A machine that creates artificial respiration -- that is, it breathes for you. Early iron lungs were huge cylinders that enclosed the entire body, except the head. (The patient lay horizontal, and the patient's head was supported just outside the apparatus.)

To create inhalation, a vacuum pump lowers the air pressure inside the cylinder. This causes the chest to expand, drawing air in. Normal air pressure is then restored inside the chamber, letting air out of the chest.

Although modern respirators and ventilators are now portable and less bulky, some iron lungs are still in use.