Exhaled nitric oxide: a novel biomarker of adverse respiratory health effects in epidemiological studies

Genetic susceptibility to airway inflammation and exposure to short-term outdoor air pollution

BACKGROUND

Air pollution is a large environmental health hazard whose exposure and health effects are unequally distributed among individuals. This is, at least in part, due to gene-environment interactions, but few studies exist. Thus, the current study aimed to explore genetic susceptibility to airway inflammation from short-term air pollution exposure through mechanisms of gene-environment interaction involving the SFTPA, GST and NOS genes.

METHODS

Five thousand seven hundred two adults were included. The outcome measure was fraction of exhaled nitric oxide (FeNO), at 50 and 270 ml/s. Exposures were ozone (O₃), particulate matter < 10 µm (PM₁₀), and nitrogen dioxide (NO₂) 3, 24, or 120-h prior to FeNO measurement. In the SFTPA, GST and NOS genes, 24 single nucleotide polymorphisms (SNPs) were analyzed for interaction effects. The data were analyzed using quantile regression in both single-and multipollutant models.

RESULTS

Significant interactions between SNPs and air pollution were found for six SNPs (p < 0.05): rs4253527 (SFTPA1) with O₃ and NO_x, rs2266637 (GSTT1) with NO₂, rs4795051 (NOS2) with PM₁₀, NO₂ and NO_x, rs4796017 (NOS2) with PM₁₀, rs2248814 (NOS2) with PM₁₀ and rs7830 (NOS3) with NO₂. The marginal effects on FeNO for three of these SNPs were significant (per increase of 10 µg/m³):rs4253527 (SFTPA1) with O₃ (β: 0.155, 95%CI: 0.013-0.297), rs4795051 (NOS2) with PM₁₀ (β: 0.073, 95%CI: 0.00-0.147 (single pollutant), β: 0.081, 95%CI: 0.004-0.159 (multipollutant)) and NO₂ (β: -0.084, 95%CI: -0.147; -0.020 (3 h), β: -0.188, 95%CI: -0.359; -0.018 (120 h)) and rs4796017 (NOS2) with PM₁₀ (β: 0.396, 95%CI: 0.003-0.790).

CONCLUSIONS

Increased inflammatory response from air pollution exposure was observed among subjects with polymorphisms in SFTPA1, GSTT1, and NOS genes, where O₃ interacted with SFTPA1 and PM10 and NO₂/NO_x with the GSTT1 and NOS genes. This provides a basis for the further exploration of biological mechanisms as well as the identification of individuals susceptible to the effects of outdoor air pollution.

Cardiorespiratory responses to low-level ozone exposure: The inDoor Ozone Study in childrEn (DOSE)

BACKGROUND

Indoor air pollution has emerged as a significant environmental and public health concern in recent years. However, evidence regarding the cardiorespiratory effects of indoor ozone is limited, and the underlying biological mechanisms are unclear, especially in children. Our study aimed to assess the cardiorespiratory responses to indoor ozone exposure in children.

METHODS

A repeated-measure study was conducted in 46 middle-school children in Beijing, China. Real-time concentrations of ozone, along with co-pollutants including particulate matter (PM) and black carbon (BC), were monitored in classrooms from Monday to Friday. Three repeated health measurements of cardiorespiratory functions, including ambulatory electrocardiogram (ECG), blood pressure, fractional exhaled nitric oxide (FeNO) and lung function, were performed on each participant. Mixed-effect models were used to evaluate the effects of indoor ozone exposure.

RESULTS

The mean (SD) indoor ozone concentration was 8.7 (6.6) ppb during the study period, which was largely below the current guideline and standards. However, even this low-level ozone exposure was associated with reduced cardiac autonomic function and increased heart rate (HR) in children. For instance, per interquartile range (IQR) increase in ozone at 2-hour moving average was associated with -7.8% (95% CI: -9.9%, -5.6%) reduction in standard deviation of all normal-to-normal intervals (SDNN), and 2.6% (95% CI: 1.6%, 3.6%) increment in HR. In addition, the associations were stronger at high BC levels (BC ≥ 3.7 μg/m³). No significant associations were found for airway inflammation and pulmonary function.

