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April 14 (UPI) -- Slowly but surely, scientists are gaining better insights into the effects of prolonged exposure to microgravity on human health. Previous studies have shown lengthy space missions can affect the eyesight of astronauts. Now, new research suggests long-duration space travel is responsible for more widespread neural changes, including shifts in brain volume and the deformation of the pituitary gland.
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The health of astronauts is closely examined and monitored before, during and after missions about the International Space Station. In addition to ensuring the safety of the astronauts, the research can help scientists develop protective measures for future missions.
Previous post-mission exams have revealed vision changes in more than half of the astronauts returning from prolonged stays on the space station. Doctors have observed swelling of the optic nerve, retinal hemorrhage and other ocular structural anomalies.
According to researchers, these changes are likely influenced by increased intracranial pressure.
On Earth, gravity ensures pressure inside the body is distributed across a hydrostatic gradient. Internal pressure increases moving from the head to a person's toes. No such gradient is present in space.
"When you're in microgravity, fluid such as your venous blood no longer pools toward your lower extremities but redistributes headward," lead study author Dr. Larry A. Kramer, researcher at the University of Texas Health Science Center at Houston, said in a news release. "That movement of fluid toward your head may be one of the mechanisms causing changes we are observing in the eye and intracranial compartment."
For the study, Dr. Kramer and his colleagues performed brain MRIs on 11 astronauts, 10 men and one woman, upon returning from the space station. The brain images revealed increases in brain and cerebrospinal fluid volumes. Followup MRIs a year later showed the changes in fluid volume were still present, suggesting the effects of microgravity on the brain are permanent or semi-permanent.
"What we identified that no one has really identified before is that there is a significant increase of volume in the brain's white matter from preflight to postflight," Dr. Kramer said. "White matter expansion in fact is responsible for the largest increase in combined brain and cerebrospinal fluid volumes postflight."
Scientists also observed changes to the pituitary gland, a small structure that controls a variety of other hormonal glands from its position at the base of the skull.
"We found that the pituitary gland loses height and is smaller postflight than it was preflight," Dr. Kramer said. "In addition, the dome of the pituitary gland is predominantly convex in astronauts without prior exposure to microgravity but showed evidence of flattening or concavity postflight. This type of deformation is consistent with exposure to elevated intracranial pressures."
MRIs also showed increased fluid volumes inside the cerebral aqueduct, a slim channel connecting the brain's ventricles. Under normal conditions on Earth, patients with a condition known as hydrocephalus, characterized by abnormally enlarged ventricles, report symptoms of dizziness, dementia and bladder control issues. So far, no astronauts have reported such symptoms.
Researchers are currently considering potential remedies for the absence of the hydrostatic gradient in space. Scientists have proposed the use of artificial gravity produced by a large centrifuge that spins astronauts around. The use of negative pressure on an astronaut's lower extremities -- to replicate hydrostatic gradient inside the body -- is also being considered.
"If we can better understand the mechanisms that cause ventricles to enlarge in astronauts and develop suitable countermeasures, then maybe some of these discoveries could benefit patients with normal pressure hydrocephalus and other related conditions," Dr. Kramer said.
