Target temperature of local cryotherapy

BACKGROUND: local cryotherapy (LC) is a promising method of treating various diseases, as a result of which the effects of anesthesia and reduction of inflammation are achieved. The main factor of efficiency from a physical point of view is the achievement of the target temperature on the surface of the impact area. At the same time, during the procedure, the surface temperature of the tissue should not fall below the minimum permissible the limit temperature for safety. 
AIMS: identification of the range of target and limit temperatures in terms of safety parameters based on the results of literature analysis, carrying out experiments with the use of ice bag for cooling the biotissue phantom, determining the most appropriate impact modes. 
MATERIALS AND METHODS: a series of experiments was carried out on the developed stand to compare the two modes of the contact method of LC, depending on the working substance used (sodium chloride solution, a mixture of ice and water). The comparison was carried out according to the following parameters: the time to reach the target temperature on the surface, the temperature at the depth of the model medium. The temperature was measured by resistance thermometers (Pt100). 
RESULTS: when cooled with a sodium chloride solution, the surface temperature of the model medium dropped to 10 C in 6 minutes of exposure, and after 17 minutes reached its minimum value of 6.2 C. In the case of using a mixture of water and ice, the minimum temperature of 12.5 C was reached in 58 minutes. The minimum temperature at a depth of 8 mm in both cases was approximately the same and was about 17 C. It was reached by 19 minutes with a solution of sodium chloride and for 58 minutes with a mixture of water and ice. 
CONCLUSIONS: as a result of the experiments carried out, the most suitable contact cooling mode with the use of ice bag was determined - a mode using sodium chloride as a working substance with an initial temperature of minus 18.4 C with a possible impact time from 6 to 19 minutes.