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.
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.
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), and space anemia, which results as the number of red cells decreases. Russian astronauts undergo strenuous exercise routines twice daily to try and maintain bone and large muscle mass. Nevertheless, some have had to be carried on stretchers when they first return to earth.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 leukemia. 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 space shuttle may be as little as 11∕2 hours long. All body rhythms, such as heartbeat, respiration, and changes in body temperature, are regulated by biological clocks (see biorhythm). 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 uses a pure oxygen atmosphere or a mixture of oxygen and nitrogen.
See A.E. Nicogossian, C.L. Huntoon, and S.L. Pool, Space Physiology and Medicine (1989).
Branch of medicine, pioneered by Paul Bert, dealing with atmospheric flight (aviation medicine) and space flight (space medicine). Intensive preflight simulator training and attention to design of equipment and spacecraft promote the safety and effectiveness of humans exposed to the stresses of flight and can prevent some problems. The world's first unit for space research was established in the U.S. in 1948. Physicians trained in aerospace medicine are known as flight surgeons.
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the cyclotron at NASA’s center in Cleveland, Ohio—which had been utilized for testing nuclear propulsion systems for air and space craft—was used in the first clinical trials for the treatment and evaluation of neutron radiation therapy for cancer patients.
John Glenn, the first American astronaut to orbit the Earth, returned with much fanfare to space once again at 77 years of age to confront the physiological challenges preventing long-term space travel for astronauts—loss of bone density, loss of muscle mass, balance disorders, sleep disturbances, cardiovascular changes, and immune system depression—all of which are problems confronting aging people as well as astronauts. Once again Glenn stepped forward to play an historic role in the future of space exploration, but this time he would provide new medical research in the field of gerontology as well.
In space, astronauts use a space suit, essentially a self-contained individual spacecraft, to do spacewalks, or extra-vehicular activities (EVAs). Spacesuits are generally inflated with 100% oxygen at a total pressure that is less than a third of normal atmospheric pressure. Eliminating inert atmospheric components such as nitrogen allows the astronaut to breathe comfortably, but also have the mobility to use their hands, arms, and legs to complete required work, which would be more difficult in a higher pressure suit.
After the astronaut dons the spacesuit, air is replaced by 100% oxygen in a process called a "nitrogen purge". In order to reduce the risk of decompression sickness, the astronaut must spend several hours "pre-breathing" at an intermediate nitrogen partial pressure, in order to let their body tissues outgas nitrogen slowly enough that bubbles are not formed. When the astronaut returns to the "shirt sleeve" environment of the spacecraft after an EVA, pressure is restored to whatever the operating pressure of that spacecraft may be, generally normal atmospheric pressure. Decompression illness in spaceflight consists of decompression sickness (DCS) and other injuries due to uncompensated changes in pressure, or barotrauma.
Decompression sickness is the injury to the tissues of the body resulting from the presence of nitrogen bubbles in the tissues and blood. This occurs due to a rapid reduction in ambient pressure causing the dissolved nitrogen to come out of solution as gas bubbles. In space the risk of DCS is significantly reduced by using a technique to wash out the nitrogen in the body’s tissues. This is achieved by breathing 100% oxygen for a specified period of time before donning the spacesuit, and is continued after a nitrogen purge. DCS may result from inadequate or interrupted pre-oxygenation time, or other factors including the astronaut’s level of hydration, physical conditioning, prior injuries and age. Other risks of DCS include inadequate nitrogen purge in the EMU, a strenuous or excessively prolonged EVA, or a loss of suit pressure. Non-EVA crewmembers may also be at risk for DCS if there is a loss of spacecraft cabin pressure.
Symptoms of DCS in space may include chest pain, shortness of breath, cough or pain with a deep breath, unusual fatigue, lightheadedness, dizziness, headache, unexplained musculoskeletal pain, tingling or numbness, extremities weakness, or visual abnormalities.
Primary treatment principles consist of in-suit repressurization to re-dissolve nitrogen bubbles, 100% oxygen to re-oxygenate tissues, and hydration to improve the circulation to injured tissues.
To date there have been no reported cases of DCS in the NASA space program.
Barotrauma is the injury to the tissues of air filled spaces in the body as a result of differences in pressure between the body spaces and the ambient atmospheric pressure. Air filled spaces include the middle ears, parananal sinuses, lungs and gastrointestinal tract. One would be predisposed by a pre-existing upper respiratory infection, nasal allergies, recurrent changing pressures, dehydration, or a poor equalizing technique.
Positive pressure in the air filled spaces results from reduced barometric pressure during the depressurization phase of an EVA. It can cause abdominal distension, ear or sinus pain, decreased hearing, and dental or jaw pain. Abdominal distension can be treated with extending the abdomen, gentle massage and encourage passing flatus. Ear and sinus pressure can be relieved with passive release of positive pressure. Pretreatment for susceptible individuals can include oral and nasal decongestants, or oral and nasal steroids.
Negative pressure in air fill spaces results from increased barometric pressure during repressurization after an EVA or following a planned restoration of a reduced cabin pressure. Common symptoms include ear or sinus pain, decreased hearing, and tooth or jaw pain.
Treatment may include active positive pressure equalization of ears and sinuses, oral and nasal decongestants, or oral and nasal steroids, and appropriate pain medication if needed.
Altitude Decompression Sickness Susceptibility, MacPherson, G; Aviation, Space, and Environmental Medicine, Volume 78, Number 6, June 2007 , pp. 630-631(2)
Decision Analysis in Aerospace Medicine: Costs and Benefits of a Hyperbaric Facility in Space, John-Baptiste, A; Cook, T; Straus, S; Naglie, G; et al. Aviation, Space, and Environmental Medicine, Volume 77, Number 4, April 2006 , pp. 434-443(10)
Incidence of Adverse Reactions from 23,000 Exposures to Simulated Terrestrial Altitudes up to 8900 m, DeGroot, D; Devine JA; Fulco CS; Aviation, Space, and Environmental Medicine, Volume 74, Number 9, September 2003 , pp. 994-997(4)