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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 FEV(1) 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 FEV(1) 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 FEV(1)) were selected for each subject. For those with acceptable spirometry results, two groups were created: group 1, normal FEV(1)/FVC ratio; group 2, reduced FEV(1)/FVC ratio. For each subject, the difference between the highest and lowest PEF (DeltaPEF) and the associated difference between the highest and lowest FEV(1) (DeltaFEV(1)) were calculated. Regression analysis was performed using the largest PEF and best FEV(1), and the percentage of DeltaPEF (%DeltaPEF) and percentage of DeltaFEV(1) (%DeltaFEV(1)) were calculated in both groups.


RESULTS
Regression analysis for group 1 and group 2 showed an insignificant association between %DeltaPEF and %DeltaFEV(1) (r(2) = 0.0001, p = 0.59, and r(2) = 0.040, p = 0.15, respectively). For both groups, a 29% DeltaPEF was associated with a 1% DeltaFEV(1).


CONCLUSION
Within a single spirometry test session, %DeltaPEF and %DeltaFEV(1) contain independent information. PEF has a higher degree of intrinsic variability than FEV(1). Changes in PEF do not have a significant effect on FEV(1). Spirometry maneuvers should not be excluded based on peak flow variability.