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Gravity Deprivation: Is It Ethical for Optimal Physiology?

Authors:
OPINION
published: 08 May 2020
doi: 10.3389/fphys.2020.00470
Frontiers in Physiology | www.frontiersin.org 1May 2020 | Volume 11 | Article 470
Edited by:
Marc-Antoine Custaud,
Université d’Angers, France
Reviewed by:
Olga Vinogradova,
Russian Academy of Sciences, Russia
Laurence Vico,
Institut National de la Santé et de la
Recherche Médicale
(INSERM), France
*Correspondence:
Jack J. W. A. van Loon
j.vanloon@amsterdamumc.nl
Specialty section:
This article was submitted to
Environmental, Aviation and Space
Physiology,
a section of the journal
Frontiers in Physiology
Received: 05 March 2020
Accepted: 16 April 2020
Published: 08 May 2020
Citation:
van Loon JJWA, Cras P,
Bouwens WHACM, Roozendaal W
and Vernikos J (2020) Gravity
Deprivation: Is It Ethical for Optimal
Physiology? Front. Physiol. 11:470.
doi: 10.3389/fphys.2020.00470
Gravity Deprivation: Is It Ethical for
Optimal Physiology?
Jack J. W. A. van Loon 1
*, Patrick Cras 2,3,4 , Willem H. A. C. M. Bouwens 5,
Willemijn Roozendaal 5and Joan Vernikos 6
1Department Oral & Maxillofacial Surgery/Pathology, Amsterdam Movement Sciences & Amsterdam Bone Center (ABC),
Amsterdam University Medical Center Location VUmc & Academic Center for Dentistry Amsterdam (ACTA), Amsterdam,
Netherlands, 2Faculty of Medicine & Health Sciences, Translational Neurosciences, University of Antwerp, Antwerp, Belgium,
3Department of Neurology, Antwerp University Hospital, Edegem, Belgium, 4Institute Born-Bunge, University of Antwerp,
Antwerp, Belgium, 5Faculty of Law, Social Law, VU University Amsterdam, Amsterdam, Netherlands, 6Thirdage Health,
Culpeper, VA, United States
Keywords: microgravity, pathology, ethics, chronic accelerations, artificial gravity, large diameter centrifuge,
countermeasure, treatment
Probably a question nobody ever asked. It goes without saying that one takes care of persons for
whom you are responsible especially when those persons totally depend on you. Papers in Frontiers,
like in a recent special issue on “Gravitational Physiology, Aging, and Medicine” (Goswami et
al., 2019) in Integrative Physiology but also in “Environmental, Aviation, and Space Physiology”
identify various issues directly related to the lack of gravity and efforts to define countermeasures
to possibly prevent pathologies. Also the recent papers by Trudel et al. (2019) regarding spaceflight
related anemia or the works by Marshall-Goebel et al. (2019) showing in-flight thrombosis clearly
illustrate our hiatus in the task of taking care when it comes to astronauts’ and cosmonauts’ health.
So, do we really take the best care of our fellow humans on their extraterrestrial travels? Based
on the work mentioned above and the recent review by Stepanek et al. (2019), it is time to raise
such health-ethics’ related questions, in particular with respect to astronauts living and working in
microgravity. Is it ethical to deprive astronauts of gravity?
Yes, astronauts are provided with food and oxygen, they are working in a cozy short-sleeve
environment, they can drink water ad lib and call their loved ones at will. However, especially
since Skylab in the 70s, it became clear that e.g., several bone parameters decreased significantly in
crew members (Bikle and Halloran, 1999), later quantified by DEXA for Shuttle and International
Space Station (ISS) crews to an average rate of 1% or more per space/month (Lang et al.,
2017). And although the crew has a strict in-flight training protocol, bone parameters stay below
pre-flight/pre-microgravity values even 1 year after return to Earth (Vico et al., 2017).
Some 50 to 75% of highly trained astronauts report suffering from the Space Adaptation
Syndrome (SAS) in their first days of flight (Waldrop, 1982). Others experience some combination
of headache, malaise, lethargy, anorexia, nausea, vomiting, and gastric discomfort during the first
few hours or even days in microgravity, despite the use of various drugs (Zhang and Hargens, 2017).
