We are still learning about the potential effect that prolonged periods in space can have on the human body. A new health threat has now been identified, which could endanger the lives of long journeys through the cosmos.
The problem lies in the internal jugular vein (IJV), the main blood vessel that runs through the neck of the brain. A study of 11 astronauts spending time at the International Space Station (ISS) found that six of them developed stagnant or backward blood flow in this particular vein in just 50 days.
One crew member was found to develop thrombosis or blockage in the internal jugular vein, the first time it was recorded as a result of space flight.
According to the team behind the new discoveries, this issue should be explored before we start sending astronauts on long trips to Mars. It is not yet clear just what the consequences of this type of thrombosis are, but the implications could be serious and possibly even fatal.
"Exposure to weightless environments during space flight results in a chronic displacement of blood and head fluids relative to the upright position of the Earth, with unknown consequences of cerebral venous outflow," the researchers wrote in the paper.
Down here on Earth, of course, gravity takes care of the work of pulling blood from the head to the rest of the body – that's one of the reasons you would start to feel very strange if you stayed on your hands for a long period of time
In the microgravity environment of the ISS, that's another story – and problems with blood flow aren't the only health risks we need to worry about.
"Objects of fluid change during prolonged weight loss lead to facial puffiness, decreased leg volume, increased stroke volume, and reduced plasma volume," the researchers write.
Medical experts used readings and images collected by the ISS to identify a potential issue with the IJV, while the astronaut who developed the occlusive thrombus was treated with anticoagulants for the rest of the mission (the identities of the astronauts are held back for privacy reasons).
More research is needed to determine how big this problem actually is and how it can be mitigated against it in future space flows; but worrying is the large number of astronauts who have developed a problem with blood flow.
We already know that time in space can reduce bone density, alter the make-up of our gut bacteria, and put a squeeze on our brains. At least we are working to detect these effects before trying to move away from the moon, so there is a better chance of developing potential solutions.
"[These] are new insights that could have significant health impacts on human health in the civilian space, as well as on future research-class missions, such as the Mars mission. "
The research is published in Jama Network is open.