Space sleeping bag

Vacuum sleeping bag prevents eyeball damage in zero gravity

Image credit: UT Southwestern Medical Centre

Researchers from UT Southwestern Medical Centre have developed a vacuum-equipped sleeping bag intended for astronauts. The sleeping bag pulls down body fluids that naturally flow to the head and squash the eyeballs, preventing associated vision problems.

This little-known phenomenon has vexed scientists for more than a decade, and it remains a key health dilemma of human space exploration, particularly as Nasa looks towards longer voyages to Mars.

“We don’t know how bad the effects might be on a longer flight, like a two-year Mars operation,” said Dr Benjamin Levine, a cardiologist at UT Southwestern who is working with Nasa to address risks associated with abnormal blood flow in space. “It would be a disaster if astronauts had such severe impairments that they couldn’t see what they’re doing and it compromised the mission.”

The condition, spaceflight-associated neuro-ocular syndrome (SANS), is characterised by the progressive flattening of the eyeball, swelling of the optic nerve, and vision impairment. Studies have shown it is likely to be caused by the constant pressure applied to the brain by body fluids in zero-gravity. On Earth, gravity pulls fluids down into the body when a person climbs out of bed, but in space there is no such “unloading”, allowing more than half a gallon (1.8L) of body fluids to gather in the head and apply pressure to the eyeball.

“You can’t stand up in space to unload the pressure. That’s the problem,” said Dr Michael Stenger, a Nasa scientist.

At present, astronauts can use custom glasses with lenses that correct their changing vision while they are in zero gravity. However, this does not address the possible long-term effects on the eyeball or potential cardiovascular complications, such as increased risk of atrial fibrillation. Levine explained: “It’s certainly possible there are other effects of brain pressure we haven’t documented yet. The astronauts report something they call the “space stupids”. They make more mistakes than they think they should. Whether that has anything to do with the inability to lower the pressure, we don’t know.”

Levine tested the theory that constant fluid pressure may contribute to SANS by putting people receiving chemotherapy on zero-gravity flights into the upper atmosphere and measuring brain pressure. This confirmed that space does not provide relief from pressure that comes on Earth when a person stands.

The researchers started working to develop a sleeping bag that could be used by astronauts to unload pressure in the brain. Although similar lower body negative pressure technology has been used for decades to maintain muscle and bone mass in space, previous prototypes were not designed for many hours of use or as an antidote for SANS.

The sleeping bag as a solid frame that fits over a person from the waist down. Participants lay in bed and in the sleeping bag, and researchers compared changes in the brain after each stint. They found that just three days of lying flat induced enough pressure to slightly alter the shape of the eyeball, while no such change occurred while using the vacuum-equipped sleeping bag.

Although further questions must be answered before Nasa brings the technology onto the International Space Station, Levine says the study indicates SANS won’t be a health risk by the time humans are sent to Mars.

“This is perhaps one of the most mission-critical medical issues that has been discovered in the last decade for the space program,” said Levine. “I’m thankful for the volunteers who are helping us understand, and hopefully, fix the problem.”

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