Six of the astronauts experienced stagnation or reversed blood flow, one had a blood clot and the other was found to have a potential partial blood clot.
This is the first time researchers have observed this condition in astronauts and the implications of their discovery could have an impact on long-term spacecraft in the future, such as missions to Mars.
After more than 50 years of human space travel, researchers know some of the risks posed to the human body by being in zero gravity. Motion sickness occurs in the first 48 hours, causing loss of appetite, dizziness, and vomiting.
Over time, astronauts who stay for six months at the station can experience weakness and loss of bone and muscle that stops developing. Astronauts also experience loss of blood volume, a weakened immune system, and cardiovascular deconditioning, because floating requires less effort and the heart doesn't have to work as hard as pumping blood. Scott Kelly and other astronauts in their late 40s and 50s also complained about their slightly changed views. Some of them need glasses in flight.
And the Twin Study, comparing changes in astronaut Scott Kelly during a spaceflight mission for a year while his twin, Mark, was on Earth revealed many other changes that affect the expression of genes and microbiomes.
A gravityless environment without gravity causes a shift in fluid in the body towards the head, the opposite of what we experience when standing on Earth. On Earth, humans spend about two thirds of the day in an upright position and about one third lie down at night. This causes daily fluid changes that vary based on our position.
But for astronauts, this fluid shift lasts a long time. This causes swelling in the face, "bird's foot" syndrome where the foot loses volume, and decreases plasma volume while increasing stroke volume – the volume of blood pumped per beat.
"The medical problem recently identified with long-duration spaceflight on the International Space Station is a constellation of neuro-ocular problems that we have created SANS – Spaceflight Associated Neuro-ocular Syndrome," said Michael Stenger, study author and director of NASA Johnson. Central Cardiovascular and Vision Laboratory.
"About 10 years ago, we noticed that astronauts developed optical disc edema, globe folding, choroidal folds and permanent bias error changes. The aim of our experiment was to calculate the forward fluid transfer to all astronauts by examining the structure and flow of arteries and veins. characteristics in the head and neck (as well as several other parameters) and determine the relationship between these parameters and ocular structural and functional changes. "
The researchers wanted to assess how this fluid change affected the left jugular vein. This vein carries deoxygenated blood from the head and neck to the vena cava, the largest vein in the upper body.
The researchers revealed that one limitation of this study was that they did not image the right jugular vein, but had been analyzed in a previous spaceflight study and there were no signs of stagnation or freezing.
Astronauts provide measurements of blood flow before and after spaceflight while sitting, lying down and tilted 15 degrees down. Measurements during the flight are carried out on the 50th and 150th day of the mission.
Astronauts who develop blood clots are treated with anticoagulants for the remainder of space flight and have not participated in the last 50 days of research.
The observation that blood clots to healthy astronauts, both men and women, because its weight is a surprise to researchers, who worry about other problems that can cause blood clots.
"Newly formed and small blood clots are easily filtered out of circulation in the lungs," Stenger said. "If a person grows too large and hardens, then a person will be at risk of developing pulmonary embolism. The formation of these clots is a major concern associated with stasis flow."
The idea of reversing blood flow requires further examination.
"The backflow is very interesting, and we are not sure if it is dangerous," Stenger said. "Backflow in the jugular vein can be completely harmless because blood only leaves the head through one of the other venous pathways. However, backflow implies changes in the dynamics of venous pressure, which can have an impact on the brain's ability to drain cerebral spinal fluid. in the brain. This is something we continue to investigate. "
A possible way to reverse the head-ward fluid shift is to apply lower body negative pressure.
The Russian side of the space station includes the Chibis suit used to test this method. The suit basically acts as a tightly closed pair of pants, according to the study authors.
"This includes the lower limbs in hard enclosures that are sealed at the waist and connected to a vacuum pump to reduce pressure in the space around the lower limbs for subatmosphere pressure," the authors write. "Negative body pressure decreases fluid volume, especially venous blood, in the lower extremities and is used by cosmonauts on ISS as a prevention of postflight orthostatic intolerance."
Other possible ways to move fluid from the upper body can include thigh cuffs, breathing apparatus and acceleration through cetrifugation, Stenger said.
Stenger points out that research must be tracked quickly to better understand this problem, as well as consider the limits of medical and research capabilities on vehicles used in future exploration missions.
"Maybe this is scary, this novel and interesting findings are not too alarming," Stenger said. "The reality is that this might have happened since we started flying in space, we have never seen before. This gives us the opportunity to now conduct further research to determine what caused this before speculating too much on potential consequences. & # 39;
Of the 17 sessions in the Chibis suit during the flight, 10 were associated with increased blood flow, two actually showed worsening flow and five did not cause changes, according to the study. During a session when blood flow increased, three astronauts actually changed from stagnating or reversing blood flow to being regular.
"This study underscores the need to monitor vascular changes in astronauts," said Christopher Mason, one of the authors of the Twin Studies and a professor of physiology and biophysics at Weill Cornell Medicine. Mason is not affiliated with this research. "Stagnant and retrograde blood flow can cause complications, such as thrombosis [blood clotting], but fortunately it can be tracked and treated. Also, as with taking long flights, this risk will almost certainly resolve when landing back on Earth. "