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This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. Progressing through the final decade, one pauses to reflect upon the many accomplishments of the 20th century, not the least of which is human spaceflight.
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Space Physiology and Medicine (eBook, PDF)
Astronauts coming back from long-term space missions present with different health problems potentially affecting mission performance, involving all functional systems and organs and closely resembling those found in the elderly. This review points out the most recent advances in the literature in areas of expertise in which specific research groups were particularly creative, and as they relate to aging and to possible benefits on Earth for disabled people.
Astronauts coming back from long-term space missions present with different health problems potentially affecting mission performance and closely resembling those found in the elderly.
The latter mostly involve the immune system, bones, muscles, eyes balance and coordination and the cardiovascular system Strollo, ; Vernikos, ; Vernikos and Schneider, The identification of appropriate measures of astronaut performance and of individual genetic or acquired stress resilience features has thus become a research priority along with psychological investigations designed to enhance cognitive performance, sleep, and team-building 1.
We are fully aware that this is not an exhaustive review and should be viewed as a partial synthesis of research findings in this field designed to stimulate the interest of young specialists in the direction we mentioned above. It also is designed to build on earlier reviews rather than repeat them. We will not deal with cardiovascular physiology Norsk, , which is by far the most studied system in space Scano and Strollo, , or with pulmonary physiology, an extremely important area where a few groups have done a lot of work Prisk, , as the reader can easily refer to recent dedicated reviews Antonutto and di Prampero, We chose instead to point out the most recent advances in the literature in areas of expertise in which specific research groups were proven to be creative, as well as with respect to aging and to possible benefits on Earth for disabled people.
Since the very beginning of the space era immune defects were identified in response to real and simulated microgravity Cogoli, Many research groups involved in this field confirmed those defects, such as increased virulence, antibiotic resistance, enhanced susceptibility to infections during space missions Pierson et al.
They then explored in greater detail the possible underlying molecular and systemic mechanisms Sonnenfeld and Miller, These data were used to identify appropriate countermeasures that might be most beneficial during long-duration missions per se Sonnenfeld et al. These could also be exploited for elderly people on the ground, most of whom undergo some kind of immune deficiency over time as well.
Recently, after describing space-related immune system alterations and administering a questionnaire to many experts in the field, the need for longer duration missions devoted to immune research was suggested Frippiat et al.
Animal research studied adult male mice that were exposed to chronic unpredictable mild psychosocial and environmental stressors CUMS model for 3 weeks. This period is long enough to simulate in mice a long human flight. This exposure induced an increase of serum IgA, a reduction of normalized splenic mass and reduced production of pro-inflammatory cytokines, as has been previously reported during or after space missions.
However, they did not modify either major splenic lymphocyte sub-populations or their proliferative responses, suggesting that the observed inflight changes could be due to other factors such as gravity variations Gaignier et al.
Sarcopenia is a typical aging-like effect of microgravity on the muscle-tendon unit structure and function that is still awaiting effective physical, nutritional, or pharmacological countermeasure. These could also be of benefit on Earth for the rehabilitation of injured elderly people.
Since the early space flight era, the research in the field has been extensive. Many papers have dealt with the problem of muscle changes Hargens et al. Branched chain amino-acids, however, were found to be somewhat effective, when tested during hind limb suspension in growing rats Jang et al.
After many years of poor results obtained with the exercise programs routinely carried out onboard the international space station, a possible solution may be provided by the horizontal sled jump method Kramer et al. However, compared with resistance training, whole-body vibration WBV is safer and more convenient while avoiding the risk of injury in older adults.
A recent study using 12 Hz — 3 mm WBV 10 repetitions, each lasting 60 s, followed by a 30 s resting period per session, 3 times a week for 3 months showed significantly positive effects on muscle mass, physical fitness standing on one foot, flexibility, sit-to-stand, and grip strength in sarcopenic institutionalized elderly people Chang et al. Effective signal manipulation methods are needed that are applicable to muscle wasting prevention in the elderly.
In mice. Tendon physiology still awaits greater understanding. Appropriate training should be taken into account in preventing unexplained injuries especially in elderly people trying to get fit after decades of sedentary life Magnusson and Kjaer, Insulin sensitivity changes that typically accompany aging on Earth and that gradually may progress to diabetes a condition of decompensated insulin resistance have been repeatedly reported as a consequence of space flight Tobin et al.
Based on cross-sectional intervention studies Lillioja et al. However, a paper published more recently, clearly showed that after only 4 days of bed rest both insulin sensitivity and skeletal muscle fiber cross-sectional area decreased, while capillary density increased, in healthy young subjects Montero et al.
This suggests that muscle capillaries do not primarily influence insulin sensitivity through impaired nutrient delivery in the absence of aging or pathological conditions Montero et al. Eventually, liver dysfunction may further contribute to insulin-resistance during long duration missions Jonscher et al.
Since the beginning of manned flights other possible endocrine defects involved in aging have also been investigated in space but uncertainties remain, probably due to the fact that all of them are extremely sensitive to the stress experienced by astronauts both in flight and upon re-entry. Therefore, many of the observed changes can reflect other factors rather than the effects of microgravity per se.
