By Paul Rincon
The science editor is on the website.
The image caption is.
The sleeping bag has a frame that sucks fluid from the brain towards the feet.
Some astronauts experience vision problems while living in space, and scientists have developed a sleeping bag that could help.
In zero-gravity, fluids float into the head and squash the eyeball over time.
It's considered one of the riskiest medical problems affecting astronauts, with some experts concerned that it could compromise missions to Mars.
The sleeping bag sucks fluid out of the head and feet to counter the build-up of pressure.
Dr Benjamin Levine, a cardiologist at the University of Texas (UT) Southwestern Medical Center in Dallas, is working on having the device deployed on the International Space Station.
More than half of the astronauts who served for at least six months on the International Space Station had vision problems. Some became far-sighted and needed crewmates to help with experiments.
Dr Levine says they don't know how bad the effects will be on a longer flight.
It would be a disaster if astronauts had severe impairments that made it hard for them to see what they were doing.
The image is from NASA.
The image caption is.
Serena Aun-Chancellor uses a Funduscope to examine her eyes.
In 2005, JohnPhillips went to the International Space Station and came back six months later with a vision of 20/100. Some people experience a less severe version of the condition.
When a person gets out of bed, gravity pulls fluids down into the body. In space, the low gravity allows body fluids to accumulate in the head and apply pressure to the eyeball.
It can cause a condition called SANS. This can lead to progressive flattening at the back of the eye, swelling of the brain and vision impairment.
The pressure in zero-g is lower than in one-g. It's not as low as standing up. Normally, we spend one-third of our time lying down at night and two-thirds upright during the day. Dr Levine said that Nasa astronauts can't stand up.
Even though the brain pressure in a person lying down on Earth is slightly higher than in someone in space, astronauts can't relieve it by shifting to an upright position.
They never get to take the brain. We asked if we could re-introduce a gravitational gradient.
The sleeping bag, developed with outdoor equipment manufacturer REI, fits around the person's waist, enclosing their lower body within a solid frame.
The image is from David Gresham.
The image caption is.
SANS could be mission-critical on deep space missions, according to Dr Benjamin Levine.
The same principle as a vacuum cleaner is used to create a pressure difference that draws fluid towards the feet. This prevents it from damaging the eyeball by building up in the brain.
The optimal amount of time astronauts should spend in the sleeping bag each day is one of several questions that need to be answered.
Does everyone need to do this, or is it just the people who are at risk of developing SANS? Can you wait and see if your vision changes, or do you need to do it as soon as possible?
He said that the kind of dose still needs to be worked out.
The development means that SANS may not be a health risk when Nasa launches to the Red Planet.
Cancer survivors were crucial in clarifying the causes. The volunteers still had ports in their heads used to deliver drugs, and these allowed the scientists to measure brain pressure while they were flown on a flight that mimicked zero-gravity.
Volunteers tested the technology. Scientists were lying down and without a sleeping bag. The researchers found that lying flat for three days caused enough pressure to change the eyeball's shape, but not enough to change it with the technology used.
The team at UT Southwestern found that microgravity may cause the heart to shrink in space and may lead to a condition called arrhythmia, where the organ beats in an irregular manner.
The sleeping bag could help counteract the abnormal blood flow that can cause an irregular heartbeat in microgravity.
The work was described in a journal.
