Can you breathe underwater with fluid-filled lungs?

Question

How can the respiratory system of my genetically engineered people be arranged, having one or two pairs of lungs, one of which uses the tactics of liquid breathing to breathe underwater? (not gills, like ichthyander, but lungs filled with a special fluid that delivers oxygen) Liquid breathing involves filling the lungs with liquid saturated with dissolved oxygen, which enters the bloodstream. The most suitable substances for this purpose are perfluorocarbon compounds that dissolve oxygen and carbon dioxide well, have a low surface tension, are highly inert, and are not metabolized in the body.

So since the creation of the first corresponding fluids, this technology has been improved and the most advanced solution at the moment is called Perflubron or "Liquid" (commercial name). This oil-like transparent liquid with a density twice the density of water has many useful qualities: it can carry twice as much oxygen as ordinary air, has a low boiling point, so after use, its final removal from the lungs is done by evaporation. Alveoli under the influence of this liquid open better, and the substance gains access to their contents, this improves the exchange of gases.

In short, how will a liquid breathing system work?

Note: if someone does not understand, then I want to create a biologically reliable system that synthesizes the above liquid in a natural way, just like our body creates blood or gastric juice. How about creating a special third lung for storing respiratory fluid, where it is drained if it is not needed?

Answer 1

I'm not sure that this would be possible due to how the respiratory system works, more changes than just to the lungs would probably have to be made, unbalanced amounts of fluid intake into places like the heart can cause serious problems.

Problems with this may include: Pulmonary Edema, lung damage due to allot more stress being put on the lungs to move the fluid, possible accidental fluid intake into the bloodstream. This condition is called pericardial effusion and can cause strain on the heart's ability to pump blood efficiently.

In short, lungs would be ineffective and short term solutions for breathing fluids at best even with serious modifications.

Answer 2

Storing instead of lungs

Although I know quite a lot of biology, I'm by no means an expert nor are respiratory systems my field. Still I think I can offer a possible solution. I'll not go into liquid breathing as I think your specific liquid breathing would be near impossible to create biologically.

Humans require to breathe near constantly. This is in part due to our muscles, which are a fast form of muscle that require a lot of energy, thus oxygen, when used. The second is our brain. Brains famously require a lot of energy and aren't able to store much of it. They are very vulnerable to damage if nutrition or oxygen fails.

You say you want an extra lung or lungs. Unfortunately lungs take a lot of space. Making the current lungs smaller creates huge problems. Because the lungs gave less capacity, you need to breathe faster. To breathe faster means to use your muscles more, which consumes more oxygen. In that case you need to breathe more. For genetically engineered people you often want them to have access to a lot of oxygen for their tasks, so you wouldn't want to compromise on the lungs. Although your question seems to be able to handle it a bit, as you could have a preparation period where the soldier is mostly breathing and storing the oxygen, so they can use the liquid lung for an abundant amount of oxygen in case of need.

The problem here is that even with twice as much oxygen in the liquid, your soldiers would run out of oxygen incredibly fast. As stated before, we breathe near constantly, refreshing all the air in our lungs quite quickly. I think within a minute, maybe two the advantage of an extra (set of) lungs is gone, which isn't including the compromises you made on the lungs. The advantage is very low.

Nature is in constant requirement of oxygen. This means if a way to store it has been found, nature often (not always) has the best solutions. Lung breathers under water would seem a good bet. Looking at whales and dolfins we can see they store the oxygen in just a lot of haemoglobin and myoglobin, which simply reside in the muscles and the bloodstream. They do have different muscles, so it's likely to be more efficient for them.

You might make extra storage options inside the body to store the extra oxygen with the liquid you suggest. Pockets just under the skin, or if you can somehow use the ventricles of the brain to store oxygen along the cerebral spine fluid (which by my professional opinion is impossible), or line most organs with a storage part. But again, the amount of oxygen we use is so incredibly high, any advantage is high stress situations would dwindle very quickly. At the start of an intensive task it can be nice, but quickly after that you're left with organs that serve no use until a resting period fills them again.