One of the physiological consequences of long-term spaceflight is a headward shift of body fluids. Such cephalic fluid shifts may be tied to clinical syndromes of visual acuity changes associated with long-term spaceflight.

The persistence of changes in cerebrospinal fluid volume following spaceflight has not been previously quantified. Researchers conducted MRI scans on 11 cosmonauts before and after their assignments on the International Space Station, with an average mission duration of 169 days in space. The authors also conducted follow-up scans 7 months after spaceflight.

The volume of the cosmonauts’ brain ventricles increased by an average of 12% after spaceflight—a potential mechanism to cope with the increased fluid volume. In the follow-up scans, the cosmonauts’ ventricle sizes had decreased but did not return to baseline levels, with overall ventricle volume around 6% larger than preflight volume.

The patterns of ventricle size variation suggest decreased cerebrospinal fluid reabsorption during microgravity exposure, possibly partly due to the compression of cranial venous structures associated with reabsorption.

According to the authors, although the ventricle size effects and cosmonauts’ altered visual acuity both persisted several months after their return to Earth, further studies are needed to establish links between the two phenomena. 

https://www.pnas.org/content/early/2019/05/01/1820354116

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