Efficacy and Mechanism Evaluation Programme, funded by the Medical Research Council (MRC) and managed by the National Institute for Health Research (NIHR) on behalf of the MRC-NIHR partnership.

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The significance of severe airflow obstruction in severe asthma is unclear. The current study determined whether severe airflow obstruction is related to inflammatory or structural changes in the airways.Patients with severe asthma from a tertiary referral clinic were divided into two groups according to their postbronchodilator forced expiratory volume in one second (FEV1): severe persistent airflow limitation (FEV1v50% predicted; group S; n=37) and no obstruction (FEV1w80% pred; group N; n=29). Smoking history, atopic status, lung function tests, exhaled NO, blood eosinophil count, quality of life scores using St George9s Respiratory Questionnaire and high resolution computed tomography (HRCT) of the lungs were assessed.Patients from group S were older and had longer disease duration. There was no difference in smoking history, atopic status, hospital admissions, quality of life scores and amount of treatment with inhaled or oral corticosteroids. Exhaled NO and peripheral blood eosinophils were higher in group S (21.0¡2.4 versus 12.8¡2. , respectively). HRCT scores for bronchial wall thickening and dilatation were higher in group S with no differences in air trapping. Peripheral blood eosinophilia and bronchial wall thickening on HRCT scan were the only parameters significantly and independently associated with persistent airflow obstruction.Patients with severe asthma and irreversible airflow obstruction had longer disease duration, a greater inflammatory process and more high resolution computed tomography airway abnormalities suggestive of airway remodelling, despite being on similar treatments and experiencing equivalent impairment in quality of life.

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