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PubMed2001

Physical and biological studies with protons and HZE particles in a NASA supported research center in radiation health.

NASA has established and supports a specialized center for research and training (NSCORT) to specifically address the potential deleterious effects of HZE particles on human health. The NSCORT in radiation health is a joint effort between Lawrence Berkeley National Laboratory (LBNL) and Colorado State University (CSU). The overall scope of research encompasses a broad range of subjects from microdosimetric studies to cellular and tissue responses to initial damage produced by highly energetic protons and heavy charged particles of the type found in galactic cosmic rays (GCR) spectrum. The objectives of the microdosimetry studies are to determine the response of Tissue Equivalent Proportional Counter (TEPC) to cosmic rays using ground based accelerators. This includes evaluation of energy loss due to the escape of high-energy delta rays and increased energy deposition due to the enhanced delta ray production in the wall of the detector. In this report major results are presented for 56Fe at 1000, 740, 600 and 400 MeV/nucleon. An assessment of DNA repair and early development of related chromosomal changes is extremely important to our overall understanding of enhanced biological effectiveness of high LET particle radiation. Results are presented with respect to the fidelity of the rejoining of double strand breaks and the implications of misrejoining. The relationship between molecular and cytogenetic measurements is presented by studying damage processing in highly heterochromatic supernumerary (correction of sypernumerary) X chromosomes and the active X-chromosome. One of the important consequences of cell's inability to handle DNA damage can be evaluated through mutation studies. Part of our goal is the assessment of potential radioprotectors to reduce the mutation yield following HZE exposures, and some promising results are presented on one compound. A second goal is the integration of DNA repair and mutation studies. Results are presented on a direct comparison of initial double strand breaks induction, the time course and fidelity of double strand break rejoining, cell killing and mutation induction in the same human model system. In order to understand the carcinogenic potential of protons and HZE particles, the role of damaged microenvironment in this process must be understood. In this project it has been postulated that radiation affects the microenvironment, which then modifies cell interactions in a manner conducive to neoplastic progression. Both TGF-beta and FGF-2 are important components of microenvironment. A recent result on the assessment of the role of FGF-2 and its cross-talk with TGF-beta as a function of radiation quality is presented. Theoretical modeling has so far played a central role in analyzing and integrating experimental data on repair and mutation studies and predicting new phenomena. The integrated NSCORT program also provides a broad training experience for students and postdoctoral fellows in space radiation health.

Animals↗

PubMed1995

CD4+/CD8+ T-lymphocyte ratio: effects of rehydration before exercise in dehydrated men.

Effects of fluid ingestion on CD4+/CD8+ T-lymphocyte cell ratios were measured in four dehydrated men (ages 30-46 yr) before and after 70 min of supine submaximal (71% VO2max) lower extremity cycle exercise. Just before exercise, Evans blue dye was injected for measurement of plasma volume. The subjects then drank one of six fluid formulations (12 ml.kg-1) in 3-4 min. All six mean posthydration (pre-exercise) CD4+/CD8+ ratios (Becton-Dickinson Fluorescence Activated Cell Sorter and FACScan Consort-30 software program [San Jose, CA]) were below the normal range of 1.2-1.5; mean (+/- SE) and range were 0.77 +/- 0.12 and 0.39-1.15, respectively. The post-exercise ratios increased: mean = 1.36 +/- 0.15 (P < 0.05) and range = 0.98-1.98. Regression of mean CD4+/CD8+ ratios on mean plasma osmolality resulted in pre- and post-exercise correlation coefficients of -0.76 (P < 0.10) and -0.92 (P < 0.01), respectively. The decreased pre-exercise ratios (after drinking) were probably not caused by the Evans blue dye but appeared to be associated more with the stress (osmotic) of dehydration. The increased post-exercise ratios to normal levels accompanied the rehydration and were not due to the varied electrolyte and osmotic concentrations of the ingested fluids or to the varied vascular volume shifts during exercise. Thus, the level of subject hydration and plasma osmolality may be factors involved in the mechanism of immune system modulation induced by exercise.

