Gas trapping is associated with severe exacerbation in asthmatic children

Inter-relationships among neutrophilic inflammation, air trapping and future exacerbation in COPD: an analysis of ECOPD study

BACKGROUND

The inter-relationships among neutrophilic airway inflammation, air trapping and future exacerbation in chronic obstructive pulmonary disease (COPD) remain unclear.

OBJECTIVE

To evaluate the associations between sputum neutrophil proportions and future exacerbation in COPD and to determine whether these associations are modified by significant air trapping.

METHODS

Participants with completed data were included and followed up to the first year in the Early Chronic Obstructive Pulmonary Disease study (n=582). Sputum neutrophil proportions and high-resolution CT-related markers were measured at baseline. Sputum neutrophil proportions were dichotomised based on their median (86.2%) to low and high levels. In addition, subjects were divided into the air trapping or non-air trapping group. Outcomes of interest included COPD exacerbation (separately any, severe and frequent exacerbation, occurring in the first year of follow-up). Multivariable logistic regressions were performed to examine the risk of severe exacerbation and frequent exacerbation with either neutrophilic airway inflammation groups or air trapping groups.

RESULTS

There was no significant difference between high and low levels of sputum neutrophil proportions in the exacerbation in the preceding year. After the first year of follow-up, subjects with high sputum neutrophil proportions had increased risks of severe exacerbation (OR=1.68, 95% CI: 1.09 to 2.62, p=0.020). Subjects with high sputum neutrophil proportions and significant air trapping had increased odds of having frequent exacerbation (OR=3.29, 95% CI: 1.30 to 9.37, p=0.017) and having severe exacerbation (OR=2.72, 95% CI: 1.42 to 5.43, p=0.003) when compared with those who had low sputum neutrophil proportions and non-air trapping.

CONCLUSIONS

We found that subjects with high sputum neutrophil proportions and significant air trapping are prone to future exacerbation of COPD. It may be a helpful predictor of future exacerbation.

Indoor environmental exposures and obstructive lung disease phenotypes among children with asthma living in poor urban neighborhoods

BACKGROUND

Air trapping is an obstructive phenotype that has been associated with more severe and unstable asthma in children. Air trapping has been defined using pre- and postbronchodilator spirometry. The causes of air trapping are not completely understood. It is possible that environmental exposures could be implicated in air trapping in children with asthma.

OBJECTIVE

We investigated the association between indoor exposures and air trapping in urban children with asthma.

METHODS

Children with asthma aged 5 to 17 years living in Baltimore and enrolled onto the Environmental Control as Add-on Therapy for Childhood Asthma study were evaluated for air trapping using spirometry. Aeroallergen sensitization was assessed at baseline, and spirometry was performed at 0, 3, and 6 months. Air trapping was defined as an FVC z score of less than -1.64 or a change in FVC with bronchodilation of ≥10% predicted. Logistic normal random effects models were used to evaluate associations of air trapping and indoor exposures.

RESULTS

Airborne and bedroom floor mouse allergen concentrations were associated with air trapping but not airflow limitation (odds ratio 1.19, 95% confidence interval 1.02-1.37, P = .02 per 2-fold increase in airborne mouse allergen; odds ratio 1.23, 95% confidence interval 1.07-1.41, P = .003 per 2-fold increase in bedroom floor mouse allergen). Other indoor exposures (cockroach, cat, dog, dust mite, particulate matter, and nicotine) were not associated with air trapping or airflow limitation.

CONCLUSION

Mouse allergen exposure, but not other indoor exposure, was associated with air trapping in urban children with asthma.

Frequência de alterações espirométricas, aprisionamento aéreo e hiperinsuflação pulmonar em crianças e adolescentes com asma grave resistente à terapia

