-3-like protein, and hydrogen sulfide in sputum and serum. Thymic stromal lymphoprotein (TSLP)/T-helper 17 pathways, bacterial colonization/microbiome, neutrophil extracellular traps, and activation of nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 pathways are involved in the pathophysiology of neutrophilic asthma and coexistence of obesity, gastroesophageal reflux disease, and habitual cigarette smoking have been associated with its pathogenesis. Thus, targeting neutrophilic asthma is important. Smoking cessation, neutrophil-targeting treatments, and biologics have been tested as treatments for severe asthma, but most clinical studies have not focused on neutrophilic asthma. Phosphodiesterase inhibitors, anti-TSLP antibodies, azithromycin, and anti-cholinergic agents are promising drugs for neutrophilic asthma. However, clinical research targeting neutrophilic inflammation is required to elucidate the optimal treatment.

Evaluation of respiratory function and biomarkers of exposure to mixtures of pollutants in brick-kilns workers from a marginalized urban area in Mexico

Brick-kilns are polluted environments due to the use of low-quality technologies and fuels, which generates black fumes with a large number of pollutants. The objective of this research was to analyze environmental exposure and biomarkers of exposure to polycyclic aromatic hydrocarbons, metals, and respiratory health in brickmakers to assess the baseline state of contamination in a brick-kiln area of San Luis Potosi, Mexico. Lead was quantified in soil and particulate matter of 2.5 μm (PM_2.5) and 10 μm (PM₁₀) in brick-kiln areas. In brickmakers, lead was evaluated in whole blood and 10 hydroxylated metabolites of polycyclic aromatic hydrocarbons were determined in urine. Respiratory health was assessed by spirometry, exhaled breath condensate, and a COPD-PS questionnaire. Data association was performed by Spearman correlation. Environmental concentrations and biomarkers of exposure are presented as medians, for lead, it was 60.4 mg/kg, for PM10, it was 2663.1 μg/m³, and for PM2.5, it was 166.6 μg/m³. For blood lead, it was 1.06 μg/dL, and the summed concentration of OH-PAHs in urine was 16.1 μg/L. Spirometry values were 2.8 ± 0.6 L and 2.9 ± 1.3 L/s FEV1 and FEV 25-75 respectively. The correlation results indicate that the older the age of the workers is and the extensive period they have been working, their lung function is affected the most. The health vulnerability present in these occupational activities is high, so it is necessary to make visible, address these economic activities in Mexico, and apply surveillance systems based on the health of the worker.

Optical biosensing of markers of mucosal inflammation

We report the design and adaptation of iron/iron oxide nanoparticle-based optical nanobiosensors for enzymes or cytokine/chemokines that are established biomarkers of lung diseases. These biomarkers comprise ADAM33, granzyme B, MMP-8, neutrophil elastase, arginase, chemokine (C-C motif) ligand 20 and interleukin-6. The synthesis of nanobiosensors for these seven biomarkers, their calibration with commercially available enzymes and cytokines/chemokines, as well as their validation using bronchoalveolar lavage (BAL) obtained from a mouse model of TLR3-mediated inflammation are discussed here. Exhaled Breath Condensate (EBC) is a minimally invasive approach for sampling airway fluid in the diagnosis and management of various lung diseases in humans (e.g., asthma, COPD and viral infections). We report the proof-of-concept of using human EBC in conjunction with nanobiosensors for diagnosis/monitoring airway inflammation. These findings suggest that, with nanosensor technology, human EBC can be utilized as a liquid biopsy to monitor inflammation/remodeling in lung disease.

Exhaled breath condensate pH determinants in school-aged children: A population-based study

BACKGROUND

Exhaled breath condensate (EBC) pH is a promising biomarker of airway inflammation. Lack of method standardization and interstudy variability precludes its use in clinical practice. While endogenous determinants have been described, underlying mechanisms for variability are mostly unknown. Thus, we aimed to assess the association between asthma and EBC pH in children, while studying potential environmental factors for interstudy variability.

METHODS

A cross-sectional analysis of exhaled breath condensates from 613 children, aged 7-12 years, was conducted. Assessments included lung function and airway reversibility, exhaled nitric oxide, allergic sensitization, and body mass index (BMI). Indoor air quality (IAQ) was assessed in children's classrooms during 5 school days. Post-deaeration EBC pH showed a bimodal distribution, and the sample was split into acidic and alkaline groups. Regression models were constructed to assess the effects of asthma and asthma adjusted to IAQ parameters on EBC pH.

RESULTS

Following adjustment to gender and BMI, asthma was significantly associated with a lower EBC pH in the acidic group. The effect of asthma on EBC pH was independent of IAQ, in both groups. In the acidic group, EBC pH was significantly affected by temperature [β = -0.09 (-0.15, -0.02)] and PM 2.5 concentration [β = -0.16 (-0.32, -0.01)], and in the alkaline group by relative humidity [β = 0.07 (0.02, 0.13)] and concentration of endotoxins [β = -0.06 (-0.1, -0.01)].

CONCLUSION

Our study shows that in addition to individual determinants such as asthma, environmental factors may influence and should be taken into consideration when interpreting EBC pH level in children.

