Vampires don’t normally breath because they are in fact dead. Although considered members of the animated dead that’s usually refereed to as Living Dead creatures. Since they’re more or less modified humans with demonic DNA, vampires still have lungs, and most other human organs lying in a mostly dormant state. This means they can survive in any hostile air environment such as a room full of toxic smoke, or gases along with outer space if they stay out of the holy sunlight. Despite no requirement for oxygen, or any other type of gas found in the air, they can still use their lungs as glorified air pumps. A vampire can breath in air, and then shoot it out at great speeds. Those standing close enough to a First Generation Vampire could easily be knocked over by their super breeze. It’s also possible for a powerful vampire to inhale deadly gasses, or smoke in a room, and then later expel it outdoors. Complete absorption into their bodies may be possible as well.
Deeply weakened, or overexerted vampires will display hints of humanity. Lungs will actually activate, and they will seem out of breath if engaged in a difficult battle. If vampire lungs become temporarily active they will filter oxygen from inhaled air but instead of the normal carbon dioxide exhaling forth we get a sulfur compound. The sulfurous gas creation comes from their Demonic Hell tied genes. Once the weakened state has passed their lungs return to a dormant stasis once again.