Objetivos: avaliar a frequência de alterações espirométricas e pletismográficas em crianças e adolescentes com asma grave resistente à terapia (AGRT). Além disso, testaram-se possíveis associações entre esses desfechos.Métodos: trata-se de um estudo retrospectivo, no qual foram incluídas crianças e adolescentes (6-18 anos), com diagnóstico de AGRT, e que se encontravam em acompanhamento ambulatorial regular. Todos deveriam possuir informações antropométricas (peso, altura, índice de massa corporal), demográficas (idade, etnia e sexo), clínicas (teste cutâneo, teste de controle da asma, tabagismo familiar e medicações em uso) e de função pulmonar (espirometria e pletismografia corporal) registradas no banco de dados do serviço. Os testes de função pulmonar seguiram as recomendações das diretrizes nacionais e internacionais. Para fins estatísticos, utilizou-se análise descritiva e o teste de qui-quadrado de Pearson.Resultados: de um total de 15 pacientes com AGRT, 12 deles foram incluídos na amostra. A média de idade foi de 12,2 anos, com predomínio do sexo feminino (66,7%). Destes, 50,0% apresentaram a doença controlada, 83,3% foram considerados atópicos e 50,0% tinham histórico de tabagismo familiar. Em relação aos testes de função pulmonar (% do previsto), as médias dos parâmetros espirométricos e de plestismografia corporal encontraram-se dentro dos limites inferiores da normalidade. Apenas 16,7% da amostra apresentou espirometria alterada (<percentil 5), 25,0% aprisionamento aéreo (volume residual>130,0%) e 16,7% hiperinsuflação pulmonar (capacidade pulmonar total>120,0%). Houve frequência estatisticamente maior (p=0,045) de aprisionamento aéreo nos participantes com espirometria alterada, em comparação à espirometria normal. Contudo, não se observou diferença (p=0,341) em relação à hiperinsuflação pulmonar.Conclusões: os achados demonstraram pouco comprometimento espirométrico e dos volumes e das capacidades pulmonares em crianças e adolescentes com AGRT. Além disso, aqueles participantes com espirometria alterada obtiveram frequência maior de aprisionamento aéreo no exame de pletismografia corporal.

Peripheral airways involvement in children with asthma exacerbation

Objective

The literature provides some evidence of peripheral airways key role in the pathogenesis of asthma. However, the extent to which lung periphery including acinar zone contribute to asthma activity and control in pediatric population is unclear. Therefore, the aim of the study was to estimate peripheral airways involvement in children with asthma exacerbation and stable asthma simultaneously via different pulmonary function tests.

Methods

Children with asthma exacerbation (n = 20) and stable asthma (n = 22) performed spirometry, body plethysmography, exhaled nitric oxide, impulse oscillometry (IOS), and multiple‐breath washout (MBW).

Results

Peripheral airway's function indexes were increased in children with asthma, particularly in group with asthma exacerbation when compared with stable asthma group. The prevalence of abnormal results was significantly higher in asthma exacerbation. All children with asthma exacerbation had conductive ventilation inhomogeneity; 76% had acinar ventilation inhomogeneity. According to IOS measurements, resistance and reactance were within normal range, but other IOS parameters were significantly higher in children with asthma exacerbation compared with stable asthma group. The 36% of children with acute asthma had air trapping.

Conclusion

Significant involvement of peripheral airways was observed in children with asthma, particularly in asthma exacerbation, which determine lung periphery as important additional target for therapy and provide new insights into pathophysiological process of pediatric asthma.

Residual Volume Responsiveness Testing May Improve the Detection of Reversible Airway Obstruction in Asthma

BACKGROUND

Residual volume responsiveness to bronchodilator administration has been observed in subjects with chronic obstructive pulmonary disease. However, the prevalence of residual volume (RV) responsiveness has not been formally studied in asthma.

OBJECTIVE

To identify the prevalence and magnitude of RV responsiveness in asthma.

METHODS

Physician-diagnosed adult subjects with asthma on treatment for >12 months were prospectively recruited to perform spirometry and measurement of lung volumes using body plethysmography before and after administration of 360 μg of albuterol.

RESULTS

Among 120 subjects, 76% were women. The ethnic composition was 64% Caucasian, 32% Hispanic, and 13% African American. The mean age was 52 ± 15 years. The mean duration of asthma was 16 ± 15 years. The mean RV% responsiveness was -7.74 ± 14. Whereas patients with the lowest baseline forced expiratory volume in 1 second (FEV1) value showed the highest mean responsiveness (P = .001), the baseline RV value had minimal influence on RV responsiveness. Using -7.74% to define significant RV responsiveness, and ≥12% and ≥200 mL to define significant FEV1 responsiveness, more subjects showed isolated RV responsiveness (37%) compared with 6% with isolated FEV1 responsiveness and 14% with both FEV1 and RV responsiveness (P = .04). There was a minimal correlation between FEV1 responsiveness and RV responsiveness (r = 0.17, P = .06). The RV responsiveness was significantly associated with the wheeze score (P = .006) and dyspnea score (P = .029).

