Elevated exhaled nitric oxide in newborns of atopic mothers precedes respiratory symptoms

Novel biomarkers of fetal and neonatal environmental exposure, effect and susceptibility

Rapid advancements in science and technology have allowed medical providers to treat wider ranges of diseases with safer and more effective therapies than ever before. One of the areas of health that has been consistently understudied, however, is one that affects us all: environmental health or the effects that the chemicals we are exposed to every day have on our acute and chronic health. This effect can be exacerbated during and shortly after pregnancy, as an individual exposure is often shared by both the mother and the fetus/neonate. The diagnosis and monitoring of chemical exposure can be quite challenging, and improving our understanding of the effects of exposure will therefore require effective use of an expanding set of biomarker tests and biological matrices. This review covers the background and history of neonatal biomarkers of exposure, effect, and susceptibility, focusing on the potential uses for the non-invasive matrix of exhaled breath for the detection and monitoring of chemical exposures. IMPACT: Provides a brief overview of Food and Drug Administration and National Institutes of Health Joint Leadership Council BEST (Biomarkers, EndpointS, and other Tools) Resource. Summarizes new and potential biomarkers for fetal exposure. Collates studies using breath as a matrix for environmental exposures.

The association of exhaled nitric oxide with air pollutants in young infants of asthmatic mothers

BACKGROUND

Exhaled nitric oxide is a marker of airway inflammation. Air pollution induces airway inflammation and oxidative stress. Little is known about the impact of air pollution on exhaled nitric oxide in young infants.

METHODS

The Breathing for Life Trial recruited pregnant women with asthma into a randomised controlled trial comparing usual clinical care versus inflammometry-guided asthma management in pregnancy. Four hundred fifty-seven infants from the Breathing for Life Trial birth cohort were assessed at six weeks of age. Exhaled nitric oxide was measured in unsedated, sleeping infants. Its association with local mean 24-h and mean seven-day concentrations of ozone, nitric oxide, nitrogen dioxide, carbon monoxide, sulfur dioxide, ammonia, particulate matter less than 10 μm (PM10) and less than 2.5 μm (PM2.5) in diameter was investigated. The air pollutant data were sourced from local monitoring sites of the New South Wales Air Quality Monitoring Network. The association was assessed using a 'least absolute shrinkage and selection operator' (LASSO) approach, multivariable regression and Spearman's rank correlation.

RESULTS

A seasonal variation was evident with higher median exhaled nitric oxide levels (13.6 ppb) in warmer months and lower median exhaled nitric oxide levels (11.0 ppb) in cooler months, P = 0.008. LASSO identified positive associations for exhaled nitric oxide with 24-h mean ammonia, seven-day mean ammonia, seven-day mean PM10, seven-day mean PM2.5, and seven-day mean ozone; and negative associations for eNO with seven-day mean carbon monoxide, 24-h mean nitric oxide and 24-h mean sulfur dioxide, with an R-square of 0.25 for the penalized coefficients. These coefficients selected by LASSO (and confounders) were entered in multivariable regression. The achieved R-square was 0.27.

CONCLUSION

In this cohort of young infants of asthmatic mothers, exhaled nitric oxide showed seasonal variation and an association with local air pollution concentrations.

25 Years of translational research in the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC)

The Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) mother-child cohorts have provided a foundation of 25 years of research on the origins, prevention, and natural history of childhood asthma and related disorders. COPSAC's approach is characterized by clinical translational research with longitudinal deep phenotyping and exposure assessments from pregnancy, in combination with multi-omic data layers and embedded randomized controlled trials. One trial showed that fish oil supplementation during pregnancy prevented childhood asthma and identified pregnant women with the highest benefits from supplementation, thereby creating the potential for personalized prevention. COPSAC revealed that airway colonization with pathogenic bacteria in early life is associated with an increased risk of asthma. Further, airway bacteria were shown to be a trigger of acute asthma-like symptoms, with benefit from antibiotic treatment. COPSAC identified an immature gut microbiome in early life as a risk factor for asthma and allergy and further demonstrated that asthma can be predicted by infant lung function. At a molecular level, COPSAC has identified novel susceptibility genes, early immune deviations, and metabolomic alterations associated with childhood asthma. Thus, the COPSAC research program has enhanced our understanding of the processes causing childhood asthma and has suggested means of personalized prevention and treatment.

Higher exhaled nitric oxide at 6 weeks of age is associated with less bronchiolitis and wheeze in the first 12 months of age

BACKGROUND

Nitric oxide in exhaled air (eNO) is used as a marker of type 2 immune response-induced airway inflammation. We aimed to investigate the association between eNO and bronchiolitis incidence and respiratory symptoms in infancy, and its correlation with eosinophil protein X (EPX).

METHODS

We followed up infants at 6 weeks of age born to mothers with asthma in pregnancy and measured eNO during natural sleep using a rapid response chemiluminescense analyser (CLD88; EcoMedics), collecting at least 100 breaths, interpolated for an expiratory flow of 50 mL/s. EPX normalised to creatinine was measured in urine samples (uEPX/c). A standardised questionnaire was used to measure symptoms in first year of life. Associations were investigated using multiple linear regression and robust Poisson regression models.

RESULTS

eNO levels were obtained in 184 infants, of whom 125/184 (68%) had 12 months questionnaire data available and 51/184 (28%) had uEPX/c measured. Higher eNO was associated with less respiratory symptoms during the first 6 weeks of life (n=184, ß-coefficient: -0.49, 95% CI -0.95 to -0.04, p=0.035). eNO was negatively associated with uEPX/c (ß-coefficient: -0.004, 95% CI -0.008 to -0.001, p=0.021). Risk incidence of bronchiolitis, wheeze, cold or influenza illness and short-acting beta-agonist use significantly decreased by 18%-24% for every unit increase in eNO ppb.

CONCLUSION

Higher eNO levels at 6 weeks of age may be a surrogate for an altered immune response that is associated with less respiratory symptoms in the first year of life.

Neonatal FeNO, risk factors, and respiratory morbidity in infants: A cohort study

BACKGROUND

Respiratory symptoms in infancy are more common in premature infants. Nitric oxide (NO) is involved in prenatal and neonatal lung development. Measurement of exhaled NO is easy and well-tolerated by neonates. We investigated whether neonatal exhaled NO can be used to predict subsequent respiratory symptoms. Furthermore, we sought to determine prenatal and postnatal factors associated with increased respiratory symptom risk during the first year of life in premature and mature infants.

METHODS

Tidal fractional exhaled NO (FeNO) was measured in a birth cohort (n = 135) of premature and mature infants, up to six times during the first month of life. Primary outcomes were troublesome respiratory symptoms (TRS) and doctor-diagnosed asthmatic bronchitis (AB) at 1 year of age.

