Lung functions:
FEV1: Forced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t seconds. In obstructive lung disease, the FEV1 is reduced due to an obstruction of air escaping from the lungs. Thus, the FEV1/FVC ratio will be reduced.

FEV1:
I: >80%
M: >80%
M: 60-80%
S: <60%


FVC:
I: normal
M: normal
M: reduced <5%
S: reduced >5%