Persistent Airflow Limitation Found Common in Severe Asthma

A new study has found that persistent airflow limitation (PAFL) is prevalent in patients with severe or difficult-to-treat asthma and is associated with identifiable risk factors such as age, gender, and duration of disease.

Researchers at Genentech (San Francisco, CA, USA) conducted a prospective, observational three-year study that included 1,017 adult patients aged 18 or older with severe or difficult-to-treat asthma. The purpose of the study was to evaluate a wide range of potential risk factors in these high-risk asthma patients. Six hundred twelve (60%) had PAFL, defined as post-bronchodilator ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) of 70% or lower at two annual consecutive visits. The remaining 405 patients had a post-bronchodilator FEV1/FVC ratio between 75% and 85%, and made up the no-PAFL group.

Study findings identified several factors independently associated with PAFL, including older age, male gender, black ethnicity, aspirin sensitivity, a longer duration of disease, and current or past smoking. Consistent with other studies, PAFL was also associated with more severe asthma. Protective factors for PAFL included Hispanic ethnicity, a college education or advanced degree, a family history of atopic dermatitis, having a pet or pets in the home, and reported dust sensitivity. Rates of urgent health care utilization, however, were similar between patients with and without PAFL. The study was published in the December 2007 issue of the journal Chest.

"The findings help define which patients are at risk for PAFL, and the factors that may prevent or reduce progression into a predominantly irreversible form,” concluded lead author Dr. June H. Lee, M.D., and colleagues.

Asthma is defined as a chronic inflammatory disease of the airways and characterized by reversible airflow obstruction. However, for many patients with asthma, the obstruction fails to reverse after treatment. The structural changes associated with asthma include increased airway smooth-muscle mass, mucous gland and goblet-cell hyperplasia, and thickening of the reticular basement membrane. Currently, the relationship between airway physical changes and the degree of PAFL obstruction is not well understood.


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