In the movie The Abyss, SCUBA Divers are operating with
experimental Liquid Breathing systems. There is one particular scene
where Virgil "Bud" Brigman (played by Ed Harris) is gearing up for his
first test with the Navy test equipment. Navy seal Ensign Monk fills
up Bud's diving helmet with a colored fluorocarbon goo, and watches
him frantically fighting the impulse not to breathe the liquid:
Relax, now, Bud. Don't hold your breath, take it in, just
let yourself take it in. We all breathed liquid for 9 months, Bud, the
body will remember
Bud is at the point of suffocating, when he inhales the
liquid, floods his lungs, and starts breathing the liquid.
Sounds farfetched? Actually, the first experiments with liquid
breathing systems were conducted in the mid 1960s. Researchers found
that salt solutions could be saturated with high
concentrations of dissolved oxygen at elevated pressures.
These saturated solutions were fed to mice, that were kept alive up to
18 hours while breathing the saline solutions. Eventually, the mice did
not die from oxygen deprivation, but from a buildup of carbon dioxide
in their lungs.
Later research focused on the use of fluorocarbons (e.g.
freon): chemically inert liquids that can contain high
concentrations of dissolved oxygen and carbon dioxide. The problem with
high (toxic) carbon dioxide concentrations remained, and this could
only be solved by using an active recirculation system that fed fresh
oxygenated liquid to the lungs, and stripped carbon dioxide from the
exhaust stream. Using this system, larger animals (such as rats,
and eventually dogs could be kept alive. This led the way to
adapting the system for human applications.
So what is the purpose of these liquid breathing systems? As it is
portrayed in The Abyss, liquid breathing may have a use in SCUBA diving
at extreme depths. Oxygen becomes toxic at high pressures, and is
therefore always mixed with an inert gas. Regular SCUBA diving to
moderate depths is done with compressed air (mainly oxygen and
nitrogen), but this becomes troublesome at higher depths due to the
risks of nitrogen narcosis. At higher depths, mixtures of oxygen,
helium (and a small amount of nitrogen) are used. This works well for
depths up to approximately 200 meters (or 20 bar pressure). Higher
depths are risky, if not impossible with SCUBA gear. Also, dissolved
gases in the blood stream may cause big problems during the ascend
(decompression sickness, "the bends"). A liquid breathing system could
circumvent these problems, since the lungs are completely filled with an
incompressible fluid, and you could dose the oxygen at a safe, low
concentration without having to worry about additional inert gases entering
the bloodstream. However, the problems with fluid recirculation and carbon
dioxide buildup are still too complex to make this technology work.
Liquid breathing does have a current application in medical
treatments. Alliance Pharmaceutical Corporation makes a
perfluorooctyl bromide (perflubron), marketed under the name
LiquiVent ®. This product is used for partial liquid
ventilation. The fluid is administered to the lungs in conjunction with
mechanical ventilation in patients with acute respiratory failure
(caused by severe burns, infection, inhalation of toxic substances, or
premature birth). The perflubron aids in opening the alveoli (air
sacs) of the patients to facilitate the gas exchange in the lungs, and
reduce the negative effects of mechanically assisted breathing. It can
also wash out debris from the alveoli, deliver drugs to the lungs,
function as an anti-inflammatory agent, and can be used as a contrast
liquid for x-ray imaging. | 
