Lung volume indices predict morbidity in smokers with preserved spirometry

It is high time to discard a cut-off of 0.70 in the diagnosis of COPD

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) has traditionally been diagnosed based on the criterion of an FEV1/FVC <0.70. However, this definition has limitations as it may only detect patients with later-stage disease, when pathologic changes have become irreversible. Consequently, it potentially omits individuals with early-stage disease, in whom the pathologic changes could be delayed or reversed.

AREAS COVERED

This narrative review summarizes recent evidence regarding early-stage COPD, which may not fulfill the spirometric criteria but nonetheless exhibits features of COPD or is at risk of future COPD progression.

EXPERT OPINION

A comprehensive approach, including symptoms assessment, various physiologic tests, and radiologic features, is required to diagnose COPD. This approach is necessary to identify currently underdiagnosed patients and to halt disease progression in at- risk patients.

Lung Hyperinflation as Treatable Trait in Chronic Obstructive Pulmonary Disease: A Narrative Review

Lung hyperinflation (LH) is a common clinical feature in patients with chronic obstructive pulmonary disease (COPD). It results from a combination of reduced elastic lung recoil as a consequence of irreversible destruction of lung parenchyma and expiratory airflow limitation. LH is an important determinant of morbidity and mortality in COPD, partially independent of the degree of airflow limitation. Therefore, reducing LH has become a major target in the treatment of COPD over the last decades. Advances were made in the diagnostics of LH and several effective interventions became available. Moreover, there is increasing evidence suggesting that LH is not only an isolated feature in COPD but rather part of a distinct clinical phenotype that may require a more integrated management. This narrative review focuses on the pathophysiology and adverse consequences of LH, the assessment of LH with lung function measurements and imaging techniques and highlights LH as a treatable trait in COPD. Finally, several suggestions regarding future studies in this field are made.

Clinical features and 1-year outcomes of variable obstruction in participants with preserved spirometry: results from the ECOPD study in China

BACKGROUND

There are limited data on the clinical features and longitudinal prognosis of variable obstruction, particularly among never smokers and different variable obstruction types. Therefore, we aimed to evaluate the clinical characteristics of the participants with variable obstruction and determine the relationship between variable obstruction and the development of chronic obstructive pulmonary disease (COPD) and the decline of lung function in a community-dwelling study of Chinese, especially among never smokers and different variable obstruction subtypes.

METHODS

Participants with preserved spirometry (postbronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ≥0.70) at baseline from the Early COPD cohort were included in our analysis. Participants with variable obstruction (prebronchodilator FEV1/FVC <0.70) were compared with those without variable obstruction (prebronchodilator FEV1/FVC ≥0.70). We performed subgroup analyses in never smokers, former and current smokers, and different variable obstruction types (postbronchodilator FVC

RESULTS

The final analysis included 1140 participants with preserved spirometry (169 in the variable obstruction group) at baseline. Participants with variable obstruction were older, had lower lung function and had greater severe emphysema and computed tomography-defined air trapping than participants without variable obstruction. Participants with variable obstruction had a significantly increased risk of incident spirometry-defined COPD (relative risk: 3.22, 95% confidence interval 2.23 to 4.64, p <0.001) than those without variable obstruction after adjustment for covariates. These findings remained consistent among both former and current smokers, never smokers, and different variable obstruction types. Additionally, participants with variable obstruction had a faster decline in postbronchodilator FEV1/FVC (2.3±0.5%/year vs 0.9±0.4%/year, mean difference: 1.4 (95% confidence interval 0.5 to 2.3), p=0.002) than participants without variable obstruction after adjustment for covariates.

CONCLUSIONS

The results of our study revealed that variable obstruction can identify individuals who are at risk for the development of COPD and accelerated postbronchodilator FEV1/FVC decline in preserved spirometry.

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Key Words

• COPD epidemiology
• Respiratory Function Test

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MESH Headings

• Humans
• Male
• Spirometry
• Female
• Pulmonary Disease, Chronic Obstructive/physiopathology
• Pulmonary Disease, Chronic Obstructive/epidemiology
• Pulmonary Disease, Chronic Obstructive/diagnosis
• Middle Aged
• China/epidemiology
• Aged
• Forced Expiratory Volume
• Vital Capacity
• Smoking/epidemiology
• Smoking/adverse effects
• Lung/physiopathology
• Prognosis

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Grants

• the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Programme
• the National Key Research and Development Programme

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Affiliation(s)

Fan Wu State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China Guangzhou National Laboratory, Guangzhou, Guangdong, China
Haiqing Li State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Zhishan Deng State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Huajing Yang State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China Guangzhou National Laboratory, Guangzhou, Guangdong, China
Youlan Zheng State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China Guangzhou National Laboratory, Guangzhou, Guangdong, China
Ningning Zhao State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Cuiqiong Dai State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Jieqi Peng State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China Guangzhou National Laboratory, Guangzhou, Guangdong, China
Lifei Lu State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Zihui Wang State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Xiang Wen State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Shan Xiao State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Kunning Zhou State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Xiaohui Wu State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Gaoying Tang State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Qi Wan State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Ruiting Sun State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Jiangyu Cui State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
Changli Yang Wengyuan County People's Hospital, Shaoguan, Guangdong, China
Shengtang Chen Wengyuan County People's Hospital, Shaoguan, Guangdong, China
Jianhui Huang Lianping County People's Hospital, Heyuan, Guangdong, China
Shuqing Yu Lianping County People's Hospital, Heyuan, Guangdong, China
Yumin Zhou State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China Guangzhou National Laboratory, Guangzhou, Guangdong, China
Pixin Ran State Key Laboratory of Respiratory Disease & National Clinical Research Center for Respiratory Disease & National Center for Respiratory Medicine & Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China Guangzhou National Laboratory, Guangzhou, Guangdong, China

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Long COVID symptoms after 8-month recovery: persistent static lung hyperinflation associated with small airway dysfunction

BACKGROUND

Limited research has investigated the relationship between small airway dysfunction (SAD) and static lung hyperinflation (SLH) in patients with post-acute sequelae of COVID-19 (PASC) especially dyspnea and fatigue.

