SOURCES OF VARIATION IN FEV(1)

The American Thoracic Society (ATS) recommendations to establish reproducibility of the forced expiratory volume in one second (FEV(1)) are that the value come from ''at least 3 acceptable forced expiratory curves'' where ''the largest forced vital capacity maneuver (FVC) and the second largest FVC should not vary by more than 5%.'' It has been suggested that there is a ''negative effort dependence'' of the FEV(1) and, alternatively, that the magnitude of the FVC influences the FEV(1). We examined the relationship between FEV(1) and a direct measurement of effort, or work, defined as the area under the alveolar pressure-volume curve in 1 s. Thirteen normal individuals and 17 patients with cystic fibrosis or asthma were instructed to make a series of maximal efforts, as in routine testing. Comparing the maneuver that resulted in the greatest work to that with the lowest work, all with FVCs within 5% of one another, there was no correlation between change in work and change in FEV(1) (Delta FEV(1)). There was a significant relationship between Delta FEV(1) and changes in FVC (r = 0.49, p < 0.01). The Delta FEV(1) did not correlate with the degree of hyperinflation (the FRC) or degree of airflow limitation (the initial FEV(1)). The magnitude of changes in FEV(1) was small and almost always within acceptable limits for reproducibility. Because a larger FVC is due either to an increased inspiration, which could affect the FEV(1), or to an increased expiratory reserve volume, which occurs only after the first second, these results emphasize the importance of a maximal inspiration at the start of the test.