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How were iron lungs used to help people with paralytic polio breathe?

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Polio vaccine — polio A health care worker giving a polio vaccine to a child in Katsina state, Nigeria, 2014.

The iron lung was a mechanical respirator used to assist patients with paralytic polio who were unable to breathe independently. The device consisted of a large, horizontal metal cylinder that enclosed the patient’s entire body, leaving only the head and neck exposed outside a rubber seal.1

The machine functioned by mimicking the natural process of human respiration. A bellows at the foot of the cylinder moved in and out to create rhythmic pressure changes:

Inspiration: The bellows pulled air out of the chamber, creating negative pressure. This caused the patient's thoracic cavity to expand, drawing fresh air into the lungs.
Expiration: The bellows moved in the opposite direction, creating positive pressure that forced the lungs to contract and expel air.1

While some patients required the device only temporarily during recovery or physical therapy, others relied on it for extended periods or even their entire lives. Following the development of the polio vaccine in the 1950s, the use of the iron lung declined significantly, and it is now considered obsolete.1