space medicine


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space medicine,

study of the medical and biological effects of space travel on living organisms. The principal aim is to discover how well and for how long humans can withstand the extreme conditions encountered in space, as well as how well they can readapt to the earth's environment after a space voyage. The medically significant aspects of space travel include weightlessnessweightlessness,
the absence of any observable effects of gravitation. This condition is experienced by an observer when he and his immediate surroundings are allowed to move freely in the local gravitational field.
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, strong inertial forces experienced during liftoff and reentry, radiation exposure, absence of the earth's day-and-night cycle, and existence in a closed ecological environment. Less critical factors are the noise, vibration, and heat produced within the spacecraft. On longer space flights, the psychological effects of isolation and living in close quarters have been a concern, especially among multinational crews with inherent differences in language and culture.

A large body of useful medical data on the effects of a prolonged U.S. space flight was obtained during the Skylab program of the early 1970s and from several medical missions of the space shuttles Challenger and Columbia. The Soviet Union's Soyuz program began Russia's experience with long stays in space; the current record of nearly 439 days was set by Russian cosmonaut Valery Polyakov (Jan. 8, 1994–Mar. 22, 1995) on the space station Mir. With the change in the international political climate in the 1990s, the two countries began to cooperate in life-science research that combined the more sophisticated diagnostic and monitoring equipment of the NASA missions with the greater long-term-stay experience of the Russians. In May, 1995, the Spektr module, containing U.S. medical and research equipment, was added to the Mir. A few months later, American physician-astronaut Norman E. Thagard broke the former U.S. record of 84 continuous days in space when he spent 111 days on the Russian space station. The American record was subsequently broken by Miguel López-Alegría, who spent 215 days aboard the International Space Station (ISS; 2006–7), and then by Scott Kelly, who spent 340 days aboard the ISS (2015–16). Cosmonaut Gennady Padalka, who has served for 5 periods on Mir and the ISS, holds the record for most cumulative time in space, 879 days.

There have been many indirect benefits to medicine from space science. The need to maintain close watch over the physiological conditions of astronauts has spurred the development of improved means for electronically monitoring essential body functions. The development of programmable heart pacemakers, implantable drug administration systems, magnetic resonance imaging (MRI), and computerized axial tomography (CAT) all depended to some extent on knowledge gained from the space program. Studies of how astronauts would walk in the moon's weak gravitational field led to a deeper understanding of human locomotion.

See also aviation medicineaviation medicine,
scientific study of the biological effects of aviation, especially on human beings. Although aviation medicine is concerned with such problems as the spread of diseases by persons traveling by air and the harmful effects of noise and air pollution, its
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; space sciencespace science,
body of scientific knowledge as it relates to space exploration; it is sometimes also called astronautics. Space science draws on the conventional sciences of physics, chemistry, biology, and engineering, as well as requiring specific research of its own.
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.

Medically Significant Aspects of Space Flight

Weightlessness

Of all the medically significant conditions experienced in space flight, weightlessness has the most drastic effects; moreover, it will be impossible to eliminate this aspect of space travel unless large space stations can be constructed that produce artificial gravity, as by rotating. Because life evolved under the constant influence of gravity, the effects of weightlessness even on the cellular level have been a concern. It was at first feared that a human being in space might lose all coordination and become completely incapacitated. While the human body does appear to adjust fairly quickly in a state of weightlessness, associated problems do occur, often causing difficulties only upon return to earth. Problems include space adaptation syndrome (nausea, motion sickness, and sensory disorientation during the first few days), weakened immune defenses, loss of bone mass, loss of muscle mass (including loss of heart muscle), a reduction in the amount of blood in the body (which may lead to low blood pressure for a time upon return to earth), and space anemia, which results as the number of red cells decreases. Many astronauts also have vision problems upon their return due to the effects of weightlessness. Space-station astronauts undergo strenuous exercise routines to maintain bone and large muscle mass, but deterioration is only slowed and rehabilition is still required after the return to earth to restore bones and muscles to their preflight conditions.

