Recapturing a Future for Space Exploration Life and Physical Sciences Research for a New Era (2011) / Chapter Skim
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7 Crosscutting Issues for Humans in the Space Environment
7 Crosscutting Issues for Humans in the Space Environment
Pages 205-248
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From page 205... ...
Consider the effects of reduced mechanical loading on bone and muscle loss in space. Whereas the effects of reduced loading per se on the individual systems are discussed thoroughly in Chapter 6 using a vertical translation strategy, detrimental changes in musculoskeletal mass and function in the space environment may be further influenced by horizontal integration of multiple factors that include, but are 205
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From page 206... ...
Decompression Sickness Human spaceflights in low Earth orbit or on exploration missions to the Moon, asteroids, or Mars all require many thousands of hours of extravehicular activity (EVA) and inherently carry a higher risk of decompression sickness.1 Suits are necessarily designed to operate at as low a pressure as practicable (e.g., Apollo, 3.8 psi; space shuttle/International Space Station (ISS)
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From page 207... ...
Knowing the lowest suit pressure and compatible habitat atmospheres that would allow EVA without pre breathe is important for space exploration missions. Crews could live in an 8 psi, 32 percent O 2 habitat and perform EVAs in a conventional 4.2 psi, 100 percent O2 suit without prebreathe.
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From page 208... ...
However, the amount of surface EVA activity on exploration missions potentially far exceeds that on the space shuttle and the ISS, so the statistical likelihood of a DCS episode is higher. The effect of gravitational level on DCS incidence is not well understood.
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From page 209... ...
Space Motion Sickness Of all the physiological difficulties astronauts encounter during their first days in orbit, space motion sick ness has been the most overt and prevalent. Symptoms are often triggered by head and body movements or visual disorientation in the microgravity environment.40,41 There were no reports of space sickness in the Mercury or Gemini program, probably because the cabins were so small that the crew had limited ability to move around.
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From page 210... ...
Existing anti-motion sickness drugs are sedating and only partially effective, so they are used primarily for treatment in orbit, rather than prophylaxis. Space sickness will doubtless affect passengers and crews on commercial orbital and suborbital flights and during the early microgravity and post-return days of future transportation system options.
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From page 211... ...
ISS studies are needed of cognitive side effects of anti-motion sickness drugs under operational conditions. Recommendations More effective and operationally acceptable motion sickness countermeasures will soon be needed if com mercial suborbital and orbital flights are to succeed.
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From page 212... ...
Supine and seated crews must eventually stand up after landing, and even with fluid loading the prevalence of orthostatic hypotension on the day of landing has been 20 to 30 percent after 1- to 2-week space shuttle missions and at least 80 percent after long-duration flights. The origin of individual differences in postflight orthostatic tolerance and neurovestibular vertigo and ataxia is not well understood.
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From page 213... ...
For the success of long-duration space missions, it is also essential that the diet remains nutritionally complete for the prescribed amount of time and that steps are taken to ensure that individuals consume appropriate amounts of the diet's elements to meet their nutrient and energy needs. Impact of Spaceflight on Nutritional Status, Nutrient and Energy Intake, and Nutrient Stability in the Food Supply Nutritional Status in Space A substantial amount of information has been generated about nutrient status in space, although data are lack ing on the mechanisms by which nutrient status in space differs from that on Earth.
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From page 214... ...
. Acidotic conditions promote bone loss and kidney stone formation because of release of calcium as part of a compensatory mechanism.77 Nutrient Stability in the Astronaut Food Supply Under space conditions, nutrients are obtained from food, with the single exception being supplementation for vitamin D
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From page 215... ...
A recent report from the latter study suggests that storage conditions are more important than exposure to microgravity, because both ground controls and space-flown foods decreased in nutri ent potency over time.80 However, the ISS may provide limited information related to exposure to space radiation that would occur on the Moon or Mars. Thus, to date NASA has had to rely on published data from external shelf life studies as guidance in designing diets and optimizing processing conditions for long-duration spaceflight.
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From page 216... ...