Adult↗

PubMedDate not supplied

Analysis and modeling of information flow and distributed expertise in space-related operations.

Evolving space operations requirements and mission planning for long-duration expeditions require detailed examinations and evaluations of information flow dynamics, knowledge-sharing processes, and information technology use in distributed expert networks. This paper describes the work conducted with flight controllers in the Mission Control Center (MCC) of NASA's Johnson Space Center. This MCC work describes the behavior of experts in a distributed supervisory coordination framework, which extends supervisory control/command and control models of human task performance. Findings from this work are helping to develop analysis techniques, information architectures, and system simulation capabilities for knowledge sharing in an expert community. These findings are being applied to improve knowledge-sharing processes applied to a research program in advanced life support for long-duration space flight. Additional simulation work is being developed to create interoperating modules of information flow and novice/expert behavior patterns.

Communication↗

PubMed1999

Searching for biological rhythms: peak detection in the periodogram of unequally spaced data.

The classical power spectrum, computed in the frequency domain, outranks traditionally used periodograms derived in the time domain (such as the chi2 periodogram) regarding the search for biological rhythms. Unfortunately, classical power spectral analysis is not possible with unequally spaced data (e.g., time series with missing data). The Lomb-Scargle periodogram fixes this shortcoming. However, peak detection in the Lomb-Scargle periodogram of unequally spaced data requires some careful consideration. To guide researchers in the proper evaluation of detected peaks, therefore, a novel procedure and a computer program have recently become available. It is recommended that the Lomb-Scargle periodogram be the default method of periodogram analysis in future biomedical applications of rhythm investigation.

Computer Simulation↗

PubMed1999

Monte Carlo mixture model of lifetime cancer incidence risk from radiation exposure on shuttle and international space station.

Estimating uncertainty in lifetime cancer risk for human exposure to space radiation is a unique challenge. Conventional risk assessment with low-linear-energy-transfer (LET)-based risk from Japanese atomic bomb survivor studies may be inappropriate for relativistic protons and nuclei in space due to track structure effects. This paper develops a Monte Carlo mixture model (MCMM) for transferring additive, National Institutes of Health multiplicative, and multiplicative excess cancer incidence risks based on Japanese atomic bomb survivor data to determine excess incidence risk for various US astronaut exposure profiles. The MCMM serves as an anchor point for future risk projection methods involving biophysical models of DNA damage from space radiation. Lifetime incidence risks of radiation-induced cancer for the MCMM based on low-LET Japanese data for nonleukemia (all cancers except leukemia) were 2.77 (90% confidence limit, 0.75-11.34) for males exposed to 1 Sv at age 45 and 2.20 (90% confidence limit, 0.59-10.12) for males exposed at age 55. For females, mixture model risks for nonleukemia exposed separately to 1 Sv at ages of 45 and 55 were 2.98 (90% confidence limit, 0.90-11.70) and 2.44 (90% confidence limit, 0.70-10.30), respectively. Risks for high-LET 200 MeV protons (LET=0.45 keV/micrometer), 1 MeV alpha-particles (LET=100 keV/micrometer), and 600 MeV iron particles (LET=180 keV/micrometer) were scored on a per particle basis by determining the particle fluence required for an average of one particle per cell nucleus of area 100 micrometer(2). Lifetime risk per proton was 2.68x10(-2)% (90% confidence limit, 0.79x10(-3)%-0. 514x10(-2)%). For alpha-particles, lifetime risk was 14.2% (90% confidence limit, 2.5%-31.2%). Conversely, lifetime risk per iron particle was 23.7% (90% confidence limit, 4.5%-53.0%). Uncertainty in the DDREF for high-LET particles may be less than that for low-LET radiation because typically there is very little dose-rate dependence. Probability density functions for high-LET radiation quality and dose-rate may be preferable to conventional risk assessment approaches. Nuclear reactions and track structure effects in tissue may not be properly estimated by existing data using in vitro models for estimating RBEs. The method used here is being extended to estimate uncertainty in spacecraft shielding effectiveness in various space radiation environments.