FINDINGS

The correlation between FeNO and TRS changed significantly in an age-dependent pattern in moderately premature infants (p = .02). Moderately premature infants with a low FeNO of 2 ppb on postnatal Day 3 had a 48% (95% confidence interval [CI]: 17%-80%) probability of TRS, compared with a probability of 12% (95% CI: 1%-64%) for otherwise similar infants with a FeNO of 11 ppb. Respiratory syncytial virus infection and parental smoking significantly increased the TRS risk in premature infants. Parental asthma and maternal antibiotic use during pregnancy significantly increased the TRS risk in mature infants.

INTERPRETATION

An age-specific association between neonatal FeNO and respiratory symptoms was seen in moderately premature infants. TRS risk was associated with postnatal factors in premature and prenatal factors in mature infants.

Exhaled nitric oxide in premature and mature infants during the first months of life

AIM

In this review, we aim to describe how exhaled Nitric Oxide(NO) changes during the first months of life in premature and mature infants.

METHOD

Review of the literature up to August 2020, on online, tidal breathing NO measurements in unsedated infants. The association between Fractional exhaled NO(FeNO) values, postnatal age, and prematurity was analysed using linear mixed modeling and Spearman's rank correlation.

RESULTS

Median FeNO during the first months of life was 5.9 and 8.5 ppb in premature and mature infants, respectively. The linear mixed model analysis showed a significant effect of postnatal age on FeNO (p = 0.007).

CONCLUSION

Our study suggests that FeNO is higher in mature infants than premature infants, and FeNO increased with postnatal age at approximately the same pace in both groups.

Predicting asthma exacerbation by impulse oscillometry evaluation of small airway function and fractional exhaled nitric oxide in preschool children

OBJECTIVE

To study impulse oscillometry (IOS) indices of peripheral airway function and FeNO as predictors of future loss of asthma control in preschool children.

METHODS

Patients aged 3 to 6 years who were actively being treated for asthma and children without asthma were enrolled in the study. Participants had no change in medication on visit 1 and returned for a follow-up visit within 8 to 12 weeks. At the first visit, nursing assessment, symptom history, IOS analysis, FeNO, and physician evaluation were repeated.

RESULTS

Fifty-one (64.6%) subjects had lost asthma control (UC-Group) and 28 (35.4%) subjects had maintained asthma control (C-Group) at their follow-up visit. Thirty-two children without asthma were enrolled in the study as a normal control group (N-Group). R5, R5-20, AX, and Z5 values were all significantly higher in subjects whose symptoms remained uncontrolled compared with those in the controlled asthma group (P < .01) and also significantly higher than those in the normal control group (P < .01). FeNO showed no significant difference between the UC-Group and C-Group (P = .399). Four indices-R5, R5-20, AX, and Z5-had an estimated area under the curve (AUC) of greater than 0.8 and were thus easily able to distinguish the UC-Group from the C-Group.

CONCLUSIONS

AX had the highest overall AUC (0.884) of the investigated parameters, and the optimal cut-off point of 37.435 cm H₂ O/L was able to predict future loss of asthma control in preschool children.

Tidal breath eNO measurements in a cohort of unsedated hospitalized neonates-A method validation

AIM

Exhaled Nitric oxide (eNO) is an inflammatory marker. In 2002 Hall et al. [J Appl Physiol. 92:59-66] established an infant eNO measurement method, fulfilling four criteria of feasibility: simple, non-invasive, without impact on the natural breathing pattern, and accounting for flow by NO output (V'NO). Although tidal breathing is accepted as an eNO measurement method in uncooperative patients, it is seldom used outside research labs. The variability and lack of validated methods have restrained from exploring the area in preterm and term neonates the last years. This study aimed to validate clinically feasible longitudinal online tidal eNO and V'NO in a real-life birth cohort of un-sedated, hospitalized preterm, and term neonates.

METHOD

We included 149 newborns, GA 28-42 weeks. Each scheduled for six repeated, non-invasive, on-line eNO measurements with Ecomedics CLD 88sp and NO-free air. We used three 60-second-eNO measurements. The method was adapted to fit preterm and term neonates with unstable respiration, without excluding sighs and surrounding breaths.

RESULT

Protocol measurements with a maximum mutual difference of 1 ppb succeeded in 85-99%, increasing with postnatal age. We performed mixed model analyses in three hierarchical measurement levels. Despite the irregular breathing of newborns, the predictions of individual eNO levels in the average infant was a 0.05 SD. Exhaled NO was flow-dependent (P = 0.028); V'NO but not eNO was associated with preterm birth (P < 0.001) and >24 h CPAP treatment (P = 0.0316).

CONCLUSION

We validated clinically, non-invasive, online eNO measurements in neonates. The method was well tolerated and exhibited low subject-specific-prediction-variance and high success rates.

6q12 and 11p14 variants are associated with postnatal exhaled nitric oxide levels and respiratory symptoms

BACKGROUND

Exhaled nitric oxide (eNO) is a biomarker of airway inflammation and seems to precede respiratory symptoms, such as asthma, in childhood. Identifying genetic determinants of postnatal eNO levels might aid in unraveling the role of eNO in epithelial function or airway inflammation and disease.

OBJECTIVE

We sought to identify genetic determinants of early postnatal eNO levels and subsequent respiratory symptoms during the first year of life.

METHODS

Within a population-based birth cohort, eNO levels were measured in healthy term infants aged 5 weeks during quiet tidal breathing in unsedated sleep. We assessed associations of single nucleotide polymorphisms with eNO levels in a genome-wide association study and subsequent symptoms of lower respiratory tract infections during the first year of life and asked whether this was modified by prenatal and early-life environmental factors.

RESULTS

We identified thus far unknown determinants of infant eNO levels: rs208515 (P = 3.3 × 10^-8), which is located at 6q12, probably acting in "trans" and explaining 10.3% of eNO level variance, and rs1441519 (P = 1.6 × 10^-6), which is located at 11p14, potentially affecting nitric oxide synthase 3 (NOS3) expression, as shown by means of in vitro functional analyses. Moreover, the 6q12 locus was inversely associated with subsequent respiratory symptoms (P < .05) and time to recovery after first respiratory symptoms during the first year of life (P < .05).

CONCLUSION

The identification of novel genetic determinants of infant eNO levels might implicate that postnatal eNO metabolism in healthy infants before first viral infections and sensitization is related to mechanisms other than those associated with asthma, atopy, or increased risk thereof later in life.

Rhinovirus Infections and Associated Respiratory Morbidity in Infants: A Prospective Cohort Study

BACKGROUND

Risk factors promoting rhinovirus (RV) infections are inadequately described in healthy populations, especially infants.

OBJECTIVES

To determine the frequency of symptomatic and asymptomatic RV infections and identify possible risk factors from host and environment among otherwise healthy infants.

METHODS

In a prospective birth cohort, respiratory health was assessed in 41 term-born infants by weekly telephonic interviews during the first year of life, and weekly nasal swabs were collected to determine RV prevalence. In a multilevel logistic regression model, associations between prevalence and respiratory symptoms during RV infections and host/environmental factors were determined.

