| The chemical structure of perfluorocarbons | |
 |
Perfluorocarbons (PFCs) are organic compounds that are not dissimilar to hydrocarbons, the only real difference being the presence of fluorine, rather than hydrogen, atoms. The compounds are clear, odourless fluids, they are chemically very unreactive and can be linear, cyclic or polycyclic. The stability of PFC compounds stems from their strength of the carbon-fluorine bonds. These are also responsible for the inert nature of PFCs in biological systems such as the bloodstream. Two of the most commonly used PFCs are:
|
|
Gas carriage by PFC emulsions
|
|
|
Unlike the active binding of oxygen, seen at the haem sites of Hb molecules, PFC liquids become saturated with oxygen by a passive process in which oxygen molecules dissolve into molecular cavities within droplets of the liquid. For this reason the saturation of a PFC liquid with oxygen is directly proportional to the partial pressure of oxygen in contact with the liquid. This produces a linear relationship that contrasts with the sigmoid shape seen in Hb binding with oxygen. This is illustrated in the graph opposite. |
|
Due to the passive process of PFC dissolution with oxygen, patients infused with PFC emulsions, (emulsion is required since PFCs are immiscible with blood plasma) must breathe high concentrations of oxygen to ensure adequate delivery to the tissues.
PFC emulsions are transported in the bloodstream and become saturated with oxygen as they pass through the lungs. Their subsequent passage through oxygen-deprived tissues results in oxygen extraction from the PFC emulsion.
PFCs are exhaled as a vapour from the lungs. The flu-like symptoms seen in some patients infused with PFC emulsions are thought to result from uptake of PFC droplets by phagocytic cells in tissues (e.g. the liver).
