Lung function trajectories and chronic obstructive pulmonary disease: current understanding and knowledge gaps

Respiratory System Dynamics

While static mechanical forces govern resting lung volumes, dynamic forces determine tidal breathing, airflow, and changes in airflow and lung volume during normal and abnormal breathing. This section will examine the mechanisms, measurement methodology, and interpretation of the dynamic changes in airflow and lung volume that occur in health and disease. We will first examine how the total work of breathing can be described by the parameters of the equation of motion, which determine the pressure required to move air into and out of the lung. This will include a detailed description of airflow characteristics and airway resistance. Next, we will review the changes in pressure and flow that determine maximal forced inspiration and expiration, which result in the maximal flow-volume loop and the clinically important forced expired volume in 1 second. We will also assess the mechanisms and interpretation of bronchodilator responsiveness, dynamic hyperinflation, and airways hyperresponsiveness.

Year-to-year trajectories of hospital utilisation rates among patients with COPD: a real-world, single-centre, retrospective cohort study

OBJECTIVES

The long-term clinical trajectory of chronic obstructive pulmonary disease (COPD) in terms of year-to-year hospital utilisation rates can be highly variable and is not well studied. We investigated year-to-year trends of hospitalisation or emergency department (ED) visits among patients with COPD over 3 years, identified distinct trajectories and examined associated predictive factors.

DESIGN

A retrospective cohort study.

SETTING

Data were extracted from the Changi General Hospital, Singapore COPD data warehouse.

PARTICIPANTS

Patients with COPD aged ≥40 years with 3 years of follow-up data.

PRIMARY AND SECONDARY OUTCOME MEASURES

The yearly rates of hospitalisations or ED visits, stratified by COPD-related or all-cause, were described. Group-based trajectory modelling was used to identify clinically distinct trajectories year-by-year. Baseline predictive factors associated with different trajectories were examined.

RESULTS

In total, 396 patients were analysed (median age 70 years; 87% male). Four trajectories were generated for year-to-year trends in COPD-related hospitalisations/ED visits (C1-C4: consistently frequent, consistently infrequent, improving and worsening); post-bronchodilator forced expiratory volume in 1 second (FEV1) was a significant predictor of trajectory, with worse lung function being the main factor associated with less favourable trajectories. For all-cause hospitalisations/ED visits, four trajectories were identified (A1-A4: infrequent and stable, frequent and stable, frequent and decreasing, frequent and increasing); significant differences in age (p=0.041), sex (p=0.016) and ethnicity (p=0.005) were found between trajectories. Higher overall comorbidity burden was a key determinant in less favourable trajectories of all-cause hospitalisations/ED visits.

CONCLUSIONS

Distinct trajectories were demonstrated for hospitalisations/ED visits related to COPD or all causes, with predictive associations between FEV1 and COPD trajectory and between comorbidities and all-cause trajectory. Trajectories carry nuanced prognostic information and may be useful for clinical risk stratification to identify high-risk individuals for preventative treatments.

Association of Childhood Respiratory Status with Adult Occupational Exposures in a Birth Cohort

Rationale: People with better early-life respiratory health may be more likely to work in occupations with high workplace exposures in adult life compared with people with poor respiratory health. This may manifest as a healthy worker effect bias, potentially confounding the analysis of environmental exposure studies. Objectives: To evaluate associations between lung function in adolescence and occupational exposures at initial adult employment. Methods: The TCRS (Tucson Children's Respiratory Study) is a long-term prospective study of respiratory health beginning at birth. Associations between respiratory function at age 11 years and occupational exposures at first job at age 26 years were evaluated with logistic regression. We calculated percentage predicted values for forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1:FVC ratio, and forced expiratory flow from 25% to 75% of vital capacity at age 11. At the 26-year visit, participants self-reported occupational exposures to dust, smoke, and fumes/gas at first job in a standardized interview. Results: Forced expiratory flow from 25% to 75% of vital capacity and FEV1:FVC ratio at age 11 were positively associated with dust workplace exposures at the first job. Each 10% increase in percentage predicted prebronchodilator FEV1:FVC ratio was associated with 30% higher odds of workplace dust exposure (odds ratio for a 1% increase, 1.03 [95% confidence interval, 1.00-1.06; P = 0.045]). Similar associations were observed for FEV1 and FVC with workplace smoke exposures. We also observed modification by time at job: associations were stronger for those who remained in their jobs longer than 12 months. In addition, those with better function at age 11 were more likely to stay in their jobs longer than 12 months if their first jobs involved exposure to dust. Conclusions: Childhood lung function affects initial career choice. This study supports the premise of the healthy worker effect.

