FEV6 as a surrogate for FVC in detecting airways obstruction and restriction in the workplace

Compared with measurements of forced vital capacity (FVC), using the forced expiratory volume in six seconds (FEV6) reduces test time and frustration. It was hypothesised that using FEV6 in the workplace setting would result in an acceptably low misclassification rate for detecting airways obstruction and spirometry-defined restriction when compared with using the traditional FVC. Experienced technicians from the National Institute for Occupational Safety and Health performed spirometry using dry rolling-seal spirometers as per American Thoracic Society guidelines in four workplace investigations. Airways obstruction was defined as an FEV1/FVC % below the lower limit of normal (LLN) using National Health and Nutrition Examination Survey III reference equations. Restriction was defined as an FVC below the LLN with a normal FEV1/FVC %. These "gold standard" definitions were compared with definitions based on FEV6 (obstruction: FEV1/FEV6 below the LLN; restriction: FEV6 below the LLN with a normal FEV1/FEV6). The median (range) age of the 1,139 workers was 37 yrs (18-71 yrs) and 51.4% were male. A significantly high overall agreement was obtained between the two definitions. In conclusion, the current results confirm that forced expiratory volume in six seconds can be used as a surrogate for forced vital capacity in detecting airways obstruction and restriction in workers, although with some misclassification when compared to obtaining American Thoracic Society-acceptable manoeuvres of longer duration.