Life Sciences Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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6. Human Biology and Space Medicine
6. Human Biology and Space Medicine
Pages 77-129
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From page 77... ...
This task group wishes to emphasize several of the conclusions contained in the Space Science Board report: ~ Basic and clinical research complement one another in that clinical observations often pose basic research problems. Conversely, solutions to medical probe usually depend on an understanding of the underlying biology.
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From page 78... ...
There has been little substantial progress made in the development of animal holding units and research modules for the U.S. and Soviet space programs.
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From page 79... ...
Such design characteristics should be evaluated on short missions prior to a commitment to longer-term space missions. NEUROS1:NSORY PHYSIOLOGY Introduction Since its inception, NASA's neurosensory physiology research program has centered on the neurovestibular area largely because of the space motion sickness (SMS)
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From page 80... ...
4. One-g motion sickness susceptibility tests do not predict susceptibility aloft.
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From page 81... ...
Given the formidable obstacles to inflight life sciences research outlined above, both reason and past experience indicate that the bulk of any proposed systematic, well-structured scientific research program in the neurophysiological discipline will have to await the Space Station era. All available Shuttle flight opportunities will
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From page 82... ...
It would be invaluable in determining the optimal g level to prevent or reduce the adverse effects of m~crogravity such as cardiovascular Reconditioning, bone demineralization, muscle atrophy, and abnormal plant growth. Research involving subhuman surrogates is detailed in A Strategy for Space Biology and Medical Science for the 1980s and 1990~.
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From page 83... ...
The correlations between the selected predictors and motion sickness have been of limited use in predicting susceptibility. Individual variations in preflight experience, medications, inflight tasks (i.e., mobility)
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From page 84... ...
Proposed Research Overview Investigations using noninvasive methods and human subjects during long-duration orbital flight will be required for an understanding of human adaptability to microgravity and the return to Earth. Possible areas of investigation include: 1.
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From page 85... ...
Tactile and Proprioceptive Systems The gravity vector is a fundamental factor ~ human spatial orientation, which results from the integration of a complex of sensory inputs including visual, vestibular, tactile, and proprioceptive. The latter two systems are important both in spatial orientation and in postural control.
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From page 86... ...
Such experiments will provide information regarding the psycho-physiological basis for establishing spatial orientation aloft. Postural mechanisms require investigation in long-duration space missions.
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From page 87... ...
Background Flight Experience A variety of studies of humans during long-term bed rest, of humans in space, and of rats in space have shown that prolonged inactivity and weightlessness result both in significant and continuing losses of calcium from the skeleton and nitrogen from muscle, and In notable atrophy of both body systems. These changes were consistent but quite difl.erent in degree from subject to subject.
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From page 88... ...
In more recent research, bed rest studies under NASA sponsorship have been continued in search of so-called "countermeasures" that could be applied to astronauts in space to suppress or prevent calcium loss. All of the mechanical procedures tested thus far have been ineffective.
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From page 89... ...
. Bed rest studies have shown a slight rise in urinary pH and a lack of change in urinary citrate, which in ambulatory states rises with increases in urinary calcium.
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From page 90... ...
The rat and primate studies, including a number of rat studies on U.S.S.R.Cosmos flights, have been mainly observational, but with the intent of obtaining data on the rate, degree, location, and pathophysiological processes of the bone loss occurring in inactivity and in weightlessness. While appropriate plans for Space Station research relative to the musculoskeletal system are being addressed, certain studies will be especially pertinent to learning more about the effects of long-term weightlessness, on the musculoskeletal system.
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From page 91... ...
More precise measurements of magnetic and streaming potentials and of piezoelectric energies are becoming available for use in a wide variety of studies, including the interrelationships of mechanical and electrical forces and biochemical signals In bone cell cultures. Despite the steady development of more sophisticated techniques, the capabilities for diet control and specimen collections of metabolic balance studies will still be needed aboard space vehicles.
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From page 92... ...
Schneider and Associates) , high calcium and phosphate intakes kept calcium balance from going negative for the first three months of bed rest, but during the fourth month increasing fecal calcium excretion resulted in continuing losses of calcium (negative balance)
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From page 93... ...
Background Flight Experience The increased urinary excretion of nitrogen by astronauts in Skylab reflected mainly muscle loss as is observed in bed rest, but was variable and generally greater in degree. At least a small part of this excess nitrogen excretion could reflect gluconeogenesis related to observed increased cortiso!
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From page 94... ...
The uncertain value of physical exercise for suppressing muscle atrophy in human flight has been noted previously; no controlled studies of exercise in flight have been attempted. Proposed Research NASA-sponsored research is now addressing basic mechanisms relating muscle demand or load to hypertrophy, and decreased demand to atrophy.
