Space can be an unfriendly place for the human body as weightlessness and other factors affect our physiology from head to toe – the head is of course a major concern.
A new NASAThe funded study provides a deeper understanding of the issue. Researchers said Thursday that astronauts who have traveled with the International Space Station (ISS) or NASA space shuttles, on missions lasting at least six months, experienced marked dilatation of the cerebral ventricles — spaces in the middle of the brain that contain cerebrospinal fluid.
This colorless and watery fluid flows in and around the brain and spinal cord. It cushions the brain to protect it from sudden impacts and removes waste products.
Based on brain scans of 30 astronauts, the researchers found that after such voyages, it took the heart chambers three years to fully recover, suggesting a gap of at least that duration between longer space missions would be advisable.
“If the ventricles don’t have enough time to recover between consecutive missions, this can impair the brain’s ability to cope with fluid shifts in microgravity. For example, if the ventricles are already enlarged from a previous mission, they may be less compliant and/or have less room to expand and accommodate fluid shifts during the next mission,” said Heather McGregor, a neuroscientist at the University of Florida, lead author of the study published in the journal Scientific Reports.
Age-related ventricular enlargement—caused not by weightlessness but by cerebral atrophy—may be associated with cognitive decline.
“The effects of ventricular expansion in astronauts are currently unknown. Longer-term health surveillance is required. This ventricular expansion likely compresses the surrounding brain tissue,” said Rachael Seidler, professor of applied physiology and kinesiology at the University of Florida and senior author of the study.
The absence of EarthGravity changes the brain.
“It appears to be a mechanical effect,” Seidler said. “On Earth, our vascular systems have valves that prevent all of our fluids from pooling at our feet due to gravity. In microgravity, the opposite happens – liquids shift towards the head. This upward shift of fluid likely results in ventricular expansion and the brain “sits higher in the skull.”
The study involved 23 male and seven female astronauts – average age about 47 years – from US, Canadian and European space agencies. Eight traveled on approximately two-week space shuttle missions. Eighteen were on ISS missions of around six months and four on ISS missions of around a year.
Little or no changes in ventricular volume occurred in astronauts after short missions. Enlargement occurred in astronauts after missions of six months or longer, although there was no difference between those who flew for six months versus those who did so for a year.
“This suggests that most of the ventricular enlargement occurs in the first six months in space and then tapers off after about a year,” McGregor said.
The fact that the magnification didn’t deteriorate after six months could be good news for future Mars missions, where astronauts may spend two years in zero gravity during the voyage.
“This preliminary finding shows promise for the brain health of astronauts on long-term missions, but it’s still important that we examine MRI data from a larger group of astronauts and after even longer missions,” McGregor said.
The lack of expansion after short flights is good news for people who may be considering short trips into space tourism, Seidler added, as that industry evolves.
Microgravity conditions also cause other physiological effects due to less physical stress on the human body. These include bone and muscle wasting, cardiovascular changes, problems with the balance system in the inner ear, and eye syndrome. Another problem is the increased risk of cancer from the increased solar radiation to which astronauts can be exposed the farther they are from Earth.
© Thomson Reuters 2023
