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.
Biophysics
Chilling a limited portion of the body results in a number of local and distant physiologic changes. Although there is some controversy, most clinicians feel that there is an initial period of vasoconstriction due to the local reflexes and increased sympathetic constrictor tone. 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. 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. 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. 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.
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. Some of the possible mechanisms include the following:
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Cold decreases nerve transmission in the pain fibers
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Cold reduces the activity of nerve endings
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Cold causes a release of endorphins
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Cold raises the pain threshold
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Cold sensations override the pain sensation
Reduction of Bleeding and Swelling
By cooling the surface of the skin and the underlying tissues, ice causes the narrowing of the blood vessels, a process known as vasoconstriction. The vasoconstriction leads to a decrease in the amount of blood being delivered to the area and, subsequently, lessens the amount of swelling. After a number of minutes, the blood vessels reopen (dilate) allowing blood to return to the area. This phase is followed by another period of vasoconstriction—this process of vasoconstriction followed by dilation is known as the hunting response .
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. 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.
General Indications for Cold Modalities
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Acute musculoskeletal trauma (e.g., edema, hemorrhage, analgesia)
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Pain
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Muscle spasm
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Spasticity
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Adjunct in muscle reeducation
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Reduction of local and systemic metabolic activity
General Precautions and Contraindications for Cold Modalities
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Ischemia
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Cold intolerance
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Raynaud phenomenon and disease
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Severe cold pressor responses
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Cold allergy
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Insensitivity
Research Studies
Taber, and others have evaluated local vascular response during cryotherapy. Their study was performed to determine whether application of a cold pack reduced blood volume in a nontraumatized ankle. Changes in local blood volume at the ankle were measured over a 20-minute period for the following three conditions: rest, room-temperature gel pack application, and cold gel pack application. A significant reduction in local blood volume was found for the cold gel pack condition in comparison with the resting condition. Maximum decrease in blood volume occurred at 13.5 minutes after cold gel pack application. Reactive vasodilation was not observed. The results lend support to the clinical use of a cold gel pack when a reduction in local circulation is desired, such as in the management of acute-phase soft tissue trauma.
Belitsky, and others compared the ability of wet ice (WI), dry ice (DI), and cryogen packs (CGPs) to reduce and maintain the reduction of skin temperature directly under the cooling agent and to determine whether the cooling effect on skin extended beyond the surface area in contact with the cooling agent. Each of the three cold modalities was applied randomly to the skin overlying the right triceps surae muscle. The only significant differences in cooling were between WI and DI and between WI and CGP. Fifteen minutes after removal of the cold modalities, no significant differences were found in mean skin temperature between WI, DI, and CGP. No cooling was demonstrated 1 cm proximal or distal to any of the cooling agents after 15 minutes of cold application.
Akgun and colleagues concluded that with increased cold gel pack application time, the duration of cooling effect increased while the deep tissue temperature decreased. The length of application time and the duration of cooling effect were not linearly related. This ratio decreased progressively after 20 minutes.
The ice pack and mixture of water and alcohol were found to be significantly more efficient in reducing skin surface temperature than the gel pack and frozen peas. Cold whirlpool was found to be superior to crushed-ice packs in maintaining prolonged significant temperature reduction after treatment. Wetted ice was found to be superior to cubed or crushed ice at reducing surface temperatures, whereas both cubed ice and wetted ice were superior to crushed ice at reducing intramuscular temperatures. Application of an ice pack containing at least 0.6 kg of ice leads to a greater magnitude of cooling compared with application of a 0.3 kg ice pack, regardless of the size of the contact area.
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