Most venture capitalists considering commercial space flight should probably think twice before
investing in a business model where there is a high probability that the majority of their potential
clientele might get sick in the first couple of days of their pricy space trip. To address this issue, a
sufficient level of gravity may be provided by a large diameter rotating space hotel.
For some years crew members began reporting vision deficiencies. This phenomenon, first
described by Mader and colleagues as VIIP (Visual Impairment due to Intracranial Pressure)
(Mader et al., 2011) and now termed Spaceflight Associated Neuro-ocular Syndrome (SANS), urged
ISS partners and especially NASA to identify a possible course of action. Recent reports argued
that very significant changes in brain morphology, in particular long duration flights of astronauts
(Roberts et al., 2017) and cosmonauts (Van Ombergen et al., 2018), might be associated to SANS.
Although no clear cause was identified, one of these might be the high level of CO2. The initial
van Loon et al. Gravity Deprivation: Is It Ethical for Optimal Physiology?
ppCO2levels in ISS started at 7.6 mm Hg (Law et al., 2014),
some 25 times higher than we have on Earth! It was later
lowered to 5.3, and because of the possible contribution of
this hypercapnia to SANS, again quickly lowered to 4.0. Law
et al. (2014) recommended a ppCO2level of 1.97 mm Hg since
this would keep the risk of headache to below 1%, a standard
threshold used in toxicology and aerospace medicine. Note the
average ppCO2on Earth at sea level is around 0.3 mm Hg. One
wonders why space agencies never reacted like this when it came
to surviving microgravity.
Space agencies are engineering entities, created to develop
and apply space related hardware and technology. Although their
main focus is to keep the crew alive and safe, long duration flight
health issues have not been fully identified and understood. As
is clear from the carbon dioxide problem but also from the less
than effective countermeasures, there is more to human health
than keeping the crew alive.
In the various definitions for Life Support Systems used
by space agencies such as NASA (U.S.A.) or the European
Space Agency (ESA), for either physicochemical or biological
systems, surprisingly there is no mention of gravity as an essential
element for maintaining a healthy environment, while oxygen or
humidity are.
In order to counteract the deleterious effects of gravity
deprivation, astronauts spend hours of valuable crew time
exercising each day. However, exercise is not tantamount to
gravity, nor do we really know how effective it is. We have
never flown an astronaut that did not exercise and therefore do
not know how much worse it would be. Even assuming that
exercise may indeed be partially beneficial, it generates other
problems, such as increased core body temperature while training
in microgravity (Stahn et al., 2017) and possibly increased
intracranial pressure due to high loads during resistive training
(Dickerman et al., 2000; Stenger et al., 2017).
Muscular and cardiovascular deconditioning are believed to
be mostly addressed by exercise countermeasures. The alternative
countermeasure of Lower Body Negative Pressure (LBNP) was
found to be only 55% effective in the case of venous blood
flow stasis (Marshall-Goebel et al., 2019). Yet, other issues
remain unsolved such as impaired cognitive performance, renal
stones, SANS, reduced immune sensitivity, loss of quality and
duration of sleep, low back pain and osteopenia, as well as post-
flight balance and coordination issues, orthostatic intolerance
or spinal compression with intervertebral disk damage (Barger
et al., 2014; Yaqub, 2015; Stepanek et al., 2019). These
are believed to be due to inadequate body gravity loading
in space.
When it comes to meeting the necessary gravity requirements
for the health and safety of astronauts, space agencies should
go beyond arguments of flight complexity and costs. What is
the price of health and safety? Systems for large radius chronic
centrifugation should form a serious part of their implementation
plans for space exploration. It is technically feasible to have large
rotating spacecraft (Joosten, 2007; Paloski and Charles, 2014;
Hall, 2016; Martin et al., 2016). Ground based devices could
be used to develop specific requirements, such as identifying
minimum gravity and radius thresholds, while, as an add-
on, treating contemporary diseases on Earth such as obesity
and aging (van Loon et al., 2012). The resources required for
an in-flight infrastructure are an investment in crew health
and well-being and as shown by Joosten (2007) the additional
cost in particular for configurations would only be around
5% supplementary structural or propellant mass. Physiological,
psychological and social well-being should be an integral part of
space station designs. It is unethical, life and mission threatening
to withhold gravity from human beings just as the denial of
oxygen would be.
