Exhaled nitric oxide in asthma in adults: the end is the beginning?

Biomarkers in Asthma, Potential for Therapeutic Intervention

Asthma is a heterogeneous disease with multiple phenotypes that have variable risk factors and therapeutic responses. Airway hyperreactivity, inflammation and airway remodeling are hallmarks of asthma. Asthmatics exhibiting an increase in airway T2 inflammation is now classify as having T2-"high" asthma. Type 2 cytokines, IL-4, IL-5, and IL-13, along with other inflammatory mediators, lead to increased eosinophilic inflammation along with elevated FeNO in this endotype. There is no clear definition for T2-"low" asthma. Biomarkers can help identify different phenotypes and endotypes, treatment response to standard treatment or potential therapeutic targets particularly for biologics. As our knowledge of phenotypes and endotypes improved, biologics have increasingly integrated into treatment strategies for severe asthma. These treatments block specific inflammatory pathways or single mediators. Single or composite biomarkers may help to identify subsets of patients who will benefit from these treatments. However, only a few inflammatory biomarkers have validated for clinical application. As knowledge emerges, the goal would be to provide individualized care to asthmatic patients.

Association between pre-biologic T2-biomarker combinations and response to biologics in patients with severe asthma

Background

To date, studies investigating the association between pre-biologic biomarker levels and post-biologic outcomes have been limited to single biomarkers and assessment of biologic efficacy from structured clinical trials.

Aim

To elucidate the associations of pre-biologic individual biomarker levels or their combinations with pre-to-post biologic changes in asthma outcomes in real-life.

Methods

This was a registry-based, cohort study using data from 23 countries, which shared data with the International Severe Asthma Registry (May 2017-February 2023). The investigated biomarkers (highest pre-biologic levels) were immunoglobulin E (IgE), blood eosinophil count (BEC) and fractional exhaled nitric oxide (FeNO). Pre- to approximately 12-month post-biologic change for each of three asthma outcome domains (i.e. exacerbation rate, symptom control and lung function), and the association of this change with pre-biologic biomarkers was investigated for individual and combined biomarkers.

Results

Overall, 3751 patients initiated biologics and were included in the analysis. No association was found between pre-biologic BEC and pre-to-post biologic change in exacerbation rate for any biologic class. However, higher pre-biologic BEC and FeNO were both associated with greater post-biologic improvement in FEV1 for both anti-IgE and anti-IL5/5R, with a trend for anti-IL4Rα. Mean FEV1 improved by 27-178 mL post-anti-IgE as pre-biologic BEC increased (250 to 1000 cells/µL), and by 43-216 mL and 129-250 mL post-anti-IL5/5R and -anti-IL4Rα, respectively along the same BEC gradient. Corresponding improvements along a FeNO gradient (25-100 ppb) were 41-274 mL, 69-207 mL and 148-224 mL for anti-IgE, anti-IL5/5R, and anti-IL4Rα, respectively. Higher baseline BEC was also associated with lower probability of uncontrolled asthma (OR 0.392; p=0.001) post-biologic for anti-IL5/5R. Pre-biologic IgE was a poor predictor of subsequent pre-to-post-biologic change for all outcomes assessed for all biologics. The combination of BEC + FeNO marginally improved the prediction of post-biologic FEV1 increase (adjusted R2: 0.751), compared to BEC (adjusted R2: 0.747) or FeNO alone (adjusted R2: 0.743) (p=0.005 and <0.001, respectively); however, this prediction was not improved by the addition of IgE.

Conclusions

The ability of higher baseline BEC, FeNO and their combination to predict biologic-associated lung function improvement may encourage earlier intervention in patients with impaired lung function or at risk of accelerated lung function decline.

Effect of Buteyko breathing technique on clinical and functional parameters in adult patients with asthma: a randomized, controlled study

BACKGROUND

The established therapy of asthma might be supported by additional non-pharmaceutical measures, such as the Buteyko breathing technique (BBT); however, the available data are mixed. To clarify the effects of BBT in patients with asthma, we investigated whether it led to clinical improvements with correlation to functional parameters.