CONCLUSION

The addition of RV responsiveness testing to spirometry based responsiveness testing can improve the identification of reversible airway obstruction in asthma. RV responsiveness may be useful in monitoring symptoms associated with air trapping in asthma.

Small Airway Dysfunction Links Asthma Severity with Physical Activity and Symptom Control

BACKGROUND

Little is known about the role of small airway dysfunction (SAD) and its complex relation with asthma control and physical activity (PA).

OBJECTIVE

To investigate the interrelations among SAD, risk factors for asthma severity, symptom control, and PA.

METHODS

We assessed SAD by impulse oscillometry and other sophisticated lung function measures including inert gas washout in adults with asthma (mild to moderate, n = 140; severe, n = 128) and 69 healthy controls from the All Age Asthma Cohort. We evaluated SAD prevalence and its interrelation with risk factors for asthma severity (older age, obesity, and smoking), type 2 inflammation (sputum and blood eosinophils, fractional exhaled nitric oxide), systemic inflammation (high-sensitivity C-reactive protein), asthma control (AC), and PA (accelerometer for 1 week). We applied a clinical model based on structural equation modeling that integrated causal pathways among these clinical variables.

RESULTS

The prevalence of SAD ranged from 75% to 90% in patients with severe asthma and from 53% to 64% in mild to moderate asthma. Severe SAD was associated with poor AC and low PA. Structural equation modeling indicated that age, obesity, obesity-related systemic inflammation, T2 inflammation, and smoking are independent predictors of SAD. Small airway dysfunction was the main determinant factor of AC, which in turn affected PA. Obesity affected AC directly and through its contribution to SAD and low PA. In addition, PA had bidirectional associations with obesity, SAD, and AC. Structural equation modeling also indicated interrelations among distal airflow limitation, air trapping, and ventilation heterogeneity.

CONCLUSIONS

Small airway dysfunction is a highly prevalent key feature of asthma that interrelates a spectrum of distal lung function abnormalities with risk factors for asthma severity, asthma control, and physical activity.

The 'clinically significant' bronchodilator responsiveness (BDR) in children: a comparative study between six definitions of scholarly societies and a mini-review

Objective: To compare the percentages of children with and without airway obstruction (obstructive and non-obstructive groups, respectively) presenting a 'clinically significant' BDR according to the following definitions: GINA: FEV₁ increase >12% predicted (∆_Predicted), ATS/ERS: FEV₁ increase ≥12% initial (∆_Initial) and ∆FEV₁ absolute (∆) ≥200 ml and/or ∆FVC_Initial ≥12% and ∆FVC ≥200 ml, British thoracic society (BTS): ∆FEV_1Initial ≥12%, National asthma education and prevention program (NAEPP): ∆FEV_1Initial ≥12% and ∆FEV₁ > 200 ml, Group of research on advances in pediatric pneumology: ∆FEV_1Initial ≥12% or ∆PEF_Initial ≥20%, and South African thoracic society (SATS): ∆FEV_1Initial ≥12% or ∆FEV₁ >200 ml and/or ∆FVC_Initial ≥12% or ∆FVC >200 ml.Methods: This was a multicenter comparative study involving 278 children aged 6 to16 years: obstructive group (FEV₁/FVC < lower-limit-of-normal, n = 116) and non-obstructive group (FEV₁/FVC ≥ lower-limit-of-normal, n = 162). Spirometry was performed before/after a bronchodilator test. The Cochrane Q test was used to compare the percentage of responders according to the six definitions.Results: The percentages of responders among the obstructive [ranging from 51.72 (NAEPP) to 74.14% (SATS)] and the non-obstructive [ranging from 0.62 (NAEPP, BTS) to 8.64% (SATS)] groups were definition-dependent.Conclusion: In children, a 'clinically significant' BDR is definition-dependent.

