Liquid Breathing

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. Liquid breathing is only a theory and has not been tested in the field. Deep water commercial divers use saturation diving as a way of coping with the extreme pressure of deep water diving but they still use mixed gas not liquid to breathe.

Perfluorochemical (perfluorocarbon) molecules have very different structures that impart different physical properties such as respiratory gas solubility, density, viscosity, vapor pressure, and lipid solubility. Thus, it is critical to select the appropriate PFC for a specific biomedical application, such as liquid ventilation, drug delivery, blood substitutes, etc. The physical properties of PFC liquids vary substantially; however, the one common property is their high solubility for respiratory gases. In fact, these liquids carry more oxygen and carbon dioxide than blood.

Computer models of three perfluorochemical molecules used for biomedical applications and for liquid ventilation studies: a) FC-75, b) perflubron, and c) perfluorodecalin.

In theory, liquid breathing could assist in the treatment of patients with severe pulmonary or cardiac trauma, especially in pediatric cases. Liquid breathing has also been proposed for use in deep diving and space travel. Despite some recent advances in liquid ventilation, a standard mode of application has not been established yet.

Liquid breathing is sometimes called "fluid breathing", but this can be misleading, as normal atmospheric air is also a fluid.

Physicochemical properties (37 °C at 1 atm) of 18 perfluorochemical liquids used for biomedical applications. This table characterizes the most significant physical properties related to systemic physiology and their range of properties.

Gas solubility
Oxygen	33-66 mL / 100 mL PFC
Carbon dioxide	140-166 mL / 100 mL PFC
Vapor pressure	0.2-400 torr
Density	1.58-2.0 g/mL
Viscosity	0.8-8.0 cS