METHODS

Using a randomized, controlled design, we studied two groups (n = 30 each) of patients with asthma under either BBT or usual therapy (UT) w/o BBT over a period of 3 months. The primary outcome comprised the voluntary control pause (CP) after 3 months, secondary outcomes an additional breathhold parameter, forced expiratory volume in 1 s (FEV1), capnovolumetry, exhaled nitric oxide (FeNO), Asthma Control Questionnaire (ACQ) and Nijmegen Questionnaire (NQ), and the use of medication (β2-agonists; inhaled corticosteroids, ICS).

RESULTS

CP showed significant time-by-group interaction [F(1,58.09) = 28.70, p < 0.001] as well as main effects for study group [F(1,58.27) = 5.91, p = 0.018] and time [F(1,58.36) = 17.67, p < 0.001]. ACQ and NQ scores were significantly (p < 0.05 each) improved with BBT. This was associated with reductions in the use of β2-agonists and ICS (p < 0.05 each) by about 20% each. None of these effects occurred in the UT group. While FEV1 and the slopes of the capnovolumetric expiratory phases 2 and 3 did not significantly change, the capnovolumetric threshold volume at tidal breathing increased (p < 0.05) with BBT by about 10 mL or 10%, compared to baseline, suggesting a larger volume of the central airways. No significant changes were seen for FeNO.

CONCLUSIONS

BBT was clinically effective, as indicated by the fact that the improvement in symptom scores and the small increase in bronchial volume occurred despite the significant reduction of respiratory pharmacotherapy. As the self-controlled Buteyko breathing therapy was well-accepted by the participants, it could be considered as supporting tool in asthma therapy being worth of wider attention in clinical practice. Trial registration Retrospectively registered on 10 March 2017 at ClinicalTrials.gov (NCT03098849).

Exhaled Breath Analysis Using Selected Ion Flow Tube Mass Spectrometry and Disease Severity in Heart Failure

Exhaled breath volatile organic compounds (VOCs) are elevated in heart failure (HF). The ability of VOCs to predict long term cardiovascular mortality and morbidity has not been independently verified. In 55 patients admitted with acute decompensated heart failure (ADHF), we measured exhaled breath acetone and pentane levels upon admission and after 48 h of diuresis. In a separate cohort of 51 cardiac patients undergoing cardiopulmonary exercise testing (CPET), we measured exhaled breath acetone and pentane levels before and at peak exercise. In the ADHF cohort, admission acetone levels correlated with lower left ventricular ejection fraction (LVEF, r = -0.297, p = 0.035). Greater weight loss with diuretic therapy correlated with a greater reduction in both acetone levels (r = -0.398, p = 0.003) and pentane levels (r = -0.309, p = 0.021). In patients with above-median weight loss (≥4.5 kg), patients demonstrated significantly greater percentage reduction in acetone (59% reduction vs. 7% increase, p < 0.001) and pentane (23% reduction vs. 2% reduction, p = 0.008). In the CPET cohort, admission acetone and pentane levels correlated with higher VE/VCO2 (r = 0.39, p = 0.005), (r = 0.035, p = 0.014). However, there were no significant correlations between baseline or peak exercise acetone and pentane levels and peak VO2. In longitudinal follow-up with a median duration of 33 months, patients with elevated exhaled acetone and pentane levels experienced higher composite adverse events of death, ventricular assist device implantation, or orthotopic heart transplantation. In patients admitted with ADHF, higher exhaled breath acetone levels are associated with lower LVEF and poorer outcomes, and greater reductions in exhaled breath acetone and pentane tracked with greater weight loss. Exhaled acetone and pentane may be novel biomarkers in heart failure worthy of future investigation.

