Clinical Significance of Reduced Forced Expiratory Volume in 3 Seconds to Forced Expiratory Volume in 6 Seconds in...

The forced expiratory volume in 3 seconds (FEV₃) to forced expiratory volume in 6 seconds (FEV₆) ratio is a novel spirometry measure that identifies early airflow abnormalities, but its long-term prognosis value in the general population remains unclear. We aimed to evaluate the long-term all-cause mortality risk among participants with a reduced FEV₃/FEV₆.

Data were obtained from the National Health and Nutrition Examination Survey cycles 1988–1994 and 2007–2012. Reduced FEV₃/FEV₆ was defined as an FEV₃/FEV₆ less than the lower limit of normal. Multivariable logistic regression was used to assess the relationship of reduced FEV₃/FEV₆ with comorbidities and chronic respiratory symptoms. The relationship between reduced FEV₃/FEV₆ and all-cause mortality was evaluated using Cox regression models. The nonlinear relationship between FEV₃/FEV₆ and all-cause mortality was assessed using restricted cubic splines. Subgroup analyses were conducted to validate the robustness of the relationship.

Overall, 25,159 participants were enrolled in the 308-month median follow-up analysis, of whom 8.8% (2225/25,159) had reduced FEV₃/FEV₆. Participants with reduced FEV₃/FEV₆ exhibited increased risks of congestive heart failure, asthma, chronic bronchitis, emphysema, respiratory symptoms, and all-cause mortality risk (adjusted hazard ratio=1.23, 95% confidence interval: 1.13–1.34, P<0.001). The findings remained consistent across subgroups. A nonlinear U-shaped association was observed between FEV₃/FEV₆ and all-cause mortality, with the turning point at 1.04.

Participants with reduced FEV₃/FEV₆ had worse respiratory health outcomes, suggesting that FEV₃/FEV₆ can be used as a prognostic spirometry indicator.