FE(NO): relationship to exhalation rates and online versus bag collection in healthy adolescents

Association of Sputum Eosinophilia With Easily Measured Type-2 Inflammatory Biomarkers in Untreated Mild Persistent Asthma

BACKGROUND

A multicenter clinical trial in patients with mild persistent asthma indicated that response to inhaled corticosteroids (ICS) is limited to those with sputum eosinophilia. However, testing for sputum eosinophilia is impractical in most clinical settings.

OBJECTIVE

We examined associations between sputum eosinophilia and type 2 inflammatory biomarkers in untreated mild persistent asthma.

METHODS

Induced sputum, blood eosinophil count (BEC), fractional exhaled nitric oxide (FeNO), and serum periostin were obtained twice during the 6-week run-in period in a clinical trial that enrolled patients 12 years and older with symptomatic, mild persistent asthma without controller therapy. The optimal threshold for each biomarker was based on achieving 80% or greater sensitivity. Performance of biomarkers (area under the receiver operating characteristics curve [AUC], range 0.0-1.0) in predicting sputum eosinophilia 2% or greater was determined; AUCs of 0.8 to 0.9 and more than 0.9 define excellent and outstanding discrimination, respectively.

RESULTS

Of 564 participants, 27% were sputum eosinophilic, 83% were atopic, 70% had BEC of 200/uL or higher or FeNO of 25 ppb or greater; 64% of participants without sputum eosinophilia had elevated BEC or FeNO. The AUCs for BEC, FeNO, and both together in predicting sputum eosinophilia were all below the threshold for excellent discrimination (AUC 0.75, 0.78, and 0.79, respectively). Periostin (in adults) had poor discrimination (AUC 0.59; P = .02).

CONCLUSIONS

In untreated mild persistent asthma, there is substantial discordance between sputum eosinophilia, BEC, and FeNO. Until prospective trials test the ability of alternative biomarkers to predict ICS response, BEC or FeNO phenotyping may be an option to consider ICS through a shared decision-making process with consideration of other clinical features.

Clinical Utility Of The Exhaled Nitric Oxide (NO) Measurement With Portable Devices In The Management Of Allergic Airway Inflammation And Asthma

Nitric oxide (NO) is a potential bioactive gas produced continuously and constantly in the airways of healthy subjects. In allergic airway inflammation, the level of exhaled NO is usually increased and mediated by inducible nitric oxide synthase (iNOS) enzyme presenting in the epithelium and different inflammatory cells. The measurement of NO concentration in the airway is possible with portable devices which use an electroluminescence technique. In subjects with upper airway with allergic inflammation such as in allergic rhinitis, the measurement of nasal NO (nNO) may help to diagnose and manage the disease. In the lower airway, increased fractional exhaled NO (FENO) reflects directly the inflammatory process that occurs in the airways that are typically seen in asthma. It has been shown that there is a strong correlation between FENO levels and increased activity of airway inflammation mediated by immuno-allergic cells and mediators. Thus, FENO has higher specificity and sensitivity than other methods in diagnosing the severity of inflammation in asthmatic patients. Moreover, the correlation between increased FENO levels and a high risk of bronchial hyperresponsiveness has also been demonstrated. FENO is also a relevant biomarker to evaluate asthma status due to the change of its values occurring earlier than clinical manifestations and spirometry parameters. In addition, the measurement of FENO with portable devices helps to support the diagnosis of asthma, to follow-up the control of asthma and to personalize asthmatic patients for target treatment with biologic therapy. Therefore, measuring FENO with portable devices in the diagnosis and treatment of allergic airway inflammation, especially in asthma, is one of the most essential applications of NO biomarkers in exhaled breath.

Nitric Oxide in the Pathogenesis and Treatment of Tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is globally known as one of the most important human pathogens. Mtb is estimated to infect nearly one third of the world's population with many subjects having a latent infection. Thus, from an estimated 2 billion people infected with Mtb, less than 10% may develop symptomatic TB. This indicates that the host immune system may constrain pathogen replication in most infected individuals. On entering the lungs of the host, Mtb initially encounters resident alveolar macrophages which can engulf and subsequently eliminate intracellular microbes via a plethora of bactericidal mechanisms including the generation of free radicals such as reactive oxygen and nitrogen species. Nitric oxide (NO), a key anti-mycobacterial molecule, is detected in the exhaled breath of patients infected with Mtb. Recent knowledge regarding the regulatory role of NO in airway function and Mtb proliferation paves the way of exploiting the beneficial effects of this molecule for the treatment of airway diseases. Here, we discuss the importance of NO in the pathogenesis of TB, the diagnostic use of exhaled and urinary NO in Mtb infection and the potential of NO-based treatments.

Normal values of offline exhaled and nasal nitric oxide in healthy children and teens using chemiluminescence

Nitric oxide (NO) can be used to detect respiratory or ciliary diseases. Fractional exhaled nitric oxide (FeNO) measurement can reflect ongoing eosinophilic airway inflammation and has a diagnostic utility as a test for asthma screening and follow-up while nasal nitric oxide (nNO) is a valuable screening tool for the diagnosis of primary ciliary dyskinesia. The possibility of collecting airway gas samples in an offline manner offers the advantage to extend these measures and improve the screening and management of these diseases, but normal values from healthy children and teens remain sparse.

METHODS

Samples were consecutively collected using the offline method for eNO and nNO chemiluminescence measurement in 88 and 31 healthy children and teens, respectively. Offline eNO measurement was also performed in 30 consecutive children with naïve asthma and/or respiratory allergy.

