Flow-volume loop

A flow-volume loop plots airflow rate vs volume. Peak Expiratory Flow (PEF) is the fastest exhalation. Forced Expiratory Flow (MEF) rates are also measured at different volumes.

Deviations from the normal curve can indicate various abnormalities.

Restrictive disorders will decrease the available lung volume, but airflow willl increase. The loop will appear narrower.

In obstructive disorders, the same amount of volume will be left, but airflow will decrease. MEF will be less than MIF.