Background: Several recent studies have suggested that 1 minus-forced expiratory volume expired in 3 seconds / forced vital capacity (1-FEV₃/FVC) may be an indicator of distal airway obstruction and a promising measure to evaluate small airways dysfunction.
Aims: To investigate the associations of 1-FEV₃/FVC with the spirometric measures and lung volumes that assess small airways dysfunction and reflects hyperinflation and air trapping.
Study Design: Retrospective cross-sectional study.
Methods: Retrospective assessment of a total of 1110 cases who underwent body plethysmographic lung volume estimations between a time span from 2005 to 2012. Patients were assigned into two groups: firstly by FEV₁/FVC (FEV₁/FVC <70% vs. FEV1/FVC ≥70%); secondly by FEV₃/FVC < lower limits of normal (LLN) (FEV₃/FVC < LLN vs. FEV₃/FVC ≥ LLN). Spirometric indices and lung volumes measured by whole-body plethysmography were compared in groups. Also the correlation of spirometric indices with measured lung volumes were assessed in the whole-study population and in subgroups stratified according to FEV₁/FVC and FEV₃/FVC.
Results: Six hundred seven (54.7%) were male and 503 (45.3%) were female, with a mean age of 52.5±15.6 years. Mean FEV₃/FVC and 1-FEV₃/FVC were 87.05%, 12.95%, respectively. The mean 1-FEV3/FVC was 4.9% in the FEV₁/FVC ≥70% group (n=644) vs. 24.1% in the FEV₁/FVC <70% group (n=466). A positive correlation was found between 1-FEV₃/FVC and residual volume (r=0.70; p<0.0001), functional residual capacity-pleth (r=0.61; p<0.0001), and total lung capacity (r=0.47; p<0.0001). 1-FEV₃/FVC was negatively correlated with forced expiratory flow_25-75 (r=−0.84; p<0.0001). The upper limit of 95% confidence interval for 1-FEV₃/FVC was 13.7%. 1-FEV₃/FVC showed significant correlations with parameters of air trapping and hyperinflation measured by whole-body plethysmography. Importantly, these correlations were higher in study participants with FEV₁/FVC <70% or FEV₃/FVC < LLN compared to those with FEV₁/FVC ≥70% or FEV₃/FVC ≥ LLN, respectively.
Conclusion: 1-FEV₃/FVC can be easily calculated from routine spirometric measurements. 1-FEV₃/FVC is a promising marker of air trapping and hyperinflation. We suggest that 1-FEV₃/FVC is complementary to FEV₁/FVC and recommend clinicians to routinely report and evaluate together with FEV₁/FVC during spirometry.

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