Increase in alveolar nitric oxide in the presence of symptoms in childhood asthma

Identification and treatment of persistent small airway dysfunction in paediatric patients with asthma: a retrospective cohort study

BACKGROUND

Asthma is a common respiratory disease. In asthma, the small airways have more intensive inflammation and prominent airway remodelling, compared to the central airways. We aimed to investigate the predictive value of risk factors and the fractional concentration of exhaled nitric oxide (FeNO) for persistent small airway dysfunction (p-SAD), and compare the effects of different treatment modalities.

METHODS

This retrospective cohort study included 248 children with asthma (aged 4-11 years). Binary logistic regression was used to analyse the risk factors for p-SAD. Correlations among FEV1/FVC, small airway function parameters, and FeNO levels in patients with asthma were analysed using Spearman's rank correlation. The receiver operating characteristic curve and the Delong test were used to analyse the predictive value of FeNO for p-SAD. Differences in the treatment effects of inhaled corticosteroids (ICS) and ICS with a long-acting beta-agonist (ICS/LABA) on p-SAD were analysed using Fisher's exact test.

RESULTS

Asthmatic children with older age of receiving the regular treatment (OR 1.782, 95% CI 1.082-2.935), with younger age at the time of onset of suspected asthma symptoms (OR 0.602, 95% CI 0.365-0.993), with longer duration of using ICS or ICS/LABA (OR 1.642, 95% CI 1.170-2.305) and with worse asthma control (OR 3.893, 95% CI 1.699-8.922) had increased risk for p-SAD. Significant negative correlations of small airway function parameters with FeNO at a 200 mL/s flow rate (FeNO200), and the concentration of nitric oxide in the alveolar or acinar region (CaNO) were observed. The areas under the curve of FeNO200 (cut-off:10.5ppb), CaNO (cut-off:5.1ppb), and FeNO200 combined with CaNO were 0.743, 0.697, and 0.750, respectively, for asthma with p-SAD. After using ICS or ICS/LABA, switching to ICS/LABA was easier than continuing with ICS to improve small airway dysfunction (SAD) in the 8th month.

CONCLUSIONS

Paediatric asthma with p-SAD is associated with older age at receiving regular treatment, younger age at the time of onset of suspected asthma symptoms, longer duration of using ICS or ICS/LABA, worse asthma control, and higher FeNO200 and CaNO levels, all of which can be combined with small airway function indicators to distinguish p-SAD from asthma. ICS/LABA improves SAD better than ICS alone.

Small airways in asthma: From inflammation and pathophysiology to treatment response

Small airways are characterized as those with an inner diameter less than 2 mm and constitute a major site of pathology and inflammation in asthma disease. It is estimated that small airways dysfunction may occur before the emergence of noticeable symptoms, spirometric abnormalities and imaging findings, thus characterizing them as "the quiet or silent zone" of the lungs. Despite their importance, measuring and quantifying small airways dysfunction presents a considerable challenge due to their inaccessibility in usual functional measurements, primarily due to their size and peripheral localization. Several pulmonary function tests have been proposed for the assessment of the small airways, including impulse oscillometry, nitrogen washout, body plethysmography, as well as imaging methods. Nevertheless, none of these methods has been established as the definitive "gold standard," thus, a combination of them should be used for an effective assessment of the small airways. Widely used asthma treatments seem to also affect several parameters of the small airways. Emerging biologic treatments show promising results in reducing small airways inflammation and remodelling, providing evidence for potential alterations in the disease's progression and outcomes. These novel therapies have implications not only in the clinical aspects of asthma but also in its inflammatory and functional aspects.

Physicochemical characterization and oxidative potential of size fractionated Particulate Matter: Uptake, genotoxicity and mutagenicity in V-79 cells

For many years, the impact of Particulate Matter (PM) in the ambient air has been one of the major concerns for the environment and human health. The consideration of the heterogeneity and complexity of different size fractions is notably important for the assessment of PM toxicological effects. The aim of the study was to present a comprehensive size-composition-morphology characterization and to assess the oxidative potential, genotoxicity, and mutagenicity of the atmospheric PM fractions, collected by using MOUDI near a busy roadside in Lucknow, India. Physicochemical characterization of ambient coarse particles (1.8-10 µm), fine particles (0.32-1.8 µm), quasi-ultrafine (0.1-0.32 µm) and ultrafine particles (≤0.1 µm) along with SRM 1649b was done using TEM, SEM, DLS, NTA, ICP-MS, and IC in parallel with the estimation of exogenous Reactive Oxygen Species (ROS) by acellular assays. In this study, two different acellular assays, dithiothreitol (DTT) and the CM-H₂DCFDA assay, indicated stronger mass-normalized bioactivity for different size ranges. Enrichment factor analysis indicated that the different size fractions were highly enriched with elements of anthropogenic origin as compared to elements of crustal origin. The endotoxin concentration in different size fractions was also estimated. Cellular studies demonstrated significant uptake, cytotoxicity, ultrastructural changes, cellular ROS generation, and changes in the different phases of the cell cycle (Sub G1, G1, S, G2/M) exposed to different size fractions. The Comet assay and the Micronucleus assay were used to estimate genotoxicity. Mutagenic potential was revealed by the HGPRT gene forward mutation assay in V-97 cells. Conclusively, our results clearly indicate that the genotoxic and mutagenic potential of the coarse PM was greater than the other fractions, and interestingly, the ultrafine PM has higher bioactivity as compared to quasi-ultrafine PM.

Small Airway Dysfunction in Asthma Is Associated with Perceived Respiratory Symptoms, Non-Type 2 Airway Inflammation, and Poor Responses to Therapy

BACKGROUND

Emerging evidence has indicated that small airway dysfunction (SAD) contributes to the clinical expression of asthma.

OBJECTIVES

The aim of the study was to explore the relationships of SAD assessed by forced expiratory flow between 25 and 75% (FEF25-75%), with clinical and inflammatory profile and treatment responsiveness in asthma.

METHOD

In study I, dyspnea intensity (Borg scale), chest tightness, wheezing and cough (visual analog scales, VASs), and pre- and post-methacholine challenge testing (MCT) were analyzed in asthma patients with SAD and non-SAD. In study II, asthma subjects with SAD and non-SAD underwent sputum induction, and inflammatory mediators in sputum were detected. Asthma patients with SAD and non-SAD receiving fixed treatments were prospectively followed up for 4 weeks in study III. Spirometry, Asthma Control Questionnaire (ACQ), and Asthma Control Test (ACT) were carried out to define treatment responsiveness.

RESULTS

SAD subjects had more elevated ΔVAS for dyspnea (p = 0.027) and chest tightness (p = 0.032) after MCT. Asthma patients with SAD had significantly elevated interferon (IFN)-γ in sputum (p < 0.05), and Spearman partial correlation found FEF25-75% significantly related to IFN-γ and interleukin-8 (both having p < 0.05). Furthermore, multivariable regression analysis indicated SAD was significantly associated with worse treatment responses (decrease in ACQ ≥0.5 and increase in ACT ≥3) (p = 0.022 and p = 0.032).

CONCLUSIONS

This study indicates that SAD in asthma predisposes patients to greater dyspnea intensity and chest tightness during bronchoconstriction. SAD patients with asthma are characterized by non-type 2 inflammation that may account for poor responsiveness to therapy.

Flow-independent nitric oxide parameters in asthma: a systematic review and meta-analysis

INTRODUCTION

Fractional exhaled nitric oxide (F_ENO) has been proposed as a non-invasive marker of inflammation in the lungs. Measuring F_ENO at several flow rates enables the calculation of flow independent NO-parameters that describe the NO-exchange dynamics of the lungs more precisely. The purpose of this study was to compare the NO-parameters between asthmatics and healthy subjects in a systematic review and meta-analysis.

METHODS

A systematic search was performed in Ovid Medline, Web of Science, Scopus and Cochrane Library databases. All studies with asthmatic and healthy control groups with at least one NO-parameter calculated were included.

