The study was designed to study different, well-known side effects of space travel. A decade ago, scientists started noticing that astronauts who spent months on the International Space Station came home with swollen optic nerves, slightly flattened eyeballs, and changes in vision. NASA started putting glasses on board the station for astronauts who found that their eyesight had worsened. Scientists have suspected that the cause involves an accumulation of the body’s fluids such as blood and water. Free from the steady tug of gravity, the fluids float toward the head and can increase pressure inside the skull. [...]
Scans showed that blood flow in the vein stalled in five of the 11 astronauts. “Sometimes it was sloshing back and forth a bit, but there was no net-forward movement,” Marshall-Goebel says. Seeing stagnant blood flow in this kind of vein is rare, she says; the condition usually occurs in the legs, such as when people sit still for hours on a plane. The finding was concerning. Stagnant blood, whether it’s in the neck or in the legs, can clot. Blood clots can dissolve on their own or with the help of anticoagulants, but the blockages can also cause serious problems, such as lung damage. [...]
The researchers attribute the effects they observed to the space environment. All the astronauts were considered to be in good health before they launched. And when they came home, the conditions vanished in nearly all of them. When the researchers analyzed the data, they found that a second astronaut may have developed a blood clot no one had seen while they were in orbit. But no one experienced any health troubles. “None of the crew members actually had any negative clinical outcomes,” Marshall-Goebel says.
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