Exhaled breath condensate nitrite/nitrate and pH in relation to pediatric asthma control and exhaled nitric oxide

[The relationship between inflammation and symptoms in asthma]

In asthma, symptoms are the main reason for recourse to healthcare and are a fundamental parameter for the evaluation of asthma control. Currently, asthma is defined as a chronic inflammatory disease. Uncontrolled asthmatics have an increased number of eosinophils in induced sputum and an increased production of exhaled NO. Control by anti-inflammatory treatment is accompanied by a reduction in bronchial eosinophilia and exhaled NO. Asthma symptoms are the result of complex mechanisms and many factors modify their perception. Experimental data suggests that there is a relationship between the perception of symptoms and eosinophilic inflammation, and that inhaled corticoid therapy improves this perception. Although they are still not applicable in routine practice, follow-up strategies based on the evaluation of inflammation are thought to be more effective in reducing exacerbations than those usually recommended based on retrospective evaluation of symptoms and sequential analysis of respiratory function. Inhaled corticosteroid therapy is the reference maintenance therapy for persistent asthma and adjustment of anti-inflammatory treatment based on symptoms is an effective strategy to prevent exacerbations and reduce the total dose of inhaled corticosteroids. A French expert group has undertaken a study of the association between inflammation and asthma symptoms by carrying out a critical review of the international literature.

Exhaled breath condensate in patients with asthma: implications for application in clinical practice

Exhaled breath condensate (EBC) analysis, a rather appealing and promising method, can be used to evaluate conveniently and non-invasively a wide range of molecules from the respiratory tract, and to understand better the pathways propagating airway inflammation. A large number of mediators of inflammation, including adenosine, ammonia, hydrogen peroxide, isoprostanes, leukotrienes, prostanoids, nitrogen oxides, peptides and cytokines, have been studied in EBC. Concentrations of such mediators have been shown to be related to the underlying asthma and its severity and to be modulated by therapeutic interventions. Despite the encouraging positive results to date, the introduction of EBC in everyday clinical practice requires the resolution of some methodological pitfalls, the standardization of EBC collection and finally the identification of a reliable biomarker that is reproducible has normal values and provides information regarding the underlying inflammatory process and the response to treatment. So far, none of the parameters studied in EBC fulfils the aforementioned requirements with one possible exception: pH. EBC pH is reproducible, has normal values, reflects a significant part of asthma pathophysiology and is measurable on-site with standardized methodology although some methodological aspects of measurement of pH in EBC (e.g. the effect of ambient CO(2), sample de-aeration, time for pH measurement) require further research. However, EBC pH has not been evaluated prospectively as a guide for treatment, in a manner similar to exhaled NO and sputum eosinophils. EBC represents a simple and totally non-invasive procedure that may contribute towards our understanding of asthma pathophysiology. Besides the evaluation of new biomarkers, the standardization of the already existing procedures is warranted for the introduction of EBC in clinical practice.

Exhaled breath condensate in children: present knowledge and future prospects

Exhaled breath condensate (EBC) is a safe and easy technique that enables several biomarkers of lung disease to be detected. Condensate collection requires only minimal cooperation and can easily be done by children as young as 4 years old. Some condensers have been adapted for use by younger children but EBC collection with these devices still poses significant drawbacks. EBC has been applied in the study of various respiratory diseases in children (mostly asthma and cystic fibrosis, but also other diseases such as primary ciliary dyskinesia). Several biomarkers of airway inflammation and oxidative stress have been detected in the EBC of these patients, demonstrating the role of different inflammatory pathways in the pathophysiology of respiratory diseases. Lately EBC has also been analyzed using new techniques, such as metabolomic analysis, an approach that enables the simultaneous assessment of several biocompounds with the potential identification of metabolite profiles characteristic of a given disease. Studies published so far support the promising role of EBC in investigating the pathophysiology of lung diseases. The noninvasiveness of this technique makes it particularly suitable for application in children.

Biomarkers in exhaled breath condensate: a review of collection, processing and analysis

Exhaled breath condensate (EBC) is a potential rich source for countless biomarkers that can provide valuable information about respiratory as well as systemic diseases. EBC has been studied in a variety of diseases including allergic rhinitis, asthma, chronic obstructive lung disease, cystic fibrosis, lung cancer, and obstructive sleep apnea syndrome. Although numerous biomarkers have been discovered and studied in EBC, the methods of collection and biomarker detection have not been fully standardized. While leaving standardization methods up to individual labs for the present time is optimal for the continued discovery of new biomarkers in EBC, this decreases the reproducibility and generalizability of the findings. In this review we will discuss specific biomarkers studied in specific diseases as well as some of the related technical issues including collection, processing and analysis.