RESULTS

The normal offline eNO value was determined by the following regression equation -8.206 + 0.176 × height. The upper limit of the norm for the offline eNO value was 27.4 parts per billion (ppb). A separate analysis was performed in children, pre-teens and teens, for which offline eNO was 13.6 ± 4.7 ppb, 16.3 ± 13.7 ppb and 20.0 ± 7.2 ppb, respectively. The optimal cut-off value of the offline eNO to predict asthma or respiratory allergies was 23.3 ppb, with a sensitivity and specificity of 77% and 91%, respectively. Mean offline nNO was determined at 660 ppb with the lower limit of the norm at 197 ppb.

CONCLUSION

The use of offline eNO and nNO normal values should favour the widespread screening of respiratory diseases in children of school age in their usual environment.

Head-to-head comparison of single-breath and tidal-breath exhaled nitric oxide measurements

BACKGROUND

Exhaled nitric oxide (eNO) is an endogenous gas involved in airway pathophysiology and is determined in orally exhaled air by various techniques. However, traditional single-breath technique (eNO(SB)) requires active cooperation and is not always easily practicable (especially in young children); simpler techniques including tidal breathing measurements (eNO(TB)) are not standardized. The aim of this study was to evaluate the possible correlation and correspondence between eNO(SB) and eNO(TB) and the impact of potential confounders in children with chronic adenotonsillar disease.

METHODS

Eighty-six children (mean age 8.7 ± 3.2 y) underwent eNO assessment by means of eNO(SB) and eNO(TB). The correlation among eNO(TB), eNO(SB), and other potential confounders (i.e., gender, age, weight, height, BMI, and passive smoking exposure) were studied.

RESULTS

The analyses showed a poor correspondence between eNO(SB) and eNO(TB), with the latter underestimating (P < 0.001) mean eNO values: 6.4 parts per billion (ppb) (95% confidence interval (CI): 8.4-11.4 ppb) vs. 9.8 ppb (95% CI: 5.6-7.3 ppb). A greater correlation was found between eNO(SB) and eNO(TB) in children younger than 6 y. Only eNO(SB) and age predicted eNO(TB) (R2 = 43.6%).

CONCLUSION

eNO(TB) is not a good predictor of eNO(SB) in children. Constant-flow eNO(SB) is the technique of choice for eNO assessment in young children.

Exhaled nitric oxide concentration upon acute exposure to moderate altitude

The purpose of this study was to assess immediate changes in the partial pressure of nitric oxide (NO) in exhaled gas (PE NO ) in healthy trained subjects who were acutely exposed to moderate altitude. One group of nine and another group of 20 healthy subjects were exposed to an ambient pressure of 728 hPa (546 mmHg) corresponding to an altitude of 2800 m for 5 and 90 min, respectively, in an altitude chamber. PE NO was measured offline by sampling exhaled gas in tight metal foil bags at 5, 30, 60, and 90 min. A correction for increased expiratory flow rate due to gas density effects at altitude was performed (PE NO corr). PE NO was significantly decreased by 13-16%, while the fraction of NO in exhaled gas (FE NO) was increased by 16-19% compared to sea level. There was no significant change in PE NO corr after exposure to altitude for 5, 30, 60, and 90 min. We conclude that there was no change in PENO upon arrival at altitude after correcting for gas density effects on expiratory flow rate. Corrections for altitude effects must be done before comparing measurements performed at different altitudes when using measurements of FENO to monitor athletes who have asthma during training at altitude.

Exhaled nitric oxide in asthma: progress since the introduction of standardized methodology

The measurement of nitric oxide (NO) in exhaled breath has given us the ability to learn about and monitor the inflammatory status of the airway through a non-invasive method that is easy to perform and repeat. This has been most useful in the diagnosis and management of asthma and has promised a seemingly unlimited potential for evaluating the airways and how clinical decisions are made (Grob N M and Dweik R A 2008 Chest133 837-9). The exhaled NO field was initially limited, however, due to the absence of standardized methodology. The ATS and ERS jointly released recommendations for standardized methods of measuring and reporting exhaled NO in 1999 that were revised in 2005 (1999 Am. J. Respir. Crit. Care. Med. 160 2104-17; 2005 Am. J. Respir. Crit. Care. Med. 171 912-30). In this paper, we summarize the literature that followed this standardization. We searched the literature for all papers that included the term 'exhaled nitric oxide' and selected those that followed ATS guidelines for online measurement for further review. We also reviewed cut-off values suggested by groups studying exhaled nitric oxide. We found a wide range of NO values reported for normal and asthma populations. The geometric mean for FE(NO) ranged from 10 ppb to 33 ppb in healthy adult control populations. For asthma, the FE(NO) geometric mean ranged from 6 ppb to 98 ppb. This considerable variation likely reflects the different clinical settings and purposes of measurement. Exhaled NO has been used for a multitude of reasons that range from screening, to diagnosis, to monitoring the effect of therapy. The field of exhaled NO has made undeniable progress since the standardization of the measurement methods. Our challenge now is to have guidelines to interpret exhaled NO levels in the appropriate context. As the utility of exhaled NO continues to evolve, it can serve as a good example of the crucial role of the standardization of collection and measurement methods to propel any new test in the right direction as it makes its way from a research tool to a clinically useful test.

Effects of age, gender, and environmental exposures on exhaled nitric oxide level in healthy 12 to 18 years Qatari children

CONTEXT:

Fractional exhaled nitric oxide (FENO) is a useful noninvasive diagnostic tool for asthma and some other pediatric respiratory diseases. Factors affecting FENO level are variable in different populations and studies.

AIMS:

To estimate the normal values of exhaled nitric oxide for Qataris 12 to 18 years of age. Other objectives were to measure the correlation of anthropometric and other potential factors with FENO levels.

SETTINGS AND DESIGN:

Community-based, cross-sectional study.

METHODS:

A total of 438 Qatari national school children from both genders were randomly recruited in cross-sectional study. Of them, 203 were non-atopic and hence included in the statistical analysis. Questionnaires including personal data, demographic data, and other factors that may affect FENO level were distributed.

