Computed tomography-quantified emphysema distribution is associated with lung function decline

Abstract

Emphysema distribution is associated with chronic obstructive pulmonary disease. It is, however, unknown whether computed tomography (CT)-quantified emphysema distribution (upper/lower lobe) is associated with lung function decline in heavy (former) smokers.587 male participants underwent lung CT and pulmonary function testing at baseline and after a median (interquartile range) follow-up of 2.9 (2.8-3.0) yrs. The lungs were automatically segmented based on anatomically defined lung lobes. Severity of emphysema was automatically quantified per anatomical lung lobe and was expressed as the 15th percentile (Hounsfield unit point below which 15% of the low-attenuation voxels are distributed (Perc15)). The CT-quantified emphysema distribution was based on principal component analysis. Linear mixed models were used to assess the association of emphysema distribution with forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC), FEV1 and FVC decline.Mean¡SD age was 60.2¡5.4 yrs, mean baseline FEV1/FVC was 71.6¡9.0% and overall mean Perc15 was -908.5¡20.9 HU. Participants with upper lobe-predominant CT-quantified emphysema had a lower FEV1/FVC, FEV1 and FVC after follow-up compared with participants with lower lobe-predominant CT-quantified emphysema (p50.001), independent of the total extent of CTquantified emphysema.Heavy (former) smokers with upper lobe-predominant CT-quantified emphysema have a more rapid decrease in lung function than those with lower lobe-predominant CT-quantified emphysema.

Quantitative Emphysema Distribution in Anatomic and Non-anatomic Lung Regions

“…Th e fi ndings of this study are in keeping with another publication showing that in patients with a severe smoking history the subsequent emphysema is rather equally distributed between the upper and lower lung lobes (3). Th is article elucidates in detail the lung functional impact of the emphysema distribution with upper lobe distribution of emphysema being associated with a lower lung function.…”

“…Th e defi nition of the leading component of the disease and further subclassifi cation of changes in these components by means of CT are termed CTphenotyping. A clear phenotypisation would enhance studies of pathophysiologic mechanisms and genetic determinants of the disease in terms of predisposition/ risk to develop the disease generally or a specifi c phenotype of the disease (3).…”

Racial Differences in CT Phenotypes in COPD

“…Recently, studies have suggested that emphysema distribution is independently associated with COPD progression. For instance, in one study upper-lobe predominant CT quantified emphysema was associated with more rapid decrease in lung function than lower-lobe predominant disease (27); and in another recent study, more homogenous emphysema distribution was associated with accelerated decline in lung function as compared to heterogenous disease (28). AAs may have less lower-lung emphysema because of genetic differences, such as α 1 anti-trypsin deficiency, which occurs at higher frequency among Whites of European descent (29).…”

CT-Based Local Distribution Metric Improves Characterization of COPD

“…The understanding that unique spatial patterns of emphysema serve as indicators of COPD subtypes has spawned progress in lobe segmentation algorithms 17, 18 as well as the need to evaluate CT-based features 19 . Although our understanding related to the clinical implications of the spatial patterns of emphysema is emerging 20 , little is understood about the non-emphysematous component of COPD, commonly associated with small airways disease.…”