Adult↗

PubMed1993

The relationship between space sickness and preflight diet.

The nine astronauts who flew three Skylab missions during 1973 and 1974 were on carefully planned diets. Each astronaut selected his preferences from a list of approximately 70 food items, from which dietitians developed a rotating sequence of six daily menus. In addition to strict control of the inflight diet, each crewman consumed his planned diet for 21 days preflight and for 18 days postflight. While the amount consumed at each particular meal was largely discretionary, all deviations from the planned meals (which were few) were fully documented. Diets were controlled to provide adequate calcium, phosphorus, and protein because of bone and muscle losses observed on previous flights. Each day's menu had a similar elemental composition; if any particular item was not consumed, supplements in the form of capsules or tablets were prescribed the next day to make up for the shortfall. However, the dieticians did not so carefully control the relative proportions of carbohydrate, fat, and protein (though meticulous records were kept), which were instead selected somewhat incidentally as menus were constructed around each astronaut's food preferences. There are several possible physiologic determinants for food preferences and the regulation of dietary macro-nutrients. Monozygotic twins chose more similar intakes of total energy, protein, fat, and carbohydrate than did dizygotic twins, suggesting a genetic component of dietary regulation. The biosynthesis of neurotransmitters is directly influenced by the availability of their precursor nutrients, such as tryptophan for serotonin and choline for acetylcholine. Diet affects behavior, and it has been suggested that dietary self-selection by rats is regulated by effects of the diet on brain neurotransmitters. Some preflight variables relating to fluid, electrolyte and cardiovascular status, and to environmental exposures, have previously been found to have significant relationships to space sickness. The purpose of this study was to determine if diet could be another factor contributing to space sickness, since diet determines so much of physiology and behavior.

Diet Records↗

PubMed1996

Diet and nitrogen metabolism during spaceflight on the shuttle.

Human spaceflight is associated with a loss of body protein. To investigate this problem, dietary intake, nitrogen balance, the whole body protein, and fibrinogen protein synthesis rates were measured on the crews of two Spacelab Life Sciences (SLS) shuttle missions before, during, and after spaceflight. The first mission, SLS-1, lasted 9.5 days, and the second, SLS-2, lasted 15 days. The 15N-glycine method was used for the protein synthesis measurements. The following results were obtained. 1) There was a rapid decline in weight for the first 5 days and then the body weight appeared to stabilize. 2) The mean energy intake preflight was 39.0 +/- 2.5 kcal x kg-1 x day-1 (n = 10). There was a sharp drop in dietary intake on flight day 1, with recovery by the second day, and then energy intake was constant at 30.4 +/- 1.5 kcal x kg-1 x day-1 (n = 12) for the remainder of the flight period (P < 0.05). 3) Nitrogen retention was decreased during flight, with the magnitude of the decrease lessening toward the end of the mission. The daily mean nitrogen balance changed from 58 +/- 9 mg x kg-1 x day-1 (n = 9) preflight to 16 +/- 3 mg N x kg-1 x day-1; P < 0.05; n = 11) in flight, corresponding to a loss of approximately 1 kg of lean body mass over 14 days. 4) Whole body protein synthesis was increased early in flight and on recovery, as was fibrinogen synthesis. We conclude that 1) the rapid readjustment and stabilization of energy intake and the improved nitrogen retention with increasing flight duration are consistent with a rapid metabolic accommodation to the novel environment; and that 2) the increased protein turnover indicates that a metabolic stress response is an important factor in this adjustment process.

Adult↗

PubMed2000

[Individual peculiarities of adaptation to long-term space flights: 24-hour heart rhythm monitoring].

