Advances in space biology and medicine最新文献

The objectives of this study were to investigate the social behavior, interrelations, cohesion, efficiency and team formation of the crew during 60 days of isolation and confinement, to make a critical comparison of a variety of test methods used for this purpose and to formulate recommendations for their applications in selection, training and support for future studies of this kind. The study consisted of three phases: (1) the pre-isolation period, in which initial individual and group assessment were made to understand the motivation, characteristics, and styles of the crew members, the state of the crew, and to make a prognosis for the behavior of the group and its members, (2) the isolation period, with tests and observations to follow and analyze behavior and group dynamics of the crew, and to detect manifestations of stress, and (3) the post-isolation period with final assessment and debriefing. During these three periods individual and group tests were carried out. Direct methods, questionnaires and tests, as well as indirect methods, observations of behavior, were used. These had cognitive, affective-emotional and social components; they were quantitative, qualitative or a combination. Before isolation the crew members expressed strong confidence in the team and in their own personal capability. The leadership of the Commander seemed uncontested. Crew functioning during this period was conflict-free, but was structured in a rather rigid and defensive way (isolation of affects, denial of anxiety). Apparently, the members strongly needed to present a good image image of themselves. The relatively short period of the experiment, and the absence of real risk suggested that the crew would be able to maintain their cohesion, but in a real spaceflight situation this behavior could be inadequate and even dangerous. The pre-isolation prognosis for crew behavior during isolation was validated to a large extent. During isolation there were no clear manifestations of stress. Nevertheless, the confinement and isolation were experienced as the major stress factors. The crew members described themselves as a heterogeneous but harmonious group that was successful in their mission. In fact, the team maintained its cohesion by opposing external authority, using management as a scapegoat. Occasionally, in times of crisis, they also criticized ground crew. The Commander supported this attitude. Strongly differences in personality and behavior were noted. Analysis of the sociometric data showed that the asserted harmony was more apparent than real. It is questionable whether the group cohesion would have persisted in a life threatening crisis or even in a prolongation of the experiment. The most reliable instruments for this type of survey seem to be: group methods, non-obstructive tests, indirect instruments, and qualitative tools. The least reliable are: strictly quantitative methods, self-evaluations, standard debriefing techniques, since these rein

The EXEMSI experiment has made it clear that it is difficult to perform psychological and physiological protocols satisfactorily in the same study. It is, therefore, essential that the objectives of study be defined clearly before the start. While behavioral and psychological studies may be possible and provide valid results for a small group of mixed gender, it is more difficult to conduct valid physiological studies due to large differences between individuals and even in the same individual over time. As stated before, it is unusual in space research on humans and even during space simulation studies to have large and homogeneous groups of subjects. The consequence is that the results remain tentative. For a better understanding of the physiological data collected during the ISEMSI ad EXEMSI experiments, they should be correlated with the results of the psychological studies. One of the conclusions drawn from the ISEMSI experiment was that confinement provides a valuable parallel to other simulations of weightlessness, such as bedrest. The same pattern of changes in parameters like the blood volume regulating hormones renin and aldosterone was observed as in bedrest. After the EXEMSI study we can say that the conditions imposed by confinement, high work load, and stress, potentiate these effects. This implies that in using head-down bedrest as a weightlessness simulation the confinement effects must be identified by setting adequate control conditions for the head-down position, for short-term as well as for long-term simulations. Indeed, we have seen in the two isolation studies that confinement may have its effects at the beginning of the isolation period (EXEMSI) as well as during the entire isolation period (ISEMSI). In planning for EXEMSI we wanted to obtain more insight in some of the phenomena observed during ISEMSI by the introduction of new techniques such as the doubly labeled water method for determination of total body water. However, in some cases the opposite effects of those encountered in ISEMSI were found. This was probably due to the many changes in the experimental scenario, like number of subjects, mixed gender, living space per subject, and workload. Thus, for future isolation studies the operational scenario should be better examined and preferably standardized. Nevertheless, in such studies as well as in long-term sojourns in a space station, the crew size will not be larger than that of the EXEMSI crew. Physiologists will, therefore, have to become familiar with the study of small groups of subjects and to try to overcome the problems of large individual differences and statistical analysis of data from small groups.

Cognitive fatigue and subjective state were assessed in four healthy subject (three males and one female), confined for a period of 60 days in a hyperbaric chamber stimulating a space station environment. They were required to carry out daily a working memory/decision-making test, simulating the management of the levels of contaminants present in a spacecraft atmosphere. Information about a set of contaminants is presented on a 'reference screen.' This has to be memorized, then used to make decisions about the need for corrective action across a sequence of four 'status screens.' Subjects may check back to the reference information at any time. A low error rate was emphasized in the instructions and training. In addition to error rate, performance was also measured in terms of the time taken to make decisions and checks of reference screens (decision time and check time). Subjective measures were also made of workload and environmental resources (personal control and support), levels of anxiety and fatigue before the task, and cognitive effort expended during the task. The search for decrements during the second half of the isolation period was complicated by evidence of a continued learning process during the first half, probably because of insufficient practice before isolation. Learning curves (negative exponential functions) were fitted to the data points for the first half of the isolation period, and residuals between predicted and observed data for the second four weeks were analyzed. All subjects showed increases in decision time and check time during the last weeks of isolation, with one subject also showing an increase in errors. Workload levels were reported as moderate, but varied across the four subjects, The same was true for resources. Anxiety was low and relatively stable over the entire 60-day period, but fatigue levels were elevated during the second half. This was particularly true for the two subjects who maintained the required low error rate. Effort was also quite stable, through it tended to follow changes in work demands and fatigue. Individual subjects are seen to adapt to the stress of prolonged isolation in different ways. Two subjects maintained low error rates under increasing subjective demands by additional cognitive effort and slowing of performance. The other two subjects exhibit more widespread decrement, including high error rates, without increase in subjective demands. The analysis of individual patterns of adaptation is recommended as a way of understanding and predicting the impact of isolation and confinement during spaceflights.

