Peak expiratory flow is not a quality indicator for spirometry -: Peak expiratory flow variability and FEV1 are poorly correlated in an elderly population

Background: Peak forced expiratory flow (PEF) and FEV1 are spirometry measures used in diagnosing and monitoring lung diseases. We tested the premise that within-test variability in PEF is associated with corresponding variability in FEV1 during a single test session. Methods: A total of 2,464 healthy adults from the Health, Aging, and Body Composition Study whose spirometry results met American Thoracic Society acceptability criteria were screened and analyzed. The three "best" test results (highest sum of FVC and FEV1) were selected for each subject. For those with acceptable spirometry results, two groups were created: group 1, normal FEV1/FVC ratio; group 2, reduced FEV1/FVC ratio. For each subject, the difference between the highest and lowest PEF (Delta PEF) and the associated difference between the highest and lowest FEV1 (Delta FEV1) were calculated. Regression analysis was performed using the largest PEF and best FEV1,and the percentage of Delta PEF (%Delta PEF) and percentage of Delta FEV1 (%Delta FEV1) were calculated in both groups. Results: Regression analysis for group I and group 2 showed an insignificant association between %Delta PEF and %Delta FEV1 (r(2) = 0.0001, p = 0.59, and r(2) = 0.040, p = 0.15, respectively). For both groups, a 29% Delta PEF was associated with a 1% Delta FEV1. Conclusion: Within a single spirometry test session, %Delta PEF and %Delta FEV1 contain independent information. PEF has a higher degree of intrinsic variability than FEV1. Changes in PEF do not have a significant effect on FEV1. Spirometry maneuvers should not be excluded based on peak flow variability.