Acupuncture and the Endogenous Opiods
Advances in our understanding of the body's endogenous pain control mechanisms should allow for improvement of therapies aimed at producing analgesia by stimulation, such as transcutaneous nerve stimulation (TNS) and electro-acupuncture.
A number of neurochemical mechanisms have been explored, and the most important of these are the body's endogenous opioid systems.
Three families of endogenously produced opioid substances have been studied in depth - the endorphins, encephalins and dynorphans. Each of these has specific sites of action and can be precipitated by various afferent stimulation techniques. The endorphins act in the brain, the encephalins in the brain and the spinal cord. The dynorphans act at a spinal level.
Endorphins and encephalins are potent blockers or modulators of pain arising from the musculoskeletal system.
Dynorphan is a powerful modulator of visceral pain; it has a weaker effect on musculoskeletal pain modulation.
Stimulation frequencies produce specific opiod responses.
Low frequency stimulation, that is, 1-2 Hz (1-2 cycles per second), causes the release of the endorphins and encephalins.
High frequency (100Hz) results in dynorphin release and has no effect on the endorphins or encephalins.
12-15 Hz stimulation results in the production of all three opiod classes. There is no further gain in opioid peptide release beyond 100 Hz and below 1Hz is ineffectual.
Thus we can produce spinal visceral analgesia by using high frequency stimulation, a more generalised analgesia ( Spine and Brain mediated) by using a low frequency stimulation or a mixed response that utilises all three opiod peptides by using a mid range frequency.
With the latter the analgesic effects of precipitating all three go well beyond an additive effect (1+1=2) to a synergistic effect (1+1=>3)
The amplitude of stimulation
Between 1-3 milliamperes is the usual range used clinically. This intensity produces a non painful fasciculation of the muscle in which the needle is embedded. Higher amplitudes cause pain and give rise to a stress response. Stress induced analgesia depends in part on Diffuse Nocious Inhibitory Control (DNIC) and is not a usual part of Acupuncture analgesia.
Duration of stimulation
The duration of stimulation is also important. At least 10 minutes is required for the production of the endorphins, with maximal release after 20 minutes.
However when stimulation is prolonged beyond an hour, or if the stimulation is repeated, for example 30 minute bursts repeated after an hour's interval, then the analgesic effect is attenuated.
This 'tolerance' has the same time course as that seen with repeated doses of morphine, and is due to the stimulation of the anti-opiate systems. Two anti-opiates have been studied in depth, cholecystokinin (CCK) and angiotensin II. Although there is not yet a drug that can be used clinically to block the effects of CCK, captopril, the highly specific angiotensin-converting enzyme antagonist which also blocks the degradation of the encephalins - shows promise in the reversal of electro-acupuncture tolerance and in the augmentation of electro-acupuncture analgesia.
The Meso-Limbic Loop of Analgesia
The neuro-anatomy of stimulation-produced analgesia is under the microscope, and an exciting concept - the meso-limbic loop of analgesia- has begun to be explored.
It is postulated that, in chronic-pain patients, the meso-limbic loop is 'warmed up'. Following a relatively brief (half an hour) period of stimulation with TNS or electro-acupuncture, a self-sustaining reverberation is set up, causing a re-setting of the pain-modulation pathways. This theory may well account for the long-term analgesic effects seen frequently in clinical practice.
Around 15% of the population are non-responders to acupuncture like TNS or electro-acupuncture. Captopril may alter their status.
A patient with a good response initially followed by a non-response, or even worsening, may have 'turned on' his endogenous anti-opiates.
Turn off the stimulator for 24 hours and then re-try with half-hour bursts once or twice a day.
Stimulating two segments (for example, an arm and a leg) gives a better effect than stimulating a single segment.TNS-like acupuncture, whereby the electrodes are placed on either side of the muscle, thus forcing the current through the muscle and causing it to fasciculate, is probably as powerful as electro-acupuncture, whereby the needle impales the muscle. Both are more powerful than normal TNS.Visceral pain may respond better to high frequency segmental stimulation.When in doubt, use 16 Hz.
Beyond four inputs there is no extra gain;
beyond 100 Hz there is no extra gain;
below I Hz there is no gain;
and beyond 2-3 milli-amperes there is extra pain.
Good acupuncture stimulators and TNS machines cost between $50 - $1,000 plus. Don't be misled the expensive machines aren't necessarily the most effective. When choosing a TNS device or electroacupuncture stimulator look for the ability to set the frequency at 1-2 Htz, 12-20Htz and 100Htz. The amperage should be able to be set from 0 - 3 milliamps. The number of leads need not exceed four. Dense disperse and variable frequencies are rarely used successfully for pain control and frequently exacerbate sympathetically associated/maintained pain states.
NB. Manual needling can be used to produce similar specific afferent stimulation frequencies and intensities as those mentioned above. Historically these different needling methods have been described as: Bu the warming / tonifying and Xie the cooling / reducing methods. The Bu method where the needle is inserted painlessly and is manipulated lightly provides low frequency afferent nerve input. The Xie method where the needle is forcefully and vigorously manipulated provides high frequency stimulation. Bu and Xie are the cornerstones of Traditional Chinese Acupuncture.