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Needling sensation has been considered by many acupuncturists to be an important component of acupuncture since the early classical texts. From a traditional Chinese medicine perspective, needling sensation, de qi, is a composite of unique sensations interpreted as the flow of Qi or ‘the arrival of vital energy’. Based on the theory of traditional Chinese medicine, acupuncture is successful only when de qi is experienced.
From a medical acupuncture perspective, needling sensation is a sensation mediated by sensory afferent nerves. Although the perception of needling sensation may vary in individuals and with manual technique, this distinct sensation is generally characterised by soreness, numbness, heaviness, distension and aching in the deep tissues surrounding the inserted needle.1–3 Thus, the needling sensation is not a single but a composite sensation that is generated from the activation of various sensory receptors and their afferent fibres in acupuncture sites—in particular, small fibre-innervated nociceptors and myelinated fibre-innervated mechanoreceptors.4 It has recently been hypothesised that numbness, heaviness and distension are elicited when manual manipulation is performed at acupuncture sites rich in muscle spindles and tendon organs, whereas the sensation evoked in sites rich in receptors is characterised by aching and soreness.5
Studies by Hui and coworkers have shown that acupuncture stimulation induces deactivation of a limbic–paralimbic–neocortical network (LPNN) and activation of somatosensory brain regions. On the other hand, when acupuncture induced sharp pain, there was an activation of LPNN. Tactile stimulation induced greater activation of the somatosensory regions but less extensive deactivation of the LPNN. These results imply that acupuncture mobilises the anticorrelated functional networks of the brain to mediate its actions.6
Psychophysical experience of needling
The process of eliciting Qi with needles is experienced by both patient and acupuncturist. Patients experience de qi as multiple unique sensations at the needle site itself and around the site of needle manipulation. Simultaneously, acupuncturists feel a change in the mechanical behaviour of the tissues surrounding the needle (needle grasp). This change is described as tense, tight and full, like ‘a fish biting onto the bait’.7 Needle grasp is a biomechanical phenomenon of de qi, which was characterised by an increase in the force necessary to pull the needle out of the tissue (pullout force).8 Langevin's trial supports connective tissue winding as the mechanism responsible for the increase in pullout force induced by needle rotation.9–11
The sensory component of de qi is difficult to study because of its subjective nature and because it is influenced by many factors, such as the constitution of a patient, severity of the illness, location of the acupuncture points and the needling techniques. There appears to be a limit to the number of sensations that can be discriminated by each individual patient. A number of researchers have sought to establish a credible rating scale for de qi. In the linked review, Park and coauthors12 reviewed de qi questionnaires and tried to evaluate the relationship between de qi and acupuncture points, acupuncture stimulation and treatment effects. They reported that in several questionnaires developed to evaluate de qi, the most frequent sensation reported was ‘heavy’ and ‘numb’. Although a few studies showed specificity to acupuncture points, information was lacking to allow any conclusion about the relationship between de qi and acupuncture points. In most studies ‘real’ acupuncture was reported to induce greater de qi than sham acupuncture.
Although de qi might have been traditionally intended to designate both the acupuncturist's and patient's perceptions, most of these scales have chosen to measure only one.
Needling sensation and autonomic tone
Also in this issue, David Yu and coworkers13 report on the relationship between de qi intensity and mean arterial blood pressure, heart rate and heart rate variability in healthy volunteers. The 36 volunteers were randomised to one of three groups;
Group 1—received electroacupuncture at 2 Hz, to the right LI4 and LI11 for 30 min;
Group 2—electroacupuncture stimulation to bilateral knee caps for 30 min;
Group 3—sham electroacupuncture to right the LI4 and LI1 for 30 min.
A significant increase in mean arterial blood pressure, heart rate and heart rate variability was seen in group 1. A small and significant increase in heart rate variability was seen in group 2 but the changes in mean arterial blood pressure and heart rate in groups 2 and 3 were not significant. Interestingly, the de qi index was highest in group 1, moderate in group 2 and lowest in the sham group (group 3). A positive correlation between the de qi intensity and changes in mean arterial blood pressure, heart rate and heart rate variability was seen, suggesting that de qi is associated with an increase in sympathetic activity.