"Poor Effort" Does Not Account for Reduced Forced Vital Capacity in Asthmatic Children

Purpose: Poor forced vital capacity (FVC) effort has been considered to be the main reason for FVC reduction by the ATS/ERS guideline; however, this has rarely been mentioned in previous studies. The present study aims to determine whether reduced FVC in asthmatic children is correlated to poor FVC effort. Methods: A total of 209 asthmatic children within 5-13 years old were included and divided into reduced FVC ("restricted," n = 66) and typical obstruction group ("obstructed," n = 143). Forced expiratory flows before and after bronchodilation were recorded in asthmatic children. The differences in clinical characteristics, spirometric results, FVC effort, and bronchodilator response were compared between two groups. Exhalation time (ET) was divided into effective ET (ETe) and plateau ET (ETp) by the start point of exhalation plateau on the time-volume curve. FVC effort was assessed by ET, ETp, and back extrapolated volume (EV)/FVC (%). Results: Asthmatic children in the restricted group had significantly higher slow vital capacity (SVC)/FVC (%), higher EV/FVC (%), shorter ET, shorter ETe, and longer ETp, when compared with those with obstructed. In the obstructed group, ET (r = 0.201, P = 0.016) and ETe (r = 0.496, P < 0.001) positively correlated with FVC, and ETp (r = -0.224, P = 0.007) negatively correlated with FVC. In the restricted group, FVC positively correlated with ETe (r = 0.350, P = 0.004) but not ET and ETp. FVC z-score significantly correlated with total IgE (n = 51, r = -0.349, P = 0.012) and with FEF_25-75% z-score (n = 66, r = 0.531, P < 0.001) in the restricted group. The further logistic regression revealed that the risk of restricted increased by 1.12 (95% CI, 1.04-1.22, P = 0.005) with every 1% increase in %ΔFVC. In subjects with restricted and bronchodilation tests, %ΔFVC was significantly associated with FeNO (n = 29, r = 0.386, P = 0.039), FEF_25-75% z-score (n = 29, r = -0.472, P = 0.010), and SVC/FVC (%) (n = 19, r = 0.477, P = 0.039) but not with EV/FVC (%), ET, ETe, or ETp (P > 0.05). Conclusion: These findings suggested that "poor FVC effort" does not account for the FVC reduction in asthmatic children. Short ET and high SVC/FVC (%) are characteristics of reduced FVC.

Cross-sectional phenotyping of small airway dysfunction in preschool asthma using the impulse oscillometry system

Objective. Asthma is a chronic inflammatory airway disorder known to induce small airways dysfunction (SAD). It is important to develop tools to assess the presence and extent of SAD in daily clinical practice. An Impulse Oscillometry System (IOS) might detect SAD, but the validity of the underlying model (serial Resistive airway and Compliant tissue model: RC model) in diseased lungs remains questionable.Methods. Our objective was to evaluate the usefulness of parameters obtained from six electrical circuit models that were fitted to the measurements of impedance obtained with IOS in asthmatic children characterized by an abnormal lung function defined by an increased baseline interrupter resistance (Rint, z-score > +1.645).Results. The six models were tested in 102 asthmatic children (median age: 5.5 years). Two models allowed the description of 92/102 (90%) children: 74 by the extended RIC model (central and peripheral Resistance, Inertance and peripheral airway Compliance) and 18 by the Mead₁₉₆₉ model (extended RIC plus lung compliance). Thus, peripheral airway compliance and resistance were essential to describe lung function abnormalities of these asthmatic children. Parenchyma impairment (increased lung compliance) which was responsive to salbutamol was present in 18% of asthmatic children. After salbutamol, peripheral airway resistance decreased while peripheral airway compliance increased, arguing for asthma-related SAD. R5-20Hz independently correlated with the two latter parameters but was increased in two thirds of children with increased Rint only.Conclusion. Additional modeling of IOS results can be a reliable tool to assess the presence and extent of SAD in young asthmatic children.

Asthma control in children: Body plethysmography in addition to spirometry

BACKGROUND

There is a lack of agreement among measures of asthma control in children. In Central Europe, body plethysmography is additionally used for asthma monitoring. However, its value is still unclear.

OBJECTIVES

We investigated the possible additional value of body plethysmographic measures (specific resistance, residual volume-total lung capacity ratio [RV/TLC]) compared with spirometric measures forced expiratory volume in 1 second (FEV ₁ ), forced vital capacity (FVC), FEV ₁ /FVC, forced expiratory flow at 25% to 75% of forced vital capacity (FEF _25-75 ), and fraction of exhaled nitric oxide (FeNO) for assessment of asthma control.

METHODS

One hundred and forty-five asthmatic children aged 5 to 17 were included. All children performed measurements of FeNO, spirometry, and body plethymography. Asthma control was assessed by the asthma control test (c-ACT/ACT) and a doctor's assessment of asthma control.