Inertial Forces

Inertial forces due to acceleration are experienced only during liftoff and reentry, but the consequences can be traumatic. The circulatory system is most strongly affected; deprivation of blood to the brain causes dimming of vision and sometimes loss of consciousness. However, lying on a body-contoured couch, astronauts have survived inertial forces eight times stronger than normal gravity.

Ionizing Radiation

In space the astronauts are exposed to ionizing radiation from particles trapped in the earth's magnetic field, from solar flares, and from the onboard nuclear reactors that help power the spacecraft. This radiation can produce deleterious effects, ranging from nausea and lowered blood count to genetic mutations and leukemialeukemia
, cancerous disorder of the blood-forming tissues (bone marrow, lymphatics, liver, spleen) characterized by excessive production of immature or mature leukocytes (white blood cells; see blood) and consequently a crowding-out of red blood cells and platelets.
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. Protective shielding, shielding chemicals, and careful monitoring of the doses of radiation received by each astronaut have been used to reduce radiation exposure to acceptable levels.

Absence of Day and Night

The absence of the earthly cycle of day and night during space travel produces subtle effects, both physiological and psychological. The period from sunrise to sunset in a quickly orbiting spacecraft may be as little as 1 1/2 hours long. All body rhythms, such as heartbeat, respiration, and changes in body temperature, are regulated by biological clocks (see biorhythmbiorhythm
or biological rhythm,
cyclic pattern of changes in physiology or in activity of living organisms, often synchronized with daily, monthly, or yearly environmental changes.
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). These rhythms are related to human patterns of sleep and wakefulness, which in turn are based on the alternation of day and night. On most flights, adherence to "home" schedules maintains normal human cycles.

A Closed Environment

In the closed environment of the spacecraft care must be taken to prevent the buildup of toxic material to dangerous levels; this is accomplished by recycling waste material. The nature of the artificial atmosphere astronauts breathe is an important biomedical consideration. Ideally, this atmosphere would be identical in composition and pressure to the earth's atmosphere. Any alteration involves the risk of decompression sickness. The space shuttle used a pure oxygen atmosphere or a mixture of oxygen and nitrogen.

Bibliography

See A.E. Nicogossian, C.L. Huntoon, and S.L. Pool, Space Physiology and Medicine (1989).

Space Medicine

 

the group of sciences engaged in medical, biological, engineering, and other scientific research to develop safety measures and create optimal life conditions for man during space flight, both inside and outside the vehicle.

Space medicine is concerned with investigating the effects of the factors of space flight on the human body, eliminating unfavorable influences and devising suitable preventive measures and means; formulating and substantiating the medical (physiologically hygienic) demands on life-support systems in spacecraft and various space installations and on the means of rescuing crews in emergency situations; formulating the medical grounds for the rational construction of spacecraft control systems and equipment; developing medical (psychophysiological and clinical) methods of screening and training astronauts; and formulating and substantiating effectiveness criteria for the system of medically preparing astronauts for flight.

Man’s first successful orbital flight—that of Iu. A. Gagarin in Vostok 12 on Apr. 12, 1961—was an outstanding event in the history of space medicine. Other important stages in space exploration were man’s first walk in space (A. A. Leonov on Voskhod 2; Mar. 18–19, 1965) and the first moon landing (by the American astronauts N. Armstrong and E. Aldrin on Apollo 11; July 20,1969). About 40 manned space flights had been made by the USSR and the USA by 1972. These flights made it possible to evaluate their medical support systems and to accumulate data to improve them.

