As you can see in the diagram on the right...

We normally have about 10 to 30% of residual capacity. In other words we don't go all the way empty. And then we have an in and out movement of air which is called the Tidal Volume.

Shallow breathing is brought on by holding our stomach in to look sveldt or trim or we cease to breath due to fear or anxieties or dread or other not so good feelings entertained by our mind.

Its better if we were to learn to fill our lungs to a greater capacity and then hold that breath under pressure. Why under pressure? So a greater amount of oxygen is pressurized into the lungs.

This is called HyperBaric Breathing.

Why would we want to breath under pressure?

So we can have a greater amount of oxygen in our blood stream.