We see instances of humans breathing liquids in sci-fi movies, TV shows and in books. An individual will be immersed in an exotic fluid solution and, usually after a brief bit of panic, they’ll find they can breathe normally. One of the most iconic examples of this can be seen in the movie “The Abyss“.

Actor Ed Harris, who plays ‘Bud’, needs to go deeper than anyone has ever been. He must go to the bottom of The Mariana Trench to save his crew-mates by defusing an armed nuclear bomb. They’re aware that a normal gas based SCUBA unit couldn’t handle the immense pressure at those depths. Luckily for them, liquids diffuse pressure evenly and are harder to compress than a gas. Much harder. Enter the experimental liquid breathing suit. In the end, after some difficulty adjusting, he is able to “breathe” the liquid and ends up saving the day.

But is there any science behind it?

There is some… For any fluid to work for human respiration, it has to perform two functions extremely well — delivering oxygen to the lungs and removing carbon dioxide. Air does both excellently, as do other combinations of gases (Nitrogen is replaced with Helium when divers need to go below a certain depth). It’s not unreasonable to ponder if some liquids can do the same thing. The first experiments involving liquid breathing took place in the 1960s. Mice and rats were made to breathe a saline solution with a high concentration of dissolved oxygen. They survived for a short while, but even though the solution delivered adequate oxygen, it was ineffective at removing carbon dioxide; over time, it caused irreparable damage to the lungs.

Some years later, scientists began experimenting with perfluorinated hydrocarbons — liquids similar to freon that (despite being harmful to the ozone layer) are able to dissolve both oxygen and carbon dioxide easily. The first results were much better than with the oxygenated saline solutions, and the mice were able to go back to normal gas breathing afterward. Over the next few decades, the formulas for breathable perfluorocarbons (PFCs) have been more refined. Currently, the best known liquid of this kind is called perflubron, also known by its brand name ‘LiquiVent‘. LiquiVent is an oily, clear liquid which is twice the density of water. It can carry more than double the oxygen (per unit of volume) as air can. It’s also inert, which means that it’s extremely unlikely to damage lung tissue. Because it has a very low boiling point, it can be cleared from the lungs easily and quickly by evaporation.

While it does seem fascinating, the primary reason for the experiments is medicinal since liquid breathing would be extremely beneficial for certain lung problems.

For example, infants born prematurely can have underdeveloped lungs. Because perflubron can carry much more oxygen than air, it can help relieve respiratory distress until their lungs are able to function on their own. It has also been used for adults with acute respiratory failure, whether due to burns, trauma, disease, or the inhalation of smoke or other toxins. The liquid encourages the collapsed alveoli to open, which washes out contaminants, and provides better exchange of oxygen and carbon dioxide for lungs that are not yet fully functional. In clinical practice though, the lungs are usually not filled completely with the liquid; instead, liquid ventilation is usually used in tandem with conventional gaseous ventilation.

But there must be a downside, right?

Unfortunately, yes. For all the benefits, liquid breathing still involves one major difficulty — it’s much harder for a human’s lungs to move liquid in and out than it is to breathe a gas. The exchange rate of moving oxygen in and expelling carbon dioxide out falls sharply because our lungs are just not strong enough to efficiently move the liquid in and out of our lungs. Even though perflubron is so much better at carrying oxygen and carbon dioxide, that advantage is lost if you can’t circulate it rapidly enough. Without the use of a mechanical ventilator, it is especially problematic for someone who’s ill, and even a diver in top condition could get very tired after a few minutes of such laborious breathing during a deep and strenuous dive.

So yes, humans can technically “breathe” certain oxygen rich liquids. Unfortunately, we are only able to do it for a few short minutes because our lungs are not strong enough to circulate the mixture for any extended period of time. This may change in the future however, as scientists continue to experiment with new methods and exotic combination of chemical liquids.

References:

Maria Laura Costantino, Philippe Micheau (2009). “Clinical Design Functions: Round table discussions on bioengineering of liquid ventilators“.

Shaffer, T. H., M. R. Wolfson, and L. C. Clark: State of art review : Liquid ventilation. Pediatr. Pulmonol. 14:102 109, 1992.

“Partial liquid ventilation in critically ill infants receiving extracorporeal life support“. Philadelphia Liquid Ventilation Consortium

Wolfson MR and Shaffer. “Pulmonary applications of perfluorochemical liquids: Ventilation and beyond” Rev 6(2): 117-27, 2005.

“Pulmonary applications of perfluorochemical liquids: Ventilation and beyond“