A Resuscitator is a device that is used to inflate the lungs of an unconscious person who is not breathing, to keep them oxygenated and alive. There are three basic types: a manual version (also known as a bag valve mask) consisting of a mask and a large hand-squeezed plastic bulb using ambient air, or with supplemental oxygen from a high-pressure tank. The second type is the Expired Air or breath-powered resuscitator. The third type is an oxygen-powered resuscitator. They are all driven by pressurized gas delivered by a regulator and can either be automatic or manually controlled. The most popular type of gas-powered resuscitators are Time Cycled, Volume Constant Ventilators.