Zero gravity made some astronauts’ blood flow backwards
Being weightless can have strange effects on the body; for example, it can have an effect on blood flow. The changes in blood flow caused two astronauts to form small blood clots, which could have been fatal, but fortunately, the weightless man and woman suffered no damage.
Weightlessness can cause blood clots
These changes occurred in a blood vessel called the left internal jugular vein, one of the two blood vessels that normally draw blood out of the head when we are lying down. When we are standing, they usually narrow to prevent too much blood from flowing out of the head, with our blood flow taking a different route through the veins with more resistance.
On Earth, people can sometimes have a change in the direction of blood flow in the left inner jugular vein if there is a blockage, for example due to a tumour developing in the chest. Weightlessness can also affect people's blood flow, so Karina Marshall-Goebel of KBR in Houston and her colleagues wondered if it could also affect this vein.
They performed measurements and ultrasounds of this blood vessel in nine men and two women before and after their mission on the International Space Station, as well as 50 and 150 days after their departure. In two of these astronauts, the blood flow was reversed - perhaps because the lack of gravity caused the organs to move in their chest, putting pressure on the vein lower in their bodies, says Marshall-Goebel. She adds that this vein is predisposed to be blocked depending on its location in the body.
Blood clots can be fatal if they pass through the lungs
In the other five crew members, the blood in this vein was more or less stagnant, and in one of them, the analysis revealed a clot blocking the blood vessel. "It was really alarming," says Marshall-Goebel. Blood clots can be fatal if they pass through the lungs, if this person has started taking anticoagulant drugs to break them down.
As a result of this unexpected discovery, the team asked a group of experts to examine all previous scans and another small clot was found in an astronaut who had already returned to Earth.
The team also asked participants to test a device on board the Space Station that wraps the lower body in a chamber with a lower atmospheric pressure for one hour to allow more blood to flow into their legs. They found that this improved blood circulation in ten of the seventeen tests - but worsened it in two cases.
In female astronauts, the contraceptive pill increases the risk
According to Marshall-Goebel, these findings could lead astronauts to reconsider taking the contraceptive pill to suppress their periods while on the Space Station, as it increases the risk of blood clots forming. The two astronauts in this study who had a clot included a man and a woman, although the team gave no further details to protect their privacy.