However, an integrative approach across all human studies in which nutrition and energy intake could be controlled or documented is missing. Valuable data are lost when, for example, human intervention studies are done on countermeasures to protect against muscle wasting, bone loss, cardiovascular effects, and immune response without any documentation as to what the subjects were eating or if they were meeting their energy requirements.
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From page 217... ...
Radiation Biology Space Radiation Biology Today The area of space radiation biology has been studied in detail in recent years, with the NRC issuing several reports on the current status of the field, including strengths and weaknesses in the existing programs sponsored by NASA.83,84,85 Further, the most recent NRC report, Managing Space Radiation Risk in the New Era of Space Exploration,86 reviewed the current knowledge of the radiation environments likely to be experienced by astronauts; the effects of radiation on biological systems, electronics, and missions; and NASA's current protection plans. The findings and recommendations from that report covered a number of issues relevant to the current report, including (1)
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From page 218... ...
, which runs Brookhaven National Laboratory, and NASA, which uses the facility to generate protons and heavy charged ions that can be used for irradiation.92 While there is one proton facility used by NASA at Loma Linda University, the NSRL is the only facility in the United States that can generate appropriate heavy ions and mixed field beams for NASA's studies requiring simulated space radiation. Thus, this facility -- and as a consequence the partnership with DOE -- is essential for NASA's space radiation biology endeavors not only now but also well into the future; assurance of this continued cooperation is therefore important.
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From page 219... ...
and into radiation countermeasures. Space Radiation Biology in the Next Decade The heart of NASA's radiation biology program during the coming decade will be the development of a better understanding of radiation risks associated with spaceflight.
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From page 220... ...
This is likely to impact space radiation biology significantly in the coming decade. Continued interaction of NASA with other agencies such as DOE will facilitate this transition within NASA, since DOE has a well-developed systems biology group for studying radiation effects.
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The inclusion of training programs for graduate students, postdoctoral fellows, and junior faculty members will be essential for ensuring a proper cadre of personnel trained in radiation biology and radiation sciences and able to address questions relevant to NASA's space radiation needs. The relationship with NIAID (counterterrorism and countermeasures)
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From page 222... ...
However, studies of large population groups have found gender differences in anthropometry, exercise capacities, and sensory function. Women tend to have a higher percentage of body fat, less muscle mass, more flexibility, and lower blood pressure.136 Women may have a more aggressive immune response to an infectious challenge, but are thought to be more susceptible to autoimmune diseases.
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From page 223... ...
An effort should be made to address this issue, to be certain that physics and not legacy determines who can participate in EVA. From limited ground-based comparisons, exercise countermeasures are similarly effective in men and women in terms of maintaining aerobic capacity165 and muscle strength.166 A critical area of research is to develop countermeasures for bone loss during spaceflight, because low bone mass (more common in women)
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From page 224... ...
More studies, with larger numbers of animals, are in progress, particularly using the resources of the NSRL, although little attention has yet been paid to gender differences. DOE conducted a series of large-scale animal studies from the 1960s to the1990s examining gender effects in mice and dogs exposed to high-LET neutrons (which have biological properties similar, although not identical, to those of heavy charged particles in space radiation and can be produced by interactions of charged particles in spacecraft and in astronauts' bodies)
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From page 225... ...
Also, whenever feasible, modifications to the EVA suit design should accommodate smaller individuals or crew members with less upper body strength, to enhance mobility during EVA tasks. Summary and Conclusions The most significant gender issues that should be addressed in the next decade include an understanding of possible differences in bone loss and radiation risks and development of effective countermeasures.
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From page 226... ...
During spaceflight, conductive heat loss becomes an issue when the insulative property of the EVA suit is insuf ficient to prevent heat exchange between the astronaut and a surface in contact with the astronaut. For example, due to insufficient glove insulation a crew member experienced frostbite while training for an EVA to repair the Hubble Space Telescope.189 Convective heat exchange refers to the exchange of thermal energy between hot and cold objects by the physical transfer of matter such as a liquid or gas.