CONCLUSIONS

Exposure to low-level indoor ozone that is not associated with respiratory effects was significantly related to disturbed cardiac autonomic function and increased HR in children, which suggested a possible mechanism through which ozone may affect cardiovascular health in children, and indicated more protective measures should be taken to alleviate the acute adverse effects of indoor ozone in this susceptible population.

The effects of fine particulate matter constituents on exhaled nitric oxide and DNA methylation in the arginase-nitric oxide synthase pathway

BACKGROUND

Fine particulate matter (PM_2.5) has been widely associated with airway inflammation represented by increased fractional concentration of exhaled nitric oxide (FeNO). However, it remains unclear whether various PM_2.5 constituents have different impacts on FeNO and its production process from the arginase (ARG)-nitric oxide synthase (NOS) pathway.

OBJECTIVES

To investigate the acute effects of PM_2.5 constituents on FeNO and DNA methylation of genes involved.

METHODS

We conducted a longitudinal panel study among 43 young adults in Shanghai, China from May to October in 2016. We monitored the concentrations of 25 constituents of PM_2.5. We applied the linear mixed-effect model to evaluate the associations of PM_2.5 constituents with FeNO and DNA methylation of the ARG2 and NOS2A genes.

RESULTS

Following PM_2.5 exposure, NOS2A methylation decreased and ARG2 methylation increased only on the concurrent day, whereas FeNO increased most prominently on the second day. Nine constituents (OC, EC, K, Fe, Zn, Ba, Cr, Se, and Pb) showed consistent associations with elevated FeNO and decreased NOS2A methylation or increased ARG2 methylation in single-constituent models and models adjusting for PM_2.5 total mass and collinearity. An interquartile range increase of these constituents was associated with respective decrements of 0.27-1.20 in NOS2A methylation (%5mC); increments of 0.48-1.56 in ARG2 methylation (%5mC); and increments of 7.12%-17.54% in FeNO.

CONCLUSIONS

Our results suggested that OC, EC, and some metallic elements may be mainly responsible for the development and epigenetic regulation of airway inflammatory response induced by short-term PM_2.5 exposure.

Different metrics (number, surface area, and volume concentration) of urban particles with varying sizes in relation to fractional exhaled nitric oxide (FeNO)

Background

There have been increasing concerns on potential health effects of ultrafine particles (UFP); but little is known as to what are the most biologically relevant metrics for these particles that make up very little mass concentration. We examined a range of particle metrics (number, surface area, active surface area, and volume concentration) in relation to fractional exhaled nitric oxide (FeNO), a well-established biomarker of pulmonary inflammation.

Methods

We conducted a panel study in 17 non-asthmatic children who attended schools and resided near a monitoring site at which particles in the size range of 3-800 nm were measured using a TDMPS and particles in the size range of 0.5 to 10 µm were measured using an APS. Particles were classified by size into the nucleation, Aitken, accumulation, or coarse mode, respectively, for calculating mode-specific number, surface area, active surface area, and volume concentrations. Each participating child was measured for FeNO daily for 30 days. We used linear mixed-effects models to assess the associations between various particle metrics and FeNO.

Results

In terms of number concentration, ambient particles in the Aitken mode and in the accumulation mode were significantly and positively associated with FeNO; but particles in the nucleation mode were significantly and negatively associated with FeNO. Moreover, UFP as a lump sum of both nucleation-mode and Aikten-mode particles did not show a significant association with FeNO. In terms of surface area concentration, ambient particles only in the accumulation mode were significantly and positively associated with FeNO. In terms of volume concentration, ambient particles in both the accumulation mode and the coarse mode were significantly and positively associated with FeNO. Analyses of the relationships between FeNO and metrics for particles deposited in the respiratory tract generated consistent findings, showing a negative association for the number concentration of deposited particles (driven by nucleation-mode particles), a positive association for the surface area concentration of deposited particles (driven by accumulation-mode particles), and a positive association for the volume concentration of deposited particles (driven by accumulation-mode and coarse-mode particles).

