ISS TopJAXA Top  sitemap

1. What is Space Medicine?
2. Physiological Changes in Space
3. Flight Surgeon; FS
4. Health Care for Astronauts
5. Spin-offs
6. Conclusion
Space medicine booklets

What is Space Medicine ?

Manned space missions used to be the dream of mankind for years, but became reality with the blast-off by Y. Gagarin in 1961 and the first small steps on the moon by N. Armstrong on Apollo 11. Since then, human activity in space has increased steadily. More than 200 people have been to space, and the duration of stays in space has progressed from 2 hours to more than a year. Now we are entering a new era: the 21st century International Space Station (ISS). Those who have been to space so far are highly specialized, dedicated "astronauts," but in the 21st century, common citizens will be able to travel and sight-see or to live in space. However, before space can become a safe, habitable place, we must solve so many problems. Here we have a powerful tool which will establishes the countermeasures to overcome the physiological effects in space, and that is "Space Medicine."

Physiological Changes in Space

The physiological changes in the adaptive process to space mainly involve:

2.1.Effects on cardiovascular system
2.2.Effects on bone
2.3.Effects on muscle
2.4.Space motion sickness
2.5.Effects on hematologic and immunologic system
2.6.Effects of space radiation
2.7.Effects of isolated environment on psychological aspects

2.1. Effects on cardiovascular system

Fluid shift and the change of body
mass caused by spaceflight
cited from "The Bone"(Vol. 11 No.2 1997.6)
Medical View Co., Ltd.

Human beings living on Earth are effected by gravity because about two-thirds of our daily activities are standing or sitting. Great amounts of body fluids such as blood pool in the lower part of the body. The human body is equipped with various mechanisms to oppose gravity to maintain sufficient blood flow to the brain.
In microgravity environment, the quantity and the distribution of body fluid alter, being free of the gravitational effect. This is the concept of "fluid shift."

This figure shows photographs of Dr. Chiaki Mukai, JAXA astronaut, on Earth and in space. Facial edema, especially around the eyes, appears and the cranial veins dilate early in spaceflight. Subjective symptoms caused by fluid shift are stuffy nose, headache, and puffy face.
Because of this fluid shift in the early stage of spaceflight, the thick veins such as central veins dilate, which is interpreted by the body as an overall increment of the circulating volume. This activates mechanisms which counteract hypervolemia, leading to a significant loss of water.
It is expected that despite the fluid shift and the consequent loss of body mass in the early stage of spaceflight, the cardiovascular system adapts to the microgravity environment if the astronaut continues to stay in space.
However, on return to Earth, the fluid shifts rapidly to the lower body again, which causes a tendency to develop orthostatic hypotension and syncope. Technically speaking, this is called "orth ostatic intolerance."

One countermeasure is to apply the Lower Body Negative Pressure (LBNP). This provides an equivalent physiologic stress by creating suction on the lower body (i. e., legs and abdominal regions) as a substitute for Earth gravity and the upright exercise on Earth. Ingestion of isotonic saline just before reentry is also thought to be effective.
Orthostatic intolerance and the loss of exercise capacity after spaceflight are thought to be caused by overall changes in the cardiovascular system. The process leading to the appearance of these symptoms is called "cardiovascular deconditioning." Significant countermeasures have been made so that the astronauts should not suffer from syncope when the Space Shuttle returns to the Earth.

2.2. Effects on bone

Bones are important systems involved in locomotion and posture maintenance under 1G. The adult human body has 1,000 to 1,200 grams of calcium and 400 to 500 grams of phosphorus. More than 99% of the calcium exists in the form of hydroxyapatite in bone, whereas approximately 85% of phosphorus exists in bone. Thus, bone tissue stocks calcium and phosphorus. However, once gravitational stress is removed, bone calcium and phosphorus are excessively excreted in urine and feces. It is reported that 3.2% of average bone loss occurred after nearly 10 days of weightlessness. The loss of calcium in urine may produce urinary stone which might cause severe pain; the decrease of bone density will lead to bone fracture. Therefore, countermeasures are necessary.
One countermeasure proposed to prevent bone loss is onboard exercise (training program) mainly with the treadmill and ergometer.
For future spaceflight, nutritional supplements and medications might be administrated. The bone research advanced due to aerospace medicine contributes to the research on osteoporosis, which is increasing yearly on Earth.

2.3. Effects on muscle

The human body floats within the orbiting spacecraft. Therefore, astronauts can move around in spacecraft just by softly pushing against its wall. In a microgravity environment, muscles rapidly atrophy due to the lack of use.
Muscles can be roughly classified into anti-gravity muscles which support body weight and other muscles. The former are composed of slow-twitch muscle fibers, and the latter, fast-twitch muscle fibers.
The characteristic changes in muscles in microgravity are the rapid degradation of anti-gravity muscle and the transformation of slow-twitch muscle fibers into fast-twitch muscle fibers. Considering the characteristic of the anti-gravity muscle, exercise to prevent muscle atrophy is not short-duration intensive training, but should be designed to expend less than 30% of the maximum muscle power continuously over a long duration. It is a matter of course that simpler training methods with maximum effects should be established for the coming ISS era.

