Aerospace Medicine - astronomy.
Publié le 11/05/2013
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medically as aeroembolism and popularly as the bends, leads to confusion, paralysis, or neurocirculatory collapse.
The most characteristic symptoms of the bends arepain in the large joints resulting from pressure of the gas on tendons and nerves, together with spasm of the blood vessels.
Preflight inhalation of pure oxygen toeliminate nitrogen from the system has proved valuable as a preventive measure.
Rapid decompression, resulting from accidental failure at high altitudes of thepressure within the cabin, causes major damage to the heart and other organs by the ram effect of gases formed in the body cavities.
B5 Airsickness
This condition is produced by a disturbance of the labyrinthine mechanism of the inner ear ( see Ear: Equilibrium), although psychogenic factors such as apprehension can also play a part.
Motion sickness can be prevented by taking drugs containing scopolamine or some antihistamines ( see Antihistamine) before flight.
B6 Time Change
As transport planes became faster, pilots and passengers were able to travel across many time zones in less than a day.
The resulting disturbance in the biologicalcircadian (“about a day”) rhythm ( see Biological Clocks) can produce disorientation and reduce concentration and efficiency.
This condition is popularly known as jet lag. While troublesome to passengers, the problem is more acute for pilots, who may have to fly another assignment in a short time.
Concern has been expressed about thepossible effect of this situation on air safety, although no air accident has been clearly identified as jet-lag-induced.
III SPACE MEDICINE
The U.S.
National Aeronautics and Space Administration (NASA) is responsible for nonmilitary space flight for scientific purposes, which include medical studies.Specialists in space medicine—also known as bioastronautics—study the human factors involved in flight outside the atmosphere.
Most of the potential dangers in spacetravel (such as acceleration and deceleration forces, the need for an artificial atmosphere, and noise and vibration) are similar to those encountered in atmospheric flightand can be compensated for in similar ways.
Space medicine scientists, however, must consider two additional problems—weightlessness and the increased radiationoutside the atmosphere.
A History
The first information about human performance during space travel was gathered in Germany in the 1940s under the direction of Hubertus Strughold.
In 1949Strughold was made director of the department of space medicine at the School of Aviation Medicine at Randolph Air Force Base, Texas (now the School of AerospaceMedicine at Brooks Air Force Base, Texas).
Both the United States and the Union of Soviet Socialist Republics (USSR) conducted rocket tests with animals beginning in1948.
In 1957 the USSR put a dog into earth orbit, and the U.S.
used a monkey for tests in 1958.
The tests suggested that few biological dangers existed in spaceflight.
This was confirmed when human space flight began on April 12, 1961, with the launching of the Soviet cosmonaut Yuri Gagarin into orbit.
The United States followed with the Mercury-Redstone suborbital flights and then the orbital Mercury and Gemini flights, the Apollo moon landings, the experimentalorbital vehicle Skylab, and Space Shuttle flights.
Then, in the 1980s, when Soviet cosmonauts began setting records for time spent in the gravity-free or “microgravity” environment, the effects of long-term weightlessness began to be viewed as a serious medical problem.
B Physiological Findings
Few serious biological effects were noted during the early years of space flight.
Even the 21-day quarantine of astronauts returning from the Apollo moon mission wassubsequently abandoned, because no infectious agents were identified.
The body functions that were monitored (often with specially designed miniature instruments)included heart rate, pulse, body temperature, blood pressure, respiration, speech and mental alertness, and brain waves.
Few changes occurred.
Changes in thehormones and in the concentrations of salts in the blood did take place, but these were not detrimental.
Eating in weightlessness was accomplished by packaging food incontainers that could be squeezed directly into the mouth, and special systems were designed for collection of fluid and solid wastes.
The lack of a natural time cycle inspace was compensated for by keeping the astronauts’ schedules synchronized with earth time.
Psychological changes were anticipated because of the close confinement of a few individuals in a small space with limited activity.
Few psychological problems werenoted, however, perhaps because the astronauts were chosen for emotional stability and high motivation and because they were assigned enough tasks to keep themalmost constantly busy.
Irradiation was also found to have little effect.
Short orbital flights produced exposures about equal to one medical X ray—about the same assuborbital flight.
The crew on the longer Skylab flight sustained many times this dose.
Space flights are planned to avoid periods when solar flares are expected tooccur, as these can emit dangerous levels of gamma radiation.
However, although it was assumed that gravity is necessary for normal growth, the magnitude of physiological changes induced by extended periods in a microgravityenvironment came as something of a surprise.
Serious medical problems, including loss of bone matter and muscle strength, were observed to result from long-termweightlessness, as during the 237-day mission of three cosmonauts aboard a Salyut space station in 1984.
Moreover, atrophy of certain muscles, particularly those ofthe heart, was seen to be especially dangerous because of its effect on the functioning of the entire cardiovascular system.
The blood itself was found to be affected,with a measurable decrease in the number of oxygen-carrying cells.
On a seven-day Challenger Space Shuttle mission in 1985, these effects were studied in an experiment using 24 rats and 2 monkeys.
Post-flight examination revealed not only the expected loss of bone and muscle strength but a decrease in release of growth hormone as well.
These findings are taken into consideration now whenever plans are made for manned space flight.
Astronauts’ busy work schedules in space are designed to includeregular exercise periods, thereby maintaining muscle tone.
And plans for the operation of permanently manned space stations now include provisions for changingcrews on a regular basis, so as not to subject astronauts to weightlessness for indefinite periods of time.
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