Distal airway function assessed by oscillometry at varying respiratory rate: comparison with dynamic compliance

Correlation of Impulse Oscillometry with Spirometry in Deployed Military Personnel with Airway Obstruction

INTRODUCTION

Evaluation of chronic respiratory symptoms in deployed military personnel has been conducted at Brooke Army Medical Center as part of the Study of Active Duty Military for Pulmonary Disease Related to Environmental Deployment Exposures III study. Although asthma and airway hyperreactivity have been the most common diagnoses, the clinical findings in these patients may be multifactorial. This study aims to evaluate the utility of impulse oscillometry (IOS) in diagnosing airway obstruction in patients undergoing multiple pulmonary function testing (PFT) studies.

METHODS

Military personnel referred for deployed-related pulmonary symptoms underwent a standardized evaluation at Brooke Army Medical Center and Walter Reed National Military Medical Center over a 5-year span. Initial studies included laboratory tests, high-resolution computed tomography imaging, cardiac evaluation with electrocardiogram, and echocardiography. PFT consisted of full PFTs, forced inspiratory/expiratory pressures, post-spirometry bronchodilator testing, IOS, exhaled nitric oxide, and methacholine challenge testing.

RESULTS

A total of 360 patients have completed an evaluation to date. In this cohort, 108 patients (30.0%) have evidence of obstruction by spirometry, whereas 74 (20.6%) had IOS values of both an R5 > 150% and X5 < -1.5. Only 32 (8.9%) had evidence of obstruction by both spirometry and IOS, whereas 210 (57.3%) had neither. A comparison among R5 (resistance at 5 Hz), R20 (resistance at 20 Hz), and X5 (reactance at 5 Hz) was performed in those individuals with and without spirometric obstruction. R5 (% predicted) was 156.2 ± 57.4% (obstruction) vs. 129.1 ± 39.6% (no obstruction) (P < .001); R20 (% predicted) was 138.1 ± 37.7% (obstruction) vs. 125.3 ± 31.2% (no obstruction) (P = .007); and X5 (cmH2O/L/s) was -1.62 ± 1.28 (obstruction) vs. -1.25 ± 0.55 (no obstruction) (P < .001).

DISCUSSION

Impulse oscillometry has been advocated as a supplemental pulmonary function test to aid in the diagnosis of airway obstruction. The use of IOS has been primarily used in pediatrics and elderly populations as a validated tool to establish a diagnosis of airway obstruction but is limited in the adult population because of a well-validated set of reference values. Prior studies in adults have most often demonstrated a correlation with an elevated R5 > 150%, elevated resonant frequency, and a negative X5 < -1.5 or a decrease of 30 to 35% in R5 post-bronchodilator.

CONCLUSION

Impulse oscillometry may serve as an adjunct to diagnosis but likely cannot replace a standard spirometric evaluation. Our study highlights the future utility for diagnosing early obstructive disease in the symptomatic individual.

Pulmonary Function in Paediatric Patients with Inflammatory Bowel Disease

BACKGROUND

Among the extraintestinal manifestations of inflammatory bowel disease (IBD), those involving the lungs are relatively rare and often overlooked. There are only scarce data on the prevalence of IBD-associated lung involvement in children.

OBJECTIVES

The aim of our study was to assess pulmonary function in IBD children by different methods and to evaluate the influence of immunosuppressive therapy on disease severity.

METHODS

Seventy-two children with IBD (mean age of 14.45 ± 2.27 years) and 40 age-matched healthy controls (mean age of 14.17 ± 2.82) were included in the study. Pulmonary function tests (PFTs) were carried out by means of spirometry, oscillometry (IOS) and fractional exhaled nitric oxide (FeNO) to assess the pulmonary involvement.

RESULTS

Certain differences were observed between the study group and the control group, regarding the spirometric and oscillometry parameters. The fractions of exhaled nitric oxide did not differ between the group with IBD patients and the control group with regards to disease activity, the duration of illness and the administered immunosuppressive treatment.

CONCLUSIONS

The mean spirometry results were significantly different in the study group compared to the controls, although they were still within the normal limits. The pulmonary function abnormalities did not depend on either the disease activity or the immunosuppressive therapy. Oscillometry could be a supplementary method to assess pulmonary resistance. In turn, FeNO does not appear to be useful either in screening IBD children for pulmonary involvement or for the evaluation of disease activity. It appears then that only general screening of asymptomatic patients is a suitable method and a necessary recommendation in this population, prompting a revision of the current diagnostic approach.

Evaluation of Impulse Oscillometry in Respiratory Airway Casts with Varying Obstruction Phenotypes, Locations, and Complexities

The use of impulse oscillometry (IOS) for lung function testing does not need patient cooperation and has gained increasing popularity among both young and senior populations, as well as in patients with breathing difficulties. However, studies of the IOS sensitivity to regional lung obstructions are limited and have shown mixed results. The objective of this study was to evaluate the performance of an IOS system in 3D-printed lung models with structural abnormalities at different locations and with different severities. Lung trees of two complexity levels were tested, with one extending to the sixth generation (G6) and the other to G12. The IOS responses to varying glottal apertures, carina ridge tumors, and segmental bronchial constrictions were quantified in the G6 lung geometry. Both the G6 and G12 lung casts were prepared using high-resolution 3D printers. Overall, IOS detected the progressive airway obstructions considered in this study. The resonant frequency dropped with increasing obstructions for all three disease phenotypes in the G6 lung models. R20Hz increased with the increase in airway obstructions. Specifically, R20Hz in the airway model with varying glottal apertures agreed reasonably well with complementary measurements using TSI VelociCalc. In contrast to the high-resistance (R) sensitivity to the frequency in G6 lung models, R was nearly independent of frequency in G12 lung models. IOS R20Hz demonstrated adequate sensitivity to the structural remodeling in the central airways. However, the changes of R5Hz and X5Hz vs. airway obstructions were inconclusive in this study, possibly due to the rigid lung casts and the difference of a container–syringe system from human lungs.

Diagnostic sensitivity of impulse oscillometry in early detection of patients exposed to risk factors chronic obstructive pulmonary diseases

Background: Impulse oscillometry (IOS) is a method that does not depend on the cooperation of the patient and can detect small airway diseases with higher sensitivity than spirometry. However, the clinical application value of IOS in the screening of patients exposed to risk factors COPD and early diagnosis remains unclear. The aim of this study is to evaluate diagnostic sensitivity of IOS in the early detection of patients exposed to risk factors COPD.