Needling sensation and analgesia
Experimental studies have found that the intensities of different acupuncture sensations are associated with subsequent analgesia.14–16 Kong et al17 found a similar relationship between acupuncture analgesia and numbness and soreness, but not for other sensations commonly associated with de qi. A noticeable difference in therapeutic efficacy was found in some trials between acupuncture and ‘sham’ acupuncture, in most cases because the latter did not involve manual stimulation and an attempt to induce de qi.
In 1995 it was suggested that de qi was associated with the activation of ergo-receptors in the muscle and that the heavy ache commonly perceived by the patient during de qi was ‘equivalent’ to muscle fatigue.18 Interestingly, Lu and Needham in Celestial Lancets (1980) translated the Chinese de qi as numbness; distension/extension/fullness; heaviness; sour ache ‘like a feeling of muscular fatigue’. This suggests that there may be a peripheral correlate to the perception of de qi. It has been proposed that mechanical deformation of the skin and muscles by needles leads to release of large amounts of ATP from keratinocytes, fibroblasts and other cells.18 Probably, the ATP binds to specific receptor subtypes expressed on sensory nerve endings, resulting in activation of the sensory nerves conveying the information of de qi.19 A role of purines (ATP, ADP, adenosine) in the periphery is supported by Goldman and collaborators who have shown that activation of adenosine A1 receptors on peripheral pain fibres contributes to acupuncture-induced suppression of painful input.20–22
An obvious question is whether needling of skin or muscles makes a difference to the perception of de qi. Skin pain is a sharp, spatially localised sensation, whereas muscle pain is a dull and poorly localised one. Specific brain regions are preferentially activated by strong muscle stimulation compared with strong skin stimulation. The brain regions specifically activated by strong muscle stimulation were the midbrain, bilateral amygdala, caudate, orbitofrontal cortex, hippocampus, parahippocampus and superior temporal pole areas, which are more related to emotion.23 This would suggest that the dull sensation of de qi is characteristic of a type of muscular pain. This would be in line with studies showing that acupuncture has a more pronounced effect on the affective components of pain as opposed to the sensory components.24
The concept of diffuse noxious inhibitory controls (DNICs) has attracted attention in the past years. Under normal conditions, pain after application of an experimental nociceptive stimulus is attenuated by a conditioning noxious stimulus to a remote body region.25 According to experimental animal studies, DNICs could contribute to the needling sensation-induced analgesia.26 ,27 However, the intensity of acupuncture stimuli in animal experimental settings differs from that in clinical routine in humans. The analgesic effect might therefore be different in animals and humans.
Several further considerations raise questions about the involvement of DNICs in acupuncture. First, patients with impaired DNICs still benefit from acupuncture. Second, in a recent study of the analgesic effects of acupuncture needling no statistically significant difference was found between acupuncture and non-penetrating sham acupuncture (NPSA) at any time, but the pressure pain detection threshold was significantly higher in the DNIC test than in acupuncture and NPSA.28 In a patient population with pain and possibly altered DNICs, a difference between verum acupuncture and NPSA might be more pronounced.
A study by Treister et al29 has shown that the level of endogenous analgesia after either noxious or innocuous conditioning stimuli (water immersion at 12°C and 25°C, respectively) is highly correlated to the Numerical Rating Scale reported for the corresponding stimulus. Conceivably, acupuncture needles can be intensely stimulated, until the pain is strong enough to induce a DNIC response, but under therapeutic conditions the actual contribution of DNICs to acupuncture analgesia is questionable. Apart from the intensity of the conditioning stimulus, the time profile is another important characteristic of a DNIC response: it is most intense during application of the conditioning stimulus and usually decreases to baseline within 5–10 min.
In a recent study, Xu and collaborators performed a prospective multicentre randomised controlled trial involving 338 patients with Bell's palsy.30 Patients were randomly assigned to the de qi or control group. Both groups received acupuncture at the same points: in the de qi group, the needles were manipulated manually until de qi was reached, whereas in the control group, the needles were inserted without any manipulation. After 6 months, patients in the de qi group had better facial function, more improved disability assessment and better quality of life, suggesting that acupuncture with strong stimulation that elicited de qi had had a greater therapeutic effect.
Taken together the results suggest that needling sensation is an important factor during acupuncture and that the psychophysical response by the patient and therapist should be assessed in clinical trials.7
Competing interests None.
Provenance and peer review Commissioned; internally peer reviewed.
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