FVC Tracing: FEF25–75% Calculator

Calculates the flow slope over the middle 50% of the FVC maneuver.

Inputs

Color mode links each input to the matching equation term and solving arithmetic.

Equation and Work

Equation:
Solving steps:
FEF25–75%
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L/sec
Volume difference
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L
Reference status
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5.2 L/sec adult example
Normal/reference: FEF25–75% reference example in the book: 5.2 L/sec for a 70-inch, 20-year-old male; use appropriate predicted tables for formal interpretation.

Clinical Significance

FEF25–75% is the flow slope across the middle 50% of the FVC maneuver. The 25% and 75% terms define the two volume points used for the slope calculation.

Used to assess flows through smaller bronchi/larger bronchioles; it may decrease in early obstruction.

Requires accurate graph plotting and patient-specific predicted values for formal interpretation.

References (APA 7th Edition)

  1. Chang, D. W. (2020). Respiratory Care Calculations (Revised 4th ed.). Jones & Bartlett Learning. Formula content adapted from the uploaded text/reference packet.