Transcutaneous Electrical Nerve Stimulation (TENS)
Transcutaneous Electrical Nerve Stimulation (TENS) is a method of producing pain relief by the application of a pulsed biphasic rectangular wave form through electrodes on the skin. The principle of working is related to the pain gate theory (Melzavk and Wall, 1965, 1982). There is closing of the gate by stimulation of A–fibers and activation of the descending pain suppression system. It has been suggested that 50–100Hz achieves this effect. Low frequency (2 Hz pulsed) is said to relieve pain by increasing the body’s production of endorphins.
The Transcutaneous Electrical Nerve Stimulation stimulators are commonly small battery–operated machines with a current output of 0–50mA. The pulse widths may be fixed at 200 us or variable between 50 and 300 us. The frequency is also variable on most machines from 2 Hz to 300 Hz, although some are fixed at 150 Hz. The low frequencies are used for chronic pain and the slightly higher (80–120 Hz) for acute pain. The wide variables of pulse width, frequency and current output allow adjustments for the individual.
The electrodes are applied with conducting gel and are self–adhesive or fixed with tape. Their position may be above and below the painful spot, over the affected nerve, nerve trunk or the affected dermatome. They should not be applied over anesthetic areas because there would be no sensory input. Prolonged stimulation is necessary to be effective, e.g. 8 hours per day for a week, but 24 hours a day may be necessary. The patient may require the machine for 2–3 months.
Uses of Transcutaneous Electrical Nerve Stimulation (TENS)
- Longstanding severe pain in a variety of conditions.
- Post–herpetic neuralgia.
- Stump and phantom limb pain
- Trigeminal neuralgia
- Chronic neck, back or leg pain.
- During labor.
Contraindications of Transcutaneous Electrical Nerve Stimulation (TENS)
Patients with pacemakers or cardiac arrhythmias. Area of carotid sinus and mouth.
- Where the cause of pain has not been diagnosed by a qualified health care practitioner.
- By any person with a heart pacemaker.
- By any person with a serious/unstable heart condition.
- By any person with epilepsy.
- When electrodes are placed across the chest, i.e. both arms simultaneously.
- When electrodes are placed on the neck in the region of the carotid arteries.
- Where any area of skin is inflamed or infected.
- If an allergic reaction develops to adhesive tape or electrodes.
- Around the head.
Medium–frequency currents alternate at 1000–100 000Hz. Interferential therapy is the use of two medium–frequency currents around 4000 Hz to produce a low–frequency effect within the body without the problem of high skin resistance. Low–frequency is required to high skin resistance, require a high intensity to achieve the desired effect and this causes marked sensory stimulation to the part. Medium–frequency causes low skin resistance require a low intensity to achieve the desired effect, which in less sensory discomfort. High–frequency currents, such as short–wave diathermy and microwave, have frequencies too high to stimulate skin on muscle and produce only thermal effects.
In interferential equipment one frequency is fixed at 4000 Hz (generated by one pair of electrodes) and the other is variable between 4000 Hz and 4200 Hz (second pair of electrodes). By selecting the variable frequency, a beat frequency between 0 and 200 Hz may be generated.
Indications for Interferential Therapy
- Pain relief–Pain of sympathetic origin such as causalgia, neuralgia, pain from herpes zoster, amputation–stump complications and recent injuries.
- Swelling–Interferential aids absorption of exudates particularly for Haematoma.
- Stress incontinence–The muscle stimulating frequencies aid weak pelvic floor muscles
- Back pain or disc lesions–Interferential therapy is useful for relief of acute back pain where the pain is localized to the back or referred down a lower limb.
- Sudeck’s atrophy–This responds to interferential when other modalities have failed but treatment may need to be prolonged.
- Ligamentous and muscle injuries–Interferential can be given in acute or chronic conditions to relieve pain, promote healing and restore function. Treatment can be given with strapping in place.
- Rheumatic conditions–Relief of pain arising from Osteoarthritis, rheumatoid arthritis and Ankylosing spondylitis may be obtained, with a resulting increase in function.
- Pacemakers–Patients with pacemakers should avoid high and medium–frequency currents.
- Malignancy–Spread of the disease may occur
- Pregnancy–Treatment should not be given to the pelvic organs during pregnancy.
- Bacterial Infections–Treatment may cause spread of the infection.
- Thrombosis–Interferential tends to spread the blood clot and is contraindicated in deep venous thrombosis or thrombophlebitis. The heart and stellate ganglion should also be avoided.
Infra-red radiationWhen the radiations are absorbed the radiant energy is converted to heat.
There are two types of generators.
- Luminous, producing rays from 350 nm to 450 nm which penetrate the epidermis and dermis to the subcutaneous tissues.
- Non–luminous, producing rays from 770nm to 1500 nm which penetrate only as far as the superficial epidermis.
Owing to these effects, infra–red can be used to promote healing in uninfected wounds, relieve pain and reduce muscle spasm following trauma, and for chronic arthritic joints, when the luminous generator should be used. The sedative effect of the non–luminous generator is more suitable for recent trauma and sub acute inflammatory joints. Infra–red is used to treat large superficial areas.