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.