Cryotherapy: Mechanisms and Influencing Factors

• Cryotherapy uses cold as a therapeutic agent and lowers tissue temperature to be effective.

Mechanisms of Action for Cryotherapy

• Energy transfers through conduction, convection, and evaporation.
• Vapocoolant sprays reduce motor neuron activity.
• Cooling minimizes bleeding and acute inflammation.

Factors Influencing Response

• Temperature difference occurs between the cold object and the soft tissue.
• Exposure time is the duration of cold application.
• Thermal conductivity of a material or tissue to conduct heat, where muscles have higher conductivity than adipose tissues.
• Adipose tissue acts as an insulator, affecting cooling and rewarming rates; more adipose tissue requires longer cooling times.
• Both arterial and venous blood exchange heat, and activity impacts blood flow.
• Skin temperature drops quickly, deeper tissues take longer to cool.
• Temperatures 56.5°F and 50°F lower skin temperature to produce local analgesic effects and 33% reduction in nerve conduction velocity, respectively.
• Ice packs can take up to 30 minutes to lower muscle temperature by 6.3 degrees Fahrenheit at a depth of 4 centimeters.

Physiological Changes From Reduced Temperature

• Decreased histamine and bradykinin reduces vasodilation and inflammation.
• Increased smooth muscle tone increases vasoconstriction, reducing bleeding.
• Increased blood and tissue viscosity decreases blood flow.
• Reduced skeletal muscle spasm is due to decreased pain and muscle spindle sensitivity.
• Cold is the modality of choice for the first 24-48 hours after injury.
• It reduces fluid filtration, inflammation, pain, and local metabolism.
• Immediate cooling may reduce secondary tissue damage by decreasing dysfunction, vein diameter, and leukocyte accumulation.
• It increases the threshold for depolarization, slows nerve conduction velocity, and extreme cold can block nerve conduction
• Prolonged cold application can progressively decrease motor nerve conduction velocities, and it can impact nerve function, care should be taken when applying ice around nerves.
• Short duration cold can temporarily enhance muscle performance, but longer durations can reverse this.
• Cooling for 10 minutes or longer before strenuous exercise may negatively affect performance.
• Ice therapy can affect proprioception, hindering the ability to perform functional activities.
• Cooling can temporarily decrease deep tendon reflexes and clonus, potentially improving a patient's ability to participate in therapy, and may improve endurance, strength and walking efficiency.

Cryotherapy Indications

• This is used to managing acute trauma using a RICE/PRICE principles to reduce swelling and inflammation and prevent further injury.
• Muscle spasms and pain can be addressed.
• It is useful for elevating patient's pain threshold.
• Myofascial trigger points respond to ice massage.
• It is helpful for migraines and lateral elbow tendinopathy.

Cryotherapy Contraindications

• Cold hypersensitivity
• Impaired circulation or diminished sensation
• High blood pressure
• Over a regenerating peripheral nerve
• Over an area of circulatory compromise or peripheral vascular disease
• Cryoglobulinemia and Raynaud's phenomenon

Cryotherapy Precautions

• Monitor blood pressure before and during treatment for hypertension.
• Thermoregulatory disorders
• Over a superficial peripheral nerve (use padding)
• Open wounds
• Poor sensation or cognition
• Very young or very old
• Aversion to cold

Cryotherapy Methods

• Cold packs like ice plus water, water plus alcohol, gel or chemicals, but towels are recommended for agents below 30 degrees Fahrenheit to prevent skin damage.
• Ice massage is effective over small areas or trigger points.
• Vapocoolant spray is used for rapid evaporation provides cooling.
• Cold compression devices, with manual or electric circulation of cold water, improved pain, swelling, and range of motion post-operatively.
• Cold baths are used for immersion of distal extremities.
• Cold gels provide a perceived sensation of cold, often using chemicals like ethanol or methanol.

Considerations for Application

• Conductive cooling is usually administered for 20-30 minutes.
• Cycling, with intermittent cold applications may be more effective, 20 minutes on followed by two cycles of 10 minutes off and 10 minutes on are more effective.
• Agent choice depends on accessibility, body part treated, and need for compression/elevation.
• Home use with frozen vegetables (peas) are less effective than ice packs, frozen peas are not as effective in reducing skin temperature compared to ice packs or a mixture of water and alcohol.
• Patient education about what to expect during cold application (intense cold, burning, aching, numbness) is important: patients should be informed that they may initially feel intense cold followed by burning, then aching, and finally a numbness.

Therapeutic Heat - Principles and Physiology

• The use of heat for therapeutic purposes aims to elevate tissue temperature to produce physiological changes.
• Heat flow varies depending on the tissue type, as fat provides insulation.
• Greatest temperature elevation occurs in the skin and subcutaneous tissues (within 2.5 cm). Muscle temperature increase is less and requires longer exposure (15-30 minutes).
• Energy transfers through conduction, convection, and radiation.

Factors Influencing Temperature Changes

• Intensity of heat applied
• Time of heat exposure
• Thermal medium
• Rate at which energy is added to the tissue
• Volume of tissue exposed and composition
• Capacity of tissue to dissipate heat (blood supply)
• To provide a therapeutic effect, tissue temperature should be elevated to 104-113°F (40-45°C): below 104°F is mild heating and above 113°F can cause tissue damage.

Physiological Effects of Temperature Elevation

• Increased cell activity and metabolic rate
• Increased oxygen uptake by tissues
• Vasodilation and increased blood flow
• Mild inflammatory reaction, increased elasticity, decreased viscosity, decreased joint stiffness, and increased muscle flexibility
• Neuromuscular Effects with elevation of pain threshold, altered nerve conduction velocity, and changes in muscle spindle firing
• Heat and exercise can both increase blood flow, but exercise has a greater effect. The effects of moist heat packs plus exercise in combination were additive and greater than either modality used alone.

Therapeutic Heat: Indications and Contraindications

• Clinical Indications include reduction of pain and stiffness, decreased muscle spasm, increased range of motion and improved tissue healing.
• Guidelines: Tissue temperature should be elevated to 104-113°F (40-45°C) for an intervention time of 15-30 minutes.
• Determine status of circulation before heat intervention.
• Assess sensitivity to temperature and pain.
• There are contraindications such as lack of intact thermal sensation because of burn risk if the patient cannot distinguish between hot and cold.
• Vascular insufficiency or vascular disease: because of burn risk if circulation is inadequate to dissipate the heat in the tissues.
• It should not be applied in cases of recent or potential hemorrhage, or known malignancy.

Methods

• Moist heat packs are stored in a thermostatically controlled cabinet at 158-167°F and requires 6-8 layers of toweling between the pack and the skin.
• Paraffin wax bath is used for distal extremities (hands, feet), applied via dip and wrap or dip and re-immerse techniques.
• Electric heating pads are convenient for home use but should not be used during sleep.
• Air-activated, wearable heat wraps maintain a temperature of about 104°F, and can elevate the tissue temperature and can be worn during activities of daily living and work and during sleep.
• Fluidotherapy is a dry heat modality using air-fluidized solids (ground corn cob) which provides massaging action and sensory stimulation.
• There is limited clinical evidence to support wet over dry heat modalities, and we can consider what is available to the patient at home.
• An assessment of effectiveness can include: pain scales, questionnaires, range of motion (goniometric measures) and functional movements.

Comparison of Heat vs. Cold

• Heat or cold can be selected based on intervention objectives.
• Cold is recommended for reducing muscle spasm and pain around joints before ROM exercises.
• Heat may be better tolerated psychologically by some patients with pain or muscle spasm. It decreases joint stiffness and increases connective tissue extensibility.