Slow vital capacity may aid in identifying individuals at increased risk for COPD

Low FEV₁/slow vital capacity in current and former smokers with normal spirometry may aid in the identification of individuals who are at increased risk for COPD, researchers reported in Chest.

“In comparison to FVC, slow vital capacity may better reflect the true vital capacity in obstructive lung disease due to possible underestimation of FVC, which results from dynamic compression of the airways during the forced expiratory maneuver and reduced exhalation time,” Spyridon Fortis, MD, pulmonologist in the Center for Access & Delivery Research & Evaluation at Iowa City VA Health Care System and associate professor in the department of internal medicine in the division of pulmonary, critical care and occupation medicine at the University of Iowa Roy J. and Lucille A. Carver College of Medicine, and colleagues wrote. “In these settings, [slow vital capacity] may be more appropriate to calculate the FEV₁/VC ratio according to the American Thoracic Society guidelines.”

The researchers conducted a retrospective analysis to investigate whether slow vital capacity (SVC), instead of FVC, would increase the sensitivity of spirometry in the identification of patients with early or mild obstructive lung disease. The study included 854 current and former smokers from the SPIROMICS cohort with a post-bronchodilator FEV₁/FVC of at least 0.7 and FEV₁ of at least 80% predicted. The researchers compared baseline characteristics, chest CT features, exacerbations and COPD progression during follow-up among 734 participants with post-bronchodilator FEV₁/SVC of at least 0.7 and 120 with post-bronchodilator FEV₁/SVC less than 0.7.

Those with FEV₁/SVC less than 0.7 were older (mean age, 65.3 years vs. 59.1 years), had lower FEV₁ (2.56 vs. 2.71) and more emphysema (2.3 vs. 1.53) than participants with FEV₁/SVC of at least 0.7.

Researchers observed a greater percentage of emphysema (0.45%; 95% CI, 0.09-0.82), gas trapping (2.52%; 95% CI, 0.59-4.44) and functional small airways disease based on parametric response mapping (2.78%; 95% CI, 0.72-4.83) at baseline among those with post-bronchodilator FEV₁/SVC less than 0.7 compared with those with FEV₁/SVC of at least 0.7 in adjusted analyses.

FEV₁/SVC less than 0.7 was associated with severe exacerbations (incident rate ratio [IRR] = 2.6; 95% CI, 1.04-4.89), but not with total exacerbations (IRR = 1.61; 95% CI, 0.97-2.64) over median follow-up of 1,500 days. FEV₁/SVC less than 0.7 was also found to be associated with COPD progression (HR = 3.93; 95% CI, 2.71-5.72) during 3-year follow-up after the researchers adjusted for demographics and smoking exposure.

Researchers observed similar results when they evaluated the association between pre-bronchodilator FEV₁/SVC less than 0.7 or FEV₁/SVC less than the lower limit of normal with chest CT features and COPD progression.

“Further research should evaluate whether FEV₁/SVC should be used in addition to the current diagnostic criteria to identify high-risk individuals for COPD who potentially may benefit from early interventions like smoking cessation or pharmacotherapy,” the researchers wrote.