Children in an iron lung before the advent of the polio vaccination, 1950
An iron lung or as it is called officially a negative pressure ventilator is a form of medical ventilator that enables a person to breathe when normal muscle control has been lost or the work of breathing exceeds the person’s ability. It creates lower pressure around the thorax and this expands the rib cage and draws air into the lungs.
Polio makes the body lose muscle control, including the diaphragm. Since the diaphragm uses pressure to regulate the oxygen intake (by expanding and decreasing pressure in the lungs, causing air to flow in), this machine regulates the pressure increasing it and decreasing artificially in order to make breathing possible.