A novel approach to partition central and peripheral airway nitric oxide

Comparison of airway inflammation characteristics detected by lower exhaled nitric oxide in cough variant asthma, non-asthmatic eosinophilic bronchitis, and classic asthma

OBJECTIVE

To investigate the inflammatory profiles of non-asthmatic eosinophilic bronchitis (NAEB), cough variant asthma (CVA), and classic asthma (CA) using fractional exhaled nitric oxide (FeNO) analysis to identify their unique inflammatory phenotypes.

METHODS

This study involved cough patients newly diagnosed, corticosteroid-naïve with CVA (n = 68), NAEB (n = 53), and CA (n = 49). FeNO measurements at exhalation flow rates of 50 mL/s (FeNO50) and 200 mL/s (FeNO200) were conducted. The concentration of alveolar nitric oxide (CaNO) was calculated using a two-compartment model. Inflammatory mediators in induced sputum were also analyzed across the groups.

RESULTS

Significant differences in FeNO50, FeNO200, and CaNO levels were observed among the three groups (all p < 0.001). Compared to NAEB, CVA patients demonstrated significantly higher FeNO50 levels (27.5 [interquartile range, IQR: 12.0-33.0] ppb vs. 16.0 [IQR: 12.5-22.0] ppb; p = 0.008) but lower CaNO levels (2.6 [IQR: 1.0-4.3] ppb vs. 3.7 [IQR: 2.3-6.1] ppb; p = 0.009). CA exhibited the highest levels of FeNO50, FeNO200, and CaNO compared to both NAEB and CVA (all p < 0.01). In CVA, FeNO50 positively correlated with sputum eosinophils, IL-4, and LTC4, whereas NAEB showed elevated CaNO levels with higher sputum eosinophils, IL-5, and PGE2 (all p < 0.05).

CONCLUSIONS

Inflammation predominantly affects the central airways in CVA and the peripheral airways in NAEB, with a more uniform distribution across the airway in CA. These discrepancies in airway inflammation may suggest distinct cough mechanisms in CVA, NAEB, and CA.

Measuring exhaled nitric oxide in COPD: from theoretical consideration to practical views

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is traditionally perceived as Th1-inflammation, but some patients have Th2-inflammation. A high fraction of exhaled nitric oxide (FENO) is seen in asthma with Th2-inflammation, justifying FENO as a point-of-care biomarker. The use of FENO in COPD is much less frequent. We aimed to review the evidence in favor of FENO measurement in COPD and discuss its potential usefulness in clinical settings.

AREAS COVERED

This review covers nitric oxide production in the airways and FENO measurements in COPD patients during stable conditions and acute exacerbation. It discusses why COPD patients may have both low and high FENO levels and the potential clinical utility of FENO.

EXPERT OPINION

There is good evidence that FENO increases with an exacerbation irrespective of the initial low or high baseline value. However, there is insufficient evidence to establish a fixed cutoff value for elevated FENO in COPD today. Instead, a personal baseline FENO level should be established when the patient is in a stable phase of the disease, which will subsequently set high and low FENO levels in a personalized manner. In the future, home monitoring of FENO could help identify exacerbations early, allowing proper action to be taken.

Small airway inflammation in atypical asthma

Background

Less attention has been paid to the pathophysiological changes in atypical asthma such as cough variant asthma (CVA) and chest tightness variant asthma (CTVA). The obstruction of large and small airways is the important component in the development of asthma. We investigated whether small airway inflammation (SAI) induced small airway dysfunction (SAD) in these atypical asthmatics.

Methods

Six hundred and eighty-six patients were enrolled and analyzed in the study. The partitioned airway inflammation was assessed by fractional exhaled nitric oxide (FeNO), such as FnNO, FeNO50, FeNO200, and calculated alveolar fraction of exhaled NO (CaNOdual). Correlations between exhaled NOs and SAD-related variables were assessed, whereas cell classification was evaluated by Spearman's rank tests. Classic asthma, CVA, and CTVA about potential risk were conducted using binary logistic regression models.

Results

The whole airway inflammation increased in classic and atypical asthma than controls, whereas the central and peripheral airway inflammation in the CVA and CTVA groups increased compared with the classic asthma group. Smoking exposure was found to increase the central and peripheral airway inflammation in patients with asthma. The exhaled NO of FeNO50 and FeNO200 was associated with SAD in classic asthma, but not in CVA and CTVA. FeNO200 was the main risk (adjusted odds ratio [OR], 1.591; 95 % CI, 1.121-2.259; P = .009) in classic asthma and (adjusted OR, 1.456; 95 % CI, 1.247-1.700; P = .000) in CVA. The blood eosinophil levels were correlated with FeNO50 and FeNO200 in classic asthma and atypical asthma.

Conclusion

More severe inflammatory process was present in central and peripheral airways in CVA and CTVA, which might reflect a pre-asthmatic state. SAI was the predominant risk factor in the development of asthma before SAD.

Ambient ultrafine particles exacerbate oxygen desaturation during sleep in patients with chronic obstructive pulmonary disease: New insights into the effect spectrum of ultrafine particles on susceptible populations

The health effects of ultrafine particles (UFPs) are of growing global concern, but the epidemiological evidence remains limited. Sleep-disordered breathing (SDB) characterized by hypoxemia is a prevalent condition linked to many debilitating chronic diseases. However, the role of UFPs in the development of SDB is lacking. Therefore, this prospective panel study was performed to specifically investigate the association of short-term exposure to UFPs with SDB parameters in patients with chronic obstructive pulmonary disease (COPD). Ninety-one COPD patients completed 226 clinical visits in Beijing, China. Personal exposure to ambient UFPs of 0-7 days was estimated based on infiltration factor and time-activity pattern. Real-time monitoring of sleep oxygen saturation, spirometry, respiratory questionnaires and airway inflammation detection were performed at each clinical visit. Generalized estimating equation was used to estimate the effects of UFPs. Exposure to UFPs was significantly associated with increased oxygen desaturation index (ODI) and percent of the time with oxygen saturation below 90 % (T90), with estimates of 21.50 % (95%CI: 6.38 %, 38.76 %) and 18.75 % (95%CI: 2.83 %, 37.14 %), respectively, per 3442 particles/cm3 increment of UFPs at lag 0-3 h. Particularly, UFPs' exposure within 0-7 days was positively associated with the concentration of alveolar nitric oxide (CaNO), and alveolar eosinophilic inflammation measured by CaNO exceeding 5 ppb was associated with 29.63 % and 33.48 % increases in ODI and T90, respectively. In addition, amplified effects on oxygen desaturation were observed in current smokers. Notably, individuals with better lung function and activity tolerance were more affected by ambient UFPs due to longer time spent outdoors. To our knowledge, this is the first study to link UFPs to hypoxemia during sleep and uncover the key role of alveolar eosinophilic inflammation. Our findings provide new insights into the effect spectrum of UFPs and potential environmental and behavioral intervention strategies to protect susceptible populations.