New insights into the pathophysiology and therapeutic targets of asthma and comorbid chronic rhinosinusitis with or without nasal polyposis

Asthma and chronic rhinosinusitis with nasal polyps (CRSwNP) or without (CRSsNP) are chronic respiratory diseases. These two disorders often co-exist based on common anatomical, immunological, histopathological, and pathophysiological basis. Usually, asthma with comorbid CRSwNP is driven by type 2 (T2) inflammation which predisposes to more severe, often intractable, disease. In the past two decades, innovative technologies and detection techniques in combination with newly introduced targeted therapies helped shape our understanding of the immunological pathways underlying inflammatory airway diseases and to further identify several distinct clinical and inflammatory subsets to enhance the development of more effective personalized treatments. Presently, a number of targeted biologics has shown clinical efficacy in patients with refractory T2 airway inflammation, including anti-IgE (omalizumab), anti-IL-5 (mepolizumab, reslizumab)/anti-IL5R (benralizumab), anti-IL-4R-α (anti-IL-4/IL-13, dupilumab), and anti-TSLP (tezepelumab). In non-type-2 endotypes, no targeted biologics have consistently shown clinical efficacy so far. Presently, multiple therapeutical targets are being explored including cytokines, membrane molecules and intracellular signalling pathways to further expand current treatment options for severe asthma with and without comorbid CRSwNP. In this review, we discuss existing biologics, those under development and share some views on new horizons.

Dupilumab pharmacokinetics and effect on type 2 biomarkers in children with moderate-to-severe asthma

BACKGROUND

Type 2 inflammation is common in children with asthma. Dupilumab, a human antibody, blocks signaling of interleukin-4/-13, key and central drivers of type 2 inflammation. In the VOYAGE (NCT02948959) study, dupilumab reduced severe asthma exacerbations and improved lung function in children aged 6-11 years with uncontrolled, moderate-to-severe asthma.

OBJECTIVE

To assess pharmacokinetics of dupilumab and type 2 biomarker changes in children with type 2 asthma in VOYAGE.

METHODS

Patients were randomized to dupilumab 100 mg (≤30 kg) or 200 mg (>30 kg) or placebo every 2 weeks (q2w) for 52 weeks. Dupilumab concentrations and changes in type 2 biomarkers were assessed at each visit.

RESULTS

Dupilumab concentrations in serum reached steady state by Week 12, with mean concentrations of 51.2 mg/L and 79.4 mg/L in children receiving dupilumab 100 mg q2w and 200 mg q2w, respectively (therapeutic range in adults and adolescents: 29-80 mg/L). Reductions in type 2 biomarkers were comparable between regimens, and greater in patients treated with dupilumab vs placebo. In children treated with dupilumab 100 mg and 200 mg q2w, median percent changes (Q1, Q3) from baseline at Week 52 were, respectively, -78.6% (-86.3, -69.80) and -78.6% (-84.9, -70.1) for serum total IgE, -53.6% (-66.4, -34.6) and -43.7% (-58.6, -28.5) for TARC, -25.7% (-60.0, 27.6) and -33.3% (-60.6, 16.6) for blood eosinophils, and -47.7% (-73.8, 18.9) and -55.6% (-73.6, -20.0) for FeNO.

CONCLUSION

Weight-tiered dose regimens achieved mean concentrations within the dupilumab therapeutic range. Median decreases in type 2 biomarker levels were similar between dose regimens.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02948959.

Current Understanding of Asthma Pathogenesis and Biomarkers

Asthma is a heterogeneous lung disease with variable phenotypes (clinical presentations) and distinctive endotypes (mechanisms). Over the last decade, considerable efforts have been made to dissect the cellular and molecular mechanisms of asthma. Aberrant T helper type 2 (Th2) inflammation is the most important pathological process for asthma, which is mediated by Th2 cytokines, such as interleukin (IL)-5, IL-4, and IL-13. Approximately 50% of mild-to-moderate asthma and a large portion of severe asthma is induced by Th2-dependent inflammation. Th2-low asthma can be mediated by non-Th2 cytokines, including IL-17 and tumor necrosis factor-α. There is emerging evidence to demonstrate that inflammation-independent processes also contribute to asthma pathogenesis. Protein kinases, adapter protein, microRNAs, ORMDL3, and gasdermin B are newly identified molecules that drive asthma progression, independent of inflammation. Eosinophils, IgE, fractional exhaled nitric oxide, and periostin are practical biomarkers for Th2-high asthma. Sputum neutrophils are easily used to diagnose Th2-low asthma. Despite progress, more studies are needed to delineate complex endotypes of asthma and to identify new and practical biomarkers for better diagnosis, classification, and treatment.

