Diagnosing airflow obstruction: bronchodilator FVC response is more relevant than FEV1

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Takeaway
  • Post-bronchodilator (BD) change (∆) in FEV1% of baseline increased with increasing airflow obstruction, but ∆FEV1 z-scores or % predicted decreased with severe obstruction. ∆FVC increased with increasing impairment.

Why this matters

  • Recommendations on interpreting tests of BD responsiveness (BDR) are conflicting.

Key results

  • 32.2% had pre-BD FEV1/FVC z-score <−1.645; 8.0% had post-BD z-score >−1.645. 
  • Post-BD FEV1 increased by >12% of baseline in 18.2% of patients, irrespective of presence of airways obstruction. 
  • 7.6% changed by both >12% and >200 mL. 
  • ∆zFEV1 peaked at mild and moderate airways obstruction and then declined. ∆zFVC increased as airway obstruction became more severe. 
  • ∆FEV1 declined with age and became slightly negative after age 50 y. 
  • Adopting the criterion of ∆zFEV1 >0.78 yielded positive responses in 7.9%, compared with 14.4% and 7.5% according to American Thoracic Society (ATS)/ European Respiratory Society (ERS) and European Community for Steel and Coal (ECSC)/ERS criteria. 
  • ATS/ERS criterion suggested greater responsiveness as severity of respiratory impairment increased, whereas ECSC/ERS criterion (∆FEV1 >12% predicted and >200 mL) and the new criterion (∆zFEV1 >0.78) showed an opposite trend.

Study design

  • Analysis of data for 31,528 patients referred for BDR in 10 countries. 
  • Funding: None.

Limitations

  • Heterogeneity in BD agents and dosages used.