A simple measure to assess hyperinflation and air trapping: 1-forced expiratory volume in three second / forced vital capacity

Abstract

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 flow25-75 (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.