RESULTS

From 1137 identified studies, 33 were included in the meta-analysis. All NO-parameters (alveolar NO concentration (C_ANO), bronchial flux of NO (J_awNO), bronchial mucosal NO concentration (C_awNO) and bronchial wall NO diffusion capacity (D_awNO)) were found increased in glucocorticoid-treated and glucocorticoid-naïve asthma. J_awNO and C_ANO were most notably increased in both study groups. Elevation of D_awNO and C_awNO seemed less prominent in both asthma groups.

DISCUSSION

We found that all the NO-parameters are elevated in asthma as compared to healthy subjects. However, results were highly heterogenous and the evidence on C_awNO and D_awNO is still quite feeble due to only few studies reporting them. To gain more knowledge on the NO-parameters in asthma, nonlinear methods and standardized study protocols should be used in future studies.

Recent Advances in Inflammation and Treatment of Small Airways in Asthma

Small airways were historically considered to be almost irrelevant in the development and control of pulmonary chronic diseases but, as a matter of fact, in the past few years we have learned that they are not so "silent". Asthma is still a worldwide health issue due to the great share of patients being far from optimal management. Several studies have shown that the deeper lung inflammation plays a critical role in asthma pathogenesis, mostly in these not well-controlled subjects. Therefore, assessing the degree of small airways inflammation and impairment appears to be a pivotal step in the asthmatic patient's management. It is now possible to evaluate them through direct and indirect measurements, even if some obstacles still affect their clinical application. The success of any treatment obviously depends on several factors but reaching the deeper lung has become a priority and, for inhaled drugs, this is strictly connected to the molecule's size. The aim of the present review is to summarize the recent evidence concerning the small airway involvement in asthma, its physiopathological characteristics and how it can be evaluated in order to undertake a personalized pharmacological treatment and achieve a better disease control.

Small Airway Dysfunction in Children With Controlled Asthma

INTRODUCTION

Asthma is characterized by chronic inflammation of the central and distal airways. The aim of this study was to assess the small airway (SA) of children with moderate-severe asthma with normal FEV1.

METHODS

This was an open-label, prospective, observational, cross-sectional study with consecutive inclusion of patients with moderate-severe asthma, receiving standard clinical treatment, with normal baseline FEV₁. We determined multiflow FEno (CAno), oscillatory resistance and reactance (R5-R20, X5), forced spirometry (FEV1, FEF_25-75), total body plethysmography (RV/TLC) and bronchodilation test. SA involvement was defined as: CAno>4.5 ppb, R5-R20>0.147kPa/L/s, X5<-0.18kPa/L, FEF_25-75<-1.65 z-score, RV/TLC>33%. Poor asthma control was defined as ≤ 19 points on the ACT questionnaire or ≤ 20 on the c-ACT.

RESULTS

In a cohort of 100 cases, 76 had moderate asthma and 24 had severe asthma; 71 children were classified as poorly controlled and 29 were well-controlled. In total, 77.78% of the group with all the correct determinations (n=72) showed ≥ 1 altered SA parameter and 48.61% ≥ 2 parameters. There were no differences between well-controlled or poorly controlled cases.

CONCLUSIONS

Children with moderate-severe asthma, with normal FEV₁, show a phenotype of dysfunctional SA. In our series, the evaluation of SA using the techniques described above did not provide information on disease control.

Ameliorating effects of Nigella sativa oil on aggravation of inflammation, oxidative stress and cytotoxicity induced by smokeless tobacco extract in an allergic asthma model in Wistar rats

BACKGROUND

The comparison of smokeless tobacco (ST) exposure versus Ovalbumin (Ova) sensitized rats or asthmatic patients has hardly been studied in the literature. Thus, the present study aims to investigate the aggravation of inflammation, exacerbation of asthma, oxidative stress and cytotoxicity induced by ST.

METHODS

ST was given at the dose of 40mg/kg in an allergic asthma model in Wistar rats. Furthermore, the effects of oral administration of Nigella sativa oil (NSO), at a dose of 4mL/kg/day, were investigated.

RESULTS

The obtained results showed that ST clearly enhanced lung inflammation through interleukin-4 (IL-4) and Nitric oxide (NO) increased production. Actually, ST was found to intensify the oxidative stress state induced by Ova-challenge in rats, which was proven not only by augmenting lipid peroxidation and protein oxidation, but also by altering the non-enzymatic and enzymatic antioxidant status. Furthermore, the aggravation of inflammation and oxidative stress was obviously demonstrated by the histopathological changes observed in lung. In contrast, NSO administration has shown anti-inflammatory effects by reducing IL-4 and NO production, restoring the antioxidant status, reducing lipid peroxidation and improving the histopathological alterations by both protein oxidation and NSO treatment.

CONCLUSIONS

Our data have proven that severe concurrent exposure to allergen and ST increases airway inflammation and oxidative stress in previously sensitized rats. They also suggest that the oral NSO treatment could be a promising treatment for asthma.

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.

Optimal flow rate sampling designs for studies with extended exhaled nitric oxide analysis

INTRODUCTION

The fractional concentration of exhaled nitric oxide (FeNO) is a biomarker of airway inflammation. Repeat FeNO maneuvers at multiple fixed exhalation flow rates (extended NO analysis) can be used to estimate parameters quantifying proximal and distal sources of NO in mathematical models of lower respiratory tract NO. A growing number of studies use extended NO analysis, but there is no official standard flow rate sampling protocol. In this paper, we provide information for study planning by deriving theoretically optimal flow rate sampling designs.

METHODS

First, we reviewed previously published designs. Then, under a nonlinear regression framework for estimating NO parameters in the steady-state two compartment model of NO, we identified unbiased optimal four flow rate designs (within the range of 10-400 ml s^-1) using theoretical derivations and simulation studies. Optimality criteria included NO parameter standard errors (SEs). A simulation study was used to estimate sample sizes required to detect associations with NO parameters estimated from studies with different designs.

RESULTS

Most designs (77%) were unbiased. NO parameter SEs were smaller for designs with: more target flows, more replicate maneuvers per target flow, and a larger range of target flows. High flows were most important for estimating alveolar NO concentration, while low flows were most important for the proximal NO parameters. The Southern California Children's Health Study design (30, 50, 100 and 300 ml s^-1) had ≥1.8 fold larger SEs and required 1.1-3.2 fold more subjects to detect the association of a determinant with each NO parameter as compared to an optimal design of 10, 50, 100 and 400 ml s^-1.

CONCLUSIONS

There is a class of reasonable flow rate sampling designs with good theoretical performance. In practice, designs should be selected to balance the tradeoffs between optimality and feasibility of the flow range and total number of maneuvers.

Association between size-segregated particles in ambient air and acute respiratory inflammation

The health effects of particulate matter (PM) in ambient air are well documented. However, whether PM size plays a critical role in these effects is unclear in the population studies. This study investigated the association between the ambient concentrations of PM with varies sizes (5.6-560nm) and a biomarker of acute respiratory inflammation, the fraction of exhaled nitric oxide (FENO), in a panel of 55 elderly people in Shanghai, China. Linear mixed-effect model was fitted to estimate the association between FENO and moving average concentrations of PM, adjusting for temperature, relative humidity, day of the week, and age. Results showed that among the measured particles size range, Aitken-mode (20-100nm) particles had the strongest positive association with increased FENO when using moving average concentration of PM up to 24h prior to visits. The estimates were robust to the adjustment for gender, condition of chronic disease and use of medication, and to the sensitive analysis using different times of visits. The authors concluded that the association between acute respiratory inflammation and PM concentration of fine particulates depended on particle size, and suggested Aitken-mode particles may be the most responsible for this adverse health association.

Small airway dysfunction and bronchial asthma control : the state of the art

According to national and international guidelines, achieving and maintaining asthma control is a major goal of disease management. In closely controlled clinical trials, good asthma control can be achieved , with the medical treatments currently available, in the majority of patients , but large population-based studies suggest that a significant proportion of patients in real-life setting experience suboptimal levels of asthma control and report lifestyle limitations with a considerable burden on quality of life. Poor treatment adherence and persistence, failure to use inhalers correctly, heterogeneity of asthma phenotypes and associated co-morbidities are the main contributing factors to poor disease control. Now, it is widely accepted that peripheral airway dysfunction , already present in patients with mild asthma, is a key contributor of worse control. The aim of this paper is to investigate the association between small-airways dysfunction and asthma symptoms/control. We therefore performed a PubMed search using keywords : small airways; asthma (limits applied: Humans, English language) and selected papers with a study population of asthmatic patients, reporting measurement of small-airways parameters and clinical symptoms/control.

