Page 58 - International Space Station Benefits for Humanity, 3rd edition.

in physical fitness and an increase in sensorimotor astronauts after spaceflight. Increase in artery stiffness
impairment. These results raise new questions about and thickness after 6 months on the space station
the role of artificial gravity countermeasures to maintain corresponded with 10 to 20 years of normal aging
human health during long-duration exploration-class but was reversed within a few days of return. The same
missions. (Shiba et al., 2017). Studies have also shown pattern was seen in isolation studies (e.g., the Mars
that spaceflight activates lipotoxic pathways (i.e., 500 study), indicating this may be a stress response
an accumulation of lipid products in cells) in mouse to confinement rather than an effect of microgravity
liver, initiates a loss of retinol, and creates a possible (Arbeille et al., 2016; Hughson et al., 2016). One study
increased risk of fatty liver disease, thereby opening demonstrated that an improved rebreathing method
new research questions surrounding liver metabolism was a more accurate tool to properly monitor cardiac
and function (Jonscher et al., 2016). function during spaceflight than measuring blood
In a long-term mouse mission of 91 days, results pressure at fingertips (Hughson et al., 2017). Further
suggest that the force-producing extensor digitorum evidence from this study also showed that the elevated
longus (EDL) muscle may resist microgravity-induced CO exposure could be linked to the vision impairment
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atrophy by activating certain inherent compensatory intracranial pressure (VIIP) syndrome (Hughson et al.,
and protective pathways (Cancedda et al., 2012). 2017). Studies of astronauts’ core body temperature
These studies also show an increased sensitivity of in microgravity during periods of exercise and rest
the “antigravity” soleus muscle—the muscle responsible have shown an increase of 1°C, which is significant
for walking and standing activities—adding insight enough to impair physical and cognitive performance
into the mechanisms for resistance of EDL that could if not addressed for long-duration exploration missions
contribute to the development of countermeasures beyond LEO (Stahn et al., 2017).
to muscle loss in space (Sandonà et al., 2012). ISS crew members report a variety of neurological
Moreover, analysis of specific bone formation and symptoms that may be related to changes in cerebral
resorption marker expression in these mice suggested venous outflow. Studies on blood flow changes using
that the microgravity-induced bone loss was due to plethysmography confirm that long-duration spaceflights
both an increased bone resorption and a decreased lead to a redistribution of venous blood volume and
bone deposition. More specifically, the protection show interesting differences in the amplitude of cardiac
observed in transgenic mice overexpressing the PTN oscillations measured at the level of the neck veins.
(pleiotrophin) protein was likely due to higher osteoblast Remarkably, the proposed portable system is able to
activity, which aids in bone formation (Tavella et al., detect cross-sectional area variations of neck veins with
2012). In mouse cardiovascular studies, mice flown enough sensitivity to be useful for studies concerning
to the space station for 8 days showed a decreased cardiac oscillations (Taibi et al., 2017).
expression of calcium channels, which regulate the Research has shown that 60% of long-duration
contractibility of smooth muscle cells in portal veins astronauts (versus 29% of short-duration astronauts)
that carry blood to the liver. A similar effect was experienced a significant decrease in eyesight
observed in rat liver portal vein myocytes cultured on postflight (i.e., spaceflight-induced ocular syndrome),
the space station for 8 days, as well as in rats during accompanied by changes in the structure of the eye
hind-limb suspension on Earth (Dabertrand et al., 2011). (Mader et al., 2011; 2016). The root cause for the
decrease is under investigation; however, studies
suggest that the one-carbon metabolic pathway
Human Studies
and the fluid shifts to the head that lead to increased
ISS research has revealed astonishing similarities intracranial pressure during spaceflight may play
between spaceflight and the aging process through the significant roles (Alperin et al., 2018; Mader et al., 2013;
study of astronauts’ heart and blood vessels. Constant Mader et al., 2016; Zwart et al., 2012). A retrospective
elevation in blood pressure in the brain while in space, analysis of magnetic resonance imaging (MRIs) of
reduced physical activity, and the constant exposure ISS astronauts showed an upward brain shift with
to higher levels of carbon dioxide (CO ) might impair tissue crowding at the upper part of the brain, which
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the ability of blood vessels of the brain to respond to caused elevated intracranial pressure and optic nerve
changes in arterial blood pressure and CO . This was swelling. However, the implications of these changes
2
accompanied by insulin resistance in some astronauts on spaceflight-induced ocular syndrome was not clear
during spaceflight—an issue that is also observed in because most long-duration crew members had the
the elderly. Walls of the carotid and femoral arteries brain changes but only a few had vision problems
were found to be significantly thicker (12%) in all (Roberts et al., 2017). Additional studies show that

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