METHODS

64 patients with PASC were enrolled between July 2020 and December 2022 in a prospective observational cohort. Pulmonary function tests, impulse oscillometry (IOS), and symptom questionnaires were performed two, five and eight months after acute infection. Multivariable logistic regression models were used to test the association between SLH and patient-reported outcomes.

RESULTS

SLH prevalence was 53.1% (34/64), irrespective of COVID-19 severity. IOS parameters and circulating CD4/CD8 T-cell ratio were significantly correlated with residual volume to total lung capacity ratio (RV/TLC). Serum CD8 + T cell count was negatively correlated with forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) with statistical significance. Of the patients who had SLH at baseline, 57% continued to have persistent SLH after eight months of recovery, with these patients tending to be older and having dyspnea and fatigue. Post-COVID dyspnea was significantly associated with SLH and IOS parameters R5-R20, and AX with adjusted odds ratios 12.4, 12.8 and 7.6 respectively. SLH was also significantly associated with fatigue.

CONCLUSION

SAD and a decreased serum CD4/CD8 ratio were associated with SLH in patients with PASC. SLH may persist after recovery from infection in a substantial proportion of patients. SAD and dysregulated T-cell immune response correlated with SLH may contribute to the development of dyspnea and fatigue in patients with PASC.

Chronic obstructive pulmonary disease (COPD) and COPD-like phenotypes

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease. Historically, two COPD phenotypes have been described: chronic bronchitis and emphysema. Although these phenotypes may provide additional characterization of the pathophysiology of the disease, they are not extensive enough to reflect the heterogeneity of COPD and do not provide granular categorization that indicates specific treatment, perhaps with the exception of adding inhaled glucocorticoids (ICS) in patients with chronic bronchitis. In this review, we describe COPD phenotypes that provide prognostication and/or indicate specific treatment. We also describe COPD-like phenotypes that do not necessarily meet the current diagnostic criteria for COPD but provide additional prognostication and may be the targets for future clinical trials.

Potential pre-COPD indicators in association with COPD development and COPD prediction models in Chinese: a prospective cohort study

Background

Lung injury might take place before chronic obstructive pulmonary disease (COPD) occurs. A clearer definition of "pre-COPD" based on the effects of potential indicators on increasing risk of COPD development and a prediction model involving them are lacking.

Methods

A total of 3526 Chinese residents without COPD aged 40 years or older derived from the national cross-sectional survey of COPD surveillance in 2014-2015 were followed up for a mean of 3.59 years. We examined the associations of chronic bronchitis, preserved ratio impaired spirometry (PRISm), low peak expiratory flow (PEF), spirometric small airway dysfunction (sSAD), low maximal mid-expiratory flow (MMEF), low forced expiratory flow 50% of pulmonary volume (FEF50), and low FEF75 with subsequent COPD and constructed a prediction model with LASSO-Cox regression.

Findings

235 subjects in the cohort developed COPD during the follow-up. Subjects with PRISm, low PEF, sSAD, low MMEF, low FEF50, and low FEF75 had an increased risk of developing COPD (adjusted hazard ratio [HR] ranging from 1.57 to 3.01). Only chronic bronchitis (HR 2.84 [95% CI 1.38-5.84] and 2.94 [1.43-6.04]) and sSAD/low MMEF (HR 2.74 [2.07-3.61] and 2.38 [1.65-3.43]) showed effects independent of the other indicators and their concurrence had the strongest effect (HR 5.89 and 4.80). The prediction model including age, sex, low MMEF, low FEF50, and indoor exposure to biomass had good performance both internally and temporally. The corrected C-index was 0.77 (0.72-0.81) for discrimination in internal validation. For temporal validation, the area under the receiver operating characteristic curve was 0.73 (0.63-0.83). Good calibration was indicated in plot for internal validation and by Hosmer-Lemeshow test for temporal validation.

Interpretation

Individuals with concurrent chronic bronchitis and sSAD/low MMEF indicating pre-COPD optimally require more high attention from physicians. Our prediction model could serve as a multi-dimension tool to predict COPD comprehensively.

Funding

The Ministry of Finance and the Ministry of Science and Technology of the People's Republic of China and the National Natural Science Foundation of China.

Effect of twice daily inhaled albuterol on cardiopulmonary exercise outcomes, dynamic hyperinflation, and symptoms in secondhand tobacco-exposed persons with preserved spirometry and air trapping: a randomized controlled trial

BACKGROUND

In tobacco-exposed persons with preserved spirometry (active smoking or secondhand smoke [SHS] exposure), air trapping can identify a subset with worse symptoms and exercise capacity. The physiologic nature of air trapping in the absence of spirometric airflow obstruction remains unclear. The aim of this study was to examine the underlying pathophysiology of air trapping in the context of preserved spirometry and to determine the utility of bronchodilators in SHS tobacco-exposed persons with preserved spirometry and air trapping.

METHODS

We performed a double-blinded placebo-controlled crossover randomized clinical trial in nonsmoking individuals at risk for COPD due to exposure to occupational SHS who had preserved spirometry and air trapping defined as either a residual volume-to-total lung capacity ratio (RV/TLC) > 0.35 or presence of expiratory flow limitation (EFL, overlap of tidal breathing on maximum expiratory flow-volume loop) on spirometry at rest or during cardiopulmonary exercise testing (CPET). Those with asthma or obesity were excluded. Participants underwent CPET at baseline and after 4-week trials of twice daily inhalation of 180 mcg of albuterol or placebo separated by a 2-week washout period. The primary outcome was peak oxygen consumption (VO2) on CPET. Data was analyzed by both intention-to-treat and per-protocol based on adherence to treatment prescribed.