STATISTICAL ANALYSIS USED:

Comparison of means done using t-test. We performed Spearman's rho test to measure correlations. Data analysis was done using PASW 18.0 Release 18.0.0, 2009.

RESULTS:

The geometric mean of FENO levels for all subjects was 14.1 ppb (upper level CI 95% - 36.3 ppb). FENO was significantly higher in males (R² = −0.254, P<0.0001) and was negatively correlated with increasing age for the whole study population (P=0.036). This decline was interrupted by a significant upraise at the age of 15 years (P=0.0462) which seems to be driven by the males (P=0.0244). FENO levels were lower in subjects exposed to cats (P=0.019). We could not find significant correlation between FENO and other factors studied.

CONCLUSIONS:

Estimated FENO level with 95% CI in Qatari children, which is probably close to those in other Gulf countries, will be helpful clinically. The lower level of FENO with female gender, increasing age, and exposure to cats needs to be further studied to establish the association and to understand the underlying mechanisms.

Exhaled nitric oxide in pediatrics: what is new for practice purposes and clinical research in children?

Fractional exhaled NO (FeNO) is universally considered an indirect marker of eosinophilic airways inflammation, playing an important role in the physiopathology of childhood asthma. Advances in technology and standardization have allowed a wider use of FeNO in clinical practice in children from the age of four years. FeNO measurements add a new dimension to the traditional clinical tools (symptoms scores, lung function tests) in the assessment of asthma. To date a number of studies have suggested a possible use of FeNO in early identification of exacerbation risk and in inhaled corticosteroids titration. The aim of this paper is to address practical issues of interest to paediatric clinicians who are attempting to use FeNO measurements as an adjunctive tool in the diagnosis and management of childhood airway diseases.

Exhaled nitric oxide levels and lung function changes of underground coal miners in Newcastle, Australia

The possibility of exhaled nitric oxide (eNO) in combination with lung function as a marker of airway inflammation produced by coal mining exposure was determined presuming that workers exposed to airborne hazards would possess different concentrations of eNO and decreased lung function indices, relative to control subjects recruited from the same area. The effect of smoking was also considered. A study (exposed) group comprising 186 male subjects (aged 19-58 yr) was recruited from Newcastle coal mining companies with 86 male subjects (aged 20-64 yr) from the same area, but working outside of the coal mining location, serving as controls. The parameters examined were eNO, lung function, and variables derived from an interview-administered questionnaire survey. After adjustment for age, body weight, and smoking status, no significant differences between exposed coal mining workers and controls were found for various lung function parameters. However, the exposed group was shown to have significantly lower concentrations of eNO. In the exposed group, forced expiratory volume in 1 s (FEV(1)), forced vital capacity (FVC), and FEV(1) (%) predicted were found to be significantly different between nonsmokers and smokers. The concentrations of eNO were not significantly different between smoking and nonsmokers within the exposed group. The consideration of nonsmokers alone showed that eNO was significantly lower in the exposed group compared to the control group. The consideration of smokers alone found that eNO was significantly lower in exposed subjects. In the exposed group, no significant association was detected between eNO levels and underground work duration but a significant negative association was shown between eNO and age. Data suggest that exposure to airborne hazards in coal mining is not significantly associated with lung function changes but is correlated with decreased eNO concentrations in exposed workers. While underground work duration was not found to be significantly associated with eNO concentrations in coal mining workers in this study, the potential for using eNO as a monitoring marker still exists and further studies are needed to establish its importance.

Fractional exhaled nitric oxide in asthma: an update

In asthma, clinical symptoms and lung function are insensitive in reflecting the underlying airway inflammation, and monitoring of this process has only recently become available. Fractional exhaled nitric oxide (Fe(NO)) is now recognized as a reliable surrogate marker of eosinophilic airway inflammation and offers the advantage of being completely non-invasive and very easy to obtain. This review summarizes the clinical use of Fe(NO) in asthma. It covers the relationship between Fe(NO) and the underlying eosinophilic inflammation, the pathophysiology and production of Fe(NO), technical aspects of Fe(NO) measurement and potential confounding factors in interpreting levels. Fe(NO) reference values and the role of Fe(NO) in asthma assessment, diagnosis and management are also discussed.

Exhaled nitric oxide in the diagnosis and management of asthma: clinical implications

Exhaled nitric oxide (eNO) used as an aid to the diagnosis and management of lung disease is receiving attention from pulmonary researchers and clinicians alike because it offers a noninvasive means to directly monitor airway inflammation. Research evidence suggests that eNO levels significantly increase in individuals with asthma before diagnosis, decrease with inhaled corticosteroid administration, and correlate with the number of eosinophils in induced sputum. These observations have been used to support an association between eNO levels and airway inflammation. This review presents an update on current opportunities regarding use of eNO in patient care, and more specifically on its potential usage for asthma diagnosis and monitoring. The review will also discuss factors that may complicate use of eNO as a diagnostic tool, including changes in disease severity, symptom response, and technical measurement issues. Regardless of the rapid, convenient, and noninvasive nature of this test, additional well-designed, long-term longitudinal studies are necessary to fully evaluate the clinical utility of eNO in asthma management.

