13
Restriction
FRC/TLC or
RV/TLC >95th
percentile?
Simple
restriction
Complex
restriction
Normal lung
volumes
Mixed
disorder
FEV
1
/FVC <5th
percentile?
YES
YES
YES
NO
NO
NO
If the FRC/TLC and RV/TLC ratios are normal in the setting of reduced TLC, then simple
restriction is present. If the TLC is normal, ruling out restriction (le side of figure), then
the next step is to determine if lung volumes are overall normal or large or hyperinflated, by
following the pathways indicated. Note that hyperinflation may occur with TLC, FRC and RV,
or may occur with FRC or RV alone; in the former situation, the rise in TLC indicates loss of
elastic recoil, so is likely due to emphysema, whereas in the latter situation, the increase in FRC
or RV without increase in TLC may be seen in chronic bronchitis or asthma.