RESULTS

Overall, 42 participants completed the entire study (66 ± 8 years old, 91% female; forced expiratory volume in 1 s [FEV1] = 103 ± 16% predicted; FEV1 to forced vital capacity [FVC] ratio = 0.75 ± 0.05; RV/TLC = 0.39 ± 0.07; 85.7% with EFL). Adherence was high with 87% and 93% of prescribed doses taken in the treatment and placebo arms of the study, respectively (P = 0.349 for comparison between the two arms). There was no significant improvement in the primary or secondary outcomes by intention-to-treat or per-protocol analysis. In per-protocol subgroup analysis of those with RV/TLC > 0.35 and ≥ 90% adherence (n = 27), albuterol caused an improvement in peak VO2 (parameter estimate [95% confidence interval] = 0.108 [0.014, 0.202]; P = 0.037), tidal volume, minute ventilation, dynamic hyperinflation, and oxygen-pulse (all P < 0.05), but no change in symptoms or physical activity.

CONCLUSIONS

Albuterol may improve exercise capacity in the subgroup of SHS tobacco-exposed persons with preserved spirometry and substantial air trapping. These findings suggest that air trapping in pre-COPD may be related to small airway disease that is not considered significant by spirometric indices of airflow obstruction.

GLI-12 Reference Values versus Fixed 0.7 Ratio for the Detection of Airflow Obstruction in the Presence of Lung Hyperinflation

Introduction

Airflow obstruction (AO) is evidenced by reduced forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) with the threshold for diagnosis often being set at <0.7. However, currently the ATS/ERS standards for interpretation of lung function tests recommend the lower limit of normal (LLN), calculated by reference equations of the Global Lung Initiative from 2012 (GLI-12), as a threshold for AO diagnosis. The present study aims to investigate phenotypes, with focus on hyperinflation, which influence AO prevalence defined by FEV1/FVC < LLN when compared to the fixed 0.7 threshold.

Methods

Data from 3,875 lung function tests (56.4% men, aged 18-95) including 3,824 body plethysmography recordings performed from July 2021 to June 2022 were analysed. The difference between both classifiers was quantified, before and after stratification by sex, age, and hyperinflation.

Results

AO diagnosis was significantly less frequent with the LLN threshold (18.2%) compared to the fixed threshold (28.0%) (p < 0.001) with discordance rate of 10.5%. In the presence of mild or moderate hyperinflation, there was substantial agreement (Cohen's kappa: 0.616, 0.718) between the classifiers compared to near perfect agreement in the presence of severe hyperinflation (Cohen's kappa: 0.896). In addition, subgroup analysis after stratification for sex, age, and hyperinflation showed significant differences between both classifiers.

Conclusion

The importance of using the LLN threshold instead of the fixed 0.7 threshold for the diagnosis of AO is highlighted. When using the fixed threshold AO, misdiagnosis was more common in the presence of mild to moderate hyperinflation.

Revisiting Peter Macklem's old dream through the PRISm of lung volumes

In healthy asymptomatic smokers with normal FEV1/FVC, abnormal CT lung volumes that reflect small airway dysfunction and emphysema could be used as a biomarker to identify susceptible smokers at increased risk of progressing to COPD https://bit.ly/3XZDj1s.

Assessment of lung hyperinflation in occupational chronic obstructive pulmonary disease: a multicentric cross-sectional study

Occupational exposure is associated with elevated morbidity and lower quality of life in patients with chronic obstructive pulmonary disease (COPD). Static hyperinflation is an independent risk factor for all-cause mortality in COPD and for COPD exacerbation. In a multicentre, cross-sectional study (BPROFETIO), we sought to analyse the relationship between static hyperinflation and occupational exposure in patients with COPD with or without occupational exposure.

MATERIAL AND METHODS

An overall 'whole working life' cumulative exposure index was calculated for occupational patients with COPD. Spirometry indices and lung volumes were measured according to the 2005 American Thoracic Society/European Respiratory Society guidelines.

RESULTS

After adjustment for age, sex, height, body mass index, smoking and coexposure, the analysis for each occupational hazard showed a higher risk for hyperinflation and FEV1 decline or progression of COPD or GOLD stage for patients with COPD exposed to non-metallic inorganic dusts.

CONCLUSION

Occupational exposures should be more investigated in clinical practice and studies as they contribute to the COPD heterogeneity and are associated for some with the development of a static hyperinflation; a condition that is known to have a negative impact on quality of life and survival.

Lung volumes differentiate the predominance of emphysema versus airway disease phenotype in early COPD: an observational study of the COPDGene cohort

Rationale

Lung volumes identify the "susceptible smokers" who progress to develop spirometric COPD. However, among susceptible smokers, development of spirometric COPD seems to be heterogeneous, suggesting the presence of different pathological mechanisms during early establishment of spirometric COPD. The objective of the present study was to determine the differential patterns of radiographic pathologies among susceptible smokers.

Methods

We categorised smokers with preserved spirometry (Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 0) in the Genetic Epidemiology of COPD (COPDGene) cohort based on tertiles (low, intermediate and high) of lung volumes (either total lung capacity (TLC), functional residual capacity FRC or FRC/TLC) at baseline visit. We then examined the differential patterns of change in spirometry and the associated prevalence of computed tomography measured pathologies of emphysema and airway disease with those categories of lung volumes.

Results

The pattern of spirometric change differed when participants were categorised by TLC versus FRC/TLC: those in the high TLC tertile showed stable forced expiratory volume in 1 s (FEV1), but enlarging forced vital capacity (FVC), while those in the high FRC/TLC tertile showed decline in both FEV1 and FVC. When participants from the high TLC and high FRC/TLC tertiles were partitioned into mutually exclusive groups, compared to those with high TLC, those with high FRC/TLC had lesser emphysema, but greater air trapping, more self-reported respiratory symptoms and exacerbation episodes and higher likelihood of progressing to more severe spirometric disease (GOLD stages 2-4 versus GOLD stage 1).

Conclusions

Lung volumes identify distinct physiological and radiographic phenotypes in early disease among susceptible smokers and predict the rate of spirometric disease progression and the severity of symptoms in early COPD.

