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 (BID) FEV1/FVC. It has been proposed that the traditional FVC can be replaced with the shorter and less demanding FEV6 for detecting 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-BID 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-BID 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 FEVI/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-BID 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 spirometry maneuvers (which measure FEV6) are as sensitive and specific for post-BID airway obstruction as traditional (prolonged exhalation time) FVC maneuvers only when the definition of airway obstruction includes a low FEV6.