While astronauts have been subjected to various health studies to understand the impact of space travel on humans as several private companies prepare for space tourism, a first-of-its-kind study has found something which is not very pleasant: formation of blood clots in jugular vein. The jugular vein is an important body part because it drains deoxygenated blood from the head and neck. If you block the jugular veins, the pressure in the brain goes up.
The findings may have significant human health implications for civilian spaceflight as well as future exploration-class missions, such as a mission to Mars. The researchers led by Karina Marshall-Goebel, a senior scientist at NASA, looked to find answers to the question: Is long-duration exposure to weightlessness associated with impaired cerebral venous outflow and increased risk of jugular venous thrombosis?
In this cohort study of 11 International Space Station (ISS) crew members, six crew members demonstrated stagnant or retrograde flow in the internal jugular vein on approximate flight day 50, and one crew member developed an occlusive internal jugular vein thrombus during spaceflight. The condition normally occurs in the legs, like in air travellers on long-haul flights.
Retrograde blood flow in the jugular vein
"This cohort study found stagnant and retrograde blood flow in the jugular vein, a newly discovered risk associated with spaceflight," the researchers wrote. In two astronauts, blood in the vessel actually started moving in the opposite direction, from the heart toward the head, which is "extremely abnormal" for this vein. Humans have been flying in space for more than 50 years, yet this is the first report of venous thrombosis during spaceflight.
"Given that the thrombi detected in our study were asymptomatic, it is plausible that undetected thrombi have occurred previously during human spaceflight missions," Marshall-Goebel said in a paper published in JAMA Network Open. The team found that in microgravity, crew members were exposed to constant cerebral venous congestion with the potential to develop stagnant venous blood flow.
"Lower body negative pressure may be a promising countermeasure toenhance venous blood flow in the upper body during spaceflight," she added. "Our findings highlight the need for a more comprehensive evaluation of bilateral venous hemodynamics during spaceflight, as well as for investigation of countermeasures that can restore vascular physiology to a state similar to that seen in the upright and supine positions on Earth," the authors wrote.
Another study that examined cell-level cardiac function and gene expression in human heart cells cultured aboard the International Space Station (ISS) for 5.5 weeks, this month found that heart cells are altered in space but return to normal within 10 days on Earth. Exposure to microgravity altered the expression of thousands of genes, but largely normal patterns of gene expression reappeared within 10 days after returning to Earth, according to a study published in the journal Stem Cell Reports.
"We're surprised about how quickly human heart muscle cells are able to adapt to the environment in which they are placed, including microgravity," said senior study author Joseph C. Wu from Stanford University.