[Exhaled nitric oxide in children: a noninvasive marker of airway inflammation]

This article is an academic review of the application in children of the measurement of fractional exhaled nitric oxide (FENO). We outline the joint American Thoracic Society/European Respiratory Society recommendations for online measurement of FENO in both cooperating children and children unable to cooperate, offline measurement with uncontrolled exhalation flow rate, offline measurement with controlled exhalation flow rate using a dynamic flow restrictor, and offline measurement during tidal breathing in children unable to cooperate. This is followed by a review of the normal range of values for single-breath online measurements obtained with a chemiluminescence FENO analyzer (geometric mean, 9.7 parts per billion [ppb]; upper limit of the 95% confidence interval, 25.2 ppb). FENO values above 17 ppb have a sensitivity of 81% and a specificity of 80% for predicting asthma of an eosinophilic phenotype. We discuss the response of FENO values to anti-inflammatory treatment and the use of this marker in the management of asthma. Results obtained with chemiluminescence and portable electrochemical analyzers are compared. The portable devices offer the possibility--in children over 5 years of age--of accurate and universal monitoring of exhaled nitric oxide concentrations, an emerging marker of eosinophilic inflammation in asthma that facilitates diagnosis, monitoring of disease progression, and assessment of response to therapy.

A flow- and pressure-controlled offline method of exhaled nitric oxide measurement in children

BACKGROUND

Exhaled nitric oxide (eNO) is a noninvasive marker of airway inflammation. However, previous studies show that the offline value is lower than the online value.

OBJECTIVE

To compare a standard offline eNO measurement apparatus with a modified apparatus that can monitor flow volume and respiratory pressure.

METHODS

We studied 73 cooperative individuals aged 5 to 28 years (32 children: mean age, 8.3 years; 41 adults: mean age, 21.5 years). We modified the standard device by including a flow meter with a manometer and attaching a plastic tube connected to a 3-way valve to control the resistance. The online and offline (measured using the modified device and the standard device) eNO determinations were compared in a single session and were analyzed using a nitric oxide analyzer.

RESULTS

There was a good relationship between the online and modified offline eNO measurements in children. The modified offline method showed a stronger correlation with the online method (r = .97 vs. r = .92), and the modified offline eNO value was more similar to the online eNO value than to the standard offline value. The mean difference between the online and standard offline eNO values was 52%, whereas the mean difference between the online and modified offline eNO values was only 10%.

CONCLUSIONS

Using the offline method, we can easily control the resistance and flow volume to reach the same value measured by the online method in childhood respiratory diseases.

Height, age, and atopy are associated with fraction of exhaled nitric oxide in a large adult general population sample

STUDY OBJECTIVES

The fraction of exhaled nitric oxide (Feno) is elevated in subjects with asthma and atopy, and it has been proposed to be a noninvasive marker of airway inflammation. In addition to asthma and atopy, there is limited information about the determinants of Feno in a general population.

DESIGN

Cross-sectional.

SETTING

A random adult general population sample.

PARTICIPANTS

A total of 2,200 subjects, 1,111 women and 1,089 men, aged 25 to 75 years.

INTERVENTIONS

The subjects were examined with regard to Feno, pulmonary function, anthropometric variables, and blood samples for Ig E, and completed a respiratory questionnaire. The associations between different determinants and Feno were analyzed with multiple linear regression models.

RESULTS

The median value of Feno was 16.0 parts per billion (ppb), ranging from 2.4 to 199 ppb. Height, age, atopy, reporting of asthma symptoms in the last month, and reported use of inhaled steroids were positively associated with Feno. Current smokers had lower values of Feno. Gender was not associated with Feno.

CONCLUSIONS

In this random adult population sample, height, but not gender, was associated with Feno. Furthermore, asthma symptoms in the last month, reported use of inhaled steroids, and atopy were positively and independently associated with Feno, while there was a negative association with smoking.

Reference values for exhaled nitric oxide (reveno) study

Background

Despite the widespread use of fractional exhaled nitric oxide (FE_NO) as a biomarker of airways inflammation, there are no published papers describing normal FE_NO values in a large group of healthy adults.

Objective

The aim of this study was to establish adult FE_NO reference values according to the international guidelines.

Methods

FE_NO was measured in 204 healthy, non-smoking adults with normal spirometry values using the on-line single-breath technique, and the results were analysed chemiluminescently.

Results

The main result of the study was the significant difference in FE_NO values between men and women, thus indicating that gender-based reference FE_NO values are necessary. The FE_NO levels obtained at expiratory flows of 50 ml/s ranged from 2.6 to 28.8 ppb in men, and from 1.6 to 21.5 ppb in women.

Conclusion

We propose reference FE_NO values for healthy adult men and women that could be used for clinical and research purposes.

Assaying all of the nitrogen oxides in breath modifies the interpretation of exhaled nitric oxide

Exhaled nitric oxide (NO) assays measure the quantity of NO that emanates from the airway, not the amount of NO that is formed. Consumptive processes-including oxidation reactions-decrease the amount of gas phase NO available for exhalation. Higher oxides of nitrogen (HiNO(x)) are resulting reaction products, and are easily measured in exhaled breath condensate (EBC). We performed concurrent sampling of exhaled breath for gas phase NO and EBC HiNO(x) in controls and stable asthmatics. We identified that, mole for mole, asthma patients hourly exhale more HiNO(x) than they do NO, with a HiNO(x)/NO ratio of 1.21 (0.54-3.4). This is the reverse of the ratio found in controls, in whom the HiNO(x)/NO ratio was 0.75 (0.44-0.93), p=0.04. The sum of the hourly molar exhalation of NO and HiNO(x) was significantly higher in asthmatics (333 nmol/h (221-543) than controls (179 (138-231), p<0.001). We conclude that exhaled oxides of nitrogen are more informative when measured together as opposed to in isolation. We suggest that inflammation can be better evaluated with HiNO(x) and NO measured concurrently, and that the level of oxidation in the lung can be evaluated by comparing the easily measured ratios of HiNO(x) to NO in the exhaled breath.

