Procedures
Study 1 : In this case-control study, 135 eligible participants
attended a single clinical visit in which they were directly inquired
the clinical history, induced sputum, peripheral blood test and EB-OCT
measurements of the right anterior basal segment (RB8) and right lateral
basal segment (RB9). We performed IOS, and subsequently, spirometry
(Jaeger, Hoechberg, Germany) according to the international
guidelines13. Forced vital capacity (FVC), forced
expiratory volume in one second (FEV1) and maximal
mid-expiratory flow (MMEF) were measured in asthmatic patients before
and at 10 min after 400μg salbutamol (GlaxoSmithKline Co. Ltd., UK)
inhalation via a pressurised metered dose inhalers (pMDI) with a spacer
(DHN200, Koka Co. Ltd., China).
Study 2 : We performed EB-OCT and spirometry in 32 asthmatic
patients before and after salbutamol inhalation to assess bronchodilator
response within the same clinical visit. Spirometry was performed at
baseline before EB-OCT assessment. To secure the comparability of EB-OCT
measurement within the same segment, we advanced an OCT catheter to the
RB9 segment immediately (within 1 min) after inhaling 400 μg salbutamol
(denoted as baseline EB-OCT measurement) with the guidence of bronchial
navigation system. Next, the catheter was maintained within the bronchi
for conducting EB-OCT scanning at 5-min intervals (up to 15 min) to
directly determine the dynamic airway morphological changes. Spirometry
was performed at 60 min after salbutamol inhalation
(post-bronchodilation test). For all asthmatic patients, short- and
long-acting bronchodilators were withheld for at least 8 and 24 hours
respectively prior to spirometry or EB-OCT measurement.