Factors Associated with Persistent Airflow Limitation in Severe Asthma

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Abstract
Persistent airflow limitation can develop in nonsmoking patients with asthma. However, the prevalence and risk factors for airways obstruction with incomplete reversibility in asthma are unknown. We assessed the prevalence of persistent airflow limitation (defined as postbronchodilator FEV1 or FEV1/VC < 75% predicted) in 132 nonsmoking outpatients with severe asthma visiting chest physicians in general hospitals in The Netherlands. They had used inhaled corticosteroids ( ⩾ 1,600 μ g/d) and/or daily oral prednisone and long-acting bronchodilators for > 1 yr. In addition, we examined whether persistent airways obstruction in these patients was associated with specific clinical characteristics (age at onset, smoking history, atopic status, bronchodilator reversibility, provocative concentration of histamine causing a 20% decrease in FEV1 [PC20histamine]) or markers of inflammation (exhaled nitric oxide [NO], blood eosinophils, total IgE; and eosinophilia or neutrophilia in induced sputum). Multiple logistic regression analyses were used to calculate adjusted odds ratios (OR). Persistent airflow limitation was observed in 49% of the patients in the study, and apart from older age and longer asthma duration, was strongly associated with a sputum eosinophils percent ⩾ 2% (OR = 7.7; confidence interval [CI]: 2.4 to 25), PC20histamine ⩽ 1.0 mg/ml (OR = 3.9; CI: 1.2 to 13), and adult onset ( ⩾ 18 yr) of asthma (OR = 3.3; CI: 1.2 to 9). Only sputum eosinophilia appeared to be independently associated with persistent airflow limitation (OR = 8.9; CI: 1.3 to 59). In conclusion, persistent airflow limitation is common in adult patients with severe asthma, and is associated with adult onset of the disease, airway hyperresponsiveness, and most importantly, sputum eosinophilia. These findings suggest that eosinophilic airway inflammation contributes to persistent airflow limitation in severe asthma. Whether reduction of sputum eosinophils with more vigorous treatment leads to a better prognosis in severe asthma is still an open question. Keywords: asthma; severity of illness index; airway obstruction; sputum; eosinophilia