Ratio of Forced Expiratory Volume in 1 second /Slow Vital Capacity (FEV1/SVC)<0.7 is associated with clinical, functional, and radiologic features of obstructive lung disease in smokers with preserved lung function.

Mild expiratory flow limitation may not be recognized using traditional spirometric criteria based on the ratio of Forced Expiratory Volume in 1 second (FEV1) to Forced Vital Capacity (FVC).Does slow vital capacity (SVC) instead of FVC increase the sensitivity of spirometry to identify patients with early or mild obstructive lung disease?We included 854 current and former smokers from the SPIROMICS cohort with a post-bronchodilator FEV1/FVC≥0.7 and FEV1%predicted≥80% at enrollment. We compared baseline characteristics, chest CT features, exacerbations, and progression to COPD (post-bronchodilator FEV1/FVC<0.7) during the follow-up period between 734 participants with post-bronchodilator FEV1/SVC≥0.7 and 120 with post-bronchodilator FEV1/SVC<0.7 at the enrollment. We performed multivariable linear and logistic regression models, negative binomial and interval-censored proportion hazards regression models adjusted for demographics and smoking exposure to examine the association of FEV1/SVC<0.7 with those characteristics and outcomes.Participants with FEV1/SVC<0.7 were older, had lower FEV1 and more emphysema than those with FEV1/SVC≥0.7. In adjusted analysis, individuals with post-bronchodilator FEV1/SVC<0.7 had greater %emphysema by 0.45% (95%CI=0.09-0.82), % gas trapping by 2.52% (95%CI=0.59-4.44), and %functional small airways disease based on parametric response mapping (PRMfSAD) by 2.78%(95%CI = 0.72-4.83) at baseline than those with FEV1/SVC≥0.7. During a median follow-up time of 1500 days, FEV1/SVC<0.7 was not associated with total exacerbations (IRR=1.61;95%CI=0.97-2.64) but was associated with severe exacerbations (IRR=2.60;95%CI=1.04-4.89). FEV1/SVC<0.7 was associated with progression to COPD during a 3-year follow-up even after adjustment for demographics and smoking exposure (HR=3.93;95%CI=2.71-5.72). We found similar results when we examined the association of pre-bronchodilator FEV1/SVC<0.7 or FEV1/SVC

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