Ultrafine particle exposure and biomarkers of effect on small airways in children.

The small size and large surface area of ultrafine particles (UFP) enhance their ability to deposit in the lung periphery and their reactivity. The Ultrafine Particles from Traffic Emissions and Children's Health (UPTECH) cross-sectional study was conducted in 8-11-year-old schoolchildren attending 25 primary (elementary) schools, randomly selected from the Brisbane Metropolitan Area, Queensland, Australia. Main study findings outlined indirect evidence of distal airway deposition (raised C reactive protein) but as yet, there is no direct evidence in the literature of effects of UFP exposure on peripheral airway function. We present further UPTECH study data from two sensitive peripheral airway function tests, Oscillometry and Multiple Breath Nitrogen Washout (MBNW), performed in 577 and 627 children (88% and 96% of UPTECH study cohort) respectively: mean(SD) age 10.1(0.9) years, 46% male, with 50% atopy and 14% current asthma. Bayesian generalised linear mixed effects regression models were used to estimate the effect of UFP particle number count (PNC) exposure on key oscillometry (airway resistance, (Rrs), and reactance, (Xrs)) and MBNW (lung clearance index, (LCI) and functional residual capacity, (FRC)) indices. We adjusted for age, sex, and height, and potential confounders including socio-economic disadvantage, PM2.5 and NO2 exposure. All models contained an interaction term between UFP PNC exposure and atopy, allowing estimation of the effect of exposure on non-atopic and atopic students. Increasing UFP PNC was associated with greater lung stiffness as evidenced by a decrease in Xrs [mean (95% credible interval) -1.63 (-3.36 to -0.05)%] per 1000#.cm-3]. It was also associated with greater lung stiffness (decrease in Xrs) in atopic subjects across all models [mean change ranging from -2.06 to -2.40% per 1000#.cm-3]. A paradoxical positive effect was observed for Rrs across all models [mean change ranging from -1.55 to -1.70% per 1000#.cm-3] (decreases in Rrs indicating an increase in airway calibre), which was present for both atopic and non-atopic subjects. No effects on MBNW indices were observed. In conclusion, a modest detrimental effect of UFP on peripheral airway function among atopic subjects, as assessed by respiratory system reactance, was observed extending the main UPTECH study findings which reported a positive association with a biomarker for systemic inflammation, C-reactive protein (CRP). Further studies are warranted to explore the pathophysiological mechanisms underlying increased respiratory stiffness, and whether it persists through to adolescence and adulthood.

Maternal asthma is associated with reduced lung function in male infants in a combined analysis of the BLT and BILD cohorts.

RATIONALE: Asthma in pregnancy is associated with respiratory diseases in the offspring. OBJECTIVE: To investigate if maternal asthma is associated with lung function in early life. METHODS: Data on lung function measured at 5-6 weeks of age were combined from two large birth cohorts: the Bern Infant Lung Development (BILD) and the Australian Breathing for Life Trial (BLT) birth cohorts conducted at three study sites (Bern, Switzerland; Newcastle and Sydney, Australia). The main outcome variable was time to reach peak tidal expiratory flow as a percentage of total expiratory time(tPTEF:tE%). Bayesian linear hierarchical regression analyses controlling for study site as random effect were performed to estimate the effect of maternal asthma on the main outcome, adjusting for sex, birth order, breast feeding, weight gain and gestational age. In separate adjusted Bayesian models an interaction between maternal asthma and sex was investigated by including an interaction term. MEASUREMENTS AND MAIN RESULTS: All 406 BLT infants were born to mothers with asthma in pregnancy, while 193 of the 213 (91%) BILD infants were born to mothers without asthma. A significant interaction between maternal asthma and male sex was negatively associated with tPTEF:tE% (intercept 37.5; estimate: -3.5; 95% credible interval -6.8 to -0.1). Comparing the model posterior probabilities provided decisive evidence in favour of an interaction between maternal asthma and male sex (Bayes factor 33.5). CONCLUSIONS: Maternal asthma is associated with lower lung function in male babies, which may have lifelong implications on their lung function trajectories and future risk of wheezing and asthma.

Association between peripheral airway function and neutrophilic inflammation in asthma.

