Notes on a talk delivered by Dr Daniel Grant, Aerospace Development Director for CASE medicine at Final Frontiers in Healthcare, organised by ReThinkX at Citylabs, Manchester, 16th February 2017.
Dr Grant began by explaining that, in space travel, micro-gravity is the largest factor effecting human health, particularly if people plan on coming back to earth. Note that there is gravity in space – it's just coming, in varying amounts, from every single large mass, none of which are close enough to stick you to the floor the way earth does. When in orbit, you're actually in free-fall, which isn't really much better. Human bodies experience a fluid shift, with blood pooling in the head. The blood pressure set point also changes, causing problems when they come back home. Even after as little as two weeks in space, astronauts struggle to stand up for ten minutes at a time.
Your balance is affected, and to understand this, we'll first need to understand how balance works. Your body uses a combination of factors; your eyes, your proprioception (where your body is in relation to itself), and a small amount of fluid in your inner ears. This fluid – which is actually rather gel-like – sloshes about, and this sloshing is sensed by tiny hairs in your inner ears. It is this feedback which your body uses to figure out what's happening.
When these things get out of sync – like when your eyes see you moving at high speed, but your ears don't get the amount of sloshing they would get if you were moving of your own accord – you get travel sick. The reason why alcohol makes you dizzy is related to this system. Alcohol is thinner than blood, and is able to diffuse into the inner ear, throwing off the normal signals sent by the sloshing of the fluid. It takes approximately three hours after you quit drinking before the alcohol diffuses out again, and you stop feeling dizzy.
So, when astronauts enter space, they begin by feeling very sick and dizzy indeed. They're in freefall, their eyes don't match their inner ears, their bodies don't feel like they usually do…
Astronauts do get used to this, and gain their sky legs fairly rapidly. Unfortunately, they then get dizzy back on earth, once the space-travel has stopped!
One method to combat this – and most of the problems caused by microgravity – is to mimic gravity using a centrifuge. You may have been on a ride which uses centrifugal force at a fairground; it's the one that spins round and round, until you can feel the force of the spin sticking you to the side.
At this point, I recommend a short break to listen to This Kiss.
This works fine as long as astronauts walk within the plane of motion, i.e., at 90 degrees to the angle of spin. If you start trying to walk up the sides...well, Dr Grant had a demonstration for this. Do not try this at home unless, like Dr Grant, you also appoint two people to catch you.
First, spin round and round with your eyes shut. Open them. Dizzy right? That'll pass.
Now do the exact same thing but keep one ear pressed to your shoulder while you do it. You see how much dizzier you feel? Go throw up, I'll wait.
Oh, and also your eyes become more pressurised and start to bulge against your eye sockets. Fun!
Bones & Muscle
Your bones are constantly being remodelled, which causes problems when you're in space. Assuming you're at sea level, and the surface area of the top of your head and shoulders is approximately 0.1m2, you're carrying about a ton of air. You don't notice this, because you've never known anything different.
In space, however, this weight is suddenly lost. Which means our bones don't need to be as dense, which means they begin to lose mass.
Dr Grant used a demonstration to illustrate the effect of this as well, and I highly recommend obtaining the props to carry this out. Take a crunchie, and snap it in half. That's your bones on earth. Now take an aero and do the same thing. Voila, your bones in space!
Your body also begins to lose calcium, since it needs less of it with your new aero-bones. That ends up passing in your urine, or forming into kidney stones.
Like bones, muscles also begin to weaken in space, for the exact same reason – you don't need them to do as much when you're not holding up a ton of sky. Your body has two types of muscle fibres: fast-twitch muscle fibres – for rapid responses – and slow-twitch muscles fibres – for endurance. In space the slow-twitching muscle fibres “learn” how to become fast-twitching which is just weird once you get back to earth.
Astronauts can lift weights to deal with these effects...but how do you lift weights with no gravity? Well, here's an astronaut to explain.
The Mind & Circadian Rhythms
There is also the psychiatric effect to consider. As Dr Velho discussed in her talk, it's very hard to predict how being alone in space will affect people. The science-fiction thriller Sunshine (one of Alice's favourite films) took this idea to an extreme level, and the science-fiction comedy Rocket Man touches on it as well. Space is big and lonely, and we simply can't mimic those effects on our little blue planet. We're getting better at learning, for example, what sorts of personalities work best, but there is still a long way to go. If you want another movie recommendation, then The Martian also talks about this. I (Kali) personally prefer the audiobook.
'Sunshine' Q&A with Danny Boyle, Mark Kermode and Brian Cox
It doesn't help that your circadian rhythm gets completely out of sync in space. Your circadian rhythm is, basically, your little internal clock. It predicts when morning is coming and starts pumping hormones through you, so you're ready to get up and make breakfast and down some coffee. It also predicts when night is coming, so you start to get sleepy at the right time.
Interestingly, your circadian rhythm isn't exactly 24 hours. Since we're not vampires who die if we stay up a minute past our bedtimes, perhaps there simply isn't enough evolutionary pressure to make our circadian rhythms exactly one earth day in length. Regardless of why this occurs, our circadian rhythm is adjusted daily by the sight of sunlight, which is why it's a good idea to step outside and look at the sun in the mornings. If you don't see sunlight at the right time, there are some interesting (by which we mean horrifying) effects.
On earth, there are a few places which do not have a regular day-night rhythm. These include the north and south poles, and also areas far to the north like Alaska and parts of Norway.
|The reason we don't see this as much in the south is simply because the equivalent strip of land is actually ocean down there!|
SAD or seasonal depression disorder is also a concern. That's when people become severely depressed in winter, another illustration of how much seasons affect our mental health. One way to deal with this is with lighting which mimics the natural rhythm of an earth day, and by selecting astronauts who are less prone to being affected.
The Future of Space Travel?
As you can see, there are a lot of problems to deal with...but we're generating a lot of solutions for them. Dr Grant ended with the idea of space-tourism. Short flights, where you shoot up into orbit and go from England to Sydney in the time it takes to watch a movie. Longer trips. Colonising the moon, and Mars. Maybe some people will want to stay there; consider the therapeutic effects of microgravity on patients with severe arthritis, for example. If people don't intend to come back to earth some of the problems – like decreased bone density – stop mattering as much.
You can read more about Dr Grant's research online, at CASE Medicine. CASE Medicine has a number of exciting events coming up, including an appearance from NASA astronaut Scott D. Altman, and a free talk from Professor Mike Grocott on how we adapt to high altitudes. CASE Medicine also run a Space Medicine and Extreme Environment Physiology module at University College London. As CASE Medicine is based in London, most of their activities are there.
For now, I'll leave you with an interview from Canadian Astronaut Chris Hadfield, on adjusting to his return to earth.