RESULTS

Investigating single lung function parameters, FEV₁ , FEV ₁ /FVC, FEF _25-75 and RV/TLC differed between controlled and partly controlled asthma. However, we found no differences between controlled and uncontrolled asthma with regard to single lung function parameters or for any parameter if investigated in a multivariable approach. This was also true if we combined obtained parameters from spirometry (comparing pathologic vs normal spirometry). Investigating the combination of body plethysmography and doctor's assessment of asthma control a significant association was found ( P = 0.02). Furthermore, combined spirometry and body plethysmography showed a significant association with both doctor's assessed asthma control ( P = 0.009) and the c-ACT/ACT ( P = 0.04). The addition of FeNO did not improve the results.

CONCLUSIONS

The combination of body plethysmography and spirometry shows best agreement with asthma control in children compared with spirometry or body plethysmography alone. Further studies are needed to find out whether additional measurements of body plethysmography improve the outcome of children in asthma monitoring.

Small Airway Dysfunction in Children With Controlled Asthma

INTRODUCTION

Asthma is characterized by chronic inflammation of the central and distal airways. The aim of this study was to assess the small airway (SA) of children with moderate-severe asthma with normal FEV1.

METHODS

This was an open-label, prospective, observational, cross-sectional study with consecutive inclusion of patients with moderate-severe asthma, receiving standard clinical treatment, with normal baseline FEV₁. We determined multiflow FEno (CAno), oscillatory resistance and reactance (R5-R20, X5), forced spirometry (FEV1, FEF_25-75), total body plethysmography (RV/TLC) and bronchodilation test. SA involvement was defined as: CAno>4.5 ppb, R5-R20>0.147kPa/L/s, X5<-0.18kPa/L, FEF_25-75<-1.65 z-score, RV/TLC>33%. Poor asthma control was defined as ≤ 19 points on the ACT questionnaire or ≤ 20 on the c-ACT.

RESULTS

In a cohort of 100 cases, 76 had moderate asthma and 24 had severe asthma; 71 children were classified as poorly controlled and 29 were well-controlled. In total, 77.78% of the group with all the correct determinations (n=72) showed ≥ 1 altered SA parameter and 48.61% ≥ 2 parameters. There were no differences between well-controlled or poorly controlled cases.

CONCLUSIONS

Children with moderate-severe asthma, with normal FEV₁, show a phenotype of dysfunctional SA. In our series, the evaluation of SA using the techniques described above did not provide information on disease control.

Obstruction phenotype as a predictor of asthma severity and instability in children

BACKGROUND

Small-airways instability resulting in premature airway closure has been recognized as a risk for asthma severity and poor control. Although spirometry has limited sensitivity for detecting small-airways dysfunction, a focus on the air-trapping component of obstruction might identify a risk factor for asthma instability.

OBJECTIVE

We sought to use spirometric measurements to identify patterns of airway obstruction in children and define obstruction phenotypes that relate to asthma instability.

METHODS

Prebronchodilation and postbronchodilation spirometric data were obtained from 560 children in the Asthma Phenotypes in the Inner City study. An air-trapping obstruction phenotype (A Trpg) was defined as a forced vital capacity (FVC) z score of less than -1.64 or an increase in FVC of 10% of predicted value or greater with bronchodilation. The airflow limitation phenotype (A Limit) had an FEV1/FVC z score of less than -1.64 but not A Trpg. The no airflow limitation or air-trapping criteria (None) phenotype had neither A Trpg nor A Limit. The 3 obstruction phenotypes were assessed as predictors of number of exacerbations, asthma severity, and airway lability.

RESULTS

Patients with the A Trpg phenotype (14% of the cohort) had more exacerbations during the 12-month study compared with those with the A Limit (P < .03) and None (P < .001) phenotypes. Patients with the A Trpg phenotype also had the highest Composite Asthma Severity Index score, the highest asthma treatment step, the greatest variability in FEV1 over time, and the greatest sensitivity to methacholine challenge.

CONCLUSIONS

A Trpg and A Limit patterns of obstruction, as defined by using routine spirometric measurements, can identify obstruction phenotypes that are indicators of risk for asthma severity and instability.

Longer duration of asthma is significantly associated with increased RV/TLC ratio

BACKGROUND

Although FEV1/FVC ratio has been shown to be negatively associated with longer duration of asthma; an association between RV/TLC ratio and longer duration of asthma has not been explored.