Low alveolar and bronchial nitric oxide in severe uncomplicated obesity

BACKGROUND

Fractional concentration of exhaled nitric oxide (FeNO) is a recognized biomarker of the lower respiratory tract, where it is produced by the proximal conducting airways and the expansible peripheral bronchoalveolar compartment. We have previously shown that large increase in body mass decreases FeNO. Here we evaluated bronchial and alveolar components of the NO output of the lower respiratory tract in subjects with severe uncomplicated obesity (OB).

METHODS

Fifteen OB subjects (BMI 45.3 ± 5.6 kg/m(2)), 15 healthy controls (HC) (BMI 22.4 ± 2.4 kg/m(2)) and 10 obese subjects who experienced weight loss after bariatric surgery (OBS) (BMI 31.2 ± 3.4 kg/m(2)), were examined. Anthropometry and respiratory lung tests were performed. Exhaled NO was assessed using multiple single-breath NO analysis at different constant expiratory flow rates. From the fractional NO concentration measured at each flow-rate, the total NO flux between tissue and gas phase in the bronchial lumen (J'awNO), and the alveolar NO concentration (CANO) were extrapolated.

RESULTS

Measured FeNO levels at 50 mL/s were lower in OB compared with HC and OBS (11.6 ± 2.8 ppb, 18.0 ± 4.1 ppb and 17.6 ± 2.9 ppb, respectively, p < 0.05). In OB, both J'awNO and CANO resulted significantly lower than OBS and HC values.

CONCLUSIONS

Respiratory NO output is decreased in severe uncomplicated obesity for the reduction of both large/central airway maximal NO flux and alveolar NO concentration. The pathophysiological relevance of airway NO abnormalities in severe obese phenotype remains to be investigated.

Unlocking the quiet zone: the small airway asthma phenotype

The small airways in the distal lung have been called the quiet zone because they are difficult to assess and treat in patients with asthma who have disproportionate impairment of small airway function. Evidence is accumulating to support a distinct clinical phenotype for patients with asthma who have impaired small airway function. The small airway asthma phenotype, which is prevalent in patients at all steps of management guidelines, seems to be associated with poor disease control. Alternatively, small airway dysfunction might be a sensitive indicator of early disease rather than a phenotype. Conventional coarse-particle inhalers, which emit particles larger than 2 μm, might not address persistent small airway dysfunction in patients with asthma. To target the entire lung with extra-fine particle formulations (smaller than 2 μm) of inhaled corticosteroids alone or in combination with long-acting β-agonists might result in improved long-term asthma control along with a commensurate improvement in small airway function. Prospective randomised controlled trials with extra-fine-particle inhaled drugs are now needed for patients with the small airway asthma phenotype.

Inflammatory patterns in asthmatic children based on alveolar nitric oxide determination

INTRODUCTION

Nitric oxide (NO) levels can be measured at proximal (maximum airway NO flux [J'aw(NO)]) and distal (alveolar NO concentration [C(ANO)]) levels. Four inflammatory patterns have been described in asthmatic individuals, although their relevance has not been well established. The objective was to determine J'aw(NO) and C(ANO) in order to establish four inflammatory categories in asthmatics.

MATERIAL AND METHODS

Cross-sectional study of a sample consisting of healthy and asthmatic children. Exhaled NO was determined at multiple flows. J'aw(NO) and C(ANO) were obtained according to the two-compartment model. The asthma control questionnaire (ACQ) and spirometry were administered to asthmatic children. Patients were categorized as type I (normal J'aw(NO) and C(ANO)), type II (elevated J'aw(NO) and normal C(ANO)), type III (elevated J'aw(NO) and C(ANO)) and type IV (normal J'aw(NO) and elevated C(ANO)). Correlation between FE(NO,50), J'aw(NO) and C(ANO) was analyzed using Spearman's R Correlation Test. Analysis of variance and paired comparisons were performed using the Bonferroni correction.

RESULTS

One hundred sixty-two children were studied, of whom 49 (32.23%) were healthy controls and 103 (67.76%) asthmatics. In the control subjects, FE(NO,50) (ppb)(median and range) was 11.5 (1.6 to 27.3), J'aw(NO) (pl/s) was 516 (98.3 to 1470) and C(ANO) (ppb) was 2.2 (0.1 to 4.5). Forty-four (42.7%) of the asthmatic participants were categorized as type I, 41 (39.8%) as type II, 14 (13.5%) as type III and 4 (3.88%) as type IV. Good correlation was observed between J'aw(NO) and FE(NO,50) (r=0.97). There was no association between J'aw(NO) and C(ANO). FEV1/FVC decreased significantly in type III (mean 79.8±7.5). Morbidity was significantly higher in types III and IV.

CONCLUSIONS

Normal values obtained are similar to those previously reported. Asthmatics with high C(ANO) showed higher morbidity. No correlation was found between proximal and distal inflammation.

Alveolar nitric oxide and its role in pediatric asthma control assessment

Background

Nitric oxide can be measured at multiple flow rates to determine proximal (maximum airway nitric oxide flux; Jaw_NO) and distal inflammation (alveolar nitric oxide concentration; CA_NO). The main aim was to study the association among symptoms, lung function, proximal (maximum airway nitric oxide flux) and distal (alveolar nitric oxide concentration) airway inflammation in asthmatic children treated and not treated with inhaled glucocorticoids.

Methods

A cross-sectional study with prospective data collection was carried out in a consecutive sample of girls and boys aged between 6 and 16 years with a medical diagnosis of asthma. Maximum airway nitric oxide flux and alveolar nitric oxide concentration were calculated according to the two-compartment model. In asthmatic patients, the asthma control questionnaire (CAN) was completed and forced spirometry was performed. In controls, differences between the sexes in alveolar nitric oxide concentration and maximum airway nitric oxide flux and their correlation with height were studied. The correlation among the fraction of exhaled NO at 50 ml/s (FE_NO50), CA_NO, Jaw_NO, forced expiratory volume in 1 second (FEV₁) and the CAN questionnaire was measured and the degree of agreement regarding asthma control assessment was studied using Cohen’s kappa.

Results

We studied 162 children; 49 healthy (group 1), 23 asthmatic participants without treatment (group 2) and 80 asthmatic patients treated with inhaled corticosteroids (group 3). CA_NO (ppb) was 2.2 (0.1-4.5), 3 (0.2-9.2) and 2.45 (0.1-24), respectively. Jaw_NO (pl/s) was 516 (98.3-1470), 2356.67 (120–6110) and 1426 (156–11805), respectively. There was a strong association (r = 0.97) between FE_NO50 and Jaw_NO and the degree of agreement was very good in group 2 and was good in group 3. There was no agreement or only slight agreement between the measures used to monitor asthma control (FEV₁, CAN questionnaire, CA_NO and Jaw_NO).

Conclusions

The results for CA_NO and Jaw_NO in controls were similar to those found in other reports. There was no agreement or only slight agreement among the three measure instruments analyzed to assess asthma control. In our sample, no additional information was provided by CA_NO and Jaw_NO.

Alveolar nitric oxide concentration reflects peripheral airway obstruction in stable asthma

BACKGROUND AND OBJECTIVE

Increased fraction of exhaled nitric oxide (FeNO) has been shown to reflect airway inflammation in asthma. Central airway NO flux (J'awNO; nL/s) and peripheral airway/alveolar NO concentration (CANO; ppb) can be calculated separately. CANO has been reported to reflect small airway inflammation. The aim of the present study is to correlate CANO levels with clinical and physiological parameters in patients with stable asthma.

METHODS

Seventy-three well-controlled asthmatics (mean age 61) were enrolled. Measurement of FeNO (at 50, 100, 150 and 200 mL/s) and pulmonary function test were performed. J'awNO(TMAD) and CANO(TMAD) were calculated and corrected by the trumpet shape of the airway tree and axial back-diffusion (TMAD).

