Quantitative computed tomography (QCT) measured 5th generation airways, emphysema and airflow obstruction in chronic obstructive pulmonary disease (COPD) from a COPDMAP cohort

Background: Airflow obstruction in COPD is due to small airway obliteration and emphysema. QCT can be used to measure airway geometry in airways bigger than 2mm diameter. Whether the absence of visible 5th generation airways is associated with airflow obstruction and emphysema is unknown. Aims: Use QCT to describe presence and size of 5 th generation segmental airways and explore relationships with lung function in COPD. Methods: COPD MAP subjects underwent low dose thoracic CT (Siemens 16) and spirometry. Fully automated software (Apollo,VIDA Diagnostics, Iowa) was used for post processing of CT scans. Patients were divided into 2 groups according to whether or not 15 or more 5 th generation segmental bronchi were visualised by CT. Spirometry was correlated with QCT measured emphysema (Percentile 15) and airway morphometry (mean percentage wall area [%WA]) for 5 th generation airways). Results: 86 patients were recruited; 67% male, 81% ex-smokers, with mean (SEM) age 69(1) years, and post-bronchodilator FEV 1 % predicted and FEV 1 /FVC ratio of 54(2)% and 52(1)% respectively. Subjects with 15 or more 5th generation airways visible had higher mean (SEM) FEV 1 % predicted (57[2]% versus 48[3]% ; p=0.024) and less severe QCT determined emphysema (-959.03[2.51] versus -972.47[3.93]; p Discussions: In COPD obliteration of smaller airways determined from QCT reconstructed airways is associated with more airflow obstruction and emphysema. The role of QCT in evaluating small airways disease, and the clinical implications of these observations require further investigation.