Three Major Efforts to Phenotype Asthma: Severe Asthma Research Program, Asthma Disease Endotyping for Personalized Therapeutics, and Unbiased Biomarkers for the Prediction of Respiratory Disease Outcome

The SARP, ADEPT, and U-BIOPRED programs are all significant efforts in characterizing asthma and reporting clusters that will assist in designing personalized therapies for asthma, and especially severe asthma. Key aspects of the design of these programs are summarized and major findings are reported in this review.

Priorities for future research into asthma diagnostic tools: A PAN-EU consensus exercise from the European asthma research innovation partnership (EARIP)

The diagnosis of asthma is currently based on clinical history, physical examination and lung function, and to date, there are no accurate objective tests either to confirm the diagnosis or to discriminate between different types of asthma. This consensus exercise reviews the state of the art in asthma diagnosis to identify opportunities for future investment based on the likelihood of their successful development, potential for widespread adoption and their perceived impact on asthma patients. Using a two-stage e-Delphi process and a summarizing workshop, a group of European asthma experts including health professionals, researchers, people with asthma and industry representatives ranked the potential impact of research investment in each technique or tool for asthma diagnosis and monitoring. After a systematic review of the literature, 21 statements were extracted and were subject of the two-stage Delphi process. Eleven statements were scored 3 or more and were further discussed and ranked in a face-to-face workshop. The three most important diagnostic/predictive tools ranked were as follows: "New biological markers of asthma (eg genomics, proteomics and metabolomics) as a tool for diagnosis and/or monitoring," "Prediction of future asthma in preschool children with reasonable accuracy" and "Tools to measure volatile organic compounds (VOCs) in exhaled breath."

Pruning of the Pulmonary Vasculature in Asthma. The Severe Asthma Research Program (SARP) Cohort

RATIONALE

Loss of the peripheral pulmonary vasculature, termed vascular pruning, is associated with disease severity in patients with chronic obstructive pulmonary disease.

OBJECTIVES

To determine if pulmonary vascular pruning is associated with asthma severity and exacerbations.

METHODS

We measured the total pulmonary blood vessel volume (TBV) and the blood vessel volume of vessels less than 5 mm2 in cross-sectional area (BV5) and of vessels less than 10 mm2 (BV10) in cross-sectional area on noncontrast computed tomographic scans of participants from the Severe Asthma Research Program. Lower values of the BV5 to TBV ratio (BV5/TBV) and the BV10 to TBV ratio (BV10/TBV) represented vascular pruning (loss of the peripheral pulmonary vasculature).

MEASUREMENTS AND MAIN RESULTS

Compared with healthy control subjects, patients with severe asthma had more pulmonary vascular pruning. Among those with asthma, those with poor asthma control had more pruning than those with well-controlled disease. Pruning of the pulmonary vasculature was also associated with lower percent predicted FEV1 and FVC, greater peripheral and sputum eosinophilia, and higher BAL serum amyloid A/lipoxin A4 ratio but not with low-attenuation area or with sputum neutrophilia. Compared with individuals with less pruning, individuals with the most vascular pruning had 150% greater odds of reporting an asthma exacerbation (odds ratio, 2.50; confidence interval, 1.05-5.98; P = 0.039 for BV10/TBV) and reported 45% more asthma exacerbations during follow-up (incidence rate ratio, 1.45; confidence interval, 1.02-2.06; P = 0.036 for BV10/TBV).

CONCLUSIONS

Pruning of the peripheral pulmonary vasculature is associated with asthma severity, control, and exacerbations, and with lung function and eosinophilia.

Clinical phenotypes in asthma during childhood

Asthma is a heterogeneous disease characterized by numerous phenotypes relating to age of onset, triggers, comorbidities, severity (assessed by multiple exacerbations, lung function pattern) and finally the inflammatory cells involved in the pathophysiologic pathway. These phenotypes can vary over time in relation to changes in the principal triggers involved in the aetiology of the disease. Nevertheless, in a patient with multiple allergies and early-onset disease (defined as multiple sensitizations and allergic comorbidities), the prognosis of asthma is poor with a high risk of persistence and severity of the disease during childhood. Future research will focus on classifying phenotypes into groups based on pathophysiologic mechanisms (endotypes) and the biomarkers attached to these endotypes, which could predict prognosis and lead to targeted therapy. Currently, these biomarkers are related to inflammatory cells associated with the asthma endotype, essentially eosinophils and neutrophils (and related cytokines) attached to Th-2 and non Th-1 pathways, respectively. The most severe asthma (refractory asthma) is linked to neutrophil-derived inflammation (frequently associated with female sex, obesity and possibly disorganized airway microbiota) encountered in very young children or teenagers. Severe asthma is also linked to or a marked eosinophil inflammatory process (frequently associated with multiple atopy and, more rarely, with non-atopic hypereosinophilic asthma in children) and frequently encountered in teenagers. Severe phenotypes of asthma could also play a role in the origin of chronic obstructive pulmonary disease in adult life.

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.

Neutrophilic Steroid-Refractory Recurrent Wheeze and Eosinophilic Steroid-Refractory Asthma in Children

BACKGROUND

Little is known about inflammatory pathways of severe recurrent wheeze in preschool children and severe asthma in children.

