During normal breathing, your lungs expand when you breathe in. This is caused by the diaphragm, which is the main muscle of breathing in your chest, going in a downward direction. This causes the pressure to drop inside the tubes and sacs of your lungs. This decrease in pressure sucks air into your lungs. They fill with oxygenated air.
If you have trouble breathing, a BiPap machine can help push air into your lungs. You wear a mask or nasal plugs that are connected to the ventilator. The machine supplies pressurized air into your airways. It is called “positive pressure ventilation” because the device helps open your lungs with this air pressure.