Space has a more profound impact on the human body than we realised, and astronauts on regular flight schedules may be exposing themselves to brain damage.
A study published in the journal Scientific Reports examined before and after brain scans of 30 astronauts.
The well-known problem of bodily fluids pooling in different body parts under zero gravity extends to the brain. But the University of Florida study, led by Professor Rachael Seidler, also found these changes don’t always return to normal before an astronaut once again gets boosted back into a zero-gravity environment.
Australian space health researcher Dr Vienna Tran says the human body has evolved for life on Earth, and that means we still have a long way to go when understanding the implications of life in space.
“Overall, this involves the fluids in our body shifting upwards – a cephalic shift – towards the head, neck and chest,” Tran explains. “And this induces changes in all the systems in our body,” Tran says.
The most obvious effect, she says, has been on the human eye. Gathering fluids puts pressure on the eyeball. And that affects the shape of the optic nerve.
The new study looked at a series of cavities around the human brain known as cerebral ventricles. This is where cerebrospinal fluids are produced, stored and circulated through the skull and spinal cord.
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The fluid acts as a shock absorber. But it also distributes nutrients and removes wastes.
MRI scans of astronauts’ brains returning from orbit reveal these ventricles tend to expand in a weightless environment.
This was true for astronauts returning from a two-week trip and those deployed for six months or longer.
But the researchers found the longer the time spent in space, the longer the brain’s systems needed for recovery.
Most importantly, the study found “inter-mission intervals of less than three years may not allow sufficient time for the ventricles to recover fully”.
The study showed astronauts who had more than three years between missions demonstrated changes in their ventricle volume after returning from space. But those who went back up again after a shorter period recorded little to no enlargement upon their return.
Professor Seidler says this indicates their ventricles had not recovered their ability to adapt to increased fluid loads and had remained enlarged between missions.
And while the implications of this are not yet understood, it could expose brain tissue to unwanted pressures. This condition, known as hydrocephalus, can result in brain damage or death.
“There’s really not enough that we know about the human body and space for us to safely send someone to Mars and back on a three-year round trip,” says Dr Tran. “So it’s going to be many years until we can safely do that.”
Tran says she has a particular interest in the musculoskeletal system in space.
“I’m strongly of the mind that if we don’t have a healthy and strong body, we can’t perform our jobs properly or enjoy optimal well-being,” she adds.
Possible ways of addressing these physical problems include medical exercise and artificial or simulated gravity.
But, she adds, both have their limitations.
Astronauts currently have to exercise two hours a day to slow the degradation of their bones and muscles. But it doesn’t help other issues, such as fluid pooling.
Artificial gravity could help, Tran adds. But centrifugal forces mean an astronaut must be locked motionless in a large, rapidly spinning arm to avoid overwhelming dizziness and nausea.
“Artificial gravity hasn’t even been proven to be effective because it’s in the early stages of research,” she explains.
But those same challenges make it an exciting time to be in space health, Tran adds.
“It can seem really overwhelming when we think about all the different problems that we have in space and how we’re going to solve them,” she says. “But every time I see a problem, I think about how to solve it and how exciting that will be. I think we are on the cusp of developing some really, really interesting technologies to move humanity forward. And that’s one of the most inspiring things a human can do.”