OBJECTIVES

The aim of the Severe Asthma Molecular Phenotype cohort was to characterize phenotypes of severe recurrent wheeze and severe asthma during childhood in terms of triggers (allergic or not), involved cells (eosinophil or neutrophil), and corticoid responsiveness.

METHODS

Children with moderate-to-severe asthma and preschool children with moderate-to-severe recurrent wheeze were enrolled prospectively. They underwent standardized clinical and blood workup, and bronchoalveolar lavage (BAL) evaluation. Cluster analysis was applied to 350 children with 34 variables.

RESULTS

Three clusters were identified: cluster 1, Neutrophilic steroid-refractory recurrent wheeze phenotype, with 138 children uncontrolled despite high-dose inhaled corticosteroids (ICS) (92%, P < .001), with more history of pneumonia (31%, P < .001), more gastroesophageal reflux disease (37%, P < .001), and the highest blood neutrophil count (mean 4.524 cells/mm³, P = .05); cluster 2, Severe recurrent wheeze with sensitization to a single aeroallergen (12%, P = .002), with 104 children controlled with high-dose ICS (63%, P < .001); cluster 3, Eosinophilic steroid-refractory asthma phenotype, with 108 children uncontrolled despite high-dose ICS (76%, P < .001) with more allergic rhinitis, atopic dermatitis, and food allergies (82%, 40%, 31%, P < .001, respectively). They also had a higher blood eosinophil count and a higher percentage of BAL eosinophil (506/mm³, 2.6%, P < .001 respectively).

CONCLUSIONS

Inflammation pathway of asthma and recurrent wheeze are related to eosinophil cells in older children and neutrophil cells in younger children. These results could improve personalized treatments.

Severe Asthma in Children: Lessons Learned and Future Directions

Severe asthma in children is a complicated and heterogeneous disorder that is extremely challenging to treat. Although most children with asthma derive clinical benefit from daily administration of low-to-medium-dose inhaled corticosteroid (ICS) therapy, a small subset of children with "severe" or "refractory" asthma require high doses of ICS and even systemic corticosteroids to maintain symptom control. These children with severe asthma are at increased risk for adverse outcomes including medication-related side effects and recurrent and life-threatening exacerbations that significantly impair quality of life. This review highlights findings on severe asthma in school-age children (age 6-17 years) from the National Heart, Lung and Blood Institute's Severe Asthma Research Program (SARP) over a 10-year period, between 2001 and 2011. Although SARP has advanced knowledge of the unique clinical, biological, and molecular attributes of severe asthma in children, considerable gaps remain for which additional studies are needed.

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.

Nitrogen chemistry and lung physiology

The versatile chemistry of nitrogen is important to pulmonary physiology. Indeed, almost all redox forms of nitrogen are relevant to pulmonary physiology and to pathophysiology. Here we review the relevance to pulmonary biology of (a) elemental nitrogen; (b) reduced forms of nitrogen such as amines, ammonia, and hydroxylamine; and (c) oxidized forms of nitrogen such as the nitroxyl anion, the nitric oxide free radical, and S-nitrosothiols. Our focus is on oxidized nitrogen in the form of S-nitrosothiol bond-containing species, which are now appreciated to be important to every type of cell-signaling process in the lung. We also review potential clinical applications of nitrogen oxide biochemistry. These principles are being translated into clinical practice as diagnostic techniques and therapies for a range of pulmonary diseases including asthma, cystic fibrosis, adult respiratory distress syndrome, primary ciliary dyskinesia, and pulmonary hypertension.

Biomarkers and severe asthma: a critical appraisal

Severe asthma (SA) is a clinically and etiologically heterogeneous respiratory disease which affects among 5–10 % of asthmatic patients. Despite high-dose therapy, a large patients percentage is not fully controlled and has a poor quality of life. In this review, we describe the biomarkers actually known in scientific literature and used in clinical practice for SA assessment and management: neutrophils, eosinophils, periostin, fractional exhaled nitric oxide, exhaled breath condensate and galectins. Moreover, we give an overview on clinical and biological features characterizing severe asthma, paying special attention to the potential use of these ones as reliable markers. We finally underline the need to define different biomarkers panels to select patients affected by severe asthma for specific and personalized therapeutic approach.

Childhood asthma biomarkers: present knowledge and future steps

Asthma represents the most common chronic respiratory disease of childhood. Its current standard diagnosis relies on patient history of symptoms and confirmed expiratory airflow limitation. Nevertheless, the spectrum of asthma in clinical presentation is broad, and both symptoms and lung function may not always reflect the underlying airway inflammation, which can be determined by different pathogenetic mechanisms. For these reasons, the identification of objective biomarkers of asthma, which may guide diagnosis, phenotyping, management and treatment is of great clinical utility and might have a role in the development of personalized therapy. The availability of non-invasive methods to study and monitor disease inflammation is of relevance especially in childhood asthma. In this sense, a promising role might be played by the measurement of exhaled biomarkers, such as exhaled nitric oxide (FE(NO)) and molecules in exhaled breath condensate (EBC). Furthermore, recent studies have shown encouraging results with the application of the novel metabolomic approach to the study of exhaled biomarkers. In this paper the existing knowledge in the field of asthma biomarkers, with a special focus on exhaled biomarkers, will be highlighted.

