Effects of small airway dysfunction on the clinical expression of asthma: a focus on asthma symptoms and bronchial hyper-responsiveness.

Abstract

The small airways are an important site of inflammation in asthma. However, the relation between small airway dysfunction and clinical expression of asthma has hardly been studied. To investigate the association of small and large airway dysfunction with asthma symptoms and bronchial hyper-responsiveness (BHR). Fifty-eight patients with asthma were characterized with spirometry, body plethysmography, impulse oscillometry, alveolar and bronchial exhaled nitric oxide, and a methacholine provocation. Symptoms of nocturnal asthma, exercise-related symptoms, BHR symptoms, and respiratory symptoms were assessed with the Asthma Control Questionnaire and Bronchial Hyper-responsiveness Questionnaire. Perception of dyspnea was rated with the Borg score during the provocation test. Small and large airway dysfunction did not associate with higher scores for nocturnal, exercise-related, or BHR symptoms. Only higher scores on wheezing were significantly associated with higher values of difference between R5 and R20 (R5-R20) (r=0.367, P<0.01) and AX (r=0.354, P<0.01). Lower FEF25-75% (P=0.024) and higher R5-R20 (P=0.003) values were independently associated with more severe BHR to methacholine, but not FEV1 or R20 values. The increase in dyspnea during the methacholine provocation was strongly and independently correlated with the decrease in FEV1 and reactance of the respiratory system at 5Hertz. Small and large airway dysfunction poorly associate with asthma symptoms in our patients. However, deteriorations in small airway dysfunction are strongly related to an increase in dyspnea during bronchial provocation with methacholine. Small airway dysfunction contributes also independently to the clinical expression of asthma, as reflected by the severity of BHR.