Aspiring astronauts: Beware of the health risks of space travel

Space: the final frontier. But before we embark on voyages to strange new worlds, we must first find ways of keeping our astronauts' brains from swelling and their hearts from being damaged. Researchers say we are on the right track.

Like many others, I dreamt of being an astronaut when I was younger. Inspired by a trip to the Kennedy Space Center in Florida in my early teens, I saw myself boldly going where no man had gone before.

The problem is that I don't particularly like heights, or flying, for that matter. With my feet firmly rooted on the ground, my curiosity took me into the field of human biology instead. But my interest in all things to do with galaxies far, far away never faltered.

So, I hope you appreciate my excitement about two new papers dealing with the effects of spaceflight on the human body.

Many people will be familiar with the concept that during time in space, astronauts' muscles shrink because of the lack of gravity. But it's not just the muscles that are affected.

"The whole body is under stress in the space environment, and the different stressor (microgravity, radiation, psychological, etc.) are entangled," Prof. Marco Durante, from the Trento Institute for Fundamental Physics and Applications in Italy, told me.

Prof. Durante and his colleagues published an article about the effects of space on the cardiovascular system in Nature Reviews Cardiology a couple of weeks ago.

But, before we delve into the effects of extraterrestrial experiences on the heart, let's look first at research hot off the press on how space distorts the brain.

Brain shifts upward on long-term missions

Astronauts live in virtually weightless conditions during their space travels. The scientific term for this is microgravity.

Some astronauts aboard the International Space Station have experienced problems with their vision and increased pressure in their brains as a result of microgravity. The National Aeronautics and Space Administration (NASA) call this visual impairment and intracranial pressure (VIIP) syndrome.

To explore how microgravity affects the brain, neuroradiologists Drs. Donna R. Roberts and Michael U. Antonucci — both associate professors at Medical University of South Carolina in Charleston — and colleagues studied MRI scans of astronauts before and after both short-term and long-term space missions.

The fascinating results were published yesterday in The New England Journal of Medicine.

The study involved 18 astronauts on long-term missions to the International Space Station, lasting on average 164 days, and 16 astronauts who had been on short-term space shuttle flights averaging 13 days.

The team found that 94 percent of the astronauts on long-term missions experienced a narrowing of a groove at the top of the brain, called the central sulcus, while this only happened in 19 percent of the space shuttle travelers.

Additional data showing multiple sequential brain scans were available for a subset of the astronauts. Analysis of these revealed that the brains of all of the long-term space explorers, but not of those on short-term missions, had shifted upward in response to the microgravity conditions.

These are not the signs you're looking for

Of the astronauts on long-term missions, three developed severe VIIP. But the team couldn't pinpoint any specific changes in their brains that could explain why they had developed VIIP.

Dr. Antonucci told me, "NASA has noted that approximately 60 percent of astronauts on long-duration missions experience decreased visual acuity and [roughly] 40 percent of astronauts are classified as having VIIP."

In this study, he added, only astronauts with severe VIIP symptoms had follow-up assessments. The lack of additional data from those with less severe symptoms, made it challenging to draw conclusions about what causes the symptoms of VIIP.

"Ideally, a full complement of information would be available for each returning astronaut to allow a more thorough comparison of imaging findings with clinical symptoms and other non-imaging testing," Dr. Antonucci said.

"Exposure to the space environment has permanent effects on humans that we simply do not understand," Dr. Roberts comments not the findings. "What astronauts experience in space must be mitigated to produce safer space travel for the public."

The areas most affected during long-term space missions were those that control movement of the body and higher executive function, pretty essential to an astronaut on a space mission.

What might happen on extended missions, like NASA's journey to Mars planned for the early 2030s, is as yet unclear.

"We know these long-duration flights take a big toll on the astronauts [...]; however, we don't know if the adverse effects on the body continue to progress or if they stabilize after some time in space."

Dr. Roberts

Well, we can only hope that our intrepid explorers' brains will acclimatize during their extended time in space. But let's turn out attention now to matters of the heart.

Swollen veins and puffy faces

A fully functioning ticker is essential to an astronaut's health. The two biggest risk factors for the cardiovascular system in the extraterrestrial environment are microgravity and space radiation.

The gravity that we experience on Earth causes a pressure gradient in our cardiovascular system. Take away gravity, and the pressure is the same across the body.

Right after take-off, this means that blood rushes into the chest and head, causing swollen veins and puffy faces all around.

In microgravity, the heart doesn't have to work as hard to pump the blood around the body. This is bad news because the system quickly becomes accommodated to what would equate to an extremely sedentary lifestyle on Earth.

Blood vessel walls thicken and become stiffer, which might predispose the astronauts to cardiovascular disease.

Radiation is a known risk factor for cardiovascular disease, which in turn is a leading cause of death on Earth. Even quite low doses of radiation, such as 0.5 Grays (Gy or Grays are the units of absorbed radiation) are known to increase the risk of developing cardiovascular disease.

For comparison, emergency workers involved in the cleanup after the Chernobyl nuclear disaster in 1986 were left with a higher risk for cardiovascular disease at levels as low as 0.15 Grays.

Radiation 'potentially most important hazard'

Space is full of radiation, which doesn't sit well with our ambitions of exploring distant stellar objects. But, we really don't know enough about cosmic rays to be sure that they will have the same damaging effects as radiation back on Earth.

"Radiation is potentially the most important hazard. But this will depend very much on whether radiation effects have a threshold at low doses, say around 0.5 G[rays]," Prof. Durante told me.

Deep-space missions, like the one to Mars, would need to take the potential hazards of radiation into consideration and develop specific countermeasures, he added.

More research is needed. "Accelerator-based studies to identify cardiovascular damage at low doses are very urgent for answering this question," Prof. Durante said.

He also told me that studying what happens to the cardiovascular system during space missions is no mean feat. "One of the main problems is that the cardiovascular system is connected to essentially all other organs, so it is not easy to make a cause-effect distinction," he explained.

So, how will our astronauts protect themselves on their journeys into uncharted territory? Prof. Durante thinks that we are on the right track to finding out.

"I am personally very optimist and we are making very fast progress. Countermeasures include physical exercise, antioxidants, nutraceuticals and, for radiation exposure, shielding."

Prof. Durante

To infinity and beyond

Dr. Antonucci shares this sentiment. "[...] we strongly believe that [the results of our study are] the first step in making long-duration space missions safer for our astronauts and others who ultimately travel in space," he told me.

"Now that we have demonstrated [brain changes] on MRI, we can begin to design ways of either minimizing the changes themselves or mitigating their physiological manifestation."

He said that certain medications can counteract the symptoms of VIIP, but "whether these would work in a microgravity environment [...] is uncertain."

"[An alternative] approach might be to design a vehicle which replicates our terrestrial environment — such as a transport vehicle with artificial gravity to minimize the changes that occur in a microgravity environment," he suggested.

"Ultimately, there are so many talented people working on our space program that we are confident that our findings will facilitate extensive discussion and study to determine approaches to minimizing the changes and/or mitigating the effects of these changes on astronaut function."

Dr. Antonucci

Before we zoom off to the stars at warp speed, there are clearly some kinks that will need to be ironed out.

With just over a decade left before a group of intrepid explorers will set to embark on the first trip to the Red Planet, I have my fingers crossed that we can address these issues and keep their brains and tickers in good enough shape to get them there and back safely.