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The iron lung is typically a large horizontal cylinder, in which a person is laid, with their head protruding from a hole in the end of the cylinder, so that their head (particularly nose and mouth) is outside the cylinder, exposed to ambient air, and the rest of their body sealed inside the cylinder, where air pressure is continuously cycled up and down, to stimulate breathing.^[1][2][9]

To cause the patient to inhale, air is pumped out of the cylinder, causing a slight vacuum, which causes the patient's chest and abdomen to expand (drawing air from outside the cylinder, through the patient's exposed nose or mouth, into their lungs). Then, for the patient to exhale, the air inside the cylinder is compressed slightly (or allowed to equalize to ambient room pressure), causing the patient's chest and abdomen to partially collapse, forcing air out of the lungs, as the patient exhales the breath through their exposed mouth and nose, outside the cylinder.^[1][2][9]

Examples of the device include the Drinker respirator, the Emerson respirator, and the Both respirator. Iron lungs can be either manually or mechanically powered, but normally are powered by an electric motor linked to a flexible pumping diaphragm (commonly on opposite the end of the cylinder from the patient's head).

Smaller, single-patient versions of the iron lung include the so-called Cuirass ventilator (named for the Cuirass, a torso-covering body armor). 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. A modern version is the exovent. A lightweight variation on the cuirass ventilator is the jacket ventilator or poncho or raincoat ventilator, which uses a flexible, impermeable material (such as plastic or rubber) stretched over a metal or plastic frame over the patient's torso.^{[1][5][10][11]}

Method and use

Normal breathing

Main section: breathing

Humans, like most mammals, breathe by negative pressure breathing:

The iron lung encloses the patient entirely, except for their head -- which includes their main airway orfices: nose and mouth, which remain exposed to outside ("ambient") air. A pump (typically a mechanically-powered diaphragm) momentarily reduces the air pressure inside the iron lung, to a pressure lower than outside (ambient) air.[1]^[2][3][9]

This causes the air within the iron lung, but outside the chest wall, to be at a lower pressure than the air inside the patient's lungs (thus, the term "negative pressure"), so the patient's lungs and chest expand to equalize their air pressure to the lower pressure of the interior of the iron lung.^[1][2][3][9]

Now, the expanded lungs are at a lower pressure than the ambient air outside the iron lung. As a result, outside (ambient) air forces its way in through the patient's exposed nose and mouth, into their airway, to fill the lower-pressure space inside the patient's lungs -- and the patient has thus "taken a breath" ("inhaled").^[1][2][3][9]

Exhaling is stimulated by allowing the pressure inside the iron lung to return to normal, matching the outside (ambient) air pressure. As a result, the patient's chest is no longer being expanded by negative pressure, and the natural elasticity of the patient's chest causes it to collapse, squeezing air from the patient's lungs, through the patient's airway, and out of their exposed mouth and nose -- and the patient has thus "exhaled."^[1][2][3][9]

The process continues cycling, repetitively, at a rate set by the person operating the iron lung's controls, to maintain continuous patient artificial respiration (artificial "breathing").^[1][2][3][9]

Normal application

The iron lung may assist normal patient respiration, or it may completely substitute for it, depending upon the patient's condition. It may be used temporarily, or it may be a permanent, lifetime source of respiration support for the patient (though only a handful of people still rely on it for daily life).^[1][3][4][9]

Advantages

Advantages over modern positive-pressure ventilators include:

• Superior oxygenation
• Reduced lung trauma (such as pneumothorax)
• Reduced heart stress
• No airway intubation required, so:

• Can serve patient with little or no sedation required
• Patient can speak
• Patient can eat and drink
• Patient can receive oral medication

• Greater patient comfort
• Low-tech simplicity, requiring less difficulty and expense in design, development, production, acquisition and maintenance.
• Low-tech reliability (though dependent upon continuous external power, manual power is an option on some units)
• Operable by minimally-trained healthcare workers.
• Low-cost, readily producible, largely from parts not in competition with other ventilation options.

Disadvantages

Disadvantages, compared to modern positive-pressure ventilators include:

• Risk of patient respiratory aspiration (inhalation of, and choking on, regurgitated or misdirected esophagus contents).
• Lack of metered, pure-oxygen air supply, or oxygen-enriched air supply (although possible to be added on by use of normal supplemental-oxygen equipment or
  CPAP
  devices).
• Patient inhales and exhales unfiltered air, to and from the surrounding ambient environment, exposing both the patient to others' germs, and vice-versa.
• Lack of modern monitoring and signaling, typically, to alert healthcare providers of device malfunctions and other respiratory and health emergencies.
• Size and weight -- and lack of portability.
• Extreme restrictions to patient movement (patient typically must lay in supine position, continuously; limited excursions from the iron lung usually require external support, from both human aides and positive-pressure ventilation equipment).
• Requirement that patient be continuously or frequently attended by healthcare worker or other support person (though, in a different way, this is generally also true of modern positive-pressure ventilators, as well)
• Unfamiliarity, and traditional unacceptability, to the modern medical community -- and thus not readily integrated into the current practices of medicine.
• Greater power requirements than positive-pressure ventilators. (Iron lungs must move larger quantities of air for every breath, because they must change the pressure of the air in the entire vessel, not just inflate the lungs).
• Electrical power failure can result in prompt patient death. (Most iron lungs and similar devices lack backup power supplies. Manual power is an option on some units, but requires multiple attendants, working alternately, to provide direct, continuous physical pumping of the iron lung's pump or diaphragm.)
• Physical hazard to people and things in the immediate vicinity, because of exposed moving parts (Not true of all iron lungs).
• Low-tech design creates low barrier to entry -- along with low historical demand -- resulting in lack of support from manufacturers of competing complex ventilator systems, who currently dominate and shape the market for ventilation equipment.

Invention and early use

Initial development

In 1670, English scientist John Mayow came up with the idea of external negative pressure ventilation. Mayow built a model consisting of bellows and a bladder to pull in and expel air.^[13] The first negative pressure ventilator was described by Scottish physician John Dalziel in 1832. Successful use of similar devices was described a few years later. Early prototypes included a hand-operated bellows-driven "Spirophore" designed by Dr Woillez of Paris (1876),^[14] and an airtight wooden box designed specifically for the treatment of polio by Dr Stueart of South Africa (1918). Stueart's box was sealed at the waist and shoulders with clay and powered by motor-driven bellows.^[15]

Drinker and Shaw tank

The first of these devices to be widely used however was developed in 1928 by Drinker and Shaw of the United States.

Boston manufacturer Warren E. Collins began production of the iron lung that year.[23]^[24] Although it was initially developed for the treatment of victims of coal gas poisoning, it was most famously used in the mid-20th century for the treatment of respiratory failure caused by poliomyelitis.^[17]

Danish physiologist August Krogh, upon returning to Copenhagen in 1931 from a visit to New York where he saw the Drinker machine in use, constructed the first Danish respirator designed for clinical purposes. Krogh's device differed from Drinker's in that its motor was powered by water from the city pipelines. Krogh also made an infant respirator version.^[25]

In 1931, John Haven Emerson (5 February 1906 – 4 February 1997) introduced an improved and less expensive 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.^[21] Drinker and Harvard University sued Emerson, claiming he had infringed on patent rights. Emerson defended himself by making the case that such lifesaving devices should be freely available to all.^[21] Emerson also demonstrated that every aspect of Drinker's patents had been published or used by others at earlier times. Since an invention must be novel to be patentable, prior publication/use of the invention meant it was not novel and therefore unpatentable. Emerson won the case, and Drinker's patents were declared invalid.

The United Kingdom's first iron lung was designed in 1934 by Robert Henderson, an Aberdeen doctor. Henderson had seen a demonstration of the Drinker respirator in the early 1930s, and built a device of his own upon his return to Scotland. Four weeks after its construction, the Henderson respirator was used to save the life of a 10-year-old boy from New Deer, Aberdeenshire, who was suffering from poliomyelitis. Despite this success, Henderson was reprimanded for secretly using hospital facilities to build the machine.^[28][29]

Both respirator

The Both respirator, a negative pressure ventilator, was invented in 1937 when Australia's epidemic of poliomyelitis created an immediate need for more ventilating machines to compensate for respiratory paralysis. 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), bulky, and expensive. In the US, an adult machine cost about $2000 in 1930, and £2000 delivered to Melbourne in 1936. The cost in Europe in the mid-1950s was around £1500. Consequently, there were few of the Drinker devices in Australia and Europe.^[30]

The South Australia Health Department asked Adelaide brothers Edward and Don Both to create an inexpensive "iron lung".^[31] Biomedical engineer Edward Both designed and developed a cabinet respirator made of plywood that worked similarly to the Drinker device, with the addition of a bi-valved design which allowed temporary access to the patient's body.^[30] Far cheaper to make (only £100) than the Drinker machine, the Both Respirator also weighed less and could be constructed and transported more quickly.^[30][32] Such was the demand for the machines that they were often used by patients within an hour of production.^[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.^[33] Soon, the Both-Nuffield respirators were able to be produced by the thousand at about one-thirteenth the cost of the American design.^[31] By the early 1950s, there were over 700 Both-Nuffield iron lungs in the United Kingdom, but only 50 Drinker devices.^[34]

Polio epidemic

Rows of iron lungs filled hospital wards at the height of the polio outbreaks of the 1940s and 1950s -- helping children, and some adults, with bulbar polio and bulbospinal polio. A polio patient with a paralyzed diaphragm would typically spend two weeks inside an iron lung while recovering.^[35][36]

Modern development and usage