Measurement of exhaled nitric oxide in young children during tidal breathing through a facemask

Measurement of exhaled nitric oxide (eNO) offers a non-invasive means for assessment of airway inflammation. The currently available methods are difficult to apply in preschool children. We evaluated four methods potentially applicable for eNO measurement during tidal breathing in young children. eNO was assessed during tidal breathing in 24 children, 2-7 yr old, using a facemask which separated nasal and oral airflow. Facemasks with and without a one-way valve allowing exhalation through the nose were used. Expiratory flow control was not attempted. Measurements of eNO were performed both on-line and off-line. In 11 children, 8-12 yr old, measurements were compared with the standard single breath on-line method. eNO was significantly lower applying the one-way valve in on-line and off-line measurements in comparison with measurements without the valve [4.6 and 3.9 parts per billion (ppb) vs. 6.9 ppb and 6.5 ppb]. The mean within subject coefficient of variation (CV) was significantly lower in on-line measurements with the one-way valve (9.6%) compared with the other three methods (18.8, 27.7 and 29.3% respectively). Measurements with a facemask fitted with a one-way valve yielded similar eNO levels as the standard single breath method (7.0 ppb vs. 6.9 ppb) and reproducibility (9.8% vs. 7.1%). In conclusion, reproducible measurements of eNO can be obtained without control of expiration flow using a facemask fitted with a one-way valve on the nasal compartment. The likely explanation to this is that the one-way valve reduces the admixture of nasal NO, thereby improving the reliability of eNO measurements.

Minimal exhaled nitric oxide production in the lower respiratory tract of healthy children aged 2 to 7 years

BACKGROUND

Exhaled nitric oxide (eNO) is elevated in inflammatory airway conditions, e.g. asthma. We measured eNO levels in normal preschool children for whom there is little data available and in whom the prevalence of asthma is high.

SUBJECTS AND METHODS

Fifty children, 2-7 years old, undergoing elective surgery, excluding airway procedures, were recruited. Children with known respiratory disease or acute viral infections were excluded. Gas for eNO measurement was collected in a non-diffusion bag via 1) the mask after inhalation induction of anesthesia, 2) endotreacheal tube (ETT) or laryngeal mask airway (LMA), and 3) during emergence. Measurement was off-line by chemiluminescent analyzer.

RESULTS

Mean eNO level by mask was 10.23 ppb (mean value+/-SD of 8.8-11.1 ppb) after induction and 8.35 ppb (mean value+/-SD of 5.9-10.8 ppb) on emergence. Mean eNO for the intubated group (n=25) was 0.75 ppb (mean value+/-SD of 0.4-1 ppb) (P<0.0001 vs mask); mean eNO for the LMA group (n=25) was 2.6 ppb (mean value+/-SD of 2-3.2 ppb), which differed from the mask (P<0.0001), and from ETT values (P<0.0001).

CONCLUSIONS

Most eNO is produced by the upper airway in healthy pre-school children. The lower airway constitutive eNO production is very low. The LMA does not completely isolate the upper airway and current mask collection techniques allow significant contamination of samples by sino-nasal eNO production in young children.

Measuring exhaled nitric oxide levels in adults: the importance of atopy and airway responsiveness

BACKGROUND

Raised exhaled nitric oxide (Feno) levels have been associated with asthma. However, we have found that in children, Feno was increased in atopic children with increased airway responsiveness (AR), and this was independent of a diagnosis of asthma.

STUDY OBJECTIVES

The current study was designed to test the hypothesis that in adults there is no association between Feno and asthma after controlling for atopy and AR.

MEASUREMENTS

One hundred fifteen adults (77 women; mean age, 41 years) underwent an assessment that included Feno measurements, spirometry, skin-prick testing, blood eosinophil count, and inhaled histamine challenge (results are expressed as a dose-response slope [DRS]).

RESULTS

When only atopic individuals were considered (n = 73), Feno was positively associated with the DRS (p = 0.003), male gender (0.02), and negatively associated with current smoking (p = 0.09). Only male gender (p = 0.03) was associated with Feno among nonatopic individuals (n = 36). In multivariate analysis, there was no association between Feno and current asthma, current wheeze, or asthma ever.

CONCLUSIONS

We conclude that in adult subjects, elevated Feno measurements are associated with a phenotype characterized by atopy and increased AR regardless of the presence of asthma or asthma-like symptoms.

[The measurement of exhaled nitric oxide, a new tool in the management of asthma?]

A GOOD DIAGNOSTIC TEST FOR ASTHMA: Chronic airway inflammation, main feature of asthma, can be assessed by measuring the exhaled nitric oxide (NO) level. Measurement of NO is standardized, non-invasive and easy to use in both children and adults. Studies have shown that it is a good diagnostic test for asthma when NO is high. However, other conditions or pathologies must be searched for because they may influence the results. ITS PLACE IN TREATMENT: Although exhaled NO helps to characterise the patients with asthma, other studies are required to show that it can help to improve the follow-up of such patients. Nevertheless, this tool has not yet been validated in the daily treatment of asthma and further research is still ongoing.

Exhaled nitric oxide and asthma: complex interactions between atopy, airway responsiveness, and symptoms in a community population of children

BACKGROUND

Exhaled nitric oxide (FE(NO)) is raised in asthmatic children, but there are inconsistencies in the relationship between FE(NO) and characteristics of asthma, including atopy, increased airway responsiveness (AR), and airway inflammation. The aim of this study was to investigate the relationship between FE(NO) and asthma, atopy, and increased AR in children.

METHODS

One hundred and fifty five children (79 boys) of mean age 11.5 years underwent an assessment that included FE(NO) measurements, spirometric tests, inhaled histamine challenge, and a skin prick test. Blood was collected for eosinophil count. Current and past asthma like symptoms were determined by questionnaire.

RESULTS

In multiple linear regression analyses FE(NO) was associated with atopy (p<0.001), level of AR (p = 0.005), blood eosinophil count (p = 0.007), and height (p = 0.002) but not with physician diagnosed asthma (p = 0.1) or reported wheeze in the last 12 months (p = 0.5). Separate regression models were conducted for atopic and non-atopic children and associations between FE(NO) and AR, blood eosinophils and height were only evident in atopic children. Exhaled NO was raised in children with a combination of atopy and increased AR independent of symptoms.