Determination of nitric oxide using light-emitting diode-based colorimeter with tubular porous polypropylene membrane cuvette

On the basis of the Griess-Saltzman (GS) reaction, an optical device for nitric oxide (NO) detection in exhaled breath and atmosphere was developed by employing the light-emitting diode (LED, 560 nm) as the light source, light-to-voltage converter (LVC) as the detector, and porous polypropylene membrane tube (PPMT) as the cuvette. The PPMT was filled with GS reagents and covered with a coaxial jacket tube for gas collection and color reaction; two ends of the PPMT were connected with the LED and LVC to detect the change of light transmissivity in the wavelength range of 530 to 590 nm mainly. A gas absorber filled with GS reagents was installed prior to another absorber filled with KMnO₄ solution to eliminate the interference of coexisting NO₂. Under the optimized experimental conditions, the device achieved a limit of detection (3σ/k) of 4.4 ppbv for NO detection. The linearity range of this device was divided into two segments, i.e., 25 to 100 ppbv and 50 to 1000 ppbv, with both coefficients of determination > 0.99. The relative standard deviation was 2.7% (n = 9, c = 100 ppbv), and the analytical time was 5.5 min per detection. The minimum detectable quantity was decreased to 1.18 ng, which was ~ 100 times lower than the original GS method (115 ng). The present device was applied for determination of NO in exhaled breath, vehicle exhaust, and air. In addition to satisfactory spiking recoveries (i.e., 103% and 107%), the analytical results of the present device were in agreement with the results obtained by the standard method. These results assured the practicality of the developed device for NO detection in real environmental samples.

Toward clinically applicable biomarkers for asthma: An EAACI position paper

Inflammation, structural, and functional abnormalities within the airways are key features of asthma. Although these processes are well documented, their expression varies across the heterogeneous spectrum of asthma. Type 2 inflammatory responses are characterized by increased levels of eosinophils, FeNO, and type 2 cytokines in blood and/or airways. Presently, type 2 asthma is the best-defined endotype, typically found in patients with allergic asthma, but surprisingly also in nonallergic patients with (severe) asthma. The etiology of asthma with non-type 2 inflammation is less clear. During the past decade, targeted therapies, including biologicals and small molecules, have been increasingly integrated into treatment strategies of severe asthma. These treatments block specific inflammatory pathways or single mediators. Single or composite biomarkers help to identify patients who will benefit from these treatments. So far, only a few inflammatory biomarkers have been validated for clinical application. The European Academy of Allergy & Clinical Immunology Task Force on Biomarkers in Asthma was initiated to review different biomarker sampling methods and to investigate clinical applicability of new and existing inflammatory biomarkers (point-of-care) to support diagnosis, targeted treatment, and monitoring of severe asthma. Subsequently, we discuss existing and novel targeted therapies for asthma as well as applicable biomarkers.

Severe Eosinophilic Asthma

Asthma is a heterogeneous disease with varying severity. Severe asthma is a subject of constant research because it greatly affects patients’ quality of life, and patients with severe asthma experience symptoms, exacerbations, and medication side effects. Eosinophils, although at first considered insignificant, were later specifically associated with features of the ongoing inflammatory process in asthma, particularly in the severe case. In this review, we discuss new insights into the pathogenesis of severe asthma related to eosinophilic inflammation and the pivotal role of cytokines in a spectrum that is usually referred to as “T2-high inflammation” that accounts for almost half of patients with severe asthma. Recent literature is summarized as to the role of eosinophils in asthmatic inflammation, airway remodeling, and airway hypersensitivity. Major advances in the management of severe asthma occurred the past few years due to the new targeted biological therapies. Novel biologics that are already widely used in severe eosinophilic asthma are discussed, focusing on the choice of the right treatment for the right patient. These monoclonal antibodies primarily led to a significant reduction of asthma exacerbations, as well as improvement of lung function and patient quality of life.

