Cryobiology and Thermodynamics

Cryobiology is the branch of biology that studies the effects of low temperatures on living tissues. Cryosurgery involves performance of one or more freeze-thaw cycles in order to destroy tissue. Heat transfer between the cryogen and tissue occurs followed by tissue damage. Distinction is made between direct and indirect tissue damage mechanisms. Direct mechanisms involve both extracellular and intracellular formation of ice crystals as well as movement of water towards osmotic gradient. Also direct impact of cold on protein structure and enzyme systems is significant. Indirect tissue damage mechanisms involve vascular stasis, tissue ischaemia, and inflammatory and immunological responses. Mechanisms of crystal forming will be described, namely, by way of heterogeneous and homogeneous nucleation; likewise, the explanation on why forming of intracellular crystals is impaired in comparison with forming of extracellular crystals. Notion of the osmotic gradient determining movement of water molecules during freezing and thawing will be elaborated, and the impact of parameters upon change of which it is possible to monitor depth, width and circumscription of cryogenic lesion will also be discussed in this chapter.