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A ventilator is a type of breathing apparatus, a class of medical technology that provides mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. Ventilators may be computerized microprocessor-controlled machines, but patients can also be ventilated with a simple, hand-operated bag valve mask. Ventilators are chiefly used in intensive-care medicine, home care, and emergency medicine and in anesthesiology. Ventilators are sometimes called "respirators", a term commonly used for them in the 1950s. However, contemporary medical terminology uses the word "respirator" to refer to a face-mask that protects wearers against hazardous airborne substances.