Fig. 17:  Looking specifically at dynamic hyperinflation, this Figure shows the same lung volumes discussed in Figure 16 in a stacked bar graphic: residual volume, full reserver capacity (FRC) tidal volume, inspiratory capacity, and inspiratory reserve volume. 

When a normal person [without COPD] exercises to maximal on a treadmill or bicycle, so that the patient is gasping for air and cannot exercise anymore, notice that the end-expiratory lung volume actually goes down (shown in the downward diagonal line).  This is to make room for the increased tidal volume, so the patient can get more minute ventilation.  Although this graph cannot show respiratory rate, that eventually goes up toward the later stages of maximal exercise.  However as a person without COPD increases their “minute ventilation” to meet the metabolic demands, notice that the inspiratory reserve volume does not change very much. 

Now looking at the patient with COPD, it can be seen that lung volumes are bigger throughout, and we notice that the FRC is much greater.  This patient may have, or does have, hyperinflation at rest.  While this hyperinflation is partly static (from differences in elastic recall), this may be partly dynamic, in which case the patient is breathing in before getting the preceding breath all the way out –and that would cause hyperinflation.  

Now if that person exercises to maximum (which will be much lower than in the patient without COPD), notice what happens: the end-expiratory lung volumes increase.  The patient with COPD is breathing closer to total lung capacity.  Remember that when a person without COPD tries that, the result makes the person very short of breath.  The result in the patient with COPD is that the elastic work of breathing, trying to stretch out already hyperinflated lungs, is dramatically increased, and as seen in the Figure, the inspiratory reserve volume is really low.  That is a marker of marked hyperinflation.