How is it possible to breathe perflurocarbon?
In liquid breathing systems the perfluorocarbons are simply an inert carrier for dissolved oxygen. It turns out that oxygen and other atmospheric gasses readily dissolve in perfluorocarbons without chemically reacting with them. Some perfluorocarbons can carry over 300 times as much oxygen as the equivalent amount of water. Perfluorocarbons are incredibly stable under conditions compatible with life, they aren't being broken down into free fluorine in you lungs or blood, or reacting with your tissues much at all. The perfluorocarbons don't cross the lung-blood interface in significant amounts.