Conclusions

Particles contributing largely to the surface area concentration and/or the volume concentration of ambient particles or particles deposited in the respiratory tract had a significant positive association with pulmonary inflammation. Nucleation-mode particles, that have large number concentrations but contribute little to the surface area or volume concentration of ambient or deposited particles, had a significant negative association with FeNO. This may indicate a different biological process or may simply be due to the negative and strong correlation between nucleation-mode and accumulation-mode particles. Given that particles in different modes may have different biological actions, measuring UFP as a whole may not necessarily be useful from a biological effect standpoint.

Respiratory symptoms, asthma and levels of fractional exhaled nitric oxide in schoolchildren in the industrial areas of Estonia

OBJECTIVES

Exposure to air pollutants in the ambient environment has been associated with various respiratory symptoms, and with increased asthma diagnosis, in both children and adults. Most research to date has focussed on core pollutants, such as PM₁₀, PM_2.5, SO₂ and NO₂, and less attention has been given to the effects of industry-specific contamination. The current study aimed to examine the associations between respiratory symptoms, asthma, increased levels of fractional exhaled nitric oxide (FeNO) (as a marker of eosinophilic airway inflammation) and ambient levels of industrial pollutants (such as benzene, phenol, formaldehyde and non-methane hydrocarbons) for schoolchildren living near oil shale industries in Ida-Viru County, Estonia.

METHODS

A total of 1326 schoolchildren from Ida-Viru, Lääne-Viru and Tartu Counties participated in a cross-sectional study, consisting of questionnaires on respiratory symptoms and asthma, as well as clinical examinations to measure FeNO. Dispersion modelling was used to characterize individual-level exposure to industrial air pollutants at each subject's home address. Associations between exposure and respiratory health were investigated using logistic regression analysis, and differences in results between regions were analysed using the Chi-squared test.

RESULTS

The prevalence of respiratory symptoms (p < 0.05) in children living near (i.e. within 5 km) of an oil shale industry site in Ida-Viru County was 2-4 times higher than in children living in the reference area of Tartu County. Children exposed to 1 μg/m³ higher levels of benzene and formaldehyde had a higher odds ratio (OR) of having rhinitis without a cold (OR 1.03, 95% confidence interval (CI) 1.01-1.06), of ever having had attacks of asthma (OR 1.05, 95% CI 1.01-1.10) and of having a dry cough a few days per year (OR 1.05, 95% CI 1.01-1.10). Children exposed to 1 μg/m³ higher levels of benzene, formaldehyde, phenol and non-methane hydrocarbons had a higher odds ratio of having high FeNO levels (≥30 ppb): OR and 95% CI of 1.05, 1.01-1.09; 1.22, 1.06-1.41; 1.01, 1.00-1.01; and 1.75, 1.75-2.62, respectively.

Fractional Exhaled Nitric Oxide (FeNO) and Spirometry as Indicators of Inhalation Exposure to Chemical Agents in Pathology Workers

OBJECTIVE

The objective of this study was to examine whether fractional exhaled nitric oxide (FeNO) and spirometry can be used as indices to evaluate adverse health effects of low-concentrated chemical inhalation exposure, mainly to formaldehyde.

METHODS

Thirty-three subjects (pathology technicians) and 30 controls (workers without handling any chemicals in the same hospitals) participated in this study. All participants underwent FeNO measurement and spirometry before and after 5 days of work.

RESULTS

FeNO significantly increased in the subjects with a history of asthma (P < 0.05), whereas forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1) decreased in the subjects (P < 0.05). Furthermore, work duration and pre-work levels of FEV1 in the subjects had a significant association.

CONCLUSION

The results suggest that FeNO, FVC, and FEV1 represent effective health-effect indices of low-concentrated chemical inhalation exposure.