COPD: Providing the right treatment for the right patient at the right time

Chronic Obstructive Pulmonary Disease (COPD) is a common disease associated with significant morbidity and mortality that is both preventable and treatable. However, a major challenge in recognizing, preventing, and treating COPD is understanding its complexity. While COPD has historically been characterized as a disease defined by airflow limitation, we now understand it as a multi-component disease with many clinical phenotypes, systemic manifestations, and associated co-morbidities. Evidence is rapidly emerging in our understanding of the many factors that contribute to the pathogenesis of COPD and the identification of "early" or "pre-COPD" which should provide exciting opportunities for early treatment and disease modification. In addition to breakthroughs in our understanding of the origins of COPD, we are optimizing treatment strategies and delivery of care that are showing impressive benefits in patient-centered outcomes and healthcare utilization. This special issue of Respiratory Medicine, "COPD: Providing the Right Treatment for the Right Patient at the Right Time" is a summary of the proceedings of a conference held in Stresa, Italy in April 2022 that brought together international experts to discuss emerging evidence in COPD and Pulmonary Rehabilitation in honor of a distinguished friend and colleague, Claudio Ferdinando Donor (1948-2021). Claudio was a true pioneer in the field of pulmonary rehabilitation and the comprehensive care of individuals with COPD. He held numerous leadership roles in in the field, provide editorial stewardship of several respiratory journals, authored numerous papers, statement and guidelines in COPD and Pulmonary Rehabilitation, and provided mentorship to many in our field. Claudio's most impressive talent was his ability to organize spectacular conferences and symposia that highlighted cutting edge science and clinical medicine. It is in this spirit that this conference was conceived and planned. These proceedings are divided into 4 sections which highlight crucial areas in the field of COPD: (1) New concepts in COPD pathogenesis; (2) Enhancing outcomes in COPD; (3) Non-pharmacologic management of COPD; and (4) Optimizing delivery of care for COPD. These presentations summarize the newest evidence in the field and capture lively discussion on the exciting future of treating this prevalent and impactful disease. We thank each of the authors for their participation and applaud their efforts toward pushing the envelope in our understanding of COPD and optimizing care for these patients. We believe that this edition is a most fitting tribute to a dear colleague and friend and will prove useful to students, clinicians, and researchers as they continually strive to provide the right treatment for the right patient at the right time. It has been our pleasure and a distinct honor to serve as editors and oversee such wonderful scholarly work.

Precision medicine in chronic obstructive pulmonary disease: how far have we come?

PURPOSE OF REVIEW

In this review, we will discuss the current status and recent developments in precision medicine in chronic obstructive pulmonary disease (COPD) through the lens of treatable traits.

RECENT FINDINGS

Although the term 'treatable traits' in the treatment of COPD is relatively recent, this concept has been used for many years if one considers interventions such as long-term oxygen therapy or alpha-1 antitrypsin replacement therapy. Recent advances have included expanding the definition of COPD to include a broader population of people with lower respiratory disease but not meeting the strict criteria for obstruction, advances in imaging to aid in the diagnosis and treatment of COPD, advances in understanding symptoms and exacerbations to define severity, using biomarkers to guide therapy and better understanding and addressing polymorbidity and frailty. In addition, there is a concerted effort to use these concepts to identify COPD patients earlier in the disease process wherein disease modification may be possible.

SUMMARY

Focusing on subsets of patients with COPD with certain characteristics should lead to better outcomes and fewer adverse effects from treatment.

VIDEO ABSTRACT

http://links.lww.com/COPM/A30.

