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. Itís been experimented on for a little while because also thereís some occasions when forcing gas into lungs is bad. If youíve 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. Itís a sticky molecule and one molecule tries to stick onto another. This would collapse the alveoli down and make them disappear if you didnít 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 Ė premature babies donít have this stuff, adults can have conditions where they lack this stuff Ė you donít 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 deep-sea-divers. Some of the fluids theyíve been exploring are fluids that donít mix with water so theyíre organic chemicals and per-fluorocarbons are the class of chemicals involved. Theyíve done experiments with chemicals with six carbon atoms in a line: Thatís per-fluorohexane. Theyíve also done experiments with eight atoms linked together: thatís per-fluoro-octanes. They havenít done experiments on humans. Theyíve been done on sheep which is a good model for us because theyíre 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. Itís very difficult to move large amounts of liquid like this. Really the only time itís 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 youíre well acquainted with, Helen, thereís a risk of the bends. As you go down underwater the pressure of gas youíre having to breathe in is increased from your tank by your regulator to overcome the fact that youíre under pressure under water. Youíre 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. Itís 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. Thatís 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? Itís one of my favourites with a diver and I think they use liquid breathing. They put a mouse in a plastic bag and itís fine but that would be fun if it could happen one day.
Ricardo asked the Naked Scientists: Years ago (10-12) someone told me that there is some sort of liquid/water that was developed by scientist for Military Special Operation Groups, such as Navy Seals, SAS and some others. Now if it's true, then what its composed of? What do you think? Ricardo, Wed, 5th Nov 2008
I COULD BE WRONG BUT I believe what they used was a highly aerated & low viscosity fluoro carbon. Low viscosity as it takes a lot to move fluids it in and out of your lungs and to high a viscosity would put strain on your heart causing it to fail.
Or just to rinse your lungs out when you've got a cold! BRValsler, Wed, 5th Nov 2008
Fluorocarbons. There goes the greenhouse effect again. lyner, Wed, 5th Nov 2008