Exhaled Breath Condensate pH in Lung Cancer, the Impact of Clinical Factors

PURPOSE

Lung cancer may be associated with airway acidification due to enhanced airway inflammation and oxidative stress. Exhaled breath condensate (EBC) pH is a non-invasive indicator of airway acidity; however, it is still unclear how EBC pH changes in lung cancer. The aim of the study was to investigate EBC pH in lung cancer together with clinical variables.

METHODS

Thirty-five patients with lung cancer and 37 control subjects (21 patients with stable COPD and 16 non-COPD smokers) were enrolled. EBC was collected for pH, which was determined with the argon-purging method, compared among the groups and correlated with clinical variables of patients with lung cancer.

RESULTS

No difference was found in EBC pH between patients with lung cancer and control subjects. However, endobronchial tumour localisation, squamous-cell carcinoma subtype and gastro-oesophageal reflux were associated with low EBC pH values. No relationship was observed between EBC pH and the presence of COPD, lung function variables or smoking history.

CONCLUSIONS

Although, EBC pH is unchanged in lung cancer, lower EBC pH values are associated with distinct phenotypes. Our findings could facilitate further research on airway acidity in lung cancer.

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.

Exhaled breath condensate pH does not discriminate asymptomatic gastroesophageal reflux or the response to lansoprazole treatment in children with poorly controlled asthma

BACKGROUND

Although exhaled breath condensate (EBC) pH has been identified as an "emerging" biomarker of interest for asthma clinical trials, the clinical determinants of EBC pH remain poorly understood. Other studies have associated acid reflux-induced respiratory symptoms, for example, cough, with transient acidification of EBC.

OBJECTIVE

We sought to determine the clinical and physiologic correlates of EBC acidification in a highly characterized sample of children with poorly controlled asthma. We hypothesized that (1) children with asymptomatic gastroesophageal reflux determined by 24-hour esophageal pH monitoring would have a lower EBC pH than children without gastroesophageal reflux, (2) treatment with lansoprazole would alter EBC pH in those children, and (3) EBC acidification would be associated with increased asthma symptoms, poorer asthma control and quality of life, and increased formation of breath nitrogen oxides (NOx).

METHODS

A total of 110 children, age range 6 to 17 years, with poor asthma control and esophageal pH data enrolled in the Study of Acid Reflux in Children with Asthma (NCT00442013) were included. Children submitted EBC samples for pH and NOx measurement at randomization and at study weeks 8, 16, and 24.

RESULTS

Serial EBC pH measurements failed to distinguish asymptomatic gastroesophageal reflux and was not associated with breath NOx formation. EBC pH also did not discriminate asthma characteristics such as medication and health care utilization, pulmonary function, and asthma control and quality of life both at baseline and across the study period.

CONCLUSION

Despite the relative ease of EBC collection, EBC pH as a biomarker does not provide useful information of children with asthma who were enrolled in asthma clinical trials.

Airway nitric oxide and psychological processes in asthma and health: a review

OBJECTIVE

The fraction of exhaled nitric oxide (FeNO) has been widely used as a marker of airway inflammation in asthma in recent years. However, NO serves multiple functions throughout the organism, and various influences on FeNO levels beyond inflammation have been documented. Emerging literature indicates that psychological processes are systematically linked to FeNO.

DATA SOURCES

Academic Search Complete, PubMed, PsychArticles, and PsychInfo databases.

STUDY SELECTIONS

Relevant studies were identified using keywords exhaled nitric oxide paired with psychological stress, stress psychology, emotion, major depression, anxiety, or psychopathology. Studies measuring FeNO during naturalistic observation of emotion and stress, laboratory stress and emotion-induction protocols, and correlational designs using psychological questionnaires were included.

RESULTS

Acute stress, anxiety, and negative affect have been repeatedly linked with higher FeNO levels, whereas more prolonged states of stress, in particular depression, have been associated with lower FeNO levels. The literature on FeNO is paralleled by research on NO in the cardiovascular and central nervous systems, which also shows systematic associations with psychosocial variables. Potential mechanisms of association include stimulation of NO release from different cells, including the epithelia and macrophages, through noradrenaline, interferon-γ, or vascular endothelial growth factor, changes in oxidative stress or arginase levels, or facilitation of diffusion by mechanical factors.

CONCLUSION

Psychosocial factors may need to be considered in the interpretation of longitudinal FeNO changes in monitoring and management of patients with asthma. The distinction between constitutive and inducible sources of NO will be essential for future research.

