Iron lung and other respirators

The iron lung is a mechanical respiratory device used to force air into and out of the lungs of a person unable to breathe for themselves. Invented in 1929 by Philip Drinker (1893-1977), a professor at the School of Public Health at Harvard University, the iron lung was one of the first of several inventions designed for this purpose. During the 1920s, people with respiratory failure were aided by a pulmotor, a contraption similar to fireplace bellows, which inflated and deflated the lungs by forcing air in and sucking it out.This process worked; however patients experienced chest pain becausethe amount of air forced into the lungs was not adjustable to the individualpatient's lung capacity. Many people suffering from poliomyelitis--which often paralyzes muscles of the diaphragm, the large, dome-shaped muscle above the stomach which rises and falls to draw air into and push it out of thelungs--required the aid of these devices to keep them alive.

Drinker's idea for a breathing device came from a Swedish physician named Thunberg who had been experimenting with a vacuum to help patients breathe. Enlisting the help of his brother, Cecil, and Louis Shaw (1886-1940) Drinker, built a prototype, tested it on cats, and designed a device large enough for humans. The patient's body was positioned inside an airtight metal box while thehead remained outside. The box was connected to a pump which reduced the airpressure inside the box, causing a negative change in pressure in the chestcavity similar to that which occurs when the diaphragm moves downward allowing air to rush into the lungs. With this decrease in air pressure inside the box, the weight of the atmosphere outside the box forced air through the noseand mouth of the patient into the lungs. In October 1928 an eight-year-old girl unable to breathe as a result of polio was the first person to be put intothe iron lung. Drinker's invention was initially known as the "Drinker tankrespirator," but was soon earned the nickname iron lung. Drinker and Shaw received numerous awards for their invention, which allowed many polio patients to be kept alive, and it remained the standard treatment for this purpose well into the 1950s.

Since Drinker's invention, a class of breathing machines called ventilators and respirators has been developed. A modern ventilator consistsof an electrical pump connected to an air supply, a humidifier which adds moisture to the air, and a tube which is inserted into the patient's nose or mouth. Ventilators, unlike the iron lung, use positive air pressure from the pump to force air into the lungs and the patient exhales the air naturally. Toadjust the oxygen-carbon dioxide ratio supplied by the ventilator, blood samples from the patient are analyzed to determine the metabolic rate. The volumeof air required and the number of times per minute the patient needs to breathe in order to maintain the desired metabolic rate, is also calculated, andpositive air pressure administers the correct mix and volume into the lungs,which deflate passively. Today's sophisticated hospital respiratory care units may utilize up to 15 different kinds of respirators. Ventilators assist patients unable to breathe for themselves, who suffer from degenerative muscle disease, or burns to the nose and throat. Some patients may be connected to a ventilator for months at a time, in which case a breathing tube is surgically inserted directly into the trachea (windpipe). Today, in such placesas Stanford University Hospital in California, the iron lung of the 1950s ismaking a comeback due to it's non-invasive, negative air pressure which eliminates the possibility of infections or scarring prevalent with respirators which require a tracheotomy. The iron lung can also be used at home to help a patient rest respiratory muscles either during the day or night.

Miniature ventilators are also used to help premature babies breathe and provide temporary breathing assistance to patients undergoing surgery requiring anesthesia. At University Hospital in Stony Brook, New York, mini-iron lungs are used for some patients. Nicknamed turtles because of their green color and shell-like shape, these miniature iron lungs can be strapped onto a patient's chest. For treating sleep apnea, a sleep disorder in which breath becomes obstructed, a small ventilator about the size of a vanitycase is connected to a tiny mask placed over the nose. Intermittent positiveair pressure is delivered through the nostrils and the timing can be presetto correspond with the patient's natural breathing rate.

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