Changes in Lung Volumes with Spirometric Disease Progression in COPD

Background

Abnormal lung volumes representing air trapping identify the subset of smokers with preserved spirometry who develop spirometric chronic obstructive pulmonary disease (COPD) and adverse outcomes. However, how lung volumes evolve in early COPD as airflow obstruction develops remains unclear.

Methods

To establish how lung volumes change with the development of spirometric COPD, we examined lung volumes from the pulmonary function data (seated posture) available in the U.S. Department of Veterans Affairs electronic health records (n=71,356) and lung volumes measured by computed tomography (supine posture) available from the COPD Genetic Epidemiology (COPDGene®) study (n=7969) and the SubPopulations and InterMediate Outcome Measures In COPD Study (SPIROMICS) (n=2552) cohorts, and studied their cross-sectional distributions and longitudinal changes across the airflow obstruction spectrum. Patients with preserved ratio-impaired spirometry (PRISm) were excluded from this analysis.

Results

Lung volumes from all 3 cohorts showed similar patterns of distributions and longitudinal changes with worsening airflow obstruction. The distributions for total lung capacity (TLC), vital capacity (VC), and inspiratory capacity (IC) and their patterns of change were nonlinear and included different phases. When stratified by airflow obstruction using Global initiative for chronic Obstructive Lung Disease (GOLD) stages, patients with GOLD 1 (mild) COPD had larger lung volumes (TLC, VC, IC) compared to patients with GOLD 0 (smokers with preserved spirometry) or GOLD 2 (moderate) disease. In longitudinal follow-up of baseline GOLD 0 patients who progressed to spirometric COPD, those with an initially higher TLC and VC developed mild obstruction (GOLD 1) while those with an initially lower TLC and VC developed moderate obstruction (GOLD 2).

Conclusions

In COPD, TLC, and VC have biphasic distributions, change in nonlinear fashions as obstruction worsens, and could differentiate those GOLD 0 patients at risk for more rapid spirometric disease progression.

The Role of Pulmonary Function Testing in the Diagnosis and Management of COPD

Pulmonary function testing (PFT) has a long and rich history in the definition, diagnosis, and management of COPD. For decades, spirometry has been regarded as the standard for diagnosing COPD; however, numerous studies have shown that COPD symptoms, pathology, and associated poor outcomes can occur, despite normal spirometry. Diffusing capacity and imaging studies have called into question the need for spirometry to put the "O" (obstruction) in COPD. The role of exercise testing and the ability of PFTs to phenotype COPD are reviewed. Although PFTs play an important role in diagnosis, treatment decisions are primarily determined by symptom intensity and exacerbation history. Although a seminal study positioned FEV1 as the primary predictor of survival, numerous studies have shown that tests other than spirometry are superior predictors of mortality. In years past, using spirometry to screen for COPD was promulgated; however, this only seems appropriate for individuals who are symptomatic and at risk for developing COPD.

A Model to Predict Residual Volume from Forced Spirometry Measurements in Chronic Obstructive Pulmonary Disease

Background

Lung hyperinflation with elevated residual volume (RV) is associated with poor prognosis in adults with chronic obstructive pulmonary disease (COPD) and is a critical criterion for lung volume reduction selection. Here, we proposed that patterns within spirometric measures could represent the degree of hyperinflation.

Methods

Fractional polynomial multivariate regression was used to develop a prediction model based on age, biological sex, forced expiratory volume in 1 second (FEV₁), and forced vital capacity (FVC) to estimate plethysmography measured RV in patients in the Pittsburgh Specialized Center for Clinically Oriented Research (SCCOR) cohort (n=450). Receiver operating characteristic area under the curve (ROC-AUC) and optimal cut-points from the model were identified. The model was validated in a separate cohort (n=793).

Results

The best fit model: RV %est=[FVC %predicted] x 3.46-[FEV₁/FVC] x 179.80- [FVC % (sqrt)] x 79.53-[age] x 0.98- [sex] x 10.88 + 737.06, where [sex], m=1. R² of observed versus %predicted RV was 0.71. The optimal cut-point to predict an RV % >175% was 161. At this cut-point, ROC-AUC was 0.95, with a sensitivity 0.95, specificity 0.86, positive predictive value (PPV) of 97%, negative predictive value (NPV) of 76%, positive likelihood ratio (LR) of 6.6, and negative LR of 0.06. In a validation cohort of COPD patients (n=793), the model performed similarly, with a sensitivity of 0.82, specificity of 0.83, PPV of 85%, NPV of 79%, positive LR of 4.7, and negative LR of 0.21.

Conclusion

In patients with COPD, a model using only spirometry, age, and biological sex can estimate elevated RV. This tool could facilitate the identification of candidates for lung volume reduction procedures and can be integrated into existing epidemiologic databases to investigate the clinical impact of hyperinflation.

Two-dimensional shear wave elastography: a new tool for evaluating respiratory muscle stiffness in chronic obstructive pulmonary disease patients

BACKGROUND

Impaired respiratory function caused by respiratory muscle dysfunction is one of the common consequences of chronic obstructive pulmonary disease (COPD). In this study, two-dimensional shear wave elastography (2D-SWE) was used to measure diaphragm stiffness (DS) and intercostal muscle stiffness (IMS) in patients with COPD; in addition, the value of 2D-SWE in evaluating respiratory function was determined.

METHODS

In total, 219 consecutive patients with COPD and 20 healthy adults were included. 2D-SWE was used to measure the DS and IMS, and lung function was also measured. The correlation between respiratory muscle stiffness and lung function and the differences in respiratory muscle stiffness in COPD patients with different severities were analysed.

