[4] In 2020 however, the COVID-19 pandemic revived some interest in them as a cheap, readily-producible substitute for positive-pressure ventilators, which were feared to be outnumbered by patients potentially needing temporary artificially assisted respiration.

[5][6][7] The iron lung is a large horizontal cylinder designed to stimulate breathing in patients who have lost control of their respiratory muscles.

Breathing in humans occurs through negative pressure, where the rib cage expands and the diaphragm contracts, causing air to flow in and out of the lungs.

Initially used for coal gas poisoning treatment, the iron lung gained fame for treating respiratory failure caused by polio in the mid-20th century.

During the polio outbreaks of the 1940s and 1950s, iron lungs filled hospital wards, assisting patients with paralyzed diaphragms in their recovery.

In response to the COVID-19 pandemic and the shortage of modern ventilators, some enterprises developed prototypes of new, easily producible versions of the iron lung.

[9] Larger "room-sized" iron lungs were also developed, allowing for simultaneous ventilation of several patients (each with their heads protruding from sealed openings in the outer wall), with sufficient space inside for a nurse or a respiratory therapist to be inside the sealed room, attending the patients.

The cuirass ventilator encloses only the patient's torso, or chest and abdomen, but otherwise operates essentially the same as the original, full-sized iron lung.

[26][27] The Emerson iron lung had a bed that could slide in and out of the cylinder as needed, and the tank had portal windows which allowed attendants to reach in and adjust limbs, sheets, or hot packs.

Although the Drinker model was effective and saved lives, its widespread use was hindered by the fact that the machines were very large, heavy (about 750 lbs or 340 kg), bulky, and expensive.

[30] The South Australia Health Department asked Adelaide brothers Edward and Don Both to create an inexpensive "iron lung".

[33] Visiting London in 1938 during another polio epidemic, Both produced additional respirators there which attracted the attention of William Morris (Lord Nuffield), a British motor manufacturer and philanthropist.

Nuffield, intrigued by the design, financed the production of approximately 1700 machines at his car factory in Cowley and donated them to hospitals throughout all parts of Britain and the British Empire.

A polio patient with a paralyzed diaphragm would typically spend two weeks inside an iron lung while recovering.

Positive pressure ventilators work by blowing air into the patient's lungs via intubation through the airway; they were used for the first time in Blegdams Hospital, Copenhagen, Denmark, during a polio outbreak in 1952.

By using the positive pressure ventilators instead of iron lungs, the Copenhagen hospital team was able to decrease the fatality rate eventually down to 11%.

Most patients with paralysis of the breathing muscles use modern mechanical ventilators that push air into the airway with positive pressure.

It may also be preferable in certain rare conditions,[1] such as central hypoventilation syndrome, in which failure of the medullary respiratory centers at the base of the brain results in patients having no autonomic control of breathing.

At least one reported polio patient, Dianne Odell, had a spinal deformity that caused the use of mechanical ventilators to be contraindicated.

[48] In 2013, the Post-Polio Health International (PHI) organizations estimated that only six to eight iron lung users were in the United States; as of 2017, its executive director knew of none.

Press reports then emerged, however, of at least three (perhaps the last three)[49] users of such devices,[50] sparking interest amongst those in the makerspace community such as Naomi Wu[51] in the manufacture of the obsolete components, particularly the gaskets.

[55] In early 2020, reacting to the COVID-19 pandemic, to address the urgent global shortage of modern ventilators (needed for patients with advanced, severe COVID-19), some enterprises developed prototypes of new, readily-producible versions of the iron lung.