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.