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From page 227... ...
Because of changes in blood flow distribution and increased peripheral blood flow after adaptation to microgravity, there may be an accumulation of heat near the surface of the skin and under clothing. Changes in convective heat exchange may alter thermal com fort and must be considered when choosing clothing and environmental conditions in the spacecraft or EVA suit.
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From page 228... ...
Animal Models Altered circadian control of body temperature during spaceflight has been demonstrated in primates, rats, beetles, and even fungi.218 In constrained primates, spaceflight is associated with an early drop in core tempera ture,219 a dampening of circadian temperature fluctuation, and desychronization of circadian rhythm. 220,221,222 Animal models in microgravity or simulated microgravity may be required to study physiological responses and molecular pathways that determine thermotolerance.
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Summary and Conclusions Maintaining a safe level of body temperature is critical for the health and productivity of the crew during spaceflight. Normally, humans thermoregulate within an approximately 5°C range of core temperature (35°C to 40°C)
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, which now represent the nation's major capability for intensive patient-oriented research -- for example, as might be required in microgravity models such as bed rest, nutritional interventions, exercise interventions, energy balance, drug trials, and imaging capabilities that permit visualization of human physiology in real time. Findings and Recommendations The reorganization of the nation's biomedical research infrastructure into a clinical translational science network represents a substantial opportunity for NASA to emulate and to partner in this 21st century approach to applying new biomedical knowledge.
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From page 231... ...
It is fortunate that the full ISS capability comes when NIH is rolling out its national CTSA network. There is, at one level, an analogy between the CTSA Clinical Research Units, which provide the capability for complex and intensive clinical studies of basic and clinical physiology and pathophysiology, and the U.S.
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From page 232... ...
NIH Program Announcement 09-120, "Biomedical Research on the International Space Station," is a notable example of such cooperation, but it is limited to cell biology and molecular biology experiments. Building on this model, the facilities of the CTSA Clinical Research Units could be made available to NASA as a research capability for bed rest studies and complex land-based protocols that could provide preliminary data for future research on the U.S.
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From page 233... ...
. While this specific interaction has received the greatest attention, there are 14 drugs in the current space shuttle and ISS formularies that have CYP2D6 effects.
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International Collaboration Between Space Agencies There is a need to reinvigorate international scientific cooperation, specifically the International Space Life Sciences Working Group. Such cooperation worked well in the decades before 2000 and will undoubtedly reduce costs to NASA.
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(CC2) EVA Because human space exploration involves significant EVA activity, the risk of decompression sickness must be mitigated.
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(CC7) Animal Studies Much of the ongoing work in the field of space radiation biology is being done at the molecular and cellular levels in order to identify end points that should be examined in whole animals.
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Effective use of the International Space Life Sciences Working Group and joint research announcements will promote efficient use of resources and internationalize space life sciences, offering opportunities for collaboration in ground studies prior to flight experiments.
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2008. A Constrained Space Exploration Technology Program: A Review of NASA's Explora tion Technology Development Program.
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2007. Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins.
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From page 240... ...
2005. The nutritional status of astronauts is altered after long-term space flight aboard the International Space Station.
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From page 241... ...
2008. Managing Space Radiation Risk in the New Era of Space Exploration.
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From page 242... ...
2010. p53-dependent adaptive responses in human cells exposed to space radiations.
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From page 243... ...
2008. WISE-2005: Supine treadmill exercise within lower body negative pressure and flywheel resistive exercise as a countermeasure to bed rest-induced bone loss in women during 60-day simulated microgravity.
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From page 244... ...
European Journal of Applied Physiology 105(6)
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From page 245... ...
2007. Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins.
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From page 246... ...
1991. Our experience in the evaluation of the thermal comfort during space flight and in the simulated space environment.
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From page 247... ...
2007. Use of Thermoregulatory Models to Enhance Space Shuttle and Space Station Operations and Review of Human Thermoregulatory Control.
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From page 248... ...
2008. Heavy ion carcinogenesis and human space exploration.
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