Asthma across the ages: knowledge gaps in childhood asthma

The Eunice Kennedy Shriver National Institute of Child Health and Human Development convened an Asthma Group in response to the Best Pharmaceuticals for Children Act. The overall goal of the Best Pharmaceuticals for Children Act Program is to improve pediatric therapeutics through preclinical and clinical drug trials that lead to drug-labeling changes. Although significant advances have been made in the understanding and management of asthma in adults with appropriately labeled medications, less information is available on the management of asthma in children. Indeed, many medications are inadequately labeled for use in children. In general, the younger the child, the less information there is available to guide clinicians. Because asthma often begins in early childhood, it is incumbent on us to continue to address the primary questions raised in this review and carefully evaluate the medications used to manage asthma in children. Meanwhile, continued efforts should be made in defining effective strategies that reduce the risk of exacerbations. If the areas of defined need are addressed in the coming years, namely prevention of exacerbations and progression of disease, as well as primary intervention, we will see continuing reduction in asthma mortality and morbidity along with improved quality of life for children with asthma.

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.

Changes in exhaled breath condensate pH in healthy and asthmatic pregnant women

OBJECTIVE

Asthma is a common chronic disease complicating pregnancy with a risk for perinatal complications. Control of airway inflammation in the asthmatic pregnancy improves pregnancy outcomes. Our aim was to evaluate pH of exhaled breath condensate (EBC), a non-invasive method for the assessment of asthmatic airway inflammation, in healthy and asthmatic pregnancies.

DESIGN

Cross-sectional study.

SETTING

Hungarian university clinics.

POPULATION

Seventeen healthy pregnant women, 21 asthmatic pregnant women, 23 healthy non-pregnant women and 22 asthmatic non-pregnant women.

METHODS

EBC samples were collected using a portable condenser, EBC pH was measured after argon deaeration.

MAIN OUTCOME MEASURE

EBC pH.

RESULTS

EBC pH (mean ± SD) of healthy non-pregnant and asthmatic non-pregnant women was similar (7.75 ± 0.27 vs. 7.54 ± 0.57; p = 0.118), probably indicating an optimal control of airway inflammation in asthmatic women. On the other hand, EBC pH was higher in healthy pregnant women compared with healthy non-pregnant women (8.02 ± 0.43 vs. 7.75 ± 0.27; p = 0.017). Higher EBC pH accompanying healthy pregnancy was absent in asthmatic pregnant patients whose EBC pH was lower (7.65 ± 0.38) than that of healthy pregnant women (p = 0.006), and it was similar to that in asthmatic and healthy non-pregnant women (p = 0.470 and p = 0.300, respectively). The EBC pH in asthmatic pregnant women correlated positively with birthweight (r = 0.49, p = 0.047) and negatively with forced vital capacity (r = 0.45, p = 0.039). EBC pH was not related to blood pH.

CONCLUSIONS

EBC pH is higher in healthy pregnant women but not in asthmatic pregnant women compared with data from healthy non-pregnant women, indicating that oxidative inflammatory processes induced by asthma may compromise the regulatory mechanisms causing alkaline pH in the airways during pregnancy.

An association between L-arginine/asymmetric dimethyl arginine balance, obesity, and the age of asthma onset phenotype

RATIONALE

Increasing body mass index (BMI) has been associated with less fractional exhaled nitric oxide (Fe(NO)). This may be explained by an increase in the concentration of asymmetric dimethyl arginine (ADMA) relative to L-arginine, which can lead to greater nitric oxide synthase uncoupling.

OBJECTIVES

To compare this mechanism across age of asthma onset groups and determine its association with asthma morbidity and lung function.

METHODS

Cross-sectional study of participants from the Severe Asthma Research Program, across early- (<12 yr) and late- (>12 yr) onset asthma phenotypes.

MEASUREMENTS AND MAIN RESULTS

Subjects with late-onset asthma had a higher median plasma ADMA level (0.48 μM, [interquartile range (IQR), 0.35-0.7] compared with early onset, 0.37 μM [IQR, 0.29-0.59], P = 0.01) and lower median plasma l-arginine (late onset, 52.3 [IQR, 43-61] compared with early onset, 51 μM [IQR 39-66]; P = 0.02). The log of plasma L-arginine/ADMA was inversely correlated with BMI in the late- (r = -0.4, P = 0.0006) in contrast to the early-onset phenotype (r = -0.2, P = 0.07). Although Fe(NO) was inversely associated with BMI in the late-onset phenotype (P = 0.02), the relationship was lost after adjusting for L-arginine/ADMA. Also in this phenotype, a reduced L-arginine/ADMA was associated with less IgE, increased respiratory symptoms, lower lung volumes, and worse asthma quality of life.

CONCLUSIONS

In late-onset asthma phenotype, plasma ratios of L-arginine to ADMA may explain the inverse relationship of BMI to Fe(NO). In addition, these lower L-arginine/ADMA ratios are associated with reduced lung function and increased respiratory symptom frequency, suggesting a role in the pathobiology of the late-onset phenotype.

Exhaled breath condensate pH in mechanically ventilated patients

OBJECTIVES

In this prospective clinical trial we aimed to answer if spontaneous exhaled breath condensate (EBC) in the trap of the expiratory arm of the ventilator could replace EBC collected by coolant chamber standardized with Argon as an inert gas. Second, if EBC pH could predict ventilator associated pneumonia (VAP) and mortality.

PATIENTS

We included 34 critically ill patients (males = 26), aged = 54.85 ± 19.86 (mean ± SD) yrs, that required mechanical ventilation due to non-pulmonary direct cause (APACHE II score = 23.58 ± 14.7; PaO(2)/FiO(2) = 240.00 ± 98.29).

