title: Fixed airways obstruction among patients with severe asthma: findings from the Singapore General Hospital-Severe Asthma Phenotype Study.
abstract: BACKGROUND
  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 (Post BD) 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% predicted.
  
  
  CONCLUSIONS
  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.
authors.forename: Anthony Chau Ang
authors.initials: AC
authors.lastname: Yii
authors.forename: Gan Liang
authors.initials: GL
authors.lastname: Tan
authors.forename: Keng Leong
authors.initials: KL
authors.lastname: Tan
authors.forename: Therese Sophie
authors.initials: TS
authors.lastname: Lapperre
authors.affiliation: Department of Respiratory and Critical Care Medicine, Singapore General Hospital, 20 College Road, Singapore 169856, Singapore. mariko.koh.s.y@sgh.com.sg.
authors.forename: Mariko Siyue
authors.initials: MS
authors.lastname: Koh
mesh_terms: D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000188:drug therapy / Q000453:epidemiology* / Q000503:physiopathology; D001249:Asthma / Q000188:drug therapy / Q000453:epidemiology* / Q000503:physiopathology; D001993:Bronchodilator Agents / Q000627:therapeutic use; D003430:Cross-Sectional Studies; D003876:Dermatitis, Atopic / Q000453:epidemiology; D004351:Drug Resistance; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D012846:Singapore / Q000453:epidemiology; D012907:Smoking / Q000453:epidemiology*; D014797:Vital Capacity / Q000187:drug effects*
chemical_list: D001993:Bronchodilator Agents