Natural history and mechanisms of COPD

The natural history of COPD is complex, and the disease is best understood as a syndrome resulting from numerous interacting factors throughout the life cycle with smoking being the strongest inciting feature. Unfortunately, diagnosis is often delayed with several longitudinal cohort studies shedding light on the long 'preclinical' period of COPD. It is now accepted that individuals presenting with different COPD phenotypes may experience varying natural history of their disease. This includes its inception, early stages and progression to established disease. Several scenarios regarding lung function course are possible, but it may conceptually be helpful to distinguish between individuals with normal maximally attained lung function in their early adulthood who thereafter experience faster than normal FEV₁ decline, and those who may achieve a lower than normal maximally attained lung function. This may be the main mechanism behind COPD in the latter group, as the decline in FEV₁ during their adult life may be normal or only slightly faster than normal. Regardless of the FEV₁ trajectory, continuous smoking is strongly associated with disease progression, development of structural lung disease and poor prognosis. In developing countries, factors such as exposure to biomass and sequelae after tuberculosis may lead to a more airway-centred COPD phenotype than seen in smokers. Mechanistically, COPD is characterized by a combination of structural and inflammatory changes. It is unlikely that all patients share the same individual or combined mechanisms given the heterogeneity of resultant phenotypes. Lung explants, bronchial biopsies and other tissue studies have revealed important features. At the small airway level, progression of COPD is clinically imperceptible, and the pathological course of the disease is poorly described. Asthmatic features can further add confusion. However, the small airway epithelium is likely to represent a key focus of the disease, combining impaired subepithelial crosstalk and structural/inflammatory changes. Insufficient resolution of inflammatory processes may facilitate these changes. Pathologically, epithelial metaplasia, inversion of the goblet to ciliated cell ratio, enlargement of the submucosal glands and neutrophil and CD8-T-cell infiltration can be detected. Evidence of type 2 inflammation is gaining interest in the light of new therapeutic agents. Alarmin biology is a promising area that may permit control of inflammation and partial reversal of structural changes in COPD. Here, we review the latest work describing the development and progression of COPD with a focus on lung function trajectories, exacerbations and survival. We also review mechanisms focusing on epithelial changes associated with COPD and lack of resolution characterizing the underlying inflammatory processes.

Co-methylation analysis in lung tissue identifies pathways for fetal origins of COPD

COPD likely has developmental origins; however, the underlying molecular mechanisms are not fully identified. Investigation of lung tissue-specific epigenetic modifications such as DNA methylation using network approaches might facilitate insights linking in utero smoke (IUS) exposure and risk for COPD in adulthood.We performed genome-wide methylation profiling for adult lung DNA from 160 surgical samples and 78 fetal lung DNA samples isolated from discarded tissue at 8-18 weeks of gestation. Co-methylation networks were constructed to identify preserved modules that shared methylation patterns in fetal and adult lung tissues and associations with fetal IUS exposure, gestational age and COPD.Weighted correlation networks highlighted preserved and co-methylated modules for both fetal and adult lung data associated with fetal IUS exposure, COPD and lower adult lung function. These modules were significantly enriched for genes involved in embryonic organ development and specific inflammation-related pathways, including Hippo, phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT), Wnt, mitogen-activated protein kinase and transforming growth factor-β signalling. Gestational age-associated modules were remarkably preserved for COPD and lung function, and were also annotated to genes enriched for the Wnt and PI3K/AKT pathways.Epigenetic network perturbations in fetal lung tissue exposed to IUS and of early lung development recapitulated in adult lung tissue from ex-smokers with COPD. Overlapping fetal and adult lung tissue network modules highlighted putative disease pathways supportive of exposure-related and age-associated developmental origins of COPD.

Expression of Matrix Metalloproteinase-2, Matrix Metalloproteinase-9, Tissue Inhibitor of Metalloproteinase-1, and Changes in Alveolar Septa in Patients with Chronic Obstructive Pulmonary Disease

Background

This study investigated the relationship between the pathological alteration of alveolar septa and (1) pulmonary function and (2) matrix metalloproteinase (MMP)-2, MMP-9, and tissue inhibitor matrix metalloproteinase 1 (TIMP-1) expression in chronic obstructive pulmonary disease (COPD).

Material/Methods

Sixty patients with pulmonary disease were divided into control (n=20) and COPD (n=40) groups. Postoperative lung tissue specimens were examined. Hematoxylin and eosin and elastin van Gieson staining detected pathological alterations of pulmonary alveolar septa. Septa thickness was measured. MMP-2, MMP-9, and TIMP-1 expression levels were detected by immunohistochemical staining. Correlations were determined by Pearson analysis.

Results

Forced expiratory volume in 1 s (FEV₁), forced vital capacity, FEV₁ percent predicted (FEV₁%pre), and diffusion capacity of carbon monoxide percent predicted (DLCO%pre) in COPD patients were significantly lower than in those of the control group (P<0.05). MMP-2, MMP-9, and TIMP-1 expression levels were significantly higher in the COPD group than in control, especially the severe group (P<0.05). Septa thickness was negatively correlated with FEV₁%pre (r=−0.335; P<0.05) and positively correlated with MMP-2 and TIMP-1 expression (P<0.05). Proportion of collagenous fiber was negatively correlated with FEV₁%pre and DLCO%pre (P<0.01), and positively correlated with MMP-2, MMP-9, and TIMP-1 expression (P<0.01). Proportion of elastic fibers was negatively correlated with collagenous fiber.

