On the other hand, a negative pressure ventilator, also known as an "iron lung" or a tank respirator, is a chamber which is enclosed around the patient's chest and lowers the pressure inside the chamber around the chest area to a point in which the pressure inside the chamber is less than the pressure outside allowing the patient to breathe in, and then the pressure inside heightens to a point in which the pressure inside the chamber is greater than the pressure outside allowing the patient to breathe out. This process occurs periodically. Negative pressure ventilators are now considered obsolete and instead positive pressure ventilators are used in its place.