Transcutaneous Electrical Nerve Stimulation: TENS for pain relief and part of a programme of treatment for acute or chronic pain.
This is a way of applying a low voltage electrical current for the purposes of pain relief. As a treatment, TENS is safe and non-invasive making it a popular and relatively inexpensive mode of pain relief that can be controlled by the patient. It is important that the patient fully understand the TENS unit and how it is applied for pain relief, for both acute pain and chronic pain. If TENS is suggested as a treatment, you will receive the appropriate instructions on usage to maximise the potential for pain relief.
The TENS unit allows for adjustment of various settings including the pulse duration, frequency, amplitude and type of output (constant, burst or modulated).
Frequency: number of pulses delivered per second (hertz)
Amplitude: output strength (milliamps or volts)
Output type: the pattern of pulses (constant, bursts of pulses at low frequency with a high internal frequency or variable parameters)
The two most common modes applied for pain relief are high frequency (> 50Hz) and low frequency (1-10Hz).
TENS works by inhibiting the nocicepitive responses in the spinal cord through stimulation of large diameter nerves. With low and high frequency stimulation there is also the release of our natural pain killers (endogenous opioids). Research has identified a number of other mechanisms for pain relief using both high and low frequency TENS. TENS does have a widespread effect upon the nervous system including the peripheral nerves and the central components (spinal cord & brain). Essentially we know that TENS must be applied with a sufficient intensity to activate the large diameter nerves for significant pain relief.
Pad placement should be at the injury site and also on the other side in the mirror position to gain the greatest effect.
Effects of high frequency TENS: increased concentration of B-endorphins, reduced release of excitatory neurotransmitters (chemicals that allow nerves to communicate) in the spinal cord, increased release of GABA (inhibitory neurotransmitter) and reduced substance P with high frequency, sensory intensity TENS. High frequency also has an effect on autonomic function and blood flow.
Pain relief from low frequency TENS is obtained by activation of the descending pathways from the brain. Spinal cord (dorsal horn) excitability is reduced by low frequency TENS by stimulating the release of opioids, GABA and serotonin, thereby reducing nociception and consequent pain. Low frequency also has an effect upon blood flow and the autonomics.
Medication
If you are taking opioids, high frequency TENS can be better. This is because the use of low frequency TENS in those with opioid tolerance will be ineffective. Other interactions include a possible increased effect of low frequency TENS if you are taking selective serotonin reuptake inhibitors (SSRIs), increased effect of low and high frequency TENS with an acute dose of morphine and a reduced effect if taking ACE inhibitors. Talk to your doctor if you have any questions about medications.
TENS units are available from TensCare: 01372 723434
