Dizzying Heights: Your Body in Orbit
Summary of a public talk given at a BC Balance and Dizziness Disorders Society (BADD) meeting at St. Paul’s Hospital in Vancouver on May 15, 2013.
Speaker: Cam Cronin, Public Programmer at the HR MacMillan Space Centre in Vancouver.
Two days before our May talk, most of us had seen news clips of Canadian astronaut Chris Hadfield being carried from the Soyuz landing capsule in a reclining chair. Clearly, Commander Hadfield and his crew would face significant challenges readjusting to Earth’s gravity after 146 days aboard the International Space Station. What effect did outer space have on their bodies?
Everyone who goes into space suffers from some form of a balance disorder called Space Motion Sickness. In addition, other body changes take place when astronauts go up into orbit and return to Earth.
As there is no zero-gravity chamber on Earth, astronauts train for the physical challenges of space in the ‘Vomit Comet.’ This aptly-named aircraft plunges up and down, allowing astronauts to experience nauseating 30-second bursts of micro-gravity and the floating sensation of being in space. Here on Earth, you can experience brief sensations of micro-gravity when free-falling on the Hellevator amusement park ride or when flying on a plane that hits an air pocket.
Contrary to popular belief, there is lots of gravity in space. The reason astronauts ‘float’ in space isn’t because of zero gravity but because of the way they travel around the Earth. Astronauts orbiting in the Space Station are actually continually falling around the outside of the Earth at an astonishing rate of 28,000 kilometres per hour without ever striking the Earth. Astronauts in orbit are unable to feel gravity; they feel and look like they are floating because everything around them in their space craft is falling at exactly the same rate.
One of the first things astronauts experience up in space is some sort of difficulty with their vestibular system. The balance organs are designed to work with Earth’s gravity. The fluid in the semicircular canals sloshes back and forth; electrical signals sent to your brain from your inner ear help you figure out your spatial positioning. Surprisingly enough, this part of the vestibular system works quite well in outer space.
It is another part of the balance system, the otoliths (also called otoconia), that causes temporary problems for all astronauts. The otoliths are tiny rocks that sit on top of equally tiny hair-like structures within the inner ear. On Earth, gravity causes the otoliths to swing back and forth as you move. This tells your brain whether you are moving up or down, to the right or left, or backwards or forwards.
The otoliths cause problems for astronauts because a little bit of pressure is required for them to work properly. Without pressure in outer space, the otoliths no longer move back and forth; or if they do move back and forth, they do so independently of any force of gravity. Consequently, the otoliths are unable to give the correct signal to the astronaut’s brain.
While the semi-circular canal part of the balance system works properly in outer space, the gravity receptor part (otoliths) does not. As a result, part of the astronaut’s brain sends correct signals, but another part signals the wrong thing; the two messages simply don’t add up. This mixed message causes what is termed a sensory mismatch. It is this conflict between the messages received by the brain that is the big key to Space Motion Sickness. The sensory mismatch is believed to be one of the direct causes of astronauts feeling dizzy and confused as well as getting sick to their stomachs.
Every astronaut will suffer to some degree from Space Motion Sickness for the first few days in space. This makes them an ideal test-bed for learning about vestibular problems.
To help their bodies adapt to outer space, astronauts take medication, such as Gravol®. They also refrain from doing strenuous or highly technical tasks, such as operating heavy machinery or undertaking space walks, for the first 72 hours in the Space Station.
The degree to which astronauts are affected by Space Motion Sickness varies. Even astronauts who have been up in space before don’t necessarily react the same way when they go up again.
There is still some mystery involved in how the human body experiences the effects of Space Motion Sickness. After about three days, astronauts adapt to being in outer space. It is thought that they just somehow start ignoring those parts of their brain that are sending them the wrong signal. This process is somewhat similar to getting your sea legs after being on a boat for a while; your body is able to adapt to the motion.
The connection between vision and the vestibular system is being studied by astronauts. Several years ago Canadian astronaut Robert (Bob) Thirsk took part in a program on the Space Station to investigate how where you look influences the balance system up in space.
Thirsk wore a contraption to track what visual clues he was using to try and maintain his balance. He was trying to figure out exactly what happens during the process of vestibular adaptation in space.
What is being learned in space from experiments like this may very well end up trickling down to help those with vestibular disorders here on Earth. Don’t hold your breath, however, for a quick fix to our problems: the process of analyzing and applying the information learned in space takes a very long time.
When astronauts return to Earth, gravity takes over right away. Their balance systems start to give them the correct signals again. Astronauts may have spent five or six months ignoring the signals from the otoliths and now all of a sudden they have to relearn to trust the signals to be correct. For the first few days they will feel nauseated and their balance will be out of kilter.
The body is generally quite malleable up in space. Temporary changes include:
- feet shrinking by a full shoe size;
- getting thinner around the waist-line; and
- gaining up to three inches in height.
The circulatory system adjusts to life in the Space Station by decreasing blood volume by around half a litre after about 10 days.
The body excretes calcium because it realizes a strong skeletal system isn’t really necessary in space. It adjusts by losing about one and a half percent of bone density for every month spent in orbit.
It is amazing that, after millions of years of evolution and adaptation to being on Earth, the balance system is able to adapt to being in space within three days. The digestive system, however, cannot adjust. It needs gravity to separate ingested solids, liquids and gas into well-defined layers. This allows gas bubbles to be expelled as burps or farts. In space, instead of a clear delineation, you get quite a mess!
To maintain muscle strength, which isn’t needed in space, astronauts work out for two hours daily. As regular weight lifting doesn’t work in a micro-gravity environment, they do a variety of resistance exercises.
All astronauts need about six weeks to readjust to life back on Earth and feel themselves again, following a detailed program of rehabilitation training.