|Negative pressure ventilator|
An Emerson iron lung. The patient lies within the chamber, which when sealed provides an effectively oscillating atmospheric pressure. This particular machine was donated to the Centers for Disease Control and Prevention Museum by the family of poliomyelitis patient Barton Hebert of Covington, Louisiana, who had used the device from the late 1950s until his death in 2003.
A negative pressure ventilator, often referred to colloquially as an iron lung, 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. Examples of the device include both the Drinker respirator and the Both respirator. The negative form of pressure ventilation has been almost entirely superseded by positive pressure ventilation or biphasic cuirass ventilation.
Method and use
Humans, like most mammals, breathe by negative pressure breathing: the rib cage expands and the diaphragm contracts, expanding the chest cavity. This causes the pressure in the chest cavity to decrease, and the lungs expand to fill the space. This, in turn, causes the pressure of the air inside the lungs to decrease (it becomes negative, relative to the atmosphere), and air flows into the lungs from the atmosphere: inhalation. When the diaphragm relaxes, the reverse happens and the person exhales. If a person loses part or all of the ability to control the muscles involved, breathing becomes difficult or impossible.
The person using the iron lung is placed into the central chamber, a cylindrical steel drum. A door allowing the head and neck to remain free is then closed, forming a sealed, air-tight compartment enclosing the rest of the person's body. Pumps that control airflow periodically decrease and increase the air pressure within the chamber, and particularly, on the chest. When the pressure is below that within the lungs, the lungs expand and atmospheric pressure pushes air from outside the chamber in via the person's nose and airways to keep the lungs filled; when the pressure goes above that within the lungs, the reverse occurs, and air is expelled. In this manner, the iron lung mimics the physiological action of breathing: by periodically altering intrathoracic pressure, it causes air to flow in and out of the lungs. The iron lung is a form of non-invasive therapy.
Invention and early use
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. 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), 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 a motor-driven bellows. The first of these devices to be widely used however was developed by Drinker and Shaw in 1928. The iron lung, often referred to in the early days as the "Drinker respirator", was invented by Philip Drinker (1894–1972) and Louis Agassiz Shaw, Jr., professors of industrial hygiene at the Harvard School of Public Health. The machine was powered by an electric motor with air pumps from two vacuum cleaners. The air pumps changed the pressure inside a rectangular, airtight metal box, pulling air in and out of the lungs.
The first clinical use of the Drinker respirator on a human was on October 12, 1928, at the Boston Children's Hospital. The subject was an eight-year-old girl who was nearly dead as a result of respiratory failure due to polio. Her dramatic recovery, within less than a minute of being placed in the chamber, helped popularize the new device.
Boston manufacturer Warren E. Collins began production of the iron lung that year. 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.
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.
In 1931, John Haven Emerson (February 5, 1906 – February 4, 1997) introduced and improved upon a less expensive iron lung. 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. 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. 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 1933 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.
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 102 kg), bulky, and expensive. In the US, an adult machine cost about $2000 in 1930, and £2000 delivered 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.
The South Australia Health Department asked Adelaide brothers Edward and Don Both to create an inexpensive "iron lung". Biomedical engineer Edward Both designed and developed a cabinet respirator made of plywood that worked similarly as the Drinker device, with the addition of a bi-valved design which allowed temporary access to the patient’s body. Far cheaper to make (only £100) than the Drinker machine, the Both Respirator also weighed less and could be constructed and transported more quickly. Such was the demand for the machines that they were often used by patients within an hour of production.
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. Soon, the Both-Nuffield respirators were able to be produced by the thousand at about one-thirteenth the cost of the American design. By the early 1950s, there were over 700 Both-Nuffield iron lungs in the United Kingdom, but only 50 Drinker devices.
Rows of iron lungs filled hospital wards at the height of the polio outbreaks of the 1940s and 1950s, assisting the breathing of children and adults (mostly children) with bulbar polio and bulbospinal polio. A polio patient with paralyzed lungs could spend up to a week inside an iron lung.
Polio vaccination programs have virtually eradicated new cases of poliomyelitis in the United States. Because of this, and the development of modern ventilators, and widespread use of tracheal intubation and tracheotomy, the iron lung has mostly disappeared from modern medicine. In 1959, there were 1,200 people using tank respirators in the United States, but by 2004 there were only 39. By 2014, there were only 10 people left with an iron lung.
Positive pressure ventilation systems are now more common than negative pressure systems. 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. It proved a success and soon superseded the iron lung throughout Europe.
The iron lung now has a marginal place in modern respiratory therapy. Most patients with paralysis of the breathing muscles use modern mechanical ventilators that push air into the airway with positive pressure. These are generally efficacious and have the advantage of not restricting patients' movements or caregivers' ability to examine the patients as significantly as an iron lung does. However, negative pressure ventilation is a truer approximation of normal physiological breathing and results in more normal distribution of air in the lungs. It may also be preferable in certain rare conditions, 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. There are patients who today still use the older machines, often in their homes, despite the occasional difficulty of finding the various replacement parts. Joan Headley of Post-Polio Health International stated to CNN that as of May 28, 2008, there were approximately 30 patients in the USA still using an iron lung. That figure may be inaccurately low; Houston alone had 19 iron lung patients living at home in 2008. Martha Mason of Lattimore, North Carolina, died on May 4, 2009, after spending 60 of her 72 years in an iron lung.
On October 30, 2009, June Middleton of Melbourne, Australia, who had been entered in the Guinness Book of Records as the person who spent the longest time in an iron lung, died aged 83, having spent more than 60 years in her iron lung.
Biphasic cuirass ventilation
Biphasic cuirass ventilation (BCV) is a modern development of the iron lung, consisting of a wearable rigid upper-body shell (a cuirass) which functions as a negative pressure ventilator. The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory and expiratory phases of the respiratory cycle. This method is a modern improvement of 'negative pressure ventilation' (NPV), which could only control inspiratory breathing, relying on passive recoil for exhalation. BCV was developed by Dr Zamir Hayek, a pioneer in the field of assisted ventilation. Some of Dr Hayek's previous inventions include the Hayek Oscillator, an early form of the technology.
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