CNN News:零重力可能导致宇航员血液倒流

Here on Earth where most of us live, we spend about a third of everyday lying down sleeping and two-thirds standing or sitting in an upright position.
That's not really how it goes in space when people are weightless and the zero gravity environment causes more fluid to shift to the head. Faces get puffy, legs lose volume and appear to be smaller. Many astronauts have complained of eye and back problems after coming back down to Earth and its gravity.
And now scientists say they've discovered some new risks with long term space flight. A study published recently in JAMA Network Open, a medical journal, examined 11 healthy astronauts who'd been on the International Space Station for six months. Eight of the them had unusual characteristics observed in their blood. For instance, six of the astronauts had either stagnant or reverse blood flow from their heads.

The lead author of the study says he doesn't know if that's actually harmful. The blood's still leaving the head from other pathways, so flowing backwards through a jugular vein may not be dangerous. But he says it does show a change in how blood moves through the body while in space.
Another issue the study found was blood clots. One astronaut had one. Another showed signs of a partial blood clot. That is potentially harmful as the clots can block the flow of blood to the lungs. The astronaut who had one was treated for the rest of the spaceflight and made it home safely.
What does all this mean? Well, one researcher says these issues have probably been occurring since humans first ventured into space and that they would likely resolve themselves when astronauts came back down to Earth. Knowing about them now gives doctors something else to monitor when people leave our atmosphere.