Acute effects of ambient temperature and particulate air pollution on fractional exhaled nitric oxide: A panel study among diabetic patients in Shanghai, China

Background

Epidemiological studies have shown the associations of ambient temperature and particulate matter (PM) air pollution with respiratory morbidity and mortality. However, the underlying mechanisms have not been well characterized. The aim of this study is to investigate the associations of temperature and fine and coarse PM with fractional exhaled nitric oxide (FeNO), a well-established biomarker of respiratory inflammation.

Methods

We conducted a longitudinal panel study involving six repeated FeNO tests among 33 type 2 diabetes mellitus patients from April to June 2013 in Shanghai, China. Hourly temperature and PM concentrations were obtained from a nearby fixed-site monitoring station. We then explored the associations between temperature, PM, and FeNO using linear mixed-effect models incorporated with distributed lag nonlinear models for the lagged and nonlinear associations. The interactions between temperature and PM were evaluated using stratification analyses.

Results

We found that both low and high temperature, as well as increased fine and coarse PM, were significantly associated with FeNO. The cumulative relative risk of FeNO was 1.75% (95% confidence interval [CI], 1.04–2.94) comparing 15 °C to the referent temperature (24 °C) over lags 0–9 days. A 10 μg/m³ increase in fine and coarse PM concentrations were associated with 1.18% (95% CI, 0.18–2.20) and 1.85% (95% CI, 0.62–3.09) FeNO in lag 0–1 days, respectively. PM had stronger effects on cool days than on warm days.

Conclusions

This study suggested low ambient temperature, fine PM, and coarse PM might elevate the levels of respiratory inflammation. Our findings may help understand the epidemiological evidence linking temperature, particulate air pollution, and respiratory health.

•

Both low and high temperatures were significantly associated with FeNO.

•

The increases of fine and coarse PM concentrations were associated with FeNO.

•

Both fine and coarse PM had stronger effects in cool days.

Design and characterization of human exposure to generated sulfate and soot particles in a pilot chamber study

A number of literatures have documented adverse health effects of exposure to fine particulate matter (PM2.5), and secondary sulfate aerosol and black carbon may contribute to health impacts of PM2.5 exposure. We designed an exposure system to generate sulfate and traffic soot particles, and assessed the feasibility of using it for human exposure assessment in a pilot human exposure study. In the designed exposure system, average mass concentrations of generated sulfate and soot particles were 74.19 μg/m3 and 11.54 μg/m3 in the chamber and did not vary significantly during two-hour human exposure sessions. The size ranges of generated sulfate were largely between 20 to 200 nm, whereas those of generated soot particles were in the size ranges of 50 to 200 nm. Following two-hour exposure to generated sulfate and soot particles, we observed significant increases in fractional exhaled NO (FeNO) in young and health subjects. Building on established human exposure system and health response follow-up methods, future full-scale studies focusing on the effects of mixed particulates and individual PM2.5 components would provide data in understanding the underpinning cardio-respiratory outcomes in relation to air pollution mixture exposure.

IMPLICATIONS

Controlled exposure is a useful design to measure the biological responses repeatedly following particulate exposures of target components and set exposure at target levels of health concerns. Our study provides rational and establishes method for future full-scale studies to focus on examining the effects of mixed particulates and individual PM2.5 components.

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.

Reference values and factors associated with exhaled nitric oxide: U.S. youth and adults

BACKGROUND

Normative values for fractional exhaled nitric oxide (FeNO) and the associated co-factors are important in understanding the role of FeNO as a biomarker in airway disease. The objective of this study is to establish reference FeNO values for youth and adult asymptomatic, lifetime nonsmokers in the United States, and to describe the factors affecting these levels.

METHODS

Cross-sectional analyses of the National Health and Nutrition Examination Survey from 2007 to 2010. The analytic sample consisted of 4718 youth and adults, ages 6-79 years, who were lifelong nonsmokers, and free of asthma, and other respiratory conditions and symptoms. Loge FeNO values were used as dependent variables to test associations of demographic and health related-covariates. Multivariable regression models were used to assess the independent effect and covariate-adjusted contribution of the factors.