As for thyroid hormones, production was reported to be impaired in rats and monkeys kept at a low temperature for 2 days after a day Cosmos flight and rat thyroid hyperactivity was reported up to 14 days after re-entry Plakhuta-Plakutina et al.
In fact, this was contradicted when iodine was no longer added to drinking water for hygienic purposes as after the Spacelab 2 flight. Blunted thyroid C-cell calcitonin secretion Plakhuta-Plakutina et al. Testosterone was measured occasionally in male astronauts Smith et al. Carefully designed dedicated studies are still needed to resolve conflicting results Strollo et al.
Much more would be learned from future inflight endocrine signal measurements, which will require conditions and equipment specifically designed for space, such as miniaturization, use of dry chemistry methods or minimization of liquid handling procedures and quality control assurance of laboratory equipment analysers. A well-known negative consequence of the unloading in spaceflight is osteoporosis which also affects most of the geriatric population.
Their study has been addressed by leading groups in the field since the very beginning of the space era. We encourage young readers to study thoroughly the original work Morey-Holton and Globus, ; Alexandre and Vico, ; Cappellesso et al. With respect particularly to postflight rehabilitation needs, a very interesting finding is worth mentioning: loading during the early post-fracture stages, while matrix deposition and remodeling are prevalent, may enhance repair through the formation of additional cartilage and bone Liu et al.
In fact, not only bone but also cartilage problems have been reported in microgravity. These include smaller chondrogenic pellets, less proteoglycan synthesis and reduced dynamic stiffness of three-dimensional engineered cartilage constructs Freed et al. These observations warrant further investigation because synovial joints, which contribute to articular cartilage, subchondral bone, meniscal fibro-cartilage, tendon and ligaments bathed in synovial fluid and enclosed in a fibrous capsule, may undergo damage, especially upon reloading on return to Earth Joint instability and compensatory connective tissue changes resulting in joint degradation would follow Fitzgerald, Space osteoporosis is characterized by a lower bone formation rate and enhanced bone resorption, which calls for careful and timely preventative strategies, including Vitamin D 3 and K 2 supplementation and antiresorptive drug administration Iwamoto et al.
Bisphosphonates are the most commonly used anti-bone-resorptive drugs on Earth. Although they have also been used to prevent space-related osteoporosis, the results are conflicting Cavanagh et al. This seems to be particularly the case during unloading.
However, as significant increases in bone microarchitecture can be achieved with low-dose anti-resorptive therapy without reducing bone formation, such an anti-resorptive dosing approach could be used to preserve bone quality by limiting it to the period of disuse. This could provide astronauts with faster recovery and less adverse effects Lloyd et al. Meanwhile, the current combination of bisphosphonates with exercise Leblanc et al. A progressive decrease in night-time melatonin secretion is observed during aging accompanied by and often causing severe sleep disturbances Bubenik and Konturek, ; Duffy et al.
A similar reduction in melatonin has been reported in microgravity Holley et al. Furthermore, cosmonaut Atkov reported the discomforting absence of the sensation of putting the weight of his head down on a pillow in microgravity Vernikos, personal communication.
Others report although they seem to have slept enough hours they do not feel rested when they wake up. All of these may be responsible for disturbing normal variations in sleep-wake markers and therefore sleep and circadian rhythms need to be explored systematically both on the ground and in space, in humans and non-humans, for the sake of healthy sleep and consequent work efficiency and for better quality of life.
Related to this a recent paper was published though apparently dealing with something else: the bone resorption marker amino-terminal cross-linked collagen I telopeptide NTx was found to be increased in 20 premenopausal women volunteering for continuous wake and dim light conditions as compared to normal environmental conditions, thus confirming both the existence of an endogenous circadian rhythm in NTx with a night-time peak and the synchronizing influence of environmental factors on it St Hilaire et al.
Lower bone mineral density Kim et al. Similar effects, though maybe only additive to the already known role of muscle and bone unloading, may be expected for others with chronic circadian misalignment, such as astronauts. These should be taken into account when dealing with integrative physiology, which in fact often opens unexpected connecting paths among seemingly unrelated systems.
Cognition and behavior may be impaired in microgravity due to changes in cerebrovascular circulation including the increased blood pressure caused by the redistribution of body fluid Strollo et al. The anatomical configuration of the brain and cerebrospinal fluid CSF spaces were found to change as a consequence of long term space flight: magnetic resonance imaging MRI studies showed narrowing of the central sulcus, upward shift of the brain, and narrowing of CSF spaces at the vertex in most astronauts studied Roberts et al.
The duration and clinical significance of such findings warrants further systematic study of previously observed anatomical brain changes during bed rest and evidence from functional MRI fMRI signs of performance related cortical reorganization Roberts et al. This may be relevant to vestibular patients and elderly people with multisensory deficit syndromes or in merely inactive individuals Van Ombergen et al. Most pertinent functional studies concentrated on spatial orientation, object recognition, motion perception and high-level cognitive functions including learning, memory, reasoning and calculation Kornilova, ; Leone, ; Koga, ; Shehab and Schlegel, ; Kelly et al.