BACKGROUND AND OBJECTIVE: Small airway dysfunction is associated with asthma severity and control, but its association with airway inflammation is unknown. The aim was to determine the association between sputum inflammatory cells and the site of small airway dysfunction, measured by multiple breath nitrogen washout in convection-dependent (Scond) and more peripheral diffusion-dependent (Sacin) airways. METHODS: Fifty-three (20-67 years) subjects with asthma on inhaled corticosteroid (ICS) treatment were characterized by spirometry, Scond, Sacin and induced sputum differential counts. %Predicted values for Scond and Sacin were calculated from published reference equations to adjust for the effects of age. Univariate correlations were assessed using the Spearman test. Multivariate linear regressions were performed to account for potential confounders, including age, gender, disease duration, body mass index and ICS dose. RESULTS: Sacin (%predicted) correlated significantly with neutrophil% (rs = 0.33, P = 0.02), ICS dose (rs = -0.28, P = 0.04) and age (rs = 0.27, P = 0.05). In multivariate analysis, Sacin related only to neutrophil% (adjusted R(2) = 0.18, P = 0.001). Scond (%predicted) correlated significantly only with eosinophil% (rs = 0.39, P = 0.004). There was a trend for a negative relationship with ICS dose (rs = -0.26, P = 0.06). In multivariate analysis, Scond related to eosinophil% and ICS dose independently (adjusted R(2) = 0.12, P = 0.02). CONCLUSIONS: Acinar and conductive airway dysfunction is associated with different inflammatory profiles in asthmatic airways, independently of the effects of age and disease duration. The association between acinar airway dysfunction and neutrophilic airway inflammation may have implications for asthma treatment.

The role of the small airways in the clinical expression of asthma in adults.

BACKGROUND: The clinical relevance of increased ventilation heterogeneity, a marker of small-airways disease, in asthmatic patients is unclear. Ventilation heterogeneity is an independent determinant of airway hyperresponsiveness (AHR), improves with bronchodilators and inhaled corticosteroids (ICSs), and worsens during exacerbations, but its relationship to asthma control is unknown. OBJECTIVE: We sought to determine the association between ventilation heterogeneity and current asthma control before and after ICS treatment. METHODS: Adult subjects with asthma had lung function and asthma control (5-item Asthma Control Questionnaire [ACQ-5 score] ≥1.5 = poorly controlled, ACQ-5 score ≤0.75 = well controlled) measured at baseline. A subgroup with AHR had repeat measurements after 3 months of high-dose ICS treatment. The indices of ventilation heterogeneity in the regions of the lung where gas transport occurs predominantly through convection (ventilation heterogeneity in convection-dependent airways [Scond]) and through diffusion (ventilation heterogeneity in diffusion-dependent airways [Sacin]) were derived by using the multiple-breath nitrogen washout technique. RESULTS: At baseline (n = 105), subjects with poorly controlled asthma had worse FEV(1), fraction of exhaled nitric oxide measured at 200 mL/s (Feno), Scond, and Sacin values. In the treatment group (n = 50) spirometric, Feno, residual volume (RV)/total lung capacity (TLC), AHR, and Scond values significantly improved. Asthma control also improved (mean ACQ-5 score, 1.3-0.7; P < .0001). The change in ACQ-5 score correlated with changes in Feno (r(s) = 0.31, P = .03), Sacin (r(s) = 0.32, P = .02), and Scond (r(s) = 0.41, P = .003) values. The independent predictors of a change in asthma control were changes in Scond and Sacin values (model r(2) = 0.20, P = .005). CONCLUSIONS: Current asthma control is associated with markers of small-airways disease. Improvements in ventilation heterogeneity with anti-inflammatory therapy are associated with improvements in symptoms. Sensitive measures of small-airway function might be useful in monitoring the response to therapy in asthmatic subjects.

Long-term morbidity of respiratory viral infections during chemotherapy in children with leukaemia.

BACKGROUND: Respiratory viruses are a common cause of infection in immunosuppressed children undergoing cancer therapy. Pulmonary sequelae have been documented following respiratory viral infections (RVIs) in hematopoietic stem cell transplant (HSCT) recipients; however potential late effects in children undergoing nonmyeloablative chemotherapy have not been investigated. AIM: To evaluate the long-term pulmonary morbidity of respiratory viral infections during chemotherapy in children with acute lymphoblastic leukemia (ALL). METHODS: Childhood ALL survivors, aged 7 to 18 years, greater than 6 months posttreatment were recruited. Exclusion criteria included HSCT or proven bacterial/fungal respiratory infection during treatment. Subjects were classified into "viral" or "control" groups according to retrospective medical records that documented the presence of laboratory-proven RVIs during chemotherapy. Symptom questionnaires (Liverpool, ISAAC) and lung function testing (spirometry, plethysmography, diffusing capacity, forced oscillation technique to ATS/ERS standards) were then performed cross-sectionally at the time of recruitment. RESULTS: Fifty-four patients (31 viral, 23 control) were recruited: median (range) age 11.2 (7.2-18.1) years, and at 4.9 (0.5-13) years posttherapy. Abnormalities were detected in 17 (31%) individuals (8 viral, 9 control), with the most common being DLCO impairment (3 viral, 4 control) and reduced respiratory reactance at 5 Hz (5 viral, 6 control). Children with RVIs during chemotherapy reported more current respiratory symptoms, particularly wheeze (odds ratio [OR], 3.0; 95% confidence interval [CI]: 0.9-10.0; P = .09) and cough (OR, 2.7; 95% CI: 0.8-9.5; P = .11). No differences in lung function tests were observed between the two groups. CONCLUSIONS: Our study found children with RVIs during chemotherapy developed more long-term respiratory symptoms than controls; however, differences did not reach statistical significance. No differences in static lung function were found between the two groups. Overall, pulmonary abnormalities and/or significant ongoing respiratory symptoms were detected in nearly a third of ALL survivors treated without HSCT. Larger, prospective studies are warranted to evaluate the etiology and clinical significance of these findings.