RESULTS

The geometric mean FeNO level was 8.3, 12.1, and 16.2 ppb for males 6-11, 12-19, and 20-79 years, and 8.4, 10.9, and 12.6 ppb for females in the corresponding age groups. Overall, FeNO levels increased with increasing age (p < 0.001), and height (p < 0.001). In all age groups, FeNO levels were positively associated with eosinophil counts, and with testing in the morning. Among youths 6-11 and 12-19 years, non-Hispanics whites had lower FeNO values than non-Hispanic blacks and Hispanic youths. No race-ethnic difference in FeNO levels was evident for adults 20-79 years. Among adolescents and adults, FeNO levels were higher for males than for females, controlling for all other factors.

CONCLUSIONS

These reference values and associated attributes in youths and adults are useful in evaluating the role of FeNO in airway diseases.

Children's urinary phthalate metabolites and fractional exhaled nitric oxide in an urban cohort

RATIONALE

Phthalates are used widely in consumer products. Exposure to several phthalates has been associated with respiratory symptoms and decreased lung function. Associations between children's phthalate exposures and fractional exhaled nitric oxide (Fe(NO)), a biomarker of airway inflammation, have not been examined.

OBJECTIVES

We hypothesized that urinary concentrations of four phthalate metabolites would be positively associated with Fe(NO) and that these associations would be stronger among children with seroatopy or wheeze.

METHODS

In an urban ongoing birth cohort, 244 children had phthalate metabolites determined in urine collected on the same day as Fe(NO) measurement. Repeated sampling gathered 313 observations between ages 4.9 and 9.1 years. Seroatopy was assessed by specific IgE. Wheeze in the past year was assessed by validated questionnaire. Regression models used generalized estimating equations.

MEASUREMENTS AND MAIN RESULTS

Log-unit increases in urinary concentrations of metabolites of diethyl phthalate (DEP) and butylbenzyl phthalate (BBzP) were associated with a 6.6% (95% confidence interval [CI] 0.5-13.1%) and 8.7% (95% CI, 1.9-16.0%) increase in Fe(NO), respectively, adjusting for other phthalate metabolites and potential covariates/confounders. There was no association between concentrations of metabolites of di(2-ethylhexyl) phthalate or di-n-butyl phthalate and Fe(NO). There was no significant interaction by seroatopy. The BBzP metabolite association was significantly stronger among children who wheeze (P = 0.016).

CONCLUSIONS

Independent associations between exposures to DEP and BBzP and Fe(NO) in a cohort of inner-city children were observed. These results suggest that these two ubiquitous phthalates, previously shown to have substantial contributions from inhalation, are positively associated with airway inflammation in children.

Domestic airborne black carbon and exhaled nitric oxide in children in NYC

Differential exposure to combustion by-products and allergens may partially explain the marked disparity in asthma prevalence (3-18%) among New York City neighborhoods. Subclinical changes in airway inflammation can be measured by fractional exhaled nitric oxide (FeNO). FeNO could be used to test independent effects of these environmental exposures on airway inflammation. Seven- and eight-year-old children from neighborhoods with lower (range 3-9%, n=119) and higher (range 11-18%, n=121) asthma prevalence participated in an asthma case-control study. During home visits, FeNO was measured, and samples of bed dust (allergens) and air (black carbon; BC) were collected. Neighborhood built-environment characteristics were assessed for the 500 m surrounding participants' homes. Airborne BC concentrations in homes correlated with neighborhood asthma prevalence (P<0.001) and neighborhood densities of truck routes (P<0.001) and buildings burning residual oil (P<0.001). FeNO concentrations were higher among asthmatics with than in those without frequent wheeze (≥4 times/year) (P=0.002). FeNO concentrations correlated with domestic BC among children without seroatopy (P=0.012) and with dust mite allergen among children with seroatopy (P=0.020). The association between airborne BC in homes and both neighborhood asthma prevalence and FeNO suggest that further public health interventions on truck emissions standards and residual oil use are warranted.

Air pollution, airway inflammation, and lung function in a cohort study of Mexico City schoolchildren

BACKGROUND

The biological mechanisms involved in inflammatory response to air pollution are not clearly understood.