CONCLUSION

Raised FE(NO) seems to be associated with an underlying mechanism linking atopy and AR but not necessarily respiratory symptoms.

Measuring exhaled nitric oxide in infants during tidal breathing: methodological issues

Exhaled nitric oxide (FENO) may provide a tool for identifying infants at risk of developing allergic disease in childhood. In infants there is no standardized collection technique; however, the easiest method is to measure FENO during tidal breathing. In this study we investigated various methodological issues for tidal breathing (TB) FENO in infants. These included the effect of ambient NO, oral or nasal breathing, sedation, and tidal expiratory flow. Furthermore, we compared TB FENO in 88 infants with and without wheeze. Ambient NO greater than 5 ppb significantly affected FENO. There was no significant difference between NO levels measured during either oral or nasal breathing; however, there was a significant difference between levels collected from infants before and after sedation (P < 0.001). Tidal breathing FENO decreased with increasing tidal flows (P < 0.001) and increased with age (P = 0.002). There was no significant difference in mixed expired NO between healthy and wheezy children, but children with doctor-diagnosed eczema had significantly raised levels (P = 0.014). There seem to be important methodological limitations for measuring FENO in infants during TB.

Exhaled nitric oxide reflects asthma severity and asthma control

INTRODUCTION

This study was undertaken to a) evaluate whether exhaled nitric oxide (fraction of exhaled nitric oxide [FENO]) levels are reflective of asthma severity in concordance with the National Asthma Education and Prevention Program categorization and b) determine the usefulness of FENO using the single-breath exhalation technique for monitoring asthma control and compliance with steroid treatment.

METHODS

Thirty patients with asthma (7-17 yrs old; 14 males and 16 females) that was mild (n=8), moderate (n=17), or severe (n=5) were included in the study. Fifteen patients were seen on more than one occasion for a total of 53 visits. Information obtained at each visit included asthma symptoms, beta-agonists and corticosteroids use, compliance to steroids, and forced expiratory volume in 1 sec (FEV1) and FENO measurements. Asthma control was judged by a pulmonologist based on overall evaluation of symptoms, FEV1 measurements, and the frequency of beta-agonists use at each visit.

RESULTS

The mean +/- SD FENO was significantly different in the mild, moderate, and severe asthma categories (30 +/- 12, 65 +/- 48, 104 +/- 68, respectively; F(2,52)=6.02 p=.005). FENO was significantly correlated with asthma severity (r=.44, p=.001), compliance (r=-.75, p=.001), and control (r=-.51, p=.001). There were no statistically significant differences between asthma severity and compliance or FEV1.

DISCUSSION

Our data suggest that a) FENO may be a practical tool to evaluate asthma severity and asthma control over time and b) FENO may be used as a marker of compliance with steroids even when FEV1 has not decreased significantly.

NOS1 polymorphism is associated with atopy but not exhaled nitric oxide levels in healthy children

Exhaled nitric oxide (FENO) is raised in atopy. The mechanism for this is unclear. The aim of this study was to investigate whether the number of AAT repeats in intron 20 of the NOS1 gene, recently associated with variations in FENO in adults with asthma and cystic fibrosis, was associated with the raised FENO in healthy atopic children. Eighty-seven healthy children (44 girls, 42 atopic, age range 6-18 years) underwent measurements of FENO, spirometry, airway responsiveness and skin prick testing. Genotyping was carried out to determine the number of AAT repeats. There was no association between the number of AAT repeats and FENO in either the whole sample of healthy children (n = 87) or in the subsample of healthy atopics (n = 42). However, a greater number of atopic children had two high repeat alleles compared with non-atopic children (33.3% vs. 13.6%, respectively, p = 0.03). This suggests that variations in the NOS1 gene may contribute to atopy without this relationship being reflected by FENO.

Flow dependency and off-line measurement of exhaled NO in children

Levels of exhaled nitric oxide (eNO) are flow-dependent, and the choice of an optimal flow rate for off-line and on-line eNO measurement has raised much debate. Recently, a flow rate of 50 ml/s was recommended, but children younger than 5-6 years are not capable of stabilizing their expiratory flow at low flow rates. The power of off-line eNO values to discriminate between normal and atopic children was therefore evaluated at different exhalation flow rates. At flow rates of both 8.3 ml/s and of 350 ml/s, children (8-12 years) sensitive to house dust mite have two-fold higher eNO values (p < 0.001) as compared with children lacking such a sensitivity. The power of eNO to discriminate between normal and atopic subjects was similar at the two flow rates (no difference in AUC of receiver operation curves, p = 0.89). All children from 4.5 to 5 years of age (n = 29) could perform a single off-line exhalation manoeuvre at high (>350 ml/s) but not at low (8.3 ml/s) flow rates. At high exhalation flow rate, eNO was 7.1 +/- 2.4 (mean +/- SD) median, 6.5 p.p.b. with a mean variation coefficient of 5.5%. Depending on their developmental level, about half of the younger children (35-46 months of age) could perform an off-line exhalation manoeuvre at high flow rate with good reproducibility (mean variation coefficient of 6.6%). It is concluded that an exhalation flow rate of 350 ml/s is feasible to determine off-line eNO-values in children from 3.5 years of age, and that this high flow rate does not compromise the power of eNO to detect allergic disease.

