TENS- Transcutaneous Electrical Nerve Stimulation-

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Introduction-

The American neurosurgeon and pain relief pioneer Clyde Norman Shealy had designed the first TENS unit device in 1974 .Transcutaneous Electrical Nerve Stimulation is a non-invasive analgesic technique of low frequency that is used to relieve nociceptive, neuropathic and musculoskeletal pain. TENS is very beneficial for chronic pain patients. Over a 77% of therapist use TENS for managing chronic pain and more than half of the patient got relief who have been given TENS and report says that they found very beneficial . TENS has been found that it is used clinically by a physiotherapist to reduce pain.

Mechanism of Action

The use of TENS which is high frequency current is based upon the Pain Gate Theory which results in stimulation of nervous system and could modify the perception of pain. In 1965, Wall and Melzack produced a Pain Gate Theory. They described that interneurons in the substantia gelatinosa in the dorsal horn of the spinal cord acted as a gate to modulate sensory input.

The small diameter of myelinated A-delta fibers of neurons and unmyelinated C fiber also known as pain carrying nociceptive which are projected to spinal cord where they synapse directly or through interneurons with the transmission cells which is (T cells) in the dorsal horn of grey matter. The A-delta fiber or alpha fibers are also said to be Pain Inhibiting fibers, which arise from the peripheral part and ends on T-cells through substantia gelatinosa of the spinal cord.

The stimulation of the large diameter mechanoreceptors alpha fiber inhibit nociceptors at the T-cells and prevent transmission to the higher centers. The inhibitory input caused by the activation of the large diameter, mechanosensitive afferent is instruct to close the Gate to Nociceptor transmission. This is known as Pain Gate Control Theory.

Parameter of TENS

Most of TENS unit produce an electric output having one characteristic waveform ,usually of symmetric or balanced asymmetric biphasic type with zero net current to minimize skin irritation.

• Pulse Width/Pulse Duration- Up-to 500microseconds, Pulse width is the length of time for which the current act on the nerve. The range of the pulse width is 40 microsecond to 500 microseconds, A microsecond is a millionth of a second and short duration pulses are used to achieve analgesic effect. Long duration impulses are not required in order to force a sensory nerve to depolarized, Therefore stimulation for less than a millisecond is sufficient. In clinical practice the most commonly used pulse duration is 200 microsecond.
• Frequency- Between 1Hz and 200Hz , In TENS the frequency is one of the important parameters which alter the result if selected wrongly, the frequency may range between 1Hz to 200Hz. High frequency TENS reduce primary hyperalgesia to heat and mechanical stimuli for up-to a day after treatment. In contrast Low frequency TENS is ineffective in reducing primary Hyperalgesia. The use of high frequency stimulation produce greater analgesic effect.
• Amplitude- The amplitude range from 1mA to 100mA. These amplitude is sufficient the primary target of stimulation of the sensory nerve, which can easily depolarized the sensory nerve. The intensity of amplitude depend on the condition and severity of pain.
• Waveform- It is of two type Rectangular monophasic and Biphasic. The waveform is used in the physiotherapy practice in TENS is biphasic which has positive and negative phases. The waveform minimize any type of skin reaction due to the build up of electrolytes under the electrode. The waveform can be modified into square, triangular, rectangular and sine wave.
• Duration- TENS current are used for long period of time.
• Modulation- The pulse of different frequency , pulse duration and intensity are modulated in a way that lead to less irregular pulses, These modulation help in minimizing the effect of accommodation.

Modes of Transcutaneous Electrical Nerve Stimulation

There are six types of TENS MODE-

• Conventional TENS- It is also known as High Tens. It is characterized by high frequency and low amplitude. It has the frequency between 10Hz to 100Hz. The amplitude produce comfortable cutaneous stimulation without muscle contraction. The optimum frequency 60Hz for relieving pain. Frequency above 80 to 200 Hz may worsen pain of few patients.
• Acupuncture like TENS- It is also known as by Low TENS. It is characterized by High amplitude and low frequency. Acupuncture mode of Tens has a frequency below 10Hz. The most commonly used is 1Hz to 4Hz. With pulse duration ranging from 100microsecond to 300microseconds. The amplitude is usually higher above 30mA. This type of TENS selectively stimulate the a-delta and C-fiber. This TENS is effective in Chronic and deep situated pain.
• Brief Intense Mode TENS- It is characterized by High amplitude and High Frequency. The frequency ranging from 60Hz to 150Hz. Pulse duration 50 microseconds to 250 microseconds. The amplitude can be adjusted to produce uncomfortable muscle contraction or non-rhythmic muscle fasciculation. This type of TENS is produce significant muscle fatigue with continuous stimulation.
• Pulse Burst Mode- This type of mode is also called burst or pulse train. It consist of both high setting and low setting. The patient experience either uncomfortable tetanic muscle contraction in high amplitude and non rhythmic muscle fasciculation in low amplitude. This type is characterized by a high carrier frequency of 50Hz to 100Hz which is modulated by a low burst frequency of 1Hz to 4Hz.
• Modulated Mode- This type of TENS to prevent accommodation and to improve tolerance of the patient. The modulated mode allow one of the parameter of the TENS like pulse duration, frequency, amplitude to change modulated mode automatically.
• Hyperstimulation Mode- This type of TENS also known as Non-invasive electro-acupuncture TENS. It is a only mode that utilize either direct or mon0phasic pulse current. This mode use high amplitude that produce very noxious cutaneous stimulation which is sharp and burning in character without resultant muscle contraction. This TENS is applied through a small probe type electrode.

Clinical use/Indication –

The primary use of TENS has been recognized as the symptomatic relief of chronic pain, post surgical pain and post traumatic acute pain. The indication are as follows-

• Neuropathic pain
• Post surgical pain
• Labor pain
• Phantom Limb pain or sensation is experience by the individual after amputation.
• Dysmenorrhea (Painful menstrual cramps in the uterus.
• Musculoskeletal pain
• Relief of acute pain
• Relief of Chronic pain
• Bone fracture pain
• Low backache
• Arthritis
• Peripheral nerve injury
• Metastatic bone pain
• Fascial pain

Contraindications

• Pacemaker
• Cardiovascular Disorder
• Pregnancy
• Hemorrhage
• Thrombosis
• Epilepsy
• Undiagnosed pain
• Carotid sinus
• Active infection
• Hypersensitivity of skin (Any skin related conditions)
• Impaired or absent sensation
• Arrhythmia
• Stroke
• Region of neck
• Non-cooperative patient
• Mucosal surface

Electrode Placements

• The placement of electrode directly over the painful area.
• Over the trigger point.
• Over the motor point.
• Over the nerve.

To learn more about TENS watch this video given below-

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