RESULTS

Twenty-seven percent of nasal swabs in 41 infants tested positive for RVs. Risk factors for RV prevalence were autumn months [odds ratio (OR) = 1.71, P = 0.01, 95% confidence interval (CI): 1.13-2.61], outdoor temperatures between 5 and 10°C (OR = 2.33, P = 0.001, 95% CI: 1.41-3.86), older siblings (OR = 2.60, P = 0.001, 95% CI: 1.50-4.51) and childcare attendance (OR = 1.53, P = 0.07, 95% CI: 0.96-2.44). Fifty-one percent of RV-positive samples were asymptomatic. Respiratory symptoms during RV infections were less likely during the first 3 months of life (OR = 0.34, P = 0.003, 95% CI: 0.17-0.69) and in infants with atopic mothers (OR = 0.44, P = 0.008, 95% CI: 0.24-0.80). Increased tidal volume (OR = 1.67, P = 0.03, 95% CI: 1.04-2.68) and outdoor temperatures between 2 and 5°C (OR = 2.79, P = 0.02, 95% CI: 1.17-6.61) were associated with more symptoms.

CONCLUSIONS

RVs are highly prevalent during the first year of life, and most infections are asymptomatic. Frequency of RV infections is associated with environmental factors, while respiratory symptoms during RV infections are linked to host determinants like infant age, maternal atopy or premorbid lung function.

The Effect of Viral Infection on Exhaled Nitric Oxide in Children with Acute Asthma Exacerbations

BACKGROUND

Fraction of exhaled nitric oxide (Feno) level is used as an aid in the diagnosis and management of chronic asthma. Its role in acute asthma remains to be studied.

OBJECTIVE

To determine whether Feno levels are elevated in children with asthma exacerbations compared with baseline, and whether there is a difference in Feno levels based on PCR positive (+) (respiratory virus isolated by PCR analysis) versus PCR negative (-) (respiratory virus not isolated by PCR analysis) status.

METHODS

Children with a previous Feno level measurement while stable and who presented to an urgent care facility with an asthma exacerbation were enrolled. Feno levels, spirometry, and nasal swabs for viral PCR were obtained at the time of the exacerbation and following a course of prednisone. Data were available on 66 children. Linear mixed models were used to regress the outcomes of interest (FEV1, FEV1/forced vital capacity, forced expiratory flow at 25% to 75% of forced vital capacity, and natural log Feno) on detected virus (yes/no), visit (baseline, exacerbation, follow-up), and the interaction between the detected virus and visit.

RESULTS

Compared with baseline, higher Feno values and lower lung function were found at the time of an exacerbation. A respiratory virus was detected in 59% of the exacerbations. The interaction between PCR (+) and PCR (-) groups and visit on log Feno was marginally significant (P = .07). There was no difference in log Feno between the PCR (+) and PCR (-) groups at baseline, while higher log Feno was found in the PCR (-) group at the time of exacerbation and following prednisone (P = .05 and .001, respectively).

CONCLUSIONS

Higher Feno concentration in PCR (-) exacerbations suggests an eosinophilic predominance in nonviral compared with viral exacerbations.

DENND1B gene variants associate with elevated exhaled nitric oxide in healthy high-risk neonates

RATIONALE OF THE STUDY

Increased neonatal fraction of exhaled nitric oxide (FeNO) is associated with lung symptoms early in life, while predictors of neonatal FeNO levels are unknown. The objective of this study was to investigate perinatal and genetic predictors of FeNO in healthy at-risk neonates.

METHODS

FeNO was measured during sedation by single-breath and tidal-breathing techniques in 253 one-month-old neonates from the Copenhagen Prospective Study on Asthma in Childhood (COPSAC2000 ) birth cohort. The risk factor analyses included genetic variants in DENND1B, Filaggrin, and ORMDL3; anthropometrics; demographics; socioeconomics; paternal atopy; maternal smoking, and mother's consumption of paracetamol and antibiotics during 3rd trimester; and neonatal bacterial airway colonization.

RESULTS

FeNO values measured by the single-breath versus tidal-breathing technique yielded slightly higher values (median, 21.0 ppb; range, 2.0-74.0 ppb vs. 16.0 ppb; 1.0-67.0 ppb; P<0.0001) with increasing differences conditional on increasing FeNO values (P<0.0001). The multivariable analysis including all risk factors showed that the DENND1B rs2786098 C allele was associated with increasing levels of FeNO (additive model; +2.30 ppb per C allele; 95% CI, 0.10-5.00 ppb; P=0.04) and that children of atopic fathers had elevated FeNO (+2.90 ppb; 95% CI, 0.38-5.43 ppb; P=0.02). We did not detect association between the remaining risk factors and neonatal FeNO levels.

CONCLUSION

Increased FeNO in healthy newborns seems strongly influenced by genetics including father's atopy and child's variants in the DENND1B locus at chromosome 1q31.3.

Exhaled nitric oxide during infancy as a risk factor for asthma and airway hyperreactivity

Childhood asthma is often characterised by elevated exhaled nitric oxide (eNO), decreased lung function, increased airway reactivity and atopy; however, our understanding of when these phenotypic airway characteristics develop remains unclear. This study evaluated whether eNO, lung function, airway reactivity and immune characteristics during infancy are risk factors of asthma at age 5 years. Infants with eczema, enrolled prior to wheezy illness (n=116), had eNO, spirometry, airway reactivity and allergen sensitisation assessed at entry to the study and repeated at age 5 years (n=90). Increasing eNO at entry was associated with an increased risk of asthma (p=0.037) and increasing airway reactivity (p=0.015) at age 5 years. Children with asthma at 5 years of age had a greater increase in eNO between infancy and age 5 years compared with those without asthma (p=0.002). Egg sensitisation at entry was also associated with an increased risk of asthma (p=0.020), increasing eNO (p = 0.002) and lower forced expiratory flows (p=0.029) as a 5 year-old. Our findings suggest that, among infants at high risk for developing asthma, eNO early in life may provide important insights into the subsequent risk of asthma and its airway characteristics.

A new index to identify risk of multi-trigger wheezing in infants with first episode of wheezing

OBJECTIVE

Identification of young children who are likely to have multi-trigger wheezing is very important for early diagnosis and treatment of asthma. We investigate an index for predicting multi-trigger wheezing in infants with first episode of wheezing.

METHODS

One-hundred twenty-eight infants (2-20 months) with first episode of wheezing were followed for two years. Personal and family history of atopic diseases was recorded. Wheezing severity was evaluated using the Preschool Respiratory Assessment Measure. Sputum samples were collected from patients, stained with hematoxylin and eosin and studied by optical microscopy. The largest Creola body in sputum was located and the number of shed exfoliated airway epithelial cells (EAECs) counted. Recurrent wheezing was observed and classified as multi-trigger wheezing or non-multi-trigger wheezing. The predictive value of EAECs, family or personal history of atopic disease and the severity of wheezing for subsequent development of multi-trigger wheezing was analyzed.