Inflammatory profile in optimally treated patients with adult versus early-onset asthma

Introduction: The age of asthma onset is often implicated in clinical manifestation, diagnosis, and management of the disease. Aim: To define demographic, clinical and functional features and inflammatory characteristics in induced sputum in patients with adult-onset asthma. Methods: Optimally treated patients from asthma clinics of two tertiary hospitals were included in the study. Patients underwent assessment of demographic characteristics, severity and treatment regimes, pulmonary function tests, and skin prick tests, as well as measurement of blood eosinophils and sputum induction for the assessment of sputum inflammatory cells, IL-8 and IL-13 levels in the supernatant. Results: Of the 333 patients recruited, 234 (70.2%) had adult-onset asthma. Adult-onset asthmatics were older, had a higher BMI, a shorter disease duration, and were less often atopic, compared to patients with early onset asthma. Higher proportions of patients with severe asthma presented increased levels of FeNO and blood eosinophils, both in the early and the adult-onset patient groups. Finally, obese patients with early onset asthma were characterized by less atopy compared to non-obese patients in the same group. Conclusion: Adult-onset asthma was characterized by less sputum eosinophilia, a nonatopic profile and a higher BMI compared to early-onset asthma. The presence of blood eosinophilia and increased FeNO in patients with severe asthma was comparable in the two groups.

Altered pattern of monocyte differentiation and monocyte-derived TGF-β1 in severe asthma

CD14⁺ monocytes contain precursors for macrophages and fibrocytes, known to be involved in regulating airway remodeling in human asthma and distinguishable by the PM-2K marker. We sought to identify circulating subsets of PM-2K⁺ macrophage-like cells and evaluate their relationships to lung function, severity and control status. Circulating PM-2K⁺ macrophage-like cells and fibrocytes could be identified and distinguished between normal individuals (N = 152) and asthmatic subjects (N = 133) using multi-parametric flow cytometry. PM-2K⁺ macrophage-like cells were found to be significantly lower in asthmatic subjects, particularly noted for the CD14⁻PM-2K⁺ subset and PM-2K⁺CCR7⁻CD86⁺ cells in subjects with poor lung function (FEV%/FVC% < 80%) as compared to those of normal subjects and asthmatics with normal lung function, whereas the frequency of fibrocytes was higher in asthmatics and the CCR7⁻CD86⁺ subset distribution was significantly different in subjects with varying severity. Moreover, exogenous transforming growth factor beta 1 (TGF-β1) was found to inhibit the generation of PM-2K⁺ macrophage^-like cells, but promote the growth of fibrocytes, from CD14⁺ monocytes^, and monocyte-derived TGF-β1 was found to correlate with the lung function, severity and control status in asthmatic patients. Collectively, aberrant differentiation of monocytes into PM-2K⁺ macrophage-like cell subsets and fibrocytes, together with increased monocyte-derived TGF-β1, characterized patients with severe asthma.

Biomarkers in asthmatic patients: Has their time come to direct treatment?

Asthma is a heterogeneous disease with multiple phenotypes that have variable risk factors and responses to therapeutics. Mild-to-moderate asthma often responds to traditional medications, whereas severe disease can be refractory to inhaled corticosteroids, long-acting β-agonists, and leukotriene receptor antagonists. There is robust research into the variable phenotypes of asthma. Biomarkers help define the specific pathophysiology of different asthma phenotypes and identify potential therapeutic targets. The following review will discuss the current use of biomarkers for the diagnosis of asthma, triaging the severity of a patient's disease, and the potential efficacy of treatments. This information can be used to define certain patient populations that are more likely to respond to inhaled corticosteroids or biologics. As knowledge of patient phenotypes and endotypes and biological agents to target specific classes of asthma emerge, the ability to provide personalized care to asthmatic patients will follow.

