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 weightlessness, 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.

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 medicine; space science.

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), 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.

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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Space medicine is the practice of medicine on astronauts in outer space.

Who benefits from space medicine research?

Astronauts are not the only ones who benefit from space medicine research. Several medical products have been developed that are space spinoffs, that is practical applications for the field of medicine arising out of the space program. Because of joint research efforts between NASA, the National Institutes on Aging (a part of the National Institutes of Health), and other aging-related organizations, space exploration has benefitted a particular segment of society, seniors. Evidence of aging related medical research conducted in space was most publicly noticeable during STS-95 (See below).

Medical space spinoffs from the early space exploration years (pre-Mercury through Apollo projects)

• Radiation therapy for the treatment of cancer. In conjunction with Cleveland Clinic,

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.

• Foldable walkers. Made from a lightweight metal material developed by NASA for aircraft and spacecraft, foldable walkers are portable and easy to manage.
• Personal alert systems. These are emergency alert devices that can be worn by individuals who may require emergency medical or safety assistance. When a button is pushed, the device sends a signal to a remote location for help. To send the signal, the device relies on telemetry technology developed at NASA.
• CAT Scans and MRIs. These devices are used by hospitals to see inside the human body. Their development would not have been possible without the technology provided by NASA after it found a way to take better pictures of the Earth’s moon.
• Muscle stimulator device. This device is used for ½ hour per day to prevent muscle atrophy in paralyzed individuals. It provides electrical stimulation to muscles which is equal to jogging three miles per week. Christopher Reeves used these in his therapy.
• Orthopedic evaluation tools. Equipment to evaluate posture, gait, and balance disturbances was developed at NASA, along with a radiation-free way to measure bone flexibility using vibration.
• Diabetic foot mapping. This technique was developed at NASA’s center in Cleveland, Ohio to help monitor the effects of diabetes in feet. These efforts helped
• Foam cushioning. Special foam used for cushioning astronauts during liftoff is used in pillows and mattresses at many nursing homes and hospitals to help prevent ulcers, relieve pressure, and provide a better night’s sleep.
• Kidney dialysis machines. These machines rely on technology developed by NASA in order to process and remove toxic waste from used dialysis fluid.
• Talking wheelchairs. Paralyzed individuals who have difficulty speaking may use a talking feature on their wheelchairs which was developed by NASA to create synthesized speech for aircraft.
• Collapsible, lightweight wheelchairs. These wheelchairs are designed for portability and can be folded and put into trunks of cars. They rely on synthetic materials that NASA developed for its air and space craft
• Surgically implantable heart pacemaker. These devices depend on technologies developed by NASA for use with satellites. They communicate information about the activity of the pacemaker, such as how much time remains before the batteries need to be replaced.
• Implantable heart defibrillator. This tool continuously monitors heart activity and can deliver an electric shock to restore heartbeat regularity.
• EMS Communications. Technology used to communicate telemetry between Earth and space was developed by NASA to monitor the health of astronauts in space from the ground. Ambulances use this same technology to send information—like EKG readings—from patients in transport to hospitals. This allows faster and better treatment.
• Weightlessness. While not an invention per se, the weightlessness of space one day may allow individuals with limited mobility on Earth--even those normally confined to wheelchairs--the freedom to move about with ease. A notable individual to take advantage of weightlessness in the "Vomit Comet" during 2007 was physicist Stephen Hawking.

Major historical medical investigations in space during the Space Shuttle era

STS-95

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.

What are the effects of space on the body?

Accident investigation

Decompression sickness

Decompression illness in spaceflight

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

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

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.

References

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)

Decreased immune system functioning

Astronauts in space have weakened immune systems, which means that in addition to increased vulnerability to new exposures, viruses already present in the body—which would normally be suppressed—become active. In space, T-cells (a part of white blood cells that produces antibodies) do not reproduce properly. T-cells that do exist are less able to fight off infection. NASA research is measuring the change in the immune systems of its astronauts as well as performing experiments with T-cells in space.

Effects of fatigue

Human performance

Loss of balance

Leaving and returning to Earth’s gravity causes “space sickness,” dizziness, and loss of balance in astronauts. By studying how changes can affect balance in the human body--involving the senses, the brain, the inner ear, and blood pressure--NASA hopes to develop treatments that can be used on Earth and in space to correct balance disorders. Until then, NASA’s astronauts must rely on a medication called Midodrine (an “anti-dizzy” pill that temporarily increases blood pressure) to help carry out the tasks they need to do to return home safely.