OBJECTIVE

In this study we assessed the association of short-term air pollutant exposure with inflammatory markers and lung function.

METHODS

We studied a cohort of 158 asthmatic and 50 nonasthmatic school-age children, followed an average of 22 weeks. We conducted spirometric tests, measurements of fractional exhaled nitric oxide (Fe(NO)), interleukin-8 (IL-8) in nasal lavage, and pH of exhaled breath condensate every 15 days during follow-up. Data were analyzed using linear mixed-effects models.

RESULTS

An increase of 17.5 microg/m(3) in the 8-hr moving average of PM(2.5) levels (interquartile range) was associated with a 1.08-ppb increase in Fe(NO) [95% confidence interval (CI), 1.01-1.16] and a 1.07-pg/mL increase in IL-8 (95% CI 0.98-1.19) in asthmatic children and a 1.16 pg/ml increase in IL-8 (95% CI, 1.00-1.36) in nonasthmatic children. The 5-day accumulated average of exposure to particulate matter <2.5 microm in aerodynamic diamter (PM(2.5)) was significantly inversely associated with forced expiratory volume in 1 sec (FEV(1)) (p=0.048) and forced vital capacity (FVC) (p=0.012) in asthmatic children and with FVC (p=0.021) in nonasthmatic children. Fe(NO) and FEV(1) were inversely associated (p=0.005) in asthmatic children.

CONCLUSIONS

Exposure to PM(2.5) resulted in acute airway inflammation and decrease in lung function in both asthmatic and nonasthmatic children.

Ambient and microenvironmental particles and exhaled nitric oxide before and after a group bus trip

OBJECTIVES

Airborne particles have been linked to pulmonary oxidative stress and inflammation. Because these effects may be particularly great for traffic-related particles, we examined associations between particle exposures and exhaled nitric oxide (FE(NO)) in a study of 44 senior citizens, which involved repeated trips aboard a diesel bus.

METHODS

Samples of FE(NO) collected before and after the trips were regressed against microenvironmental and ambient particle concentrations using mixed models controlling for subject, day, trip, vitamins, collection device, mold, pollen, room air nitric oxide, apparent temperature, and time to analysis. Although ambient concentrations were collected at a fixed location, continuous group-level personal samples characterized microenvironmental exposures throughout facility and trip periods.

RESULTS

In pre-trip samples, both microenvironmental and ambient exposures to fine particles were positively associated with FE(NO). For example, an interquartile increase of 4 microg/m(3) in the daily microenvironmental PM(2.5) concentration was associated with a 13% [95% confidence interval (CI), 2-24%) increase in FE(NO). After the trips, however, FE(NO) concentrations were associated pre-dominantly with microenvironmental exposures, with significant associations for concentrations measured throughout the whole day. Associations with exposures during the trip also were strong and statistically significant with a 24% (95% CI, 15-34%) increase in FE(NO) predicted per interquartile increase of 9 microg/m(3) in PM(2.5). Although pre-trip findings were generally robust, our post-trip findings were sensitive to several influential days.

CONCLUSIONS

Fine particle exposures resulted in increased levels of FE(NO) in elderly adults, suggestive of increased airway inflammation. These associations were best assessed by microenvironmental exposure measurements during periods of high personal particle exposures.

Exhaled nitric oxide in children with asthma and short-term PM2.5 exposure in Seattle

