In the comics Bane used his mask as a permanent establishment of a powerful poison called steroid that keeps you strong. I have ever in mistake for he wearing a bane mask with voice modulator.
However, Nolan does not follow the tradition of comics. In the movie “The Dark Knight Rises” as Bane girl saves the attackers in prison, Bane striker beat almost to death. The attack left the spine and back of Bane. The doctors had his entire cervical fusion spine (hence the scar on Bane was back when I had met in the sewers) perform. The operation was a success, but left in debilitating pain. The mask was constantly throwing an anesthetic in the blood / lung pain. When Batman falls through the lines of his mask, part of the drug against pain and back pain-inch released slowly paralyzed him. This is also the reason I went crazy Bane in Batman to kill him before the pain increases.