Motion Sickness
Published on Jan 17, 2009 at 9:26 pm.
3 Comments.
Filed under microgravity flight.
NASA’s reduced gravity aircraft have been known officially as “The Weightless Wonder;” however, they are known around the world informally as “The Vomit Comet.” NASA doesn’t like to use that nickname, though. It really isn’t in keeping with the image that they want to portray. In point of fact, they do everything that they can to minimize how many people get sick. So far this week, though, there have been sick people on each flight. But, the majority of people make it through the flight without major motion sickness episodes.
Motion sickness has been something that has haunted the space program from the very first days. In fact, most of the early astronauts got motion sick. Even today, a large number get sick. This is one reason that NASA is reluctant to let an astronaut do a spacewalk until they know for certain that they won’t get sick in their spacesuit (a potentially life threatening event).
So, what causes motion sickness? I am not sure that anyone really knows for sure. A leading theory that has been around for decades is that the brain gets confused signals from multiple conflicting sensory inputs, and that confusion leads to an upset stomach. I am not really sure why, but it does.
Most of the sensory input about one’s environment comes from visual cues. I’ve heard that it is estimated that for most people, nearly 80% of your environmental cues come from visual inputs. But, there are other inputs.
Your inner ear is also very important for motion and balance. Everyone knows that your ears are how you hear. But, the inner ear also uses similar sensors to detect motion and orientation. The inner ear has fluid filled semi-circular canals that detect motion three planes of motion. There are also otolith organs in the inner ear that act as accelerometers, determining direction and magnitude of acceleration (or the force of gravity). They help to determine the tilt of the head.
Another sensory input is simply the sense of touch. You can feel where things are pressing against your body. When you are sitting down, you can feel the seat pushing up on you. You know that means that the side of your body in the downward direction will feel a higher pressure because of the downward pull of gravity and the resistance of whatever is keeping you from falling. Related to the sense of touch is simply the sense of knowing where your own body is, and how your arms, legs, etc are oriented with respect to you.
All of these senses serve humans quite well on the surface of the Earth. They help you maintain your balance and help you to react if something under your feet were to move, throwing you off balance. However, modern technology can confuse these senses. A common example of motion sickness experienced by many people is riding in a car. The motion of the car tells your inner ear that you are moving. But, if you are looking at things in the car, your vision is telling you that you are sitting still relative to those things. So, your sense of motion and balance gets confused, and you get an upset stomach.
Astronauts in space experience even worse sensory discrepancies. Whenever they accelerate in any direction, their body feels as if gravity is in the other direction. And, if they float in any direction other than with their feet towards what is supposed to be the floor, then their body tries to tell them that “down” is towards their feet, while their eyes put “down” towards the floor. Again, this gives rise to motion sickness. Similar thing come up in the microgravity flight, so they warned us not to float upside down.
To help quell the motion sickness, the NASA doctors gave us SCOP-DEX, a mixture of scopolomine and dexadrine. The dosage was determined by body weight. We had several briefings on how to avoid motion sickness. Still, a number of people got sick. Everyone reacts differently, and apparently even people who fly on the aircraft all the time without problems occasionally even get sick themselves once in a while. The medication apparently works, at least on me, because I tend to be quite sensitive to motion sickness in automobiles, boats, etc, but I didn’t get get sick on the aircraft. The only problem was several hours later, when the drugs were starting to wear off, I got a little light headed.
Since so many people tend to get sick, they required each of us to carry motion sickness bags: two per person. I didn’t use mine, so I kept it as a souvenir of the flight. It was a plain white plastic bag in a paper envelope with directions. They told us to put it over our mouths, holding it with both hands, in case we felt sick. They promised that someone would be by our side to keep us from floating away if that happened. In fact, people on either side of me did just that, and they did get assistance quite quickly. Here is a picture of the bag, something that you are not likely to find on a NASA web site!
-Astroprof
(Ear diagram courtesy Wikimedia)
Ed Davies on January 18, 2009 at 5:44 am: 1
A theory I’ve heard as to why sensory confusion causes an upset stomach is that it’s an evolutionary adaptation to poisoning - if your average hunter-gatherer tried a berry which made them feel giddy then it would be a good idea to get rid of any more still in their belly. I don’t know how well established this is but it seems plausible.
Week of January 19th, 2009 « Dad2059’s Webzine of Science Fiction, Science Fact and Esoterica on January 19, 2009 at 2:31 pm: 2
[…] Motion Sickness […]
Motion Sickness Researcher on January 20, 2009 at 8:17 am: 3
Dear Sirs:
The evolutionary theory is called “Triesman’s hypothesis,” while the theory in the blog concerning sensory input is variously called “sensory conflict” (e.g., see Reason and Brand’s 1975 book) “neural mismatch,” etc.
There is currently no universally accepted theory of motion sickness etiology.