Contribution of small airway inflammation to the development of COPD

BACKGROUND

Little attention has been paid to the pathophysiological changes in the natural history of chronic obstructive pulmonary disease (COPD). The destructions of the small airways were visualized on thoracic micro-computed tomography scan. We investigated whether small airway inflammation (SAI) was the risk for the development of COPD.

METHODS

A total of 1062 patients were enrolled and analyzed in the study. The partitioned airway inflammation was determined by exhaled nitric oxide (NO) of FnNO, FeNO50, FeNO200, and calculated CaNOdual. Both FeNO200 and CaNOdual were compared to detect the promising predictor for peripheral airway/alveolar inflammation in COPD. The correlation between exhaled NO and white cell classification was evaluated to determine the inflammation type during the development of COPD.

RESULTS

Exhaled NO levels (FnNO, FeNO50, FeNO200, and CaNOdual) were the highest in the COPD group compared with all other groups. Furthermore, compared with controls, exhaled NO levels (FeNO50, FeNO200, and CaNOdual) were also significantly higher in the emphysema, chronic bronchitis, and smoking groups. FeNO200 was found to be a promising predictor for peripheral airway/alveolar inflammation (area under the curve [AUC] of the receiver operating characteristic [ROC] curve, area under the curve [AUC] = 0.841) compared with CaNOdual (AUC ROC = 0.707) in COPD. FeNO200 was the main risk factor (adjusted odds ratio, 2.191; 95% CI, 1.797-2.671; p = 0.002) for the development of COPD. The blood eosinophil and basophil levels were correlated with FeNO50 and FeNO200.

CONCLUSION

The complete airway inflammations were shown in COPD, whereas SAI was the main risk factor for the development of COPD, which might relate to eosinophil and basophil levels.

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.

Role of alveolar nitric oxide in gastroesophageal reflux-associated cough: prospective observational study

BACKGROUND

Fractional exhaled nitric oxide (FeNO) measured at multiple exhalation flow rates can be used as a biomarker to differentiate central and peripheral airway inflammation. However, the role of alveolar nitric oxide (CaNO) indicating peripheral airway inflammation remains unclear in gastroesophageal reflux-associated cough (GERC).

OBJECTIVES

We aimed to characterize the changes in alveolar nitric oxide (CaNO) and determine its clinical implication in GERC.

DESIGN

This is a single-center prospective observational study.

METHODS

FeNOs at exhalation flow rates of 50 and 200 ml/s were measured in 102 patients with GERC and 134 patients with other causes of chronic cough (non-GERC). CaNO was calculated based on a two-compartment model and the factors associated with CaNO were analyzed. The effect of anti-reflux therapy on CaNO was examined in 26 GERC patients with elevated CaNO.

RESULTS

CaNO was significantly elevated in GERC compared with that in non-GERC (4.6 ± 4.4 ppb versus 2.8 ± 2.3 ppb, p < 0.001). GERC patients with high CaNO (>5 ppb) had more proximal reflux events (24 ± 15 versus 9 ± 9 episodes, p = 0.001) and a higher level of pepsin (984.8 ± 492.5 versus 634.5 ± 626.4 pg/ml, p = 0.002) in sputum supernatant than those with normal CaNO. More GERC patients with high CaNO required intensified anti-reflux therapy (χ2 = 3.963, p = 0.046), as predicted by a sensitivity of 41.7% and specificity of 83.3%. Cough relief paralleled a significant improvement in CaNO (8.3 ± 3.0 versus 4.8 ± 2.6 ppb, p < 0.001).

CONCLUSION

Peripheral airway inflammation can be assessed by CaNO measurement in GERC. High CaNO indicates potential micro-aspiration and may predict a necessity for intensified anti-reflux therapy.

Exhaled Nitric Oxide as Biomarker of Type 2 Diseases

Nitric oxide (NO) is a short-lived gas molecule which has been studied for its role as a signaling molecule in the vasculature and later, in a broader view, as a cellular messenger in many other biological processes such as immunity and inflammation, cell survival, apoptosis, and aging. Fractional exhaled nitric oxide (FeNO) is a convenient, easy-to-obtain, and non-invasive method for assessing active, mainly Th2-driven, airway inflammation, which is sensitive to treatment with standard anti-inflammatory therapy. Consequently, FeNO serves as a valued tool to aid the diagnosis and monitoring of several asthma phenotypes. More recently, FeNO has been evaluated in several other respiratory and/or immunological conditions, including allergic rhinitis, chronic rhinosinusitis with/without nasal polyps, atopic dermatitis, eosinophilic esophagitis, and food allergy. In this review, we aim to provide an extensive overview of the current state of knowledge about FeNO as a biomarker in type 2 inflammation, outlining past and recent data on the application of its measurement in patients affected by a broad variety of atopic/allergic disorders.

Validity of fractional exhaled nitric oxide and small airway lung function measured by IOS in the diagnosis of cough variant asthma in preschool children with chronic cough

BACKGROUND

To investigate the role of combined impulse oscillometry (IOS) and fractional exhaled nitric oxide (FeNO) in the diagnosis of cough variant asthma (CVA) in preschool children.

METHODS

A total of 197 preschool-aged children with chronic cough were selected from the paediatric outpatient clinic. Allergy histories were collected for all children along with IOS and FeNO. Paediatric respiratory specialists divided the children into a CVA group (n = 90) and a noncough variant asthma (nCVA) group (n = 107) according to the diagnostic criteria for CVA After diagnostic treatment, the correlation between the FeNO and IOS values and the diagnosis in the two groups was analysed, and the area under the curve (AUC) of each index was calculated.