The objective of this study was to evaluate associations between short-term (hourly) exposures to particulate matter with aerodynamic diameters < 2.5 microm (PM2.5) and the fractional concentration of nitric oxide in exhaled breath (FE(NO) in children with asthma participating in an intensive panel study in Seattle, Washington. The exposure data were collected with tapered element oscillation microbalance (TEOM) PM2.5 monitors operated by the local air agency at three sites in the Seattle area. FE(NO) is a marker of airway inflammation and is elevated in individuals with asthma. Previously, we reported that offline measurements of FE(NO) are associated with 24-hr average PM2.5 in a panel of 19 children with asthma in Seattle. In the present study using the same children, we used a polynomial distributed lag model to assess the association between hourly lags in PM2.5 exposure and FE(NO) levels. Our model controlled for age, ambient NO levels, temperature, relative humidity, and modification by use of inhaled corticosteroids. We found that FE(NO) was associated with hourly averages of PM2.5 up to 10-12 hr after exposure. The sum of the coefficients for the lag times associated with PM2.5 in the distributed lag model was 7.0 ppm FE(NO). The single-lag-model FE(NO) effect was 6.9 [95% confidence interval (CI), 3.4 to 10.6 ppb] for a 1-hr lag, 6.3 (95% CI, 2.6 to 9.9 ppb ) for a 4-hr lag, and 0.5 (95% CI, -1.1 to 2.1 ppb) for an 8-hr lag. These data provide new information concerning the lag structure between PM2.5 exposure and a respiratory health outcome in children with asthma.

Exhaled nitric oxide: sources of error in offline measurement

Delayed offline measurement of exhaled nitric oxide (eNO), although useful in environmental and clinical research, is limited by the instability of stored breath samples. The authors characterized sources of instability with the goal of minimizing them. Breath and other air samples were stored under various conditions, and NO levels were measured repeatedly over 1-7 d. Concentration change rates varied positively with temperature and negatively with initial NO level, thus "stable" levels reflected a balance of NO-adding and NO-removing processes. Storage under refrigeration for a standardized period of time can optimize offline eNO measurement, although samples at room temperature are effectively stable for several hours.

Pulmonary effects of indoor- and outdoor-generated particles in children with asthma

Most particulate matter (PM) health effects studies use outdoor (ambient) PM as a surrogate for personal exposure. However, people spend most of their time indoors exposed to a combination of indoor-generated particles and ambient particles that have infiltrated. Thus, it is important to investigate the differential health effects of indoor- and ambient-generated particles. We combined our recently adapted recursive model and a predictive model for estimating infiltration efficiency to separate personal exposure (E) to PM2.5 (PM with aerodynamic diameter < or = 2.5 microm) into its indoor-generated (Eig) and ambient-generated (Eag) components for 19 children with asthma. We then compared Eig and Eag to changes in exhaled nitric oxide (eNO), a marker of airway inflammation. Based on the recursive model with a sample size of eight children, Eag was marginally associated with increases in eNO [5.6 ppb per 10-microg/m3 increase in PM2.5; 95% confidence interval (CI), -0.6 to 11.9; p = 0.08]. Eig was not associated with eNO (-0.19 ppb change per 10 microg/m3). Our predictive model allowed us to estimate Eag and Eig for all 19 children. For those combined estimates, only Eag was significantly associated with an increase in eNO (Eag: 5.0 ppb per 10-microg/m3 increase in PM2.5; 95% CI, 0.3 to 9.7; p = 0.04; Eig: 3.3 ppb per 10-microg/m3 increase in PM2.5; 95% CI, -1.1 to 7.7; p = 0.15). Effects were seen only in children who were not using corticosteroid therapy. We conclude that the ambient-generated component of PM2.5 exposure is consistently associated with increases in eNO and the indoor-generated component is less strongly associated with eNO.

Measurement of offline exhaled nitric oxide in a study of community exposure to air pollution

