Liquid breathing
http://en.wikipedia.org/wiki/Liquid_breathingUsed in the tv show "UFO"
http://en.wikipedia.org/wiki/UFO_%28TV_series%29
Liquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen-rich liquid (such as a perfluorocarbon), rather than breathing air.
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Space travel
Liquid immersion provides a way to reduce the physical stress of G forces. Forces applied to fluids are distributed as omnidirectional pressures. Because liquids cannot be practically compressed, they do not change density under high acceleration such as performed in aerial maneuvers or space travel. A person immersed in liquid of the same density as tissue has acceleration forces distributed around the body, rather than applied at a single point such as a seat or harness straps. This principle is used in a new type of G-suit called the Libelle G-suit, which allows aircraft pilots to remain conscious and functioning at more than 10 G acceleration by surrounding them with water in a rigid suit.
Acceleration protection by liquid immersion is limited by the differential density of body tissues and immersion fluid, limiting the utility of this method to about 15 to 20 G.<51> Extending acceleration protection beyond 20 G requires filling the lungs with fluid of density similar to water. An astronaut totally immersed in liquid, with liquid inside all body cavities, will feel little effect from extreme G forces because the forces on a liquid are distributed equally, and in all directions simultaneously. However effects will be felt because of density differences between different body tissues, so an upper acceleration limit still exists.
Liquid breathing for acceleration protection may never be practical because of the difficulty of finding a suitable breathing medium of similar density to water that is compatible with lung tissue. Perfluorocarbon fluids are twice as dense as water, hence unsuitable for this application.<52> On the other hand, although perfluorochemicals are denser than water, lung tissue floats within the PFC filled lungs, and if the lungs are not over-filled, there is no compromise in pulmonary or systemic blood flow.<53> Therefore, if the astronaut is immersed in liquid and their lungs are filled with liquid PFC, they should not experience adverse effects, in spite of the almost twofold density difference. Based on interviews with adult patients that experienced partial liquid ventilation, when they became conscious they were unaware that 20-30 ml/kg of PFC was in their lungs during recovery.