Negative pressure ventilator

A negative pressure ventilator, also known as iron lung (colloquialism) or pulmotor (generic trademark), is a mechanical respirator which enables a person to breathe on his or her own in a normal manner, when muscle control is lost, or the work of breathing exceeds the person's ability. Need for this treatment may result from certain diseases (e.g. polio, botulism) and certain poisons (e.g. barbiturates, tubocurarine). A negative pressure ventilator, also known as iron lung (colloquialism) or pulmotor (generic trademark), is a mechanical respirator which enables a person to breathe on his or her own in a normal manner, when muscle control is lost, or the work of breathing exceeds the person's ability. Need for this treatment may result from certain diseases (e.g. polio, botulism) and certain poisons (e.g. barbiturates, tubocurarine). Its use is largely obsolete in modern medicine, as superior breathing therapies have been developed, and due to the eradication of polio. Examples of the device include both the Drinker respirator, the Emerson respirator, and the Both (or Emerson-Drinker) respirator. The negative form of pressure ventilation (decreasing surrounding pressure to induce inhalation then repressurizing to 1 bar (15 psi; 750 mmHg)) has been almost entirely superseded by positive pressure ventilation (forcing air into the lungs with a pressure greater than 1 bar then allowing the body to naturally exhale before repeating) or negative pressure cuirass ventilation 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. An opening allowing the head and neck to remain outside is then sealed off, forming an air-tight compartment enclosing the rest of the person's body from the neck down. Pumps that control airflow periodically decrease and increase the air pressure within the chamber, and thus, 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 upper respiratory tract 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 also a form of non-invasive therapy. 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 motor-driven bellows.The first of these devices to be widely used however was developed in 1928 by Drinker and Shaw of the United States. 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 12 October 1928, at the Boston Children's Hospital in the US. 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.