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.