Exhaled nitric oxide: still alive, not laid to rest

Role of exhaled nitric oxide as a predictor of atopy

BACKGROUND

The fractional exhaled nitric oxide (FeNO) is a quantitative, noninvasive and safe measure of airways inflammation that may complement the assessment of asthma. Elevations of FeNO have recently been found to correlate with allergic sensitization. Therefore, FeNO may be a useful predictor of atopy in the general population. We sought to determine the diagnostic accuracy of FeNO in predicting atopy in a population-based study.

METHODS

We conducted a cross-sectional study in an age- and sex- stratified random sample of 13 to 15 year-olds in two communities in Peru. We asked participants about asthma symptoms, environmental exposures and sociodemographics, and underwent spirometry, assessment of FeNO and an allergy skin test. We used multivariable logistic regression to model the odds of atopy as a function of FeNO, and calculated area-under-the-curves (AUC) to determine the diagnostic accuracy of FeNO as a predictor of atopy.

RESULTS

Of 1441 recruited participants, 1119 (83%) completed all evaluations. Mean FeNO was 17.6 ppb (SD=0.6) in atopics and 11.6 ppb (SD=0.8) in non-atopics (p<0.001). In multivariable analyses, a FeNO>20 ppb was associated with an increase in the odds of atopy in non-asthmatics (OR=5.3, 95% CI 3.3 to 8.5) and asthmatics (OR=16.2, 95% CI 3.4 to 77.5). A FeNO>20 ppb was the best predictor for atopy with an AUC of 68% (95% CI 64% to 69%). Stratified by asthma, the AUC was 65% (95% CI 61% to 69%) in non-asthmatics and 82% (95% CI 71% to 91%) in asthmatics.

CONCLUSIONS

FeNO had limited accuracy to identify atopy among the general population; however, it may be a useful indicator of atopic phenotype among asthmatics.

The importance of imaging and physiology measurements in assessing the delivery of peripherally targeted aerosolized drugs

Considerable recent effort has been directed towards developing new aerosol formulations and delivery devices that can target drugs to the lung periphery. In order to determine the efficacy of targeted drug therapy, it is essential that the peripheral lung region be adequately assessed. Imaging of the airways structure and pathology has greatly advanced in the last decade and this rate of growth is accelerating as new technologies become available. Lung imaging continues to play an important role in the study of the peripheral airways and, when combined with state-of-the-art lung function measurements and computational modeling, can be a powerful tool for investigating the effects of inhaled medication. This article focuses on recent strategies in imaging and physiological measurements of the lungs that allow the assessment of inhaled medication delivered to the periphery and discusses how these methods may help to further optimize and refine future aerosol delivery technology.

Bronchial nitric oxide flux (J'aw) is sensitive to oral corticosteroids in smokers with asthma

BACKGROUND

Exhaled nitric oxide provides a convenient, non-invasive insight into airway inflammation. However it is suppressed by current smoking, reducing its potential as an endpoint in studies of smokers with asthma, a group with increased symptoms and poor clinical responses to corticosteroids. We examined extended nitric oxide analysis as some derived variables are thought to be unaffected. Therefore this approach could reveal hidden inflammation and enable its use as an exploratory endpoint in this group.

METHODS

Smokers (n = 22) and never smokers (n = 21) with asthma performed exhaled nitric oxide measurements and spirometry before and after two weeks of oral dexamethasone (6 mg/1.74 m(2)/day). Linear and non-linear nitric oxide analysis was performed to derive estimates for alveolar nitric oxide (C(alv)) and nitric oxide flux (J'(aw)) for each subject.

RESULTS

FE(NO50) was significantly lower in smokers with asthma and did not change significantly in response to dexamethasone. C(alv) derived by linear modelling was lower in smokers with asthma and did not change significantly in response in either group. J'(aw) was substantially lower in smokers with asthma (smokers (median (IQR)); 573 pl/s (217, 734), non-smoker; 1535 pl/s (785, 3496), p = 0.001) and was reduced in both groups following dexamethasone (non-smokers change (mean (95% CI)); -743.3 pl/s (-1710, -163), p = 0.005, smokers; -293 pl/s (-572, -60), p = 0.016). Correction for axial flow did not substantially change the derived results.

