Local application of heat can provide pain relief and reduce muscle spasm. Most chronic pain patients are aware of superficial heat applied locally in the form of a hot water bottle, or generally in the form of a hot bath or shower.
There are different ways by which heat therapy can be provided. They are broadly classified as:
Superficial heat therapy
- Paraffin wax
- Infrared radiation
- Heat pad
- Hot moist packs
Deep heat therapy
- High frequency currents
- Medium frequency currents
- Low frequency currents
The superficial heat can reach up to 1 to 2 cm depth, while deep heat has the reach beyond this.
This superficial heat produces different response including changes in neuromuscular activity, blood flow, capillary permeability, enzymatic activity and pain.
The deep heat delivers energy directly to deeper tissue, which improves muscular function, blood flow and local reflexes by suppressing sympathetic over-activity.
Superficial Heat Therapy
Paraffin Wax
This wax has a low melting point and is contained in a bath controlled between 40 degree Celsius and 44 degree Celsius. The wax heats more slowly but retains its heat for a longer period than water. As the wax solidifies on the skin, the energy released by the latent heat of fusion results in heating of the tissues.
It completely surrounds the part being treated and there is very little danger of burns. It is difficult to apply extremities and hence its main use will be for hands and feet.
Indications
Painful conditions like
- Pain after trauma
- Degenerative joint disease
- Chronic inflammatory arthritis
Contraindications
- Open wounds
- Skin infections
Infrared Radiation
the electromagnetic rays beyond 770 mm to 1000 mm are termed as infrared radiation. The infrared radiations can reach only up to superficial epidermis. When these radiations hit the body, the radiant heat is converted into heat.
Any part of body can be treated, but the patient must be positioned so that the rays strike the part at 90 degree Celsius for maximum absorption. However it has drawback of providing heat on one aspect only and patient has to remain in one position for treatment.
- Tissues are heated directly on one aspect only.
- Patient should remain in one position throughout the treatment.
Indication
- Large superficial areas can be treated.
- Promoting healing in uninfected wound
- Relieving pain and muscle spasm following trauma.
- Chronic arthritis.
Heat Pads
Heat pads supply dry heat. A heating pad has three levels of heat, and heat passes to tissues by conduction. However, dry heat is conducted less uniformly than moist heat. It is very useful in neck and back pain.
Hot Moist Packs
These are canvas bags filled with a hydrophilic substance and stored in a thermostatically controlled cabinet of water between 75 degree Celsius to 80 degree Celsius. The packs vary in size and shape and are returned to the cabinet for reheating after use.
The area to be treated should be totally covered by the pack, which is moulded to the contour of the body. Layers of towels must be placed round the pack to separate it from the patient’s skin. The superficial tissues are heated by conduction, relieving pain and muscle spasm.
Heat in this is conducted more uniformly than dry heat. These packs are useful on uneven surfaces because they can be easily molded to the surface. But they are heavey and discomforting.
Deep Therapy
The electromagnetic fields are applied in electrotherapy to tissues at different frequencies for therapeutic effect. All these frequencies are used for different benefits.
These electric fields are classified in the following way on the basis of frequencies generated.
High frequency (10,000 Hz and above)
High frequency currents cannot stimulate skin or muscle because of their high frequencies. They can produce only thermal effects, e.g., short wave diathermy, microwave diathermy.
Medium frequency currents (1000 Hz to 10,000)
These currents reduce the skin resistance (frequency and skin resistance are inversely proportional) and hence require low current intensity to achieve the desired effects. Because of low intensity it results in less sensory discomfort, e.g., interferential therapy.
Low frequency currents (1 Hz to 1000 Hz)
The low frequency require high intensity current to overcome the skin resistance. This high current leads to marked sensory stimulation to the patient, e.g., faradic and direct current.
High Frequency Currents
Short wave diathermy
Short wave diathermy is an application to tissues of electrical field which oscillates at a frequency of 27.12 MHz and a wavelength of 11.06 M. This field generates heat within the tissues by movement of molecules and ions.
The heat distribution depends on arrangement of field of electrical impedance of tissues. The diathermy may be applied in a continuous fashion or pulse wave form.
The therapeutic effect of continuous mode is same as pulsed mode.
Short wave diathermy produces a greater and more rapid raise in temperature than the conductive methods of heat to a depth of 3 to 5 cm.
Advantages
- Both superficial and deep lesions can be attended
- Large areas can be treated
- Useful for soft tissue injuries
Indications
- Soft tissue injuries
- Inflammatory arthritis
- Degenerative arthritis
Microwave diathermy
This is an application of electromagnetic radiations with a wavelength of 12.25 cm and frequency of 2450 MHz. When these microwaves are absorbed in the tissues, heat is produced. The depth of penetration is up to 3 cm which is more superficial than shortwave diathermy. These waves are absorbed by fluid tissues such as muscles and less by fat and bone. This therapy is good for superficial tissues.
Medium Frequency Currents
Interferential therapy
In this therapy two medium frequency currents at constant intensity but different frequencies are applied to the body at the same time, the intensity of the combined current will increase and decrease rhythmically.
Indications
- Chronic degeneration arthritis
- Backache
- Complex regional pain syndrome
- Soft tissue injuries
Low Frequency Currents
Low frequency currents stimulate both motor and sensory component of nerve. If these currents are not modified, they an produce titanic contractions.
Most often these currents are used for reduction of muscle contraction which must be normally innervated to respond to these currents.
These currents other wise do not find much use in clinical practice, because of their sensory stimulation.
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