MATERIAL AND METHODS

Patients with established asthma for more than a year and met inclusion and exclusion criteria were recruited. Data obtained by questionnaire after informed consent was obtained, Pulmonary function tests and laboratory results were collected through chart review. Correlation and multiple linear regressions were used to analyze the data.

RESULTS

Among the 93 subjects, 61 were women. The mean age of patients was 58 ± 15 years, and the mean duration of asthma was 21 ± 18 years. The ethnic composition included: Caucasians 64%, Hispanics 28% and other groups 8%. The FEV1/FVC ratio was not significantly associated with duration of asthma (R2 = 0.15, p = 0.05). However, the RV/TLC ratio was significantly associated with duration of asthma (R2 = 0.46, p < 0.001).

CONCLUSION

RV/TLC ratio may be a better indicator than FEV1/FVC ratio to detect airway obstruction related to longer duration of asthma. Lung volume measurements should be done in addition to spirometry to detect changes related to airway obstruction in patients with longer duration of asthma.

Clinical Roles of Lung Volumes Detected by Body Plethysmography and Helium Dilution in Asthmatic Patients: A Correlation and Diagnosis Analysis

Roles of lung volumes in asthma remain controversial. We aimed to evaluate the efficacy of lung volumes in differentiating asthma severity levels. Consecutive outpatients with chronic persistent asthma were enrolled, and body plethysmography (BP) and helium dilution (HD) were performed simultaneously to extract RV%pred, TLC%pred, and RV/TLC. Significant negative correlations were found between FEV₁%pred and RV%pred (r = -0.557, P < 0.001), TLC%pred (r = -0.387, P < 0.001), and RV/TLC (r = -0.485, P < 0.001) measured by BP, as well as difference in volumes between these two techniques (ΔRV%pred, ΔTLC%pred and ΔRV/TLC). In mild and moderate asthma, AUC of RV%pred detected by BP and ΔTLC%pred was 0.723 (95%CI 0.571-0.874, P = 0.005) and 0.739 (95%CI 0.607-0.872, P = 0.002) with sensitivity and specificity being 79.41% and 88.24%, and 65.22% and 56.52% at cut-off of 145.40% and 14.23%, respectively. In moderate and severe asthma, AUC of RV%pred detected by BP and ΔTLC%pred was 0.782 (95%CI 0.671-0.893, P < 0.001) and 0.788 (95%CI 0.681-0.894, P < 0.002) with sensitivity and specificity being 77.78% and 97.22%, and 73.53% and 52.94% at cut-off of 179.85% and 20.22%, respectively. In conclusion, lung volumes are reliable complement of FEV₁ in identifying asthma severity levels.

Small airway dysfunction and bronchial asthma control : the state of the art

According to national and international guidelines, achieving and maintaining asthma control is a major goal of disease management. In closely controlled clinical trials, good asthma control can be achieved , with the medical treatments currently available, in the majority of patients , but large population-based studies suggest that a significant proportion of patients in real-life setting experience suboptimal levels of asthma control and report lifestyle limitations with a considerable burden on quality of life. Poor treatment adherence and persistence, failure to use inhalers correctly, heterogeneity of asthma phenotypes and associated co-morbidities are the main contributing factors to poor disease control. Now, it is widely accepted that peripheral airway dysfunction , already present in patients with mild asthma, is a key contributor of worse control. The aim of this paper is to investigate the association between small-airways dysfunction and asthma symptoms/control. We therefore performed a PubMed search using keywords : small airways; asthma (limits applied: Humans, English language) and selected papers with a study population of asthmatic patients, reporting measurement of small-airways parameters and clinical symptoms/control.

What long-term changes in lung function can tell us about asthma control

Asthma severity is typically classified according to lung function, but asthma control in relation to lung function is often harder to define. In this paper, we will review how lung function measured at rest, as well as over time, relates to asthma control. We will explore not only conventional lung function as measured by spirometry, such as peak expiratory flow and forced expiratory volume in 1 s, but also more sophisticated measurements of peripheral airway function related to respiratory system impedance and ventilation heterogeneity. In particular, we will review the emerging area of assessing the fluctuation of lung function over time and how it may correlate to both past and future asthma control.