As such, gravity should be regarded an integral part of a space
station Life-Support System, just as regulated oxygen, humidity,
carbon dioxide or temperature is. The exact requirements
for the minimal g-profile for adequate to optimal Earth-like
physiology in space are unknown and must be established
(National Research Council, 2018). The preferred solution is a
very large diameter rotating system, with a diameter of some
150 m (van Loon et al., 2012) or smaller at 50 to 110 m (Globus
and Hall, 2017). Though one could start with a short arm on-
board centrifuges but such systems would have problems of their
own like large body g-gradients, not exposing the whole body
including the vestibular system (Fuller et al., 2002; Levasseur
et al., 2004; Ogoh et al., 2018) to functional gravity. it is to
be expected that short-arm centrifuges will not generate the
foreseen optimal treatment. A short arm system would also not
decrease the valuable crew time spend on exercise. On the other
hand, besides providing a 1 g countermeasure, a large rotating
spacecraft could also be used to discover the long term effects
of partial gravity in a relatively safe Lower Earth Orbit (LEO)
in preparation for Moon and Mars explorations before being
confronted with the unknown effects of chronic partial Mars and
Lunar gravity.
Space agencies, as employers, carry an obligation to provide
a safe and healthy working environment for their employees.
Consequently, from a labor-legal point of view astronauts should
be provided with the necessary means to work in a healthy
environment, including the multi-system countermeasure of
chronic artificial gravity which eliminates the occupational
hazards of microgravity. A European Commission directive on
this subject states: “Within the context of his responsibilities, the
employer shall take the measures necessary for the safety and health
protection of workers, including prevention of occupational risks
and provision of information and training, as well as provision
of the necessary organization and means”(EEC_Council, 1989).
Similar wording to guide national policies is used in Convention
155 of the International Labor Organization (ILO) (International
Labor Organization, 1983).
There is also the other occupational hazard especially
prominent when going outside the protective Earth magnetic
field of the van Allen belt, i.e., solar flares and high charge and
the very energetic particles from galactic cosmic rays. For the
latter there are strong indications that such radiation is prone
to induce e.g. malignancies or retard brain functions (Delcourt
et al., 2018; Raber et al., 2019). In contrast to providing gravity to
astronauts in case of the micro-gravity hazard, it is much more
difficult to mitigate the impact of especially the galactic radiation.
Similarly, attention to a suitable station architecture, procedures
and nutritional provisions are needed as well (Bergouignan et al.,
2016).
Frontiers in Physiology | www.frontiersin.org 2May 2020 | Volume 11 | Article 470
van Loon et al. Gravity Deprivation: Is It Ethical for Optimal Physiology?
Very few papers address the ethics with respect to spaceflight.
The very high-tech and heroic nature of human spaceflight
would appear to be exempt from addressing labor-related, safe
and healthy working environments. The one example we could
find where spaceflight is related to ethical issues was actually
more linked to future commercial spaceflight and possible legal
issues for tourist customers (Marsh, 2006). However, the issue
of ethical conduct in the working environment is very current
and actually started already at the time we became aware of
the deleterious effects of long duration microgravity, quite some
decades ago.
Is it ethical to withhold gravity? No it is not! Career space
workers as well as future space tourists should be provided with
adequate levels of gravity in order to mitigate or completely
abolish the microgravity-related pathologies we currently see. It
is technologically feasible and financially achievable but most of
all unethical not to do so.
AUTHOR CONTRIBUTIONS
All authors listed have made a substantial, direct and intellectual
contribution to the work, and approved it for publication.
