When interpreting pulmonary function tests, do you routinely distinguish between hyperinflation and gas trapping?  

Hyperinflation refers to elevated TLC (>ULN, sometimes >120% predicted). Air trapping refers to elevated RV (>ULN, sometimes >120% predicted) and/or elevated RV/TLC (same criteria).

Although they are related and are most often seen in COPD with an emphysematous phenotype, air trapping generally refers to an increased volume of air after complete exhalation, ie. Residual Volume, related to early (small) airway closure. The RV/TLC is also usually increased. On the other hand, hyp...