RESULTS

Better predictive performance was achieved by considering the three measures together than by considering each separately. Receiver operator characteristic analysis showed that an index combining wheezing severity score of 9495 sputum EAECs and a family or personal history of atopic disease had a sensitivity of 95.1%, specificity of 74.2%, a positive predictive value of 58.6% and a negative predictive value of 93.6% for prediction of multi-trigger wheezing.

CONCLUSION

For infants with first episode of wheezing, wheezing severity score, family or personal history of atopic disease and number of EAECs in sputum can predict future multi-trigger wheezing.

Effect of intubation and mechanical ventilation on exhaled nitric oxide in preterm infants with and without bronchopulmonary dysplasia measured at a median postmenstrual age of 49 weeks

Background

Exhaled nitric oxide (eNO) is a marker of established airway inflammation in adults and children, but conflicting results have been reported in preterm infants when postnatal eNO is measured during tidal breathing. This study investigated the extent to which intubation and mechanical ventilation (MV) affect eNO and NO production (V’_NO) in preterm infants with and without bronchopulmonary dysplasia (BPD).

Patients and methods

A total of 176 very low birth weight (VLBW) infants (birth weight <1500 g), including 74 (42%) with and 102 (58%) without BPD, were examined at a median postmenstrual age of 49 weeks. Of the 176 infants, 84 (48%) did not require MV, 47 (27%) required MV for <7 days and 45 (26%) required MV for ≥7 days. Exhaled NO and tidal breathing parameters were measured in sleeping infants during tidal breathing, respiratory mechanics were assessed by occlusion tests, and arterialized capillary blood gas was analyzed.

Results

eNO was significantly correlated with tidal breathing parameters, while V’_NO was correlated with growth parameters, including age and body length (p < 0.001 each). Infants who were intubated and received MV for <7 days had significantly lower eNO (p < 0.01) and V’_NO (p < 0.01) than non-ventilated infants. In contrast, eNO and V’_NO did not differ significantly in non-ventilated infants and those receiving MV for ≥7 days. Multivariate analysis showed that independent on the duration of MV eNO (p = 0.003) and V’_NO (p = 0.018) were significantly increased in BPD infants comparable with the effects of intubation and MV on eNO (p = 0.002) and V’_NO (p = 0.017).

Conclusions

Preterm infants with BPD show only weak postnatal increases in eNO and V’_NO, but these changes may be obscured by the distinct influences of breathing pattern and invasive respiratory support. This limits the diagnostic value of postnatal eNO measurements in the follow-up of BPD infants.

Predictive value of fractional nitric oxide in asthma diagnosis-subgroup analyses

BACKGROUND

There are no studies investigating the benefit of using FeNO measurements in correlation with sensitization to perennial and seasonal allergens in children with asthma.

OBJECTIVE

To define the group of children with respiratory symptoms in whose FeNO measurement has predictive value for asthma. We assessed the effect of age, allergy profile, atopy, lung function and the presence of allergic rhinitis on interpretation of FeNO levels for clinical applications.

METHODS

It was a retrospective, cross-sectional study. We evaluated data from medical documentation of 1767 children with symptoms of allergic diseases such as asthma and/or allergic rhinitis. We included in the analyses subjects who had the following tests done during diagnostic procedures (single measurement): FeNO, spirometry, specific IgE results. All subjects had undergone a minimum 3-years prospective clinical observation after the first FeNO measurement until the later assignment (or not) of an asthma/allergic rhinitis diagnosis.

RESULTS

We included 1767 children into the analysis; asthma diagnosis was confirm in 1054 (59.6%) children. We showed that only atopy (OR: 1.9; 95%CI: 1.5-2.4) and presence of allergic rhinitis (OR: 1.6; 95%CI: 1.4-1.9) were independently associated with increased FeNO level. Only among patients with atopy and allergic rhinitis FeNO level (above 23 ppb) was associated with asthma diagnosis. Sensitivity, specificity, positive predictive value and negative predictive value of FeNO >23 ppb for asthma diagnosis were as follows: 0.9(95%CI: 0.68-0.98), 0.52(95%CI: 0.42-0.61), 0.25(95%CI: 0.16-0.37), 0.97(95%CI: 0.88-0.99).

CONCLUSION

We showed that in children with atopy and with allergic rhinitis a negative predictive value for asthma diagnosis was very high with the optimal cut-off point of FeNO 23 ppb. Therefore we showed the utility of FeNO measurements to exclude asthma in the subgroup of patients with atopy and allergic rhinitis.

Birth cohorts in asthma and allergic diseases: report of a NIAID/NHLBI/MeDALL joint workshop

Population-based birth cohorts on asthma and allergies increasingly provide new insights into the development and natural history of the diseases. More than 130 birth cohorts focusing on asthma and allergy have been initiated in the last 30 years. A National Institute of Allergy and Infectious Diseases; National Heart, Lung, and Blood Institute; Mechanisms of the Development of Allergy (MeDALL; Framework Programme 7 of the European Commission) joint workshop was held in Bethesda, Maryland, on September 11-12, 2012, with 3 objectives: (1) documenting the knowledge that asthma/allergy birth cohorts have provided, (2) identifying the knowledge gaps and inconsistencies, and (3) developing strategies for moving forward, including potential new study designs and the harmonization of existing asthma birth cohort data. The meeting was organized around the presentations of 5 distinct workgroups: (1) clinical phenotypes, (2) risk factors, (3) immune development of asthma and allergy, (4) pulmonary development, and (5) harmonization of existing birth cohorts. This article presents the workgroup reports and provides Web links (AsthmaBirthCohorts.niaid.nih.gov or www.medall-fp7.eu), where the reader will find tables describing the characteristics of the birth cohorts included in this report, the type of data collected at differing ages, and a selected bibliography provided by the participating birth cohorts.

Exhaled nitric oxide in symptomatic children at preschool age predicts later asthma

BACKGROUND

Prediction of asthma in young children with respiratory symptoms is hampered by the lack of objective measures applicable in clinical routine. In this prospective study in a preschool children cohort, we assessed whether the fraction of exhaled nitric oxide (FeNO), a biomarker of airway inflammation, is associated with asthma at school age.

METHODS

At baseline, IgE and eosinophils were measured in the blood, and FeNO was measured offline in 391 children aged 3-47 months with lower airway symptoms. We developed an asthma predictive index (API) including high FeNO as major criterion. At follow-up, primary outcome was physician-diagnosed asthma based on standardized interviews in those children reaching school age (n = 166).

RESULTS

FeNO was significantly elevated in those children with later asthma (68/166) as compared to children not developing asthma. Median (IQR) FeNO was 10.5 (6.6-17.2) vs. 7.4 (5.3-10.3) ppb. Per 5 ppb FeNO increase, the odds ratio (95% CI) for asthma increased by 2.44 (1.61-3.70) without changing when adjusting for confounders. Using the new API, children scored at risk had 58.0% probability for later asthma, whereas the negative predictive value was 78.2%, which was comparable to the classical API.