Long-term repeatability of exhaled breath condensate pH in asthma

Exhaled breath condensate (EBC) is being used increasingly to sample airway fluid. EBC pH may be a biomarker of airway inflammation in asthma. In this study, we assessed the long-term reproducibility of EBC pH in asthma. We examined 31 asthmatic patients and eight healthy subjects three times over a 1-year period (winter, autumn and summer). EBC pH was measured after argon deaeration. Repeatability of pH measurements was assessed using intraclass correlation coefficients (ICC) and the limits of agreement (LOA) between seasons were calculated according to Bland-Altman method. No significant differences in EBC pH between seasons were detected in healthy subjects and asthmatic patients. EBC pH showed high repeatability either in healthy subjects (ICC=0.94) or in asthmatics (ICC=0.97). Variability between seasons was greater in asthmatics than in healthy subjects: winter-autumn LOA -0.68/+0.52 and -0.31/+0.31, autumn-summer LOA -0.75/+0.67 and -0.24/+0.15, winter-summer LOA -0.92/+0.67 and -0.34/+0.23 in asthmatic and healthy subjects, respectively. In a subgroup of 11 asthmatics who remained in stable conditions during the study, no substantially different LOA were observed in EBC pH compared with the whole group of asthmatics. Asthmatic smokers (n=10) tended to have lower EBC pH (7.57+/-0.46) than asthmatic non-smokers (n=21) (7.74+/-0.21; p=0.063) and wider LOA. In conclusion, we demonstrated that EBC pH exhibits good repeatability in long-term assessment. EBC pH in asthmatics tended to fluctuate more than in healthy subjects. However, EBC pH variability in asthma was not influenced by changes in clinical status. Rather, we suggest that cigarette smoke may be implicated in EBC pH variability.

Exhaled breath condensate pH in infants and children with acute and recurrent wheezy bronchitis

The analysis of exhaled breath condensate (EBC) is a promising new method to measure airway inflammation. So far only limited data exist about methodological issues of EBC sampling in infants and young children. We evaluated 18 children with acute wheezy bronchitis (median age 24.3 months (min-max: 4-89.9)), 54 children with recurrent wheezy bronchitis (median age 52.5 months (7.2-94.8)), and 32 healthy controls (median age 49.6 months (25.3-67.8)). EBC was sampled with a modified commercially available EBC-sampler, pH was measured after deaeration. EBC volume was significantly correlated to age (r = 0.56, P < 0.001). EBC pH was significantly decreased in all patients compared to the healthy controls (acute wheezy bronchitis 7.87 (7.16-8.19), P = 0.003, recurrent wheezy bronchitis 7.86 (6.95-8.39), P = 0.002, and healthy controls 8.04 (7.81-8.87), respectively). There were no significant differences of the EBC pH between the disease groups. When divided into different subgroups, an influence of inhaled steroid treatment was found with steroid-naive recurrent wheezers having significantly lower EBC pH levels compared to healthy controls (7.80 (6.95-8.37), P = 0.018), but not so steroid treated (7.94 (7.24-8.39), P = 0.055). Both, recurrent wheezers with or without a positive allergy test had significantly lower EBC pH compared to healthy controls (7.91 (6.95-8.37), P = 0.007 and 7.82 (7.32-8.39), P = 0.005, respectively). This study indicates that EBC can be collected with a modified commercially available EBC sampler in infants and young children. Further studies need to be performed to evaluate the relevance and meaning of pH differences of EBC in this age group.

Are exhaled breath condensates useful in monitoring asthma?

Exhaled breath condensate (EBC) has emerged as a novel noninvasive technique for assessment of airway inflammation, and it also provides useful information on the airway lining fluid composition. Examples of markers that can be identified in the EBC of patients with asthma include pH, eicosanoids, nitrogen oxides and related products, markers of oxidative stress, certain cytokines, chemokines, and growth factors. There is some evidence that certain markers in EBC differ between patients with asthma and controls, and some markers may correlate with asthma severity and lung function, but there are many methodologic pitfalls with EBC assessment that limit its clinical applicability at present. More studies are needed before this technique can be recommended for clinical use.

Exhaled breath condensate: a new method for lung disease diagnosis

Analysis of exhaled breath composition in lung disease patients can indirectly point to biochemical changes that occur in the fluid lining airway surfaces. The parameters of redox and acid-base changes, and of inflammatory changes relevant in the pathogenesis of most pulmonary diseases are currently most widely determined in exhaled breath condensate. The collection of exhaled breath condensate is a safe, non-invasive, easy and simple diagnostic procedure that is suitable for longitudinal studies and applicable in patients of all age groups, irrespective of the disease severity. In spite of many scientific studies involving lung disease patients, methodology for exhaled breath condensate collection and analysis has not yet been realized for daily utilization. Additional studies of the exact origin of condensate constituents and standardization of the overall analytical process, including collection, storage, analysis and result interpretation, are needed. Irrespective of these limitations, further investigation of this sample type is fully justified by the fact that classical specimens used in the management of pulmonary disease are either obtained by invasive procedures (e.g., induced sputum, biopsy, bronchoalveolar lavage) or cannot provide appropriate information (e.g., urine, serum). Analysis of exhaled breath condensate in the future might contribute significantly to our understanding of the physiological and pathophysiological processes in lungs, to early detection, diagnosis and follow up of disease progression, and to evaluation of therapeutic response.