RESULTS

(1) X5 was significantly different between the CVA group and the nCVA group (- 4.22 vs. - 3.64, p < 0.001), as was the FeNO value (29.07 vs. 16.64, p < 0.001). (2) Receiver operating characteristic (ROC) analysis showed that the AUCs of FeNO alone and X5 alone were 0.779 and 0.657, respectively, while the AUC of FeNO (cut-off value of 18 ppb) plus X5 (cut-off value of -4.15 cmH2O/(l/s)) reached 0.809.

CONCLUSIONS

Children with CVA may have small airway dysfunction at an early stage. For preschool children with chronic cough, the combination of FeNO and X5 can better identify those with CVA.

TRIAL REGISTRATION NUMBER

This trial was registered with and approved by the Chinese Clinical Trial Registry, with registration number ChiCTRcRRC-17011738, and was reviewed and approved by the Ethics Committee of Southwest Hospital.

Small airways in asthma: Pathophysiology, identification and management

Background

The aim of this review is to summarize the current evidence regarding small airway disease in asthma, focusing on recent advances in small airway pathophysiology, assessment and therapeutic implications.

Methods

A search in Medline was performed, using the keywords "small airways", "asthma", "oscillometry", "nitrogen washout" and "imaging". Our review was based on studies from adult asthmatic patients, although evidence from pediatric populations is also discussed.

Results

In asthma, inflammation in small airways, increased mucus production and airway wall remodelling are the main pathogenetic mechanisms of small airway disease. Small airway dysfunction is a key component of asthma pathophysiology, leading to increased small airway resistance and airway closure, with subsequent ventilation inhomogeneities, hyperresponsiveness and airflow limitation. Classic tests of lung function, such as spirometry and body plethysmography are insensitive to detect small airway disease, providing only indirect measurements. As discussed in our review, both functional and imaging techniques that are more specific for small airways, such as oscillometry and the multiple breath nitrogen washout have delineated the role of small airways in asthma. Small airways disease is prevalent across all asthma disease stages and especially in severe disease, correlating with important clinical outcomes, such as asthma control and exacerbation frequency. Moreover, markers of small airways dysfunction have been used to guide asthma treatment and monitor response to therapy.

Conclusions

Assessment of small airway disease provides unique information for asthma diagnosis and monitoring, with potential therapeutic implications.

Association of multiple air pollutants with oxygen saturation during sleep in COPD patients: Effect modification by smoking status and airway inflammatory phenotypes

Air pollution contributes substantially to the development of chronic obstructive pulmonary disease (COPD). To date, the effect of air pollution on oxygen saturation (SpO₂) during sleep and potential susceptibility factors remain unknown. In this longitudinal panel study, real-time SpO₂ was monitored in 132 COPD patients, with 270 nights (1615 h) of sleep SpO₂ recorded. Exhaled nitric oxide (NO), hydrogen sulfide (H₂S) and carbon monoxide (CO) were measured to assess airway inflammatory characteristics. Exposure levels of air pollutants were estimated by infiltration factor method. Generalized estimating equation was used to investigate the effect of air pollutants on sleep SpO₂. Ozone, even at low levels (<60 μg/m³), was significantly associated with decreased SpO₂ and extended time of oxygen desaturation (SpO₂ < 90%), especially in the warm season. The associations of other pollutants with SpO₂ were weak, but significant adverse effects of PM₁₀ and SO₂ were observed in the cold season. Notably, stronger effects of ozone were observed in current smokers. Consistently, smoking-related airway inflammation, characterized by higher levels of exhaled CO and H₂S but lower NO, significantly augmented the effect of ozone on SpO₂ during sleep. This study highlights the importance of ozone control in protecting sleep health in COPD patients.

A comparative study on the value of lower airway exhaled nitric oxide combined with small airway parameters for diagnosing cough-variant asthma

BACKGROUND

The diagnosis of cough-variant asthma (CVA) is based on bronchial provocation test, which is challenging to be conducted. Most CVA patients have type 2 airway inflammation and small airway dysfunction. FeNO200, reflecting small airway inflammation, may be used to diagnose CVA.

OBJECTIVE

This study aimed to explore and compare the value of lower airway exhaled nitric oxide (FeNO50, FeNO200, and CaNO) combined with small airway parameters for diagnosing CVA.

METHODS

Chronic cough patients who attended the clinic from September 2021 to August 2022 were enrolled and divided into CVA group (n = 71) and non-CVA (NCVA) group (n = 212). The diagnostic values of FeNO50, FeNO200, concentration of alveolar nitric oxide (CaNO), maximal mid-expiratory flow (MMEF), forced expiratory flow at 75% of forced vital capacity (FEF75%) and forced expiratory flow at 50% of forced vital capacity (FEF50%) for CVA were evaluated.

RESULTS

FeNO50 [39(39) ppb versus 17(12) parts per billion (ppb), p < 0.01], FeNO200 [17(14) ppb versus 8(5) ppb, p < 0.01] and CaNO [5.0(6.1) ppb versus 3.5(3.6) ppb, p < 0.01] in CVA group were significantly higher than those in NCVA group. The optimal cut-off values of FeNO50, FeNO200, and CaNO for diagnosis of CVA were 27.00 ppb [area under the curve (AUC) 0.88, sensitivity 78.87%, specificity 79.25%], 11.00 ppb (AUC 0.92, sensitivity 88.73%, specificity 81.60%) and 3.60 ppb (AUC 0.66, sensitivity 73.24%, specificity 52.36%), respectively. For diagnosing CVA, the value of FeNO200 was better than FeNO50 (p = 0.04). The optimal cut-off values of MMEF, FEF75%, and FEF50% for the diagnosis of CVA were 63.80% (AUC 0.75, sensitivity 53.52%, specificity 86.32%), 77.9% (AUC 0.74, sensitivity 57.75%, specificity 83.49%) and 73.50% (AUC 0.75, sensitivity 60.56%, specificity 80.19%), respectively. The AUCs of FeNO50 combined with MMEF, FEF75%, and FEF50% for the diagnosis of CVA were all 0.89. The AUCs of FeNO200 combined with MMEF, FEF75%, and FEF50% for the diagnosis of CVA were all 0.93.

