More rarely, forced expiratory flow may be given at intervals defined by how much remains of total lung capacity.

Forced expiratory flow (FEF)

Forced expiratory flow (FEF) is the flow (or speed) of air coming out of the lung during the middle portion of a forced expiration.

In addition, forced vital capacity, peak expiratory flow (by spirometry), and forced expiratory flow at 75% of forced vital capacity (FEF 75% ) were similar in both groups.