Computed tomography structural lung changes in discordant airflow limitation.

Firdaus A A Mohamed Hoesein,Jan-Willem J Lammers,Michael Schmidt,Harry J De Koning,Matthijs Oudkerk,Bram Van Ginneken,Carlijn Van Der Aalst,Willem Pthm Mali,Rozemarijn Vliegenthart,Pim A De Jong,Eva M Van Rikxoort,Pieter Zanen

doi:10.1371/journal.pone.0065177

Abstract

BackgroundThere is increasing evidence that structural lung changes may be present before the occurrence of airflow limitation as assessed by spirometry. This study investigated the prevalence of computed tomography (CT) quantified emphysema, airway wall thickening and gas trapping according to classification of airflow limitation (FEV1/FVC <70% and/or < the lower limit of normal (LLN)) in (heavy) smokers.MethodsA total number of 1,140 male former and current smokers participating in a lung cancer screenings trial (NELSON) were included and underwent chest CT scanning and spirometry. Emphysema was quantified by the 15th percentile, air way wall thickening by the square root of wall area for a theoretical airway with 10mm lumen perimeter (Pi10) and gas trapping by the mean lung density expiratory/inspiratory (E/I)-ratio. Participants were classified by entry FEV1/FVC: group 1>70%; group 2<70% but >LLN; and group 3<LLN. 32 restricted subjects, i.e. FEV1/FVC >70% but FEV1 <80% predicted, were excluded. Multivariate regression analysis correcting for covariates was used to asses the extent of emphysema, airway wall thickening and gas trapping according to three groups of airflow limitation.ResultsMean (standard deviation) age was 62.5 (5.2) years and packyears smoked was 41.0 (18.0). Group 2 subjects when compared to group 1 had a significantly lower 15th percentile, −920.6 HU versus −912.2 HU; a higher Pi10, 2.87 mm versus 2.57 mm; and a higher E/I-ratio, 88.6% versus 85.6% (all p<0.001).ConclusionSubjects with an FEV1/FVC<70%, but above the LLN, have a significant greater degree of structural lung changes on CT compared to subjects without airflow limitation.

Highlights

[2] Chronic obstructive pulmonary disease (COPD) is characterized by the presence of airflow limitation, i.e. when the forced vital capacity (FVC) to the forced expiratory volume in one second (FEV1) -ratio is below a predefined threshold and currently spirometry is used to diagnose COPD. [3]
In this study we examined the degree of structural changes in the lung, emphysema, airway wall thickness and gas trapping, by computed tomography (CT) in a cohort of relatively healthy male smokers according to their FEV1/FVC
A number of 1,140 males with were included. Of these 1,140 subjects, 32 had a restrictive lung function pattern, i.e. FEV1/FVC . 70% but FEV1,80% predicted, which were excluded resulting in 1,108 subjects included in the current study

Summary

Introduction

Chronic obstructive pulmonary disease (COPD) is one of the important causes of morbidity and mortality worldwide and its mortality rates are still rising. [1] Paradoxically, it still is being under diagnosed. [2] COPD is characterized by the presence of airflow limitation, i.e. when the forced vital capacity (FVC) to the forced expiratory volume in one second (FEV1) -ratio is below a predefined threshold and currently spirometry is used to diagnose COPD. [3]The airflow limitation is the result of several structural changes in the lung like destruction of airway parenchyma (emphysema) and small airway disease (gas trapping and airway wall thickening). [4] Computed tomography (CT) of the chest is used to quantify the extent of these structural changes. [5] Assessing the degree of these structural changes can give a better insight in the background of airflow limitation in individual subjects and assess the heterogeneity of the disease. The airflow limitation is the result of several structural changes in the lung like destruction of airway parenchyma (emphysema) and small airway disease (gas trapping and airway wall thickening). While the Global Initiative for Chronic Obstructive Lung Disease (GOLD) propose a fixed value of FEV1/FVC ,70% as cut-off for diagnosing airflow limitation others advocate the lower limit of normal (LLN). In this study we examined the degree of structural changes in the lung, emphysema, airway wall thickness and gas trapping, by CT in a cohort of relatively healthy male smokers according to their FEV1/FVC. This study investigated the prevalence of computed tomography (CT) quantified emphysema, airway wall thickening and gas trapping according to classification of airflow limitation (FEV1/FVC ,70% and/ or , the lower limit of normal (LLN)) in (heavy) smokers

Methods

Results

Discussion

Conclusion