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Space motion sickness: combating nausea in space

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There has been much fuss in the media recently about the launch into space of Tim Peake, the first British astronaut to visit the International Space Station (ISS).

To quote the late David Bowie’s “Space oddity”, Major Tim is now “sitting in a tin can, far above the world” and “floating in a most peculiar way”.

Unfortunately, “floating in a most peculiar way” is likely to induce nausea. In Earth’s gravity, the liquid-filled vestibular system in the inner ear tells us whether we are upright or at an angle and allows us to keep balanced while moving. Within its three-dimensional network of looped tubes, the liquid stimulates microscopic hair cells whenever you move your head, and messages from these cells allow the brain to calculate your position. But in space the vestibular liquid floats around aimlessly, activating the hair cells at random and sending signals to the brain that contradict visual information and leave you feeling sick. The effect is similar to the feeling you get if you spin round on the spot. Because the liquid takes a while to settle down, and continues to activate the hair cells, you become dizzy and feel as if you are still spinning.

Space motion sickness (SMS) affects about half of all space travellers during their first few days, and they can experience nausea, visual illusions and disorientation. It is hard to predict who will suffer. Doing well in weightlessness on parabolic training flights in the “Vomit Comet” does not indicate how well an astronaut will cope in the reality of Earth orbit. Luckily for Major Tim, early reports from the ISS suggest that he has escaped SMS.

Thankfully, most SMS sufferers gradually adapt to their new circumstances and the sickness subsides after a few days in space. One astronaut who suffered particularly badly was Jake Garn, a former US senator who is remembered not for his political achievements but for his unwitting contribution to the study of SMS. Senator Garn flew as a payload specialist on a 1985 Space Shuttle mission, when part of his role was to be subjected to tests designed to increase the understanding of space sickness. Unfortunately, his sickness was so severe that the Astronaut Corps adopted his experience as the standard for the maximum possible level of space sickness. They devised a scale on which being totally incapable was dubbed 1 Garn. Most astronauts apparently reach no more than 0.1 Garn.

On early space flight, astronauts took cyclizine for space sickness. Later they used hyoscine as an antinausea agent, combined with dexamfetamine as a stimulant to counteract any sedative effect of the hyoscine. Nowadays, although modern antinausea agents can counteract space sickness, they are sparingly used. It is thought better to let space travellers adapt naturally over the first day or two rather than suffer the side effects of medication. However, because vomiting inside a space suit is messy — and potentially fatal — even astronauts with low Garn ratings typically apply a dimenhydrinate transdermal patch as a precaution during a space walk or when they don a space suit as a safety measure during launch and landing.

When Major Tim completes his six-month stint on the ISS and returns to Earth he will be advised not to make any swift head movements because he will have to relearn how to move with gravity, and it may take a while for his body to get used to it again.

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