Liquid Breathing

Liquid Breathing

Last week I covered how the EVA pilots would die if they actually had to sit in, let alone pilot, their EVA’s while immersed in LCL or the primordial soup. I also mentioned last week that it was possible for mammals to breathe a liquid as seen in the video below. This process is referred to liquid breathing.

This week we will be exploring the potential for humans to breath liquids as seen in Neogenesis Evangelion, minus the toxic materials, of course. Before we get into breathing liquids we have to take a quick look at how humans actually breathe.

Respiratory system

The Respiratory System is the body system that allows us to obtain oxygen, and remove carbon dioxide from the body. This involves breathing, something that we do hundreds of thousands of time every single day. However, it is not quite as simple as breathe in, breathe out and breathing can be broken down into two parts.

1- Ventilation– moving air in and out of the lungs

Inspiration- breath in

Expiration- breath out

2- Respiration– moving oxygen and carbon dioxide in and out of the body tissues

External- exchanging gas between the blood and the lungs

Internal- exchanging gas between the blood and the rest of the body


The process of ventilation is driven by changing the pressure of the air inside the lungs. When the lungs expand (breathing in) the pressure drops inside the lungs (758mm Hg at sea level) and outside air (760mm Hg at sea level) naturally flows into the lungs. This would be analogous to pulling back or up the plunger on a bicycle pump.

When the lungs contract (breathing out) the pressure increases inside the lungs (761mm Hg at sea level), which is higher than the outside air (760mm Hg at sea level), as such the air leaves the lungs. This would be analogous to depressing the plunger on a bicycle pump. This is also why you can sometimes have the wind knocked out of you from a hard hit, due to the hit compressing your lungs artificially.


Respiration is a bit more complex, but I think a simplified version will suffice for examining breathing in water. The idea of air, or in this case oxygen and carbon dioxide, moving from high pressure areas to low pressure areas will be important just like it was in ventilation. At sea level the pressure of oxygen in the lungs is 100mm Hg and carbon dioxide is 40mmHg. This causes oxygen to move into the blood as the pressure of oxygen there is only 40mm Hg. Carbon dioxide is 46mm Hg, which is higher than in the lungs, so carbon dioxide will move out of the blood and into the lungs.

Gas exchange in the lungs

This exchange of gases happens again in the tissues of the body as seen in the diagram above. A higher pressure of oxygen in the blood, and a low level of oxygen in the body tissue, causes the oxygen to move into the body. The reverse occurs for carbon dioxide where a high level of carbon dioxide in the tissues causes it to move into the blood.

Breathing in Water

If you’ve kept reading, then now we can get to the fun part. As you saw at the beginning of the post, it is possible to breathe underwater. That being said, it is nowhere as simple as it looks. First off, the oxygen in water can move into our blood if it reaches our lungs, just like air does as described above, but there are several problems with this and it is the reason we drown when our lungs fill up with water.

1- There isn’t enough oxygen in the water to meet the needs of the body

2- Our lungs have no real way of moving the water in and out of our lungs, so once they fill up that’s it

3- No removal of carbon dioxide from the body, so the blood pH drops rapidly

4- The cells of our lungs haven’t evolved to be submerged in water and are damaged (it’s how they can tell if someone drowned in fresh or salt water)


According to Henry’s Law the pressure of a gas in water is equal to the pressure of the gas next to the water. Simplified it means that the amount of oxygen in water is equal to the amount of oxygen in the atmosphere. However, this can change as the temperature of the water increases. The human body normally has a temperature of 37 degrees Celsius, and any liquid in our lungs would need to be at or at least very close to 37 degrees Celsius. This would mean that the water would hold much less oxygen than expected and it would be less than the amount needed to support a person at even a resting state.

Other Liquids

Since plain old water is not going to work, scientists have been using other liquids that can hold higher amounts of oxygen. The first of these that was tried in the 1960s was highly oxygenated saline solution and it worked for a short time, providing the researcher with oxygen. However, the test subject still developed pneumonia, and there was still one other problem, namely the buildup of carbon dioxide in the fluid present in the lungs. Having large amounts of oxygen is no good if the carbon dioxide level builds up due it being unable leaving the body.

The second liquid that was tried was perfluorocarbons, which held even more oxygen and are much gentler on the lungs. This is what was used in the mouse video, and it does actually work quite successfully. Rats, could survive for about 20 hours on the fluid while cats have survived as long as several weeks. There was no mention of the issue of carbon dioxide, so either perfluorocarbons can hold an inordinate amount of carbon dioxide or some method was devised to cycle fluid through the lungs to keep it fresh.

Carbon Dioxide Removal

There really are only two ways of effectively removing carbon dioxide from the body: one, let the lungs do their job, or two, try and make an artificial lung to do the job for you. No I am not talking about the iron lung, as that only provided mechanical ventilation when the diaphragm and the accessory muscles of respiration stopped working. What I am talking about is an actual artificial lung that can exchange gases between the air and the blood. It has just entered clinical trials, and it’s meant as a stop gap until the individual can receive a lung transplant.

An early version of a carbon dioxide removal device was used in the 1960’s as a way to remove carbon dioxide from the body while on liquid breathing. The test subject was able to breath for several hours on the device, but it was recommended that it never be tried again due to the subject only being able to lie still, and also describing it as less than pleasant experience. Science has, however, come a long way since then and newer methods of liquid breathing have been invented.

Liquid Ventilation Systems

Liquid ventilation or liquid breathing can be broken into two different systems.

1- Total– In this system the lungs are completely filled with liquid and systems must be put in place to cycle the fluid through the lungs and refresh the fluid so that it has the correct balance of gasses when it enters the lungs. It is currently undergoing animal trials in France and Canada. Total liquid ventilation can potentially benefit individuals with severe lung failure and as a method to cool the body rapidly after heart attacks to slow the body’s metabolism and prevent cell death.

2- Partial– Here the lungs are only filled to about 40% of their total volume. A system is still used to cycle the fluid through the lungs and is less technologically complex than a total liquid ventilation system. Unlike total systems that are still in development, partial liquid ventilation is currently used as a way to help support the underdeveloped lungs of premature infants.

liquid breathing
Neonatal treatment

Other benefits of liquid breathing

1- Deep sea diving- Nitrogen levels in the blood
2- Deep space exploration- protection against high G forces (I’d like to think this is why Hideki Anno went with his who entry plug thing in Evangelion, but to be honest it probably was the womb analogy)


FYI- Liquid Breathing turned out to be a much more interesting and revealing topic than I anticipated. I knew about the pleurofluorocarbons, and the mouse using them to breathe underwater, from back when I was in college. What I did not know was how far the research had come and that a version of liquid breathing was now being used to treat premature infants. You can bet my students are going to get some of this during their respiratory system unit next year. It’s the first one I cover so it’s a bit late to throw this in now. Anyway, yes, we can actually breathe liquids but don’t expect anything like Evangelion anytime soon.


If you have any comments or questions please leave them in the comments section below.


2 thoughts on “Liquid Breathing

  1. Pingback: Anime Science 101- LCL from Neogenesis Evangelion

  2. Pingback: Anime Science 101- How Anime and the real world are connected

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