Conclusions

The pathological alteration of alveolar septa was correlated with pulmonary function and expression levels of MMP-2, MMP-9, and TIMP-1, which can play vital roles in COPD progression.

Lung Function Trajectories Leading to Chronic Obstructive Pulmonary Disease as Predictors of Exacerbations and Mortality

Rationale: Chronic obstructive pulmonary disease (COPD) can develop not only through a lung function trajectory dominated by an accelerated decline of FEV1 from normal maximally attained FEV1 in early adulthood (normal maximally attained FEV1 trajectory) but also through a trajectory with FEV1 below normal in early adulthood (low maximally attained FEV1 trajectory).Objectives: To test whether the long-term risk of exacerbations and mortality differs between these two subtypes of COPD.Methods: The cohort included 1,170 young adults enrolled in the Copenhagen City Heart Study during the 1970s and 1980s. In 2001-2003, which served as the baseline for the present analyses, 79 participants had developed COPD through normal maximally attained FEV1 trajectory, 65 had developed COPD through low maximally attained FEV1 trajectory, and 1,026 did not have COPD.Measurements and Main Results: From 2001 until 2018, we observed 139 severe exacerbations of COPD and 215 deaths, of which 55 were due to nonmalignant respiratory disease. In Cox models, there was no difference with regard to risk of severe exacerbations between the two trajectories, but individuals with normal maximally attained FEV1 had an increased risk of nonmalignant respiratory disease mortality (using inverse probability of censoring weighting with adjusted hazard ratio [HR], 6.20; 95% confidence interval [CI], 2.09-18.37; P = 0.001) and all-cause mortality (adjusted HR, 1.93; 95% CI, 1.14-3.26; P = 0.01) compared with individuals with low maximally attained FEV1.Conclusions: COPD developed through normal maximally attained FEV1 trajectory is associated with an increased risk of respiratory and all-cause mortality compared with COPD developed through low maximally attained FEV1 trajectory.

Exploration of n-6 and n-3 Polyunsaturated Fatty Acids Metabolites Associated with Nutritional Levels in Patients with Severe Stable Chronic Obstructive Pulmonary Disease

Background and Objective

Severe chronic obstructive pulmonary disease (COPD) is the terminal stage of the disease characterized by declined lung function, malnutrition, and poor prognosis. Such patients cannot tolerate long-time sports rehabilitation owing to dyspnea and fail to achieve the desired therapeutic effect; therefore, increasing nutritional support will be an important strategy for them. The present study applied metabolomics technology to evaluate the correlation between serum concentrations of polyunsaturated fatty acid (PUFA) metabolites, nutritional status, and lung function in patients with COPD to provide a theoretical basis for accurate nutritional support.

Materials and Methods

We enrolled 82 patients with stable severe COPD in our hospital. The general characteristics including height, weight, and lung function were recorded. Metabolomics was used to detect the concentrations of serum metabolites of n-3 and n-6 at baseline and at 24 and 52 weeks after enrollment. The correlations between nutrition level and pulmonary function and clinical indicators were evaluated.

Results

The concentrations of n-3 and n-6 increased over time along with the progression of COPD. Body mass index (BMI) and percent of ideal body weight (IBW%) decreased with disease development, and BMI was found to be significantly correlated with FEV1% predicted and FEV1/FVC. Serum levels of n-6 metabolites such as linoleic acid (LA), γ-linoleic acid (GLA), and arachidonic acid (ARA) (all P < 0.01) and the n-3 metabolites such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (all P < 0.05) showed significant correlations with BMI and were closely correlated with FEV1% predicted and FEV1/FVC of lung function (all P< 0.05).

Conclusion

This study demonstrates that malnutrition in patients with severe COPD is progressive and is positively correlated with n-3 and n-6 polyunsaturated fatty acids and lung function.

Distinctive lung function trajectories from age 10 to 26 years in men and women and associated early life risk factors - a birth cohort study

Pre-bronchodilator lung function including forced vital capacity (FVC), forced expiratory flow in 1 second (FEV1), their ratio (FEV1/FVC), and forced expiratory flow 25-75% (FEF25-75) measured at age 10, 18, and 26 years in the Isle of Wight birth cohort was analyzed for developmental patterns (trajectories). Early life risk factors before the age of 10 years were assessed for the trajectories.