RESULTS

CANO(TMAD) was significantly correlated with forced expiratory flow between 25-75% of the forced vital capacity (FVC) (FEF(25 -75)), FEF(25 -75) percentage of the predicted value (%pred), forced expiratory flow at 50% of the FVC (FEF(50)) and FEF(50) %pred (R = -0.39 P = 0.002, R = -0.29 P = 0.02, R = -0.39 P = 0.001, R = -0.29 P = 0.02, respectively). CANO(TMAD) was positively correlated with age (R = -0.45 P = 0.0002) and weakly correlated with duration of asthma (R = -0.27 P = 0.03). Forced expiratory volume in 1 s/FVC was negatively correlated with CANO(TMAD), J'awNO(TMAD) and FeNO 50 mL/s. Among these, correlation between forced expiratory volume in 1 s/FVC and FeNO 50 mL/s was the strongest (R = -0.34 P = 0.004).

CONCLUSIONS

CANO(TMAD) may be a more specific marker of peripheral airway obstruction than FeNO and J'awNO(TMAD) in stable asthma.

Techniques for assessing small airways function: Possible applications in asthma and COPD

In recent years special interest has been expressed for the contribution of small airways in the pathophysiology, clinical manifestations and treatment of asthma and COPD. Small airways contribute little to the total respiratory resistance so that extensive damage of small airways may occur before the appearance of any symptoms, and this is the reason why they are characterized as the "silent zone" of airways. Furthermore, the peripheral localization of the small airways and their small diameter constitutes difficult their direct assessment. Thus, they are usually studied indirectly, taking advantage of the effects of their obstruction, such as premature closure, air trapping, heterogeneity of ventilation, and lung volume dependence of airflow limitation. Today, several heterogeneous methods for the assessment of small airways are available. These can be either functional (spirometry, plethysmography, resistance measurements, nitrogen washout, alveolar nitric oxide, frequency dependence of compliance, flow-volume curves breathing mixture of helium-oxygen) or imaging (mainly through high resolution computed tomography). The above-mentioned methods are summarized in Table 1. However, no method is currently considered as the "gold standard" and it seems that combinations of tests are needed. Furthermore, it is not clear whether the small airways are affected in all patients with asthma or COPD and their clinical significance remains under investigation. Well-designed future studies with large numbers of patients are expected to reveal which of the methods for assessing the small airways is the most accurate, reliable and reproducible, for which patients, and which can be used for the evaluation of the effects of treatment.

The effect of spirometry on bronchial and alveolar nitric oxide in subjects with asthma

OBJECTIVE

The effect of spirometric maneuvers on exhaled nitric oxide (NO) at the constant flow rate of 50 ml/s (FE(NO)) has been studied with equivocal results. Furthermore, the effects of spirometry on bronchial NO flux (J'aw(NO)) and alveolar NO (CA(NO)), two measurements increasingly being used in clinical and research protocols, are unknown. The aim of this study was to evaluate the effect of spirometry on FE(NO), J'aw(NO), and CA(NO) in adults with asthma.

METHODS

Forty-four adults with asthma were studied. To assess the impact of exhaled NO measurement itself on exhaled NO values, FE(NO), J'aw(NO), and CA(NO) were obtained twice, at baseline and after a resting period of 10 min. Then spirometry (with or without bronchodilator) was performed followed by exhaled NO measurements at 10 min.

RESULTS

In the group with pre-bronchodilator study only (n = 26), mean (95% CI) values before spirometry were 37.3 ppb (22.2-52.4) for FE(NO), 2375 pl/s (1613-3137) for J'aw(NO), and 1.65 ppb (0.95-2.35) for CA(NO), compared with 35.5 ppb (21.1-49.0, p = .10), 2402 pl/s (1663-3141, p = .85), and 1.60 ppb (0.64-2.56, p = .87) after spirometry, respectively. Spirometry-induced changes in exhaled NO values were also not significant in the group with both pre- and post-bronchodilators (n = 18). Furthermore, changes in FE(NO), J'aw(NO), and CA(NO) values were similar in the two groups.

CONCLUSIONS

Our findings demonstrate that spirometry (with or without bronchodilator) does not induce significant changes in bronchial NO flux or alveolar NO values. Therefore, exhaled NO values may be obtained after spirometric maneuvers.

Alveolar nitric oxide and asthma control in mild untreated asthma

BACKGROUND

The role of the peripheral airways in asthma is increasingly being recognized as a potential target for the achievement of optimal control of the disease. We postulated that the inflammatory changes of the small airways are implicated in the lack of asthma control in mild asthma.

OBJECTIVE

To test this hypothesis, we measured the alveolar fraction of exhaled NO (CalvNO) in patients with mild asthma with different levels of control of symptoms.

METHODS

Seventy-eight patients with asthma (35 men, age, 37 ± 15 years; FEV1 percentage of predicted, 100% ± 9%) were studied. Asthma control was assessed by using the Asthma Control Test (ACT). Measurements of exhaled NO at multiple constant flows were performed.

RESULTS

Bronchial NO concentrations were 27.1 ± 20 nL/min, [corrected] and CalvNO levels were 5.7 ± 3.4 ppb. The ACT score was 20 ± 4.2. The level of asthma control was not associated with bronchial NO concentrations (rs = 0.16, P = .15). However, a significant correlation was found between the ACT score and CalvNO (rs = 0.25, P = .03). Moreover, CalvNO was significantly higher in patients with uncontrolled asthma than in patients with controlled/partially controlled asthma (6.7 ± 2.6 ppb vs 4.9 ± 2.6 nL/min, [corrected] respectively, P = .02). In the subgroup of patients with asthma who underwent extrafine inhaled corticosteroid treatment, the magnitude of the inhaled corticosteroid-induced improvement in asthma control positively correlated with baseline CalvNO at 1 month (rs = 0.39, P = .003) and at 3 months (rs = 0.49, P < .0001).

CONCLUSIONS

The alveolar component of exhaled NO is associated with the lack of asthma control in patients with mild, untreated asthma. This observation supports the notion that abnormalities of the peripheral airways are implicated in the mildest forms of asthma.

Alveolar concentration and bronchial flux of nitric oxide: two linear modeling methods evaluated in children and adolescents with allergic rhinitis and atopic asthma

OBJECTIVE

Alveolar concentration (C(A)NO) and bronchial flux (J(aw)NO) of nitric oxide (NO) characterize the contributions of peripheral and proximal airways to exhaled NO. Both parameters can be estimated using a two-compartment model if the fraction of NO in orally exhaled air (FE(NO)) is measured at multiple constant expiratory flow rates (V). The aim of this study was to evaluate how departures from linearity influence the estimates of C(A)NO and J(aw)NO obtained with the help of linear regression analysis of the relationships between FE(NO) and 1/V (method P), and between the NO output (V(NO) = FE(NO) × V) and V (method T). Furthermore, differences between patients with atopic asthma (AA) and allergic rhinitis (AR) and between methods P and T were assessed.

DESIGN

Measurements of FE(NO) were performed with a chemiluminiscence analyzer at five levels of V ranging from 50 to 250 ml/sec in school children and adolescents with mild to moderate-severe AA treated by inhaled corticosteroids (N = 42) and AR (N = 20).

RESULTS

Violation of the linearity condition at V ≤ 100 ml/sec caused shifts between methods with regard to the partition of exhaled NO into alveolar (C(A)NO: P > T) and bronchial (J(aw)NO: T > P) components. Both methods gave similar results in the linear range of 150-250 ml/sec: The mean ratios P/T and limits of agreement calculated in AA and AR patients were 1.03 (0.49-1.56) and 1.07 (0.55-1.59) for C(A)NO and 1.03 (0.73-1.33) and 0.99 (0.90-1.10) for J(aw)NO, respectively. No significant differences between AA and AR were found in C(A)NO and J(aw)NO calculated in the linear range by the T method {medians (inter-quartile ranges): 1.7 ppb (0.9-3.9) vs. 2.3 ppb (0.8-3.7), P = 0.91; 1,800 pl/sec (950-3,560) vs. 1,180 pl/sec (639-1,950), P = 0.061}. However, the flow-dependency of the estimates was markedly higher in AA than in AR patients: C(A) NO was decreased 2.8-fold vs. 1.5-fold and J(aw) NO was increased 1.5-fold vs. 1.2-fold in the linear range as compared to the range of 50-250 ml/sec. In both groups, the median standard errors (SE) of the J(aw) NO estimates were similar for the metods P and T and small (<15%) regardless of the range for expiratory flows. The precision of C(A) NO estimates was less in all ranges. For both methods, the SE of the estimates obtained in the range of 150-250 ml/sec exceeded 50% in asthmatics and 30% in AR patients, respectively. The results show that FE(NO) has to be measured at several expiratory flows ≥100 ml/sec for the accurate estimation of C(A) NO and J(aw) NO using linear methods P and T in children and adolescents with AA and AR. A stepwise procedure for detecting nonlinearity and evaluating the quality of FE(NO) measurements is suggested.

