Solving the case of the fainting astronaut
Friday, 16 January, 2009
Heidemarie Stefanyshyn-Piper has fast become an internet favourite, for all of the wrong reasons.
Despite a stellar career as a captain in the US Navy, a mechanical engineer and twice a mission specialist on space shuttles, she is unfortunately best known for losing a tool bag while on a space walk – or extra-vehicular activity, in space-speak – which apparently can be spotted from Earth.
And before that unfortunate drama, she was captured by the cameras fainting twice at a news conference following re-entry from her first mission.
While video netheads may spoof her, which they have done mercilessly, there is actually a serious side to the fainting spells she experienced.
It is in no way unusual for astronauts to faint in the hours after landing, with conservative estimates suggesting that up to 40 per cent of all astronauts will experience fainting or at least dizzy spells on their return home.
To investigate the reasons behind this phenomenon, and to find out how to avoid it in future, a fascinating research project is underway on the International Space Station.
Called the Cardiovascular and Cerebrovascular Control on Return from ISS experiment (CCISS), this Canadian-led project aims to study the effects of long-duration spaceflight on the heart function and blood pressure of space crew.
There are plenty of earthly reasons for the project as well. The project involves learning more about long-distance data acquisition, the potential of telemedicine, common disease states like hypertension and blood pressure dysregulation, and the differences in blood pressure between men and women.
The team is led by principal investigator Richard Hughson from the University of Waterloo and co-investigators Andrew Blaber from Simon Fraser University in Vancouver and Kevin Shoemaker from the University of Western Ontario. These researchers are all exercise physiologists, also known as work physiologists, with an interest in the control of blood pressure and blood flow.
They are investigating the autonomic nervous system, which controls temperature, digestion, heart rate and blood pressure amongst others, and which does so automatically through a variety of different reflexes.
In space, where things are a little different, those reflexes are upset – or deconditioned – by the lack of gravity. What the researchers hope to do is understand more about the normal state of blood pressure by testing it in unusual circumstances.
“The point of all this is that you have reflexes that sense and regulate blood pressure, and these are very sensitive to gravity,” Kevin Shoemaker says.
“Just like training an athlete or training a muscle, it may be that this nervous system can be trained and can be de-trained. We are testing the idea that when you take away gravity you cause a deconditioning stimulus for this nervous system.”
When the system is deconditioned, and then returned to gravity, all of a sudden that gravity is sucking blood away for the heart, he says. “The system has changed and the net result, the most common symptom that you might see – and you can see it on Youtube – is astronauts fainting.”
Fainting or dizziness is the primary symptom of deconditioning, and no one is entirely sure what causes it, Shoemaker says. It could be due to the brain, the nervous system, the heart itself or the blood vessels (the most promising candidate). Either way, something has changed.
“If this were to occur long-term, we don’t know what kind of problems could develop. What we are able to do with the space station is study this system over six months, which is the longest time ever that people have had the opportunity to study the deconditioning of space travel.”
---PB--- Flight experiments
The Canadian team has been working on this project since about 1999, but for one reason or another was unable to begin in earnest until 2006. It is a long-term project, expected to last for several more years, involving at least six astronauts who are on long-term missions.
The experiment protocol has three levels: pre-flight, in-flight and post-flight. The pre-flight testing is the easiest as there is a wide window of time, Shoemaker says. A month or so before the mission takes off, the research team heads to Houston to collect data on the astronaut.
The data collected include blood pressure, heart rate, brachial artery and aortic blood flows, cerebrovascular responses, arm vein pressure, breathing rate and carbon dioxide exhaled, baroreflex sensitivity, and blood flow regulation.
The astronauts are also subjected to lower-body negative pressure, in which suction is applied to the lower body in a negative pressure tank to simulate gravity, and from that the researchers are studying how much and how fast blood vessels constrict.
“The rate of change is one of the primary objectives,” Shoemaker says. “And also in the brain – how well blood vessels dilate, especially when you stand up. If this blood flow into the brain falls too far, then you will faint.”
The team then re-tests the astronauts to study their responses immediately upon their return to Earth.
They are eagerly awaiting their fifth subject, experienced flight engineer Sandy Magnus. The 44-year-old is on her second mission in space and is part of the Expedition 18 crew, due back in February.
The reason the researchers want to get their hands on her data is simple – she’s female.
“In terms of blood pressure control, men and women typically have very similar blood pressures, but the way that women get there is different from men,” Shoemaker says.
“A lot of our research is studying the role of oestrogen in blood pressure reconditioning. It seems to have quite a potent effect.
“One of the interesting things with space travel is that women are much more susceptible to this problem of fainting than men are, so studying a few women is very valuable to us, because we do expect dramatic differences between the sexes.”
---PB--- Faint of heart
Running the experiments is no easy thing, as the researchers have to work within the time schedule set by NASA. To perform the tests, equipment is shipped to the NASA sites in Florida and California, where temporary laboratories are set up.
The pressure has been eased somewhat by an Australian connection – one of the pieces of equipment being used is the PowerLab, from Australian company ADInstruments.
PowerLab is a data acquisition system that records physiological signals for easy analysis on a normal PC or Mac. It is being used to co-ordinate the collection and analysis of the variables related to all aspects of this study.
Shoemaker is happy to give ADInstruments a plug as he’s "not on a retainer", because the company donated some of the equipment for the project’s second lab.
The main laboratory is at the Kennedy Space Centre in Florida, where NASA prefers its space shuttles to land. If the weather over Florida is a bit dodgy, the alternative is Edwards Air Force Base in California, where the project has a second, equally well-equipped lab just in case. Teams of four investigators are placed at each site to optimise the data collections.
“To help us get going [ADInstruments] donated some equipment to us to use; they shipped us a couple of pieces of brand new equipment to make sure we collected the data, should we need to, in California."
Apart from the pre- and post-flight tests, the team is also collecting data on the astronauts while they are on the station itself, data that is downloaded to Earth straightaway.
"So, in addition to studying blood pressure control in astronauts, this research is, in a small way, contributing to the growing field of telemedicine – how to obtain data from a distance, look at it somewhere else in the world and make a decision about the health of the individual," he says.
In addition to maintaining crew member health and pioneering telemedicine from space, the project does have a very earthly component: blood pressure dysregulation and hypertension are two obvious disease states of interest.
“There are many different problems with blood pressure regulation, so to know how the system works as an integrated system between the nerves, the heart and blood vessels, and the brain, is important.
“What we are looking for is the weak link in that whole reflex loop – if we can identify that link that will be helpful.” Right now, he says, the culprit is looking very likely to be the blood vessels themselves.
Then there is the growing issue of physical deconditioning, particularly in the industrialised world.
“If you think about cardiovascular disease and diabetes, the number one modifiable risk is physical inactivity, and this is associated with all of these deconditioning problems. It is primarily the cardiovascular system that is deconditioned so we are keeping one eye on the astronauts who are deconditioning for a variety of different reasons.
The lack of gravity also affects the way astronauts move about the Space Station, as they use their arms to move about but don't use their legs, "so it is important to have countermeasures such as cycling and treadmill-running that regularly challenge the large muscles and cardiovascular system,” he says.
“It’s pretty cool to be part of [the project]. It gains a lot of attention as space has a lot appeal to it, but it is difficult research to do and takes a lot of time. It’s not for the faint of heart.”
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