Eli5 Why does hanging upside down for too long cause cardiac arrest, but being in space is fine?


Like, do astronaughts not have this problem?

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3 Answers

Anonymous 0 Comments


Anonymous 0 Comments

When you hang upside down, your body is affected by gravity in the “wrong way”. Your heart is used to pump blood around in your body and your whole system has adjusted to doing this while you are not hanging upside down, with gravity affecting your body the “right way” around.

When you are in space, your body isn’t affected by gravity. Your body also wasn’t made for this either – there are other problems like your muscles degenerate quickly and your eye-sight deteriorates, amongst other things, but your heart can continue to operate normally.

Anonymous 0 Comments

Astronauts in low-Earth orbit are free falling around the planet. This causes blood to accumulate in the body at the opposite end to the direction of travel.

Astronauts on the ISS experience a phenomenon, I forget the name, of swollen heads and skinny legs because of this accumulation.

Thus when they are “upside down”, which in this context means they’ve changed their orientation in relation to the direction they are free-falling, all they are doing is changing which part of the body the blood accumulates in.

Whichever way they are facing their heart is having to work harder because it’s not getting a gravity assist and other facets of the body’s design that promote efficient blood flow against the pull a gravity become far less effective.