Are air cavities in the body a problem when diving deep?

10 April 2011

Part of the show Are Dogs Ticklish?

Question

Hi Naked Scientists,

I love your podcasts and listen to them regularly in my car to and from work. It's inspiring, intriguing and a wonderful way to spend some spare time that otherwise would've gone to waste!

In regard to your listener's questions section, I do have a question that you may be able to answer.

You probably heard about deep-sea diving with suits in which the divers breath fluids. The movie "The Abyss" portrays it wonderfully. The diver is put into a diving suit which is filled with an oxygen-rich fluid that he can breath. After some disorientation, the diver starts to breath the fluid and can dive to depths of up to hunderds or thousands of meters. (Don't you love sci-fi?)

Still, one thing puzzles me. There's more air in a body than just in your lungs. What about all the air in the Eustachian tubes in your ears? Won't your eardrums rip when the pressure changes that much and there's still air in those tubes? And what about the gasses in your bowls or stomache? Will they dissolve or will you also need some sort of an enema when you dive to those depths? Is it vital to burp so that all the gasses in your stomache are gone? And are there any other air bubbles inside a body that usually are harmless but could seriously injure someone at those depths?

Kind regards,

Eelko de Vos, the Netherlands

Answer

Chris - It is a very good film and it does seem very futuristic, but it is actually partly reality. These chemicals, these liquids do exist. They're called perfluorocarbons. They include fluorohexane for example, so a string of 6 to 8 carbon atoms with lots of flourines hanging off the side and they're very good at dissolving oxygen. So, one way of doing this would be to instil these fluids into the respiratory tract and you saturate them with the oxygen, and then you move the fluid in and out, in the same way that you would when you were breathing.

Why this is helpful is that when a person descends underwater, the pressure they feel from the surrounding water goes up and up, the deeper they go. So, you have to therefore put the gas into the lungs to keep the lungs inflated, under progressively higher and higher pressures. One consequence of this is that it drives other gases like nitrogen and things into the tissues at extremely high pressures which means that then when you decompress, those gases come out of solution in the tissues and form bubbles which can cause the bends, they can cause damage to the brain, and cause damage to bones and muscles and so on. So if you use a fluid in the lung, because fluids are incompressible then you wouldn't have the same problem because the fluid would withstand the pressure being applied by the outside water much better.

The issue with these fluids though is that they're not very good at removing CO2. They're very good at putting oxygen in. They're not good at getting carbon dioxide out and to compensate for the fact that they don't move CO2 very well, you'd have to move a lot of the fluid a lot of the time, and that's one of the major hold ups with doing this. In terms of the liquid getting into other body cavities and body parts, this isn't such a problem actually. The eustachian tubes that you mentioned, they run between the back of the throat and the ear, so they would just fill up with the fluid anyway. The other body cavities, well, they wouldn't actually be exposed to the fluid directly because it will be in the respiratory tree. So, there wouldn't be a problem there and if there were any leakages of the fluid into other places, you would just pass it, I would think. It certainly wouldn't become part of the systemic circulation, so it should be okay.

I make it sound like it's all easy and a problem that's been solved. It is being used in a limited way, but it's certainly not mainstream yet by any stretch of the imagination.