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Credit: Texas A&M Engineering
As space travel becomes more commonplace, it is important to consider the effects of spaceflight and changes in gravity on the human body. Researchers at Texas A&M University, led by Dr. Ana Diaz-Altiles, are studying these effects, specifically on the eyes. Their findings are published in the journal npj Microgravity.
The changes in gravity that astronauts experience during space travel can cause fluids to shift in the body, which can lead to changes in the cardiovascular system, including the blood vessels in and around the eye.
As spaceflight becomes more commercialized and private space travel becomes more common, astronauts will not be the only ones experiencing these changes. Commercial space travelers may not be as fit or healthy as astronauts, so understanding how these fluid changes affect cardiovascular and eye health becomes even more important.
“When you experience microgravity, you see changes in your cardiovascular system because gravity isn't pulling all these fluids down like it normally does when you're in an upright position on Earth,” said Diaz-Altiles, an assistant professor in the Department of Aerospace Engineering and faculty fellow at Williams Brothers Construction Company.
“When we're upright, most of our body fluids are stored in our legs, but in microgravity, that fluid is redistributed to the upper body.”
These fluid changes may be related to a phenomenon called Spaceflight-Associated Neuro-Ophthalmic Syndrome (SANS), which can cause astronauts to experience eye symptoms, including changes in the shape of the eyeball and alterations in ocular perfusion pressure (OPP). At this time, researchers aren't sure what the exact cause of SANS is, but DÃaz-Artiles hopes to understand the underlying mechanism behind it.
Diaz-Artiles and her team are investigating potential countermeasures to counter the shift of fluid to the head caused by SANS. In a recent study, they looked at whether lower body negative pressure (LBNP) could be a potential aid in combating SANS. This countermeasure could counter the effects of microgravity by re-accumulating fluid in the lower body.
Although the role of ocular perfusion pressure in the development of SANS remains unclear, DÃaz-Artiles and her team hypothesized that exposure to microgravity results in a small but chronic increase in OPP (compared to upright posture), which may play a role in the development of SANS.
Studies have shown that although lower body negative pressure is effective in inducing fluid shift to the lower body, it is not an effective method for reducing OPP.
If elevated ocular perfusion pressure is clearly associated with SANS, then the use of LBNP may not theoretically be an effective countermeasure to this syndrome. However, the researchers emphasize that as part of countermeasure development, future studies should seek to better understand the relationship between OPP and SANS, and how LBNP affects these ocular responses.
“This study is just one experiment in a three-part study to better understand the effects of fluid shifts in the body and their relationship to SANS. In previous experiments in this study, a tilt table was used to allow researchers to understand the cardiovascular effects of fluid shifts at different gravity levels, which were replicated using different tilt angles,” Diaz Artiles said.
Published and upcoming research is focused on addressing fluid shifts, in this case negative pressure in the lower body.
In future studies, the researchers plan to examine the effects of using a centrifuge to counteract fluid shifts and their effects. Diaz-Artiles and her team aim to gather cardiovascular responses using each measure and compare the effects on ocular perfusion pressure and other cardiovascular functions that may be affected by microgravity.
Because these studies are conducted on Earth, the changes in gravity that occur in space may produce different results, which is why the researchers hope to conduct future studies under true microgravity conditions, such as parabolic flights.
Further information: Eric A. Hall et al. “Ocular perfusion pressure does not decrease in response to lower body negative pressure.” npj Microgravity (2024). DOI: 10.1038/s41526-024-00404-5
Journal information: npj Microgravity