The asthma-COPD overlap syndrome: do we really need another syndrome in the already complex matrix of airway disease?

The term asthma–COPD overlap syndrome (ACOS) is one of multiple terms used to describe patients with characteristics of both COPD and asthma, representing ~20% of patients with obstructive airway diseases. The recognition of both sets of morbidities in patients is important to guide practical treatment decisions. It is widely recognized that patients with COPD and coexisting asthma present with a higher disease burden, despite the conceptual expectation that the “reversible” or “treatable” component of asthma would allow for more effective management and better outcomes. However, subcategorization into terms such as ACOS is complicated by the vast spectrum of heterogeneity that is encapsulated by asthma and COPD, resulting in different clinical clusters. In this review, we discuss the possibility that these different clusters are suboptimally described by the umbrella term “ACOS”, as this additional categorization may lead to clinical confusion and potential inappropriate use of resources. We suggest that a more clinically relevant approach would be to recognize the extreme variability and the numerous phenotypes encompassed within obstructive airway diseases, with various degrees of overlapping in individual patients. In addition, we discuss some of the evidence to be considered when making practical decisions on the treatment of patients with overlapping characteristics between COPD and asthma, as well as the potential options for phenotype and biomarker-driven management of airway disease with the aim of providing more personalized treatment for patients. Finally, we highlight the need for more evidence in patients with overlapping disease characteristics and to facilitate better characterization of potential treatment responders.

Measurement of exhaled nitric oxide concentration in asthma: a systematic review and economic evaluation of NIOX MINO, NIOX VERO and NObreath

BACKGROUND

High fractions of exhaled nitric oxide (FeNO) in the breath of patients with symptoms of asthma are correlated with high levels of eosinophils and indicate that a patient is likely to respond to inhaled corticosteroids. This may have a role in the diagnosis and management of asthma.

OBJECTIVE

To assess the diagnostic accuracy, clinical effectiveness and cost-effectiveness of the hand-held electrochemical devices NIOX MINO(®) (Aerocrine, Solna, Sweden), NIOX VERO(®) (Aerocrine) and NObreath(®) (Bedfont Scientific, Maidstone, UK) for the diagnosis and management of asthma.

DATA SOURCES

Systematic searches were carried out between March 2013 and April 2013 from database inception. Databases searched included MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews, the Database of Abstracts of Reviews of Effects, Science Citation Index Expanded and Conference Proceedings Citation Index - Science. Trial registers such as ClinicalTrials.gov and the metaRegister of Controlled Trials were also searched in March 2013. All searches were updated in September 2013.

REVIEW METHODS

A rapid review was conducted to assess the equivalence of hand-held and chemiluminescent FeNO monitors. Systematic reviews of diagnostic accuracy and management efficacy were conducted. A systematic review of economic analyses was also conducted and two de novo health economic models were developed. All three reviews were undertaken according to robust high-quality methodology.

