EB-OCT imaging
EB-OCT scans was performed by using Lightlabs C7XR OCT system (St. Jude Medical, St. Paul, MN). The OCT catheter (0.9 mm in diameter) was advanced to the right lower bronchus under flexible bronchoscopy (B260F, Olympus, Japan) and via the DirectPath navigation system (Olympus Co. Ltd., Japan)9. The 3rd to 9th generation of bronchi were detected upon breath hold at the end of full inspiration. At least three reproducible EB-OCT measurements were performed for each segment.
The generation of bronchi was determined based on the airway branch-points in longitudinal section of EB-OCT images14. The EB-OCT imagings were analyzed with the Lightlabs C7XR software system workstation, which automatically measured and calculated the airway inner area (Ai) and total airway wall area (Ao) based upon the luminal perimeter and the inner perimeter of the cartilage8, 9, 15. The airway wall area percentage (Aw%) was calculated as (Ao–Ai) /Ao×100%. The Ai was further corrected for the body surface area (BSA). The ΔAi/BSA was defined as the difference of Ai/BSA before and after inhalation of salbutamol. Given that small airways refers to the airways with an inner diameter less than 2 mm, we defined the small airways as the 7th generation and more distal bronchi based on our latest publication10, 11. Accordingly, the Ai/BSA and Aw% detected from the 3rd to 6th, and from the 7th to 9th generation of bronchi were averaged respectively to reflect the morphology of the medium-sized and small airways.