CONCLUSION

FeNO200 > 11 ppb contributed strongly for differentiating CVA from chronic cough, especially in patients with small airway dysfunction.

Effect of exhalation flow rates and level of nitric oxide output on accuracy of linear approximation of pulmonary nitric oxide dynamics

The method of Tsoukias and George (T and G) is a commonly used linear approximation of pulmonary nitric oxide (NO) dynamics that can be used to calculate bronchial NO output (J_awNO) and alveolar NO concentration (C_ANO). We aimed to investigate how flow rate range in exhaled NO measurements and levels of pulmonary NO parameters affect the accuracy of the T and G method. This study has three parts. (a) A theoretical part demonstrating how different exhalation flow rates and NO parameter levels affect the accuracy of the T and G method, (b) testing how exhalation flow rate range affects the method in a sample of asthmatic and healthy subjects, and (c) a meta-analysis of published literature to test whether minimum flow rate has an association with the NO parameter values. We found that both the chosen exhalation flow rates and magnitude of the pulmonary NO parameters affect the accuracy of the T and G method. Underestimation ofJ_awNO increased with lower flow rates and higher bronchial diffusion factor of NO (D_awNO), while overestimation of C_ANO increased with higher D_awNO and bronchial wall NO concentration (C_awNO) and lower C_ANO. Of the NO parameters, C_ANO was the most prone to bias and high D_awNO was the most significant factor causing the bias. Furthermore, we found that using 40 ml s^-1as the lowest flow rate in our sample and 50 ml s^-1in the meta-analysis compared to 100 ml s^-1resulted in higher C_ANO, but J_awNO was not statistically significantly affected. We have provided objective evidence that not only the flow rates used but also the magnitude of NO output in the test subjects affect the accuracy of the T and G method. We suggest that flow rates below 100 ml s^-1should not be used with the T and G method to maintain accuracy.

Clinical Utility of Central and Peripheral Airway Nitric Oxide in Aging Patients with Stable and Acute Exacerbated Chronic Obstructive Pulmonary Disease

Purpose

Exhaled nitric oxide has been used as a marker of airway inflammation. The NO concentration in the central and peripheral airway/alveolar can be measured by a slow and fast exhalation flow rate to evaluate inflammation in different divisions within the respiratory tract. We hypothesized that FeNO₂₀₀ (exhaled NO at a flow rate of 200mL/s) could be used as an evaluation tool for peripheral airway/alveolar inflammation and corticosteroid therapy in chronic obstructive pulmonary disease (COPD) patients.

Methods

We recruited 171 subjects into the study: 73 healthy controls, 59 stable COPD patients, and 39 acute exacerbations of COPD (AECOPD) patients. Exhaled nitric oxide (FeNO₅₀ (exhaled NO at a flow rate of 50mL/s)), FeNO₂₀₀ and CaNO (peripheral concentration of NO/alveolar NO) and clinical variables including pulmonary function, COPD Assessment Test (CAT), C-reactive protein concentration (CRP) and circulating eosinophil count were measured among the recruited participants. FeNO_50, FeNO₂₀₀ and CaNO were repeatedly evaluated in 39 AECOPD patients after corticosteroid treatment.

Results

FeNO₂₀₀ was significantly higher in stable COPD and AECOPD patients than in healthy controls. Nevertheless, CaNO could not differentiate COPD from healthy controls. No correlation was found between circulating eosinophil counts or FEV1 and exhaled nitric oxide (FeNO_50, FeNO₂₀₀, CaNO) in COPD patients. For AECOPD patients, 64% of patients had eosinophil counts >100 cells/µL; 59% of patients had FeNO₂₀₀ >10 ppb; only 31% of patients had FeNO₅₀ > 25 ppb. Among AECOPD patients, the high FeNO₅₀ and FeNO₂₀₀ groups’ levels were significantly lower than their baseline levels, and significant improvements in CAT were seen in the two groups after corticosteroid treatment. These implied a good corticosteroid response in AECOPD patients with FeNO₂₀₀>10ppb.

Conclusion

FeNO₂₀₀ is a straightforward and feasible method to evaluate the peripheral NO concentration in COPD. FeNO200 can be a type 2 inflammation biomarker and a useful tool for predicting corticosteroid therapy in COPD.

Clinical Values of Nitric Oxide Parameters from the Respiratory System

BACKGROUND

Fractional exhaled nitric oxide (FENO) concentration reliably reflects central airway inflammation, but it is not sensitive to changes in the NO dynamics in the lung periphery. By measuring FENO at several different flow rates one can estimate alveolar NO concentration (C_ANO), bronchial NO flux (J_awNO), bronchial wall NO concentration (C_awNO) and the bronchial diffusivity of NO (D_awNO).

OBJECTIVE

We aimed to describe the current knowledge and clinical relevance of NO parameters in different pulmonary diseases.

METHODS

We conducted a systematic literature search to identify publications reporting NO parameters in subjects with pulmonary or systemic diseases affecting the respiratory tract. A narrative review was created for those with clinical relevance.

RESULTS

Estimation of pulmonary NO parameters allows for differentiation between central and peripheral inflammation and a more precise analysis of central airway NO output. C_ANO seems to be a promising marker of parenchymal inflammation in interstitial lung diseases and also a marker of tissue damage and altered gas diffusion in chronic obstructive pulmonary disease and systemic diseases affecting the lung. In asthma, C_ANO can detect small airway involvement left undetected by ordinary FENO measurement. Additionally, C_awNO and D_awNO can be used in asthma to assess if FENO is increased due to enhanced inflammatory activity (increased C_awNO) or tissue changes related to bronchial remodelling (altered D_awNO).

CONCLUSION

NO parameters may be useful for diagnosis, prediction of disease progression and prediction of treatment responses in different parenchymal lung and airway diseases. Formal trials to test the added clinical value of NO parameters are needed.

