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 those effects, specifically on the eyes.
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 of these fluids down like it normally does when you're upright on Earth. When you're upright, most of your fluids are stored in your legs, but in microgravity, the fluid gets redistributed to your upper body.”
Diaz Artiles, assistant professor in the Department of Aerospace Engineering and faculty fellow at Williams Brothers Construction Company
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 to be determined, DÃaz-Artiles and her team hypothesized that exposure to microgravity may result in a small but chronic elevation of OPP (compared to upright posture), which may play a role in the development of SANS. Results of a recently published study showed that lower body negative pressure is effective in inducing fluid shift to the lower body, but is not an effective way to reduce OPP. If elevated ocular perfusion pressure is clearly related to SANS, the use of LBNP may not theoretically be an effective countermeasure against this syndrome. However, as part of countermeasure development, they emphasize that future research should further understand the relationship between OPP and SANS, and the impact of LBNP on 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.
The published study and future research focuses on countermeasures to fluid shifts, in this case lower body negative pressure. In future studies, the researchers plan to investigate the effects of using a centrifuge to counter fluid shifts and their effects. Diaz-Artiles and her team aim to collect cardiovascular responses using each countermeasure and compare their effects on ocular perfusion pressure and other cardiovascular functions that may be affected by a microgravity environment. Because these studies will be conducted on Earth, the results may differ due to the changes in gravity that occur in space. That's why they hope to conduct future studies in true microgravity conditions, such as parabolic flights.
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Journal References:
Hall, EA, et al. (2024). Ocular perfusion pressure does not decrease in response to lower body negative pressure. npj Microgravity. doi.org/10.1038/s41526-024-00404-5.