CONCLUSIONS

In this cohort of high-risk preschool children, elevated FeNO is associated with increased risk for school-age asthma. The new API including FeNO identifies children at risk of later asthma comparably to the classical API, but does not require blood sampling.

Fractional exhaled nitric oxide in healthy non-asthmatic 7-year olds and prenatal exposure to polycyclic aromatic hydrocarbons: nested regression analysis

The main goal of the study was to assess possible association between transplacental exposure to genotoxic PAH compounds assessed by the cord blood PAH-DNA adducts and fractional exhaled nitric oxide (FeNO) measured in healthy non-asthmatic children at the age of 7 years. The subjects included the subsample of 89 children who took part in the ongoing population based birth cohort study in Krakow and attended FeNO testing. The effect of transplacental PAH exposure was adjusted for potential confounders, such as maternal allergy and children's specific atopy to common domestic allergens.

RESULTS

FeNO values were significantly elevated in children with higher prenatal PAH exposure (gmean = 7.7 ppb; 95% CI: 5.8-10.2 ppb) compared with those at low exposure level (gmean = 3.8 ppb; 95% CI: 2.3-6.3) (P = 0.011). Children with maternal allergy had also significantly higher mean FeNO values (gmean = 13.7 ppb, 95% CI: 8.8-21.4 ppb) compared with the subjects whose mothers denied allergy (gmean = 5.6 ppb, 95% CI: 4.3-7.3 ppb) (P = 0.012). Similarly, FeNO values in atopic children were higher (gmean = 11.2 ppb; 95% CI: 3.8-32.8 ppb) than in non-atopic individuals (gmean = 6.0 ppb; 95% CI: 4.7-7.7 ppb, P = 0.079). The results of the nested multivariable linear regression analysis showed that both maternal allergy and sensitization of children to domestic aeroallergens jointly explained 10.4% of FeNO variance, however, the additional 10.9% was determined by prenatal PAH exposure.

CONCLUSION

FeNO is more than a marker useful for screening atopy or symptomatic bronchial inflammation and may also be a proxy for cytokine deregulation and "allergic response" phenotype possibly established in fetal period due to transplacental PAH exposure. Preliminary results of our study should encourage more studies on intrauterine PAH exposure and later respiratory symptoms.

Increased exhaled nitric oxide predicts new-onset rhinitis and persistent rhinitis in adolescents without allergic symptoms

BACKGROUND

The fraction of nitric oxide in exhaled air (FE(NO)) is increased in rhinitis and asthma. We have previously suggested that elevated FE(NO) levels in the absence of asthma symptoms may be a sign of 'early asthma'. In the present study, we hypothesize that elevated exhaled NO levels may also precede rhinitis symptoms.

OBJECTIVE

To investigate in a cohort of adolescents whether or not increased exhaled NO levels at the age of 13-14 years predicted new-onset or persistent rhinitis within a 4-year period.

METHODS

A total of 959 randomly selected adolescents (13-14 years) completed a questionnaire on respiratory symptoms at baseline and follow-up, 4 years later. Exhaled NO was measured at baseline. After exclusion of subjects with asthma diagnosis or asthma symptoms at baseline, 657 participants were eligible for the present study.

RESULTS

Higher FE(NO) levels at baseline were associated with increased risk for new-onset (P = 0.009) and persistent rhinitis (P = 0.03) within a 4-year period. The risk of new-onset rhinitis was 2.32 (1.23, 4.37) [OR (95% CI)] times higher if FE(NO) > 90th percentile of the group without rhinitis at baseline. This increased risk for new-onset rhinitis was significant [2.49 (1.24, 5.01)] after excluding subjects with allergic symptoms. The risk of persistent rhinitis was 5.11 (1.34, 19.57) times higher if FE(NO) > 90th percentile of the group without rhinitis at baseline.

CONCLUSION

Elevated exhaled nitric oxide levels predicted incident and persistent rhinitis in this population-based study of adolescents. Moreover, these findings were consistent after excluding subjects with allergic symptoms. Thus, it appears that elevation of exhaled NO precedes airway symptoms and predicts development of rhinitis in subjects without allergic symptoms or family history of allergic disease.

Exhaled Nitric Oxide in Acute Phase of Bronchiolitis and Its Relation with Episodes of Subsequent Wheezing in Children of Preschool Age

BACKGROUND: Fractional exhaled nitric oxide (FENO) levels are increased in children with asthma and in infants with recurrent wheezing, but the role of FENO in the acute phase of bronchiolitis is still not defined. OBJECTIVE: The aim of this study is to evaluate FENO values in the acute phase of bronchiolitis, compare them with healthy infants, and relate those values with the appearance of other wheezing episodes. METHODS: FENO values were determined in infants between 2 months and 2 years affected with RVS bronchiolitis by offline method. The FENO values collected in the acute phase were related with the respiratory clinical symptoms presented in the 2 years following the episode. RESULTS: A total of 30 patients were recruited: 15 in the bronchiolitis group and 15 in the control group. The average of the FENO values in the acute phase was 18.74 ppb (range 2-88) in the bronchiolitis group, and 8.75 ppb (range 2-24) in the control group. However, these results showed no significant statistical differences (p=0.176). Nevertheless, we found a positive correlation between the FENO values and the clinical score (Downes) of the bronchiolitis episode (p=0.023). In infants that presented other wheezing episodes in the 2 years after, the average of FENO in the acute phase of the first episode was 23.1 ppb (average of 10.25 ppb) versus 8.4 ppb (average 5.4 ppb) in the group of patients with no other episodes. The comparison of averages has no statistical significance. CONCLUSION: We found no differences in FENO between infants with bronchiolitis and healthy ones. The FENO values in the acute phase seems to be related to the severity of the disease but do not predict the appearance of wheezing episodes in the following 2 years.

Exhaled nitric oxide and urinary EPX levels in infants: a pilot study

BACKGROUND

Objective markers of early airway inflammation in infants are not established but are of great interest in a scientific setting. Exhaled nitric oxide (FeNO) and urinary eosinophilic protein X (uEPX) are a two such interesting markers.

OBJECTIVE

To investigate the feasibility of measuring FeNO and uEPX in infants and their mothers and to determine if any relations between these two variables and environmental factors can be seen in a small sample size. This was conducted as a pilot study for the ongoing Swedish Environmental Longitudinal Mother and child Asthma and allergy study (SELMA).

METHODS

Consecutive infants between two and six months old and their mothers at children's health care centres were invited, and 110 mother-infant pairs participated. FeNO and uEPX were analysed in both mothers and infants. FeNO was analyzed in the mothers online by the use of the handheld Niox Mino device and in the infants offline from exhaled air sampled during tidal breathing. A 33-question multiple-choice questionnaire that dealt with symptoms of allergic disease, heredity, and housing characteristics was used.