Feasibility study on exhaled-breath analysis by untargeted Selected-Ion Flow-Tube Mass Spectrometry in children with cystic fibrosis, asthma, and healthy controls: Comparison of data pretreatment and classification techniques

Selected-Ion Flow-Tube Mass Spectrometry (SIFT-MS) has been applied in a clinical context as diagnostic tool for breath samples using target biomarkers. Exhaled breath sampling is non-invasive and therefore much more patient friendly compared to bronchoscopy, which is the golden standard for evaluating airway inflammation. In the actual pilot study, 55 exhaled breath samples of children with asthma, cystic-fibrosis and healthy individuals were included. Rather than focusing on the analysis of target biomarkers or on the identification of biomarkers, different data analysis strategies, including a variety of pretreatment, classification and discrimination techniques, are evaluated regarding their capacity to distinguish the three classes based on subtle differences in their full scan SIFT-MS spectra. Proper data-analysis strategies are required because these full scan spectra contain much external, i.e. unwanted, variation. Each SIFT-MS analysis generates three spectra resulting from ion-molecule reactions of analyte molecules with H₃O⁺, NO⁺ and O₂⁺. Models were built with Linear Discriminant Analysis, Quadratic Discriminant Analysis, Soft Independent Modelling by Class Analogy, Partial Least Squares - Discriminant Analysis, K-Nearest Neighbours, and Classification and Regression Trees. Perfect models, concerning overall sensitivity and specificity (100% for both) were found using Direct Orthogonal Signal Correction (DOSC) pretreatment. Given the uncertainty related to the classification models associated with DOSC pretreatments (i.e. good classification found also for random classes), other models are built applying other preprocessing approaches. A Partial Least Squares - Discriminant Analysis model with a combined pre-processing method considering single value imputation results in 100% sensitivity and specificity for calibration, but was less good predictive. Pareto scaling prior to Quadratic Discriminant Analysis resulted in 41/55 correctly classified samples for calibration and 34/55 for cross-validation. In future, the uncertainty with DOSC and the applicability of the promising preprocessing methods and models must be further studied applying a larger representative data set with a more extensive number of samples for each class. Nevertheless, this pilot study showed already some potential for the untargeted SIFT-MS application as a rapid pattern-recognition technique, useful in the diagnosis of clinical breath samples.

Fractional exhaled nitric oxide in adult congenital heart disease

BACKGROUND

Fractional exhaled nitric oxide levels are related to various clinical diseases. This study investigated the associations between the clinical characteristics and the level of fractional exhaled nitric oxide in patients with adult congenital heart disease.

METHODS AND RESULTS

Fractional exhaled nitric oxide values were measured in 30 adult patients with stable congenital heart disease who had undergone right heart catheterization and 17 healthy individuals (controls). There was no significant difference in fractional exhaled nitric oxide values between patients with congenital heart disease and healthy controls. Depending on whether their fractional exhaled nitric oxide values were above or below the median value, patients with congenital heart disease were divided into two groups (low vs. high fractional exhaled nitric oxide groups). The relationship between fractional exhaled nitric oxide values and clinical characteristics was investigated. There was a higher percentage of patients with cyanosis in the low fractional exhaled nitric oxide group (50%) than in the high fractional exhaled nitric oxide group (7.1%). There was no significant difference in right heart catheterization data between the low and high fractional exhaled nitric oxide groups. The fractional exhaled nitric oxide value was correlated to the number of neutrophils in patients with cyanosis (r = 0.84 (N = 8), p = 0.005).

CONCLUSIONS

In this cohort of patients with adult congenital heart disease, lower levels of fractional exhaled nitric oxide corresponded to the presence of cyanosis.

Study of the role of exhaled nitric oxide (NO) in predicting controlled or uncontrolled asthma in asthmatic children

Background

Exhaled nitric oxide (NO), especially fractional concentration of exhaled NO (FE_NO) has been used to predict the responsiveness to inhaled corticosteroid (ICS) in children with asthma. However, the use of exhaled NO for predicting asthma control in children is still controversial.

Methods

This was a perspective observational study. Asthmatic children who were naïve to inhaled corticosteroid (ICS) were included in the present study. The measurements of FE_NO and CA_NO (concentration of NO in the gas phase of the alveolar), spirometry, blood eosinophil counts (BEC), and total IgE levels were done for each asthmatic child. All study subjects started proper asthma treatment after the enrollment.

Results

Ninety three asthmatic children (9±3 years) with moderate (63.4%) to severe (36.6%) asthma were included and finished the 3-month study. The levels of FE_NO and CA_NO at inclusion were 37±11 ppb and 5.8±1.4 ppb, respectively; the mean of BEC was 617±258 cells/μL; the level of total IgE was 1563±576 UI/mL; 89% of subjects were positive for at least one respiratory allergen. The percentage of severe asthma was reduced significantly after 3 months (P<0.001). Well controlled asthma subjects at 3 months had higher levels of FE_NO and lower levels of CA_NO at inclusion (P<0.05 and P<0.05). FE_NO<20 ppb or CA_NO>5ppb had a risk of uncontrolled asthma at 3 months (OR: 1.7, CI 95% [(0.8) - (3.3)], P<0.05; OR: 1.9, CI 95% [(0.9) - (2.7)], P<0.05; respectively). FE_NO>35 ppb at inclusion had a positive predictive value for asthma control at 3 months (OR: 3.5, CI 95% [2.2-5.9], P<0.01).

Conclusions

Exhaled NO is a biomarker of asthma which may have a potential role to predict the control of asthma in short-term follow up in asthmatic children.

Fraction of Exhaled Nitric Oxide Is Elevated in Patients With Stable Chronic Obstructive Pulmonary Disease: A Meta-analysis

BACKGROUND

Fraction of exhaled nitric oxide (FeNO) is a noninvasive indicator of eosinophilic airway inflammation and has been used for the diagnosis and treatment of asthma. The levels of FeNO are controversial in patients with stable chronic obstructive pulmonary disease (COPD). Accordingly, this study aimed to assess FeNO levels in patients with stable COPD.

MATERIALS AND METHODS

A search of the Medline, Embase, Web of Science, ClinicalTrials.gov and The Cochrane Library databases was performed in August 2019. The literature search was restricted to articles published in English. Studies were included if they reported data addressing FeNO levels in patients with stable COPD and healthy controls. Review Manager version 5.3 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark) was used for meta-analysis.

