Transcutaneous Electrical Nerve Stimulation (TENS) is a stimulating device which delivers electrical current across the intact surface of the skin via surface electrodes.
It is a simple, non-invasive, analgesic (acting to relieve pain) technique. This current is usually generated by a small battery-operated machines.
In battery, circuits modify the output in such a way that it will have a stimulatory effect. TENS is a therapy that uses low-voltage electrical current for pain relief.
Neurophysiology of pain and Gate control theory:
Before understanding how to TENS work on the body , it must be important to know all about the Neurophysiology of pain and gate control theory.
For more explanation you may visit this page- Neurophysiology of pain and Gate theory.
Parameters of TENS:
The parameters of TENS include-
1)Waveform:
- Biphasic waveform (having both the negative and positive phases)
- These waveforms can be square, rectangular, sine wave, and triangular spikes.
- For hypersensitive patients and the pain associated with nerve injury, used rectangular waves.
- The triangular (spike-shaped waves) are recommended for intense or hyper-irritating stimulation, as done in acute pain or for the resistant tissue.
2)Frequency:
- The frequency of TENS can be high (80-120Hz), which is selected for the acute conditions causing immediate pain relief.
- The frequency can be low (1-20Hz), which is used for chronic pain.
3)Pulsed width:
- It is the length of time, the current is acting on the patient in each pulse.
- The pulse width varies from 50-400 μs.
- For normal neuromuscular system, the pulse width selected is from 50-400 μs
- Patients with neurologic damage, higher widths of 200-300 μs are suggested.
4)Amplitude:
- Most TENS units have an amplitude control ranging from 1mAto100mA
- For the immediate relief of pain, referred to the high amplitude and narrow width combination.
Types of TENS(Modes):
1)Conventional (high TENS):
This mode is used to activate selectively large-diameter Aβ fibers without concurrently activating small diameter Aδ and C (pain-related) fibers. Conventional (high-frequency low intensity) TENS is the most commonly used mode of TENS.
It is effective in modulating acute pain via inhibition of pain fibers by large diameter fiber activation(gate mechanism). the stimulation parameters are as follows-
- A low intensity: 12-30 mA producing comfortable tingling sensation and paresthesia, but no muscle contraction.
- A high frequency typically above 100 Hz (80-120Hz)
- A pulse duration which is usually short (50-80μs)
- Duration of treatment: 20-60 minute
As the Aβ fibers are stimulated, this TENS mode achieves analgesia primarily by spinal segmental mechanisms,i.e. gating effect.
2)Acupuncture like (low TENS):
It is a common misconception that this mode derives its name from application over acupuncture points. Acupuncture like(low-frequency high intensity) TENS primarily stimulates the Aδ and C nociceptive fibers. the stimulation parameters are:
- low frequency usually 2-5Hz
- A high intensity: 30mA or more, (enough to produce visible muscle contraction)
- Long pulse duration (150-300μs)
- Duration of treatment: 30-40 minutes
The electrode should be positioned to produce visible muscle contractions. examples- over a myotome related to the painful area, the intensity should be increased until the patient experience the same desired muscle contractions.
This mode of TENS is operating primarily through the descending pain suppression system. Thus there is a relatively longer onset to analgesia, which lasts more than the conventional TENS.
3) Brief intense TENS:
This mode is used to provide rapid onset, but short term pain relief. It used during painful procedures done by the clinicians, such as wound debridement, joint mobilization, etc. the parameters include:
- Amplitude: to patient’s tolerance
- Pulse rate: 125-250Hz
- Pulse duration: 200-250μs
- Duration of treatment: 15 minutes
- Duration of pain relief: temporary
4) Burst mode(pulse trains) TENS:
This mode of TENS was developed by Eriksson and Sjölund in 1976. The burst mode provides a packaging of several stimuli in a group ranging from 1-10. It is presented in a burst of energy. The patient sensed it as a single stimulus.
Pain relief is through the stimulation of endogenous opiates. some patients prefer this mode because the pulse trains produce a more comfortable muscle contraction. The parameters include:
- Amplitude: comfortable intermittent paresthesia
- Frequency:50-100Hz, delivered in packets or bursts of 1-4 Hz
- Pulse duration: 50-200 Hz
- Duration of treatment: 20-30 minutes
- Duration of pain relief: long-lasting
Indication:
Relief of Acute Pain
- Postoperative pain
- Labour pain
- Dysmenorrhoea
- Musculoskeletal pain
- Bone fracture
- Dental procedures
Relief of Chronic Pain
- Low back
- Arthritis
- Stump and phantom
- Postherpetic neuralgia
- Trigeminal neuralgia
- Causalgia
- Peripheral nerve injuries
- Angina pectoris
- Facial pain
- Metastatic bone pain
Anti-emetic Effects
- Postoperative nausea associated with opioid medication
- Nausea associated with chemotherapy
- Morning sickness
- Motion/travel sickness
Improving Blood Flow
- Reduction in ischemia due to reconstructive surgery
- Reduction of symptoms associated with Raynaud’s disease and diabetic neuropathy
- Improved healing of wounds and ulcers
Contraindication:
- Undiagnosed pain (unless recommended by a medical practitioner)
- Pacemakers (unless recommended by a cardiologist)
- Heart disease (unless recommended by a cardiologist)
- Epilepsy (unless recommended by a medical practitioner)
- Pregnancy: first trimester , over the uterus
- Do not apply TENS: over the carotid sinus, on broken skin, on dysaesthetic skin, internally (mouth)
TENS and Electrodes:
A variety of TENS models are currently available ranging from single or dual-channel to multi-channel units.
There is a broad range of types and sizes of electrodes used with TENS. Electrode can be a carbon rubber electrode. which is made to be covered with a conductive gel. Probably the most popular choice of electrode is a self-adhesive type, which comes in a variety of shapes and sizes and can be mold over irregularly shaped areas of the body.
Electrode Placement for TENS:
One of the primary factors responsible for a poor response to TENS treatment is that of ineffective electrode placement. Essentially, there are four broad categories of anatomical sites to which the TENS electrodes can be applied-
- Painful area
- Peripheral nerve
- Spinal nerve root
- Other specific points (acupuncture, trigger, motor points)
Advantages of TENS:
- Noninvasive
- Portable
- User-friendly
- Safe in us
- In long-standing pain syndromes, it is cheaper than the regular prescription for analgesics.
- The change of battery and electrode is the only extra cost once the machine is purchased
- The precautions and contraindications are few and side effects are minimal
- It is nonaddictive
Disadvantages of TENS:
Disadvantages are only a few such as-
- A number of patients fail to tolerate the sensation of electrical stimulation and fail to respond to this program
- Skin irritation due to an allergic reaction to the conductive medium or tape
- A chemical burn may result