Liquid Breathing: What, How & Why?

There are many parameters which influence gases in a solution. When in a solution, the partial pressures of each gas affect the pressure that gas exerts. This means that different gases may exert different pressures, and we can add the partial pressures to find the total pressure of the system. The type of solute and type of solvent also heavily influence how gases interact and in fact become part of a solution. The type of solute influences how much of the solute can be held in the solvent until the solvent is saturated. Similarly, the type of solvent influences how much solute it can hold, thereby also influencing the amount of solute needed until the solvent is saturated. As well as this, the total temperature will definitely influence gases in a solution. As the temperature increases, the solvent will be able to hold less solute. For example, if gas was in a solution with a liquid solvent, less gas could be added when the liquid was heated. It should be noted that this is an exception, and that mostly an increase in temperature is marked by an increase in solubility – with the exception of gases dissolved in liquids. This is because at high temperatures the gases move so quickly that they will leave the liquid solvent more quickly than under a lower temperature. As well as this, pressure also has an impact on how gases act in solution, with the solubility of the gas in the solvent being higher with a higher pressure.

At deep depths, the pressures of gases change. Since the total pressure underwater increases, some partial pressures also increase more than others, such as nitrogen’s partial pressure. With an increase in the partial pressure of nitrogen, there are a variety of different issues which can arise. The general higher pressure in the ocean can cause conditions such as high-pressure diving nervous syndrome which “is characterized by neurological, psychological and electroencephalographic (EEG) abnormalities during dives deeper than 150 meters with breathing helium-oxygen mixtures” (“High Pressure Diving Nervous Syndrome”). Specifically focused on nitrogen, as a compressed inert gas, it has many side effects including nitrogen narcosis. Although our air is also made up of nitrogen, it is the fact that the nitrogen is so compressed which is the main reason for its adverse side effects when present in the water. Interesting, nitrogen narcosis does not only result from nitrogen and also may arise due to high partial pressures of neon, argon, xenon and krypton. With an increase in the pressure of the water, there is an increase in the partial pressure of nitrogen in the air tank which the diver has, causing the partial pressure of nitrogen in the blood of the Scuba Diver to also increase. Although the exact reasons are still largely debated, similarly to high pressure diving nervous syndrome, it is very likely that the higher partial pressures of nitrogen in the blood cause swelling of the lipid bilayer in cells contained within the central nervous system, a division of the nervous system which contains the brain and spinal cord. In turn, this is what causes the “change in consciousness, neuromuscular function and behaviour” (“Nitrogen Narcosis in Diving”). As the scuba diver goes deeper, the nitrogen partial pressure increases, thereby also increasing the effects of nitrogen narcosis. However, these are reversible changes and the diver regains normal levels of consciousness and neuromuscular function upon returning to sea level again.

One of the most straightforward (but not exactly practical) solutions is to stop breathing compressed air from a tank at depths below a maximum of 50m, and to instead switch to a different gas in the tank such as helium. Helium is extremely helpful since it doesn’t have the same adverse effects as nitrogen does. However, it also can cause helium tremors below 150m. If nitrogen narcosis does happen when someone is underwater, ascending slowly makes a lot of sense. On the way, there will be decompression allowing the person to recover, and sudden ascent could cause numerous problems due to the massive change in temperature over a small amount of time. Because many scuba divers need to constantly go down into the water and then ascend again, saturation diving has proved to be a very helpful method to get rid of adverse effects of decompression each time after diving. Here, the diver stays at the same pressure even when they have finished their scuba diving work, instead returning to a ship of soe sort which keeps the exact same pressure as what was experienced on the ocean floor. This way, the scuba divers could be at a very high pressure for weeks at a time without needing to decompress and compress after each time they need to go down. This definitely decreases the risks associated with developing nitrogen narcosis amongst other disorders and problems.

Liquid breathing is a technique still in development but also currently being used. Liquid breathing, otherwise known as liquid ventilation, involves an organism breathing a liquid which is rich in oxygen instead of the normal air, as implied by the “liquid” in the name. This is, however, not to say that the person is “breathing” liquids. Instead, the liquids which are chosen can hold oxygen, allowing for it to be released and involved in gas exchange at the alveoli. Currently liquid breathing most often utilises PFCs, or perfluorocarbons, in order to act as the liquid which releases oxygen and takes in carbon dioxide. Perfluorocarbons act as the solvent for the respiratory gas molecules of carbon dioxide and oxygen (the solutes). Upon their release, breathing can be done in an almost normal way.

Liquid breathing has greatly progressed recently. What started out as an idea is now already was used widely before going out of use again, however. The alternative to liquid breathing, positive-pressure ventilation, offers the same treatment as liquid ventilation but involves numerous side effects such as the development of lung disease due to high pressures. After numerous tests using perflubron, it was found that it was no better than high frequency oscillating ventilation in the short term, even though the long term side effects of each was not observed. Because it had no short-term influence, the FDA did not approve perflubron. Even though its use has almost entirely stopped in the medical field with children, it is being tried for different uses such as for cardiac arrest due to its ability to help cool down the body temperature of people (with cold liquid ventilation), and for numerous therapies. Therefore, we honestly do not know how helpful liquid breathing may be in the medical field: although it shows significant advantages over positive-pressure ventilation, we will need to study its long-term effects to see if it has an advantage over other more frequently used techniques. However, it definitely is a real idea and has actually been applied and shown to be effective.

Although there are other solutions to the problem of diving at great depths, liquid breathing may be a very helpful solution. Unlike when filled with gas, the lungs can more easily accommodate changes in surrounding pressure in the water. This allows for the diver to breathe more normally without large changes in pressure. Although it also eliminates the need (or reduces at least) for decompression, liquid breathing has a major disadvantage connected to it due to the fact that total liquid ventilation must be used which would mean that the liquid has a decreased ability to remove carbon dioxide from the blood. In turn, the amount of liquid which would be needed to do this would be too large to carry down to a dive, so other technologies may need to be developed to make the liquid lighter, develop a way of transporting the liquid or find a way of removing the carbon dioxide in a different way.

Works Cited

Cacioppo, J. T., & Freberg, L. (2019). Discovering Psychology: The Science of the Mind (3rd ed.). Cengage.

DIVER. (2011, June). Breathing From Liquid: Is Diving's Holy Grail Here? Undercurrent. https://www.undercurrent.org/UCnow/dive_magazine/2011/BreathingFromLiquid201106.html.

Divers Institute of Technology. (2021, January 8). Saturation Diving Salary Breakdown: What Can You Earn Annually? Divers Institute of Technology. https://www.diversinstitute.edu/saturation-diving-salary/.

Kangal, M. K. O. (2021, January 11). High Pressure Diving Nervous Syndrome. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK513359/.

Kirkland, P. J. (2020, August 22). Nitrogen Narcosis In Diving. U.S. National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK470304/.

Tawfic, Q. A., & Kausalya, R. (2011, January 26). Liquid ventilation. US National Library of Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3191624/.