Can you breathe liquid?
Are there a range of special liquids that people like the SAS can use to breathe at very great depths underwater?
Chris - Yeah, this is called liquid breathing. It's been experimented on for a little while because also there's some occasions when forcing gas into lungs is bad. If you've got an adult, for example, with respiratory distress syndrome. This can also affect young babies that are premature.
The problem occurs when the lungs have a deficiency of a chemical called surfactant. Because the lungs contain lots of tiny airspaces called alveoli, the linings of those airspaces are kept saturated with water. Water makes something called a hydrogen bond. It's a sticky molecule, and one molecule tries to stick onto another. This would collapse the alveoli down and make them disappear if you didn't have something there to break this water bonding and make it less sticky. This is what these surfactant molecules do. They help it to remain bigger.
When people have some kind of lung condition - premature babies don't have this stuff, adults can have conditions where they lack this stuff - you don't have any surfactant. As a result the airspace is trying to collapse. As a result it becomes very hard to inflate the lungs and so you have to use very high pressures of gas being blown into you in order to keep the lungs inflated. This can do damage, so scientists have been exploring the possibility of using fluids instead of gas under certain circumstances and also in deep-sea-divers.
Some of the fluids they've been exploring are fluids that don't mix with water so they're organic chemicals, and perfluorocarbons are the class of chemicals involved.
They've done experiments with chemicals with six carbon atoms in a line: That's perfluorohexane. They've also done experiments with eight atoms linked together: that's perfluorooctanes. They haven't done experiments on humans. They've been done on sheep, which is a good model for us because they're also big mammals and have lungs similar to ours. They make a good model and what is special about these chemicals is you can persuade lots of oxygen and gas of any kind to dissolve in this liquid. You then pump the liquid into the lung and it then passes the oxygen into the blood, picks up the carbon dioxide and you pump the liquid back out again.
The problem with this is that lungs are made to move gas, not liquid. It's very difficult to move large amounts of liquid like this. Really, the only time it's practical is when you have someone mechanically ventilating you, in other words moving the liquid in and out for you.
One place where it might therefore have a role is in things like intensive care. It might be possible to use it those setting and people with damaged lungs to get lots of extra oxygen and carbon dioxide out.
Another situation where it might be useful is in the context of deep-sea-diving. When you go deep-sea-diving, something you're well acquainted with, Helen, there's a risk of the bends. As you go down underwater the pressure of gas you're having to breathe in is increased from your tank by your regulator to overcome the fact that you're under pressure under water. You're now breathing gas which is at much higher pressure and density than gas at the surface. This forces a lot more nitrogen into the blood. Nitrogen does not dissolve well at all. It's very insoluble in water unlike oxygen. As a result when you take the pressure off the person again the extra nitrogen that has dissolved in their tissues can come out as little bubbles. It forms bubbles in blood vessels and blocks them up. That's why you get decompression sickness, the bends.
If you used a liquid in the lungs instead of gas, the liquid would not succumb to the increased compression of being down deep. Therefore it would not force extra gas into solution in the same way that air mixtures would. Therefore it might, in theory, be safer if we can overcome the other problems that are associated with it.
Helen - Have you seen the film The Abyss? It's one of my favourites with a diver and I think they use liquid breathing. They put a mouse in a plastic bag and it's fine but that would be fun if it could happen one day...