Methods: A prospective cross-sectional study was conducted in Rasoul Akram Hospital, Tehran, Iran, from 2013 to 2015. 28 patients with COPD risk factors and normal spirometry participated in the study. The IOS was performed. We obtained the respiratory resistance and impedance of 5 Hz (R5) and 20 Hz (R20) and 5 Hz (Z5), respectively. The data were analyzed using SPSS version 17 using Chi-square and two independent sample t-test. Spearman correlation test was used to measure the correlation of oscillometry parameters in the diagnosis of COPD. P-value <0.05 was considered significantfor all statistical analyses.

Results: The mean patient age was 55.50±11.27 years. In this study, the sensitivity of Z5, R5, and R20 was respectively 28.5%, 25%, and 31.5%. All oscillometry parameters were significantly correlated with each other but none of the oscillometry parameters showed significant correlations with FEV1/FVC (rZ5=0.018, rR5=0.082, rR20=0.041 and PZ5=0.932, PR5=0.711, P R20=0.850). According to the results, only 9 patients (32.5%) with normal values of FEV1/FVC had abnormal values of oscillometry.

Conclusion: IOS has a low sensitivity and cannot be used in the screening of early-stage chronic obstructive pulmonary disease.

An overview of exacerbations of chronic obstructive pulmonary disease: Can tests of small airways' function guide diagnosis and management?

Chronic obstructive pulmonary disease (COPD) is common and debilitating. Most patients with COPD experience intermittent, acute deterioration in symptoms which require additional therapy, termed exacerbations. Exacerbations are prevalent in COPD and are associated with poor clinical outcomes including death, a faster decline in lung health, and a reduced quality of life. Current guidelines highlight the need to treat exacerbations promptly and then mitigate future risk. However, exacerbations are self-reported, difficult to diagnose and are treated with pharmacological therapies which have largely been unchanged over 30 years. Recent research has highlighted how exacerbations vary in their underlying cause, with specific bacteria, viruses, and cell types implicated. This variation offers the opportunity for new targeted therapies, but to develop these new therapies requires sensitive tools to reliably identify the cause, the start, and end of an exacerbation and assess the response to treatment. Currently, COPD is diagnosed and monitored using spirometric measures, principally the forced expiratory volume in 1 s and forced vital capacity, but these tests alone cannot reliably diagnose an exacerbation. Measures of small airways' function appear to be an early marker of COPD, and some studies have suggested that these tests might also provide physiological biomarkers for exacerbations. In this review, we will discuss how exacerbations of COPD are currently defined, stratified, monitored, and treated and review the current literature to determine if tests of small airways' function might improve diagnostic accuracy or the assessment of response to treatment.

Standardized IOS Reference Values Define Peripheral Airway Impairment-Associated Uncontrolled Asthma Risk Across Ethnicity in Children

BACKGROUND

Although clinically useful in identifying peripheral airway impairment (PAI), impulse oscillometry (IOS) has not received universal acceptance. This may be due to variable cutoff points, and the perception that available standardized reference values may not be clinically relevant in all populations.

OBJECTIVE

To establish the relationship between PAI, based on standardized IOS reference values, and uncontrolled asthma as well as interchangeability between Hispanic and white reference algorithms.

METHODS

IOS reference values were established for upper and lower limits of normal (>95th and <5th percentile, respectively) using published algorithms in Hispanic and white children. Values exceeding normal limits (PAI) were compared in those uncontrolled and controlled for significance of differences. Probability estimates and odds ratio of uncontrolled asthma were determined for R5, R5-R20, AX, and X5 using adjusted generalized estimating equation analyses. Intraclass correlation coefficients determined interchangeability of Hispanic and white reference algorithm values.

RESULTS

Those with uncontrolled asthma had significantly greater PAI and a higher frequency of PAI than those well controlled (P < .05), whereas odds of uncontrolled asthma increased with increasing PAI (P < .001) for all IOS measures, particularly for X5, where odds ratios ranged from 2.70 to 11.01.There was good to excellent (>70%) agreement between Hispanic and white algorithms, except for R5-R20 (<70%).

CONCLUSIONS

PAI, defined by IOS reference values, not central airway markers (R20), is consistently related to the risk of uncontrolled asthma. This is true whether using Hispanic or white reference algorithms. Thus, standardized reference values in children offer the clinician readily available IOS cutoff points that are clinically relevant across ethnicity.

Technical standards for respiratory oscillometry

Oscillometry (also known as the forced oscillation technique) measures the mechanical properties of the respiratory system (upper and intrathoracic airways, lung tissue and chest wall) during quiet tidal breathing, by the application of an oscillating pressure signal (input or forcing signal), most commonly at the mouth. With increased clinical and research use, it is critical that all technical details of the hardware design, signal processing and analyses, and testing protocols are transparent and clearly reported to allow standardisation, comparison and replication of clinical and research studies. Because of this need, an update of the 2003 European Respiratory Society (ERS) technical standards document was produced by an ERS task force of experts who are active in clinical oscillometry research.The aim of the task force was to provide technical recommendations regarding oscillometry measurement including hardware, software, testing protocols and quality control.The main changes in this update, compared with the 2003 ERS task force document are 1) new quality control procedures which reflect use of "within-breath" analysis, and methods of handling artefacts; 2) recommendation to disclose signal processing, quality control, artefact handling and breathing protocols (e.g. number and duration of acquisitions) in reports and publications to allow comparability and replication between devices and laboratories; 3) a summary review of new data to support threshold values for bronchodilator and bronchial challenge tests; and 4) updated list of predicted impedance values in adults and children.

Reduced lung elastic recoil and fixed airflow obstruction in asthma

BACKGROUND AND OBJECTIVE

Fixed airflow obstruction (FAO) in asthma occurs despite optimal inhaled treatment and no smoking history, and remains a significant problem, particularly with increasing age and duration of asthma. Increased lung compliance and loss of lung elastic recoil has been observed in older people with asthma, but their link to FAO has not been established. We determined the relationship between abnormal lung elasticity and airflow obstruction in asthma.

METHODS

Non-smoking asthmatic subjects aged >40 years, treated with 2 months of high-dose inhaled corticosteroid/long-acting beta-agonist (ICS/LABA), had FAO measured by spirometry, and respiratory system resistance at 5 Hz (Rrs₅ ) and respiratory system reactance at 5 Hz (Xrs₅ ) measured by forced oscillation technique. Lung compliance (K) and elastic recoil (B/A) were calculated from pressure-volume curves measured by an oesophageal balloon. Linear correlations between K and B/A, and forced expiratory volume in 1 s/forced vital capacity (FEV₁ /FVC), Rrs₅ and Xrs₅ were assessed.