Comparison of facemask and mouthpiece interfaces for multiple breath washout measurements.

BACKGROUND: Different interfaces (mouthpiece/nose clip vs. facemask) are used during multiple breath washout (MBW) tests in young children. METHODS: We investigated the effect of interface choice and breathing modalities on MBW outcomes in healthy adults and preschool children. RESULTS: In adults (n = 26) facemask breathing significantly increased LCI, compared to mouthpiece use (mean difference (95% CI) 0.4 (0.2; 0.6)), with results generalizable across sites and different equipment. Exclusively nasal breathing within the facemask increased LCI, as compared to oral breathing. In preschoolers (2-6 years, n = 46), no significant inter-test difference was observed across interfaces for LCI or FRC. Feasibility and breathing stability were significantly greater with facemask (incorporating dead space volume minimization), vs. mouthpiece. This was more pronounced in subjects <4 years of age. CONCLUSION: Both nasal vs. oral breathing and mouthpiece vs. facemask affect LCI measurements in adults. This effect was minimal in preschool children, where switching between interfaces is most likely to occur.

A Systematic Approach to Multiple Breath Nitrogen Washout Test Quality.

BACKGROUND: Accurate estimates of multiple breath washout (MBW) outcomes require correct operation of the device, appropriate distraction of the subject to ensure they breathe in a manner representative of their relaxed tidal breathing pattern, and appropriate interpretation of the acquired data. Based on available recommendations for an acceptable MBW test, we aimed to develop a protocol to systematically evaluate MBW measurements based on these criteria. METHODS: 50 MBW test occasions were systematically reviewed for technical elements and whether the breathing pattern was representative of relaxed tidal breathing by an experienced MBW operator. The impact of qualitative and quantitative criteria on inter-observer agreement was assessed across eight MBW operators (n = 20 test occasions, compared using a Kappa statistic). RESULTS: Using qualitative criteria, 46/168 trials were rejected: 16.6% were technically unacceptable and 10.7% were excluded due to inappropriate breathing pattern. Reviewer agreement was good using qualitative criteria and further improved with quantitative criteria from (κ = 0.53-0.83%) to (κ 0.73-0.97%), but at the cost of exclusion of further test occasions in this retrospective data analysis. CONCLUSIONS: The application of the systematic review improved inter-observer agreement but did not affect reported MBW outcomes.

Ventilation heterogeneity is associated with airway responsiveness in asthma but not COPD.

Airway hyperresponsiveness (AHR) occurs in both asthma and COPD. In older people with asthma, AHR is associated with increased acinar ventilation heterogeneity, but it is unknown if this association exists in COPD. Thirty one COPD and 19 age-matched asthmatic subjects had measures of spirometry, lung volumes, exhaled nitric oxide, ventilation heterogeneity, and methacholine challenge. Indices of acinar (Sacin) and conducting (Scond) airway ventilation heterogeneity were calculated from the multiple breath nitrogen washout. Predictors of AHR were then determined. In COPD, AHR was predicted by lower Sacin and lower FVC (model r(2)=0.35, p=0.001). In asthma, AHR was predicted by higher Sacin and higher residual volume (model r(2)=0.62, p<0.001). These findings suggest that airway responsiveness in COPD and asthma is determined by underlying disease-specific processes, rather than a common pattern of physiological abnormality.

The effect of airway remodelling on airway hyper-responsiveness in asthma.

