Six of the astronauts had stagnant or reverse blood flow, one had a blood clot and another might have had a partial blood clot.
This is the first time that researchers observe these conditions in astronauts. The impact of their discovery could affect future long-term spaceflight, such as a mission to Mars.
After more than 50 years of human spaceflight, researchers are aware of some of the risks posed by weightlessness to the human body. Space sickness occurs in the first 48 hours, causing loss of appetite, dizziness and vomiting.
Over time, astronauts who spend six months on the ward may notice the weakening and loss of bones and atrophying muscles. Astronauts also suffer from decreased blood volume, weakened immune systems, and cardiovascular deconditioning because swimming costs little strength and the heart does not have to work so hard to pump blood. Scott Kelly and other astronauts in their late forties and fifties have also complained that their eyesight has changed slightly. Some of them needed glasses during the flight.
. The Twins Study, which compared astronaut Scott Kelly's changes during his one-year spaceflight mission while his twin Mark was on Earth, revealed numerous other changes affecting gene expression and the microbiome.
The weightless environment of weightlessness causes a fluid shift in the body towards the head, in contrast to what we experience on Earth. On Earth, people spend about two-thirds of the day in an upright position and about a third at night. This results in a daily fluid shift that varies depending on our position.
But for astronauts, fluid displacement persists for long periods of time. It causes swelling of the face, a "bird's leg" syndrome in which the legs lose volume and reduce plasma volume, while increasing the stroke volume – the blood volume pumped per beat.
The International Space Station is a constellation of neuro-ocular problems that we have referred to as SANS-Spaceflight Associated Neuro-Ocular Syndrome, "said Michael Stenger, study author and director of NASA's Johnson Space Center Cardiovascular and Vision Laboratory.  "About 10 years ago, we discovered that astronauts developed papilledema, flattening of the globe, choroid folds, and persistent refractive errors. The purpose of our experiment was to quantify the displacement of the fluid forward in all astronauts by examining the arteries and veins, structural and flow characteristics in the head and neck (as well as various other parameters) and determining the relationship between these parameters and structural and functional Changes of the eye.
The researchers wanted to investigate how this fluid shift affects the left jugular vein, transporting oxygen-free blood from the head and neck to the vena cava, the largest vein in the upper body.
The study found that they did not map the right jugular vein, but it was analyzed in previous space flight studies and there was no sign of stagnation or coagulation.
The astronauts performed blood flow measurements while sitting, lying down and at an angle of 15 degrees downwards before and after the space flight.The measurements during the flight were made on days 50 and 150 of the mission.
The astronaut who developed a blood clot was treated with anticoagulant for the remainder of space flight and did not participate in the study on the last day.
The observation that blood clotting occurred in otherwise healthy astronauts, both male and female. Because of weightlessness, it was a surprise to researchers worried about the other problems that blood clots can cause.
says in the lungs, "said Stenger." If you become overly large and solidify, you may be at risk of pulmonary embolism. This formation of clots is the main concern associated with the flow stasis. "
The idea of reverse blood flow requires a closer investigation. " The reflux is really interesting and we are unsure if it is harmful, "Stenger said. Reflux in the jugular vein could be completely harmless, as the blood simply leaves the head via one of the other venous routes, but reflux implies altered venous pressure dynamics that could affect the brain's ability to drain cerebral spinal fluid and possibly brain pressure This will be further investigated. "
One possible In order to reverse the fluid displacement in the head area, a negative pressure on the lower body must be exercised.
On the Russian side of the space station is a Chibis suit, with which this method was tested. The suit, according to the authors of the study basically acts as a vacuum-sealed pants.
"It includes the lower limbs in a hard bezel, which is sealed at the waist and connected to a vacuum pump to reduce the pressure in the chamber around the pants limbs to negative pressure," the authors wrote. "Negative pressure in the lower body binds the fluid volume, mainly venous blood, in the lower extremities and is used by cosmonauts on the ISS as a countermeasure against orthostatic incompatibility after the flight." Cuffs, resistance ventilators, and centrifugal acceleration, Stenger said.
Stenger pointed out that research should be accelerated to understand the problem better
"As scary as this may sound, this novel and interesting discovery is not particularly worrying," Stenger said. "The reality is that this has probably happened since we fly in space, we've never seen it before, which gives us the opportunity to conduct further investigations to find out what causes this before we speculate too much about possible consequences . "  Out of the 17 sessions with the Chibis suit during the flight, 10 were associated with improved blood flow, two actually showed a worsening of blood flow and five did not cause any changes, according to the study. Indeed, during sessions where blood flow improved, three astronauts actually went out "This study highlights the need to monitor vascular changes in astronauts," said Christopher Mason, one of the authors of the Twins study and Associate Professor of Physiology and Biophysics at Weill Cornell Medicine was not associated with this study. "Stagnant and retrograde blood flow can lead to complications such as thrombosis [blood clotting] but fortunately can be tracked and treated, and as with a long flight, the risk would almost certainly dissolve when landing on the earth."