RESULTS

Eighteen subjects (11 males; mean ± SD age: 64 ± 8 years, asthma duration: 39 ± 22 years) had moderate FAO measured by spirometry ((mean ± SD z-score) post-bronchodilator FEV₁ : -2.2 ± 0.5, FVC: -0.7 ± 1.0, FEV₁ /FVC: -2.6 ± 0.7) and by increased Rrs₅ (median (IQR) z-score) 2.7 (1.9 to 3.2) and decreased Xrs₅ : -4.1(-2.4 to -7.3). Lung compliance (K) was increased in 9 of 18 subjects and lung elastic recoil (B/A) reduced in 5 of 18 subjects. FEV₁ /FVC correlated negatively with K (r_s = -0.60, P = 0.008) and Rrs₅ correlated negatively with B/A (r_s = -0.52, P = 0.026), independent of age. Xrs₅ did not correlate with lung elasticity indices.

CONCLUSION

Increased lung compliance and loss of elastic recoil relate to airflow obstruction in older non-smoking asthmatic subjects, independent of ageing. Thus, structural lung tissue changes may contribute to persistent, steroid-resistant airflow obstruction.

CLINICAL TRIAL REGISTRATION

ACTRN126150000985583 at anzctr.org.au (UTN: U1111-1156-2795).

Spirometric indices of early airflow impairment in individuals at risk of developing COPD: Spirometry beyond FEV1/FVC

Spirometry is the current gold standard for diagnosing and monitoring the progression of Chronic Obstructive Pulmonary Disease (COPD). However, many current and former smokers who do not meet established spirometric criteria for the diagnosis of this disease have symptoms and clinical courses similar to those with diagnosed COPD. Large longitudinal observational studies following individuals at risk of developing COPD offer us additional insight into spirometric patterns of disease development and progression. Analysis of forced expiratory maneuver changes over time may allow us to better understand early changes predictive of progressive disease. This review discusses the theoretical ability of spirometry to capture fine pathophysiologic changes in early airway disease, highlights the shortcomings of current diagnostic criteria, and reviews existing evidence for spirometric measures which may be used to better detect early airflow impairment.

Serum perfluoroalkyl substances and lung function in adolescents exposed to the World Trade Center disaster

The effects of childhood exposure to perfluoroalkyl substances (PFASs) on lung function remain mostly unknown. Previous research indicates that children living or going to school near the World Trade Center (WTC) disaster were exposed to high levels of PFASs, among other toxic chemicals. To explore the effects of PFAS exposure on lung function, we measured serum PFASs in a cohort of children from the WTC Health Registry and a matched control group. Perfluorooctanesulfonate had the highest median concentrations in both groups (WTCHR = 3.72 ng/mL, Comparison = 2.75 ng/mL), while the lowest median concentrations were seen for perfluoroundecanoic acid (WTCHR = 0.12 ng/mL, Comparison = 0.01 ng/mL). Lung function outcomes were measured by spirometry, plethysmography, and oscillometry. Asthma diagnosis and serum eosinophil count were also recorded. We examined the relationships of each PFAS with lung function parameters and eosinophil count using linear regressions. Odds ratios for asthma were obtained for each PFAS using logistic regression. The effect of total PFASs on these outcomes was also assessed. All regression models were adjusted for sex, race/ethnicity, age, body mass index (BMI) and tobacco smoke exposure. We found that serum PFASs were not statistically associated with the measured lung function parameters, asthma diagnosis, or eosinophil count in this cohort (p < 0.05). These findings highlight the need for more longitudinal studies to explore the long-term effects of childhood PFAS exposure on lung function past adolescence and early adulthood.

Bronchodilator Response Predicts Longitudinal Improvement in Small Airway Function in World Trade Center Dust Exposed Community Members

The evolution of lung function, including assessment of small airways, was assessed in individuals enrolled in the World Trade Center Environmental Health Center (WTC-EHC). We hypothesized that a bronchodilator response at initial evaluation shown by spirometry or in small airways, as measured by forced oscillation technique (FOT), would be associated with improvement in large and small airway function over time. Standardized longitudinal assessment included pre and post bronchodilator (BD) spirometry (forced vital capacity, FVC; forced expiratory volume in 1 second, FEV₁) and FOT (resistance at 5 Hz, R₅; resistance at 5 minus 20 Hz, R_5–20). Longitudinal changes were assessed using linear mixed-effects modelling with adjustment for potential confounders (median follow-up 2.86 years; 95% measurements within 4.9 years). Data demonstrated: (1) parallel improvement in airflow and volume measured by spirometry and small airway function (R₅ and R_5–20) measured by FOT; (2) the magnitude of longitudinal improvement was tightly linked to the initial BD response; and (3) longitudinal values for small airway function on FOT were similar to residual abnormality observed post BD at initial visit. These findings suggest presence of reversible and irreversible components of small airway injury that are identifiable at initial presentation. These results have implications for treatment of isolated small airway abnormalities that can be identified by non-invasive effort independent FOT particularly in symptomatic individuals with normal spirometry indices. This study underscores the need to study small airway function to understand physiologic changes over time following environmental and occupational lung injury.

Forced oscillation technique for early detection of the effects of smoking and COPD: contribution of fractional-order modeling

Purpose

The aim of the present study was to evaluate the performance of the forced oscillation technique (FOT) for the early diagnosis of the effects of smoking and COPD. The contributions of the integer-order (InOr) and fractional-order (FrOr) models were also evaluated.

Patients and methods

In total, 120 subjects were analyzed: 40 controls, 40 smokers (20.3±9.3 pack-years) and 40 patients with mild COPD.

Results

Initially, it was observed that traditional FOT parameters and the InOr and FrOr models provided a consistent description of the COPD pathophysiology. Mild COPD introduced significant increases in the FrOr inertance, damping factor and hysteresivity (P<0.0001). These parameters were significantly correlated with the spirometric parameters of central and small airway obstruction (P<0.0001). The diagnostic accuracy analyses indicated that FOT parameters and InOr modeling may adequately identify these changes (area under the receiver operating characteristic curve – AUC >0.8). The use of FrOr modeling significantly improved this process (P<0.05), allowing the early diagnosis of smokers and patients with mild COPD with high accuracy (AUC >0.9).

Conclusion

FrOr modeling improves our knowledge of modifications that occur in the early stages of COPD. Additionally, the findings of the present study provide evidence that these models may play an important role in the early diagnosis of COPD, which is crucial for improving the clinical management of the disease.

Respiratory Health and Lung Function in Children Exposed to the World Trade Center Disaster

OBJECTIVES

To compare lung function in a representative sample of World Trade Center (WTC)-exposed children with matched comparisons, and examine relationships with reported exposures.

STUDY DESIGN

Study population consisted of 402 participants. Oscillometry, spirometry, and plethysmography were performed on WTC Health Registry (WTCHR) respondents who were ≤8 years of age on September 11, 2001 (n = 180) and a sociodemographically matched group of New York City residents (n = 222). We compared lung function by study arm (WTCHR and comparison group) as well as dust cloud (acute); home dust (subchronic); and other traumatic, nondust exposures.