RESULTS

The rapid review (27 studies) found varying levels of agreement between monitors (Bland-Altman 95% limits of agreement up to ±10 parts per billion), with better agreement at lower FeNO values. Correlation was good (generally r > 0.9). The diagnostic accuracy review identified 22 studies in adults (all ages) and four in children. No studies used NObreath or NIOX VERO and seven used NIOX MINO. Estimates of diagnostic accuracy varied widely. FeNO used in combination with another test altered diagnostic accuracy only slightly. High levels of heterogeneity precluded meta-analysis. Limited observations included that FeNO may be more reliable and useful as a rule-in than as a rule-out test; lower cut-off values in children and in smokers may be appropriate; and FeNO may be less reliable in the elderly. The management review identified five randomised controlled trials in adults, one in pregnant asthmatics and seven in children. Despite clinical heterogeneity, exacerbation rates were lower in all studies but not generally statistically significantly so. Effects on inhaled corticosteroid (ICS) use were inconsistent, possibly because of differences in management protocols, differential effectiveness in adults and children and differences in population severity. One UK diagnostic model and one management model were identified. Aerocrine also submitted diagnostic and management models. All had significant limitations including short time horizons and the selective use of efficacy evidence. The de novo diagnostic model suggested that the expected difference in quality-adjusted life-year (QALY) gains between diagnostic options is likely to be very small. Airway hyper-responsiveness by methacholine challenge test is expected to produce the greatest QALY gain but with an expected incremental cost-effectiveness ratio (ICER) compared with FeNO (NObreath) in combination with bronchodilator reversibility of £1.125M per QALY gained. All remaining options are expected to be dominated. The de novo management model indicates that the ICER of guidelines plus FeNO monitoring using NObreath compared with guidelines alone in children is expected to be approximately £45,200 per QALY gained. Within the adult subgroup, FeNO monitoring using NObreath compared with guidelines alone is expected to have an ICER of approximately £2100 per QALY gained. The results are particularly sensitive to assumptions regarding changes in ICS use over time, the number of nurse visits for FeNO monitoring and duration of effect.

CONCLUSIONS

Limitations of the evidence base impose considerable uncertainty on all analyses. Equivalence of devices was assumed but not assured. Evidence for diagnosis is difficult to interpret in the context of inserting FeNO monitoring into a diagnostic pathway. Evidence for management is also inconclusive, but largely consistent with FeNO monitoring resulting in fewer exacerbations, with a small or zero reduction in ICS use in adults and a possible increased ICS use in children or patients with more severe asthma. It is unclear which specific management protocol is likely to be most effective. The economic analysis indicates that FeNO monitoring could have value in diagnostic and management settings. The diagnostic model indicates that FeNO monitoring plus bronchodilator reversibility dominates many other diagnostic tests. FeNO-guided management has the potential to be cost-effective, although this is largely dependent on the duration of effect. The conclusions drawn from both models require strong technical value judgements with respect to several aspects of the decision problem in which little or no empirical evidence exists. There are many potential directions for further work, including investigations into which management protocol is best and long-term follow-up in both diagnosis and management studies.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42013004149.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Diagnostic accuracy of fractional exhaled nitric oxide in asthma: a systematic review and meta-analysis of prospective studies

BACKGROUND

Fractional exhaled nitric oxide (FeNO) has been proposed as a non-invasive measure of airway inflammation in asthma. However, its accuracy for the diagnosis of asthma in different populations is not completely clear. The aim of this study was to investigate the accuracy of FeNO measurement for the diagnosis of asthma through a systematic review and meta-analysis of prospective studies.

METHODS

A systematic search current to July 2014 was performed in Pubmed, EMBASE, Medline, the Cochrane databases, CNKI, Wanfang and Weipu to find relevant studies. All prospective studies on the use of FeNO for the diagnosis of asthma were included.

RESULTS

Twenty-five studies including 3983 subjects were analyzed. The pooled sensitivity, specificity and diagnostic odds ratio (DOR) for the entire population was 72% (95% CI, 70-74%), 78% (95% CI, 76-80%) and 15.92 (95% CI, 10.70-23.68), respectively. The area under the summary receiver operating characteristic (sROC) curves revealed a receiver-operating characteristic of 0.88. In subgroup analysis, the DOR for patients using corticosteroids, as well as those for steroid-naïve, non-smoking, smoking, chronic cough and allergic rhinitis patients were 4.47 (95% CI, 3.39-5.90), 21.40 (95% CI, 15.38-29.76), 19.84 (95% CI, 15.63-25.19), 5.41 (95% CI, 2.97-9.86), 35.36 (95% CI, 23.90-52.29), and 2.99 (95% CI, 0.85-10.45), respectively.

CONCLUSION

FeNO is accurate for the diagnosis of asthma in steroid-naive or non-smoking patients, particularly in chronic cough patients.

