Blood measurement in a space capsule

​Blood depletion for astronauts can endanger Mars missions. Danish-led pioneering research in blood measurement is gathering important knowledge in collaboration with the European Space Agency (ESA).

Carsten Lundby during a parabolic flight. All unnecessary interior has been removed from the specially equipped Airbus 300 aircraft, which serves as a flying laboratory for several research teams at a time. See more pictures and videos from the trials on the intranet and at

Half a century after the moon landings, space organisations the world over are still looking to realise the dream of manned missions to Mars. The entire human biology is under challenge, and blood depletion is a real problem that could obstruct the long-awaited space adventure. The astronauts have to be able to stand up and move about when they reach their far-off destination, and this entails good health and blood circulation during the long journey in the cramped physical conditions offered by a space capsule.

“We know from previous trials that blood depletes if we are physically inactive and move very little for long periods at a time. After just seven days in bed, our blood volume will fall by 20%, and after 60 days after it is likely to drop by up to 40%. This could endanger future space missions. Therefore, for the first time in the history of space travel, we’re testing whether measuring blood volume can be an effective health check for the astronauts of the future,” said Professor Carsten Lundby from the Centre for Physical Activity Research. 

Realisation of a boyhood dream

Over the past 15 years, Carsten Lundby has specialised in growth physiology, and he is an expert at measuring and regulating blood volume. This has brought him into the world of space research, more specifically the Novespace test centre at Bordeaux airport. He and 32 other researchers are testing a newly developed, Danish method to measure blood when weightless. Over three days from 21-23 May 2019, the researchers completed 30 so-called parabolic flights every day in an Airbus 300 in the air space over Bordeaux. This was one of three research projects being funded by the ESA on measuring and regulating blood volume.   

“It’s the realisation of a boyhood dream. I’m heading a space-research project to gather important knowledge about human biology and physiology under extreme conditions, and to test new methods to measure how the body functions during weightlessness,” said Carsten Lundby.

“Effective measurement of blood volume is extremely important if we’re to find solutions to ensure that blood flows sufficiently in the body during long space journeys. It’s not so important for shorter stays on the ISS, but it is vital on longer missions, where astronauts have to stay in a cramped space for months on end, and where possibilities to keep fit and move about are extremely limited. Therefore, the ESA invited us down to the test centre to test the method, and so far it has gone very well,” said Carsten Lundby, who is very satisfied after the first two days of flights.  

Thin air in the rocket

Later this year, the researchers will examine whether periods in thinner air can help alleviate the problem with blood depletion. This will be when Carsten Lundby and his French research colleagues travel to the Antarctic to measure blood volume using the same technique. Some of the researchers will be spending 11 months in a hut 3,200 metres above sea level in this southernmost part of the globe. The extreme conditions, with low temperatures and strong winds in the mountains, make it practically impossible to stay outside, and therefore it is an appropriate simulation of conditions during space travel,” said the researchers. 

"We have a strong suspicion that the thin, oxygen-poor air we know from high mountain regions, can help reduce the drop in blood volume, and this is what we’ll be testing,” said Carsten Lundby, and he continued:

 “We know that blood volume is influenced positively of hypoxia (lack of oxygen). So it’s tempting to assume that thin mountain air in the capsule could be an advantage for astronauts on long missions, and this could prevent blood depletion when physical training is not possible.
The trials under the ESA are in sharp contrast to the other research projects at the Centre for Physical Activity Research at Rigshospitalet, where Carsten Lundby and his colleagues usually investigate the effects of physical activity on blood volume, which is influenced positively by training and exercise. 

“Comparing this study with the other studies we do will give us a really good idea of what happens to blood volume from extreme physical inactivity to extreme physical activity, and we hope that this knowledge will help a large number of patients, no matter whether they are on Earth or in outer space,” said Carsten Lundby.

New technique to measure blood

Measuring blood volume has up to now been complex and expensive, preventing many from performing measurements in research and in treatment. The new method, supported by the Danish company Detalo Health, will make it much easier to measure blood volume, even in difficult situations. Measurement is done by inhaling a very small amount of carbon monoxide mixed with pure oxygen for a few minutes. On the basis of a blood sample taken before and after inhalation of the gas mixture, a machine can determine blood volume with 1-2 percent accuracy. 

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