REFERENCES
Barger, L. K., Flynn-Evans, E. E., Kubey, A., Walsh, L., Ronda, J. M., Wang,
W., et al. (2014). Prevalence of sleep deficiency and use of hypnotic drugs in
astronauts before, during, and after spaceflight: an observational study. Lancet
Neurol. 13, 904–912. doi: 10.1016/S1474-4422(14)70122-X
Bergouignan, A., Stein, T. P., Habold, C., Coxam, V. D. O. G., and Blanc, S.
(2016). Towards human exploration of space: the THESEUS review series
on nutrition and metabolism research priorities. NPJ Microgravity 2:16029.
doi: 10.1038/npjmgrav.2016.29
Bikle, D. D., and Halloran, B. P. (1999). The response of bone to unloading. J. Bone
Miner. Metab. 17, 233–244. doi: 10.1007/s007740050090
Delcourt, C., Le Goff, M., Von Hanno, T., Mirshahi, A., Khawaja, A. P., Verhoeven,
V. J. M., et al. (2018). The decreasing prevalence of nonrefractive visual
impairment in older europeans: a meta-analysis of published and unpublished
data. Ophthalmology 125, 1149–1159. doi: 10.1016/j.ophtha.2018.02.005
Dickerman, R. D., Mcconathy, W. J., Smith, G. H., East, J. W., and
Rudder, L. (2000). Middle cerebral artery blood flow velocity in elite
power athletes during maximal weight-lifting. Neurol. Res. 22, 337–340.
doi: 10.1080/01616412.2000.11740679
EEC_Council (1989). Directive 89/391/EEC of 12 June 1989 on the Introduction of
Measures to Encourage Improvements in the Safety and Health of Workers at
Work. Official Journal L. ECC (Brussels: EEC).
Fuller, P. M., Jones, T. A., Jones, S. M., and Fuller, C. A. (2002).
Neurovestibular modulation of circadian and homeostatic regulation:
vestibulohypothalamic connection? Proc. Natl. Acad. Sci. U.S.A. 99,
15723–15728. doi: 10.1073/pnas.242251499
Globus, A., and Hall, T. (2017). Space settlement population rotation tolerance.
NSS Space Settle. J.
Goswami, N., van Loon, J., Roessler, A., Blaber, A. P., and White, O. (2019).
Editorial: gravitational physiology, aging and medicine. Front. Physiol. 10:1338.
doi: 10.3389/fphys.2019.01338
Hall, T. W. (2016). “Artificial gravity in theory and practice,” in Paper presented at
the 46th International Conference on Environmental Systems (Vienna).
International Labor Organization, I. (1983). “Occupational safety and health and
the working environment,” in Convension # 155 ed Ilo (Geneva: International
Labor Organization).
Joosten, B. K. (2007). Preliminary Assessment of Artificial Gravity Impacts to
Deep-Space Vehicle Design (JSC-63743). Houston, TX.
Lang, T., Van Loon, J., Bloomfield, S., Vico, L., Chopard, A., Rittweger,
J., et al. (2017). Towards human exploration of space: the THESEUS
review series on muscle and bone research priorities. NPJ Microgravity 3:8.
doi: 10.1038/s41526-017-0013-0
Law, J., Van Baalen, M., Foy, M., Mason, S. S., Mendez, C., Wear, M. L., et al.
(2014). Relationship between carbon dioxide levels and reported headaches
on the international space station. J. Occup. Environ. Med. 56, 477–483.
doi: 10.1097/JOM.0000000000000158
Levasseur, R., Sabatier, J. P., Etard, O., Denise, P., and Reber, A. (2004).
Labyrinthectomy decreases bone mineral density in the femoral metaphysis in
rats. J. Vestib. Res. 14, 361–365.
Mader, T. H., Gibson, C. R., Pass, A. F., Kramer, L. A., Lee, A. G., Fogarty, J.,
et al. (2011). Optic disc edema, globe flattening, choroidal folds, and hyperopic
shifts observed in astronauts after long-duration space flight. Ophthalmology
118, 2058–2069. doi: 10.1016/j.ophtha.2011.06.021
Marsh, M. (2006). Ethical and medical dilemmas of space tourism. Adv. Space Res.