As part of a large panel study in Seattle, Washington, we measured levels of exhaled nitric oxide (eNO) in children's homes and fixed-site particulate matter with aerodynamic diameters of 2.5 micro m or less (PM(2.5)) outside and inside the homes as well as personal PM(2.5) during winter and spring sessions of 2000-2001. Nineteen subjects 6-13 years of age participated; 9 of the 19 were on inhaled corticosteroid (ICS) therapy. Exhaled breath measurements were collected offline into a Mylar balloon for up to 10 consecutive days. Mean eNO values were 19.1 (SD +/- 11.4) ppb in winter sessions and 12.5 +/- 6.6 ppb in spring sessions. Fixed-site PM(2.5) mean concentrations were 10.1 +/- 5.7 microg/m(3) outside homes and 13.3 +/- 1.4 inside homes; the personal PM(2.5) mean was 13.4 +/- 3.2 microg/m(3). We used a linear mixed-effects model with random intercept and an interaction term for medications to test for within-subject-within-session associations between eNO and various PM(2.5) values. We found a 10 microg/m(3) increase in PM(2.5) from the outdoor, indoor, personal, and central-site measurements that was associated with increases in eNO in all subjects at lag day zero. The effect was 4.3 ppb [95% confidence interval (CI), 1.4-7.29] with the outdoor monitor, 4.2 ppb (95% CI, 1.02-7.4) for the indoor monitor, 4.5 ppb (95% CI, 1.02-7.9) with the personal monitor, and 3.8 ppb (95% CI, 1.2-6.4) for the central monitors. The interaction term for medication category (ICS users vs. nonusers) was significant in all analyses. These findings suggest that eNO can be used as an assessment tool in epidemiologic studies of health effects of air pollution.

Transient decrease of exhaled nitric oxide after acute exposure to passive smoke in healthy subjects

Nitric oxide (NO) is produced and detected in the exhalate from the respiratory tract where it plays important regulatory functions. Exhaled nitric oxide (eNO) concentrations are reduced in active cigarette smokers between cigarettes and in nonsmoking subjects during short-term exposure to environmental tobacco smoke. In this study, the authors evaluated eNO before and after an acute exposure to environmental tobacco smoke in healthy, nonsmoking subjects (n = 12). Baseline eNO levels were measured by chemiluminescence at baseline (1 hr before exposure), shortly after the end of exposure, and 10 and 30 min after the end of exposure. Mean room air NO concentration increased from 3 ppb to 4 ppm (range, 560 ppb-8.5 ppm) during the exposure period. Carboxyhemoglobin levels were assessed before and after the exposure with spectrophotometry. All subjects had decreased eNO with exposure to environmental tobacco smoke (mean +/- standard error of the mean: 16.65 +/- 1.35 ppb to 13.86 +/- 1.33 ppb; p < .001). These concentrations remained significantly decreased at 10 min and recovered within 30 min. No modifications in airway resistance or increase in carboxyhemoglobin levels were observed. Exposure to environmental tobacco smoke transiently--but consistently--decreased eNO concentration in healthy, nonsmoking subjects, suggesting that second-hand smoke can directly affect NO in the airway environment.

Biomarkers of some pulmonary diseases in exhaled breath

Analysis of various biomarkers in exhaled breath allows completely non-invasive monitoring of inflammation and oxidative stress in the respiratory tract in inflammatory lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), bronchiectasis and interstitial lung diseases. The technique is simple to perform, may be repeated frequently, and can be applied to children, including neonates, and patients with severe disease in whom more invasive procedures are not possible. Several volatile chemicals can be measured in the breath (nitric oxide, carbon monoxide, ammonia), and many non-volatile molecules (mediators, oxidation and nitration products, proteins) may be measured in exhaled breath condensate. Exhaled breath analysis may be used to quantify inflammation and oxidative stress in the respiratory tract, in differential diagnosis of airway disease and in the monitoring of therapy. Most progress has been made with exhaled nitric oxide (NO), which is increased in atopic asthma, is correlated with other inflammatory indices and is reduced by treatment with corticosteroids and antileukotrienes, but not (beta 2-agonists. In contrast, exhaled NO is normal in COPD, reduced in CF and diagnostically low in primary ciliary dyskinesia. Exhaled carbon monoxide (CO) is increased in asthma, COPD and CF. Increased concentrations of 8-isoprostane, hydrogen peroxide, nitrite and 3-nitrotyrosine are found in exhaled breath condensate in inflammatory lung diseases. Furthermore, increased levels of lipid mediators are found in these diseases, with a differential pattern depending on the nature of the disease process. In the future it is likely that smaller and more sensitive analyzers will extend the discriminatory value of exhaled breath analysis and that these techniques may be available to diagnose and monitor respiratory diseases in the general practice and home setting.