Presented are results of studying 24-hr variability of the cardiac rhythm which characterizes individual difference in reactions of two crew members to the same set of stresses during a 115-day MIR mission. Spacelab (USA) cardiorecorders were used. Data of monitoring revealed significantly different baseline health statuses of the cosmonauts. These functional differences were also observed in the mission. In one of the cosmonauts, the cardiac regulation changed over to a more economic functioning with the autonomous balance shifted towards enhanced sympathetic activity. After 2-3 months on mission he had almost recovered pre-launch level of regulation. In the other, the regulatory system was appreciably strained at the beginning of the mission as compared with preflight baseline. Later on, on flight months 2-3, this strain kept growing till a drastic depletion of the functional reserve. On return to Earth, this was manifested by a strong stress reaction with a sharp decline in power of high-frequency and grow in power of very low frequency components of the heart rhythm. The data suggest that adaptation to space flight and reactions in the readaptation period are dependent on initial health status of crew members, and functional reserve.

Adaptation, Physiological↗

PubMed2000

How the science and engineering of spaceflight contribute to understanding the plasticity of spinal cord injury.

Space programs support experimental investigations related to the unique environment of space and to the technological developments from many disciplines of both science and engineering that contribute to space studies. Furthermore, interactions between scientists, engineers and administrators, that are necessary for the success of any science mission in space, promote interdiscipline communication, understanding and interests which extend well beyond a specific mission. NASA-catalyzed collaborations have benefited the spinal cord rehabilitation program at UCLA in fundamental science and in the application of expertise and technologies originally developed for the space program. Examples of these benefits include: (1) better understanding of the role of load in maintaining healthy muscle and motor function, resulting in a spinal cord injury (SCI) rehabilitation program based on muscle/limb loading; (2) investigation of a potentially novel growth factor affected by spaceflight which may help regulate muscle mass; (3) development of implantable sensors, electronics and software to monitor and analyze long-term muscle activity in unrestrained subjects; (4) development of hardware to assist therapies applied to SCI patients; and (5) development of computer models to simulate stepping which will be used to investigate the effects of neurological deficits (muscle weakness or inappropriate activation) and to evaluate therapies to correct these deficiencies.

Animals↗

PubMed1994

Solar modulation and nuclear fragmentation effects in galactic cosmic ray transport through shielding.

Crews of manned interplanetary missions may accumulate significant radiation exposures from the galactic cosmic ray (GCR) environment in space. Estimates of how these dose levels are affected by the assumed temporal and spatial variations in the composition of the GCR environment, and by the effects of the spacecraft and body self-shielding on the transported radiation fields are presented. In this work, the physical processes through which shielding alters the transported radiation fields are described. We then present estimates of the effects on model calculations of (1) nuclear fragmentation model uncertainties, (2) solar modulation, (3) variations between solar cycles, and (4) proposed changes to the quality factors which relate dose equivalent to absorbed dose.

Aluminum↗

PubMed2002

Medical care system for NASA-Mir spaceflights.

A fundamental goal of space medicine is to maintain the health and fitness of spacecrews. Meeting this goal requires reliable, effective, up-to-date medical support systems for use in microgravity. This article describes some of the factors considered in the design and assembly of Russian and U.S. in-flight medical care systems. The successful mutual use of U.S. and Russian medications and medical equipment under the NASA-Mir program conclusively demonstrated the importance and advantages of cooperation among participating space agencies. Continued progress toward the integration of U.S. and Russian flight medical systems will further increase the effectiveness of the medical support of joint missions aboard the International Space Station.

Emergency Medical Services↗

PubMed1991

Radiological health risks for exploratory class missions in space.

Crewmembers on missions to the Moon or Mars will be unavoidably exposed to ionizing radiation as they pass through the Van Allen belts and the Galactic Cosmic Ray (GCR) flux. There is the possibility for exposure to proton radiation from Solar Particle Events (SPE). Using absorbed doses and ICRP 26, Linear Energy Transfer (LET) -dependent quality factors, the following dose-equivalents are estimated: In a spacecraft with 0.75 cm aluminum walls (2 g/cm2) at solar minimum, the lunar round trip dose-equivalent is less than 0.05 Sv. During a Mars mission the estimated dose-equivalents are: outbound (Van Allen Belts) <0.02 Sv; Earth to Mars (205 days exposure to free space GCR) 0.32 Sv; 30 days on the Martian surface (GCR) 0.023 Sv; Mars to Earth (225 days exposure to free space) 0.35 Sv; and through the Van Allen Belts 0.02 Sv. Conventionally, the total of 0.73 Sv over 460 days could be expected to increase the risk of cancer mortality in a 35-year old male astronaut by about one percent. However three-fourths of the dose-equivalent in free space is contributed by high LET heavy ions (Z > or = 3) and target fragments with average quality factors of 10.3 and 20 respectively. The biological effectiveness of these radiations is poorly understood; so the quality factors are set at conservatively very high values. The entire concept of absorbed dose/quality factor/dose-equivalent as applied to GCR must be reconsidered.