The fraction of NO in exhaled air and estimates of alveolar NO in adolescents with asthma: methodological aspects

RATIONALE

This study investigated the oral contribution to exhaled NO in young people with asthma and its potential effects on estimated alveolar NO (Calv(NO) ), a proposed marker of inflammation in peripheral airways. Secondary aims were to investigate the effects of various exhalation flow-rates and the feasibility of different proposed adjustments of (Calv(NO) ) for trumpet model and axial diffusion (TMAD).

METHODS

Exhaled NO at flow rates of 50-300 ml/sec, and salivary nitrite was measured before and after antibacterial mouthwash in 29 healthy young people (10-20 years) and 29 with asthma (10-19 years). Calv(NO) was calculated using the slope-intercept model with and without TMAD adjustment.

RESULTS

Exhaled NO at 50 ml/sec decreased significantly after mouthwash, to a similar degree in asthmatic and healthy subjects (8.8% vs. 9.8%, P = 0.49). The two groups had similar salivary nitrite levels (56.4 vs. 78.4 µM, P = 0.25). Calv(NO) was not significantly decreased by mouthwash. Calv(NO) levels were similar when flow-rates between 50-200 or 100-300 ml/sec were used (P = 0.34 in asthmatics and P = 0.90 in healthy subjects). A positive association was found between bronchial and alveolar NO in asthmatic subjects and this disappeared after the TMAD-adjustment. Negative TMAD-adjusted Calv(NO) values were found in a minority of the subjects.

CONCLUSIONS

Young people with and without asthma have similar salivary nitrite levels and oral contributions to exhaled NO and therefore no antibacterial mouthwash is necessary in routine use. TMAD corrections of alveolar NO could be successfully applied in young people with asthma and yielded negative results only in a minority of subjects.

Breath acetone monitoring by portable Si:WO3 gas sensors

Breath analysis has the potential for early stage detection and monitoring of illnesses to drastically reduce the corresponding medical diagnostic costs and improve the quality of life of patients suffering from chronic illnesses. In particular, the detection of acetone in the human breath is promising for non-invasive diagnosis and painless monitoring of diabetes (no finger pricking). Here, a portable acetone sensor consisting of flame-deposited and in situ annealed, Si-doped epsilon-WO(3) nanostructured films was developed. The chamber volume was miniaturized while reaction-limited and transport-limited gas flow rates were identified and sensing temperatures were optimized resulting in a low detection limit of acetone (∼20ppb) with short response (10-15s) and recovery times (35-70s). Furthermore, the sensor signal (response) was robust against variations of the exhaled breath flow rate facilitating application of these sensors at realistic relative humidities (80-90%) as in the human breath. The acetone content in the breath of test persons was monitored continuously and compared to that of state-of-the-art proton transfer reaction mass spectrometry (PTR-MS). Such portable devices can accurately track breath acetone concentration to become an alternative to more elaborate breath analysis techniques.

In moderate-to-severe asthma patients monitoring exhaled nitric oxide during exacerbation is not a good predictor of spirometric response to oral corticosteroid

BACKGROUND

The importance of monitoring exhaled nitric oxide (NO) in asthma remains controversial.

OBJECTIVE

To measure exhaled NO, postnebulized albuterol/ipratropium spirometry, and Asthma Control Test (ACT) during asthma exacerbation requiring 8- to 10-day tapering oral corticosteroid in nonsmoking patients with moderate-to-severe asthma on moderate-dose inhaled corticosteroid and long-acting β(2)-agonist but not maintenance oral corticosteroid.

METHODS

After measuring the fraction of exhaled NO (Feno [ppb]) at 50, 100, 150, and 200 mL/s, the total Feno at 50 mL/s (ppb), large central airway NO flux (J'(awNO) [nL/s]), and peripheral small airway/alveolar NO concentration (C(ANO) [ppb]) were calculated and corrected for NO axial back-diffusion. Outpatient exacerbation required the patient with asthma to be afebrile with normal chest x-ray and white blood cell count.

RESULTS

Group 1 included 17 patients (6 men) with asthma, age 52 ± 12 years, studied at baseline, during 18 exacerbations with abnormal Feno at 50 mL/s, J'(awNO), and/or C(ANO), and post 8- to 10-day tapering 40 mg prednisone (recovery). Baseline: IgE, 332 ± 243 Kμ; total blood eosinophils, 304 ± 266 cells/μL; body mass index, 28 ± 6; ACT, 16 to 19; and FEV(1), 2.5 ± 0.7 L (86% ± 20% predicted); exacerbation: FEV(1), 1.7 ± 0.4 L (60% ± 17%) (P < .001); recovery: FEV(1), 2.5 ± 0.7 L (85% ± 13%) (P < .001). Group 2 included 11 (7 men) similarly treated patients with asthma, age 49 ± 14 years, studied at baseline, during 15 exacerbations with normal Feno at 50 mL/s, J'(awNO), and C(ANO). Baseline: IgE, 307 ± 133 Kμ; total blood eosinophils, 296 ± 149 cells/μL; body mass index, 28 ± 6; ACT, 16 to 19; and FEV(1), 2.7 ± 0.9 L (71% ± 12% predicted); exacerbation: FEV(1), 1.7 ± 0.6 L (54% ± 19%) (P< .006); recovery: FEV(1), 2.7 ± 0.9 L (70% ± 14%) (P= .002). On comparing group 1 versus group 2, there was no significant difference for baseline IgE, eosinophils, body mass index, and ACT and similar significant (≤.006) decrease from baseline in FEV(1) (L) during exacerbation and similar increase (≤.006) at recovery.

CONCLUSIONS

Increased versus normal exhaled NO during outpatient exacerbation in patients with moderate-to-severe asthma on inhaled corticosteroid and long-acting β(2)-agonist but not maintenance oral corticosteroid does not preclude a robust clinical and spirometric response to tapering oral prednisone.

Comparison of online single-breath vs. online multiple-breath exhaled nitric oxide in school-age children

INTRODUCTION

Standards for online multiple-breath (mb) exhaled nitric oxide (eNO) measurements and studies comparing them with online single-breath (sb) eNO measurements are lacking, although eNOmb requires less cooperation in children at school age or younger.

METHODS

Online eNOmb and eNOsb were measured in 99 healthy children and (in order to observe higher values) in 21 children with suspected asthma at a median age of 6.1 and 11.7 y, respectively. For eNOmb, we aimed for 20 tidal breathing maneuvers; eNOsb was measured according to standards. The two techniques were compared by standard methods after computing NO output or extrapolating eNOmb to the standard flow of 50 ml/s (eNOmb(50)).

RESULTS

Measurements were acceptable in 82 (eNOmb) and 81 (eNOsb) children. Paired data were available for 65 children. On a log-log scale, eNOmb(50) (geometric mean ± SD 13.1 ± 15.5 parts per billion, ppb) was correlated with eNOsb (12.5 ± 15.8 ppb), with r(2) = 0.87. The mean difference between eNOsb and eNOmb(50) was -0.7 ppb, with limits of agreement (LOAs) of 4.0 and -5.3 ppb.

DISCUSSION

Despite its correlation with eNOsb, the LOA range hampers eNOmb use in research, where exact values across the whole range are warranted. However, eNOmb might be an alternative tool especially at preschool age, when cooperation during measurements is crucial.

Fractionated breath condensate sampling: H(2)O(2) concentrations of the alveolar fraction may be related to asthma control in children

Background

Asthma is a chronic inflammatory disease of the airways but recent studies have shown that alveoli are also subject to pathophysiological changes. This study was undertaken to compare hydrogen peroxide (H₂O₂) concentrations in different parts of the lung using a new technique of fractioned breath condensate sampling.

