Cryomedicine. Application of low temperatures
Application of low temperatures in medical practice is known for a long time. So, in Ancient Egypt cold compresses were used for treatment of skull bones fractures and thoracic wounds. “The Father of medicine” Hippocratus in his works described in details the medical effect of local cold application to stop wound bleeding and at traumatic edema.
N.I. Pirogov widely used cold in treatment of wounds. “Surely, the cold is prescribed where the swollen, hot and irritated wound is accompanied with parenchymatous (capillary) bleeding”, he wrote.
Larrey, the main surgeon of Napoleon, has noted that when wounded soldiers lay on snow for a long time, it was possible to amputate damaged extremities painlessly.
One hundred years later, during the Great Patriotic War outstanding native surgeon Yudin S.S. renewed this method. All these and many other examples of treatment have allowed doctors to conclude that application of cold results in some positive effects, namely: to decrease pain, bleedings and discharge from wounds, take out unpleasant sensations, to observe reverse development in tumoral processes. Obtaining by physicists of ethylchloride, solid and fluid carbon dioxide, liquefied oxygen and, especially, fluid nitrogen allows doctors to systematize previous empirical experience of cold application and more attentively look at processes in human body.
The main conclusion that was made at that time was conclusion about two opposite effects of freezing:
- cryoconservation when structure of tissue and its elements — cells — is not broken under significant slowing of biochemical processes down;
- cryodestruction accompanied with complete destruction of tissue structure and cells.
During freezing and thawing, the chain of the physicochemical processes connected with extra- or intracellular formation crystals of ice, strengthening of osmotic components, recrystallization of crystals of ice during thawing is observed. All these processes cause damage and destruction of cellular structures. After thawing, in tissues exposed to deep freezing reactive processes are developed (disturbance in microcirculation of blood and interstitial fluids, hypoxia and ischemia, local edema, release of tissue macrophages, development of inflammatory and local immunologic processes) which complete destruction of remained intact structures and result in formation of the zone of aseptic necrosis.
Rate of thawing influences final level of developed necrotic processes. During prompt thawing, unstable crystals of ice melt easily and cause no damage in tissue whereas during slow thawing they recrystallized at temperatures from -40°? to -20°?. At this, small crystals merged and formed large crystalline structures that appear to be the powerful damaging factor.
However, the difficulty is that different tissues react to freezing in different ways. Some tissues, such as skin, mucus, nervous cells, granulation tissues, vascular endothelium are cryosensitive and are easily damaged during freezing. Others, such as nerve cords, fibrous and connective tissues, cartilages and fatty tissue are cryoresistant and response to freezing with minimal damage of the structures. Besides, different tissues have different intensity of blood supply and, accordingly, degree of thermoexchange. Therefore, identical freezing conditions in various tissues can have various consequences: while highly sensitive to cold and slightly vascularized tissues will completely destroyed, poorly sensitive to cold with high degree of vascularization can appear slightly damaged.
Cryoexposure on tumoral tissues
Tumoral tissues are significantly different in their properties and structure as compared to surrounding tissue, and it put certain requirements on regimen of their cryodestruction. If during cryodestruction such tissues are not completely destroyed, significant worsening in course of disease is possible due to deteriorated protective barrier separating healthy tissue from pathological that results in dissemination of tumor cells throughout all body provoking development of metastatic disease.
Two stages of cryoexposure
Cryoexposure can be divided into two stages. At the first stage, target area of biological tissue is to be frozen with maximal high speed to prevent occurrence of crystal ice. The obtained volume of biological tissues frozen in such a way is in the state favorable for both cryodestruction, and cryoconservation. It depends on the rate of warming of the frozen area up. For cryoconservation regimen frozen volume is necessary to warm up the maximal high speed. If the frozen volume is warmed slowly, recrystallization is performed in depth of ice, i.e. crystallizing of ice leading to destruction of cells in the frozen area, i.e. to cryodestruction. It can be illustrated with the following scheme.
Practical cryosurgery as a method of treatment for serious diseases
Having traced the development of cryosurgery and its technical support since 1960’s, the following tendency can be seen. In the first decade, cryosurgical “boom” was noted as among doctors so the developers of cryosurgical equipment. However, absence of comprehensive knowledge about mechanisms of cryodestruction, as well as specific requirements to cryosurgical technics based on these representations have led to gradual and steady decrease of activity both among doctors, and developers of cryosurgical equipment. Time of “cryoromanticism” was over; backgrounds for serious work on development of practical procedures for application of cryosurgical method in different fields of medicine were established. Cryosurgical method of treatment of some serious diseases, first of all tumours, became more and more popular both among medical professionals, and patients. Cryosurgery becomes independent field of medicine by right.