37, 1823–1827. doi: 10.1016/j.asr.2006.03.001
Marshall-Goebel, K., Laurie, S. S., Alferova, I. V., Arbeille, P., Aunon-Chancellor,
S. M., Ebert, D. J., et al. (2019). Assessment of jugular venous blood flow
stasis and thrombosis during spaceflight. JAMA Netw. Open 2:e1915011.
doi: 10.1001/jamanetworkopen.2019.15011
Martin, K. M., Landau, D. F., and Longuski, J. M. (2016). Method to maintain
artificial gravity during transfer maneuvers for tethered spacecraft. Acta
Astronaut. 120, 138–153. doi: 10.1016/j.actaastro.2015.11.030
National Research Council, S. S. B. (2018). A Midterm Assessment of
Implementation of the Decadal Survey on Life and Physical Sciences Research
at NASA NAS May 2018. NAS.
Ogoh, S., Marais, M., Lericollais, R., Denise, P., Raven, P. B., and Normand, H.
(2018). Interaction between graviception and carotid baroreflex function in
humans during parabolic flight-induced microgravity. J. Appl. Physiol. (1985)
125, 634–641. doi: 10.1152/japplphysiol.00198.2018
Paloski, W. H., and Charles, J. B. (2014). 2014 International Workshop on Research
and Operational Considerations for Artificial Gravity Countermeasures, eds P.
Norsk, L. Smith, R. Cromwell, J. Kugler, C. Gilbert, and D. Baumann (Hanover,
MD: Editorial Board).
Raber, J., Yamazaki, J., Torres, E. R. S., Kirchoff, N., Stagaman, K., Sharpton,
T., et al. (2019). Combined effects of three high-energy charged particle
beams important for space flight on brain, behavioral and cognitive
endpoints in B6D2F1 female and male mice. Front. Physiol. 10:179.
doi: 10.3389/fphys.2019.00179
Roberts, D. R., Albrecht, M. H., Collins, H. R., Asemani, D., Chatterjee, A.
R., Spampinato, M. V., et al. (2017). Effects of spaceflight on astronaut
brain structure as indicated on MRI. N. Engl. J. Med. 377, 1746–1753.
doi: 10.1056/NEJMoa1705129
Stahn, A. C., Werner, A., Opatz, O., Maggioni, M. A., Steinach, M., Von Ahlefeld,
V. W., et al. (2017). Increased core body temperature in astronauts during long-
duration space missions. Sci. Rep. 7:16180. doi: 10.1038/s41598-017-15560-w
Stenger, M. B., Tarver, W. J., Brunstetter, T., Gibson, C. R., Laurie, S. S., Lee, S., et al.
(2017). Evidence Report: Risk of Spaceflight Associated Neuro-ocular Syndrome
(SANS). NASA.
Stepanek, J., Blue, R. S., and Parazynski, S. (2019). Space medicine in
the Era of Civilian spaceflight. N. Engl. J. Med. 380, 1053–1060.
doi: 10.1056/NEJMra1609012
Trudel, G., Shafer, J., Laneuville, O., and Ramsay, T. (2019). Characterizing the
effect of exposure to microgravity on anemia, more space is worse. Am. J.
Hematol. 38, 293–303. doi: 10.1002/ajh.25699
van Loon, J. J. W. A., Baeyens, J. P., Berte, J., Blanc, S., Braak, L., Bok, K., et al.
(2012). A large human centrifuge for exploration and exploitation research.
Ann. Kinesiol. 3, 107–121.
Van Ombergen, A., Jillings, S., Jeurissen, B., Tomilovskaya, E., Rühl, R.
