Flow-Volume Loop : Mnemonics

The flow-volume loop is a plot of inspiratory and expiratory flow (on the Y-axis) against volume (on the X-axis) during the performance of maximally forced inspiratory and expiratory maneuvers.

  • TLC = Left most point on X-axis
  • RV = Right most point on X-axis
  • Expiratory flow = Positive deflection on Y-axis
  • Inspiratory flow = Negative deflection on Y-axis
  • PEFR = Highest point on expiratory flow
  • PIFR = Deepest point on inspiratory flow
flow volume curve
ConditionMnemonicFlow-volume loopFeatures
Obstructive lung disease (small airways)Shift to left
Concave/Scooped out expiratory flow (↓FEV 25-75%)
↑TLC and RV
↓FEV1 (preserved in early obstruction)
Restrictive lung diseaseRestrictive = RightShift to right↓TLC and RV
Variable intra-thoracic obstructionWhat’s in is outFlattening of expiratory curve
Variable extra-thoracic obstructionWhat’s out is inFlattening of inspiratory curve
Fixed large airway obstructionFlattening of both expiratory and inspiratory curve

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