Methods

In 52 children (9-17 years, 32 asthmatic patients, 20 controls) measurements of exhaled nitric oxide (FE_NO), lung function, H₂O₂ in exhaled breath condensate (EBC) and the asthma control test (ACT) were performed. Exhaled breath condensate was collected in two different fractions, representing mainly either the airways or the alveoli. H₂O₂ was analysed in the airway and alveolar fractions and compared to clinical parameters.

Results

The exhaled H₂O₂ concentration was significantly higher in the airway fraction than in the alveolar fraction comparing each single pair (p = 0.003, 0.032 and 0.040 for the whole study group, the asthmatic group and the control group, respectively). Asthma control, measured by the asthma control test (ACT), correlated significantly with the H₂O₂ concentrations in the alveolar fraction (r = 0.606, p = 0.004) but not with those in the airway fraction in the group of children above 12 years. FE_NO values and lung function parameters did not correlate to the H₂O₂ concentrations of each fraction.

Conclusion

The new technique of fractionated H₂O₂ measurement may differentiate H₂O₂ concentrations in different parts of the lung in asthmatic and control children. H₂O₂ concentrations of the alveolar fraction may be related to the asthma control test in children.

[Physiological characteristics associated with previous control in asthmatic children]

OBJECTIVE

To analyze MEF(50%) (central airways), RV/TLC (distal airways), reversibility of FEV(1) (bronchial tone, REV(FEV1)) and FE(NO) (inflammation) in relation to clinical events in asthmatic children on the assumption that mild symptoms and severe exacerbations in the previous 3 months could be associated with distinct functional characteristics.

PATIENTS AND METHODS

A retrospective, single center, out-patient hospital study including all asthmatic children who had complete lung function testing (without and with bronchodilation) during a period of clinical stability, without treatment on the day of the test.

RESULTS

Two hundred and forty-five children (11.4±2.4 years) were included: 114 (46%) were asymptomatic, 87 (36%) had minor symptoms and 44 (18%) had had a severe exacerbation in the past 3 months. FEV(1), FEV(1)/FVC and MEF(50%) were not different in these three groups. REV(FEV1) was higher in the symptomatic than in the asymptomatic group (P=0.019), RV/TLC was greater in the exacerbation group than in the asymptomatic group (P=0.019), and FE(NO) was higher in the symptomatic group than in the asymptomatic and exacerbation groups (P=0.006).

CONCLUSIONS

In asthmatic children, minor symptoms and severe exacerbation in the previous 3 months are associated with distinct functional characteristics that are not detected by single baseline spirometry without treatment on the day of testing.

[Physiology and physiopathology of the distal airways in asthma]

The small airways are those with an internal diameter of less than 2 mm. The contribution of these airways to total airflow resistance is small in healthy individuals but can represent 50-90 % of total airflow resistance in asthmatics. Suspicion of small airways disease has been based on reduction of midexpiratory and instantaneous flows, although wide variability in their values and the absence of a sufficiently validated cut-off point has limited their clinical application. Static pulmonary volumes can provide indirect evidence of the state of the most distal airways, revealing two effects of their alteration: air trapping and dynamic hyperinflation. While determination of airway resistance by plethysmography and of respiratory system resistance measured by flow interruption are highly non-specific, the forced oscillation technique allows obstruction of the small airways to be distinguished from that of medium-caliber airways. The characteristic pattern of peripheral obstruction includes a decrease in frequency-dependent resistance, reduced reactivity and an increase in resonance frequency. Single-or multiple-breath nitrogen washout can also provide specific information on the small airways, although the apparatus required is less frequently available. Analysis through bicompartmental models of exhaled nitric oxide allows alveolar nitric oxide concentrations to be determined, which seems to provide information on inflammatory activity in the small airways.

Utility of two-compartment models of exhaled nitric oxide in patients with asthma

Two-compartment models provide more precise information about the contribution of the different portions of the airways to exhaled nitric oxide (NO). Airway wall concentration of NO (Caw,NO) and maximum flux of NO in the airways (J'aw,NO) reflect the tissue production rate of NO and they can be modified by corticosteroids. The airway wall diffusing capacity of NO (Daw,NO) depends on diverse physical and anatomical determinants of the airways, such as gas exchange surface area. Daw,NO can be modified by structural and physiological changes that are characteristic of airway remodeling, which take place over the long term. The alveolar concentration of NO (Calv,NO) represents the degree of small airway inflammation. The persistence of high Calv,NO in patients treated with inhaled corticosteroids could reflect the incapacity of these drugs to reach distal locations due to the heterogeneity of the acinar ventilation. In this review, we evaluate the parameters provided by the compartmentalized analysis of exhaled NO that could be useful in characterizing asthma patients.

Clinical study of multiple breath biomarkers of asthma and COPD (NO, CO(2), CO and N(2)O) by infrared laser spectroscopy

Breath analysis is a powerful non-invasive technique for the diagnosis and monitoring of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Exhaled nitric oxide (NO) and carbon monoxide (CO) are markers of airway inflammation and can indicate the extent of respiratory diseases. We have developed a compact fast response quantum cascade laser system for analysis of multiple gases by tunable infrared absorption spectroscopy. The ARI breath analysis instrument has been deployed in a study of exhaled breath from patients with asthma or COPD. A total of 173 subjects participated, including both adult and pediatric patients. Patients in asthma or COPD exacerbations were evaluated twice-during the exacerbation and at a follow-up visit-to compare variations in breath biomarkers during these events. The change in exhaled NO levels between exacerbation and 'well' visits is consistent with spirometry data collected. Respiratory models are important for understanding the exchange dynamics of nitric oxide and other species in the lungs and airways. At each patient's visit, tests were conducted at four expiratory flow rates. We have applied a trumpet model with axial diffusion to the multi-flow exhaled nitric oxide data, obtaining NO alveolar concentrations and airway fluxes. We found higher airway fluxes for those with more severe asthma and during exacerbation events. The alveolar concentrations from the model were higher in adults with asthma and COPD, but this trend was less clear among the pediatric subjects.

Exhaled nitric oxide and clinical phenotypes of childhood asthma

Whether exhaled NO helps to identify a specific phenotype of asthmatic patients remains debated. Our aims were to evaluate whether exhaled NO (FENO(0.05)) is independently associated (1) with underlying pathophysiological characteristics of asthma such as airway tone (bronchodilator response) and airway inflammation (inhaled corticosteroid [ICS]-dependant inflammation), and (2) with clinical phenotypes of asthma.We performed multivariate (exhaled NO as dependent variable) and k-means cluster analyses in a population of 169 asthmatic children (age ± SD: 10.5 ± 2.6 years) recruited in a monocenter cohort that was characterized in a cross-sectional design using 28 parameters describing potentially different asthma domains: atopy, environment (tobacco), control, exacerbations, treatment (inhaled corticosteroid and long-acting bronchodilator agonist), and lung function (airway architecture and tone). Two subject-related characteristics (height and atopy) and two disease-related characteristics (bronchodilator response and ICS dose > 200 μg/d) explained 36% of exhaled NO variance. Nine domains were isolated using principal component analysis. Four clusters were further identified: cluster 1 (47%): boys, unexposed to tobacco, with well-controlled asthma; cluster 2 (26%): girls, unexposed to tobacco, with well-controlled asthma; cluster 3 (6%): girls or boys, unexposed to tobacco, with uncontrolled asthma associated with increased airway tone, and cluster 4 (21%): girls or boys, exposed to parental smoking, with small airway to lung size ratio and uncontrolled asthma. FENO(0.05) was not different in these four clusters.In conclusion, FENO(0.05) is independently linked to two pathophysiological characteristics of asthma (ICS-dependant inflammation and bronchomotor tone) but does not help to identify a clinically relevant phenotype of asthmatic children.

Exhaled breath condensate nitrates, but not nitrites or FENO, relate to asthma control

BACKGROUND

Asthma is a chronic respiratory disease, characterised by airways inflammation, obstruction and hyperresponsiveness. Asthma control is the goal of asthma treatment, but many patients have sub-optimal control. Exhaled NO and exhaled breath condensate (EBC) NO metabolites (nitrites and nitrates) measurements are non-invasive tools to assess airways inflammation. Our aim was to investigate the relationships between asthma control and the above-named biomarkers of airways inflammation.

