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A new study led by Professor Larry Kramer of the University of Texas Health Sciences Center at Houston suggests that the impact of microgravity is far-reaching, which can cause changes in brain volume and gland deformation. pituitary.
5mm sagittal orthogonal midline sagittal images in the brain using the T1 weighted 3D data sagittal set: (previous reference image of the left flight) and (right) coincident posterior flight image (subsequent flight day 1) in the same astronaut; black arrowheads show upward expansion of the superior anterior, medial, and posterior margins of the lateral ventricle with associated narrowing of the marginal sulcus of the cingulate sulcus (white arrowhead); there is a subtle expansion of the third ventricle (indicated by a 3), which has displaced the thalamus (T) from the midline, making it less visible; There is thickening of the intermediate signal of the soft tissue scalp (arrows). Image credit: Kramer et al, doi: 10.1148 / radiol.2020191413.
On Earth, the gravitational field creates a hydrostatic gradient, a fluid pressure that progressively increases from head to toe when standing or sitting. This pressure gradient is not present in space.
“When you are in microgravity, fluid, like venous blood, no longer collects towards the lower extremities, but is redistributed forward,” said Professor Kramer.
“That movement of fluid to the head may be one of the mechanisms causing the changes we are seeing in the eye and the intracranial compartment.”
For more information, Professor Kramer and his colleagues performed a brain MRI on 11 astronauts, including 10 men and a woman, before traveling to the International Space Station (ISS).
The researchers continued the MRI studies the day after the astronauts returned, and then at various intervals during the following year.
The MRI results showed that long-term exposure to microgravity caused expansions in the combined volumes of cerebrospinal fluid (CSF) from astronauts. CSF is the fluid that flows into and around the hollow spaces of the brain and spinal cord.
The combined volumes remained high for one year after the flight, suggesting a permanent alteration.
“What we identify that no one has really identified before is that there is a significant increase in white matter volume in the brain from the previous flight to the subsequent flight,” said Professor Kramer.
“In fact, the expansion of white matter is responsible for the greater increase in the combined volumes of cerebrospinal fluid and brain after flight.”
MRI also showed abnormalities in the pituitary gland, a pea-sized structure at the base of the skull, often called the “master gland,” as it governs the function of many other glands in the body.
Most astronauts had MRI evidence of deformation of the pituitary gland, suggesting elevated intracranial pressure during space flight.
“We found that the pituitary gland loses height and is smaller after the flight than it was before the flight,” said Professor Kramer.
“Furthermore, the dome of the pituitary gland is predominantly convex in astronauts without prior exposure to microgravity, but showed evidence of flattening or concavity after flight. This type of deformation is consistent with exposure to elevated intracranial pressures. “
The team also observed an increase in post-flight volume, on average, in astronauts’ lateral ventricles, spaces in the brain that contain CSF. However, the resulting overall volume would not be considered outside the range of healthy adults.
The changes were similar to those that occur in people who have spent long periods of bed rest with their heads slightly tilted down in research studies that simulate forward fluid change in microgravity.
Additionally, there was an increase in the speed of CSF flow through the cerebral aqueduct, a narrow channel connecting the ventricles in the brain.
A similar phenomenon has been observed in hydrocephalus at normal pressure, a condition in which the ventricles in the brain are abnormally enlarged. Symptoms of this condition include difficulty walking, bladder control problems, and dementia. To date, these symptoms have not been reported in astronauts after space travel.
The findings were published in the journal. Radiology.
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Larry A. Kramer et al. Intracranial effects of microgravity: a prospective longitudinal MRI study. Radiology, published online April 14, 2020; doi: 10.1148 / radiol. 2020191413