RESULTS

FeNO levels were reduced in infants with a history of upper respiratory symptoms during the previous two weeks (p < 0.002). There was a trend towards higher FeNO levels in infants with windowpane condensation in the home (p < 0.05). There was no association between uEPX in the infants and the other studied variables.

CONCLUSION

The use of uEPX as a marker of early inflammation was not supported. FeNO levels in infants were associated to windowpane condensation. Measuring FeNO by the present method may be an interesting way of evaluating early airway inflammation. In a major population study, however, the method is difficult to use, for practical reasons.

Respiratory muscle activity related to flow and lung volume in preterm infants compared with term infants

Infants with chronic lung disease (CLD) have a capacity to maintain functional lung volume despite alterations to their lung mechanics. We hypothesize that they achieve this by altering breathing patterns and dynamic elevation of lung volume, leading to differences in the relationship between respiratory muscle activity, flow and lung volume. Lung function and transcutaneous electromyography of the respiratory muscles (rEMG) were measured in 20 infants with CLD and in 39 healthy age-matched controls during quiet sleep. We compared coefficient of variations (CVs) of rEMG and the temporal relationship of rEMG variables, to flow and lung volume [functional residual capacity (FRC)] between these groups. The time between the start of inspiratory muscle activity and the resulting flow (tria)--in relation to respiratory cycle time--was significantly longer in infants with CLD. Although FRC had similar associations with tria and postinspiratory activity (corrected for respiratory cycle time), the CV of the diaphragmatic rEMG was lower in CLD infants (22.6 versus 31.0%, p = 0.030). The temporal relationship of rEMG to flow and FRC and the loss of adaptive variability provide additional information on coping mechanisms in infants with CLD. This technique could be used for noninvasive bedside monitoring of CLD.

Elevated exhaled nitric oxide in high-risk neonates precedes transient early but not persistent wheeze

RATIONALE

Elevated fractional exhaled nitric oxide (Fe(NO)) concentration has been suggested to predict early childhood wheeze and sensitization.

OBJECTIVES

To investigate the association between Fe(NO) in asymptomatic neonates and the development of wheeze patterns and atopic intermediary phenotypes in the first 6 years of life.

METHODS

We measured Fe(NO) in 253 healthy 1-month-old neonates from the Copenhagen Prospective Study on Asthma in Childhood birth cohort and monitored prospectively wheezy episodes by daily diary cards during the first 6 years of life. Total IgE, specific IgE, and blood eosinophil count were assessed at age 6 months, 4 years, and 6 years. Associations were studied by Cox regression, logistic regression, and generalized linear models.

MEASUREMENTS AND MAIN RESULTS

Increased neonatal Fe(NO) level was significantly associated with the development of recurrent wheeze in the first year of life (hazard ratio, 2.63; 95% confidence interval, 1.1 to 6.2; P = 0.026) but not thereafter. The association was unaffected by environmental tobacco smoke exposure. Fe(NO) was not associated with elevated levels of total IgE, specific IgE, or blood eosinophil count at any age point and was unrelated to neonatal lung function.

CONCLUSIONS

An elevated Fe(NO) level in asymptomatic neonates born to mothers with asthma preceded the development of transient early wheezing, but not persistent wheezing during preschool age, and was unrelated to atopy. This suggests an early disease process other than small airway caliber contributing to the transient wheezing phenotype.

Effect of elevated exhaled nitric oxide levels on the risk of respiratory tract illness in preschool-aged children with moderate-to-severe intermittent wheezing

BACKGROUND

The fractional concentration of exhaled nitric oxide (FeNO) is a noninvasive marker for airway inflammation but requires further study in preschool-aged children to determine its clinical relevance.

OBJECTIVE

To determine whether the risk of respiratory tract illnesses (RTIs), disease burden, and atopic features are related to FeNO in preschool-aged children with moderate-to-severe intermittent wheezing.

METHODS

We determined FeNO using the off-line tidal breathing technique in 89 children, aged 12 to 59 months, with moderate-to-severe intermittent wheezing. The risk of RTI was determined by comparing participants with a baseline FeNO of greater than the 75th percentile (24.4 ppb) with those with a baseline FeNO at the 75th percentile or lower using Cox regression analysis.

RESULTS

The risk of RTI was significantly higher in children with an FeNO of greater than 24.4 ppb relative to those with lower FeNO values (adjusted relative risk, 3.80; 95% confidence interval, 1.74-8.22; P < .001). FeNO levels of greater than 24.4 ppb were associated with more positive skin test results to aeroallergens (P = .03) but not with other atopic characteristics or historic parameters of illness burden.

CONCLUSIONS

An elevated FeNO in preschool-aged children with moderate-to-severe intermittent wheezing was associated with an increased risk of RTI during a 1-year follow-up. In addition, a higher FeNO was associated with aeroallergen sensitization.

Novel biomarkers in asthma: chemokines and chitinase-like proteins

PURPOSE OF REVIEW

Allergic asthma is a frequent lung disease in Western civilizations and is characterized by airway inflammation and tissue remodeling. Without early diagnosis and specific treatment, asthma results in a loss of lung function, impaired quality of life and the risk to die from uncontrolled asthma attacks. Thus, there is a need for specific biomarkers to detect asthma as soon as possible and to initiate the correct clinical treatment.

RECENT FINDINGS

Recent studies have highlighted the potential role of the chemokine (C-C motif) ligand 17 and the chitinase-like protein YKL-40 as novel biomarkers in asthma. Patient studies suggest that these proteins could be useful to identify asthmatics, to characterize disease severity or both in patients with asthma. Functional studies indicate that these molecules are more than correlated epiphenomena and instead contribute in significant ways to asthma pathogenesis.

SUMMARY

Assessments of chemokine (C-C motif) ligand 17 and YKL-40 may allow physicians to more accurately diagnose and predict the course of asthma and thereby allow therapy to be appropriately tailored for a given patient.

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 measurements in the first 2 years of life: methodological issues, clinical and epidemiological applications

Fractional exhaled nitric oxide (FeNO) is a useful tool to diagnose and monitor eosinophilic bronchial inflammation in asthmatic children and adults. In children younger than 2 years of age FeNO has been successfully measured both with the tidal breathing and with the single breath techniques. However, there are a number of methodological issues that need to be addressed in order to increase the reproducibility of the FeNO measurements within and between infants. Indeed, a standardized method to measure FeNO in the first 2 years of life would be extremely useful in order to meaningfully interpret FeNO values in this age group. Several factors related to the measurement conditions have been found to influence FeNO, such as expiratory flow, ambient NO and nasal contamination. Furthermore, the exposure to pre- and postnatal risk factors for respiratory morbidity has been shown to influence FeNO values. Therefore, these factors should always be assessed and their association with FeNO values in the specific study population should be evaluated and, eventually, controlled for.

