Researchers at Simon Fraser University have found that just a few days in simulated microgravity can change the way blood clots form in women. The findings come as space agencies increase health monitoring for astronauts, especially with more female crew members joining missions.
The study was prompted by a 2020 incident when an International Space Station mission detected an unexpected blood clot in a female astronaut's jugular vein. Historically, most space-health research has focused on male participants. With more women now traveling to space, this new joint effort between SFU and the European Space Agency aimed to better understand how microgravity affects blood clotting in females.
Tiffany Stead, lead author of the study published in Acta Astronautica, said that although changes seen during short-term simulated weightlessness are not immediately dangerous, they could pose risks for astronauts who are far from emergency medical care. "This combination - slower initiation, faster formation, stronger clots - was not shown to be inherently dangerous in the short term," Stead stated. "But it does raise concerns for astronauts because of how and where in the body these dangerous blood clots can form while in space and far from emergency medical care."
Eighteen healthy female volunteers participated over five days using a dry immersion tank—a device designed to simulate weightlessness by floating subjects on water under a waterproof sheet. Researchers used rotational thromboelastometry (ROTEM) to monitor real-time clotting responses and also tested for menstrual hormone effects on coagulation but found none.
Blood clots are potentially serious if they move through the bloodstream and block vessels in organs such as the lungs or brain, leading to conditions like pulmonary embolism or stroke. On Earth, gravity causes most clots to form in the legs where there is often more time for treatment or natural breakdown before causing severe issues.
SFU researcher Blaber explained that without gravity's influence, blood tends to pool in the head or even reverse direction during spaceflight. This creates an environment where clots may form more easily—and closer to critical organs than on Earth: "We've found that in space, blood clots are more likely to form in the jugular vein. From there, it doesn't have to travel far to reach lungs or heart, and trigger a serious medical event," he said. "Space is not a place where you want these things to happen."
Blaber’s team continues its work by analyzing similar data from male participants which will inform future astronaut health protocols.
Following previous incidents involving blood clots among astronauts—including one discovered via ultrasound scan—space agencies have increased vigilance during missions: "Now that they know it can happen, they're looking at it more frequently as part of the standard measures," Blaber added.
The Aerospace Physiology Laboratory at SFU regularly collaborates with Canadian and international partners on studies about human physiology during spaceflight.
