If an artificial placenta either currently exists or could be developed could it be hooked up to an adult and the adult would not need to breath, say if he was underwater or something like that.

The placenta needs to breath, then. Or get oxygen/get rid of CO[sub]2[/sub] in some other way. And it has to do it at the rate adults (not fetuses) breathe. You can’t sidestep breathing like that.

That’s a more limited function than a heart/lung-machine so yes, it could be done. But you’d still need a close source of oxygen, or a hell of a lot of blood to fill the lines.

Nitpick: It’s “to breathe.”

You’d need a serious amount of surface area on the placenta to get enough oxygen underwater. Here is part of a post I made a year ago in another forum (in the context of a reply to someone talking about genetically adapting humans for space travel, and mentioning adapting them to breathe water and live in water-filled ships for I forget what reason the person was arguing it would be an advantage.) Spoliered for length.

…But modifying someone so that they can breathe water? Don’t hold your breath. Water doesn’t hold enough dissolved oxygen to support large, warm-blooded organisms. According to Wikipedia, an average diver needs 1 liter of oxygen per minute. The amount of oxygen that can be dissolved in water depends on the temperature and pressure. According these tables, fresh water at a comfortable 30° C and 1 atmosphere can hold 5.9 ml/l of oxygen. This means that the “average diver” would need all the oxygen from around 170 liters (45 gallons) of water every minute. The highest oxygen saturation on the chart is 40.9 ml/l at 0° C and 4 atmospheres, so the diver would need all the oxygen from around 24 liters (6.4 gallons) of that water every minute. Also pilfered from Wikipedia, I see that the typical tidal volume (amount of air taken in/expelled from the lungs with each breath) for an adult human is around half a liter, and the average adult breathes around 12-20 times per minute. For the sake of simplifying things, let’s call it 16 breaths per minute, and 8 liters of fluid per minute pass through the lungs. So for this “average diver” to get enough oxygen, the comfortable water would need to contain around 21 times as much oxygen as the saturation point, and the fatally-cold, high-pressure water would need around 3 times the saturation amount of oxygen. And that is assuming that the lungs could extract 100 percent of the oxygen from 100 percent of the water that entered the lungs with each breath. Actual extraction numbers would be only a fraction of that, and thus dissolved oxygen amounts would have to be even higher. The people would have to be made cold-blooded and live in bone-chilling water (needing less oxygen but becoming very slow thinkers—want to have the sloths from Zootopia making sure your spaceship remains safe?), or trail along large, lacy, and very venerable external gills, or find a way to make oxygen extraction by the lungs vastly more efficient (and in the process make it impossible for them to breathe air, because the amount of oxygen in “normal air” would suddenly be toxic to them.) And you would still have to deal with the issue of releasing waste carbon dioxide.

If the blood in the placenta is not supposed to exchange oxygen with a oxygen enriched environment, aren’t we talking about gills rather than a placenta?

You’ll probably need some Placenta Helper 1st.

[quote=“Darren_Garrison, post:5, topic:785264”]

You’d need a serious amount of surface area on the placenta to get enough oxygen underwater. Here is part of a post I made a year ago in another forum (in the context of a reply to someone talking about genetically adapting humans for space travel, and mentioning adapting them to breathe water

That pretty much covers it>