45 Cold (Cryo) Therapy
Superficial physical agents such as cold, heat, light, friction, and pressure have been used in therapy for thousands of years. Cryotherapy, or the use of cold, is restricted to superficial agents that are inexpensive, easy to use and requires little time to prepare, usually simple, but effective. Ice and cold water are the usual agents, but vaporizing liquids, refrigerated units, and chemical packs may also be used. The application of ice to an injury, in the acute phase can substantially decrease the extent of the damage. Even though treatments are restricted to superficial application; cold therapy may produce longer-lasting physiologic changes than are possible from heat treatments of similar intensities.1
Biophysics
Chilling a limited portion of the body results in a number of local and distant physiologic changes. Although there is some controversy,2 most clinicians feel that there is an initial period of vasoconstriction due to the local reflexes and increased sympathetic constrictor tone.3,4 Vasoconstriction is thought to continue until subcutaneous temperatures fall to about 15° C/59° F. Below 15° C/59° F, vessels dilate, probably as a result of contractile mechanism paralysis or blockage of constrictor signals. An oscillating “hunting” pattern of constriction and reactive hyperemia may occur, at least in the digits, as was described by Lewis.2,3 At 0° C/32° F, skin blood flow may be greater than normal.
If the cooling agent is ice, skin temperature will initially decrease rapidly and then will more slowly approach as equilibrium temperature of about 12 to 13° C/54 to 55° F in 10 minutes. Subcutaneous temperatures decline more smoothly and in 10 minutes will fall to 3 to 5° C/37 to 41° F. Deep muscle temperatures decrease the least, and in 10 minutes may lessen by a degree or less.5 Chilling for longer periods result in more pronounced effects and intramuscular forearm temperature decreases of 6 to 16° C/43 to 61° F are reported following periods of 20 minutes to about 3 hours of vigorous cooling.6,7,7a Vasoconstriction reduces blood flow and the return of cooled tissue to normal temperatures is slower than in heated and hyperemic tissue.
The amount of energy that tissue will gain or lose during treatment depends on the nature of the tissue itself, the treatment modality involved, and the duration of exposure. In addition, the body places physiologic limits on the amount of cold it will tolerate. For example, exposure of skin to temperatures below 13° C/55° F are uncomfortable, and if the body is cooled below 28° C/82.4° F, death may occur.3
Effects of Cold Therapy
Pain Relief
The reason behind the application of ice resulting in pain relief is not clear. There are many theories and it is possible that a number of proposed mechanisms in combination can cause pain relief.7b,7c Some of the possible mechanisms include the following:
Reduction of Muscle Spasm
Muscle spasm is often a response to pain. The muscles surrounding an injury contract to protect the underlying tissue (muscle guarding) and prevent further damage.7e,7f,7g Ice, being useful for pain relief, is therefore advantageous in reducing muscle spasm. In addition, muscle overuse or imbalances can be improved through the use of cold therapy. This mechanism is not fully understood, but is believed to be due to ice slowing conduction velocity of sensory and motor nerves, as well as the activity of muscle spindle cells (responsible for muscle tone), resulting in a decrease in motor activity.
Slowing of the Metabolic Rate
By reducing the metabolic rate, ice reduces the oxygen requirements of the cells. Thus, when blood flow has been limited by vasoconstriction, the risk of cell death due to oxygen demands (secondary cell necrosis) will be lessened.