In general the EXEMSI project has proved to be very successful mission. It has demonstrated that it is indeed possible to perform a major and useful project in a short time and on a moderate budget. In addition to achieving the scientific objectives, this simulation project provided valuable experience in the training of members of chamber crew and ground control crew for their tasks. It covered all aspects of a mission from call for experiment proposals, crew selection and training, integration and testing of the facility and its equipment, to daily monitoring and managing of the mission, and finally post-isolation data collection and evaluation. These other activities were accomplished by a small team of experts in the astoundingly short time of 8 months. What was lacking in manpower, time and funds, was more than made up for by enthusiasm, expertise, team spirit, hard work and long hours well beyond the call of duty of all those involved. In addition to the specific and technological objectives reached, many lessons learned in this operation have been identified, which could help to improve future missions. The experience has shown pitfalls to be avoided in future mission, as well as points where some small increase in effort can make a considerable difference. With the prospect of long-term manned spaceflights looming in the near future and the ever increasing costs of such endeavors, the possibilities offered by running simulated missions on the ground should be seriously considered. Such simulations permit the study of scientific and operational aspects of a space mission prior to its actual implementation. A ground based simulation of an extended space mission may be run at a fraction of the cost of an in-orbit precursor mission of even one-week duration. However, careful planning of the simulation mission is required so that it may yield relevant information and useful experience. Lessons learned from the EXEMSI project should be taken into account in such planning. At the start clear goals should be formulated, that can provide clear guidelines for building up the infrastructure and defining the operational scenario. A long duration mission simulating the conditions on the Russian space station MIR could provide a valuable source of information and experience in preparing for the MIR '95 Mission.

Modifications of food intake by astronauts during long-duration spaceflights have been observed. Various psychological stress factors, such as isolation, confinement, constrained community and boredom, are thought to play a role in this phenomenon. For this reason it was decided to include a nutritional investigation in the EXEMSI simulation study, in which four crew members (1 female and 3 males) were isolated and confined for 60 days in a space station-like environment. The Food and Nutritional Management System, developed for this experiment, provided on-line analysis of all available foods in terms of their nutrient content (macronutrients, water, minerals, vitamins). It permitted to keep an accurate record of the daily food intake of each crew member. The system has been shown to be a powerful tool for future missions, either simulations or actual spaceflights. It permits optimal management of food and eating on board, and offers the possibility of online analysis of the nutritional status of the crew. It can provide readily usable data for future analysis of nutritional variables in relation to other physiological and metabolic parameters. It could also supply a periodic feedback to the subject for the purpose of adjusting food intake. Eating and nutrition during the experiment were not a problem, but a pleasure, and therefore played an important role in its success. Confinement and isolation apparently had no effect on either the eating habits or the nutritional status of the crew members. The good food rather helped to decrease the potentially induced stress by providing daily periods of pleasure and of social activities. Detailed analysis of food intake showed erratic eating patterns, both before and during the experiment. However, the weekly averages of macro- and micronutrient intakes were in the normal range, except for vitamins B1 and B6 that were rather low and showed the need for supplements. Food appreciation was assessed by daily questionnaires. Satisfaction with the food provided during isolation was rated very high, and there was no feeling of hunger or monotony. The satisfaction with the food was mainly due to its high palatability, the adequate selection made with direct prior involvement of the crew, the large variety, and the extra supply that allowed the crew to choose and feel free regarding food intake. Comments from the crew afterwards clearly demonstrated that food had not been considered critical during the 60 days of isolation. This is an important fact considering the importance of food in such a restricted living environment.

EGF and related polypeptides are involved in the regulation of cell growth and differentiation of continuously regenerating tissues, in tissue repair processes and in placental and fetal development. Their initial mode of action generally constitutes binding to specific plasma membrane localized receptors, transduction of the signal across the plasma membrane, subsequent activation of signalling pathways in the cell, and the induction of early nuclear gene expression. EGF-induced signal transmission from the plasma membrane to the nucleus has been studied in microgravity in order to gain insight in the molecular mechanisms that constitute the effects of gravity on cell growth. Exposure of human A431 cells to microgravity strongly suppresses EGF- and PMA-induced c-fos and c-jun expression. In contrast, forskolin- and A23187-induced c-fos expression and constitutive beta-2 microglobulin expression remain unaffected. This suggests that microgravity differentially modulates EGF-induced signal transduction pathways. Since both EGF and PMA are known to be activators of PKC, which is not the case for forskolin and A23187, PKC-mediated signal transduction may be a cellular target for microgravity. Inhibition of EGF-induced c-fos expression by microgravity occurs downstream of the initiation of EGF-induced signal transduction, i.e., EGF binding and EGFR redistribution. In addition to PKC signaling, actin microfilament organization appears to be sensitive to microgravity. Therefore, the inhibition of signal transduction by microgravity may be related to alterations in actin microfilament organization. The fact that early gene expression is affected by agents that alter the organization of the actin microfilament system supports this hypothesis. The decrease in c-fos and c-jun expression in microgravity may result in the decreased formation of the FOS and JUN proteins. Consequently, a short-term reduction in gene expression in microgravity may have a more dramatic effect over the long term, since both the JUN and FOS protein families are required for normal cell cycle progression. However, since more than 20 years of manned spaceflight have shown that humans can survive in microgravity for prolonged periods, it appears that cells in the human body can partly or completely overcome gravitational stress. Although some insight in the molecular basis on human cells has been obtained, future studies will be needed for a better understanding of the grounds for alterations in the cellular biochemistry due to altered gravity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)