Acupuncture mechanisms for clinical long-term effects, a hypothesis

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Abstract

In our clinical research, we have drawn the conclusion that meaningful long-term (>6 months) pain relieving effects can be seen in a proportion of patients suffering from nociceptive pain. What are the mechanisms behind this?

From the existing experimental data, some important conclusions can be drawn:

  • A significant proportion of the animal research only represents short-term hypoalgesia probably induced by the mechanisms behind stress-induced analgesia (SIA) and the activation of diffuse noxious inhibitory control (DNIC).

  • Almost all experimental acupuncture research has been performed with electroacupuncture (EA) in spite of the fact that therapeutic acupuncture (TA) is mostly gentle manual acupuncture (MA).

  • Most of the experimental human acupuncture pain threshold (PT) research shows only fast and very short-term hypoalgesia, and, very important, PT elevations in humans does not predict clinical outcome.

  • On the basis of these differences, the effects of acupuncture may be divided into two main components—acupuncture analgesia (AA) and therapeutic acupuncture.

A hypothesis on the mechanisms of therapeutic acupuncture will include:

  • Peripheral events that might improve tissue healing effects and local pain relief,

  • Spinal mechanisms,

  • Supraspinal mechanisms of anti-stress nature,

  • Cortical, psychological, “placebo” mechanisms.

Introduction

This article is based upon a hypothesis in the author's dissertation, where more discussion and more references can be found regarding the subject [1]. In the thesis, some of the original articles [2], [3] make it probable that acupuncture for some chronic pain patients, mostly those with nociceptive pain, can lead to a long-term pain relieving effect. In order to explain these long-term effects, the author analysed the experimental work performed to explain acupuncture analgesia. It became obvious that the animal research (and experimental human research) was almost not at all relevant for what we try to perform in the clinical setting. Thus, it became obvious to look at probable mechanisms in another way and not only in the usual neurophysiological manner. Therefore, a new hypothesis of mechanisms behind therapeutic acupuncture was put forward in the thesis. This text is a summary of the experimental work published from different research groups since about 35 years ago. From conclusions drawn after reviewing this literature, the hypothesis was formulated.

Section snippets

Acupuncture analgesia (AA)

In China, experiments began in 1958 [4] using electroacupuncture (EA) for pain relief during surgery. A success rate of 90% was claimed among those selected for the method. However, less than 10% of the patients showed a satisfactory response in acupuncture trials, and were the only ones given acupuncture for surgical pain relief. Of these 10%, only a third had acceptable analgesia according to western standards [5], [6]. It should also be realised that, in order to get this small “success”

Stress-induced analgesia or specific acupuncture induced analgesia?

Most research groups have used conscious animals where no special attention has been taken to rule out stress-induced analgesia (SIA). We now know that stress induces an increase in brain endorphins (e.g. Ref. [19]). We also know that repeated daily applications of, e.g. foot shocks, gradually lead to adaptation. Thus, SIA develops tolerance and not an increased effect after repeated applications. It has also been shown that the different endorphin receptors (μ, κ, δ) can be involved in

Peripheral effects

The insertion of a needle in the tissues induces important changes close to the needle in all the different tissues penetrated.

Vasodilatation in the skin due to axon reflexes (flare reaction) has been recognised for a very long time and the mechanisms have been clarified in detail [46], [47].

  • Stimulation of Aδ or C fibres releases vasoactive and pro-inflammatory neuropeptides (e.g. CGRP, SP, opioids, galanin, somatostatin and VIP) [48], [49].

  • EA (and TENS) produces peripheral vasodilatation, in

A hypothesis on the mechanisms of acupuncture

Based on the mechanisms mentioned, the following hypothesis may be proposed.

Clinical observations that can be understood with this hypothesis

The hypothesis presented might be a ground for new kinds of mechanism studies, which are quite obvious.

The main purpose of the hypothesis is that it can explain much more of what we see in the clinic than the usual neurophysiological model.

With this hypothesis, we can understand:

  • Why we shall use local points. The neurophysiological model only tells us that we should use some segmental points and some extrasegmental points. The points we use does not matter at all. This is not in accordance with

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