SETTING

ICU with 9 beds from a regional teaching hospital.

INTERVENTION AND RESULTS

The patients were followed up until development of VAP, successful weaning or death. There were significant differences between mean EBC pH from the 4 procedures with the exception of spontaneous EBC de-aerated with Argon (n = 79; 6.74 ± 0.28) and coolant chamber deaerated with Argon (n = 79; 6.70 ± 0.36; p = NS by Tukey's Multiple Comparison Test). However, none of the procedures were extrapolated between each other according to Bland & Altman method. The mean EBC pH from the trap without Argon was 6.50 ± 0.28. From the total of 34 patients, 22 survived and were discharged and 12 patients died in the ICU.

CONCLUSION

Spontaneous EBC pH could not be extrapolated to EBC pH from coolant chamber and it did not change in subjects who dead, neither subject with VAP in comparison with baseline data. The lack of other biomarker in EBC and the lack of a control group determinate the need for further studies in this setting.

The GPCR OGR1 (GPR68) mediates diverse signalling and contraction of airway smooth muscle in response to small reductions in extracellular pH

BACKGROUND AND PURPOSE

Previous studies have linked a reduction in pH in airway, caused by either environmental factors, microaspiration of gastric acid or inflammation, with airway smooth muscle (ASM) contraction and increased airway resistance. Neural mechanisms have been shown to mediate airway contraction in response to reductions in airway pH to < 6.5; whether reduced extracellular pH (pHo) has direct effects on ASM is unknown.

EXPERIMENTAL APPROACH

Intracellular signalling events stimulated by reduced pHo in human cultured ASM cells were examined by immunoblotting, phosphoinositide hydrolysis and calcium mobilization assays. ASM cell contractile state was examined using magnetic twisting cytometry. The expression of putative proton-sensing GPCRs in ASM was assessed by real-time PCR. The role of ovarian cancer G protein-coupled receptor 1 (OGR1 or GPR68) in acid-induced ASM signalling and contraction was assessed in cultures subjected to siRNA-mediated OGR1 knockdown.

KEY RESULTS

ASM cells responded to incremental reductions in pHo (from pH 8.0 to pH 6.8) by activating multiple signalling pathways, involving p42/p44, PKB, PKA and calcium mobilization. Coincidently, ASM cells contracted in response to decreased pHo with similar 'dose'-dependence. Real-time PCR suggested OGR1 was the only proton-sensing GPCR expressed in ASM cells. Both acid-induced signalling (with the exception of PKB activation) and contraction were significantly attenuated by knockdown of OGR1.

CONCLUSIONS AND IMPLICATIONS

These studies reveal OGR1 to be a physiologically relevant GPCR in ASM cells, capable of pleiotropic signalling and mediating contraction in response to small reductions in extracellular pH. Accordingly, ASM OGR1 may contribute to asthma pathology and represent a therapeutic target in obstructive lung diseases.

Exhaled breath condensate pH is influenced by respiratory droplet dilution

Several studies support that airway acid stress plays a role in the pathophysiology of asthma. Exhaled breath condensate pH (EBC pH) was suggested as a surrogate marker of airway acidification. The dilution of airway lining fluid (ALF) acids and bases by alveolar water may influence condensate pH, but it has not been studied yet. The aim of our study was to investigate the relationship between EBC pH and ALF dilution in EBC samples obtained from asthmatic and healthy subjects. EBC was collected from 55 asthmatic and 57 healthy subjects for pH and conductivity measurements. Fractional exhaled nitric oxide (FE(NO)) and lung function tests were also performed in asthmatic patients. EBC pH was determined after 10 min of argon deareation and the dilution was estimated by the measurement of conductivity in vacuum-treated samples. There was no difference either in EBC pH or dilution between the two groups. However, a significant relationship was found between EBC pH and dilution in both groups (p < 0.05, r = -0.35 and r = -0.29, asthmatic and healthy groups, respectively). Our results suggest important methodological aspect indicating that EBC pH is affected by respiratory droplet dilution, and this effect should be taken into consideration when interpreting EBC pH data.

Biomarkers in asthma: a real hope to better manage asthma

Diagnosis and treatment of asthma are currently based on assessment of patient symptoms and physiologic tests of airway reactivity. Research over the past decade has identified an array of biochemical and cellular biomarkers, which reflect the heterogeneous and multiple mechanistic pathways that may lead to asthma. These mechanistic biomarkers offer hope for optimal design of therapies targeting the specific pathways that lead to inflammation. This article provides an overview of blood, urine, and airway biomarkers; summarizes the pathologic pathways that they signify; and begins to describe the utility of biomarkers in the future care of patients with asthma.