RESULTS

2D-SWE measurements of the DS and IMS presented with high repeatability and consistency, with ICCs of 0.756 and 0.876, respectively, and average differences between physicians of 0.10 ± 1.61 and 0.07 ± 1.65, respectively. In patients with COPD, the DS and IMS increased with disease severity (F₁ = 224.50, F₂ = 84.63, P < 0.001). In patients with COPD, the correlation with the forced expiratory volume in one second (FEV₁)/forced vital capacity (FVC), predicted FEV₁% value, residual volume (RV), total lung capacity (TLC), RV/TLC, functional residual capacity (FRC) and inspiratory capacity (IC) of DS (r₁=-0.81, r₂=-0.63, r₃ = 0.65, r₄ = 0.54, r₅ = 0.60, r₆ = 0.72 and r₇=-0.41, respectively; P < 0.001) was stronger than that of IMS (r₁=-0.76, r₂=-0.57, r₃ = 0.57, r₄ = 0.47, r₅ = 0.48, r₆ = 0.60 and r₇=-0.33, respectively; P < 0.001).

CONCLUSION

2D-SWE has potential for use in evaluating DS and IMS. A specific correlation was observed between respiratory muscle stiffness and lung function. With the worsening of the severity of COPD and the progression of lung function impairment, the DS and IMS gradually increased.

The prevalence and physiological impacts of centrilobular and paraseptal emphysema on CT in smokers with Preserved Ratio Impaired Spirometry

Centrilobular emphysema (CLE) and paraseptal emphysema (PSE) are observed in smokers with Preserved Ratio Impaired Spirometry (PRISm, defined as the ratio of forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC)≥0.7 and FEV1<80%), but their prevalence and physiological impacts remain unestablished. This multicenter study aimed to investigate its prevalence and to test whether emphysema subtypes are differently associated with physiological impairments in smokers with PRISm.

Both never and ever smokers aged at ≥40 years who underwent CT for lung cancer screening and spirometry were retrospectively and consecutively enrolled at three hospitals and a clinic. Emphysema subtypes were visually classified according to the Fleischner system. Air-trapping was assessed as the ratio of FVC to total lung capacity on CT (FVC/TLCCT).

Of 1046 never-smokers and 772 smokers with >10 pack-years, the prevalence of PRISm was 8.2% and 11.3%, respectively. The prevalence of PSE and CLE in smokers with PRISm was comparable to that in smokers with normal spirometry (PSE 43.7% versus 36.2%, p=1.00, CLE 46.0% versus 31.8%, p=0.21), but higher than that in never-smokers with PRISm (PSE, versus 1.2%, p<0.01, CLE, versus 4.7%, p<0.01) and lower than that in smokers with airflow limitation (PSE, versus 71.0%, p<0.01, CLE, versus 79.3%, p<0.01). The presence of CLE but not PSE was independently associated with reduced FVC/TLCCT in smokers with PRISm.

Both PSE and CLE were common, but only CLE was associated with air-trapping in smokers with PRISm, suggesting different physiological roles of these emphysema subtypes.

Usefulness of P0.1 in the Follow-Up of Individuals With Air Trapping and Home Noninvasive Ventilation and CPAP

BACKGROUND

The ventilatory mechanics of patients with COPD and obesity-hypoventilation syndrome (OHS) are changed when there is air trapping and auto-PEEP, which increase respiratory effort. P0.1 measures the ventilatory drive and, indirectly, respiratory effort. The aim of the study was to measure P0.1 in subjects with COPD or OHS on treatment with positive pressure and to analyze their changes in P0.1 after treatment.

METHODS

With a prospective design, subjects with COPD and OHS were studied in whom positive airway pressure was applied in their treatment. P0.1 was determined at study inclusion and after 6 months of treatment.

RESULTS

A total of 88 subjects were analyzed: 56% were males, and the mean age of 65 ± 9 y old. Fifty-four (61%) had OHS, and 34 (39%) had COPD. Fifty (56%) had air trapping, with an initial P0.1 value of 3.0 ± 1.3 cm H2O compared with 2.1 ± 0.7 cm H2O for subjects who did not have air trapping (P = .001). After 6 months of treatment, subjects who had air trapping had similar P0.1 as those who did not: 2.3 ± 1.1 and 2.1 ± 1 cm H2O, respectively (P = .53). In subjects with COPD, initial P0.1 was 2.9 ± 1.4 cm H2O and at 6 months 2.2 ± 1.1 cm H2O (P = .02). In subjects with OHS, initial P0.1 was 2.4 ± 1.1 cm H2O and at 6 months 2.2 ± 1.0 cm H2O (P = .28).

CONCLUSIONS

COPD and air trapping were associated with greater P0.1 as a marker of respiratory effort. A decrease in P0.1 indicates less respiratory effort after treatment.

Remote exposure to secondhand tobacco smoke is associated with lower exercise capacity through effects on oxygen pulse, a proxy of cardiac stroke volume

BACKGROUND

Past exposure to secondhand tobacco smoke (SHS) is associated with exercise limitation. Pulmonary factors including air trapping contribute to this limitation but the contribution of cardiovascular factors is unclear.

OBJECTIVE

To determine the contribution of cardiovascular mechanisms to SHS-associated exercise limitation.

METHODS

We examined the cardiovascular responses to maximum-effort exercise in 245 never-smokers with remote, prolonged occupational exposure to SHS and no known history of cardiovascular disease. We estimated the contribution of oxygen-pulse (proxy for cardiac stroke volume) and changes in systolic blood pressures (SBP), diastolic blood pressures and heart rate (HR) towards exercise capacity, and examined whether the association of SHS with exercise capacity was mediated through these variables.

RESULTS

At peak exercise (highest workload completed (WattsPeak)=156±46 watts (135±33 %predicted)), oxygen consumption and oxygen-pulse (O2-PulsePeak) were 1557±476 mL/min (100±24 %predicted) and 11.0±3.0 mL/beat (116±25 %predicted), respectively, with 29% and 3% participants not achieving their predicted normal range. Oxygen saturation at peak exercise was 98%±1% and remained >93% in all participants. Sixty-six per cent showed hypertensive response to exercise. In models adjusted for covariates, WattsPeak was associated directly with O2-PulsePeak, HRPeak and SBPPeak and inversely with SHS, air trapping (residual volume/total lung capacity) and rise of SBP over workload (all p<0.01). Moreover, SHS exposure association with WattsPeak was substantially (41%) mediated through its effect on O2-PulsePeak (p=0.038). Although not statistically significant, a considerable proportion (36%) of air trapping effect on WattsPeak seemed to be mediated through O2-PulsePeak (p=0.078). The likelihood of having baseline respiratory symptoms (modified Medical Research Council score ≥1) was associated with steeper rise in SBP over workload (p<0.01).

