ventilator

noun

1. A device that circulates fresh air and expels stale or noxious air.
2. A machine that moves breathable air into and out of the lungs of a patient who is unable to breathe sufficiently.

   “Near-synonym: respirator”

3. (figuratively)Some behaviour or happening that relieves a tense atmosphere or situation.

   “A lover's quarrel is made up of jealousies, doubts, hopes, fears, and all sorts of fantastic fancies: a matrimonial dispute, on the contrary, is composed of familiar and ordinary matter, a sort of ventilator to the temper!”

4. (obsolete, slang)A play or an actor so bad as to empty the theater.