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From page 95... ...
CARDIOVASCULAR, PULMONARY, AND RENAL SYSTEMS reduction Investigation of cardiovascular ant} pulmonary physiology in manned spaceflight will continue to be an important endeavor well beyond 1995. Clearly, the cardiovascular, pulmonary, and renal systems are crucial to health.
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From page 96... ...
At current leveb of experience, both orthostatic intolerance and diminished exercise capacity become more severe with longer exposure to microgravity and require more lengthy recovery times after returning to Earth. There appears to be no qualitative difference between short- and medium-term microgravity exposure with regard to cardiovascular well being and performance in space.
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From page 97... ...
Finally, it should be recognized that the microgravity environment may provide a unique laboratory for investigation of fundamental cardiovascular and pulmonary physiology and development. Basic observations in the m~crogravity environment may find practical applications to human health on Earth, perhaps in coping with the effects of prolonged bed rest.
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From page 98... ...
In orbit or in free space, however, the carotid sinus wouIcl fire nerve impulses at a more or less constant rate, subject to accelerations generally much less than one-g. The extent to which the sensitivity of the baroreceptors may decrease with prolonged space travel, and their ability to regain the lost sensitivity, ~ unknown.
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From page 99... ...
This will be essential for adequate health maintenance. Ordered In descending priority, the following classes of agents must be investigated: antiarrhythm~cs, bronchodilators, antiallergy/antianaphylactic drugs, analgesics (including narcotics)
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From page 100... ...
What, in general, should we plan for the Earth rehabilitation of long-term space travelers?
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From page 101... ...
Nutrition Background Prior to the start of the spaceflight program, there was speculation that the decreased effort of movement in weightlessness would result in a diminished caloric requirement compared to that on Earth. Diets were actually planned, however, at caloric levels close to those needed for normal activity on Earth.
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From page 102... ...
In addition, numerous previous studies unrelated to space have indicated that increasing the protein intake increases the urinary excretion of calcium. The level of protein in the diets of astronauts, therefore, needs to be reconsidered for its possible relationship to the potential for urinary tract stone formation and possibly to the rate of loss of mineral from the skeleton.
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From page 103... ...
Bed rest studies of the effects of high phosphorus intake showed some suppression of the tendency of urinary calcium to elevate, but overall phosphorus intake manipulation was ineffective because of gradually increasing fecal calcium excretion. Furthermore, the possible deleterious effect of a phosphorus intake higher than that in an approximate calcium to phosphorus ratio of 1:1.8 must be remembered.
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From page 104... ...
For most of man's evolutionary history he spent his days out-of-doors, exposed to 1000 to 8000 foot-candles of light provided by the Sun's rays (filtered through the ozone layer) , including a small but important amount of mid- and near-ultraviolet light, and approximately equal portions of the various colors of visible light.
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From page 105... ...
Hence diets should be normal in residue, and adequate bulk should be available to afford relatively easy passage of stools once or twice a day. Proposed Research In spaceflights extending from many months to years, the acceptability of various currently available packaged, canned, freezedried, or heat-stable food items should be evaluated.
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From page 106... ...
In contrast, Cogoli et al. reported that cultures of human lymphocytes subjected to microgravity responded to concanavalin A, a lymphocyte stimulating agent, 97 percent less than ground-based controls.
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From page 107... ...
These studies assume added importance because, as discussed earlier, the concentrations of microorganisms in space vehicles may be significantly higher than normal. Proposed Research Specific questions to be answered by studies ~ crogravity include the following: I
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From page 108... ...
The evolving interest in prolonged manned space travel beyond the Earth's protective magnetic field brings to the forefront uncertainties in the physical behavior and biological effects of the so-called "free spacer radiation environment. It is generally agreed that these uncertainties must be resolved before we embark on the construction of a lunar base, the manned habitation of space platforms, manned flight to Mars, or lunar or martian habitation.
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From page 109... ...
Current knowledge of the GCR hazard, however, is inadequate because of the poor understanding of the eEects of HZE particles on biological tissue. Solar particulate radiation (solar particle events)
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From page 110... ...
GCR exposure varies with orbital inclination: from approximately 5 mrad/day at 28° to approximately 20 mrad/day for polar orbit during solar minimum, and approximately 3 mrad/day at 28° to approximately 15 mrad/day for polar orbit during solar maximum. The geomagnetic field provides some degree of protection from solar particle events, depending on the orbital inclination; flux is almost totally eliminated for a 28° orbit and reduced to about 30 percent of the free space flux for polar orbit.
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From page 111... ...
Biological Effects The biological effects of ionizing radiation have been extensively studied for almost a century. The data come from studies of controlled irradiation of cell cultures, small and large animals, and nonhuman primates, as well as from retrospective studies of humans exposed to nuclear weapons blasts, radiation used for medical treatment, and nuclear occupational hazards.