CONCLUSION

In a never-smoker population with remote exposure to SHS, abnormal escalation of blood pressure and an SHS-associated reduction in cardiac output contributed to lower exercise capacity.

Ratio of FEV1/Slow Vital Capacity of < 0.7 Is Associated With Clinical, Functional, and Radiologic Features of Obstructive Lung Disease in Smokers With Preserved Lung Function

BACKGROUND

Mild expiratory flow limitation may not be recognized using traditional spirometric criteria based on the ratio of FEV₁/FVC.

RESEARCH QUESTION

Does slow vital capacity (SVC) instead of FVC increase the sensitivity of spirometry to identify patients with early or mild obstructive lung disease?

STUDY DESIGN AND METHODS

We included 854 current and former smokers from the Subpopulations and Intermediate Outcome Measures in COPD Study cohort with a postbronchodilator FEV₁/FVC ≥ 0.7 and FEV₁ % predicted of ≥ 80% at enrollment. We compared baseline characteristics, chest CT scan features, exacerbations, and progression to COPD (postbronchodilator FEV₁/FVC, < 0.7) during the follow-up period between 734 participants with postbronchodilator FEV₁/SVC of ≥ 0.7 and 120 with postbronchodilator FEV₁/SVC < 0.7 at the enrollment. We performed multivariate linear and logistic regression models and negative binomial and interval-censored proportion hazards regression models adjusted for demographics and smoking exposure to examine the association of FEV₁/SVC < 0.7 with those characteristics and outcomes.

RESULTS

Participants with FEV₁/SVC < 0.7 were older and had lower FEV₁ and more emphysema than those with FEV₁/SVC ≥ 0.7. In adjusted analysis, individuals with postbronchodilator FEV₁/SVC < 0.7 showed a greater percentage of emphysema by 0.45% (95% CI, 0.09%-0.82%), percentage of gas trapping by 2.52% (95% CI, 0.59%-4.44%), and percentage of functional small airways disease based on parametric response mapping by 2.78% (95% CI, 0.72%-4.83%) at baseline than those with FEV₁/SVC ≥ 0.7. During a median follow-up time of 1,500 days, an FEV₁/SVC < 0.7 was not associated with total exacerbations (incident rate ratio [IRR], 1.61; 95% CI, 0.97-2.64), but was associated with severe exacerbations (IRR, 2.60; 95% CI, 1.04-4.89). An FEV₁/SVC < 0.7 was associated with progression to COPD during a 3-year follow-up even after adjustment for demographics and smoking exposure (hazard ratio, 3.93; 95% CI, 2.71-5.72). We found similar results when we examined the association of prebronchodilator FEV₁/SVC < 0.7 or FEV₁/SVC less than the lower limit of normal with chest CT scan features and progression to COPD.

INTERPRETATION

Low FEV₁ to SVC in current and former smokers with normal spirometry results can identify individuals with CT scan features of COPD who are at risk for severe exacerbations and is associated with progression to COPD in the future.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01969344T4; URL: www.clinicaltrials.gov.

Early diagnosis of COPD: myth or a true perspective

The early stages of COPD have recently become a hot topic as many new risk factors have been proposed, but substantial knowledge gaps remain in explaining the natural history of the disease. If we are to modify the outcomes of COPD, early detection needs to play a critical role. However, we need to sort out the barriers to early detection and have a better understanding of the definition of COPD and its diagnosis and therapeutic strategies to identify and treat patients with COPD before structural changes progress. In this review, we aim to clarify the differences between early COPD, mild COPD and early detection of COPD, with an emphasis on the clinical burden and how different outcomes (quality of life, exacerbation, cost and mortality) are modified depending on which definition is used. We will summarise the evidence for the new multidimensional diagnostic approaches to detecting early pathophysiologic changes that potentially allow for future studies on COPD management strategies to halt or prevent disease development.

Biomarkers in Chronic Obstructive Pulmonary Disease: The Gateway to Precision Medicine

Chronic obstructive pulmonary disease (COPD) is a highly heterogeneous disease with limited adequate treatments. Biomarkers-which may relate to disease susceptibility, diagnosis, prognosis, or treatment response-are ideally suited to dissecting such a complex disease and form a critical component of the precision medicine paradigm. Not all potential candidates, however, make good biomarkers. To date, only plasma fibrinogen has been approved by regulatory bodies as a biomarker of exacerbation risk for clinical trial enrichment. This review outlines some of the challenges of biomarker research in COPD and highlights novel and promising biomarker candidates.

Diagnosis and Treatment of Early Chronic Obstructive Lung Disease (COPD)

Chronic obstructive lung disease (COPD) is responsible for substantial rates of mortality and economic burden, and is one of the most important public-health concerns. As the disease characteristics include irreversible airway obstruction and progressive lung function decline, there has been a great deal of interest in detection at the early stages of COPD during the “at risk” or undiagnosed preclinical stage to prevent the disease from progressing to the overt stage. Previous studies have used various definitions of early COPD, and the term mild COPD has also often been used. There has been a great deal of recent effort to establish a definition of early COPD, but comprehensive evaluation is still required, including identification of risk factors, various physiological and radiological tests, and clinical manifestations for diagnosis of early COPD, considering the heterogeneity of the disease. The treatment of early COPD should be considered from the perspective of prevention of disease progression and management of clinical deterioration. There has been a lack of studies on this topic as the definition of early COPD has been proposed only recently, and therefore further clinical studies are needed.