M., Rumshiskaya, A., et al. (2018). Brain tissue-volume changes in
cosmonauts. N. Engl. J. Med. 379, 1678–1680. doi: 10.1056/NEJMc18
09011
Vico, L., Van Rietbergen, B., Vilayphiou, N., Linossier, M. T., Locrelle, H.,
Normand, M., et al. (2017). Cortical and trabecular bone microstructure did
Frontiers in Physiology | www.frontiersin.org 3May 2020 | Volume 11 | Article 470
van Loon et al. Gravity Deprivation: Is It Ethical for Optimal Physiology?
not recover at weight-bearing skeletal sites and progressively deteriorated
at non-weight-bearing sites during the year following International Space
Station missions. J. Bone Miner. Res. 32, 2010–2021. doi: 10.1002/jbmr.
3188
Waldrop, M. M. (1982). Astronauts can’t stomach zero gravity. Science 218, 1106.
doi: 10.1126/science.218.4577.1106
Yaqub, F. (2015). Space travel: medicine in extremes. Lancet Respir. Med. 3, 20–21.
doi: 10.1016/S2213-2600(14)70192-4
Zhang, L.-F., and Hargens, A. R. (2017). Spaceflight-induced
intracranial hypertension and visual impairment: pathophysiology and
countermeasures. Physiol. Rev. 98, 59–87. doi: 10.1152/physrev.00017.
2016
Conflict of Interest: The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be construed as a
potential conflict of interest.
Copyright © 2020 van Loon, Cras, Bouwens, Roozendaal and Vernikos.
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Frontiers in Physiology | www.frontiersin.org 4May 2020 | Volume 11 | Article 470
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History books are rife with examples of the role of nutrition in determining either the success or the failure of human exploration on Earth. With planetary exploration in our future, it is imperative that we understand the role of nutrition in optimizing health before humans can safely take the next giant leaps in space exploration.
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Any space exploration initiative, such as the human presence in the Moon and Mars, must incorporate plants for life support. To enable space plant culture we need to understand how plants respond to extraterrestrial conditions, adapt to them, and compensate their deleterious effects at multiple levels. Gravity is a major difference between the terrestrial and the extraterrestrial environment. Gravitropism is the process of establishing a growth direction for plant organs according to the gravity vector. Gravity signals are sensed at specialized tissues by the motion of amyloplasts called statoliths and transduced to produce a cellular polarization capable of influencing the transport of auxin. Gravity alterations eventually result in changes in the lateral balance of auxin in the root, producing deviations of the growth direction. Under microgravity, auxin changes affect the root meristem causing increased cell proliferation and decreased cell growth. The nucleolus, the nuclear site of production of ribosomes, is a marker of this unbalance, which could alter plant development. At the molecular level, microgravity induces a reprogramming of gene expression that mostly affects plant defense systems against abiotic stresses, indicating that these categories of genes are involved in the adaptation to extraterrestrial habitats. Nevertheless, no specific genes for plant response to gravitational stress have been identified. Despite this stress, plants survive, developing until the adult stage and reproducing under microgravity conditions. A major research challenge is to identify environmental factors, such as light, which could interact, modulate, or balance the impact of gravity, contributing to the tolerance and survival of plants under spaceflight conditions. Understanding the crosstalk between light and gravity sensing will contribute to the success of the next generation agriculture in human settlements outside the Earth.
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The effects of space travel have renewed importance with space tourism and plans for long‐term missions to the moon and Mars. The study of space anemia is limited by the availability of subjects and extreme conditions. An approach using the accumulated data on human space flight may characterize space anemia. 17,336 hemoglobin concentration (Hb) measures from 721 space missions and controls were used to study acute and long‐term effects of duration of exposure to space on hemoglobin decrement. Nearly half of astronauts (48%) landing after long duration missions were anemic. Returning to Earth revealed Hb decrements whose magnitude and time to recover were dependent on exposure to space: ‐0.61g/dL (4%), ‐0.82g/dL (5%) and 1.66g/dL (11%) of preflight Hb for mean exposure to space of 5.4, 11.5 and 145 days, respectively. Astronauts returning from a mean 5.4 days in space took 24 days to return to preflight Hb while astronauts 11.5‐145 days in space took 49 days. Negative effects of microgravity on Hb persisted throughout female and male astronauts’ terrestrial lives (‐0.001 and ‐0.002mg/dl Hb respectively) for every day spent in space (both p<0.05). The negative effect of exposure to space was not overcome by a statistically significant effect of being an astronaut compared to controls. Exposure to space showed a dose‐response relationship with acute and chronic Hb decrements. Space anemia contributes to the deconditioning of astronauts returning to Earth and needs to be considered for space travel to other planets, space tourism and for the care of bedridden patients. This article is protected by copyright. All rights reserved.
