Local cryotherapy investigation on the biotissue phantom

BACKGROUND: Local cryotherapy (LC) is one of the physiotherapeutic treatment methods of various diseases, including musculoskeletal disorders. When choosing the method and exposure modes, the medic relies on his experience and data from LC equipment manufacturer. This is not enough for correct dosing, impact control and understanding of the relationship of one or another effect from the cooling parameters of the biotissue. Therefore, it is advisable to conduct a study of different methods of LC and modes to perform effective and safe impact. The temperature on the surface of the biotissue acts as a convenient and measurable factor of efficiency and safety. Earlier analysis shows that the target temperature is 10 2 C, the limit temperature is 0 C, when lowering below which tissue damage is possible. 
AIM: Experimental comparison and identification of the most suitable modes of two different methods of contactless local cryotherapy. 
MATERIALS AND METHODS: An experimental installation was developed and created. A series of experiments was carried out on a model medium with thermophysical properties close to biotissues. The comparison of liquid nitrogen and air flow cooling is carried out. The temperature was measured with resistance thermometers (Pt100) on the surface and in the depth of the model medium. 
RESULTS: When cooled by liquid nitrogen vapors from a distance of 10 and 15 cm from the surface, the accepted average target temperature of 10 C was reached in 1.8 and 4.4 min, and at a depth of 8 mm, the temperature was 26.4 and 23.7 C, respectively. When cooled with air from a distance of 10 cm from the surface with maximum and minimum flow, the target temperature was reached in 2.5 and 13.3 min, at a depth of 8 mm, the temperature was 22.9 and 16.0 C, respectively. When cooled by air from a distance of 15 cm, the temperature value did not reach the target. The less intense flow made it possible to lower the temperature inside the model medium more strongly, while having a weaker effect on the surface. This effect can potentially be positive in the treatment of musculoskeletal disorders, mainly joints. 
CONCLUSIONS: The most suitable modes of the considered methods that meet the requirements of efficiency, safety and convenience of practical implementation are identified. For cooling by liquid nitrogen vapors, this is a mode spraying at a distance of 15 cm with a stable technique with a possible exposure time from 4.4 to 15 minutes. For air flow cooling, this is a mode with a stable technique with a constant flow with the nozzle fixed relative to the surface of the model medium at a distance of 10 cm with a minimum flow rate (350 l/min) with a possible exposure time from 13.3 to 21.5 min.