Physiologic Effects of Cryotherapy
a. Knight defines cryotherapy as "the therapeutic application of any substance to the body which results in the withdrawal of heat from the body, thereby lowering tissue temperature."
b. Cryotherapy is broad term that covers a number of specific techniques, including ice packs, cold gel packs, ice massage, ice immersion, cold whirlpool, and vapocoolant spray.
c. Initially, after application of ice pack, patient feels cold, which progresses to burning, warming sensation. Aching, tingling, and finally numbness follow.
d. First response is constriction of arterioles and venules (within 15 minutes or less). Blood flow to area decreases, and body attempts to conserve heat.
e. Vasodilation can be cold-induced after initial period of vasoconstriction when cold is maintained for longer than approximately 15 minutes or when temperature is reduced below 10° C.
f. Period of alternating vasodilation and vasoconstriction also may occur, known as "hunting response." This response is most predominant in apical areas where arteriovenous anastomoses are located in skin and has been shown to be absent in deeper tissues. After cold is removed, temperature rises in adjacent body parts.
g. Additional effects of cryotherapy
h. Decrease in local metabolic rate.
i. Decreased conductivity of pain receptors and nerves (when cooled to 10° C).
ii. Decreased tissue extensibility.
iii. Spasticity reduction results from decrease in gamma motor neuron activity by excitation of cutaneous afferents. It also acts by decreasing afferent-spindle discharge.
iv. Short applications of cold can be effective adjunct to therapeutic exercise by stimulating muscle function.
Knight K: Cryotherapy Theory: Technique and Physiology. Chattanooga, TN, Chattanooga Corporation. 1985