And because no pressure exists to actually push on the walls of our alveolis, in that case the walls would essentially push back and that would create this collapsed structure. So we want to keep that air inside the lungs. We want to have the residual volume of air because we want to keep the bronchioles, the passageways, as well as the individual alveoli from actually collapsing because if they do collapse, that will make the process of breathing very, very difficult. So this distance here is our residual volume. Now if we take the sum of the residual volume and the viral capacity, that will give us the total lung capacity. Now let's move on to something called the functional residual capacity.