PURPOSE: The mid-expiratory flow (FEF25-75) is the mid portion of the forced expiratory volume at 1 second (FEV1) and is felt to represent the contribution of the small airways to forced expiratory flow and be effort-independent. There is no current literature that describes the significance of an elevated FEF25-75 with otherwise normal spirometry and its significance to indications for spirometric testing.
METHODS: Pulmonary function testing (PFT) databases from two institutions were retrospectively reviewed for 5 years from 2006-2010. Those studies in patients less than 60 years of age with technically adequate spirometry were included if the FEF25-75 > 125% predicted and normal FEV1 and FVC based on NHANES III reference standards. Patient charts were reviewed to document indication for testing, established pulmonary diagnoses, radiographic findings, and additional pulmonary function testing to include lung volumes, bronchoprovocation testing, and endoscopic studies.
RESULTS: Based on preliminary analysis, 265 studies have been identified that met the inclusion criteria. The mean age was 43.8 ± 12.2 years and 53% of patients were male. PFTs demonstrated a mean FEF25-75 (% pred) = 138.4 ± 15.4%, FEV1 (% pred) = 101.5 ± 7.2%, FVC (% pred) = 94.0 ± 7.8%, FEV1/FVC = 86.8 ± 3.8%. Limited full PFTs reviewed (n = 26) demonstrated TLC (% pred) = 93.6 ± 12.4%, RV (% pred) = 71.4 ± 24.0%; and DLCO (% pred) = 85.2 ± 17.7%. The most common indications for spirometry included dyspnea (22%), screening (11%), asthma (7%), and cough (5%). Other significant findings included a mean peak expiratory flow rate of 129.5% and mean elevated FEF/FIF50 at 1.46 ± 0.82. Analysis of repeatability based on all trials is ongoing.
CONCLUSIONS: An elevated FEF25-75 with normal spirometric indices is a common finding in a variety of conditions evaluated and nearly 25% of patients have undiagnosed dyspnea. Correlation with increased peak expiratory flow (PEF) and increased mid flow-ratio (FEF/FIF50) has been demonstrated with preliminary analysis.
CLINICAL IMPLICATIONS: The clinical significance of an elevated FEF 25-75 is uncertain but may represent increased small airway elasticity and may be a contributory factor to complaints of dyspnea.
DISCLOSURE: The following authors have nothing to disclose: James Hull, Sally Del Vecchio, Ian Ward, Michael Morris
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