METHOD

Members of the birth cohort (1989/90) were followed at age 1, 2, 4, 10, 18, and 26 years. Allergic sensitization and questionnaire data were collected. Spirometry tests were performed and evaluated according to the American Thoracic Society (ATS) criteria at 10, 18, and 26 years. To identify developmental trajectories for FVC, FEV1, FEV1/FVC, and FEF25-75 from 10 to 26 years, a finite mixture model was applied to the longitudinal lung function data, separately for males and females. Associations of early life factors with the respective lung function trajectories were assessed using log-linear and logistic regression analyses.

RESULTS

Both high and low lung function trajectories were observed in men and women. FVC continued to grow beyond 18 years in men and women, whereas FEV1 peaked at age 18 years in female trajectories and in one male trajectory. For the FEV1/FVC ratios and FEF25-75 most trajectories appeared highest at age 18 and declined thereafter. However, the low FEV1/FVC trajectory in both sexes showed an early decline at 10 years. Lower birth weight was linked with lower lung function trajectories in males and females. Eczema in the first year of life was a risk factor for later lung function deficits in females, whereas the occurrence of asthma at 4 years of age was a risk factor for later lung function deficits in males. A positive skin prick test at age four was a risk for the low FEV1 trajectory in females and for the low FEV1/FVC trajectory in males.

CONCLUSION

Men and women showed distinctive lung function trajectories and associated risk factors. Lower lung function trajectories can be explained by not achieving maximally attainable function at age 18 years and by a function decline from 18 to 26 years.

A Model for Predicting Future FEV1 Decline in Smokers Using Hyperpolarized 3He Magnetic Resonance Imaging

RATIONALE AND OBJECTIVES

The purpose of this study was to assess the effectiveness of hyperpolarized helium-3 magnetic resonance (MR)-based imaging markers in predicting future forced expiratory volume in one second decline/chronic obstructive pulmonary disorder progression in smokers compared to current diagnostic techniques.

MATERIALS AND METHODS

Total 60 subjects (15 nonsmokers and 45 smokers) participated in both baseline and follow-up visits (∼1.4 years apart). At both visits, subjects completed pulmonary function testing, a six-minute walk test , and the St. George Respiratory Questionnaire. Using helium-3 MR imaging, means (M) and standard deviations (H) of oxygen tension (P_AO₂), fractional ventilation, and apparent diffusion coefficient were calculated across 12 regions of interest in the lungs. Subjects who experienced FEV1 decline >100 mL/year were deemed "decliners," while those who did not were deemed "sustainers." Nonimaging and imaging prediction models were generated through a logistic regression model, which utilized measurements from sustainers and decliners.

RESULTS

The nonimaging prediction model included the St. George Respiratory Questionnaire total score, diffusing capacity of carbon monoxide by the alveolar volume (DLCO/VA), and distance walked in a six-minute walk test. A receiving operating character curve for this model yielded a sensitivity of 75% and specificity of 68% with an overall area under the curve of 65%. The imaging prediction model generated following the same methodology included ADC^H, FV^H, and P_AO₂^H. The resulting receiving operating character curve yielded a sensitivity of 87.5%, specificity of 82.8%, and an area under the curve of 89.7%.

CONCLUSION

The imaging predication model generated from measurements obtained during ³He MR imaging is better able to predict future FEV1 decline compared to one based on current clinical tests and demographics. The imaging model's superiority appears to arise from its ability to distinguish well-circumscribed, severe disease from a more uniform distribution of moderately altered lung function, which is more closely associated with subsequent FEV1 decline.

Diagnosis and Outpatient Management of Chronic Obstructive Pulmonary Disease: A Review

IMPORTANCE

There are 30 million adults (12%) in the United States who have chronic obstructive pulmonary disease (COPD). Chronic obstructive pulmonary disease accounts for 3.2% of all physician office visits annually and is the fourth leading cause of death (126 000 deaths per year). Most patients are diagnosed by their primary care clinicians who must address the highly variable clinical features and responses to therapy. The diagnosis and treatment of COPD is rapidly changing, so understanding recent advances is important for the delivery of optimal patient care.

