12
Figures
TLC <5th
percentile?
Possible
hyperinflation
TLC >95th
percentile?
Large lungs
Hyperinflation
Hyperinflation
FRC/TLC or residual
volume (RV)/TLC
>95th percentile?
Functional residual
capacity (FRC)/TLC or RV/
TLC >95th percentile?
a
See Classification of Ventilatory Impairments Defined by Lung Volumes on pages 12–13.
Beginning with the TLC, determine whether restriction is present based on whether the TLC
is low (right side of figure). If restriction is present, then assess the relative size of FRC or RV
to the TLC: if the FRC/TLC or RV/TLC are elevated, then determine if there is airflow
obstruction based on the FEV
1
/FVC ratio. If obstruction is present, then this is a mixed disorder,
but if not present, then it may be a form of "complex restriction," which implicates more than
one process occurring to lower the FVC out of proportion to the reduction in TLC. Obesity or
neuromuscular diseases are common causes of complex restriction.
Figure 7. Approach to Interpretation of Lung Volumes
a
YES
YES
YES
NO
NO
NO
