13 May 2022

A surveillance programme has looked at whether astronauts are more likely to develop blood clots during space missions due to zero-gravity.

Dr Stephan Moll, of the UNC School of Medicine, North Carolina, first started working with NASA after an astronaut was found to have developed deep vein thrombosis (DVT) in the jugular vein during a mission to the International Space Station (ISS). The findings were described in the New England Journal of Medicine in 2020.

Dr Moll was consulted by NASA when the astronaut discovered the clot when taking ultrasounds of their own neck for a research study on how body fluid is redistributed in zero-gravity. The astronaut was asymptomatic, but Dr Moll and NASA physicians helped treat the astronaut over several months until they returned to Earth.

This initial study spurred on an occupational surveillance programme of astronauts, the results of which have now published in Vascular Medicine.

A team led by NASA scientist Dr James Pavela, including Dr Moll, monitored 11 astronauts in zero-gravity on the ISS, for a total of over 2,150 person-days.

All were evaluated before leaving Earth to get a baseline of their blood flow and blood vessel size in the veins of their neck. When they reached the ISS, the astronauts performed ultrasounds on their own necks with guidance from a radiology team on Earth to monitor any changes that occurred in zero-gravity.

 “We expected some changes in flow based on the absence of gravity,” Dr Moll said. “Gravity pulls fluid in your body down. It also creates a force on your blood vessels and this increased pressure in the veins of the legs leads to leakage of fluid from the blood vessels into the soft tissues. You can notice this when you stand for a long time and develop swelling in your ankles, feet, and sometimes hands.

 “Without gravity, fluids like blood redistribute in your body. When astronauts arrive in space, the lack of gravity causes the blood vessels in the neck to expand due to fluid shifting to the upper part of the body. Astronauts develop swelling of the neck and face from this shift. That is a normal and expected finding.”

The researchers wanted to see if this difference in flow and vessel size could put astronauts at risk for the development of blood clots.

While abnormal flow characteristics were recorded in six of the 11 astronauts, none developed blood clots. However, in two astronauts they found slowed blood flow in the neck veins, abnormal echo findings, and reversal of blood flow, which raised the question about whether or not these abnormalities could predispose these space travellers to blood clots.

Dr Moll says more research is needed, but their findings has helped to inform what medical supplies, such as blood thinners, should be available for current and future spaceflight missions.

Source: Pavela J, Sargsyan A, Bedi D, Everson A, Charvat J, Mason S, Johansen B, Marshall-Goebel K, Mercaldo S, Shah R, Moll S. (2022) “Surveillance for jugular venous thrombosis in astronauts.” Vascular Medicine, doi: 10.1177/1358863X221086619

Link: https://journals.sagepub.com/doi/10.1177/1358863X221086619

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