Mechanistic impact of outdoor air pollution on asthma and allergic diseases

Over the past decades, asthma and allergic diseases, such as allergic rhinitis and eczema, have become increasingly common, but the reason for this increased prevalence is still unclear. It has become apparent that genetic variation alone is not sufficient to account for the observed changes; rather, the changing environment, together with alterations in lifestyle and eating habits, are likely to have driven the increase in prevalence, and in some cases, severity of disease. This is particularly highlighted by recent awareness of, and concern about, the exposure to ubiquitous environmental pollutants, including chemicals with oxidant-generating capacities, and their impact on the human respiratory and immune systems. Indeed, several epidemiological studies have identified a variety of risk factors, including ambient pollutant gases and airborne particles, for the prevalence and the exacerbation of allergic diseases. However, the responsible pollutants remain unclear and the causal relationship has not been established. Recent studies of cellular and animal models have suggested several plausible mechanisms, with the most consistent observation being the direct effects of particle components on the generation of reactive oxygen species (ROS) and the resultant oxidative stress and inflammatory responses. This review attempts to highlight the experimental findings, with particular emphasis on several major mechanistic events initiated by exposure to particulate matters (PMs) in the exposure-disease relationship.

Respiratory mechanics and peripheral airway inflammation and dysfunction in asthma

BACKGROUND

Clinical application of the forced oscillation technique (FOT) has progressed with the spread of commercially available FOT devices. The correlation between respiratory impedance and spirometry has been reported; however, the association with airway inflammation and pulmonary function, in the lung periphery in particular, is unclear.

OBJECTIVE

To assess whether respiratory impedance is associated with peripheral airway inflammation and dysfunction in asthma.

METHODS

Subjects included 78 patients with overall controlled asthma. We measured whole-breath or within-breath respiratory system resistance (Rrs) and reactance (Xrs) using a commercially available multi-frequency FOT device (MostGraph-01), and assessed the correlation with the fraction of exhaled nitric oxide (FeNO), alveolar nitric oxide concentration (CANO), maximal NO flux in the conductive airways (J'awNO), and the N2 phase III slope of single breath N2 washout (delta N2 ).

RESULTS

The differences between inspiratory and expiratory phases of Xrs at 5 Hz (X5), resonant frequency (Fres), and a low-frequency reactance area (ALX) were significantly correlated with CANO; however, there was no correlation between respiratory impedance and FeNO or J'awNO. The delta N2 values were significantly correlated with whole-breath, inspiratory, and expiratory Rrs and Xrs, except for R20.

CONCLUSIONS AND CLINICAL RELEVANCE

We conclude that respiratory impedance reflects peripheral airway inflammation and ventilation inhomogeneity.

In vitro and ex vivo models of human asthma

Asthma is an inflammatory disorder of the conducting airways which undergo distinct structural and functional changes leading to non-specific bronchial hyperresponsiveness (BHR) and airflow obstruction that fluctuate over time. It is a complex disease involving multiple genetic and environmental influences whose multifactorial interactions can result in a range of asthma phenotypes. Since our understanding of these gene-gene and gene-environment interactions is very poor, this poses a major challenge to the logical development of 'models of asthma'. However, use of cells and tissues from asthmatic donors allows genetic and epigenetic influences to be evaluated and can go some way to reflect the complex interplay between genetic and environmental stimuli that occur in vivo. Current alternative approaches to in vivo animal models involve use of a plethora of systems ranging from very simple models using human cells (e.g. bronchial epithelial cells and fibroblasts) in mono- or co-culture, whole tissue explants (biopsies, muscle strips, bronchial rings) through to in vivo studies in human volunteers. Asthma research has been greatly facilitated by the introduction of fibreoptic bronchoscopy which is now a commonly used technique in the field of respiratory disease research, allowing collection of biopsy specimens, bronchial brushing samples, and bronchoalveolar lavage fluid enabling use of disease-derived cells and tissues in some of these models. Here, we will consider the merits and limitations of current models and discuss the potential of tissue engineering approaches through which we aim to advance our understanding of asthma and its treatment.