RESULTS

In multivariable models, post-9/11 risk of incident asthma was higher in the WTCHR participants than in the comparison group (OR 1.109, 95% CI 1.021, 1.206; P = .015). Comparing by exposure rather than by group, dust cloud (OR 1.223, 95% CI 1.095, 1.365; P < .001) and home dust (OR 1.123, 95% CI 1.029, 1.226; P = .009) exposures were also associated with a greater risk of incidence of post-9/11 asthma. No differences were identified for lung function measures.

CONCLUSIONS

Although we cannot exclude an alternative explanation to the null findings, these results may provide some measure of reassurance to exposed children and their families regarding long-term consequences. Further study with bronchodilation and/or methacholine challenge may be needed to identify and further evaluate effects of WTC exposure. Biomarker studies may also be more informative in delineating exposure-outcome relationships.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02068183.

Recognition of the peripheral airway impairment phenotype in children with well-controlled asthma

BACKGROUND

Peripheral airway impairment, although frequently unrecognized, is a risk factor for poor asthma control, loss of control, increased exacerbations, airway hyperresponsiveness, and loss of lung function with age, even in patients with well-controlled asthma.

OBJECTIVE

To determine the presence of peripheral airway impairment by impulse oscillometry and forced expiratory flow between 25% and 75% (FEF_25%-75%) in children whose asthma is well controlled by National Asthma Education and Prevention Program (NAEPP) guidelines.

METHODS

In this retrospective, cross-sectional analysis, outcomes were evaluated across 192 encounters in 139 patients with moderate to severe asthma, ages 4-18 years. Receiver operator characteristic curves were created and oscillometry thresholds determined by maximizing the sum of sensitivity and specificity to identify those whose condition is not well controlled. Impairment was then identified for those whose condition was well controlled when these age-dependent oscillometry thresholds were met for each IOS measure or FEF_25%-75% < 65% of predicted.

RESULTS

Reactance at 5 Hz (X5) appeared most robust to identify peripheral airway impairment. In 96 well-controlled asthma encounters, impairment was identified by X5 in approximately 20% and 45% for those younger than 12 years and adolescents, respectively, compared with a maximum of 10% with FEF_25%-75% in the adolescent cohort (P < .05).

CONCLUSION

We conclude that peripheral airway impairment, determined by oscillometry, is common in patients with well-controlled asthma across age cohorts. X5 with optimal cut points ≤ -3.8, ≤ -2.5, and ≤ -1.5 cmH₂O/L/s for ages 4-7, 8-11, and >12 years, provides the clinician with a practical tool to identify the presence of the peripheral airway impairment phenotype that is consistently superior to FEF_25%-75%. This recognition, if confirmed, may reduce the risk of asthma-associated consequences with earlier and more targeted therapy.

Impulse oscillometry measurement of distal airways obstruction in depleted uranium-exposed Gulf War veterans

INTRODUCTION

A cohort of Gulf War I veterans who sustained exposure to depleted uranium undergoes biennial surveillance for potential uranium-related health effects. We performed impulse oscillometry and hypothesized that veterans with higher uranium body burdens would have more obstructive abnormalities than those with lower burdens.

METHODS

We compared pulmonary function of veterans in high versus low urine uranium groups by evaluating spirometry and oscillometry values.

RESULTS

Overall mean spirometry and oscillometry resistance values fell within the normal ranges. There were no significant differences between the high and low uranium groups for any parameters. However, more veterans were classified as having obstruction by oscillometry (42%) than spirometry (8%).

CONCLUSIONS

While oscillometry identified more veterans as obstructed, obstruction was not uranium-related. However, the added sensitivity of this method implies a benefit in wider surveillance of exposed cohorts and holds promise in identifying abnormalities in areas of the lung historically described as silent.

Effects of combination therapy indacaterol/glycopyrronium versus tiotropium on moderate to severe COPD: evaluation of impulse oscillometry and exacerbation rate

BACKGROUND

Small airways are considered the major site of airflow limitation in COPD. Impulse oscillometry (IOS) is a forced oscillation technique, which provides passive measurement of lung mechanics. It can differentiate small airway from large airway obstruction and is more sensitive than spirometry for peripheral airway disease. In this study the efficacy of the combination of Indacaterol/Glycopirronium (IND/GLY) versus Tiotropium on airway resistance (R5, R20, R5-20), lung reactance (X) and resonant frequency in moderate to severe COPD patients has been evaluated. We also evaluated inspiratory capacity (IC), forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC), exacerbation rate and quality of life.

METHODS

Forty patients were monitored with forced oscillation technique and spirometry. Patients were randomized in 2 groups: 20 received fixed dose once daily Indacaterol/Glycopyrronium (Group A) and 20 received single Tiotropium (Group B). The oscillometry parameters were the measure of resistance in the airways at 5 Hz (R5), at 20 Hz (R20) and the lung reactance (X).

RESULTS

There was a statistically significant difference between pre-dosing at V₁ and at follow up visits in R₅, R₂₀ and X values in patients receiving dual bronchodilation but not in control group. Pre-dosing IC value at follow up visits in patients receiving dual bronchodilation had a statistical significant variation.

CONCLUSIONS

The "new" bronchodilator combination LABA/LAMA significantly reduces bronchial obstruction in small airways too. The oscillometry demonstrated greater sensitivity compared with spirometry for monitoring outcome measures of airway obstruction and the effect of long-term therapy.

Small airways disease: time for a revisit?

It is increasingly acknowledged that delays in the diagnosis of chronic inflammatory lung conditions have hampered our understanding of pathogenesis and thus our ability to design efficacious therapies. This is particularly true for COPD, where most patients are diagnosed with moderate-to-severe airflow obstruction and little is known about the inflammatory processes present in early disease. There is great interest in developing screening tests that can identify those most at risk of developing COPD before airflow obstruction has developed for the purpose of research and clinical care. Landmark pathology studies have suggested that damage to the small airways precedes the development of airflow obstruction and emphysema and, thus, presents an opportunity to identify those at risk of COPD. However, despite a number of physiological tests being available to assess small airways function, none have been adopted into routine care in COPD. The reasons that tests of small airways have not been utilized widely include variability in test results and a lack of validated reference ranges from which to compare results for some methodologies. Furthermore, population studies have not consistently demonstrated their ability to diagnose disease. However, the landscape may be changing. As the equipment that delivers tests of small airways become more widely available, reference ranges are emerging and newer methodologies specifically seek to address variability and difficulty in test performance. Moreover, there is evidence that while tests of small airways may not be helpful across the full range of established disease severity, there may be specific groups (particularly those with early disease) where they might be informative. In this review, commonly utilized tests of small airways are critically appraised to highlight why these tests may be important, how they can be used and what knowledge gaps remain for their use in COPD.