Unlocking the quiet zone: the small airway asthma phenotype

The small airways in the distal lung have been called the quiet zone because they are difficult to assess and treat in patients with asthma who have disproportionate impairment of small airway function. Evidence is accumulating to support a distinct clinical phenotype for patients with asthma who have impaired small airway function. The small airway asthma phenotype, which is prevalent in patients at all steps of management guidelines, seems to be associated with poor disease control. Alternatively, small airway dysfunction might be a sensitive indicator of early disease rather than a phenotype. Conventional coarse-particle inhalers, which emit particles larger than 2 μm, might not address persistent small airway dysfunction in patients with asthma. To target the entire lung with extra-fine particle formulations (smaller than 2 μm) of inhaled corticosteroids alone or in combination with long-acting β-agonists might result in improved long-term asthma control along with a commensurate improvement in small airway function. Prospective randomised controlled trials with extra-fine-particle inhaled drugs are now needed for patients with the small airway asthma phenotype.

Forced expiratory flows' contribution to lung function interpretation in schoolchildren

Forced expiratory flow (FEF) at low lung volumes are supposed to be better at detecting lung-function impairment in asthmatic children than a forced volume. The aim of this study was to examine whether FEF results could modify the interpretation of baseline and post-bronchodilator spirometry in asthmatic schoolchildren in whom forced expiratory volumes are within the normal range. Spirometry, with post-bronchodilator vital capacity within 10% of that of baseline in healthy and asthmatic children, was recorded prospectively. We defined abnormal baseline values expressed as z-scores <-1.645, forced expiratory volume in 1 s (FEV1) reversibility as a baseline increase >12%, FEF reversibility as an increase larger than the 2.5th percentile of post-bronchodilator changes in healthy children. Among 66 healthy and 50 asthmatic schoolchildren, only two (1.7%) children with normal vital capacity and no airways obstruction had abnormal baseline forced expiratory flow at 25-75% of forced vital capacity (FEF25-75%). After bronchodilation, among the 45 asthmatic children without FEV1 reversibility, 5 (11.1%) had an FEF25-75% increase that exceeded the reference interval. Isolated abnormal baseline values or significant post-bronchodilator changes in FEF are rare situations in asthmatic schoolchildren with good spirometry quality.

Small airway impairment in moderate to severe asthmatics without significant proximal airway obstruction

Asthma is a disease characterized by inflammation which affects both proximal and distal airways. We evaluated the prevalence of small airway obstruction (SAO) in a group of clinically stable asthmatics with both normal forced expiratory volume in the first second (FEV1) and normal FEV1/forced vital capacity (FVC) and treated with an association of inhaled corticosteroids (ICSs) and long acting β2-agonists (LABAs). Clinical evaluation included the measurement of dyspnea, asthma control test and drug compliance. The prevalence of SAO was estimated by spirometry and plethysmography and defined by the presence of one or more of the following criteria: functional residual capacity (FRC) > 120% predicted (pred), residual volume (RV) > pred + 1.64 residual standard deviation (RSD), RV/total lung capacity (TLC) > pred + 1.64 RSD, forced expiratory flow (FEF)25-75% < pred - 1.64 RSD, FEF50% < pred - 1.64 RSD, slow vital capacity (SVC) - FVC > 10%. Among the 441 patients who were included, 222 had normal FEV1 and FEV1/FVC. At least one criteria of SAO was found in 115 (52%) mainly lung hyperinflation (39% based on high FRC, RV or RV/TLC) and more rarely distal airflow limitation (15% based on FEF25-75% or FEF50%) or expiratory trapping (10% based on increased SVC - FVC). In the patients with only SAO (no PAO), there was no relationship between SAO, asthma history and the scores of dyspnea, asthma control or drug compliance. These results suggest that in asthmatics with normal FEV1 and FEV1/FVC, treated with ICSs and LABAs, SAO is found in more than half of the patients indicating that the routinely used lung function tests can underestimate dysfunctions occurring in the small airways.

Lung volume abnormalities and its correlation to spirometric and demographic variables in adult asthma

BACKGROUND

Presence of airflow obstruction in asthma has been based on a fixed FEV1(forced expiratory volume at 1 second)/FVC (forced vital capacity) ratio abnormality. The accuracy of FEV1/FVC ratio in diagnosing airflow obstruction remains controversial. Lung volume abnormalities have been observed in severe asthma. We utilized simultaneously measured spirometry and lung volume to determine the utility of residual volume (RV)/total lung capacity (TLC) ratio in diagnosing airflow obstruction and to identify predictors of abnormal RV in asthmatic subjects.

METHODS

Data from physician-diagnosed asthmatics referred for lung function tests were collected retrospectively. Patient demographics and lung function data were analyzed using general linear modeling.

