Environmental influence on the measurement of exhaled nitric oxide concentration in school children: special reference to methodology

Bronchodilator response and lung function decline: Associations with exhaled nitric oxide with regard to sex and smoking status

Background

Fractional exhaled nitric oxide (FeNO) is a marker of type-2 inflammation used both to support diagnosis of asthma and follow up asthma patients. The associations of FeNO with lung function decline and bronchodilator (BD) response have been studied only scarcely in large populations.

Objectives

To study the association between FeNO and a) retrospective lung function decline over 20 years, and b) lung function response to BD among asthmatic subjects compared with non-asthmatic subjects and with regards to current smoking and sex.

Methods

Longitudinal analyses of previous lung function decline and FeNO level at follow-up and cross-sectional analyses of BD response and FeNO levels in 4257 participants (651 asthmatics) from the European Community Respiratory Health Survey.

Results

Among asthmatic subjects, higher percentage declines of FEV₁ and FEV₁/FVC were associated with higher FeNO levels (p = 0.001 for both) at follow-up. These correlations were found mainly among non-smoking individuals (p = 0.001) and females (p = 0.001) in stratified analyses.

Percentage increase in FEV₁ after BD was positively associated with FeNO levels in non-asthmatic subjects. Further, after stratified for sex and smoking separately, a positive association was seen between FEV₁ and FeNO levels in non-smokers and women, regardless of asthma status.

Conclusions

We found a relationship between elevated FeNO and larger FEV₁ decline over 20 years among subjects with asthma who were non-smokers or women. The association between elevated FeNO levels and larger BD response was found in both non-asthmatic and asthmatic subjects, mainly in women and non-smoking subjects.

Determinants of fractional exhaled nitric oxide in healthy men and women from the European Community Respiratory Health Survey III

INTRODUCTION

The fractional exhaled nitric oxide (F_E NO) is a marker for type 2 inflammation used in diagnostics and management of asthma. In order to use F_E NO as a reliable biomarker, it is important to investigate factors that influence F_E NO in healthy individuals. Men have higher levels of F_E NO than women, but it is unclear whether determinants of F_E NO differ by sex.

OBJECTIVE

To identify determinants of F_E NO in men and women without lung diseases.

METHOD

Fractional exhaled nitric oxide was validly measured in 3881 healthy subjects that had answered the main questionnaire of the European Community Respiratory Health Survey III without airways or lung disease.

RESULTS

Exhaled NO levels were 21.3% higher in men compared with women P < 0.001. Being in the upper age quartile (60.3-67.6 years), men had 19.2 ppb (95% CI: 18.3, 20.2) higher F_E NO than subjects in the lowest age quartile (39.7-48.3 years) P = 0.02. Women in the two highest age quartiles (54.6-60.2 and 60.3-67.6 years) had 15.4 ppb (14.7, 16.2), P = 0.03 and 16.4 ppb (15.6, 17.1), P = <0.001 higher F_E NO, compared with the lowest age quartile. Height was related to 8% higher F_E NO level in men (P < 0.001) and 5% higher F_E NO levels in women (P = 0.008). Men who smoked had 37% lower F_E NO levels and women had 30% lower levels compared with never-smokers (P < 0.001 for both). Men and women sensitized to both grass and perennial allergens had higher F_E NO levels compared with non-sensitized subjects 26% and 29%, P < 0.001 for both.

CONCLUSION AND CLINICAL RELEVANCE

Fractional exhaled nitric oxide levels were higher in men than women. Similar effects of current smoking, height, and IgE sensitization were found in both sexes. F_E NO started increasing at lower age in women than in men, suggesting that interpretation of F_E NO levels in adults aged over 50 years should take into account age and sex.