METHODS

Thirty-nine non-smoking asthmatic patients (19 women) aged 50 (21-80) years performed measurements of exhaled NO (FENO), EBC nitrates, nitrites and pH, and answered Asthma Control Questionnaire (ACQ) and Asthma Control Test (ACT)-questionnaire.

RESULTS

The ACT and ACQ score were strongly interrelated (ρ = -0.84, p < 0.001). No relationships between ACT or ACQ score and FENO were found (p > 0.05). EBC nitrates were negatively related to ACT score (ρ = -0.34, p = 0.03) and positively related to ACQ score (ρ = 0.41, p = 0.001) while no relation of EBC nitrites to either ACQ or ACT score was found (p>0.05).

CONCLUSION

EBC nitrates were the only biomarker that was significantly related to asthma control. This suggests that nitrates, but not nitrites or FENO, reflect an aspect of airways inflammation that is closer related to asthma symptoms. Therefore there is a potential role for EBC nitrates in objective assessment of asthma control.

Exhaled nitric oxide in pulmonary diseases: a comprehensive review

The upregulation of nitric oxide (NO) by inflammatory cytokines and mediators in central and peripheral airway sites can be monitored easily in exhaled air. It is now possible to estimate the predominant site of increased fraction of exhaled NO (FeNO) and its potential pathologic and physiologic role in various pulmonary diseases. In asthma, increased FeNO reflects eosinophilic-mediated inflammatory pathways moderately well in central and/or peripheral airway sites and implies increased inhaled and systemic corticosteroid responsiveness. Recently, five randomized controlled algorithm asthma trials reported only equivocal benefits of adding measurements of FeNO to usual clinical guideline management including spirometry; however, significant design issues may exist. Overall, FeNO measurement at a single expiratory flow rate of 50 mL/s may be an important adjunct for diagnosis and management in selected cases of asthma. This may supplement standard clinical asthma care guidelines, including spirometry, providing a noninvasive window into predominantly large-airway-presumed eosinophilic inflammation. In COPD, large/central airway maximal NO flux and peripheral/small airway/alveolar NO concentration may be normal and the role of FeNO monitoring is less clear and therefore less established than in asthma. Furthermore, concurrent smoking reduces FeNO. Monitoring FeNO in pulmonary hypertension and cystic fibrosis has opened up a window to the role NO may play in their pathogenesis and possible clinical benefits in the management of these diseases.

Increased nitric oxide concentrations in the small airway of older normal subjects

BACKGROUND

There is a paucity of normal-age stratified data for fraction of exhaled nitric oxide (Feno). Our goal was to obtain normal data for large-airway nitric oxide flux (J'awno) and small-airway and/or alveolar nitric oxide concentration (Cano) in nonsmoking, healthy, adult subjects of various ages.

METHODS

In 106 normal volunteer subjects (60 women) aged 55 ± 20 years (mean ± SD), Feno (parts per billion [ppb]) was measured at 50, 100, 150, and 200 mL/s and J'awno (nL/s) and Cano (ppb) were calculated using a two-compartment model with correction for axial nitric oxide (NO) back diffusion. Fourteen older normal subjects were also treated with inhaled corticosteroid (540 μg budesonide bid) for 14 days.

RESULTS

We studied 34 younger normal subjects (17 women) aged 18 to 39 years (younger), 26 middle-aged normal subjects (22 women) aged 40 to 59 years (middle-aged), and 46 older normal subjects (21 women) aged 60 to 86 years (older). Feno at 50 mL/s in the younger group was 21 (14-28) ppb (median, 1-3 interquartile); in the middle-aged group it was 22 (18-30) ppb, and in the older group it was 27 (21-33) ppb, (analysis of variance [ANOVA]) P = .02. For Feno, the younger vs older groups was (Mann-Whitney) P = .03, and Feno in the combined younger and middle-aged groups was 21 (15-29) ppb vs 27 (21-33) ppb, P = .006 for the older group. Corrected J'awno in the younger group was 1.5 (1.0-2.1) nL/s; in the middle-aged group it was 1.4 (1.0-2.0) nL/s, and in the older group it was 1.8 (1.2-2.4) nL/s, (ANOVA) P = .3. Corrected Cano in the younger group was 1.9 (0.8-3.0) ppb; in the middle-aged group it was 2.8 (0.8-5.1) ppb, and in the older group it was 3.9 (1.4-6.6) ppb, (ANOVA) P = .02. Cano in the younger vs older groups was P = .003, and the combined younger and middle-aged group result was 2.0 (0.8-3.8) vs 3.9 (1.4-6.6), P = .01 in the older group. There was no change in NO gas exchange with inhaled corticosteroids.

CONCLUSIONS

In nonsmoking healthy subjects with normal spirometry, Feno at 50 mL/s and Cano increased significantly with age ≥ 60 years, whereas J'awno did not. We suspect the increase in Cano was due to a decrease in capillary blood volume with reduced NO diffusion, which is also reflected in increased Feno. Inhaled budesonide had no anti-NO-mediated inflammatory effect. Age-matched control subjects will be needed in NO comparative studies.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT00576069 and NCT00568347; URL: www.clinicaltrials.gov.

Multicentre trial evaluating alveolar NO fraction as a marker of asthma control and severity

BACKGROUND

Exhaled NO can be partitioned in its bronchial and alveolar sources, and the latter may increase in the presence of recent asthmatic symptoms and in refractory asthma. The aim of this multicentre prospective study was to assess whether alveolar NO fraction and FE(NO) could be associated with the level of asthma control and severity both at the time of measurement and in the subsequent 3 months.

METHODS

Asthma patients older than 10 years, nonsmokers, without recent exacerbation and under regular treatment, underwent exhaled NO measurement at multiple constant flows allowing its partition in alveolar (with correction for back-diffusion) and bronchial origins based on a two-compartment model of NO exchange; exhaled NO fraction at 50 ml/s (FE(NO,0.05)) was also recorded. On inclusion, severity was assessed using the four Global initiative for asthma (GINA) classes and control using Asthma Control Questionnaire (ACQ). Participants were followed-up for 12 weeks, control being assessed by short-ACQ on 1st, 4th, 8th and 12th week.

RESULTS

Two-hundred patients [107 children and 93 adults, median age (25th; 75th percentile) 16 years (12; 38)], 165 receiving inhaled corticosteroid, were included in five centres. The two-compartment model was valid in 175/200 patients (87.5%). Alveolar NO and FE(NO,0.05) did not correlate to control on inclusion or follow-up (either with ACQ /short-ACQ values or their changes), nor was influenced by severity classes. Alveolar NO negatively correlated to MEF(25-75%) (rho = -0.22, P < 0.01).

CONCLUSION

Alveolar and exhaled NO fractions are not indexes of control or severity in asthmatic children and adults under treatment.

Clinical patterns in asthma based on proximal and distal airway nitric oxide categories

BACKGROUND

The exhaled nitric oxide (eNO) signal is a marker of inflammation, and can be partitioned into proximal [J'awNO (nl/s), maximum airway flux] and distal contributions [CANO (ppb), distal airway/alveolar NO concentration]. We hypothesized that J'awNO and CANO are selectively elevated in asthmatics, permitting identification of four inflammatory categories with distinct clinical features.

METHODS

In 200 consecutive children with asthma, and 21 non-asthmatic, non-atopic controls, we measured baseline spirometry, bronchodilator response, asthma control and morbidity, atopic status, use of inhaled corticosteroids, and eNO at multiple flows (50, 100, and 200 ml/s) in a cross-sectional study design. A trumpet-shaped axial diffusion model of NO exchange was used to characterize J'awNO and CANO.