Animals↗

PubMed1995

Factors in daily physical activity related to calcaneal mineral density in men.

To determine the factors in daily physical activity that influence the mineral density of the calcaneus, we recorded walking steps and the type and duration of exercise in 43 healthy 26-to 51-yr-old men. Areal (g.cm-2) calcaneal bone mineral density (CBMD) was measured by single energy x-ray densitometry (SXA, Osteon, Inc., Wahiawa, HI). Subjects walked a mean (+/- SD) of 7902 (+/- 2534) steps per day or approximately 3.9 (+/- 1.2) miles daily. Eight subjects reported no exercise activities. The remaining 35 subjects spent 143 (2-772) (median and range) min.wk-1 exercising. Twenty-eight men engaged in exercise activities that generate single leg peak vertical ground reaction forces (GRFz) of 2 or more body weights (high loaders, HL), and 15 reported exercise or daily activities that typically generate GRFz less than 1.5 body weights (low loaders, LL). CBMD was 12% higher in HL than LL (0.668 +/- 0.074 g.cm-2 vs 0.597 +/- 0.062 g.cm-2, P < 0.004). In the HL group, CBMD correlated to reported minutes of high load exercise (r = 0.41, P < 0.03). CBMD was not related to the number of daily walking steps (N = 43, r = 0.03, NS). The results of this study support the concept that the dominant factor in daily physical activity relating to bone mineral density is the participation in site specific high loading activities, i.e., for the calcaneus, high calcaneal loads.

Absorptiometry, Photon↗

PubMed1991

Metabolic changes observed in astronauts.

Study of metabolic alterations that occur during space flight can provide insight into mechanisms of physiologic regulation. Results of medical experiments with astronauts reveal rapid loss of volume (2 L) from the legs and a transient early increase in left ventricular volume index. These findings indicate that, during space flight, fluid is redistributed from the legs toward the head. In about 2 days, total body water decreases 2 to 3%. Increased levels of plasma renin activity and antidiuretic hormone while blood sodium and plasma volume are reduced suggest that space flight-associated factors are influencing the regulatory systems. In addition to fluid and electrolyte loss. Skylab astronauts lost an estimated 0.3 kg of protein. Endocrine factors, including increased cortisol and thyroxine and decreased insulin, are favorable for protein catabolism. The body appears to adapt to weightlessness at some physiologic cost. Readaptation to Earth's gravity at landing becomes another physiologic challenge.

Humans↗

PubMed2005

Life, survival, and behavioral health in small closed communities: 10 years of studying isolated Antarctic groups.

In the late 1980s the Australian Antarctic Division collaborated with NASA to use the Australian National Antarctic Research Expeditions' (ANARE) stations to pursue research of benefit to both programs. This article outlines the data collection efforts, the development of analyses, and selected results, and describes some of the benefits for the aerospace, health, and environmental psychology communities. The Behavior and Performance Laboratory at Johnson Space Center developed a questionnaire to sample broadly the many aspects of life in extreme environments analogous to space missions. Data were collected from volunteers involved in various ANAREs conducted from 1994 to 2003. Pool-timed series regression, hierarchical models, and content analysis have all enhanced the understanding of the kinds of psychosocial variables relevant in extreme environments, and how these variables relate to each other; examples are given. Observations gathered over the last 10 yr comprise a unique, comprehensive, and advanced representation of psychosocial factors in this extreme environment and provide a strong base for future research and application.