RATIONALE: The mechanisms of airway hyper-responsiveness are only partially understood and the contribution of airway remodelling is unknown. Airway remodelling can be assessed by measuring airway distensibility, which is reduced in asthma, even when lung function is normal. We hypothesised that airway remodelling contributes to airway hyper-responsiveness in asthma, independent of steroid-responsive airway inflammation. OBJECTIVES: To determine the relationship between airway distensibility and airway responsiveness at baseline and after 12 weeks of inhaled corticosteroid therapy in a group of asthmatics with airway hyper-responsiveness. METHODS: Nineteen doctor-diagnosed asthmatics had airway distensibility measured as the slope of the relationship between conductance and lung volume by the forced oscillation technique. Lung function, exhaled nitric oxide and methacholine challenge were also measured. Subjects had inhaled corticosteroid therapy for 12 weeks after which all measurements were repeated. RESULTS: At baseline, airway distensibility (mean, 95%CI) was 0.19(0.14-0.23) cm H(2)O(-1)s(-1), exhaled nitric oxide was 13.1(10.3-16.6)ppb and airway distensibility correlated with eNO (p=0.04) and disease duration (p=0.02) but not with airway responsiveness (p=0.46), FEV(1) (p=0.09) or age (p=0.23). After treatment, exhaled nitric oxide decreased (p=0.0002), FEV(1) improved (p=0.0001), airway responsiveness improved (p=0.0002), and there was a small improvement in airway distensibility but it did not normalise (p=0.05). Airway distensibility was not correlated with either exhaled nitric oxide (p=0.49) or airway responsiveness (p=0.20). CONCLUSIONS: Uncontrolled airway inflammation causes a small decrease in the distensibility of the airways of asthmatics with airway hyper-responsiveness. The lack of association between airway responsiveness and airway distensibility, both before and after 12 weeks ICS treatment, suggests that airway remodelling does not contribute to airway hyper-responsiveness in asthma.

Obesity is a determinant of asthma control independent of inflammation and lung mechanics.

BACKGROUND: It is unclear why obesity is associated with worse asthma control. We hypothesized that (1) obesity affects asthma control independent of spirometry, airway inflammation, and airway hyperresponsiveness (AHR) and (2) residual symptoms after resolution of inflammation are due to obesity-related changes in lung mechanics. METHODS: Forty-nine subjects with asthma underwent the following tests, before and after 3 months of high-dose inhaled corticosteroid (ICS) treatment: five-item asthma control questionnaire (ACQ-5), spirometry, fraction of exhaled nitric oxide (Feno), methacholine challenge, and the forced oscillation technique, which allows for the calculation of respiratory system resistance (Rrs) and respiratory system reactance (Xrs) as indicators of airway caliber and elastic load, respectively. The effects of treatment were assessed by BMI group (18.5-24.9, 25-29.9, and ≥ 30 kg/m²) using analysis of variance. Multiple regression analyses determined the independent predictors of ACQ-5 results. RESULTS: At baseline, the independent predictors of ACQ-5 results were FEV(1), Feno, and BMI (model r² = 0.38, P < .001). After treatment, asthma control, spirometry, airway inflammation, and AHR improved similarly across BMI groups. The independent predictors of ACQ-5 results after treatment were Rrs and BMI (model r² = 0.42, P < .001). CONCLUSIONS: BMI is a determinant of asthma control independent of airway inflammation, lung function, and AHR. After ICS treatment, BMI again predicts ACQ-5 results, but independent of obesity-related changes in lung mechanics.

Predictors of airway hyperresponsiveness differ between old and young patients with asthma.

BACKGROUND: Age-related increases in morbidity and mortality due to asthma may be due to changes in pathophysiology as patients with asthma get older. There is limited knowledge about the effects of age on the predictors of airway hyperresponsiveness (AHR), a key feature of asthma. The aim of this study was to determine if the pathophysiologic predictors of AHR, including inflammation, ventilation heterogeneity, and airway closure, differed between young and old patients with asthma. METHODS: Sixty-one young (18-46 years) and 43 old (50-80 years) patients with asthma had lung function, lung volumes, fraction of exhaled nitric oxide, ventilation heterogeneity, and airway responsiveness to methacholine measured. Airway response to methacholine was measured by the dose-response slope, as the percent fall in FEV(1) per micromole of methacholine. Indices of ventilation heterogeneity were calculated for convection-dependent and diffusion-dependent airways. RESULTS: In young patients with asthma, the independent predictors of AHR were convection-dependent ventilation heterogeneity, exhaled nitric oxide, and % predicted FEV(1)/FVC (model r(2) = 0.51, P < .0001). In old patients with asthma, the independent predictors of airway responsiveness were % predicted residual volume, diffusion-dependent ventilation heterogeneity, and % predicted FEV(1) (model r(2) = 0.57, P < .0001). CONCLUSIONS: In old patients with asthma, AHR is predicted by gas trapping and ventilation heterogeneity in peripheral, diffusion-dependent airways. In the young, it is predicted by ventilation heterogeneity in less peripheral conducting airways and by inflammation. These findings suggest that there are differences in the pathophysiologic determinants of AHR between young and old patients with asthma.