ABSTRACT
Transcutaneous electrical stimulation of peripheral nerves through intact skin is effective in controlling some pains. The current is generated by a portable battery-operated device attached to electrodes on the skin. Generally the four-pad units are the most flexible to use. Typically pulses of 50-150 Hz and currents of 15-35 mA are effective. These settings stimulate low-threshold afferents (Aβ mechanoreceptors) causing inhibition of the passage of high-threshold pain fibre impulses (Aδ and C fibres) at the spinal cord level. This is thought to be via presynaptic γ-amino butyric acid (GABA) inhibition of the substantia gelatinosa cell excitation in the spinal gate. High-frequency current selectively stimulates larger afferent fibres. It may also increase the refractory period and reduce firing rate in smaller afferent pain fibres. High-frequency TENS has mainly a segmental effect. Lowfrequency stimulation (Aδ mechanism) can produce analgesia in patients who have failed to respond to the more conventional high-frequency stimulation. This is thought to work by activating inhibitory descending neuronal influence in the dorsal horn of the spinal cord.
