Ratio of FEV/Slow Vital Capacity Of < 0.7 Is Associated With Clinical, Functional, and Radiologic Features of Obstructive Lung Disease in Smokers With Preserved Lung Function

Background: Mild expiratory flow limitation may not be recognized using traditional spirometric criteria based on the ratio of FEV/FVC.

Research Question: Does slow vital capacity (SVC) instead of FVC increase the sensitivity of spirometry to identify patients with early or mild obstructive lung disease?

Study Design And Methods: We included 854 current and former smokers from the Subpopulations and Intermediate Outcome Measures in COPD Study cohort with a postbronchodilator FEV/FVC ≥ 0.7 and FEV % predicted of ≥ 80% at enrollment. We compared baseline characteristics, chest CT scan features, exacerbations, and progression to COPD (postbronchodilator FEV/FVC, < 0.7) during the follow-up period between 734 participants with postbronchodilator FEV/SVC of ≥ 0.7 and 120 with postbronchodilator FEV/SVC < 0.7 at the enrollment. We performed multivariate linear and logistic regression models and negative binomial and interval-censored proportion hazards regression models adjusted for demographics and smoking exposure to examine the association of FEV/SVC < 0.7 with those characteristics and outcomes.

Results: Participants with FEV/SVC < 0.7 were older and had lower FEV and more emphysema than those with FEV/SVC ≥ 0.7. In adjusted analysis, individuals with postbronchodilator FEV/SVC < 0.7 showed a greater percentage of emphysema by 0.45% (95% CI, 0.09%-0.82%), percentage of gas trapping by 2.52% (95% CI, 0.59%-4.44%), and percentage of functional small airways disease based on parametric response mapping by 2.78% (95% CI, 0.72%-4.83%) at baseline than those with FEV/SVC ≥ 0.7. During a median follow-up time of 1,500 days, an FEV/SVC < 0.7 was not associated with total exacerbations (incident rate ratio [IRR], 1.61; 95% CI, 0.97-2.64), but was associated with severe exacerbations (IRR, 2.60; 95% CI, 1.04-4.89). An FEV/SVC < 0.7 was associated with progression to COPD during a 3-year follow-up even after adjustment for demographics and smoking exposure (hazard ratio, 3.93; 95% CI, 2.71-5.72). We found similar results when we examined the association of prebronchodilator FEV/SVC < 0.7 or FEV/SVC less than the lower limit of normal with chest CT scan features and progression to COPD.

Interpretation: Low FEV to SVC in current and former smokers with normal spirometry results can identify individuals with CT scan features of COPD who are at risk for severe exacerbations and is associated with progression to COPD in the future.

Trial Registry: ClinicalTrials.gov; No.: NCT01969344T4; URL: www.clinicaltrials.gov.