Risk factors associated with persistent airflow limitation in severe or difficult-to-treat asthma

Background: The Epidemiology and Natural History of Asthma: Outcomes and Treatment Regimens study is among the largest to assess persistent airflow limitation and the first to evaluate a wide range of potential risk factors in high-risk patients with severe or difficult-to-treat asthma. A better understanding is needed regarding factors associated with persistent airway obstruction; this study was performed to determine demographic and clinical characteristics associated with persistent airflow limitation. Methods: Data from adult patients (>= 18 years old) with severe or difficult-to-treat asthma were evaluated. Patients with COPD, obesity with a restrictive respiratory pattern, or a >= 30 pack-year history of smoking were excluded. Patients with persistent airflow limitation (postbronchodilator FEV1/FVC ratio <= 70% at two annual consecutive visits) and normal postbronchodilator FEV1/ FVC ratio (75 to 85%) were compared. Multivariate analysis identified factors independently associated with persistent airflow limitation. Results: Of 1,017 patients, 612 patients (60%) showed evidence of persistent airflow limitation. Risk factors were as follows: older age (odds ratio [OR] per 10 years, 1.4; 95 % confidence interval [CI], 1.3 to 1.6); male gender (OR, 4.5; 95% CI, 2.3 to 8.5); black ethnicity (OR, 2.2; 95% CI, 1.3 to 3.8); current or past smoking (OR, 3.9; 95% CI, 1.8 to 8.6; and OR, 1.6; 95% CI, 1.2 to 2.3, respectively); aspirin sensitivity (OR, 1.5; 95% CI, 1.0 to 2.4); and longer asthma duration (OR per 10 years, 1.6; 95% CI, 1.4 to 1.8). Protective factors were Hispanic ethnicity, higher education, family history of atopic dermatitis, pet(s) in the home, and dust sensitivity. Conclusions: Persistent airflow limitation is prevalent in patients with severe or difficult-to-treat asthma and is associated with identifiable clinical and demographic characteristics.