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 metabolomics of asthma: novel diagnostic potential

Asthma is one of the most common chronic illnesses, especially in children. Reaching the diagnosis of asthma and its management are more difficult than for other chronic illnesses. For example, asthma is a heterogeneous syndrome with many clinical classifications based on patient symptoms, lung function, and response to therapy. The symptoms and objective measurements of lung function, often used to guide therapy, are largely based on the inflammation of the airways. Because measuring airway dysfunction and inflammation in a typical clinical setting is difficult, it is often not done. Metabolomics is the study of small molecules generated from cellular metabolic activity. It is possible that the metabolic profile of a patient with a chronic illness such as asthma is different from that of a healthy patient or from a patient with another respiratory illness. Furthermore, if this metabolome could be measured, it might also vary with disease severity. The pattern of metabolites becomes the diagnostic representing the disease. This article outlines the more recent work that has been done to develop the metabolomic profile of asthma.

Residential proximity to a major roadway is associated with features of asthma control in children

Background

While several studies suggest that traffic-related air pollutants are detrimental for respiratory health, few studies have examined relationships between residential proximity to a major roadway and asthma control in children. Furthermore, a major limitation of existing research is reliance on self-reported outcomes. We therefore determined the spatial relationship between the distance from a major roadway and clinical, physiologic and inflammatory features of asthma in a highly characterized sample of asthmatic children 6–17 years of age across a wide range of severities. We hypothesized that a closer residential proximity to a major roadway would be associated with increased respiratory symptoms, altered pulmonary function and a greater magnitude of airway and systemic inflammation.

Methodology/Principal Findings

224 children 6–17 years with confirmed asthma completed questionnaires and underwent spirometry, plethysmography, exhaled nitric oxide determination, exhaled breath condensate collection and venipuncture. Residential distance from a major roadway was determined by mapping the geographic coordinates of the residential address in Geographic Information System software. The distance between the home address and the nearest major roadway was calculated according to the shortest distance between the two points (i.e., “as the crow flies”). Asthmatic children living in closer proximity to a major roadway had an increased frequency of wheezing associated with increased medication requirements and more hospitalizations even after controlling for potential confounders. These children also had increased airway resistance, increased airway inflammation reflected by a lower breath condensate pH, and higher plasma EGF concentrations.

Conclusions/Significance

These findings suggest that closer residential proximity to a major roadway is associated with poorer asthma control in school-age children. Assessment of residential proximity to major roadways may be useful in the clinical evaluation of asthma in children.

Understanding the complexity of IgE-related phenotypes from childhood to young adulthood: a Mechanisms of the Development of Allergy (MeDALL) seminar

Mechanisms of the Development of Allergy (MeDALL), a Seventh Framework Program European Union project, aims to generate novel knowledge on the mechanisms of initiation of allergy. Precise phenotypes of IgE-mediated allergic diseases will be defined in MeDALL. As part of MeDALL, a scientific seminar was held on January 24, 2011, to review current knowledge on the IgE-related phenotypes and to explore how a multidisciplinary effort could result in a new integrative translational approach. This article provides a summary of the meeting. It develops challenges in IgE-related phenotypes and new clinical and epidemiologic approaches to the investigation of allergic phenotypes, including cluster analysis, scale-free models, candidate biomarkers, and IgE microarrays; the particular case of severe asthma was reviewed. Then novel approaches to the IgE-associated phenotypes are reviewed from the individual mechanisms to the systems, including epigenetics, human in vitro immunology, systems biology, and animal models. The last chapter deals with the understanding of the population-based IgE-associated phenotypes in children and adolescents, including age effect in terms of maturation, observed effects of early-life exposures and shift of focus from early life to pregnancy, gene-environment interactions, cohort effects, and time trends in patients with allergic diseases. This review helps to define phenotypes of allergic diseases in MeDALL.

Inflammatory biomarkers in severe asthma

PURPOSE OF REVIEW

Severe asthma remains a condition in search of deeper understanding and of newer effective therapies. Risk factors for developing severe asthma, phenotyping of disease, characterizing the inflammatory response and understanding of poor therapeutic responses to corticosteroids are important areas of research. The development of biomarkers for phenotypic diagnosis and prognostic reasons is important.

RECENT FINDINGS

Severe asthma has been defined as asthma that does not respond adequately to asthma medications, particularly corticosteroids, with continuing loss of control of asthma and future risk of exacerbations and side effects from corticosteroid therapy. This is a heterogeneous condition and cluster analyses have yielded phenotypes on the basis of age of onset of disease, sex, lung function, atopy and questionnaire data. Use of sputum eosinophil counts has further defined a group with persistent eosinophilic inflammation despite corticosteroid therapy, and a noneosinophilic group with uncontrolled asthma.

SUMMARY

Use of a single biomarker provides value in phenotyping and in predicting response to treatment but many more biomarkers such as those derived from -omic approaches remain to be used in the analysis. A systems biology approach to finding novel biomarkers is the way forward to stratify severe asthma so that appropriate and distinct therapies can be selected for each subtype.

Calcium and magnesium in exhaled breath condensate of children with endogenous and exogenous airway acidification

BACKGROUND AND AIMS

Regulation of pH in the airways is of physiological importance. As acidification of the airways causes bronchoconstriction, the aim of the present study was to find out whether there is any difference in calcium and magnesium in exhaled breath condensate (EBC) of children with uncontrolled asthma (i.e., with endogenous acidification) and children with gastroesophageal reflux disease, GERD (i.e., with exogenous acidification).