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Importance Exposure to a weightless environment during spaceflight results in a chronic headward blood and tissue fluid shift compared with the upright posture on Earth, with unknown consequences to cerebral venous outflow. Objectives To assess internal jugular vein (IJV) flow and morphology during spaceflight and to investigate if lower body negative pressure is associated with reversing the headward fluid shift experienced during spaceflight. Design, Setting, and Participants This prospective cohort study included 11 International Space Station crew members participating in long-duration spaceflight missions . Internal jugular vein measurements from before launch and approximately 40 days after landing were acquired in 3 positions: seated, supine, and 15° head-down tilt. In-flight IJV measurements were acquired at approximately 50 days and 150 days into spaceflight during normal spaceflight conditions as well as during use of lower body negative pressure. Data were analyzed in June 2019. Exposures Posture changes on Earth, spaceflight, and lower body negative pressure. Main Outcomes and Measures Ultrasonographic assessments of IJV cross-sectional area, pressure, blood flow, and thrombus formation. Results The 11 healthy crew members included in the study (mean [SD] age, 46.9 [6.3] years, 9 [82%] men) spent a mean (SD) of 210 (76) days in space. Mean IJV area increased from 9.8 (95% CI, −1.2 to 20.7) mm² in the preflight seated position to 70.3 (95% CI, 59.3-81.2) mm² during spaceflight (P < .001). Mean IJV pressure increased from the preflight seated position measurement of 5.1 (95% CI, 2.5-7.8) mm Hg to 21.1 (95% CI, 18.5-23.7) mm Hg during spaceflight (P < .001). Furthermore, stagnant or reverse flow in the IJV was observed in 6 crew members (55%) on approximate flight day 50. Notably, 1 crew member was found to have an occlusive IJV thrombus, and a potential partial IJV thrombus was identified in another crew member retrospectively. Lower body negative pressure was associated with improved blood flow in 10 of 17 sessions (59%) during spaceflight. Conclusions and Relevance This cohort study found stagnant and retrograde blood flow associated with spaceflight in the IJVs of astronauts and IJV thrombosis in at least 1 astronaut, a newly discovered risk associated with spaceflight. Lower body negative pressure may be a promising countermeasure to enhance venous blood flow in the upper body during spaceflight.
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The radiation environment in deep space includes the galactic cosmic radiation with different proportions of all naturally occurring ions from protons to uranium. Most experimental animal studies for assessing the biological effects of charged particles have involved acute dose delivery for single ions and/or fractionated exposure protocols. Here, we assessed the behavioral and cognitive performance of female and male C57BL/6J × DBA2/J F1 (B6D2F1) mice 2 months following rapidly delivered, sequential irradiation with protons (1 GeV, 60%), 16O (250 MeV/n, 20%), and 28Si (263 MeV/n, 20%) at 0, 25, 50, or 200 cGy at 4–6 months of age. Cortical BDNF, CD68, and MAP-2 levels were analyzed 3 months after irradiation or sham irradiation. During the dark period, male mice irradiated with 50 cGy showed higher activity levels in the home cage than sham-irradiated mice. Mice irradiated with 50 cGy also showed increased depressive behavior in the forced swim test. When cognitive performance was assessed, sham-irradiated mice of both sexes and mice irradiated with 25 cGy showed normal responses to object recognition and novel object exploration. However, object recognition was impaired in female and male mice irradiated with 50 or 200 cGy. For cortical levels of the neurotrophic factor BDNF and the marker of microglial activation CD68, there were sex × radiation interactions. In females, but not males, there were increased CD68 levels following irradiation. In males, but not females, there were reduced BDNF levels following irradiation. A significant positive correlation between BDNF and CD68 levels was observed, suggesting a role for activated microglia in the alterations in BDNF levels. Finally, sequential beam irradiation impacted the diversity and composition of the gut microbiome. These included dose-dependent impacts and alterations to the relative abundance of several gut genera, such as Butyricicoccus and Lachnospiraceae. Thus, exposure to rapidly delivered sequential proton, 16O ion, and 28Si ion irradiation significantly affects behavioral and cognitive performance, cortical levels of CD68 and BDNF in a sex-dependent fashion, and the gut microbiome.