2.4. Space motion sickness

A few minutes or a few hours after entering weightlessness, some astronauts experience space motion sickness, which is characterized by headaches, malaise, nausea and eventually vomiting. Sixty to seventy percent of the astronauts experience these symptoms which recur intermittently during the first or second day, but then disappear on the third to fifth day.
How do these very distressing conditions occur? Various hypotheses have been proposed for the cause of space motion sickness. The basic mechanisms responsible for developing space motion sickness are assumed to be the rearrangement of the relationship among signals from the vestibular system of the inner ear, visual, skin, joint and muscle receptors by the exposure to microgravity. It has also been proposed that fluid-shift theory should be involved in the development of space motion sickness.
In the 1960s, pre-flight adaptation training with a rotating chair was proposed as a means to build up tolerance to motion sickness by researchers. However, it proved to be not so effective and is no longer used by NASA. We are still groping for the best countermeasure. Biofeedback training, adaptation training using virtual reality, and water immersion training have been attempted so far.
Once astronaut is suffering from space motion sickness, promethazine hydrochloride, which is about 30 times as effective as commonly-used travelmine, is usually administered to reduce the discomfort. Through researches on space motion sickness, these findings contribute to research on dizziness and ground motion sickness.

2.5. Effects on hematologic and immunologic system

One significant alteration in the hematologic and immunologic system in microgravity is the transformation of red blood cells, the main component of blood. Ninety percent of our normal erythrocytes have a biconcave discoid shape (i.e.) a doughnut without a hole. In weightlessness, some erythrocytes transform into "mulberry" or spheric shapes. However, they are readily reversed even after long-term space mission. Anemia characterized by a decrease in the number of red blood cells is observed within four days of spaceflight. The number of red blood cells decreases by approximately 15% after a three-month spaceflight with few subjective symptoms, then recovers after return to the Earth. The activity of lymphocytes, which counteract against the invasion of microorganisms, slightly reduces, but this rarely causes practical problems.

2.6. Effects of space radiation

Space radiation exists in the space environment. On the Earth, the atmosphere and magnetic field provide a shield for humans, and prevent space radiation from penetrating to the Earth's surface. Due to the absence of such shielding in the space environment, astronauts are subject to greater amounts of space radiation than they would receive on the Earth. Therefore, the space radiation may seriously affect on astronauts.

The various types of space radiation can be broadly classified as: 1) galactic radiation coming from outside our solar system, 2) solar-particle radiation originating from the Sun, 3) geomagnetically trapped radiation surrounding the Earth in the plane of the geomagnetic equator. The radiation intensities are not always constant, varying incessantly according to the solar activity.
High-energy solar protons and heavy ions are emitted sporadically during solar-particle events (flares), and this represents a very serious hazard for manned spaceflight.

In order to minimize the exposure to such space radiation, the penetration capability must be predicted by measuring the intensity of the radiation and by identifying the type. Astronauts must shelter themselves from the radiation behind walls of sufficient thickness in the space vehicle, especially for the flares. In addition, it is essential to limit flight opportunities and durations to achieve permissible radiation exposure levels for preventing potential damage, to monitor exposure level with personal dosimeters, and to establish practical risk management procedures.
It is expected that these research activities related to space radiation will be applied to the health care of passenger plane pilots, who also affected by space radiation, as well as to the research for utilizing and shielding radiation sources in high-energy radiation facilities.

2.7. Effects of isolated environment on psychological aspects

On ISS, crew members of different nationalities will live together, perform experiments of various types together, and operate the space craft together in a confined place for three to six months. Psychologically speaking, the environment is different from that on ground in that they must manage to work according to a tight schedule in a monotonous room for several months without a free break back to the Earth, while getting along with other crew members of different cultural backgrounds. It is expected that the long-term confined environment may induce severe psychological stress on international crew members.
Psychological considerations must therefore be introduced into the selection criteria for astronauts to select out applicants who possess predisposed tendencies for any emotional disorders under psychological stresses. It is a matter of course that there is also significant demand for effective crew organization of high-level team performance based on psychological compatibility.
Psychological considerations must therefore be introduced into the selection criteria for astronauts to select out applicants who possess predisposed tendencies for any emotional disorders under psychological stresses. It is a matter of course that there is also significant demand for effective crew organization of high-level team performance based on psychological compatibility. The leadership required is not always the same type: for short-term missions, performance-oriented leadership has been required, but for extended-duration missions, democratic leaders, who have social sensitivity and deep concern for others' feelings, have displayed greater talents. The psychological status of the crew members is a significant key to mission success, with great effect on work efficiency and sound sleep.
Experience gained from previous spaceflights by FKA has revealed conflicts among crew members 30 days after launch, showing hostility to each other and quarreling. Conflicts also arise between crew members and the ground team; in one case, the crew even went on strike against the ground team. Psychological supports, such as private psychological counseling and periodic spouse and family conferences with two-way voice and video communication, are provided as countermeasures. As the number of those who have experienced spaceflight is limited, there is much to be learned about the effect of spaceflight on mental health. However, it is possible to simulate spaceflight in long-term isolation experiments on the ground, though there is a limitation in that the effect of weightlessness can not be taken into consideration. JAXA constructed the Isolation Chamber and initiated basic experiments on adaptation training with several volunteers. We are thus attempting to utilize the knowledge of psychology and psychiatry accumulated so far to solve the problems of psychological adaptation to spaceflight.


Last Updated :April 19, 2004

HOME| ISS & "Kibo" | Space Environment Utilization | Space Medicine |
| JAXA's Astronauts | Space Shuttle Missions | SSIPC |
| Gallery | Link to other Sites |
JAXA Top Site Policy