Subjects and data collection
The study was approved by No. 20180308 of the Xiangya Hospital Ethics Review Committee. From October 2018 to January 2019, 51 HCs and 55 asthma patients were chosen from the Respiratory Department and Physical Examination Center of Xiangya Hospital, China. FEV1/FVC ratio <0.7 and FEV1% <70% was defined as the presence of asthma. The inclusive standards for the patient group were between the age of 40 and 70 with a clear diagnosis of asthma (according to the criteria of 2018 Global Strategy for Asthma Management and Prevention) but without other respiratory orĀ otherĀ diseases [19]. The HCs had no differences in age and gender without asthma or other organic mental diseases, including smoking and non-smoking controls. Quality control methods were strictly enforced.
After obtaining the written informed consent from each subject, we collected questionnaire information (general condition, smoking history and other respiratory diseases), pulmonary function testing and peripheral blood samples. For our analysis, pulmonary function parameters were adopted including forced expiratory volume in one second as percentage of predicted volume (FEV1%), the spirometric values of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), peak expiratory force (PEF) and forced expiratory flow (FEF). Certified staff performed all interviews and examinations. Moreover, feedback on work quality would be regularly provided to field staff during the data collection process, and secondary training would be conducted when necessary.