RESULTS

A total of 19 studies were included. Analysis revealed that FeNO levels in patients with stable COPD were higher than those in the healthy control group (mean difference [MD] 2.49 [95% confidence interval {CI} 0.99-4.00]; P < 0.05), those in nonsmoking patients with stable COPD were higher than those in the healthy control group (MD 5.04 [95% CI 2.19-7.89]; P < 0.05) and those in smoking patients with stable COPD were not higher than those in the healthy control group (MD 0.30 [95% CI -2.81 to 3.41]; P = 0.85). FeNO measured using a chemiluminescence analyzer in nonsmoking patients with stable COPD was higher than those in the healthy control group (MD 4.84 [95% CI 1.83-7.86]; P < 0.05).

CONCLUSIONS

Findings suggested that FeNO levels in patients with stable COPD were elevated, and that smokers exhibited decreased levels.

Measurement of Exhaled Nitric Oxide in Cirrhotic Patients with Esophageal and Gastric Varices

Background and aims. This study aimed to detect exhaled nitric oxide (eNO) level in cirrhotic patients and explore the correlation between eNO levels and the severity of cirrhosis. Methods. Patients were enrolled to analyze the relationship of eNO with noncirrhosis, cirrhosis, and complications of decompensated cirrhosis. We explored the potential predictive values of eNO in different states of cirrhosis. Results. The eNO levels were significantly increased in cirrhotic patients compared with noncirrhotic patients (14 (10-18) vs 8 (6-13) ppb, P < 0.001). The eNO level was increased in those with ascites (15 (14-22) vs 13 (10-18) ppb, P=0.026), with portal vein thrombosis (19.5 (11.75-22) vs 13.5 (10-17) ppb, P=0.032), or with the mucosal red-color sign of esophageal and gastric varices (EGV) (16.5 (10-21.75) vs 13 (10-14.75) ppb, P=0.041). Among cirrhotic patients undergoing hepatic venous pressure gradient (HVPG) measurement, the eNO level was significantly increased in the high-HVPG group (HVPG >12 mm Hg) compared with the low-HVPG group (6 mm Hg ≤ HVPG ≤ 12 mm Hg) (15 (11.75-19.25) vs 10 (8-14) ppb, P=0.011). Conclusions. The eNO level was increased in cirrhotic patients, especially in those complicated with ascites, portal vein thrombosis, mucosal red-color sign of varices, and high HVPG.

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.

Exhalative Breath Markers Do Not Offer for Diagnosis of Interstitial Lung Diseases: Data from the European IPF Registry (eurIPFreg) and Biobank

Background: New biomarkers are urgently needed to facilitate diagnosis in Interstitial Lung Diseases (ILD), thus reducing the need for invasive procedures, and to enable tailoring and monitoring of medical treatment. Methods: In this study we investigated if patients with idiopathic pulmonary fibrosis (IPF; n = 21), non-IPF ILDs (n = 57) and other lung diseases (chronic obstructive pulmonary disease (COPD) n = 24, lung cancer (LC) n = 16) as well as healthy subjects (n = 20) show relevant differences in exhaled NO (FeNO; Niox MINO), or in eicosanoid (PGE2, 8-isoprostane; enzyme-linked immunosorbent assay (ELISA)) levels as measured in exhaled breath condensates (EBC) and bronchoalveolar lavage fluids (BALF). Results: There was no significant difference in FeNO values between IPF, non-IPF ILDs and healthy subjects, although some individual patients showed highly elevated FeNO. On the basis of the FeNO signal, it was neither possible to differentiate between the kind of disease nor to detect exacerbations. In addition, there was no correlation between FeNO values and lung function. The investigation of the eicosanoids in EBCs was challenging (PGE2) or unreliable (8-isoprostane), but worked out well in BALF. A significant increase of free 8-isoprostane was observed in BALF, but not in EBCs, of patients with IPF, hypersensitivity pneumonitis (HP) and sarcoidosis, possibly indicating severity of oxidative stress. Conclusions: FeNO-measurements are not of diagnostic benefit in different ILDs including IPF. The same holds true for PGE2 and 8-isoprostane in EBC by ELISA.

Asthma control in preschool children with small airway function as measured by IOS and fractional exhaled nitric oxide

OBJECTIVE

This study investigated the accuracy of impulse oscillometry (IOS) combined with fractional exhaled nitric oxide (FeNO) to assess asthma control among preschool children.

METHODS

A total of 79 preschool children(3-6 year old) with asthma and 25 healthy preschool children who visited a paediatrician were enrolled in this study. All of the children were tested for allergens, respiratory system resistance (at 5 and 20 Hz [R5, R20]), respiratory system reactance (at 5 Hz [X5]), the resonant frequency of reactance (Fres), and the area under the reactance curve (between 5 Hz and Fres (reactance area [AX]) using IOS and FeNO. A paediatric respiratory specialist who was unaware of the IOS and FeNO results assigned children with asthma to either the asthma-controlled group (n = 27) or the asthma-uncontrolled group (n = 52) based on the Global Initiative for Asthma (GINA) criteria. A healthy control group (n = 25) was also included. The relationships between the FeNO and IOS values as well as the asthma control of the three groups were analysed, and the areas under the curve (AUCs) were calculated for each measure.

RESULTS

(1) During the controlled group, means±standard deviations of AX, R5-20, R5, X5 and FeNO were 26.15 ± 7.534, 3.52 ± 1.311,9.97 ± 1.576,-3.85 ± 0.572,-3.85 ± 0.572. During the uncontrolled group, means±standard deviations of AX,R5-20,R5,X5 and FeNO were 38.34 ± 13.563,5.36 ± 1.545,11.41 ± 2.029,-5.07 ± 1.554,36.40 ± 21.07. Among preschool children, significant differences were observed between the controlled and uncontrolled group with regard to the small airway functional parameters (AX, R5-20, R5, and X5) and FeNO(P <0.05).(2) A receiver operating characteristic (ROC) analysis showed that the AUCs were 0.786 for FeNO alone, 0.751 for X5 alone, and 0.866 for X5 combined with FeNO (cut-off value: 27 ppb).

CONCLUSION

FeNO combined with the small airway function parameter X5 accurately assessed asthma control among preschool children.

