FEV6: a shortcut in spirometry?

D uring the past 50 yrs, the forced expiratory manoeuvre has formed the basis for the most extensively used lung function test. Although ''spirometry'' means measurement of breath and, therefore, should include all kinds of measurements related to breathing, it is now almost a convention that spirometry is synonymous with measurements involving a forced vital capacity (FVC). In his historical note, YERNAULT [1] mentions that Tiffenau and Pinelli published the first results from recording forced expiration manoeuvres in 1947. A couple of years later, the Tiffeneau test was developed, defining the ratio between the forced expiratory volume in one second (FEV1) and the vital capacity (VC). To calculate this ratio, both the FVC and the VC (always measured during expiration) became acceptable. With spirometry, there is a potential ability to diagnose obstructive and restrictive abnormalities. Obstruction is a condition with decreased FEV1/VC, whereas restriction is a condition with decreased total lung capacity (TLC). Therefore, it is important that the VC (or FVC) gives the best possible measure of TLC. A decreased VC may occur due to loss of alveolar space, which decreases TLC. Obstruction may lead to airway closure and a decrease of FVC, but TLC is not decreased. The largest VC is the inspiratory vital capacity (IVC), which is measured during a slow inspiration from residual volume to TLC, and, therefore , IVC was recommended as the denominator in the FEV1/ VC ratio [2]. As IVC cannot be obtained during the FVC manoeuvre, it requires an extra measurement, and is seldom used outside specialised lung function laboratories. The use of FVC instead is not without problems. In severely obstructed patients, the total exhalation may last for up to 20 s [3], until the current end-of-test standards for accurately measured FVC [4] are met. This may be very demanding for both the patient and the technician. Furthermore, very few spirometers have feedback systems that indicate when these criteria are met. In 1987, GLINDMEYER et al. [5] therefore suggested an end-of-test criterion based on a fixed duration for the FVC manoeuvre. It was found that 6.64 s was sufficient to obtain 99% of FVC for spirograms with FEV1/FVC as low as 50%. As a consequence, HANKINSON et al. [6] calculated FEV6 and FEV1/FEV6 reference equations and their lower limits of normal (LLN) based on 74,294 healthy subjects in the National Health and Nutrition Examination Survey III study. In a similar European …