Postural stability is yet another aspect of CNS performance that is affected both by spaceflight as well as aging Demertzi et al. Increased cortico-spinal drive from leg motor cortex to lower limb motor neurons was found following postural perturbations in the elderly along with impaired perceptual processing of sensory afferent signals, which form the basis of prolonged muscle response delays during perturbed balance Ozdemir et al.
A close association between neural and muscular factors for morphological and functional adaptation to space flight was found Ohira, This led to the proposed theory that the whole postural control system is tied together by links between vestibular, visual and somatosensory information.
On Earth, these develop and are kept spontaneously active through experience of inertial and gravitational reaction forces, while in microgravity they should be actively established for postural and perceptual stability Mergner and Rosemeier, Not to mention lunar or planetary microgravity environments where gravity levels may be at or below sensory thresholds. According to this concept, biomechanics and multi-body dynamics should be taken into account, as well as, the feedback and possibly feed forward loops used for postural control, whose complexity may be impossible to resolve in the absence of current developments in computer science and robotics.
To resolve such a sophisticated puzzle as postural control may still be far from being achieved. Precise mechanisms implemented by the brain on a neural or molecular level will probably not be achieved any time soon even with the most powerful calculation tools available. Closely linked to changes occurring in the CNS, a threatening and still poorly managed side-effect of long duration space flight is optic nerve head ONH edema causing reduced visual acuity with both health and mission consequences.
The overall eye defects range from changes in refractive error and varying degrees of disk edema to globe flattening, choroidal folds, and cotton-wool spots Mader et al. How this happens is unknown and yet to be determined. It seems to be at least partly explained by increased intracranial pressure accompanying the cephalad fluid shift, venous outflow obstruction, blood-brain barrier breakdown, and disruption in CSF flow with local effects on ocular structures Wiener, , individual differences in metabolism, and the vasodilator effects of carbon dioxide Michael, A suitable treatment of ONH depends on a better understanding of the underlying mechanisms with research moving more in this direction.
Using pre- and post-flight optical coherence tomographic scans of the ONH region, global and quadrant total retinal thickness, retinal nerve fiber layer RNFL thickness and choroidal thickness have been calculated: circumpapillary RNFL thickness was found to be increased by a median of 2.
This imaging technique is now expected to allow the assessment of longitudinal changes and the development and testing of countermeasures in astronauts, as well as potentially in patients suffering from disk edema on Earth Patel et al. Another typical problem experienced by the elderly, as well as by astronauts and cosmonauts, especially at the beginning of their space flight, is motion sickness.
Selection of candidates to minimize the risk has always been the preferred solution, nevertheless training procedures have also been investigated throughout the space program. Allocating less attention to the central field during visual motion stimulation has been recently found to be associated with more stable vection and higher resistance to motion sickness Wei et al. Virtual reality application designers may use this finding to strengthen and stabilize vection, while reducing the risk of visually induced motion sickness.
On the other hand, impaired vestibular function in the elderly can result in worsened gaze stabilization with an increased risk of falling. Ocular-counterroll OCR , a gaze-stabilizing mechanism involving ocular torsion in a compensatory direction to lateral roll-tilt of the head, is predominantly mediated by the otoliths at low frequencies of motion and has been shown to be a sensitive marker of such a defect.
In fact, a reduction in OCR gain with aging correlates with increased postural sway, suggesting OCR loss may also be a useful predictor of fall risk Serrador et al. A recent paper showed that low levels of subcutaneous electrical stochastic noise SN , known to enhance weaker signals in nonlinear systems through the phenomenon of resonance, improves otolith-ocular function in aging people with impaired otolith responses without inducing hypersensitivity or other adverse effects in those with normal function.
Electrical SN may then represent an effective and well-tolerated non-invasive alternative or add-on to existing rehabilitation strategies. Moreover, its noise-based mechanism is expected to require no adaptation by neural systems, thus theoretically making long-term treatment more feasible Serrador et al. Another possible solution may be electro-acupuncture EA , a method of applying bilaterally, an electric current by means of a special device to needles fitted to specific points, i.
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Space Flight and Crew Health: Adaptation, Pathophysiology, Rehabilitation, and Countermeasures. Front Matter. Pages PDF.
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Jetzt bewerten Jetzt bewerten. As space medicine evolved from the late s onward, the need arose for a ready reference for students and practitioners on the basic concepts of this new specialty. Through three editions edited by leaders in the development of space medicine, this classic text has met the need. This fourth edition of Space Physiology and Medicine provides succinct, evidence-based summaries of the current knowledge base in space medicine and serves as a source of information on the space environment, responses, and practices. Additionally, there is extensive online material available for each chapter, featuring overviews and self-study questions.
The restricted areas will soon be open to Academicians and Corresponding Members. An email will soon be sent with instructions. Published in March , 21 pages.
What is it really like to live in space? What happens to the body in microgravity? The course will be held between 12 and 23 October Participants will be requested to attend all sessions live. During the first week of the course, students will discover how spaceflight represents a significant physiological challenge to the human body.