Assessing Static Lung Hyperinflation by Whole-Body Plethysmography, Helium Dilution, and Impulse Oscillometry System (IOS) in Patients with COPD

Purpose

Lung hyperinflation is a feature of chronic obstructive pulmonary disease (COPD) and can determine pivotal consequence on symptoms, exercise tolerance and quality of life. Despite the relevance of assessing lung hyperinflation, there is still no single consensus as to what volume should be taken into account. We investigate which spirometric measurement is more reliable in assessing static lung hyperinflation and which is more related with impulse oscillometry system (IOS) measurements in COPD.

Patients and Methods

Fifty-five COPD patients were enrolled. TLC, RV and RV:TLC ratio were obtained both with helium and plethysmography techniques. IOS measurements (X5, Fres and R5-R20) were performed. Pearson and Spearman correlation determined the relationships between the functional parameters that evaluate static hyperinflation (RV: TLC, TLC, RV) and IOS measurements.

Results

As expected, we reported a statistically significant difference between these two techniques in terms of mean percentage values of TLC (7.57 ± 3.26 L; p= 0.02) and RV (15.24 ± 7.51 L; p=0.04), while RV:TLC measured with the two methods was similar (5.21 ± 4.69%; p=0.27). The correlation analysis showed that IOS parameters, such as difference in resistance between 5 Hz and 20 Hz (R(5–20)) and resonant frequency (Fres), were positively correlated with RV:TLC ratio, while reactance at 5 Hz (X(5)) was negatively correlated with it. In particular, we pointed out a weak correlation between RV:TLC (%) (Pleth) and R(5–20) (r=0.3, p=0.04), Fres (r=0.3; p=0.03), while X5 had a mild correlation with RV:TLC (%) (r=−0.5;p<0.0001). Moreover, we noticed a strong relationship between RV:TLC (%)(He) and X5 (r=−0.7; p=0.0001) and a mild correlation between RV:TLC (%) (He) and Fres (r=0.4; p=0.003). Between R5-R20 and RV:TLC, there was a weak correlation (r=0.3; p=0.001). No correlation between TLC, RV (L,%) (both helium and Pleth derived) and IOS parameters (R(5–20), X5, Fres) was found.

Conclusion

RV:TLC can represent the most reliable parameter in the assessment of hyperinflation, considering the absence of significant difference in its measurement between the two techniques. IOS provides supplementary information in the assessment of static hyperinflation.

Low FVC/TLC in Preserved Ratio Impaired Spirometry (PRISm) is associated with features of and progression to obstructive lung disease

One quarter of individuals with Preserved Ratio Impaired Spirometry (PRISm) will develop airflow obstruction, but there are no established methods to identify these individuals. We examined the utility of FVC/TLC in identifying features of obstructive lung disease. The ratio of post-bronchodilator FVC and TLC_CT from chest CT (FVC/TLC_CT) among current and former smokers with PRISm (FEV₁/FVC ≥ 0.7 and FEV1 < 80%) in COPDGene was used to stratify subjects into quartiles: very high, high, low, and very low. We examined the associations between FVC/TLC_CT quartiles and (1) baseline characteristics, (2) respiratory exacerbations, (3) progression to COPD at 5 years, and (4) all-cause mortality. Among participants with PRISm at baseline (n = 1,131), the very low FVC/TLC_CT quartile was associated with increased gas trapping and emphysema, and higher rates of progression to COPD at 5 years (36% versus 17%; p < 0.001) relative to the very high quartile. The very low FVC/TLC_CT quartile was associated with increased total (IRR = 1.65; 95% CI [1.07–2.54]) and severe (IRR = 2.24; 95% CI [1.29–3.89]) respiratory exacerbations. Mortality was lower in the very high FVC/TLC_CT quartile relative to the other quartiles combined. Reduced FVC/TLC_CT ratio in PRISm is associated with increased symptoms, radiographic emphysema and gas trapping, exacerbations, and progression to COPD.

Clinical and functional correlations of the difference between slow vital capacity and FVC

Objective:

To evaluate the relationship that the difference between slow vital capacity (SVC) and FVC (ΔSVC-FVC) has with demographic, clinical, and pulmonary function data.

Methods:

This was an analytical cross-sectional study in which participants completed a respiratory health questionnaire, as well as undergoing spirometry and plethysmography. The sample was divided into two groups: ΔSVC-FVC ≥ 200 mL and ΔSVC-FVC < 200 mL. The intergroup correlations were analyzed, and binomial logistic regression analysis was performed.

Results:

The sample comprised 187 individuals. In the sample as a whole, the mean ΔSVC-FVC was 0.17 ± 0.14 L, and 61 individuals (32.62%) had a ΔSVC-FVC ≥ 200 mL. The use of an SVC maneuver reduced the prevalence of nonspecific lung disease and of normal spirometry results by revealing obstructive lung disease (OLD). In the final logistic regression model (adjusted for weight and body mass index > 30 kg/m²), OLD and findings of air trapping (high functional residual capacity and a low inspiratory capacity/TLC ratio) were predictors of a ΔSVC-FVC ≥ 200 mL. The chance of a bronchodilator response was found to be greater in the ΔSVC-FVC ≥ 200 mL group: for FEV1 (OR = 4.38; 95% CI: 1.45-13.26); and for FVC (OR = 3.83; 95% CI: 1.26-11.71).

Conclusions:

The use of an SVC maneuver appears to decrease the prevalence of nonspecific lung disease and of normal spirometry results. Individuals with a ΔSVC-FVC ≥ 200 mL, which is probably the result of OLD and air trapping, are apparently more likely to respond to bronchodilator administration.

