Effect of Effort on Measurement of Forced Expiratory Volume in One Second

Publisher Website
Google Scholar
Abstract
The American Thoracic Society recommends that the largest FEV, be reported from a set of forced expiratory vital capacity maneuvers performed with maximal expiratory effort. However, increased expiratory effort can decrease the FEV1. When we evaluated the peak expiratory flow rate (PEFR) in 5 normal subjects, measured from flow-volume curves, as a noninvasive index of expiratory effort, it was positively correlated with indices of effort obtained by using an esophageal balloon. We then measured the difference (dFEV1) between the largest FEV1 and the FEV, from the maneuver with the highest PEFR during to test sessions in 10 normal subjects. Thus, dFEV1 was always .gtoreq.0. The mean dFEV, was 110 ml for all sessions but decreased to 80 ml when maneuvers with poorly reproducible PEFR of forced expiratory vital capacity values were discarded. We also reviewed 9,471 spirometry sessions from outpatients and found dFEV1 to be greater than 50 ml in 26% of this population and greater than 151 ml in 7%. We concluded that during standard spirometry, FEV1 is inversely dependent on effort. Maximal effort decreases FEV1 because of the effect of thoracic gas compression on lung volume. We recommend that values from spirometry maneuvers that demonstrate submaximal effort, indicated by a decreased PEFR, be discarded. The flow-volume curve display of superimposed efforts facillitates the recognition of submaximal efforts.