English: This diagram depicts the basic form and function of a typical negative-pressure medical ventilator ("iron lung"), which is used to help a person breathe when their body cannot do so adequately on its own. The iron lung is an enclosed, sealed cylinder.

The patient (white) lays inside the horizontal cylinder (black), with only their head protruding out through an opening in the end of the cylinder. The opening is sealed around their neck with a sealing collar (green) to avoid air leaking into or out of the cylinder chamber.

An electric motor (brown) is connected, by mechanical linkage to a flexible diaphragm (yellow), which it expands and contracts, continuously, varying the air pressure inside the cylinder chamber. When the diaphragm extends, the pressure in the chamber is lowered.-- causing the patient's chest (and lungs) to expand -- inhaling air from the outside, through patient's nose or mouth.

When the diaphragm contracts, the chamber pressure returns to normal, and the patient's chest relaxes, contracting and forcing out air (exhaling). The motor pumps the diaphragm continuously, to maintain continuous airway ventilation (artificial breathing) of the patient