How much is known about the biochemical aspects of the moment of birth when a new born mammal takes its first breath. What rapid changes are required for the lungs to start absorbing oxygen for the first time. How much is known of this field of science.
To extrapolate. Can the reactions be reversed so that a mammal, lets say a human, can then go back to surviving a flooded lung and derive oxygen from another source as in the womb.
The latter seems a pretty awful stretch. Remember that a fetus does not derive oxygen from its lungs, but from the umbilical cord, and once the cord is cut, that attachment stops working pretty quickly.
As for the former, it sounds like an interesting subject for study!
Mammals can breathe highly oxygenated liquids such as perfluorocarbons. As Trinopus notes, however, this is fundamentally different from how a fetus receives oxygen in the womb, which is via gas exchange from the mother’s blood in the placenta.
You could in theory have a machine that oxygenates and scrubs the blood, then returns it to the body that would mean you didn’t need to breathe. Without carbon dioxide building up in the blood, you might even be able to hold your breath indefinitely without triggering the breathing reflex.
Is that how the heart-blood machine works for open-heart surgery?
Yes - called extracorporeal membrane oxygenation (ECMO).
We were having a discussion regarding water births, as someone was describing a birthing video where the babies head had delivered under water, and the mother was waiting for the next contraction to finish delivering, which took over a minute. Apparently this is fine as long as the babies head stays under water, as oxygen is provided via the placenta and the lungs are not inflated. I know (from personal experience) that partially delivered babies are perfectly capable of inflating their lungs and crying through the rest of the delivery. Other babies take their time (and maybe require a sharp smack across the buttock, if modern obstetrics allows such violence in the birthing suite).
It seems to me that the first breath has some flexible timing, but is non-reversible once it occurs.
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Quite a bit is known really.
The body undergoes essentially irreversible changes - and the first breath is basically what initiates these changes. Before the first breath the lungs are compressed, and they resist bloodflow enough that the majority of blood in the fetus travels in a different path. Important parts of this different path are the presence of the placenta - and thus a pathway though it, and the presence of the foramen ovale - the “hole in the heart” which allows blood to flow directly from the right to the left sides of the heart - allowing oxygen rich blood from the placenta that is travelling into the heart via the venous supply to be pumped directly out to supply the body without needing to transit the lungs. Once the first breaths are taken the restriction through the lungs drops, blood starts to flow through them, the presure drop allows the foramen ovale closes off - and eventually it seals forever, and flow through the placenta ceases - even if it isn’t yet severed or blocked off.
I found this really neat digram of the two blood flow regimes, at the bottom of the page they discuss the manner in which fluid leaves the lungs (squeezing in the birth canal, lymphatic drainage, the rest vis adsorption into the blood.)
http://www.embryology.ch/anglais/rrespiratory/geburt01.html
Reversing the body to mimic pre-birth bloodflow would involve some heroic modifications to the bloodflow - especially the bit about creating an artificial foramen ovale. The blood vessels that carried the umbilical flow are long since gone by adulthood. So you would be doing a lot of new plumbing.
Of course. That’s what a heart-lung machine does. Blood goes into the machine, it oxygenates and pumps it back into the patient. However, there are serious problems with such equipment, but in principle you could improve it so that it works just as well as the placenta did. Blood is flowing through the lungs, but maybe you could suppress someone’s instinct to breathe since they don’t need to if they are on a heart-lung machine.
The “instinct to breathe” is not so much the absence of oxygen but the autonomic response to the presence of carbon dioxide (Wiki “control of ventilation”).
So it’s a different part of the equation with its own problems.
Well, if the heart lung machine is doing a great job and there’s very little CO2 present, the person still may want to breathe. Not sure what happens, to be honest.
In any case, the main thing is that the current heart lung machines suck, so badly that in many cases the accepted technique is to just let the patient die. Since the placenta works, maybe they could be made better. Even if it’s just figuring out how to grow a huge placenta that matches the patient’s immune markers in a bag or something.
You and me both, my brother in GQ out-of-my-depth-but-interested threads. 
This, by the way, is why carbon monoxide leakage into homes/cars/workspaces is so dangerous. The body doesn’t notice that the blood isn’t carrying enough oxygen, AND the buildup of CO doesn’t set off any physiological alarms, either.
The first “Change” that has to occur.
The baby in the womb breaths in and exhales the waters… the amniotic fluid.
The breathing rate may controlled by CO2 building up in the amniotic fluid inside the lungs.
The change is sort of unexplained so far, but it seems that if some babies suffer from drowing in amniotic fluid…
So there seems to be some reason that a lot of babies are born with no symptoms of drowning, and they must be doing something different to the ones which are born drowning.
So the suggestion is that the lungs may be absorbing the fluid.
Anyway what happens is that the naval is connected to the main artery in the babies body. After birth, the placental arteries rapidly changes into being just a tiny thread of residiual substance. This is hugely important, because otherwise the blood filled vessel could be a problem. The blood would stagnante and turn septic. Or leak out the naval. So the placental artery really shrink down to nothing quite quickly.
One effect of taking your first breath is that it triggers a reflex that causes the blood vessels surrounding your lungs to expand.
This *is *somewhat reversible, unfortunately. While the reflex is only supposed to operate once, being in rarefied high-altitude air triggers it to operate in reverse, squeezing down on the blood vessels of the lungs and making it harder to breathe up there than it already would be.
The exception being Tibetans, whose ancestors apparently gained a beneficent mutation that disables the reflex entirely after breathing begins.