Effects of bronchodilation on biomarkers of peripheral airway inflammation in COPD

Peripheral airway inflammation and dysfunction are key elements in the pathogenesis of COPD. The exhaled alveolar fraction of nitric oxide (CANO) is an indirect biomarker of lung peripheral inflammation. We tested whether inhaled long-acting bronchodilators (LABA) can affect CANO and we evaluated correlations with lung mechanics in patients with COPD. Two-centre, randomised, double blind, crossover study including COPD patients with moderate-to-severe airflow obstruction. Following a pharmacological washout, multi-flow exhaled fraction of NO (FENO), plethysmography, lung diffusion (DLCO), single breath nitrogen washout test and dyspnoea were measured in a crossover manner at baseline and 30, 60 and 180 min following administration of salmeterol (Sal) or formoterol fumarate (FF). (ClinicalTrials.gov, number NCT01853787). Fort-five patients were enrolled (median age: 71.8 years; 84.4% males). At baseline, CANO correlated with airway resistances (r = 0.422), residual volume/total lung capacity (RV/TLC; r = 0.375), transfer factor (r= -0.463) and forced expiratory volume in 1 s (FEV1; r= -0.375, all P < 0.01). After LABA administration, we found a significant reduction of FENO that reached statistical significance at 180'; no difference was found between FF and S. Consistently, a significant reduction of CANO was documented at 60' and 180' compared to baseline for both FF and S (P < 0.01 and P < 0.05, respectively). Changes in CANO were correlated with changes in vital capacity (r=-44; P < 0.001) and RV/TLC (r = 0.56; P < 0.001), but not FEV1. In COPD, direct correlations were found between the levels of CANO and the magnitude of peripheral airway dysfunction. LABA reduced CANO levels. The reduction was associated with improvement in functional parameters reflecting air trapping.

Alveolar and Bronchial Nitric Oxide in Chronic Obstructive Pulmonary Disease and Asthma-COPD Overlap

INTRODUCTION

Exhaled nitric oxide (F_ENO) measurements differentiate COPD phenotypes from asthma-COPD overlap (ACO). To date, no study has been conducted to determine whether alveolar and bronchial components differ in this group of patients.

METHODS

This was an observational cross-sectional study recruiting ambulatory COPD patients. F_ENO was measured, differentiating alveolar (C_ANO) from bronchial (J_awNO) components using a multiple-flow technique. C_ANO and J_awNO values were compared between eosinophilic COPD patients (defined as ≥ 300 eosinophils/μL in peripheral blood test, or ≥ 2% eosinophils or ≥ 3% eosinophils), and a linear regression analysis was performed to determine clinical and biological variables related to these measurements.

RESULTS

73 COPD patients were included in the study. Eosinophil counts were associated with increased values of C_ANO and J_awNO (for the latter only the association with ≥ 300 or ≥ 3% eosinophils was significant). C_ANO was also associated with CRP, and J_awNO with smoking.

CONCLUSIONS

Patients with COPD and ACO characteristics show increased inflammation in the large and small airways. C_ANO and J_awNO are associated with clinical and biological variables.

Standardisation and application of the single-breath determination of nitric oxide uptake in the lung

Diffusing capacity of the lung for nitric oxide (D_LNO), otherwise known as the transfer factor, was first measured in 1983. This document standardises the technique and application of single-breath D_LNO This panel agrees that 1) pulmonary function systems should allow for mixing and measurement of both nitric oxide (NO) and carbon monoxide (CO) gases directly from an inspiratory reservoir just before use, with expired concentrations measured from an alveolar "collection" or continuously sampled via rapid gas analysers; 2) breath-hold time should be 10 s with chemiluminescence NO analysers, or 4-6 s to accommodate the smaller detection range of the NO electrochemical cell; 3) inspired NO and oxygen concentrations should be 40-60 ppm and close to 21%, respectively; 4) the alveolar oxygen tension (P_AO2 ) should be measured by sampling the expired gas; 5) a finite specific conductance in the blood for NO (θNO) should be assumed as 4.5 mL·min^-1·mmHg^-1·mL^-1 of blood; 6) the equation for 1/θCO should be (0.0062·P_AO2 +1.16)·(ideal haemoglobin/measured haemoglobin) based on breath-holding P_AO2 and adjusted to an average haemoglobin concentration (male 14.6 g·dL^-1, female 13.4 g·dL^-1); 7) a membrane diffusing capacity ratio (D_MNO/D_MCO) should be 1.97, based on tissue diffusivity.

Effect of Inhaled β2-Agonist on Exhaled Nitric Oxide in Chronic Obstructive Pulmonary Disease

The fractional exhaled nitric oxide measured at an expiratory flow of 50mL/s (FE_NO50) is a marker of airway inflammation, and high levels are associated with greater response to steroid treatment. In asthma, FE_NO50 increases with bronchodilation and decreases with bronchoconstriction, the latter potentially causing an underestimate of the degree of airway inflammation when asthma worsens. It is unknown whether the same effect occurs in chronic obstructive lung disease (COPD). Likewise, it is not known whether changes in airway calibre in COPD patients alter flow-independent parameters describing pulmonary nitric oxide exchange, such as the maximal flux of nitric oxide (NO) from the proximal airway compartment (J’aw_NO) and the distal airway/alveolar concentration of NO (CA_NO). We recruited 24 patients with COPD and performed FE_NO analysis at multiple expiratory flows before and after treatment with inhaled β₂-agonist bronchodilator therapy. For the 21 patients analysed, FE_NO50 rose from 17.1 (1.4) ppb (geometric mean (geometric SD)) at baseline, to 19.3 (1.3) ppb after bronchodilator therapy, an increase of 2.2 ppb (95% CI, 0.7–3.6; P = 0.005). There were non-significant changes in flow-independent NO parameters. The change in FE_NO50 correlated positively with the change in J’aw_NO (r_s = 0.67, P < 0.001; r_s = 0.62, P = 0.002 before and after correction for axial back-diffusion respectively) following bronchodilation. Inhaled bronchodilator therapy can increase exhaled nitric oxide measurements in COPD. The standardisation of inhaled bronchodilator therapy before FE_NO analysis in COPD patients should therefore be considered in both research and clinical settings.