The case for impulse oscillometry in the management of asthma in children and adults

OBJECTIVE

To provide a clinical rationale for including impulse oscillometry (IOS) as a part of standard office-based asthma assessment.

DATA SOURCES

PubMed and Google search, limited to English language and human disease, with the keywords IOS and asthma.

STUDY SELECTIONS

Articles included in this review were based on the expert opinion and previous publications by the authors.

RESULTS

In children, IOS was more useful than spirometry in identifying asthma and uncontrolled asthma and predicting loss of control and exacerbations. IOS predicts young children at risk for loss of lung function with age and the potential for early intervention to prevent further sequelae. In adults, peripheral airway impairment detected by IOS or spirometry (ie, forced expiratory flow between 25% and 75%) commonly occurs across severity, and each measure may be complementary in predicting loss of control even with normal forced expiratory volume in 1 second. Extrafine inhaled corticosteroids with or without long-acting β-agonists proved superior to standard particle aerosols in improving IOS-detected peripheral airway obstruction. Our data also suggest that currently available commercial reference values for lung resistance at 5 Hz and lung reactance at 5 Hz are applicable across diverse populations, but further studies are needed.

CONCLUSION

The findings of this review suggest that IOS can add value to traditional clinical and spirometric assessment and thus improve management of asthma in children and adults, as well as have the potential to detect early dysfunction of the peripheral airways, which may result in better outcomes.

The Contribution of Small Airway Obstruction to the Pathogenesis of Chronic Obstructive Pulmonary Disease

The hypothesis that the small conducting airways were the major site of obstruction to airflow in normal lungs was introduced by Rohrer in 1915 and prevailed until Weibel introduced a quantitative method of studying lung anatomy in 1963. Green repeated Rohrer's calculations using Weibels new data in 1965 and found that the smaller conducting airways offered very little resistance to airflow. This conflict was resolved by seminal experiments conducted by Macklem and Mead in 1967, which confirmed that a small proportion of the total lower airways resistance is attributable to small airways <2 mm in diameter. Shortly thereafter, Hogg, Macklem, and Thurlbeck used this technique to show that small airways become the major site of obstruction in lungs affected by emphysema. These and other observations led Mead to write a seminal editorial in 1970 that postulated the small airways are a silent zone within normal lungs where disease can accumulate over many years without being noticed. This review provides a progress report since the 1970s on methods for detecting chronic obstructive pulmonary disease, the structural nature of small airways' disease, and the cellular and molecular mechanisms that are thought to underlie its pathogenesis.

Distal airway dysfunction identifies pulmonary inflammation in asymptomatic smokers

Smoking induced inflammation leads to distal airway destruction. However, the relationship between distal airway dysfunction and inflammation remains unclear, particularly in smokers prior to the development of airway obstruction.

Seven normal controls and 16 smokers without chronic obstructive pulmonary disease (COPD) were studied. Respiratory function was assessed using the forced oscillation technique (FOT). Abnormal FOT was defined as elevated resistance at 5 Hz (R₅). Parameters reflecting distal lung function included frequency dependence of resistance (R_5–20) and dynamic elastance (X₅). Inflammation was quantified in concentrated bronchoalveolar lavage utilising cell count differential and cytokines expressed as concentration per mL epithelial lining fluid.

All control subjects and seven smokers had normal R₅. Nine smokers had elevated R₅ with abnormal R_5–20 and X₅, indicating distal lung dysfunction. The presence of abnormal FOT was associated with two-fold higher lymphocyte and neutrophil counts (p<0.025) and with higher interleukin (IL)-8, eotaxin and fractalkine levels (p<0.01). Reactivity of R_5–20 and X₅ correlated with levels of IL-8, eotaxin, fractalkine, IL-12p70 and transforming growth factor-α (r>0.47, p<0.01).

Distal airway dysfunction in smokers without COPD identifies the presence of distal lung inflammation that parallel reported observations in established COPD. These findings were not evident on routine pulmonary function testing and may allow the identification of smokers at risk of progression to COPD.

Isolated dysfunction in distal airways identifies pulmonary inflammation in asymptomatic smokers with normal airflowhttp://ow.ly/8bVk305aVkj

Accuracy of forced oscillation technique to assess lung function in geriatric COPD population

Introduction

Performing lung function test in geriatric patients has never been an easy task. With well-established evidence indicating impaired small airway function and air trapping in patients with geriatric COPD, utilizing forced oscillation technique (FOT) as a supplementary tool may aid in the assessment of lung function in this population.

Aims

To study the use of FOT in the assessment of airflow limitation and air trapping in geriatric COPD patients.

Study design

A cross-sectional study in a public hospital in Hong Kong. ClinicalTrials.gov ID: NCT01553812.

Methods

Geriatric patients who had spirometry-diagnosed COPD were recruited, with both FOT and plethysmography performed. “Resistance” and “reactance” FOT parameters were compared to plethysmography for the assessment of air trapping and airflow limitation.

Results

In total, 158 COPD subjects with a mean age of 71.9±0.7 years and percentage of forced expiratory volume in 1 second of 53.4±1.7 L were recruited. FOT values had a good correlation (r=0.4–0.7) to spirometric data. In general, X values (reactance) were better than R values (resistance), showing a higher correlation with spirometric data in airflow limitation (r=0.07–0.49 vs 0.61–0.67), small airway (r=0.05–0.48 vs 0.56–0.65), and lung volume (r=0.12–0.29 vs 0.43–0.49). In addition, resonance frequency (Fres) and frequency dependence (FDep) could well identify the severe type (percentage of forced expiratory volume in 1 second <50%) of COPD with high sensitivity (0.76, 0.71) and specificity (0.72, 0.64) (area under the curve: 0.8 and 0.77, respectively). Moreover, X values could stratify different severities of air trapping, while R values could not.

Conclusion

FOT may act as a simple and accurate tool in the assessment of severity of airflow limitation, small and central airway function, and air trapping in patients with geriatric COPD who have difficulties performing conventional lung function test. Moreover, reactance parameters were better than resistance parameters in correlation with air trapping.

