Study design and subject selection
A retrospective cross-section of diagnostic data was collected at the initial visit of adult patients with recurrent variable symptoms of dyspnea, cough, wheeze, or chest tightness of at least 8 weeks’ duration who were referred to the Pulmonary Outpatient Clinic of Shanghai General Hospital (China). The patients had to undergone a peripheral blood test, spirometry,17 FENO (NIOX MINO, Aerocrine AB, Solna, Sweden),13 methacholine (MCH), and high-resolution computerized tomography (HRCT, GE Medical System; slice thickness 0.625 mm) from September 2016 to January 2020. The MCH bronchoprovocation was performed with a Jaeger APS Pro system using a Medic-Aid sidestream nebulizer and doubling doses of MCH (0.015 to 0.48 mg) following the American Thoracic Society/European Respiratory Society recommendations.14
Additional inclusion criteria were age 18-75 years, normal HRCT results, and predicted FEV1 of 80% or greater with spirometric measurement.
Subjects were excluded if they had had respiratory tract infections in the past 8 weeks; peripheral blood test indicating abnormal hemoglobin, platelets or neutrophils; use of montelukast, long-acting β2-agonists, theophylline, anticholinergic agents, or an inhaled or oral corticosteroid in the previous 4 weeks; or having concomitant severe systemic diseases. Patients who had more than a 10 pack-year smoking history, who currently smoked, or who had quit less than 2 years earlier were also excluded.
Descriptive characteristics, clinical history, results of bronchial provocation tests, spirometry, FENO, IOS (Jaeger Co, Hoechberg, Germany),18 EOS, and EOS% were reviewed and analyzed. The FVC, FEV1, peak expiratory flow, FEF25%, FEF50%, FEF75%, and FEF25%-75% were expressed as percentages of predicted values. FEV1/FVC and FEV3/FVC were expressed as the ratios of the absolute values of the variables. Small-airway dysfunction was identified if 2 of FEF50%, FEF75%, and FEF25%-75% were lower than 80%. IOS variables R5, R20, R5-R20, X5, and Fres were also collected. For bronchial provocation tests, the provocative dose causing a 20% fall in FEV1(PD20) was recorded, and BHR was defined as present if PD20 was ≤0.48 mg. Associations of PD20and FENO, EOS, EOS%, FEFs, and IOS were analyzed in patients positive for BHR.
The ethics committee of Shanghai General Hospital, Shanghai Jiao Tong University, approved the protocol, and a waiver of informed consent was given for our study (number 2017KY159).