There is evidence consistently suggesting that FeNO is increased in infants with family history of atopy/atopic diseases and in infants with recurrent wheezing. These findings could support the hypothesis that eosinophilic bronchial inflammation is present at an early stage in those infants at increased risk of developing persistent respiratory symptoms and asthma. Furthermore, it has been shown that FeNO measurements could represent a useful tool to assess bronchial inflammation in other airways diseases, such as primary ciliary dyskinesia, bronchopulmonary dysplasia and cystic fibrosis. Further studies are needed in order to improve the reproducibility of the measurements, and large prospective studies are warranted in order to evaluate whether FeNO values measured in the first years of life can predict the future development of asthma or other respiratory diseases.

Mannose-binding lectin cord blood levels and respiratory symptoms during infancy: a prospective birth cohort study

Respiratory infections cause considerable morbidity during infancy. The impact of innate immunity mechanisms, such as mannose-binding lectin (MBL), on respiratory symptoms remains unclear. The aims of this study were to investigate whether cord blood MBL levels are associated with respiratory symptoms during infancy and to determine the relative contribution of MBL when compared with known risk factors. This is a prospective birth cohort study including 185 healthy term infants. MBL was measured in cord blood and categorized into tertiles. Frequency and severity of respiratory symptoms were assessed weekly until age one. Association with MBL levels was analysed using multivariable random effects Poisson regression. We observed a trend towards an increased incidence rate of severe respiratory symptoms in infants in the low MBL tertile when compared with infants in the middle MBL tertile [incidence rate ratio (IRR) = 1.59; 95% confidence interval (CI): 0.95-2.66; p = 0.076]. Surprisingly, infants in the high MBL tertile suffered significantly more from severe and total respiratory symptoms than infants in the middle MBL tertile (IRR = 1.97; 95% CI: 1.20-3.25; p = 0.008). This association was pronounced in infants of parents with asthma (IRR = 3.64; 95% CI: 1.47-9.02; p = 0.005). The relative risk associated with high MBL was similar to the risk associated with well-known risk factors such as maternal smoking or childcare. In conclusion the association between low MBL levels and increased susceptibility to common respiratory infections during infancy was weaker than that previously reported. Instead, high cord blood MBL levels may represent a so far unrecognized risk factor for respiratory morbidity in infants of asthmatic parents.

Lung volume, breathing pattern and ventilation inhomogeneity in preterm and term infants

Background

Morphological changes in preterm infants with bronchopulmonary dysplasia (BPD) have functional consequences on lung volume, ventilation inhomogeneity and respiratory mechanics. Although some studies have shown lower lung volumes and increased ventilation inhomogeneity in BPD infants, conflicting results exist possibly due to differences in sedation and measurement techniques.

Methodology/Principal Findings

We studied 127 infants with BPD, 58 preterm infants without BPD and 239 healthy term-born infants, at a matched post-conceptional age of 44 weeks during quiet natural sleep according to ATS/ERS standards. Lung function parameters measured were functional residual capacity (FRC) and ventilation inhomogeneity by multiple breath washout as well as tidal breathing parameters. Preterm infants with BPD had only marginally lower FRC (21.4 mL/kg) than preterm infants without BPD (23.4 mL/kg) and term-born infants (22.6 mL/kg), though there was no trend with disease severity. They also showed higher respiratory rates and lower ratios of time to peak expiratory flow and expiratory time (t_PTEF/t_E) than healthy preterm and term controls. These changes were related to disease severity. No differences were found for ventilation inhomogeneity.

Conclusions

Our results suggest that preterm infants with BPD have a high capacity to maintain functional lung volume during natural sleep. The alterations in breathing pattern with disease severity may reflect presence of adaptive mechanisms to cope with the disease process.

Expired nitric oxide and airway reactivity in infants at risk for asthma

BACKGROUND

Family histories of atopy, as well as histories of atopic dermatitis and food allergy, are important risk factors for an infant to have asthma. Although atopic sensitization appears to contribute to the development of asthma, it is unclear when the airways become involved with the atopic process and whether airway function relates to the atopic characteristics of the infant.

OBJECTIVE

We sought to evaluate whether atopic infants without prior episodes of wheezing have increased expired nitric oxide (eNO) levels and heightened airway reactivity.

METHODS

Infants with eczema were recruited, and atopic status was defined by specific IgE levels to foods or aeroallergens and total IgE levels. eNO, forced expiratory flow at 75% exhaled volume (FEF(75)), and airway reactivity to inhaled methacholine were measured in sedated infants. Airway reactivity was quantified by using the provocative concentration to decrease FEF(75) by 30%.

RESULTS

Median age for the 114 infants evaluated was 10.7 months (range, 2.6-19.1 months). Infants sensitized to egg or milk compared with infants sensitized to neither egg nor milk had lower flows (FEF(75): 336 vs 285 mL/s, P < .003) and lower lnPC(30) (mg/mL) provocative concentrations to decrease FEF(75) by 30% (-0.6 vs -1.2, P < .02) but no difference in eNO levels. Infants with total serum IgE levels of greater than 20 IU/mL had higher eNO levels compared with infants with IgE levels of 20 IU/mL or less (14.6 vs 11.2 ppb, P < .023) but no difference in forced flows or airway reactivity.

CONCLUSIONS

Our findings suggest that atopic characteristics of the infant might be important determinants of the airway physiology of forced expiratory flows, airway reactivity, and eNO.

Complexity of chronic asthma and chronic obstructive pulmonary disease: implications for risk assessment, and disease progression and control

Although assessment of asthma control is important to guide treatment, it is difficult since the temporal pattern and risk of exacerbations are often unpredictable. In this Review, we summarise the classic methods to assess control with unidimensional and multidimensional approaches. Next, we show how ideas from the science of complexity can explain the seemingly unpredictable nature of bronchial asthma and emphysema, with implications for chronic obstructive pulmonary disease. We show that fluctuation analysis, a method used in statistical physics, can be used to gain insight into asthma as a dynamic disease of the respiratory system, viewed as a set of interacting subsystems (eg, inflammatory, immunological, and mechanical). The basis of the fluctuation analysis methods is the quantification of the long-term temporal history of lung function parameters. We summarise how this analysis can be used to assess the risk of future asthma episodes, with implications for asthma severity and control both in children and adults.

Relative impact of respiratory muscle activity on tidal flow and end expiratory volume in healthy neonates

INTRODUCTION

It has been suggested that infants dynamically regulate their tidal flow and end-expiratory volume level. The interaction between muscle activity, flow and lung volume in spontaneously sleeping neonates is poorly studied, since it requires the assessment of transcutaneous electromyography of respiratory muscles (rEMG) in matched comparison to lung function measurements.

METHODS

After determining feasibility and repeatability of rEMG in 20 spontaneously sleeping healthy neonates, we measured the relative impact of intercostal and diaphragmatic EMG activity in direct comparison to the resulting tidal flow and FRC.

