Fixed airways obstruction among patients with severe asthma: findings from the Singapore General Hospital-Severe Asthma Phenotype Study

A subset of severe asthma patients has fixed airways obstruction, which is characterized by incomplete reversibility to bronchodilator challenge. We aimed to elucidate the factors associated with fixed airways obstruction in a cohort of patients with severe asthma in Singapore.

Methods: 245 patients from the Singapore General Hospital-Severe Asthma Phenotype Study (SGH-SAPS) were screened.

These patients fulfilled World Health Organization criteria for "treatment-resistant severe asthma"and were all on combination of high-dose inhaled corticosteroids and long-acting beta2 agonists. 76 patients had pre- and postbronchodilator lung function tests and were selected for analysis.

They were divided into two groups based on postbronchodilator forced expiratory volume in one second, PostBDFEV1 % predicted: >=70% (Non-Fixed Obs) and <70% (Fixed Obs). We compared clinical and demographic parameters between the two groups.

Results: Patients in the Fixed Obs group were more frequently past or current smokers and had a higher pack-year smoking history.

Overall, pack-year smoking history had a modest negative correlation with PostBDFEV1 % predicted. Atopy, allergen sensitization (type and numbers), comorbidities, symptoms, health care utilization and medication use did not differ between the two groups.

The prebronchodilator FEV1 % predicted, FEV1/FVC and FVC % predicted were significantly lower in the Fixed Obs group. In addition, prebronchodilator FVC % predicted accounted for more variability than FEV1/FVC in predicting PostBDFEV1.

Conclusion: Smoking is associated with fixed airways obstruction in patients with treatment-resistant severe asthma in Singapore.

Furthermore, our results suggest that both small and large airways obstruction contribute independently to fixed airways obstruction in severe asthma.

Published on: 2014-12-03

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