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From page 112... ...
More generally, the assumed linear relationship between absorbed dose and observed biological effect has come into question for HZE particles or high-LET particles in general. Since the manner in which energy is deposited in tissue by HZE particles is so different from that of low-LET particles, this linearity may not apply to HZE particles.
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From page 113... ...
In other words, the report of Scientific Co~run~ttee 75 of the NCRP entitled Guidance on Radiation Received in Space Activities did not give any consideration to the effect of HZE particles. As we move into the future toward lunar colonization and long-term *
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From page 114... ...
, cS,rb (0.01 cm) , cS,r— 30 Days 25 100 150 Annual 50 200 300 Career 100-400C 400 600 aThese dose-equi~ralent limits are being recommended to NASA by NCRP Scientific Committee 75 on Guidance on Radiation Received in Space Activities.
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From page 115... ...
Although most space radiation doses will be low and received at low dose rates, a very large solar particle event can expose astronauts in polar orbit, in GEO, or in free space to high-dose and high-dose-rate radiation, which can produce clinically significant effects. These effects are nonstochastic: the severity of the effect increases with dose above some effective threshold.
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From page 116... ...
In the future, ex viva cell storage techniques may allow a bank of shielded autologous bone marrow to accompany astronauts on a long-duration mission. Proposed Research As we embark on an era of the U.S.
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From page 117... ...
A program of fundamental scientific research treating behavior interactions is as essential to ensure the success of long-duration human operations in space as are the physical science ~d engineering investments that make such initiatives possible. Before the long-term occupancy of space environments can be safely and productively assured, we must address the historical problems of individual behavioral adjustment, interpersonal conflict, and group performance effectiveness.
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From page 118... ...
BE havioral and social problems are regarded among those who have been involved in extended space missions to date as formidable obstacles to long-term voyages. Even more important from a life science perspective, it seems likely that entirely new principles of human interaction and group dynamics will emerge as a result of such research to ensure effective human behavior in space environments.
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From page 119... ...
Environmental Factors If long-term space missions are to become a reality, automation, robotics, artificial intelligence, and other advanced computer technologies will increasingly dorn~nate both the physical and the behavior features of space environments. This will necessitate empirical determinations of optimal "mixes" between human control and control by computerized management systems over the entire range of life support, work task, and general performance functions.
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From page 120... ...
This is one of the most difficult research questions associated with the long-term effects of continuous exposure to space environments. Perhaps the area of greatest long-range scientific promise is that of an exper~rnentally derived, functional account of individual
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From page 121... ...
Motivation plays a critical role in maintaining individual performances and amicable social interactions over extended intervals of isolation and confinement. It is essential that behavioral research explore the extent to which such motivational processes can be identified in the restricted environment of space travel.
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From page 122... ...
A promising new approach to leadership research involves focusing on the identification of those functions that leaders perform in enhancing electiveness and efficiency. Integrative Factors The goal of providing a scientific foundation for human behavioral transactions in space environments requires integration of the separately considered environmental, individual, and group factors within an organizational and systems management context.
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From page 123... ...
Thus, these studies can be one of several elements in the vigorous ground-based program in human behavioral research necessary to support any manned mission of long duration. HEALTH MAINTENANCE l~troduction As humane establish a permanent presence in space, whether it be on a space platform or in lunar or martian colonies, it is imperative that health care be provided to workers, scientists, and astronauts.
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From page 124... ...
To do so should positively affect not only the quality of care but also the quality of life sciences research. Types of Care The types of care that a health maintenance facility must provide on a minimal basis fall into four categories: prevention, treatment of dmease, treatment of injury, and rehabilitation.
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From page 125... ...
Equipment would be minimal and would not include integration of life sciences research with the health maintenance facility. A second-tier health maintenance facility would be a dedicated area for first aid and exercise.
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From page 126... ...
In the course of eight STS flights, numbers of bacteria in the spacecraft air ranged from 200 to 1300 colony forming units per cubic meter of air. Staphlyococcu~ aureus and Aspergillus species were commonly isolated from air and surface samples in these flights.
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From page 127... ...
A large number of volatile chemicals have been detected during flight, mostly within threshold limit values (TI`Vs) and NASA spacecraft maximum allowable concentration (SMAC)
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From page 128... ...
Proposed Research Although the health maintenance problems discussed in this section are primarily technical, their solutions require an understand~ng of biology and medicine often lacking in an engineering group. The task group stresses that these problems should be addressed early in the design of spacecraft and in frequent consultation with the biomedical community.
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From page 129... ...
7. Completing the research required to establish new NASA spacecraft maximum allowable concentration (SMAC)
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