New problems have arisen in the course of space exploration that have required their own solutions. Space physiology is concerned with the effect of the factors and conditions of space flight. Three main groups of factors affect man (or animals) during space flight: (1) factors characteristic of space as a unique habitat, such as extremely rarefied atmosphere, ionizing radiation, the properties of the thermal regime, and meteoric substances; (2) factors related to the flight dynamics of rockets, such as acceleration, vibration, noise, and weightlessness; and (3) the factors associated with prolonged stays in the artificial environment of a small sealed cabin, such as isolation, adynamia, emotional stress, aspects of the circadian rhythms, and work and rest arrangements. The designers and planners of life-support systems must take into account the number and composition of the crew, the duration of the flight, the nature of the mission, limitations on the uses of energy, and the weight and size of the required equipment and on-board supplies.

According to the most recent data, the daily support of the normal activities and the maintenance of the fitness of a single crew member requires approximately 640 g of completely assimilable food (dry weight), 2,200 g of water, 882 g of oxygen, and 2 g of salts, vitamins, and other supplementary nutrients. The biological effects of the unfavorable factors of space and space flight must be studied so that human beings may be protected against them. This is done by simulating these factors on special laboratory equipment, such as centrifuges, vibration stands, pressure chambers, and nuclear accelerators. However, prolonged weightlessness and the action of the heavy nuclei of cosmic radiation cannot yet be simulated.

The role of space medicine in the medical phase of the screening and training of astronauts becomes increasingly meaningful as space technology improves. Study of the effects of prolonged weightlessness during flight and of readaptation to normal gravity after return to earth is a serious problem. Various physical exercises have been devised to prevent cardiovascular decon-ditioning. A suit has been developed that maintains a constant load on certain muscle groups during periods of restricted motor activity, and an apparatus has been created to apply negative pressure to the lower half of the body in order to help maintain orthostatic tolerance after exposure to space flight. No practical solution has yet been found to the problem of creating artificial gravity on a spacecraft. Such matters as metabolism during space flight, changes in cardiovascular function, and electrolyte metabolism (including potassium and calcium) also require further study.

Protection of the crew against cosmic radiation is a major concern. The biological effects of cosmic rays have not been studied adequately, especially when in combination with the factors of acceleration, vibration, fluctuations in barometric pressure, possible changes in the gaseous composition of the cabin of the spacecraft, and other unfavorable factors of space flight.

In the USSR, work in space medicine is coordinated by the Space Research and Utilization Commission of the Academy of Sciences of the USSR and the Ministry of Public Health of the USSR. The I. P. Pavlov All-Union Society of Physiologists of the Academy of Sciences of the USSR has an aerospace medicine section. All-Union conferences are held on space biology and medicine, and lectures are given every year on the scientific legacy and elaboration of the ideas of K. E. Tsiolkovskii. Soviet scientists are active in several international organizations, including the Committee on Space Research (COSPAR) and the International Astronautical Federation (IAF).

The major international and national organizations in space medicine are the American Aerospace Medical Association, the Academy of Aviation and Space Medicine (with representation in Brussels), and the Committee on Bioastronautics of the International Astronautical Federation. In the USA, the National Aeronautics and Space Administration (NASA) coordinates research in space medicine.

REFERENCES

Gazenko, O. G. “Kosmicheskaia biologiia i meditsina.” In Uspekhi SSSR ν issledovanii kosmicheskogo prostranstva. Moscow, 1968. Pages 321–70.
Parin, V. V., and V. N. Pravetskii. “Kosmicheskaia biologiia i meditsina.” In Piat’desiat let sovetskogo zdravookhraneniia. Moscow, 1967. Pages 621–35.
Kratkii spravochnik po kosmicheskoi biologii i meditsine. Edited by A. Burnazian [et al.]. Moscow, 1967.
Parin, V. V., K. V. Smirnov, and N. N. Gurovskii. “Sovetskoe zdravookhranenie i kosmicheskaia meditsina.” In Aviakosmicheskaia meditsina, collection 2. Moscow, 1968.

O. G. GAZENKO and R. B. STRELKOV

space medicine

[′spās ‚med·ə·sən]
(medicine)
A branch of medicine that deals with the physiologic disturbances and diseases produced in man by high-velocity projection through and beyond the earth's atmosphere, flight through interplanetary space, and return to earth.
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