Effects of sex and of gene variants in constitutive nitric oxide synthases on exhaled nitric oxide

Genetic factors may contribute to the variability of exhaled nitric oxide in healthy individuals. We studied exhaled nitric oxide and genetic variants in both neuronal and endothelial nitric oxide synthases in 105 healthy nonsmoking and smoking subjects. Genomic DNA was screened for a repeat polymorphism in intron 20 of the neuronal nitric oxide synthase gene and for the 894G/T mutation of the endothelial nitric oxide synthase gene. Exhaled nitric oxide was significantly higher in males than females among both nonsmokers (p < 0.0001) and smokers (p = 0.003). No association was found between exhaled nitric oxide and the endothelial nitric oxide synthase gene variant. However, healthy nonsmoking females with greater numbers of repeats (i.e., both alleles with 12 or more repeats) in neuronal nitric oxide synthase had significantly lower nitric oxide levels than did females with fewer numbers of repeats (i.e., at least one allele with fewer than 12 repeats) (13.6 +/- 1.6 versus 19.4 +/- 1.6 ppb, p = 0.02). No association was found between exhaled nitric oxide and neuronal nitric oxide synthase genotype in males. These data suggest that variants in the neuronal nitric oxide synthase gene contribute to the variability of airway nitric oxide concentrations in healthy females.

Exhaled nitric oxide measurements in childhood asthma: comparison of two sampling techniques

Nitric oxide (NO) is being increasingly used to assess airway inflammation in childhood. The method recommended by the American Thoracic Society workshop is for a prolonged expiration against a resistance. However, this is very difficult to apply in young children. As a result there have been a number of studies in which mixed expired gas has been collected and analyzed for NO content as this requires very little cooperation. This method has, however, yet to be fully validated. The aims of this study were to compare the two sampling techniques of exhaled NO concentrations in asthmatic and healthy children and to assess the correlation between NO levels and spirometry values in asthmatic children We studied 25 control children, mean age 11.5 y, and 20 asthmatics, mean age 12 y. The exhaled NO was sampled using both the single breath technique (SB) and by measuring the NO content in mixed expired air after 1 min tidal breathing (ME). Forced expiratory volume in 1 s (FEV(1)) and expiratory flow rates at 25%, 50%, and 75% of vital capacity (FEF(25), FEF(50), FEF(75), respectively) were measured by compact II spirometer (best of three) in the 20 asthmatic children. The NO level was significantly higher in the asthmatics versus the control children when measured by SB (p = 0.0015) but not when measured by ME (p = 0.1913). The NO results measured by SB were significantly higher than ME results in the asthmatic children (p = 0.008). The NO levels were negatively correlated to FEV(1), FEF(25), FEF(50), and FEV(75) when measured by SB (p < 0.02) but not when measured by ME. The SB but not the ME method for measuring expired NO discriminates between asthmatic and control children and correlates well with the degree of airway obstruction. The use of the ME technique remains unproven.

Effect of beta2-agonist treatment and spirometry on exhaled nitric oxide in healthy children and children with asthma

We set out to determine the effect of spirometry and bronchodilator therapy on exhaled nitric oxide (FE(NO)) values in children. We hypothesized that there will be no difference on FE(NO) values pre- and postspirometry and following bronchodilator therapy. Sixteen children [(mean = 14.4 +/- 1.2 years; range, 12-18 years; healthy controls (n = 6); asthmatics on inhaled steroids (n = 5); and asthmatics on no steroids (n = 5)] had exhaled nitric oxide (FE(NO)) measurements on 4 consecutive days as follows: pre- and postspirometry (day 1); pre- and postalbuterol metered dose inhaler (MDI) therapy (day 2); pre- and postspirometry and albuterol MDI therapy (day 3); and pre- and postspirometry and placebo MDI (day 4). FE(NO) was measured with a chemiluminescence analyzer, using the single vital capacity exhalation technique at an exhalation flow of 50 mL/sec. There were no statistically significant differences in FE(NO) values pre- and poststudy maneuvers under all experimental conditions in healthy children. However, in healthy children, clinically relevant (>10%) differences from baseline were observed on day 1 (3-18 min) and day 4 at 18 min. In children with asthma, FE(NO) values increased significantly by 11-19% from pretreatment levels at 8 and 18 min, postbronchodilator on day 2, and 12-17% at 8 and 18 min post bronchodilator and spirometry on day 3. Spirometry and treatment with a placebo (day 4) resulted in a decrease in FE(NO) values by 11% at 3 min postbaseline in patients on inhaled steroids. The changes observed were similar in children on vs. off inhaled steroids, and also in well-controlled vs. poorly controlled asthma. We conclude that FE(NO) values should be obtained consistently either pre- and at a specific time postalbuterol treatment or spirometry. Alternatively, changes in FE(NO) values should be interpreted in relationship to the timing of these maneuvers.

Exhaled nitric oxide as a diagnostic test for asthma: online versus offline techniques and effect of flow rate

Measurement of the fraction of exhaled nitric oxide (FENO) has been proposed as a noninvasive assessment of asthmatic airway inflammation. The influence of the expiratory flow rate during the collection maneuver on the ability of FENO to discriminate healthy subjects from those with asthma is unknown. We compared online and offline measurement of FENO at different flow rates. FENO was collected with expiratory flows of 50-500 ml/second in 34 patients with asthma (PC(20) of less than 8 mg/ml) and 28 healthy subjects (PC(20) of more than 10 mg/ml) using offline collection techniques. In a subgroup of 18 individuals with asthma and 17 healthy subjects, we additionally measured FENO at multiple expiratory flow rates (47-250 ml/second) using online methods. FENO fell with an increasing expiratory flow rate; FENO was higher in subjects with asthma as compared with healthy subjects at each flow rate studied with both techniques (p < 0.001). Receiver operating characteristic (ROC) curves for the diagnosis of asthma indicated that FENO is a robust discriminator between individuals with asthma and healthy subjects (area under the ROC curves 0.79 +/- 0.06 to 0.86 +/- 0.06, p for significant discrimination < 0.0001). Neither expiratory flow rate nor collection technique (online versus offline) significantly altered this discriminatory capacity (area under the ROC curves = 0.84 +/- 0.07 with the slowest online method versus 0.80 +/- 0.07 with the fastest offline method, p = 0.46). These data indicate that the choice of expiratory flow rate and collection method can be based on practicality and patient comfort without compromising the utility of this test for asthma.

