Study population
The EBC was obtained from 58 healthy controls and 251 patients with
asthma at the Asan Medical Center between September 2014 and December
2019. Healthy controls were screened for respiratory diseases and
recruited during regular wellness examinations conducted at Asan Medical
Center if they did not have any current or previous history of pulmonary
disease, as determined by the medical examination. The eligibility
criteria for patients with asthma were as follows11,12: (1) patients aged >18 years; (2)
symptoms such as dyspnea, wheezing, or cough for more than 3 months; and
(3) airway hyperresponsiveness as indicated by a 20% reduction in
forced expiratory volume in 1 s (FEV1) with methacholine 16 mg/mL (PC20)
on a provocation test, or airway reversibility with FEV1
>12% (and at least 200 mL) after inhalation of a
short-acting beta-agonist. Patients with severe lung damage,
bronchiectasis, or a history of lung resection were excluded. The
participants’ EBC samples were collected using the
RTubeTM (Respiratory Research, Austin, USA). Informed
consent was obtained from all participants, and the study protocol was
approved by the Institutional Review Board of Asan Medical Center (IRB
No. 2006-0388).