Noninvasive effects measurements for air pollution human studies: methods, analysis, and implications

Human exposure studies, compared with cell and animal models, are heavily relied upon to study the associations between health effects in humans and air pollutant inhalation. Human studies vary in exposure methodology, with some work conducted in controlled settings, whereas other studies are conducted in ambient environments. Human studies can also vary in the health metrics explored, as there exists a myriad of health effect end points commonly measured. In this review, we compiled mini reviews of the most commonly used noninvasive health effect end points that are suitable for panel studies of air pollution, broken into cardiovascular end points, respiratory end points, and biomarkers of effect from biological specimens. Pertinent information regarding each health end point and the suggested methods for mobile collection in the field are assessed. In addition, the clinical implications for each health end point are summarized, along with the factors identified that can modify each measurement. Finally, the important research findings regarding each health end point and air pollutant exposures were reviewed. It appeared that most of the adverse health effects end points explored were found to positively correlate with pollutant levels, although differences in study design, pollutants measured, and study population were found to influence the magnitude of these effects. Thus, this review is intended to act as a guide for researchers interested in conducting human exposure studies of air pollutants while in the field, although there can be a wider application for using these end points in many epidemiological study designs.

The role of non-invasive biomarkers in detecting acute respiratory effects of traffic-related air pollution

The role of non-invasive methods in the investigation of acute effects of traffic-related air pollution is not clearly established. We evaluated the usefulness of non-invasive biomarkers in detecting acute air pollution effects according to the age of participants, the disease status, their sensitivity compared with lung function tests and their specificity for a type of pollutant. Search terms lead to 535 titles, among them 128 had potentially relevant abstracts. Sixtynine full papers were reviewed, while 59 articles were excluded as they did not meet the selection criteria. Methods used to assess short-term effects of air pollution included analysis of nasal lavage (NAL) for the upper airways, and induced sputum (IS), exhaled breath condensate (EBC) and exhaled nitric oxide (FeNO) for central and lower airways. There is strong evidence that FeNO evaluation is useful independently from subject age, while IS analysis is suitable almost for adults. Biomarker changes are generally observed upon pollutant exposure irrespective of the disease status of the participants. None of the biomarkers identified are specific for a type of pollutant exposure. Based on experimental exposure studies, there is moderate evidence that IS analysis is more sensitive than lung function tests, whereas this is not the case for biomarkers obtained by NAL or EBC. Cells and some cytokines (IL-6, IL-8 and myeloperoxidase) have been measured both in the upper respiratory tract (NAL) and in the lower airways (IS). Overall, the response to traffic exposure seems different in the two compartments. In conclusion, this survey of current literature displays the complexity of this research field, highlights the significance of short-term studies on traffic pollution and gives important tips when planning studies to detect acute respiratory effects of air pollution in a non-invasive way.

Effects of ambient air pollution on respiratory tract complaints and airway inflammation in primary school children

Respiratory health effects of ambient air pollution were studied in 605 school children 9 to 13 years in Eskişehir, Turkey. Each child performed a fractional exhaled nitric oxide (FENO) measurement and a lung function test (LFT). Self-reported respiratory tract complaints (having cold, complaints of throat, runny nose and shortness of breath/wheezing) in the last 7 days and on the day of testing were also recorded. As acute health outcomes were investigated, weekly average ambient concentrations of ozone (O3), nitrogen dioxide (NO2) and sulfur dioxide (SO2) were determined by passive sampling in the school playgrounds simultaneously with the health survey. Effects of air pollution on respiratory tract complaints and exhaled NO/lung function were estimated by multivariate logistic regression and multivariate linear mixed effects models, respectively. Upper respiratory tract complaints were significantly (p<0.05) associated with weekly average O3 concentrations during the health survey (adjusted odds ratios (OR) of 1.21 and 1.28 for a 10 μgm(-3) increment for having cold and a runny nose on day of testing, respectively). FENO levels were significantly (p<0.05) increased in children with various upper respiratory tract complaints (ratio in FENO varied between 1.16 and 1.40). No significant change in FENO levels was detected in association with any of the measured pollutants (p ≥ 0.05). Lung function was not associated with upper respiratory tract complaints and FENO levels. Peak Expiratory Flow (PEF) levels were negatively associated with weekly average O3 levels for children without upper respiratory tract complaints. In summary, elevated levels of air pollutants increased respiratory tract complaints in children.

Residential traffic-related pollution exposures and exhaled nitric oxide in the children's health study

BACKGROUND

The fractional concentration of nitric oxide in exhaled air (FeNO) potentially detects airway inflammation related to air pollution exposure. Existing studies have not yet provided conclusive evidence on the association of FeNO with traffic-related pollution (TRP).

OBJECTIVES

We evaluated the association of FeNO with residential TRP exposure in a large cohort of children.