OBSERVATIONS

Chronic obstructive pulmonary disease is characterized by incompletely reversible expiratory airflow limitation. Spirometry is the reference standard for diagnosing and assessing the severity of COPD. All patients should be counseled about and receive preventive measures such as smoking cessation and vaccination. Treatment should be guided by the severity of lung impairment, symptoms such as dyspnea, the amount of cough and sputum production, and how often a patient experiences an exacerbation. When dyspnea limits activity or quality of life, COPD should be treated with once- or twice-daily maintenance long-acting anticholinergic and β-agonist bronchodilators. Patients with acute exacerbations may benefit from the addition of inhaled corticosteroids, particularly those with elevated peripheral eosinophil levels. Pulmonary rehabilitation, which includes strength and endurance training and educational, nutritional, and psychosocial support, improves symptoms and exercise tolerance but is underutilized. Supplemental oxygen for patients with resting hypoxemia (defined as Spo2 <89%) improves survival.

CONCLUSIONS AND RELEVANCE

Chronic obstructive pulmonary disease is a complicated disease requiring intensive treatment. Appropriate use of long-acting maintenance bronchodilators, inhaled corticosteroids, and pulmonary rehabilitation decreases symptoms, optimizes functional performance, and reduces exacerbation frequency. Supplemental oxygen in patients with resting hypoxemia prolongs life, and other advanced treatments are available based on specific patient characteristics.

Bronchopulmonary dysplasia: what are its links to COPD?

Emerging evidence suggests that adverse early life events can affect long-term health trajectories throughout life. Preterm birth, in particular, is a significant early life event that affects approximately 10% of live births. Worldwide, prematurity is the number one cause of death in children less than 5 years of age and has been shown to disrupt normal lung development with lasting effects into adult life. Along with impaired lung development, interventions used to support gas exchange and other sequelae of prematurity can lead to the development of bronchopulmonary dysplasia (BPD). BPD is a chronic respiratory disease of infancy characterized by alveolar simplification, small airways disease, and pulmonary vascular changes. Although many survivors of BPD improve with age, survivors of BPD often have chronic lung disease characterized by airflow obstruction and intermittent pulmonary exacerbations. Long-term lung function trajectories as measured by FEV1 can be lower in children and adults with a history BPD. In this review, we discuss the epidemiology and manifestations of BPD and its long-term consequences throughout childhood and into adulthood. Available evidence suggests that disrupted lung development, genetic susceptibility and subsequent environment and infectious events that occur in prenatal and postnatal life likely increase the predisposition of children with BPD to develop early onset chronic obstructive pulmonary disease (COPD). The reviews of this paper are available via the supplemental material section.

Precision medicine in COPD: where are we and where do we need to go?

Chronic obstructive pulmonary disease (COPD) was the fourth leading cause of death worldwide in 2015. Current treatments for patients ease discomfort and help decrease disease progression; however, none improve lung function or change mortality. COPD is heterogeneous in its molecular and clinical presentation, making it difficult to understand disease aetiology and define robust therapeutic strategies. Given the complexity of the disease we propose a precision medicine approach to understanding and better treating COPD. It is possible that multiOMICs can be used as a tool to integrate data from multiple fields. Moreover, analysis of electronic medical records could aid in the treatment of patients and in the predictions of outcomes. The Precision Medicine Initiative created in 2015 has made precision medicine approaches to treat disease a reality; one of these diseases being COPD.

Measuring Airway Obstruction in Severe Asthma in Children

Lung function is an important tool in the diagnosis and monitoring of patients with asthma at all ages. Airway obstruction is a typical feature of asthma and it can be assessed with several lung function techniques. Spirometry, respiratory resistance and reactance, and lung volumes are available to measure it at different ages and in children. The assessment of a bronchodilator response is always recommended to show the reversibility of the obstruction. Poor lung function is a predictor of poor asthma outcome and a low Forced Expiratory Volume in the first second of expiration percent predicted measured with spirometry, has been shown to be associated with a higher risk of having an exacerbation during the following year independently of the presence of asthma symptoms. In severe asthma lung function assessment is used to distinguish different phenotypes, children with severe asthma have worse airflow limitation prior to administration of a bronchodilator than children with non severe asthma. Airway resistance and reactance are indirect measurements of airway obstruction and they can be measured with the forced oscillation technique, which is feasible also in non-collaborative children. This technique can be more informative in discriminating patients with asthma from healthy controls and is able to indicate a more peripheral involvement of the airways. The role of this technique in severe asthma is still debated. In conclusion lung function is useful in the clinical management of children with severe asthma.