Characterization of tissue response to localized cooling and design of a safer cryotherapy device

Khoshnevis, Sepideh
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Localized cooling is often used to manage both acute and chronic phases of soft tissue injuries by reducing pain, swelling, and inflammation. Cold application would result in a decline in skin temperature and reduction of blood perfusion at the treatment site. In some instances, the use of cryotherapy has been associated with tissue necrosis and nerve damage. Tissue damage was shown to be due to both the direct effect of cooling as well as tissue ischemia resulting from the reduced blood perfusion. The purpose of this research was to examine the effect of localized cooling on skin temperature and blood perfusion and to develop a method to stimulate blood perfusion in tissue following development of cold-induced vasoconstriction. Out of various methods used, thermal stimulation was shown to successfully increase tissue perfusion during cryotherapy experiments. As a part of this research, tissue response to localized cooling was quantified for each of a variety of cryotherapy units (CTU). Moreover, diverse methods were implemented to investigate and quantify the non-uniformity of surface temperature for multiple cooling pads in combinations with their brand-specific CTUs. It was demonstrated through further studies and tissue blood perfusion comparisons (caused by using different CTUs) that there were no significant differences between studied units. Additionally, no significant difference was observed between knee and ankle/foot in their vasocosnstrictive response to cooling. Using multiple statistical methods, it was illustrated that a significant degree of vasoconstriciton occurred that lasted well beyond the active cooling period while skin temperature had increased significantly. Furthermore, a hysteresis effect was observed between skin perfusion and temperature during cooling and rewarming periods. In addition, a dose-dependent response in skin perfusion in relation to applied temperature was reported. A hysteresis effect between the skin temperature and perfusion was observed for both cooling and warming experiments and the area of the hysteresis plot was shown to be linearly dependent on applied temperature. Moreover, non-uniformity of skin temperature during cryotherapy was noted, which was independent of pad temperature distribution.