Lesson 4: Flow-Volume Loops

Flow-Volume Loops Overview

• Used to differentiate between obstructive and restrictive respiratory diseases.

Inhalation Process

• Begins from residual volume (RV).
• Stops at total lung capacity (TLC).
• Produces a waveform: moves from right to left with a negative deflection.

Exhalation Process

• Exhales back to residual volume (RV).
• Produces a waveform: moves from left to right with a positive deflection.

Key Events on Flow-Volume Loop

• Zero Flow Points:
  • Flow is zero at end of inspiration and expiration.
• Volume Behavior:
  • Volume increases from right to left.
  • RV is not measured with spirometry; loop never reaches true zero.
• Maximum Lung Volume:
  • TLC is the maximum lung capacity.
• Vital Capacity (VC):
  • VC measures the width of the loop.