Respiration Lab
Forced Vital Capacity
Forced Vital Capacity - Procedure
This test is based on a vital capacity manoeuvre with an added element of speed; a subject expires as fast and as forcibly as he or she can.
  • Turn the spirometer on, choosing a chart speed of 20 mm/second, and move the piston so the pen is at the center of the chart paper.
  • The subject should put on the noseclip and place the mouthpiece attached to the hose in the mouth.
  • Press the handswitch to start recording. After recording a few normal breaths, the subject should be instructed to inhale maximally then exhale forcefully and quickly, without holding lung volume at the maximal inspiratory level. The subject should then return to normal breathing for a few breaths. Press the handswitch to stop recording. This is the Forced Vital Capacity Manoeuvre.

The figure below represents a sample tracing you might obtain in the lab. Determine values for FVC and FEV1. Check your answer by clicking on the image.