Oscillometry complements spirometry in evaluation of subjects following toxic inhalation

The World Trade Center (WTC) destruction released dust and fumes into the environment. Although many community members developed respiratory symptoms, screening spirometry was usually normal. We hypothesised that forced oscillation testing would identify functional abnormalities undetected by spirometry and that symptom severity would relate to magnitude of abnormalities measured by oscillometry. A symptomatic cohort (n=848) from the Bellevue Hospital WTC Environmental Health Center was evaluated and compared to an asymptomatic cohort (n=475) from the New York City Department of Health WTC Health Registry. Spirometry and oscillometry were performed. Oscillometry measurements included resistance (R₅) and frequency dependence of resistance (R_5-20). Spirometry was normal for the majority of subjects (73.2% symptomatic versus 87.6% asymptomatic, p<0.0001). In subjects with normal spirometry, R₅ and R_5-20 were higher in symptomatic versus asymptomatic subjects (median (interquartile range) R₅ 0.436 (0.206) versus 0.314 (0.129) kPa·L^-1·s^-1, p<0.001; R_5-20 0.075 (0.085) versus 0.004 (0.042) kPa·L^-1·s^-1, p<0.0001). In symptomatic subjects, R₅ and R_5-20 increased with increasing severity and frequency of wheeze (p<0.05). Measurement of R_5-20 correlated with the presence and severity of symptoms even when spirometry was within normal limits. These findings are in accord with small airway abnormalities as a potential explanation of the respiratory symptoms.

Advantage of impulse oscillometry over spirometry to diagnose chronic obstructive pulmonary disease and monitor pulmonary responses to bronchodilators: An observational study

Objectives:

This retrospective study was a comparative analysis of sensitivity of impulse oscillometry and spirometry techniques for use in a mixed chronic obstructive pulmonary disease group for assessing disease severity and inhalation therapy.

Methods:

A total of 30 patients with mild-to-moderate chronic obstructive pulmonary disease were monitored by impulse oscillometry, followed by spirometry. Lung function was measured at baseline after bronchodilation and at follow-up (3–18 months). The impulse oscillometry parameters were resistance in the small and large airways at 5 Hz (R5), resistance in the large airways at 15 Hz (R15), and lung reactance (area under the curve X; AX).

Results:

After the bronchodilator therapy, forced expiratory volume in 1 second (FEV₁) readings evaluated by spirometry were unaffected at baseline and at follow-up, while impulse oscillometry detected an immediate improvement in lung function, in terms of AX (p = 0.043). All impulse oscillometry parameters significantly improved at follow-up, with a decrease in AX by 37% (p = 0.0008), R5 by 20% (p = 0.0011), and R15 by 12% (p = 0.0097).

Discussion:

Impulse oscillometry parameters demonstrated greater sensitivity compared with spirometry for monitoring reversibility of airway obstruction and the effect of maintenance therapy. Impulse oscillometry may facilitate early treatment dose optimization and personalized medicine for chronic obstructive pulmonary disease patients.

Effect of gastroesophageal reflux disease on disease severity and characteristics of lung functional changes in patients with asthma

INTRODUCTION

Almost one third of patients with asthma have symptomatic evidence for coexisting gastroesophageal reflux disease (GERD), which is thought to be aggravating factor in asthma at least in some cases. We investigated the impact of coexisting GERD on asthma severity and parameters of lung function.

METHODS

Ninety two asthma patients diagnosed according to ATS criteria were studied. After full history and physical examination, asthma severity was measured in each patient using asthma control test (ACT). GERD symptoms was verified in each patient. Impulse oscillometry (IOS) and lung volume studies (using body-plethysmography and IOS) were performed. The difference between total airway resistance (TAWR) indicated by resistance at 5 Hz and central airway resistance (CAWR) as indicated by resistance at 20 Hz in oscillometry was calculated and considered as representative of resistance at peripheral airways (PAWR). The relationship between the presences of GERD symptoms, ACT score and parameters of lung function were analyzed.

RESULTS

PAWR and TAWR were both significantly higher in asthmatic patients with GERD symptoms than patients without GERD symptoms (256.64±161.21 versus 191.68±98.64; P=0.02, and 102.73±122.39 versus 56.76±71.43; P=0.01, respectively). However, no significant difference was noted in mean values of ACT, FEV1 (forced expiratory volume in 1 sec), FVC (forced vital capacity), PEF (peak expiratory flow), and CAWR in these two groups.

CONCLUSION

These findings suggest that the severity of asthma as measured by ACT score is not different in patients with and without GERD symptoms. However, total and peripheral airway resistance measured by IOS is significantly higher in asthmatic patients with GERD symptoms.

The application of impulse oscillation system for the evaluation of treatment effects in patients with COPD

There are only a few reports of the use of impulse oscillation system (IOS) for the evaluation of COPD treatment. In this study, we applied IOS and spirometry to evaluate the effectiveness of fluticasone propionate and salmeterol (SFC) combined with tiotropium (TIO) in COPD patients. Following a 4-week run-in period with TIO (18 μg once daily) treatment, COPD patients were randomized to SFC (250/50 μg twice daily; SFC+TIO group, n=25), or TIO alone (TIO group, n=31). Pulmonary functions were recorded by IOS and spirometry before and after the study period. The SFC+TIO group showed significant improvements in inspiratory resistance at 5 Hz and resonant frequency, as well as in FVC and FEV1, after the 12-week treatment (p<0.05). Since there were no significant correlations between improvements in IOS measurements and FVC or FEV1, IOS may provide a physiological point of view that is different from spirometry and seemed to be applicable as an additional assessment tool targeting COPD patients.

New developments in the assessment of COPD: early diagnosis is key

Chronic obstructive pulmonary disease (COPD) is the most common chronic lung disease in the world, and its associated health burdens and costs are mounting. Until recently, it was generally accepted that targeting the diagnosis of COPD early in its course was a relatively fruitless effort, since treatments other than already ubiquitous smoking-cessation efforts were unlikely to alter its course. However, there is strong evidence to suggest that the majority of patients with objective COPD are not aware of their condition, and this leads to a significant delay in diagnosis, more aggressive smoking-cessation intervention, and potential treatment. Novel methods of diagnostic testing, community health programs, and primary-care provider recommendations hold promise to expand the recognition of COPD in its incipient stages - where recent evidence suggests a rapid decline in lung function occurs and may be prevented if acted upon. This review explores the evidence to support the efforts to justify programs aimed at early diagnosis, alternative diagnostic strategies that may augment traditional spirometry, therapeutic modalities that could potentially be used in the future to alter early lung-function decline, and emphasizes the necessary cooperative role that physicians, patients, communities, and governments need to play to realize the significant health impact that stands to be gained.

Airway dysfunction in obesity: response to voluntary restoration of end expiratory lung volume

Introduction

Abnormality in distal lung function may occur in obesity due to reduction in resting lung volume; however, airway inflammation, vascular congestion and/or concomitant intrinsic airway disease may also be present. The goal of this study is to 1) describe the phenotype of lung function in obese subjects utilizing spirometry, plethysmography and oscillometry; and 2) evaluate residual abnormality when the effect of mass loading is removed by voluntary elevation of end expiratory lung volume (EELV) to predicted FRC.

Methods

100 non-smoking obese subjects without cardio-pulmonary disease and with normal airflow on spirometry underwent impulse oscillometry (IOS) at baseline and at the elevated EELV.

