Local cryotherapy investigation on the biotissue phantom

BACKGROUND: Local cryotherapy (LC) is a physiotherapeutic method for the treatment of various diseases, including musculoskeletal disorders. The physician relies on his experience and the data from the LC equipment manufacturer for the given method and exposure modes. This is not sufficient to determine the correct dosing and to understand the effect of the various treatment parameters on the biotissue to have precise control over the effects of the treatment on the biotissues. Hence, it is imperative to conduct a study of different LC methods and modes to perform effective and safe treatments. The surface temperature of the biotissue is a convenient measurable quantity to ensure efficiency and safety. Previous studies show that the target temperature is 10 ± 2 °C, with a lower limit of 0 °C. If the temperature drops below 0 °C, then tissue damage is possible.

AIM: Experimental comparison and identification of the most suitable modes in two methods of contactless local cryotherapy.

MATERIALS AND METHODS: An experimental installation was developed and created. A series of experiments were carried out on a model medium with thermophysical properties close to those of the biotissues. The comparison of liquid nitrogen and air cooling was performed. The temperature was measured with resistance thermometers (Pt100) on a surface and inside of a 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. Although air cooling from a distance of 15 cm was not possible to lower the temperature down to the target value, the less intense flow made it possible to lower the internal temperature in 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: Among those tested, the most suitable modes of the considered methods that meet the requirements of efficiency, safety, and convenience of practical implementation were identified. For cooling using liquid nitrogen vapors, this is a mode spraying at a distance of 15 cm with a stable technique with a possible exposure time of 4.4 to 15 minutes. For air 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 of 13.3 to 21.5 min.