Cryobiology and Thermodynamics

Cryosurgery involves the performance of one or more freeze–thaw cycles to destroy tissue. Knowledge of cryobiology—a field of science that studies the effects of low temperatures on living tissues—is essential to achieving controlled tissue damage during a cryosurgical procedure. Cooling and thawing rates, as well as the minimal tissue temperature that is reached during cryosurgery, have a significant impact on the efficacy of a cryosurgical procedure. These parameters determine the direct and indirect cryogenic tissue damage mechanisms. Direct mechanisms include extracellular and intracellular formation of ice crystals as well as movement of water toward the osmotic gradient. Tissue freezing also has a significant direct impact on the protein structure and tissue enzyme functions. Indirect tissue damage mechanisms involve tissue ischemia, inflammatory reaction, and immunological responses. Thermodynamic principles of heterogeneous and homogeneous nucleation will be discussed in this chapter to explain the mechanisms of the formation of extracellular and intracellular ice. In conclusion, an insight into the effects of cryosurgery on different tissues will be given.