METHODS

We related FeNO measured on 2,143 children (ages 7-11 years) who participated in the Southern California Children's Health Study (CHS) to five classes of metrics of residential TRP: distances to freeways and major roads; length of all and local roads within circular buffers around the home; traffic densities within buffers; annual average line source dispersion modeled nitrogen oxides (NOx) from freeways and nonfreeway roads; and predicted annual average nitrogen oxide, nitrogen dioxide, and NOx from a model based on intracommunity sampling in the CHS.

RESULTS

In children with asthma, length of roads was positively associated with FeNO, with stronger associations in smaller buffers [46.7%; 95% confidence interval (CI), 14.3-88.4], 12.4% (95% CI, -8.8 to 38.4), and 4.1% (95% CI, -14.6 to 26.8) higher FeNO for 100-, 300-, and 1,000-m increases in the length of all roads in 50-, 100-, and 200-m buffers, respectively. Other TRP metrics were not significantly associated with FeNO, even though the study design was powered to detect exposures explaining as little as 0.4% of the variation in natural log-transformed FeNO (R2 = 0.004).

CONCLUSION

Length of road was the only indicator of residential TRP exposure associated with airway inflammation in children with asthma, as measured by FeNO.

Air pollution and childhood asthma: recent advances and future directions

PURPOSE OF REVIEW

Current levels of air pollution are consistently associated with asthma development and morbidity among children, suggesting that current regulatory policies may be insufficient. This review will describe recent studies that have examined specific emission sources or components of pollutants that may be associated with pediatric asthma and identify subpopulations that may be particularly susceptible to the effects of air pollution exposure.

RECENT FINDINGS

Important advances include new characterizations of the effects of traffic-related air pollution in urban areas. They also include the application of novel exposure and outcome measures such as pollution estimates derived from land use regression modeling and biological markers of airway inflammation. Additionally, studies have identified host susceptibility characteristics that may modify responses to air pollution exposure, including polymorphisms in oxidative stress genes and epigenetic alterations.

SUMMARY

Identifying specific sources and toxic constituents of air pollution and accurately assessing air pollutant-related asthma outcomes are needed to better direct control strategies. Further research is needed to identify additional host factors that confer increased susceptibility to air pollution exposure. Future therapy to reduce the adverse effects of air pollution on respiratory disease will likely depend on targeting susceptible populations for intervention.

Relationship between exhaled nitric oxide measured by two offline methods and bronchial hyperresponsiveness in Japanese adults with asthma

BACKGROUND

Exhaled nitric oxide (eNO) is a useful marker of eosinophilic airway inflammation in asthmatics. There have been no studies to show the relationship between eNO measured by offline methods and the degree of bronchial hyperresponsiveness in asthmatic patients treated with inhaled corticosteroids.

METHODS

The study population comprised asthmatics at our outpatient clinic. We measured eNO levels by two methods ("eNOs" was measured with a Sievers kit; and "eNOc" was measured with a kit from the Center for Environmental Information Science, Japan). We also used spirometry to test bronchial hyperresponsiveness to acetylcholine (PC(20Ach)).

RESULTS

We recruited 192 stable asthmatics. There was a significant relationship between eNOs and eNOc (r = 0.919, p < 0.001). LogPC(20Ach) levels were negatively correlated with eNOs or eNOc levels (eNOs, r = -0.31, p < 0.001; eNOc, r = -0.23, p = 0.0013). We classified the subjects into two groups based on eNOs levels ((A) the subjects with high eNOs levels (n = 92) and (B) the subjects with normal eNOs levels (n = 100)) ; logPC(20Ach) was significantly correlated with eNOs (r = -0.34, p = 0.001) or eNOc (r = -0.28, p = 0.0075) but not correlated with %FEV(1) in (A), whereas logPC(20Ach) was not significantly correlated with eNO but significantly correlated with %FEV(1) (r = 0.33, p = 0.002) in (B).

CONCLUSIONS

Levels of eNOs and eNOc were correlated with the degree of bronchial hyperresponsiveness to acetylcholine in adult asthmatics treated with inhaled corticosteroids. Our findings suggest that offline monitoring of eNO will facilitate the management of bronchial asthma in patients treated with these drugs.