Adaptation, Psychological↗

PubMed1995

The food-process subsystem for CELSS: a conceptual analysis.

A controlled ecological life support system (CELSS) is required to sustain life for future long-duration space missions. Food processing is an important subsystem component of a CELSS. Factors for designing the food-process subsystem are identified and characterized in this analysis. Interactions of the subsystem with other subsystems in a CELSS are also discussed.

Crops, Agricultural↗

PubMed1997

Deviance among expeditioners: defining the off-nominal act through space and polar field analogs.

The space venture resembles other extreme environmental exploration in many respects. Since the beginning of the space program, social and behavioral scientists have predicted that space crews increasingly will begin to experience the kinds of deviant behaviors seen in other extreme environmental duty settings as mission duration, crew size, and heterogeneity increases. However, there has been a long history of neglect by the nation's space agency of those psychosocial human factors which will play such a vital role in future manned spaceflight. The author argues that this is counterproductive, even dangerous, and that social and behavioral studies must be conducted to generate baseline data regarding dysfunctional acts in extreme environments, including the milieu of the space mission. An obstacle to studying occurrences and frequencies of deviant acts is the absence of a standardized definition of such acts in the extreme environment. Borrowing the sanitized NASA term "off-nominal", which generally refers to a maladaptive action, a preliminary reliability test was conducted among five scientists who work with human interaction in extreme environments. They were asked to rate situations from several actual space and polar expeditions for numbers of off-nominal acts. They were told the object of the exercise was to derive a standardized definition and were not provided with any specific definition of off-nominality. Substantial agreement in their ratings provided reliable information to construct a working definition of off-nominality. Various interactions and behaviors which respondents deemed off-nominal could be subsumed under poor expertise, mental disorder, forms of abuse and interpersonal insensitivity, problems of authority and responsibility, task deficits, poor hygiene and fitness, poor field-base communication, and human error with equipment from violating safety procedures and poor judgment as to its usage.

Adaptation, Psychological↗

PubMed1996

Subnormal norepinephrine release relates to presyncope in astronauts after spaceflight.

Postflight orthostatic intolerance is experienced by virtually all astronauts but differs greatly in degree of severity. We studied cardiovascular responses to upright posture in 40 astronauts before and after spaceflights lasting up to 16 days. We separated individuals according to their ability to remain standing without assistance for 10 min on landing day. Astronauts who could not remain standing on landing day had significantly smaller increases in plasma norepinephrine levels with standing than did those who could remain standing (105 +/- 41 vs. 340 +/- 62 pg/ml; P = 0.05). In addition, they had significantly lower standing peripheral vascular resistance (23 +/- 3 vs. 34 +/- 3 mmHg.1l-1).min; P = 0.02) and greater decreases in systolic (-28 +/- 4 vs. -11 +/- 3 mmHg; P = 0.002) and diastolic (-14 +/- 7 vs. 3 +/- 2 mmHg; P = 0.0003) pressures. The presyncopal group also had significantly lower supine (16 +/- 1 vs. 21 +/- 2 mmHg.1l-1).min; P = 0.04) and standing (23 +/- 2 vs. 32 +/- 2 mmHg.1l-1).min; P = 0.038) vascular resistance, supine (66 +/- 2 vs. 73 +/- 2 mmHg; P = 0.008) and standing (69 +/- 4 vs. 77 +/- 2 mmHg; P = 0.007) diastolic pressure, and supine (109 +/- 3 vs. 114 +/- 2 mmHg; P = 0.05) and standing (99 +/- 4 vs. 108 +/- 3 mmHg; P = 0.006) systolic pressures before flight. This is the first study to clearly document these differences among presyncopal and nonpresyncopal astronauts after spaceflight and also offer the possibility of preflight prediction of postflight susceptibility. These results clearly point to hypoadrenergic responsiveness, possibly centrally mediated, as a contributing factor in postflight orthostatic intolerance. They may provide insights into autonomic dysfunction in Earthbound patients.

Adult↗