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Ten cosmonauts, who spent an average of 189 days in space, had changes in brain volumes — mainly decreased cortical volume and increased CSF subarachnoid and ventricular volume — with some changes persisting up to an average of 7 months after return to Earth.
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Humans’ core body temperature (CBT) is strictly controlled within a narrow range. Various studies dealt with the impact of physical activity, clothing, and environmental factors on CBT regulation under terrestrial conditions. However, the effects of weightlessness on human thermoregulation are not well understood. Specifically, studies, investigating the effects of long-duration spaceflight on CBT at rest and during exercise are clearly lacking. We here show that during exercise CBT rises higher and faster in space than on Earth. Moreover, we observed for the first time a sustained increased astronauts’ CBT also under resting conditions. This increase of about 1 °C developed gradually over 2.5 months and was associated with augmented concentrations of interleukin-1 receptor antagonist, a key anti-inflammatory protein. Since even minor increases in CBT can impair physical and cognitive performance, both findings have a considerable impact on astronauts’ health and well-being during future long-term spaceflights. Moreover, our findings also pinpoint crucial physiological challenges for spacefaring civilizations, and raise questions about the assumption of a thermoregulatory set point in humans, and our evolutionary ability to adapt to climate changes on Earth.
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As space travel expands to include civilian populations in addition to trained astronauts, physicians and space medicine experts will need to collaborate to assess and mitigate risks to participants with preexisting medical conditions that may be exacerbated by microgravity.
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Topic: To estimate the prevalence of nonrefractive visual impairment and blindness in European persons 55 years of age and older. Clinical relevance: Few visual impairment and blindness prevalence estimates are available for the European population. In addition, many of the data collected in European population-based studies currently are unpublished and have not been included in previous estimates. Methods: Fourteen European population-based studies participating in the European Eye Epidemiology Consortium (n = 70 723) were included. Each study provided nonrefractive visual impairment and blindness prevalence estimates stratified by age (10-year strata) and gender. Nonrefractive visual impairment and blindness were defined as best-corrected visual acuity worse than 20/60 and 20/400 in the better eye, respectively. Using random effects meta-analysis, prevalence rates were estimated according to age, gender, geographical area, and period (1991-2006 and 2007-2012). Because no data were available for Central and Eastern Europe, population projections for numbers of affected people were estimated using Eurostat population estimates for European high-income countries in 2000 and 2010. Results: The age-standardized prevalence of nonrefractive visual impairment in people 55 years of age or older decreased from 2.22% (95% confidence interval [CI], 1.34-3.10) from 1991 through 2006 to 0.92% (95% CI, 0.42-1.42) from 2007 through 2012. It strongly increased with age in both periods (up to 15.69% and 4.39% in participants 85 years of age or older from 1991 through 2006 and from 2007 through 2012, respectively). Age-standardized prevalence of visual impairment tended to be higher in women than men from 1991 through 2006 (2.67% vs. 1.88%), but not from 2007 through 2012 (0.87% vs. 0.88%). No differences were observed between northern, western, and southern regions of Europe. The projected numbers of affected older inhabitants in European high-income countries decreased from 2.5 million affected individuals in 2000 to 1.2 million in 2010. Of those, 584 000 were blind in 2000, in comparison with 170 000 who were blind in 2010. Conclusions: Despite the increase in the European older population, our study indicated that the number of visually impaired people has decreased in European high-income countries in the last 20 years. This may be the result of major improvements in eye care and prevention, the decreasing prevalence of eye diseases, or both.
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Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight.