| Date: | September 26, 2006 / year-entry #329 |
| Tags: | news-flash;non-computer |
| Orig Link: | https://blogs.msdn.microsoft.com/oldnewthing/20060926-19/?p=29573 |
| Comments: | 17 |
| Summary: | In an attempt to explain why astronaut Heidemarie Stefanyshyn-Piper fainted during a welcome ceremony, ABC News reported The heart of an average person on Earth pumps blood throughout the body. But when an astronaut is in space, Levine explained, the blood remains predominantly in their chest cavity. Because of this, he said, the heart tries... |
In an attempt to explain why astronaut Heidemarie Stefanyshyn-Piper fainted during a welcome ceremony, ABC News reported
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Comments (17)
Comments are closed. |
O M F G
Maybe urination of blood?
Not literally…
What I think happens is that the heart detects a higher than normal blood pressure due to the accumulation of blood in the chess cavity and triggers the kidneys to release some liquid out of the system. The kidneys are still producing the urine.
I concur. That’s what I take from this. Effectively she donated a quart of plasma, just as if she had gone into the Red Cross and given up a quart of plasma (plasma<>Red Blood cells). Which is a fair amount of plasma (in terms of TOTAL blood volume, roughly 20%.) While this isn’t a 1:1 ratio (after all she didn’t lose RBCs) But still.
What confuses me is why the blood seems to collect in the Chest Cavity. Blood defies gravity all the time (think legs and head.) So it sems to me that a lack of gravity would be a good thing. Of course I suppose gravity may in the end aid blood.
tsrblke: Actually what happens is that in normal gravity, blood tends to pool in the lower half of your body. But in zero gravity, the opposite happens (because your ciculatory system evolved in the presence of gravity, it has a slight tendency to pump blood UP). So you face and chest get all the blood, while you legs don’t get very much.
It’s kind of like when you stand on your head. All the blood rushes up because your body is used to pumping blood in to your head, not out of it.
It makes you wonder, if you stood on your head for a few months straight, would your body get used to it and then feel weird and dizzy when you stood up normal again?
Hi, Brian
There is an answer to your question. You won’t just feel dizzy. It is an ancient Chinese way to kill a man simply by giving him a full meal and then forcing him in a head down position for a few hours.
Actually, you will notice this when you get cold as well. Your body concentrates blood in your core and there is a procedure to get rid of the excess fluid by urination. That’s why you pee in the pool so much and why scuba divers smell the way they do.
Stick to Windows 95, Raymond. Human physiology is a different beast.
The first commenter is absolutely correct. When there is too much fluid the heart released Atrial Naturetic Peptide (ANP) which increases urination.
The reason the blood pools in your chest isn’t gravity, its pressure. When your chest expands to breathe in, there is negative pressure in your chest, this sucks both air and blood into your chest cavity. Exhalation, if you are not exercising, is passive and does not involve huge pressure gradients. (If you happen to make your living by doing physical exams on children, you can hear a really neat double heart sound when they breathe in, its due to this same phenomenon.)
And to brian, unfortunately the answer is yes, but you don’t even have to stand on your head. I had the misfortune of spending two weeks of my life either flat or with my head below my feet (trendelenburg’s position) after a mistake during brain surgery left a leak in my spinal cord. It took me over a week to be able to stand up again without getting dizzy. (This is also very well documented in medical literature, but the personal experience is a lot more interesting.)
"From 25 to 66 percent of all astronauts cannot stand for 10 minutes following space flight of up to two weeks"
What kind of silly stat is that?
>>What confuses me is why the blood seems to collect in the Chest Cavity. Blood defies gravity all the time (think legs and head.)
If you think about it, you answered your own question. Since the vascular system is designed to return blood to the heart *despite* gravity, when that gravity is absent it becomes all the more efficient at doing its job.
My favourite one :
Almost 50% of the people have intelligence under the average
Except that average intelligence is defined by median, not mean.
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