RESULTS

We found good feasibility, repeatability and correlation of timing indices between rEMG activity and flow. The rEMG amplitude was significantly dependent on the resistive load of the face mask. Diaphragm and intercostal muscle activity commenced prior to the onset of flow and remained active during the expiratory cycle. The relative contribution of intercostal and diaphragmatic activity to flow was variable and changed dynamically.

CONCLUSION

Using matched rEMG, air flow and lung volume measurements, we have found good feasibility and repeatability of intercostal and diaphragm rEMG measurements and provide the first quantitative measures of the temporal relationship between muscle activity and flow in spontaneously sleeping healthy neonates. Lung mechanical function is dynamically regulated and adapts on a breath to breath basis. So, non-invasive rEMG measurements alone or in combination with lung function might provide a more comprehensive picture of pulmonary mechanics in future studies. The data describing the timing of EMG and flow may be important for future studies of EMG triggered mechanical ventilation.

The value of FeNO measurement in asthma management: the motion for Yes, it's NO--or, the wrong end of the Stick!

The utility of measurements of exhaled nitric oxide (FeNO) will likely depend on context, being most helpful in moderate and severe asthma, rather than mild asthmatics and community based studies. Atopy on its own is a cause of elevation in FeNO. Adult and paediatric studies have clearly established that measurement of some aspect of airway inflammation is part of state of the art management of asthma, but it is as yet unclear which of several techniques is most useful. The relationship between FeNO and sputum eosinophils is relatively loose, but this does not preclude it being a useful test in clinical practice. In fact, there are only poor correlations between sputum, proximal mucosal, and distal eosinophils, and the importance of these different compartments is unclear. A low FeNO in the setting of supposedly poorly controlled asthma should cast doubt on the diagnosis. We certainly cannot treat an isolated elevation in FeNO, which may be due to a simple viral cold, or constitutional. If FeNO is elevated, particularly if asthma is uncontrolled, it suggests an imbalance between anti-inflammatory therapy and pro-inflammatory environmental influences. Inadequate anti-inflammatory therapy may be due to the prescribed dose being too low; the drug delivery device not being used correctly; or the medication not being taken. Adverse pro-inflammatory environmental influences driving up FeNO include IgE and non-IgE mediated allergen sensitivity in the home, and even in the child's school. Novel technology allows home monitoring of FeNO, but the role of these devices is less clear. Although more data is needed properly to define the role of FeNO measurements in clinical practice, there is sufficient data already published to conclude that 'inflammometry' is an important part of asthma management at the more severe end of the spectrum, and that FeNO measurements are probably the most useful at the moment.

[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.

[What methods can we use to measure inflammation in the asthmatic child?]

Pulmonary function tests remain the best method to assess underlying bronchial inflammation, particularly distal airway flow. However, these tests are limited in their ability to differentiate treatment-reversible small airway obstruction from definitive remodeling related to a viral infection. The increased availability of the exhaled fraction of nitric oxide (FeNO) measurement means that this method is accessible and attractive. In spite of a number of studies, mainly in adults, its use in the management of asthma needs more investigation. Threshold values that permit optimum management are poorly defined, and strategies based on variations of FeNO do not result in reduction of the number of exacerbations, although they do permit better control of drug use and better control of inflammation. Sputum eosinophil counts are of interest for the prevention of exacerbations, although while not well validated they may be useful in some asthmatic children. Also, they require an experienced cytology laboratory. Finally, recent data on bronchial biopsies in children with difficult-to-treat asthma will be summarized.

Exhaled nitric oxide in childhood asthma: a review

As an 'inflammometer', the fraction of nitric oxide in exhaled air (Fe(NO)) is increasingly used in the management of paediatric asthma. Fe(NO) provides us with valuable, additional information regarding the nature of underlying airway inflammation, and complements lung function testing and measurement of airway hyper-reactivity. This review focuses on clinical applications of Fe(NO) in paediatric asthma. First, Fe(NO) provides us with a practical tool to aid in the diagnosis of asthma and distinguish patients who will benefit from inhaled corticosteroids from those who will not. Second, Fe(NO) is helpful in predicting exacerbations, and predicting successful steroid reduction or withdrawal. In atopic asthmatic children Fe(NO) is beneficial in adjusting steroid doses, discerning those patients who require additional therapy from those whose medication dose could feasibly be reduced. In pre-school children Fe(NO) may be of help in the differential diagnosis of respiratory symptoms, and may potentially allow for better targeting and monitoring of anti-inflammatory treatment.

How can we measure the impact of pollutants on respiratory function in very young children? Methodological aspects

There is increasing evidence that air pollution particularly affects infants and small preschool children. However, detecting air pollution effects on lung function in small children is technically difficult and requires non-invasive methods that can assess lung function and inflammatory markers in larger cohorts. This review discusses the principles, usefulness and shortcomings of various lung function techniques used to detect pollution effects in small children. The majority of these techniques have been used to detect effects of the dominant indoor pollutant, tobacco exposure. However there is increasing evidence that non-invasive lung function techniques can also detect the effects of outdoor air pollution.

Deadspace estimation from CO2 versus molar mass measurements in infants

BACKGROUND

Estimation of respiratory deadspace is often based on the CO2 expirogram, however presence of the CO2 sensor increases equipment deadspace, which in turn influences breathing pattern and calculation of lung volume. In addition, it is necessary to correct for the delay between the sensor and flow signals. We propose a new method for estimation of effective deadspace using the molar mass (MM) signal from an ultrasonic flowmeter device, which does not require delay correction. We hypothesize that this estimation is correlated with that calculated from the CO2 signal using the Fowler method.

METHODS

Breath-by-breath CO2, MM and flow measurements were made in a group of 77 term-born healthy infants. Fowler deadspace (Vd,Fowler) was calculated after correcting for the flow-dependent delay in the CO2 signal. Deadspace estimated from the MM signal (Vd,MM) was defined as the volume passing through the flowhead between start of expiration and the 10% rise point in MM.

RESULTS

Correlation (r = 0.456, P < 0.0001) was found between Vd,MM and Vd,Fowler averaged over all measurements, with a mean difference of -1.4% (95% CI -4.1 to 1.3%). Vd,MM ranged from 6.6 to 11.4 ml between subjects, while Vd,Fowler ranged from 5.9 to 12.0 ml. Mean intra-measurement CV over 5-10 breaths was 7.8 +/- 5.6% for Vd,MM and 7.8 +/- 3.7% for Vd,Fowler. Mean intra-subject CV was 6.0 +/- 4.5% for Vd,MM and 8.3 +/- 5.9% for Vd,Fowler. Correcting for the CO2 signal delay resulted in a 12% difference (P = 0.022) in Vd,Fowler. Vd,MM could be obtained more frequently than Vd,Fowler in infants with CLD, with a high variability.

CONCLUSIONS

Use of the MM signal provides a feasible estimate of Fowler deadspace without introducing additional equipment deadspace. The simple calculation without need for delay correction makes individual adjustment for deadspace in FRC measurements possible. This is especially important given the relative large range of deadspace seen in this homogeneous group of infants.