Acute asthma: under attack

The burden of asthma (death, disability, and an increasing prevalence) makes it a major public health problem worldwide. In an effort to decrease this burden, investigators are studying many aspects of this disease. The role of race, ethnicity, infections, and pollutants as triggers, as well as the risk factors are now being defined. Research into methods to decrease acute exacerbations and improve emergency and in-hospital management, using standardized protocols and incentives for follow-up care, has yielded valuable information but has met with limited success. Adherence to the national guidelines has been poor and to some extent can be attributed to the lack of a practical method of measuring the degree of lung inflammation and cumbersome treatment protocols. Exhaled nitric oxide is a noninvasive marker of inflammation and may provide a rational method to titrate corticosteroid and leukotriene receptor antagonist therapy. The best route and dosing regimen for corticosteroid administration (oral vs intramuscular vs nebulized) are the subject of several studies, with no clear-cut winner. The burden of asthma in developing countries with limited financial resources has also triggered a search for simpler, cheaper, and practical methods for beta-agonist delivery using indigenous spacers. Recent research in asthma has unveiled our incomplete knowledge of the disease but has also provided a sense of where efforts should be expended. Research into the genetics and pharmacogenetics of asthma and into the societal factors limiting the delivery of optimal care is likely to yield useful and practical information.

Exhaled nitric oxide concentrations: online versus offline values in healthy children

Exhaled nitric oxide (FE(NO)) is a noninvasive and practical method to assess airway inflammation. We conducted this investigation to determine the most appropriate flow rate to measure FE(NO) and to obtain reference values for FE(NO) in children. FE(NO) was measured in 112 healthy 6-18 year olds (60 males) at 4 expiratory flow rates (46, 31, 23, and 15 mL/sec) using a chemiluminescent nitric oxide analyzer. Offline and online analyses were done to determine FE(NO) intraclass correlation coefficients, the relationship between FE(NO) and expiratory flow rates, and the effects of age and gender on these measurements. The major findings were: 1) intraclass correlation coefficients for FE(NO) and flow rates ranged from 0.92-0.99 for offline values, and 0.99 for all online values; 2) variation at an expiratory flow rate of 46 mL/sec (SD, 9.39) was considerably less than at other flows, especially at 15 mL/sec (SD, 26.55); 3) FE(NO) increased as flow rates decreased for both offline and online values; 4) there were no significant differences and good agreement between offline bag and online FE(NO) values at 31 and 46 mL/sec expiratory flows; and 5) using multiple regression, significant predictors of FE(NO) were flow, body surface area, age, and FEF(25-75). We have provided FE(NO) values in healthy children and propose that the ideal expiratory flow rate for FE(NO) measurements in children using the single breath technique is between 30-50 mL/sec.

Measurement of airway inflammation in asthma

Chronic airway inflammation is considered responsible for symptoms and disorders of airway function associated with asthma. This process is the target of anti-inflammatory therapy, so a number of standardized, noninvasive techniques have been developed to assess it. More recent approaches include the measurement of exhaled gases and nonvolatile substances in breath condensate. Results from studies using a wide variety of inflammatory markers have shown group differences between patients with asthma and healthy control subjects, but evidence for the diagnostic use of these markers in individual patients is scarce. Similarly, despite many studies demonstrating some correlation between markers of airway inflammation and a measure of disease control, none has yet convincingly shown a place for the use of these markers in an individual with corticosteroid-treated asthma. However, application of these markers continues to further our understanding of the disease process and provides the potential for more appropriate, customized therapy.

Low exhaled nitric oxide and a polymorphism in the NOS I gene is associated with acute chest syndrome

Abnormalities of nitric oxide metabolism have been implicated in the pathogenesis of acute chest syndrome in subjects with sickle cell anemia. It is not known whether exhaled nitric oxide levels (FE(NO)) are abnormal in children with a history of the acute chest syndrome (ACS). We compared FE(NO), plasma nitric oxide metabolites (NO(x)), serum arginine and citrulline levels, and the number of AAT repeats in intron 20 of NOS I in subjects with sickle cell disease (SCD) and a history of at least one episode of ACS (ACS(+), n = 13), subjects with SCD and no prior history of ACS (ACS(-), n = 7), and healthy children (HC, n = 6). Mean +/- SD FE(NO) (ppb) was lower in ACS(+) than in ACS(-) and HC: (10.4 +/- 4.3 versus 23.4 +/- 6.1 p = 0.002] and 30.4 +/- 15.8 [p = 0.0001], respectively). Plasma NO(x) (microM) were similar in all three groups (37.3 +/- 19.4, 33.0 +/- 13.2, 44.7 +/- 7.8, respectively). Arginine and citrulline levels (microM) did not differ between ACS(+) and ACS(-) groups. Spirometric data revealed a mildly diminished FEV(1) and FVC in ACS(+) that was statistically different from HC but not ACS(-): (FEV(1) as % of predicted for ACS(+), ACS(-), and HC; 83 +/- 17 versus 87 +/- 16 versus 102 +/- 16, respectively, p < 0.05 between ACS(+) and HC). The level of FE(NO) was significantly associated with the sum of AAT repeats in intron 20 of NOS I gene alleles. The correlation coefficient (r) was 0.62 (p < 0.005). We conclude that FE(NO) levels are significantly reduced in subjects who have a history of ACS and that the FE(NO) levels are significantly correlated with the number of NOS I AAT repeats. FE(NO) is a sensitive marker and may be a predictor of ACS prone children.