Radiographic lung volumes predict progression to COPD in smokers with preserved spirometry in SPIROMICS

The characteristics that predict progression to overt chronic obstructive pulmonary disease (COPD) in smokers without spirometric airflow obstruction are not clearly defined.We conducted a post hoc analysis of 849 current and former smokers (≥20 pack-years) with preserved spirometry from the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) cohort who had baseline computed tomography (CT) scans of lungs and serial spirometry. We examined whether CT-derived lung volumes representing air trapping could predict adverse respiratory outcomes and more rapid decline in spirometry to overt COPD using mixed-effect linear modelling.Among these subjects with normal forced expiratory volume in 1 s (FEV₁) to forced vital capacity (FVC) ratio, CT-measured residual volume (RV_CT) to total lung capacity (TLC_CT) ratio varied widely, from 21% to 59%. Over 2.5±0.7 years of follow-up, subjects with higher RV_CT/TLC_CT had a greater differential rate of decline in FEV₁/FVC; those in the upper RV_CT/TLC_CT tertile had a 0.66% (95% CI 0.06%-1.27%) faster rate of decline per year compared with those in the lower tertile (p=0.015) regardless of demographics, baseline spirometry, respiratory symptoms score, smoking status (former versus current) or smoking burden (pack-years). Accordingly, subjects with higher RV_CT/TLC_CT were more likely to develop spirometric COPD (OR 5.7 (95% CI 2.4-13.2) in upper versus lower RV_CT/TLC_CT tertile; p<0.001). Other CT indices of air trapping showed similar patterns of association with lung function decline; however, when all CT indices of air trapping, emphysema, and airway disease were included in the same model, only RV_CT/TLC_CT retained its significance.Increased air trapping based on radiographic lung volumes predicts accelerated spirometry decline and progression to COPD in smokers without obstruction.

Pulmonary Subtypes Exhibit Differential Global Initiative for Chronic Obstructive Lung Disease Spirometry Stage Progression: The COPDGene® Study

Rationale

We classified individuals into pulmonary disease subtypes based on 2 underlying pathophysiologic disease axes (airway-predominant and emphysema-predominant) and their increased mortality risk. Our next objective was to determine whether some subcomponents of these subtypes are additionally associated with unique patterns of Global initiative for chronic Obstructive Lung Disease (GOLD) spirometry stage progression.

Methods

After accounting for intra-individual measurement variability in spirometry measures between baseline (Phase 1) and the 5-year follow up (Phase 2) of the COPD Genetic Epidemiology (COPDGene^®) study, 4615 individuals had complete data that would characterize patterns of disease progression over 5 years (2033 non-Hispanic whites; 827 African Americans; 48% female). Individuals could express increased risk for mortality on one or both of the primary subtype axes (airway-predominant or emphysema-predominant) and thus they were further classified into 6 groups: high-risk airway-predominant disease only (APD-only), moderate-risk airway-predominant disease only (MR-APD-only), high-risk emphysema-predominant disease only (EPD-only), combined high-risk airway- and emphysema-predominant disease (combined APD-EPD), combined moderate-risk airway- and emphysema-predominant disease (combined MR-APD-EPD), and no high-risk pulmonary subtype. Outcomes were dichotomized for GOLD spirometry stage progression from Phase 1 to Phase 2. Logistic regression of the progression outcomes on the pulmonary subtypes were adjusted for age, sex, race, and change in smoking status.

Results

The MR-APD-only group was associated with conversion from GOLD 0 to preserved ratio-impaired spirometry (PRISm) status (odds ratio [OR] 11.3, 95% confidence interval [CI] 5.7-22.1) and GOLD 0 to GOLD 2-4 (OR 6.0, 95% CI 2.0-18.0). The EPD-only group was associated with conversion from GOLD 0 to GOLD 1 (OR 2.4, 95% CI 1.2-4.6), and GOLD 1 to GOLD 2-4 (OR 2.6, 95% CI 1.0-6.9). Conversion between PRISm and GOLD 2-4 (31%-38%) occurred in both the APD-only and the MR-APD-only groups.

Conclusion

Differential conversion occurs from GOLD 0 to PRISm and GOLD 0 to GOLD 1 based on groups expressing airway-predominant disease or emphysema-predominant disease independently or in combination. Airway-predominant and emphysema-predominant subtypes are highly important in determining patterns of early disease progression.

The relationship between steps of 6MWT and COPD severity: a cross-sectional study

Background and objective

The distance of 6-minute walk test (D6MWT) has been widely used in the assessment of functional status in patients with COPD, while very little attention has been paid to the role of steps of 6-minute walk test (S6MWT). The purpose of this study was to investigate the relationship between S6MWT and other physiologic parameters of COPD.

Patients and methods

Seventy patients with stable COPD were enrolled consecutively in this cross-sectional study. Pulmonary function tests, including spirometry, impulse oscillometry (IOS) and the single-breath diffusing capacity of the lungs for carbon monoxide (DL_CO), were carried out at rest. Quality of life was assessed by health-related quality of life (HRQoL) questionnaires, including modified Medical Research Council dyspnea scale (mMRC), St George’s Respiratory Questionnaire, Chronic Obstructive Pulmonary Disease Assessment Test (CAT) and Clinical Chronic Obstructive Pulmonary Questionnaire. Both steps and distance were measured in the following 6-minute walk test (6MWT).

Results

Both S6MWT and D6MWT showed significant correlation with spirometry, IOS, DL_CO parameters and HRQoL questionnaires score. Both pre- and post-6MWT inspiratory capacity showed significant correlation with S6MWT (ρ=0.338, P=0.004; ρ=0.359, P=0.002, respectively), whereas did not correlate with D6MWT (ρ=0.145, P=0.230; ρ=0.160, P=0.189, respectively). In stepwise multiple regression analysis, mMRC grade, age and CAT score remained as significant predictors in the final model for D6MWT (adjusted R²=0.445, P<0.01). DL_CO and CAT score remained as significant predictors in the final model for S6MWT (adjusted R²=0.417, P<0.01).

Conclusion

S6MWT is efficient in the evaluation of functional status and quality of life in COPD and has significant correlation with various parameters indicating disease severity. Additionally, S6MWT might be better in predicting lung hyperinflation in COPD compared with D6MWT.