Results

FRC and ERV were reduced (44±22, 62±14% predicted) with normal RV/TLC (29±9%). IOS demonstrated elevated resistance at 20 Hz (R₂₀, 4.65±1.07 cmH₂O/L/s); however, specific conductance was normal (0.14±0.04). Resistance at 5–20 Hz (R₅₋₂₀, 1.86±1.11 cmH₂O/L/s) and reactance at 5 Hz (X₅, −2.70±1.44 cmH₂O/L/s) were abnormal. During elevation of EELV, IOS abnormalities reversed to or towards normal. Residual abnormality in R₅₋₂₀ was observed in some subjects despite elevation of EELV (1.16±0.8 cmH₂O/L/s). R₅₋₂₀ responded to bronchodilator at baseline but not during elevation of EELV.

Conclusions

This study describes the phenotype of lung dysfunction in obesity as reduction in FRC with airway narrowing, distal respiratory dysfunction and bronchodilator responsiveness. When R₅₋₂₀ normalized during voluntary inflation, mass loading was considered the predominant mechanism. In contrast, when residual abnormality in R₅₋₂₀ was demonstrable despite return of EELV to predicted FRC, mechanisms for airway dysfunction in addition to mass loading could be invoked.

Lessons from the World Trade Center disaster: airway disease presenting as restrictive dysfunction

BACKGROUND

The present study (1) characterizes a physiologic phenotype of restrictive dysfunction due to airway injury and (2) compares this phenotype to the phenotype of interstitial lung disease (ILD).

METHODS

This is a retrospective study of 54 persistently symptomatic subjects following World Trade Center (WTC) dust exposure. Inclusion criteria were reduced vital capacity (VC), FEV1/VC>77%, and normal chest roentgenogram. Measurements included spirometry, plethysmography, diffusing capacity of lung for carbon monoxide (Dlco), impulse oscillometry (IOS), inspiratory/expiratory CT scan, and lung compliance (n=16).

RESULTS

VC was reduced (46% to 83% predicted) because of the reduction of expiratory reserve volume (43%±26% predicted) with preservation of inspiratory capacity (IC) (85%±16% predicted). Total lung capacity (TLC) was reduced, confirming restriction (73%±8% predicted); however, elevated residual volume to TLC ratio (0.35±0.08) suggested air trapping (AT). Dlco was reduced (78%±15% predicted) with elevated Dlco/alveolar volume (5.3±0.8 [mL/mm Hg/min]/L). IOS demonstrated abnormalities in resistance and/or reactance in 50 of 54 subjects. CT scan demonstrated bronchial wall thickening and/or AT in 40 of 54 subjects; parenchymal disease was not evident in any subject. Specific compliance at functional residual capacity (FRC) (0.07±0.02 [L/cm H2O]/L) and recoil pressure (Pel) at TLC (27±7 cm H2O) were normal. In contrast to patients with ILD, lung expansion was not limited, since IC, Pel, and inspiratory muscle pressure were normal. Reduced TLC was attributable to reduced FRC, compatible with airway closure in the tidal range.

CONCLUSIONS

This study describes a distinct physiologic phenotype of restriction due to airway dysfunction. This pattern was observed following WTC dust exposure, has been reported in other clinical settings (eg, asthma), and should be incorporated into the definition of restrictive dysfunction.

Techniques for assessing small airways function: Possible applications in asthma and COPD

In recent years special interest has been expressed for the contribution of small airways in the pathophysiology, clinical manifestations and treatment of asthma and COPD. Small airways contribute little to the total respiratory resistance so that extensive damage of small airways may occur before the appearance of any symptoms, and this is the reason why they are characterized as the "silent zone" of airways. Furthermore, the peripheral localization of the small airways and their small diameter constitutes difficult their direct assessment. Thus, they are usually studied indirectly, taking advantage of the effects of their obstruction, such as premature closure, air trapping, heterogeneity of ventilation, and lung volume dependence of airflow limitation. Today, several heterogeneous methods for the assessment of small airways are available. These can be either functional (spirometry, plethysmography, resistance measurements, nitrogen washout, alveolar nitric oxide, frequency dependence of compliance, flow-volume curves breathing mixture of helium-oxygen) or imaging (mainly through high resolution computed tomography). The above-mentioned methods are summarized in Table 1. However, no method is currently considered as the "gold standard" and it seems that combinations of tests are needed. Furthermore, it is not clear whether the small airways are affected in all patients with asthma or COPD and their clinical significance remains under investigation. Well-designed future studies with large numbers of patients are expected to reveal which of the methods for assessing the small airways is the most accurate, reliable and reproducible, for which patients, and which can be used for the evaluation of the effects of treatment.

Effect of methacholine on peripheral lung mechanics and ventilation heterogeneity in asthma

The forced oscillation technique (FOT) and multiple-breath nitrogen washout (MBNW) are noninvasive tests that are potentially sensitive to peripheral airways, with MBNW indexes being especially sensitive to heterogeneous changes in ventilation. The objective was to study methacholine-induced changes in the lung periphery of asthmatic patients and determine how changes in FOT variables of respiratory system reactance (Xrs) and resistance (Rrs) and frequency dependence of resistance (Rrs5-Rrs19) can be linked to changes in ventilation heterogeneity. The contributions of air trapping and airway closure, as extreme forms of heterogeneity, were also investigated. Xrs5, Rrs5, Rrs19, Rrs5-Rrs19, and inspiratory capacity (IC) were calculated from the FOT. Ventilation heterogeneity in acinar and conducting airways, and trapped gas (percent volume of trapped gas at functional residual capacity/vital capacity), were calculated from the MBNW. Measurements were repeated following methacholine. Methacholine-induced airway closure (percent change in forced vital capacity) and hyperinflation (change in IC) were also recorded. In 40 mild to moderate asthmatic patients, increase in Xrs5 after methacholine was predicted by increases in ventilation heterogeneity in acinar airways and forced vital capacity ( r2 = 0.37, P < 0.001), but had no correlation with ventilation heterogeneity in conducting airway increase or IC decrease. Increases in Rrs5 and Rrs5-Rrs19 after methacholine were not correlated with increases in ventilation heterogeneity, trapped gas, hyperinflation, or airway closure. Increased reactance in asthmatic patients after methacholine was indicative of heterogeneous changes in the lung periphery and airway closure. By contrast, increases in resistance and frequency dependence of resistance were not related to ventilation heterogeneity or airway closure and were more indicative of changes in central airway caliber than of heterogeneity.