RESULTS

J'awNO was not correlated with CANO, and thus asthmatic subjects were grouped into four eNO categories based on upper limit thresholds of non-asthmatics for J'awNO (>or= 1.5 nl/s) and CANO (>or= 2.3 ppb): Type I (normal J'awNO and CANO), Type II (elevated J'awNO and normal CANO), Type III (elevated J'awNO and CANO) and Type IV (normal J'awNO and elevated CANO). The rate of inhaled corticosteroid use (lowest in Type III) and atopy (highest in Type II) varied significantly amongst the categories influencing J'awNO, but was not related to CANO, asthma control or morbidity. All categories demonstrated normal to near-normal baseline spirometry; however, only eNO categories with increased CANO (III and IV) had significantly worse asthma control and morbidity when compared to categories I and II.

CONCLUSIONS

J'awNO and CANO reveal inflammatory categories in children with asthma that have distinct clinical features including sensitivity to inhaled corticosteroids and atopy. Only categories with increase CANO were related to poor asthma control and morbidity independent of baseline spirometry, bronchodilator response, atopic status, or use of inhaled corticosteroids.

Impact of analysis interval on the multiple exhalation flow technique to partition exhaled nitric oxide

Exhaled nitric oxide (eNO) is elevated in asthmatics and is a purported marker of airway inflammation. By measuring eNO at multiple flows and applying models of eNO exchange dynamics, the signal can be partitioned into its proximal airway [J' aw NO (nl/sec)] and distal airway/alveolar contributions [CA(NO)(ppb)]. Several studies have demonstrated the potential significance of such an approach in children with asthma. However, techniques to partition eNO are variable, limiting comparisons among studies. The objective of this study is to examine the impact of the analysis interval (time or volume) on eNO plateau concentrations and the estimation of J' aw NO and CA(NO). In 30 children with mild to moderate asthma, spirometry and eNO at multiple flows (50, 100, and 200 ml/sec) were measured. The plateau concentration of eNO at each flow was determined using two different methods of analysis: (1) constant time interval and (2) constant volume interval. For both methods of analysis, a two-compartment model with axial diffusion was used to characterize J' aw NO and CA(NO). At a flow of 200 ml/sec, the time interval analysis predicts values for eNO that are smaller than the volume interval analysis. As a result, there are significant differences in CA(NO) between the methods of analysis (volume > time). When using the multiple flow technique to partition eNO, the method of analysis (constant time vs. constant volume interval) significantly affects the estimation of CA(NO), and thus potentially the assessment and interpretation of distal lung inflammation.

An elevated bronchodilator response predicts large airway inflammation in mild asthma

Exhaled nitric oxide (eNO) is elevated in asthmatics and is a purported marker of airway inflammation. The bronchodilator response (BDR) has also been shown to correlate with markers of airway inflammation, including eNO at 50 ml/sec (FE(NO,50)) which is comprised of NO from both the proximal and distal airways. Using eNO at multiple flows and a two-compartment model of NO exchange, the eNO signal can be partitioned into its proximal [J'aw(NO) (nl/sec)] and distal contributions [CA(NO) (ppb)]. We hypothesized that the BDR reflects the inflammatory status of the larger airways with smooth muscle, and thus would correlate with J'aw(NO). In 179 predominantly (95%) Hispanic children with mild asthma (69 steroid naïve), and 21 non-asthmatic non-atopic controls, spirometry and eNO at multiple flows were measured prior and 10 min following inhalation of albuterol. A trumpet-shaped axial diffusion model of NO exchange was used to characterize J'aw(NO) and CA(NO). The BDR correlated moderately (r = 0.44) with proximal airway NO (J'aw(NO)), but weakly (r = 0.26) with distal airway/alveolar NO (CA(NO)), and only in inhaled corticosteroid naïve asthmatics. A BDR cut point as low as >or=8% had a positive predictive value of 83% for predicting an elevated J'aw(NO) or FE(NO,50). We conclude that the BDR reflects inflammation in the large airways, and may be an effective clinical tool to predict elevated large airway inflammation.

Feasibility of exhaled nitric oxide measurements at various flow rates in children with asthma

Measurement of bronchial and alveolar exhaled nitric oxide (NO) levels could be of clinical importance for the treatment of asthma. To discriminate between alveolar and bronchial NO, measurements need to be assessed at various flow rates. To study the feasibility, linearity, and long-term repeatability of NO measurements at four different exhalation flow rates in children with asthma. Twenty-one children with moderate persistent asthma, aged 6-12 yrs, were included in the study. NO was measured according to the ATS/ERS guidelines, using the NIOX analyzer with flow restrictors of 30, 50, 100, and 200 ml/s. Duration of the measurements ranged from 6-10 s, depending on the flow rate. The tests were repeated 3 and 6 months after the first NO measurement. Feasibility of NO measurements at these four flow rates increased from 67% to 91% and 95% at the first, second and third visit, respectively. A significant learning effect was present. Age and lung function indices did not influence success or failure of the tests. At the first measurements occasions, no problems occurred during the NO analysis at a 100 ml/s flow rate. There was a 75-90% success rate when performing the test using flow rates of 30, 50, and 200 ml/s. However, repeating the tests resulted in a 100% success rate. Measurements were not successful if: (i) children ran out of air; (ii) NO concentration exceeded 200 ppb; (iii) the measured NO flow was unstable; and (iv) the NO plateau was not formed. This study showed good feasibility and linearity of NO measurements in asthmatic children of 6 yrs and over at flow rates between 50-200 ml/s. A significant learning effect was present. The long-term reproducibility of alveolar and bronchial NO values during 6 months was moderate.

Multicomponent Breath Analysis With Infrared Absorption Using Room-Temperature Quantum Cascade Lasers

Breath analysis is a powerful noninvasive technique for the diagnosis and monitoring of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Nitric oxide (NO) and carbon monoxide (CO) are markers of airway inflammation and can indicate the extent of respiratory diseases. We have developed a compact fast response laser system for analysis of multiple gases by infrared absorption. The instrument uses room temperature quantum cascade lasers to simultaneously measure NO, CO, carbon dioxide (CO(2)) and nitrous oxide (N(2)O) in exhaled breath. Four breath flow rates are employed to explore their exchange dynamics in the lungs and airways. We obtain 1-s detection precisions of 0.5-0.8 parts-per-billion (ppb) for NO, CO, and N(2)O with an instrument response time of less than 1 s. The breath analysis system has been demonstrated in a preliminary study of volunteers. It is currently deployed in a trial clinical study.

The role of small airways in monitoring the response to asthma treatment: what is beyond FEV1?

The definition of asthma has evolved from that of an episodic disease characterized by reversible airways constriction to a chronic inflammatory disease of the airways, with at least partially reversible airway constriction. Increasing evidence supports the notion that small and large airways play a central role in asthma pathophysiology with regard to inflammation, remodeling and symptoms. The contribution of the distal airways to the asthma phenotype carries implications for the delivery of inhaled medications to the appropriate areas of the lung and for the monitoring of the response to asthma treatment. Asthma control is evaluated on the basis of symptoms, lung function and exacerbations. However, evidence suggests that dissociation between lung function and respiratory symptoms, quality of life and airway inflammation exists. In this study, common spirometric parameters offer limited information with regard to the peripheral airways, and it is therefore necessary to move beyond FEV(1). Several functional parameters and inflammatory markers, which are discussed in the present study, can be employed to evaluate distal lung function. In this study, extrafine formulations deliver inhaled drugs throughout the bronchial tree (both large and small airways) and are effective on parameters that directly or indirectly measure air trapping/airway closure.

[Lung function testing and assessment of distal airways in asthma]

INTRODUCTION

Small airways are defined (in humans) as those<2mm in diameter.

BACKGROUND

They were originally described as the "quiet zone" of the lungs contributing less than 10% of the total resistance to airflow. Pulmonary function tests remain the most used method to assess distal airway flow limitation.

VIEWPOINTS

However, these tests are limited in adults and also in children because MEF25-75% and FEF50% are highly variable spirometric indices and they depend on vital capacity, which increases with expiratory time in obstructed subjects. There is a need for promising non invasive new tools like the forced oscillation technique to measure resistance. The increased availability of the exhaled fraction of nitric oxide (FeNO) measurement means that this method is accessible and attractive.

CONCLUSION

The production of nitric oxide (NO) can be assessed by measuring the fraction of NO during a prolonged expiration (FENO) or by estimating other parameters of NO exchange including the alveolar NO concentration (CalvNO) and may provide information about small airway inflammation and assist the optimal control of the disease.