MATERIAL AND METHODS

A total of 142 children were included in the study: children with uncontrolled asthma (N = 51), children with GERD (N = 61), and healthy controls (N = 30). In addition, according to the pH cut-off value children with asthma and GERD were divided into two subgroups, that is, patients with pH ≤ 6.93 (subgroup A) and patients with pH > 6.93 (subgroup B).

RESULTS

The mean EBC pH was significantly lower in children with asthma than in children with GERD (6.791 ± 0.374 vs. 7.002 ± 0.361, p = .006). Concentration [median and interquartile range-M (IQR)] of total magnesium, but not calcium, was lower in both asthmatic [(10 (10-40) μmol/L, p = .016)] and GERD children [(20 (10-40) μmol/L, p = .012)] in comparison with controls (47 ± 27 μmol/L). There was no statistically significant difference in EBC calcium and magnesium concentrations between asthmatic and GERD children. In asthmatic children a positive correlation was confirmed between forced expiratory volume in the first second (FEV1) and magnesium in EBC (r = 0.307; p = .030), and negative correlation was found between FEV1 and calcium/magnesium ratio (r = -0.290; p = .047). In addition, positive correlation was confirmed between fractional concentration of exhaled NO and calcium/magnesium ratio (r = 0.360; p = .018). In GERD patients a negative correlation (r = -0.404; p = .003) was found between magnesium and pH values. Concentration of calcium was higher in the GERD subgroup A children [(50 (30-90) μmol/L)] than in the subgroup B children [(30 (20-45) μmol/L, p = .031)]. In addition, concentration of magnesium was higher in the GERD subgroup A children [(30 (20-70) μmol/L)] than in the subgroup B children [(10 (10-20) μmol/L, p < .001)].

CONCLUSION

The present study indicates that decreased total magnesium concentration may be found in EBCs, irrespective of whether the acidification is the result of endogenous pathomechanisms or reflux-induced mechanisms. In children with GERD, EBC pH-metry should be performed after acute coughing episode. Future research is needed to investigate the mechanisms of onset and dynamics of these changes.

SCIENTIFIC SIGNIFICANCE

Lower concentration of magnesium may indicate its role in bronchoconstiction.

The biochemistry of asthma

BACKGROUND

Asthma is not one disease. Different patients have biochemically distinct phenotypes.

SCOPE OF REVIEW

Biomarker analysis was developed to identify inflammation in the asthmatic airway. It has led to a renewed interest in biochemical abnormalities in the asthmatic airway. The biochemical determinants of asthma heterogeneity are many. Examples include decreased activity of superoxide dismutases; increased activity of eosinophil peroxidase, S-nitrosoglutathione reductase, and arginases; decreased airway pH; and increased levels of asymmetric dimethyl arginine.

MAJOR CONCLUSIONS

New discoveries suggest that biomarkers such as exhaled nitric oxide reflect complex airway biochemistry. This biochemistry can be informative and therapeutically relevant.

GENERAL SIGNIFICANCE

Improved understanding of airway biochemistry will lead to new tests to identify biochemically unique subpopulations of patients with asthma. It will also likely lead to new, targeted treatments for these specific asthma subpopulations. This article is part of a Special Issue entitled Biochemistry of Asthma.

Reduced breath condensate pH in asymptomatic children with prior wheezing as a risk factor for asthma

BACKGROUND

Early noninvasive detection of increased risk of asthma with exhaled breath condensate (EBC) pH measurement has not been applied to preschool children.

OBJECTIVE

We sought to evaluate the ability of EBC pH measurement to identify young asymptomatic children at risk of asthma using the combination of recurrent wheezing and atopic sensitization as a proxy for a high risk of asthma.

METHODS

pH values were measured in deaerated EBC from 191 children (median age, 4.4 years [interquartile range, 2.2 years]). Children were divided into one of 5 groups: asymptomatic children with recurrent wheezy bronchitis with (group 1, n = 34) or without (group 2, n = 64) allergic sensitization, acute wheezy bronchitis (group 3, n = 18), allergic rhinoconjunctivitis without recurrent wheezy bronchitis (group 4, n = 15), and healthy control subjects (group 5, n = 60). The Asthma Predictive Index score was calculated for groups 1 and 2. Statistical significance was evaluated with the appropriate nonparametric tests, and the discriminatory accuracy was evaluated with receiver operating characteristic analysis.

RESULTS

Deaerated EBC pH values were significantly lower in groups 1 and 3 than in groups 2, 4, and 5 (median, 7.49 [interquartile range, 0.94] and 7.44 [interquartile range, 0.70] vs 7.93 [interquartile range, 0.23], 8.02 [interquartile range, 0.17], and 7.96 [interquartile range, 0.25], respectively; P < .001 and area under the receiver operating characteristic curve ≥0.80 in all comparisons). The area under the curve for the differentiation between groups 1 and 2 improved from 0.80 to 0.94 (sensitivity, 0.94; specificity, 0.84; positive predictive value, 0.76) when breath condensate pH values and Asthma Predictive Index scores were combined.

CONCLUSION

A reduced deaerated EBC pH value might help identify young asymptomatic children at high risk of asthma.