Comparison of changes in lung function measured by plethymography and IOS after bronchoprovocation

AIM

Lung function tests are essential for the diagnosis and management of bronchial asthma. Impulse oscillation (IOS) system is an alternative way to measure lung mechanics for some patients. We investigated the relative sensitivities of IOS, body plethysmography and spirometry in detecting allergen- and methacholine-induced bronchoconstriction.

METHOD

Twenty-two subjects had single allergen inhalation and 8 subjects had 3 methacholine challenges. The tests were stopped when FEV1 fell by 20%. Lung function was measured using IOS (R5, R20, R5-R20, X5, AX, fres), plethysmography (sRaw, sGaw, FRC, lung volumes) and spirometry (FEV1, FVC, PEF, FEF50%) during inhalation challenges, and expressed as percent change from pre-challenge baseline.

RESULTS

All subjects were non-smoking adults with mild allergic asthma. Following allergen challenges, the most sensitive IOS index was R5-R20 and the most sensitive plethysmography and spirometry measurements were sRaw, sGaw and FEF50%. Following methacholine challenge the most sensitive IOS index was AX, the most sensitive plethysmography measurement was sRaw. Overall, IOS (R5-R20, AX, X5Hz) proved to be more sensitive than plethysmography and spirometry measurements following allergen-induced and methacholine-induced bronchoconstriction.

CONCLUSION

Our result shows that IOS is more sensitive than other lung function tests following allergen and methacholine challenge. In addition, IOS can act as an alternative measurement technique of airway resistance and obstruction in patients where manoeuvres involved in plethysmography and spirometry prove difficult to perform.

Assessing and accessing the small airways; implications for asthma management

Despite the wealth of experience in the management of asthma, the disease remains inadequately controlled in some patients, who face long-term respiratory impairment and disability. The disease has been characterised as an inflammatory condition affecting first the larger airways and eventually the smaller airways, but there is evidence that peripheral airway involvement defines a particular and more severe phenotype of asthma. For this reason, assessing functional and biological parameters reflective of small airways involvement is important prognostically. No assessment method is universally and directly representative of peripheral airway function, but the traditional spirometric tests, including vital capacity, residual volume and forced vital capacity, are somewhat correlated with this function; useful methods for further assessment include the single-breath nitrogen wash-out test, impulse oscillometry, nitrous oxide and exhaled breath concentrate measurements, as well as computed tomography to reflect air trapping and response to treatment. Formulation advancements have made for easier treatment access to the smaller airways, with the new extrafine formulations resulting in better asthma control compared with non-extrafine formulations.

Cutting edge technologies in respiratory research: lung function testing

Pulmonary function testing is part of routine clinical practice in respiratory medicine. It is based around spirometry, which will remain the central measurement of lung function given its prognostic significance and its integral role in defining severity of airways disease. However, there is an increasing body of evidence from studies using new methods of lung function measurement which are providing new insights into pathophysiology of disease. This body of data is forming a basis for their future clinical role, once the economics of producing the relevant devices becomes attractive. The forced oscillation technique and multiple breath nitrogen washout are currently the most commonly used of the newer lung function techniques, which are refinements of long-established techniques. Optical coherence tomography, optical reflection, electrical impedance and vibration response imaging have arisen by development of novel devices. The recent use of these techniques is reviewed.

Case-control study of lung function in World Trade Center Health Registry area residents and workers

RATIONALE

Residents and area workers who inhaled dust and fumes from the World Trade Center disaster reported lower respiratory symptoms in two World Trade Center Health Registry surveys (2003-2004 and 2006-2007), but lung function data were lacking.

OBJECTIVES

To examine the relationship between persistent respiratory symptoms and pulmonary function in a nested case-control study of exposed adult residents and area workers 7-8 years after September 11, 2001.

METHODS

Registrants reporting post September 11th onset of a lower respiratory symptom in the first survey and the same symptom in the second survey were solicited as potential cases. Registrants without lower respiratory symptoms in either Registry survey were solicited as potential control subjects. Final case-control status was determined by lower respiratory symptoms at a third interview (the study), when spirometry and impulse oscillometry were also performed.

MEASUREMENTS AND MAIN RESULTS

We identified 180 cases and 473 control subjects. Cases were more likely than control subjects to have abnormal spirometry (19% vs. 11%; P < 0.05), and impulse oscillometry measurements of elevated airway resistance (R5; 68% vs. 27%; P < 0.0001) and frequency dependence of resistance (R₅₋₂₀; 36% vs. 7%; P < 0.0001). When spirometry was normal, cases were more likely than control subjects to have elevated R₅ and R₅₋₂₀ (62% vs. 25% and 27% vs. 6%, respectively; both P < 0.0001). Associations between symptoms and oscillometry held when factors significant in bivariate comparisons (body mass index, spirometry, and exposures) were analyzed using logistic regression.

CONCLUSIONS

This study links persistent respiratory symptoms and oscillometric abnormalities in World Trade Center-exposed residents and area workers. Elevated R₅ and R₅₋₂₀ in cases despite normal spirometry suggested distal airway dysfunction as a mechanism for symptoms.

Disparity between proximal and distal airway reactivity during methacholine challenge

There is an increasing awareness of the role of distal airways in the pathophysiology of obstructive lung diseases including asthma and chronic obstructive pulmonary disease. We hypothesize that during induced bronchoconstriction: 1) disparity between distal and proximal airway reactivity may occur; and 2) changes in distal airway function may explain symptom onset in subjects with minimal FEV(1) change. 185 subjects underwent methacholine challenge testing (MCT). In addition to spirometry, oscillometry was performed at baseline and after maximum dose of methacholine; 33/185 also underwent oscillometry after each dose. Oscillometric parameters included resistance at 5 and 20 Hz (R(5), R(20)) and heterogeneity of distal airway mechanics assessed by frequency dependence of resistance 5-20 Hz (R(5-20)) and reactance area (AX). R(5) varied widely during MCT (range -0.8 - 11.3 cmH(2)O/L/s) and correlated poorly with change in FEV(1) (r = 0.17). Changes in R(5) reflected changes in both R(20) and R(5-20) (r = 0.59, p<0.05; r = 0.87, p<0.0001). However, R(20) increased only 0.3 cmH(2)O/L/s, while R(5-20) increased 0.7 cmH(2)O/L/s for every 1cmH(2)O/L/s change in R(5,) indicating predominant effect of distal airway mechanics. 9/33 subjects developed symptoms despite minimal FEV(1) change (<5%), while R(5) increased 42% due to increased distal airway heterogeneity. These data indicate disparate behavior of proximal airway resistance (FEV(1) and R(20)) and distal airway heterogeneity (R(5-20) and AX). Distal airway reactivity may be associated with methacholine-induced symptoms despite absence of change in FEV(1). This study highlights the importance of disparity between proximal and distal airway behavior, which has implications in understanding pathophysiology of obstructive pulmonary diseases and their response to treatment.