Weird topic that came up during weekend pizza. According to several news stories, hanging upside down for a long period of time can kill a person. The reasons I’ve read is that the blood vessels and heart are fighting against gravity to get flowing in a direction they’re not used to, causing clots in the brain leading to death. Someone countered with why we don’t die in the womb when we’re upside down in the last few weeks. I gave the response that it might be due to the blood flow from the umbilical cord. Just as a pressurized air system can push air into the lungs, the blood flow from the umbilical cord (and the mother) forces the blood through the fetus’s body. Sounds reasonable.
So, is my explanation valid? If not, has anyone discovered or even studied this and found out why babies don’t die being upside down in the womb?
Part of it has to do with blood pressure. The pressure of a column of water is proportional to the height of the water (pressure = height x density x gravitational constant), so if an adult is 10 times the height of a baby, then the difference in pressure between the head and the feet is 10 times greater in the adult. This makes it a LOT easier for the baby to regulate the blood pressure throughout its body even when inverted.
Babies are also surrounded by amniotic fluid which supposedly helps push back against the pressure of the baby’s blood.
This is surely a big factor. If you’ve ever gone SCUBA diving, spending prolonged periods upside down underwater is not nearly as unpleasant as when you do so out of water.
Nitpick: Blood doesn’t flow from the mother, through the placenta, to the fetus. The developing embryo grows its own blood supply, just as it grows all its other tissues. The fetal and maternal circulatory systems interface at the placenta (specifically at the maternal side of the placenta), and that’s where the the fetus’s blood takes on oxygen, gives up carbon dioxide, etc. The mother’s heart doesn’t do anything to force blood through the fetus’s body.* The fetus’s heart does that.
I agree with the other posters that fetal circulation is aided by the fetus’s small size and by the pressure of the amniotic fluid around it (doesn’t insufficient amniotic fluid usually lead to problems?). When the fetus is developed enough to move its limbs, the contraction of those muscles also helps, the same as moving around helps a full-sized human (think about trying to stand for long periods without moving a muscle versus being able to flex your limbs a bit).
*If the mother’s blood pressure or blood volume drops enough, the mother’s heart won’t be able to supply the placenta, and the fetus *will *suffer.
Why is it so bad up in the air then ?
In the water there is no stretching or compressing of the body.
Then this allows the legs to be used for kicking … swimming. moving…
The use of the muscles aids the blood flow into the legs…
If you are upside down in air, stationary, you must be either stretched or compressed, or held stationary, and basically going to have trouble with the breathing ,and with moving and and therefore oxygenated blood flowing around like normal. I don’t think that if you are held upside down in air by some mechanism, your legs are going to be free to kick …free of both constrictions of the bindings/support, and free of gravity ? Your legs weigh a lot and your body can’t support the legs up in the air !
And either the support is cutting off blood flow at one place, OR its holding the leg firmly in one position…
Whether you’re in air or water, there is a gradient in blood pressure from the uppermost part of your body to the bottommost part; Assuming you’re six feet tall, the gradient is about 2.6 psi from the top of your head to the bottom of your feet. This gradient is a natural consequence of fluid mechanics (and gravity) and is unrelated to the flow of blood through your vessels (pressure variations due to flow are superimposed on the aforementioned pressure gradient).
If you’re in water, then the environment surrounding you also has a vertical pressure gradient.* Since water and blood have pretty much the same density, that external pressure gradient is closely matched to the pressure gradient inside your body: the external pressure against your body will be 2.6 psi higher at the lowest part of your body than at the highest part of your body. So if you’re hanging upside down in air, the blood vessels in your head are stretched because they must bear that extra blood pressure caused by your feet being 60 inches higher than your head. If you’re upside down in water, then the extra 2.6 psi of pressure inside your head is pretty much counterbalanced by the extra 2.6 psi being applied to your head by the water around you, so your blood vessels don’t have to take all that stress. Ah, much better.
*The atmosphere also has a vertical pressure gradient, but for a height difference of just six feet, the difference in air pressure is small enough to be negligible for this discussion.
Lots of small children seem to like being upside down (Lil’ Neville, who will be three in August, loves it). Fewer adults seem to seek out that kind of thing. Could that be because being upside down is more unpleasant the bigger you are?