Online Measurement of Exhaled NO Concentration and Its Production Sites by Fast Non-equilibrium Dilution Ion Mobility Spectrometry

Exhaled nitric oxide (NO) is one of the most promising breath markers for respiratory diseases. Its profile for exhalation and the respiratory NO production sites can provide useful information for medical disease diagnosis and therapeutic procedures. However, the high-level moisture in exhaled gas always leads to the poor selectivity and sensitivity for ion spectrometric techniques. Herein, a method based on fast non-equilibrium dilution ion mobility spectrometry (NED-IMS) was firstly proposed to directly monitor the exhaled NO profile on line. The moisture interference was eliminated by turbulently diluting the original moisture to 21% of the original with the drift gas and dilution gas. Weak enhancement was observed for humid NO response and its limit of detection at 100% relative humidity was down to 0.58 ppb. The NO concentrations at multiple exhalation flow rates were measured, while its respiratory production sites were determined by using two-compartment model (2CM) and Högman and Meriläinen algorithm (HMA). Last but not the least, the NO production sites were analyzed hourly to tentatively investigate the daily physiological process of NO. The results demonstrated the capacity of NED-IMS in the real-time analysis of exhaled NO and its production sites for clinical diagnosis and assessment.

Application of nitric oxide measurements in clinical conditions beyond asthma

Fractional exhaled nitric oxide (FeNO) is a convenient, non-invasive method for the assessment of active, mainly Th2-driven, airway inflammation, which is sensitive to treatment with standard anti-inflammatory therapy. Consequently, FeNO serves as a valued tool to aid diagnosis and monitoring in several asthma phenotypes. More recently, FeNO has been evaluated in several other respiratory, infectious, and/or immunological conditions. In this short review, we provide an overview of several clinical studies and discuss the status of potential applications of NO measurements in clinical conditions beyond asthma.

The role of the small airways in the pathophysiology of asthma and chronic obstructive pulmonary disease

Chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), represent a major social and economic burden for worldwide health systems. During recent years, increasing attention has been directed to the role of small airways in respiratory diseases, and their exact contribution to the pathophysiology of asthma and COPD continues to be clarified. Indeed, it has been suggested that small airways play a distinct role in specific disease phenotypes. Besides providing information on small airways structure and diagnostic procedures, this review therefore aims to present updated and evidence-based findings on the role of small airways in the pathophysiology of asthma and COPD. Most of the available information derives from either pathological studies or review articles and there are few data on the natural history of small airways disease in the onset or progression of asthma and COPD. Comparisons between studies on the role of small airways are hard to draw because both asthma and COPD are highly heterogeneous conditions. Most studies have been performed in small population samples, and different techniques to characterize aspects of small airways function have been employed in order to assess inflammation and remodelling. Most methods of assessing small airways dysfunction have been largely confined to research purposes, but some data are encouraging, supporting the utilization of certain techniques into daily clinical practice, particularly for early-stage diseases, when subjects are often asymptomatic and routine pulmonary function tests may be within normal ranges. In this context further clinical trials and real-life feedback on large populations are desirable.

Quantitative detection of nitric oxide in exhaled human breath by extractive electrospray ionization mass spectrometry

Exhaled nitric oxide (eNO) is a useful biomarker of various physiological conditions, including asthma and other pulmonary diseases. Herein a fast and sensitive analytical method has been developed for the quantitative detection of eNO based on extractive electrospray ionization mass spectrometry (EESI-MS). Exhaled NO molecules selectively reacted with 2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) reagent, and eNO concentration was derived based on the EESI-MS response of 1-oxyl-2-phenyl-4, 4, 5, 5-tetramethylimidazoline (PTI) product. The method allowed quantification of eNO below ppb level (~0.02 ppbv) with a relative standard deviation (RSD) of 11.6%. In addition, eNO levels of 20 volunteers were monitored by EESI-MS over the time period of 10 hrs. Long-term eNO response to smoking a cigarette was recorded, and the observed time-dependent profile was discussed. This work extends the application of EESI-MS to small molecules (<30 Da) with low proton affinity and collision-induced dissociation efficiency, which are usually poorly visible by conventional ion trap mass spectrometers. Long-term quantitative profiling of eNO by EESI-MS opens new possibilities for the research of human metabolism and clinical diagnosis.

Techniques of assessing small airways dysfunction

The small airways are defined as those less than 2 mm in diameter. They are a major site of pathology in many lung diseases, not least chronic obstructive pulmonary disease (COPD) and asthma. The small airways are frequently involved early in the course of these diseases, with significant pathology demonstrable often before the onset of symptoms or changes in spirometry and imaging. Despite their importance, they have proven relatively difficult to study. This is in part due to their relative inaccessibility to biopsy and their small size which makes their imaging difficult. Traditional lung function tests may only become abnormal once there is a significant burden of disease within them. This has led to the term 'the quiet zone' of the lung. In recent years, more specialised tests have been developed which may detect these changes earlier, perhaps offering the possibility of earlier diagnosis and intervention. These tests are now moving from the realms of clinical research laboratories into routine clinical practice and are increasingly useful in the diagnosis and monitoring of respiratory diseases. This article gives an overview of small airways physiology and some of the routine and more advanced tests of airway function.

Small airways dysfunction in asthma: evaluation and management to improve asthma control

The small airways have been neglected for many years, but interest in the topic has been rekindled with recent advances in measurement techniques to assess this region and also the ability to deliver therapeutics to the distal airways. Current levels of disease control in asthmatic patients remain poor and there are several contributory factors including; poor treatment compliance, heterogeneity of asthma phenotypes and associated comorbidities. However, the proposition that we may not be targeting all the inflammation that is present throughout the whole respiratory tree may also be an important factor. Indeed decades ago, pathologists and physiologists clearly identified the importance of small airways dysfunction in asthmatic patients. With improved inhaler technology to deliver drug to target the whole respiratory tree and more sensitive measures to assess the distal airways, we should certainly give greater consideration to treating the small airway region when seeing our asthmatic patients in clinic. The aim of this review is to address the relevance of small airways dysfunction in the daily clinical management of patients with asthma. In particular the role of small particle aerosols in the management of patients with asthma will be explored.