RESULTS

Of the 321 subjects, 221 were female (69%). The ethnicity was Caucasian in 157 (49%), Hispanic in 131 (41%), and African-American in 33 (10%). The percentage of subjects with FEV(1)/FVC ratio <70%, FEV(1)-predicted <80%, and FEF25-75% <65% were 25%, 25%, and 38%, respectively. Fifty-two and fifty-seven percent of the patients had abnormal residual volume and abnormal RV/TLC ratio, respectively. A significant bronchodilator response was observed in 32% of the patients. A positive correlation was observed between RV to age (r = 0.4) and height (r = 0.3). A negative correlation was observed between RV to FEF25-75% (r = 0.5) and body weight (r = 0.07). There was no significant correlation between FEV1 reversibility and residual volume (r = 0.1). RV correlated significantly better with FEF25-75% (r(2) = 0.25) than FEV(1) (r(2) = 0.16).

CONCLUSION

A significant proportion of asthmatic patients have elevated residual volume and abnormal RV/TLC ratio in the presence of normal FEV1/FVC ratio and absence of significant bronchodilator response. The clinical significance of these findings in asthma needs further prospective study.

[Physiological characteristics associated with previous control in asthmatic children]

OBJECTIVE

To analyze MEF(50%) (central airways), RV/TLC (distal airways), reversibility of FEV(1) (bronchial tone, REV(FEV1)) and FE(NO) (inflammation) in relation to clinical events in asthmatic children on the assumption that mild symptoms and severe exacerbations in the previous 3 months could be associated with distinct functional characteristics.

PATIENTS AND METHODS

A retrospective, single center, out-patient hospital study including all asthmatic children who had complete lung function testing (without and with bronchodilation) during a period of clinical stability, without treatment on the day of the test.

RESULTS

Two hundred and forty-five children (11.4±2.4 years) were included: 114 (46%) were asymptomatic, 87 (36%) had minor symptoms and 44 (18%) had had a severe exacerbation in the past 3 months. FEV(1), FEV(1)/FVC and MEF(50%) were not different in these three groups. REV(FEV1) was higher in the symptomatic than in the asymptomatic group (P=0.019), RV/TLC was greater in the exacerbation group than in the asymptomatic group (P=0.019), and FE(NO) was higher in the symptomatic group than in the asymptomatic and exacerbation groups (P=0.006).

CONCLUSIONS

In asthmatic children, minor symptoms and severe exacerbation in the previous 3 months are associated with distinct functional characteristics that are not detected by single baseline spirometry without treatment on the day of testing.

Exhaled nitric oxide and clinical phenotypes of childhood asthma

Whether exhaled NO helps to identify a specific phenotype of asthmatic patients remains debated. Our aims were to evaluate whether exhaled NO (FENO(0.05)) is independently associated (1) with underlying pathophysiological characteristics of asthma such as airway tone (bronchodilator response) and airway inflammation (inhaled corticosteroid [ICS]-dependant inflammation), and (2) with clinical phenotypes of asthma.We performed multivariate (exhaled NO as dependent variable) and k-means cluster analyses in a population of 169 asthmatic children (age ± SD: 10.5 ± 2.6 years) recruited in a monocenter cohort that was characterized in a cross-sectional design using 28 parameters describing potentially different asthma domains: atopy, environment (tobacco), control, exacerbations, treatment (inhaled corticosteroid and long-acting bronchodilator agonist), and lung function (airway architecture and tone). Two subject-related characteristics (height and atopy) and two disease-related characteristics (bronchodilator response and ICS dose > 200 μg/d) explained 36% of exhaled NO variance. Nine domains were isolated using principal component analysis. Four clusters were further identified: cluster 1 (47%): boys, unexposed to tobacco, with well-controlled asthma; cluster 2 (26%): girls, unexposed to tobacco, with well-controlled asthma; cluster 3 (6%): girls or boys, unexposed to tobacco, with uncontrolled asthma associated with increased airway tone, and cluster 4 (21%): girls or boys, exposed to parental smoking, with small airway to lung size ratio and uncontrolled asthma. FENO(0.05) was not different in these four clusters.In conclusion, FENO(0.05) is independently linked to two pathophysiological characteristics of asthma (ICS-dependant inflammation and bronchomotor tone) but does not help to identify a clinically relevant phenotype of asthmatic children.