Associations of airway tree to lung volume ratio on computed tomography with lung function and symptoms in chronic obstructive pulmonary disease

Abstract

Background Decreased airway lumen size and increased lung volume are major structural changes in chronic obstructive pulmonary disease (COPD). However, even though the outer wall of the airways is connected with lung parenchyma and the mechanical properties of the parenchyma affect the behaviour of the airways, little is known about the interactions between airway and lung sizes on lung function and symptoms. The present study examined these effects by establishing a novel computed tomography (CT) index, namely, airway volume percent (AWV%), which was defined as a percentage ratio of the airway tree to lung volume. Methods Inspiratory chest CT, pulmonary function, and COPD Assessment Tests (CAT) were analysed in 147 stable males with COPD. The whole airway tree was automatically segmented, and the percentage ratio of the airway tree volume in the right upper and middle-lower lobes to right lung volume was calculated as the AWV% for right lung. Low attenuation volume % (LAV%), total airway count (TAC), luminal area (Ai), and wall area percent (WA%) were also measured. Results AWV% decreased as the Global Initiative for Chronic Obstructive Lung Disease (GOLD) spirometric grade increased ( p < 0.0001). AWV% was lower in symptomatic (CAT score ≥ 10) subjects than in non-symptomatic subjects ( p = 0.036). AWV% was more closely correlated with forced expiratory volume in 1 s (FEV 1 ) and ratio of residual volume to total lung capacity (RV/TLC) than Ai, Ai to lung volume ratio, and volume of either the lung or the airway tree. Multivariate analyses showed that lower AWV% was associated with lower FEV 1 and higher RV/TLC, independent of LAV%, WA%, and TAC. Conclusions A disproportionally small airway tree with a relatively large lung could lead to airflow obstruction and gas trapping in COPD. AWV% is an easily measured CT biomarker that may elucidate the clinical impacts of the airway-lung interaction in COPD. Electronic supplementary material The online version of this article (10.1186/s12931-019-1047-5) contains supplementary material, which is available to authorized users.

Association of Dysanapsis With Chronic Obstructive Pulmonary Disease Among Older Adults

“…Dysanapsis refers to a mismatch of airway tree caliber to lung size and was initially inferred from variation in spirometry among healthy adults. 11 Dysanapsis is believed to arise early in life, 11 has been implicated in obstructive lung disease susceptibility, 12,13 and can be quantified directly using computed tomography (CT). 14 This study examined the hypothesis that dysanapsis quantified by CT as the ratio of mean airway lumen diameter to total lung volume (airway to lung ratio) would statistically account for a significant proportion of the variation in forced expired volume in the first second to forced vital capacity (FEV 1 :FVC) ratio, and be associated with incident COPD among older adults in the general population.…”

Regional lung deflation with increased airway volume underlies the functional response to bronchodilators in chronic obstructive pulmonary disease

“…Notably, the multivariate analysis showed that the increase in AWV% was associated with the improvement in FEV1 independently of the changes in TAC. A previous study showed that while AWV% reflects the dimension of the central airways and TAC on CT, AWV% is associated with airflow limitation and gas trapping independent of emphysema, the dimension of the central airway, and TAC (Tanabe et al, 2019); furthermore, the study suggested that in addition to each structural change in the airway and lung, the interaction between airway and lung volumes would affect pulmonary function. Taken together, the present results suggest that LAMAs work by increasing the lumen diameter of the airways identifiable on the baseline CT scan and the number of airways in the lower lobe identifiable on the follow-up CT scan, which could reverse the ratio of the disproportionately small airway lumen volumes to the relatively large lung and might mechanistically improve breathing efficiency.…”

“…The details of the calculation method for AWV% were recently reported (Tanabe et al, 2019). Briefly, the segmentation of the airway tree was automatically generated without any manual editing using a SYNAPSE VINCENT volume analyser (FUJIFILM Medical).…”

“…The AWV% values for the RUL, RML, RLL, LUL, and LLL were calculated as a percentage ratio of the airway volume in the RUL, RML, RLL, LUL, and LLL to the volume of the RUL, RML, RLL, LUL, and LLL, respectively, using custom-made software. To assess the number of airway branches identifiable on CT, the total airway count (TAC) was separately measured using the centerline of the segmented airway trees in the RUL and RLL (Tanabe et al, 2019). The percentage ratio of voxels <−950 HU to the lung voxels, namely, the low attenuation volume percent (LAV%), was also measured for each lobe to assess emphysematous changes on CT.…”

“…However, this bronchodilation at inspiration is diminished in patients with COPD (Diaz et al, 2012;Scichilone et al, 2004). A recent CT study enabled an assessment of the interaction between the airway and parenchyma by measuring the airway tree to lung volume ratio on CT, termed the AWV%, and showed that a reduction in the AWV% is closely associated with a decrease in FEV 1 , independent of emphysema and the dimension of the central airways in COPD (Tanabe et al, 2019). Therefore, local lung deflation accompanied by an increase in corresponding airway volume could potentially and reasonably account for the improvement in FEV 1 after bronchodilator therapy in patients with COPD.…”