The effect of prolonged spaceflight on cerebrospinal fluid and perivascular spaces of astronauts and cosmonauts

Abstract

Long-duration spaceflight induces changes to the brain and cerebrospinal fluid compartments and visual acuity problems known as spaceflight-associated neuro-ocular syndrome (SANS). The clinical relevance of these changes and whether they equally affect crews of different space agencies remain unknown. We used MRI to analyze the alterations occurring in the perivascular spaces (PVS) in NASA and European Space Agency astronauts and Roscosmos cosmonauts after a 6-mo spaceflight on the International Space Station (ISS). We found increased volume of basal ganglia PVS and white matter PVS (WM-PVS) after spaceflight, which was more prominent in the NASA crew than the Roscosmos crew. Moreover, both crews demonstrated a similar degree of lateral ventricle enlargement and decreased subarachnoid space at the vertex, which was correlated with WM-PVS enlargement. As all crews experienced the same environment aboard the ISS, the differences in WM-PVS enlargement may have been due to, among other factors, differences in the use of countermeasures and high-resistive exercise regimes, which can influence brain fluid redistribution. Moreover, NASA astronauts who developed SANS had greater pre- and postflight WM-PVS volumes than those unaffected. These results provide evidence for a potential link between WM-PVS fluid and SANS.

Imaging perivascular space structure and function using brain MRI

“…The mechanistic link between BMI and PVS is not known, but it is possibly related to higher intracranial pressure ( Barisano et al, 2021b ), as linear positive relationship exists between CSF pressure and BMI ( Berdahl et al, 2012 ), and/or to a reduced vascular contractility and vascular dysfunction, which is often found in obese people ( Stapleton et al, 2008 ). That intracranial pressure might influence the burden of MRI-visible PVS has also been argued by a recent study in astronauts and cosmonauts showing enlargement of MRI-visible PVS after long-duration spaceflight on the International Space Station ( Barisano et al, 2022 ), as prolonged spaceflight is associated with some radiological and clinical findings suggestive of high intracranial pressure, including pituitary gland deformity ( Kramer et al, 2020 ), ventricular enlargement ( Barisano et al, 2022 ; Jillings et al, 2020 ; Koppelmans et al, 2016 ; Kramer et al, 2020 ; Roberts et al, 2017 ; Van Ombergen et al, 2018 , 2019 ), optic disk edema and posterior flattening of the optic globe ( Mader et al, 2011 ). Further studies should investigate whether intracranial pressure affects the visibility of PVS on MRI and the flow of the PVS fluid, as it will provide a better understanding of the cerebrospinal fluid dynamics and clearance systems with important clinical implications for a number of neurological disorders.…”

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“… Hupfeld et al (2020) also showed greater increases in ventricular volume and free water (cranial fluid) shifts following 1 year in space compared to 6 months. A recent study on the perivascular space in the brain of NASA astronauts showed that shuttle crew had no significant increase after their mission whereas astronauts who spent 6 months in the ISS demonstrated significant perivascular space increase after flight ( Barisano et al, 2022 ). Further, Scott Kelly took significantly longer to re-adapt to Earth’s gravity environment after his 1-year ISS mission compared to his previous 6-month mission ( Kelly, 2017 ; Garrett-Bakelman et al, 2019 ).…”

“…However, another earlier study on perivascular space in a group of over 40 astronauts and cosmonauts, both novice and experienced fliers, showed that both groups developed significant increases in perivascular space after spaceflight. Interestingly, a significantly larger increase in the NASA astronauts was observed compared to Roscosmos cosmonauts ( Barisano et al, 2022 ).…”

“…This hypothesis is anecdotally supported by the lower number of observed SANS cases in cosmonauts, who seem to use the ARED less often and at lower strength regimes than the USOS crew. A recent study shows that the perivascular space in the brain is significantly increased in the NASA crew with 25.5%, compared to Roscosmos crew with only 12.4% ( Barisano et al, 2022 ). As all crews experienced the same environment aboard the ISS, the authors hypothesize that the differences in PVS enlargement may have been due to, among other factors, differences in the use of ARED and LBNP, which can influence brain fluid redistribution.…”

“…In the past 6 years, substantial evidence has accumulated that spaceflight affects human brain structure ( Koppelmans et al, 2016 ; Roberts et al, 2017 ; Van Ombergen et al, 2018 , 2019 ; Lee et al, 2019b ; Riascos et al, 2019 ; Hupfeld et al, 2020 , 2022 ; Jillings et al, 2020 ; Kramer et al, 2020 ; Roy-O’Reilly et al, 2021 ; Barisano et al, 2022 ; Doroshin et al, 2022 ). These changes include an upward shift of the brain within the cranial compartment, ventricular expansion, perivascular space changes and white matter alterations.…”