Six-second spirometry for detection of airway obstruction: A population-based study in Austria

Rationale: The presence of airway obstruction is currently defined by Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines on the basis of the post-bronchodilator (BD) FEV₁/FVC. It has been proposed that the traditional FVC can be replaced with the shorter and less demanding FEV₆ fordetecting airway obstruction. Objectives: A comparison of FEV₁/FVC and FEV₁/FEV₆ for the detection of airway obstruction in population-based post-bronchodilator spirometry data. Methods: A population-based sample of 1,349 adults participated in the Burden of Obstructive Lung Disease study in Austria. Specially trained and certified technicians conducted pre-BD and post-BD spirometry according to American Thoracic Society guidelines and administered standardized questionnaires. A total of 93% of the post-BD test sessions were acceptable, and were included in this analysis. The Third National Health and Nutrition Examination Survey reference equations were used to calculate predicted values and lower limits of normal (LLN) for FEV₁, FEV₆, FVC, FEV₁/FVC, and FEV₁/FEV₆. Measurements and Main Results: The post-BD FEV₁/FVC was below the LLN in 199 (15.8%) subjects. The sensitivity of the FEV₁/FEV₆ for airway obstruction depended greatly on the threshold of percent predicted FEV₁ also used in the definition. The overall sensitivity of FEV₁/FEV₆ for a diagnosis of airway obstruction, as defined by FEV₁/ FVC (including participants with an FEV₁ above the LLN), was 72.9%, with 98.8% specificity. The sensitivity increased to 98.0% when a low FEV₁ was also required to diagnose post-BD airway obstruction. The discordant cases had long forced expiratory times, often showed a flow-volume curve pattern consistent with two-compartment emptying, and were more often never-smokers. Conclusions: Six-second spirometrymaneuvers (which measure FEV₆) are as sensitive and specific for post-BD airway obstruction as traditional (prolonged exhalation time) FVC maneuvers only when the definition of airway obstruction includes a low FEV₁.