Introduction
Bronchial asthma (asthma) is a chronic inflammatory airway disease affecting the entire bronchial tree from the large to the small airways (<2 mm diameter).1 The diagnosis is based on recurrent symptoms of dyspnea, cough, wheeze, and chest tightness, as well as reversible airway limitation or bronchial hyperresponsiveness (BHR).2 In nearly 90% of asthmatic patients with normal forced expiratory volume in 1 second (FEV1), also known as mild asthma, the bronchial dilation test is negative, so the provocation test is important for confirming or excluding asthma. However, many hospitals do not perform provocation tests because they are expensive, time-consuming, and entail a risk of severe bronchospasm.2Therefore, additional ways are needed to predict BHR safely and to detect patients with mild asthma as early as possible in order to relieve their symptoms and prevent the development of chronic inflammation and airway remodeling.
Small-airway dysfunction exists in mild asthma patient, evaluated by a variety of spirometry and IOS measurements. FEF25%-75%and FEF50% are widely used for assessing small-airway function.3-8 Impulse oscillometry (IOS) may also reliably reflect small-airway function and predict clinical asthma outcomes and BHR.9-13 FEV in 3 seconds (FEV3)/FVC is influenced by the airflow velocity in both the central and peripheral airway, normally 95% or greater in adults.14-16
In our previous study of patients with chronic cough, patients with BHR had higher fractional exhaled nitric oxide (FENO), a higher percentage of eosinophils in blood (EOS%), and lower forced expiratory flow between 25% and 75% (FEF25%-75%) than patients without BHR.3 The combination of FEF25%-75% and FENO increased the area under the curve (AUC) for BHR diagnosis substantially compared with FENO alone. In that study, FEF25%-75% < 78.5% and FENO > 43 ppb strongly predicted positive BHR in Chinese patients with chronic cough.
In the current study, we used FEFs, peripheral airway resistance as the difference between 5 and 20 Hz (R5-R20), reactance at 5 Hz (X5) , resonant frequency (Fres), FEV3/FVC, FENO, EOS, and EOS% alone or in combination, as potential predictive variables for the presence of BHR, and extended our cross-sectional study to patients with FEV1 ≥ 80% predicted who had more than 1 typical symptom of asthma, such as variable cough, dyspnea, wheeze, and chest tightness, to confirm the predictive value of small-airway function tests, FENO, and EOS for BHR.