Loss of bone density

Unlike people with osteoporosis, astronauts eventually regain their bone density. After a 3-4 month trip into space, it takes about 2-3 years to regain lost bone density. New techniques are being developed to help astronauts recover faster. Research in the following areas holds the potential to aid the process of growing new bone:

• Diet and Exercise changes may reduce osteoporosis.
• Vibration Therapy may stimulate bone growth.
• Medication could trigger the body to produce more of the protein responsible for bone growth and formation.

Loss of muscle mass

In space, muscles in the legs, back, spine, and heart weaken and waste away because they no longer are needed to overcome gravity, just as people lose muscle when they age due to reduced physical activity. Astronauts rely on research in the following areas to build muscle and maintain body mass:

• Exercise may build muscle if at least two hours a day is spent doing resistance training routines.
• Hormone supplements (hGH) may be a way to tap into the body’s natural growth signals.
• Medication may trigger the body into producing muscle growth proteins.

Man-machine interface

Orthostatic intolerance

In space, astronauts lose fluid volume—including up to 22% of their blood volume. Because it has less blood to pump, the heart will atrophy. A weakened heart results in low blood pressure and can produce a problem with “orthostatic tolerance,” or the body’s ability to send enough oxygen to the brain without fainting or becoming dizzy. "Under the effects of the earth's gravity, blood and other body fluids are pulled towards the lower body. When gravity is taken away or reduced during space exploration, the blood tends to collect in the upper body instead, resulting in facial edema and other unwelcome side effects. Upon return to earth, the blood begins to pool in the lower extremities again, resulting in orthostatic hypotension.

Psychological factors

Radiation effects

Safety/habitability

Sleep disorders

Fifty percent of space shuttle astronauts take sleeping pills and still get two hours less sleep. NASA is researching two areas which may provide the keys to a better night’s sleep, as improved sleep decreases fatigue and increases daytime productivity:

• Environmental cues and practices may be able to retrain the body’s circadian rhythm.
• Medication could improve sleep by increasing the production of melatonin, a sleep hormone

Spatial disorientation

Medical interventions

• Exercise to maintain muscle strength and function
• Sleep cap
• Medication, including hormone replacement therapy

How does one prepare for a career in space medicine?

Educational programs

• Naval Operations Medical Institute (NAMI) - Pensacola, Florida
• U.S. Air Force School of Aerospace Medicine - Brooks City-Base, San Antonio, Texas
• University of Texas Medical Branch at Galveston (UTMB) - Aerospace Medicine Residency Program
• Wright State University School of Medicine - Dayton, Ohio
• Vanderbilt Center for Space Psysiology and Medicine - (Dr. David Robertson)
• Space Studies Department at the University of North Dakota

Related degrees, areas of specialization, and certifications

• Aeromedical certification
• Aerospace Medicine
• Aerospace Studies
• Emergency Medicine
• Family Practice
• Internal Medicine
• Occupational and Preventive Medicine
• Ophthalmology
• Otolaryngology
• Public Health

Professional organizations

• Aerospace Human Factors Association
• Aerospace Medical Association
• Air Medical Physician Association
• American Psychological Association
• Association of Air Medical Services
• Aviation & Aerospace Medicine
• Federal Aviation Administration Office of Aerospace Medicine
• Human Factors & Ergonomics Society
• Human Performance in Extreme Environments

Commercial spaceflight medicine

Three major institutions teamed up to investigate space medicine applications in commercial spaceflight. The directors of those programs are listed.

• Mayo Clinic-Scottsdale - (Dr. Jan Stepanek)
• University of Texas Medical Branch at Galveston (UTMB) - (Dr. Richard Jennings)
• Wyle Laboratories Commercial Spaceflight Service Unit - (Dr. Vernon McDonald)
• National Space Biomedical Research Institute (NSBRI) Space Medicine Liaison at Baylor College of Medicine - (Dr. Jonathan Clark)

Legal aspects of space medicine research

• Authorities: Professor Joanne Irene Gabrynowicz, space law specialist from the University of Mississippi Space Law Center, and Director of the National Remote Sensing and Space Law Center.
• Publications: Journal of Space Law

External links

• Description of space medicine
• NASA History Series Publications (many of which are online)

References