CONCLUSIONS

Bronchial NO flux appears to be sensitive to oral dexamethasone and may provide a useful exploratory endpoint for the analysis of novel anti-inflammatory therapies in smokers with asthma.

Inflammation and airway function in the lung periphery of patients with stable asthma

BACKGROUND

An important role for exhaled nitric oxide (NO) measurement could be in the distinction between proximal and peripheral lung contributions to inflammation, with a particular interest for the alveolar lung zone and its implication on airway function.

OBJECTIVE

We aimed to isolate the acinar lung zone contribution to both inflammation and airway function to seek a relationship between them.

METHODS

In 30 patients with asthma with an asthma control test score exceeding 20, indices of conductive and acinar ventilation heterogeneity (Scond, Sacin) were obtained from a multiple breath washout. NO production in the conductive airways (J'aw(NO)), alveolar NO concentration (CA(NO)), and the standard exhaled NO at 50 mL/s (FENO(50)) were obtained from exhaled NO.

RESULTS

Scond was consistently abnormal in all patients with stable asthma, but without any correlation to inflammation abnormality in that compartment (J'aw(NO)). Sacin was particularly abnormal in the asthma subgroup receiving >500 microg budesonide equivalent, and a correlation was found between Sacin and CA(NO) (r = 0.61; P = .015); in this subgroup, a weak association was found between Scond and J'aw(NO) or FENO(50) (r = 0.50; P = .059 for both).

CONCLUSION

The persistent functional abnormality of small conductive airways in patients with stable asthma is largely independent of inflammation as measured by exhaled NO. In the alveolar compartment, a functional correlate of alveolar NO was found in a subgroup of patients with stable asthma on moderate-to-high maintenance doses of inhaled steroids. These patients in particular could benefit from novel therapies specifically aimed at improving airway functionality at the level of the acinar entrance and beyond.

Increased fraction of exhaled nitric oxide predicts new-onset wheeze in a general population

RATIONALE

Fraction of exhaled nitric oxide (Fe(NO)) is regarded as a marker of airway inflammation. It is unknown whether increased Fe(NO) in respiratorily healthy subjects increases the risk of developing wheeze.

OBJECTIVES

To examine if increased levels of Fe(NO) predicts later onset of wheeze.

METHODS

We followed up 2,200 men and women from a general population-based study. At baseline, the subjects were investigated with questionnaires, blood samples, pulmonary function tests, and Fe(NO). At follow-up 4 years later, all subjects were mailed a respiratory questionnaire. The association between incident wheeze and baseline levels of Fe(NO) over the 90th percentile were evaluated calculating hazard ratios using Cox regression models adjusted for smoking habits, age, height, sex, and atopy.

MEASUREMENTS AND MAIN RESULTS

The follow-up questionnaire was completed by 1,896 subjects (86.2%). All subjects reporting wheeze, asthma, or asthma symptoms at baseline were excluded resulting in a study population of 1,506 subjects. Of these, 49 subjects reported new-onset wheeze. The median concentration of Fe(NO) at baseline was significantly higher among those with new-onset wheeze (18.8 ppb vs. 15.8 ppb, P = 0.03). In a Cox regression model including all subjects, Fe(NO) over the 90th percentile predicted onset of wheeze (hazard ratio 2.7; 95% confidence interval, 1.4-5.4). In stratified models, this was most apparent among never-smokers and in atopic subjects, for whom the odds ratios were higher.

CONCLUSIONS

Our results indicate that increased Fe(NO) is associated with an increased risk of developing wheeze. The results also support the hypothesis that increased level of Fe(NO) among subjects without respiratory symptoms is a sign of subclinical airways inflammation.