Research Review By Dr. Ceara Higgins©

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Date Posted:

December 2016

Study Title:

What is the acupoint? A preliminary review of acupoints

Authors:

Li F, He T, Xu Q, et al.

Author's Affiliations:

Acupuncture and Moxibustion Department, Beijing Hospital of Traditional Chinese Medicine, China; Tianjin University of Traditional Chinese Medicine, China.

Publication Information:

Pain Medicine 2015; 16(10): 1905–1915.

Background Information:

Acupuncture has been widely used to treat pain in both eastern and western countries due to its efficacy and safety (2). In classical acupuncture theory, acupoints are believed to be points on the skin’s surface or underneath that reflect (or, somatically represent) particular organs (4). Stimulating these acupoints then, in theory, modulates the physiology of the body (1). This review focused on the function of acupoints from different perspectives to help clarify the mechanisms of acupuncture treatment in managing disease and to help provide a clear basis for clinical research.

Summary:

Local Effects of Stimulating Acupoints

The possible structure of acupoints:
A variety of stimuli may be applied to acupoints. These include needle stimulation, thermal and Chinese medical stimulation from moxibustion, electrical stimulation from electroacupuncture, or radiation from laser acupuncture (7). Early studies of morphological structure reported close relationships between acupoints and the nervous system (9), blood vessels (10), and muscles (11) and histological studies have shown a high density of nerve endings, A- and C-afferent fibers (11), and higher concentrations of neural and vascular elements, especially mast cells, at acupoints (12). It has also been demonstrated that stimulation of acupoints through acupuncture (7) or moxibustion (8) can increase the degranulation of mast cells. There is still no clear connection between acupoints and specific anatomical structural or physiological effects, suggesting that the difference between traditional acupoints and other points may be in the intensity of the response they produce, rather than their overt structure (12).

The electrical properties of acupoints:
In healthy individuals, electrical skin resistance at acupoints is significantly lower than at nearby non-acupoints (13), while in disease conditions the electrical skin resistance at acupoints is significantly higher than nearby non-acupoints (14). This has lead to electrical skin resistance being used to localize and analyze acupoints for diagnostic purposes. However, due to conflicting research, this remains highly controversial. Further, the current inadequacy in commercial electrodiagnostic technology makes this a poor method of clinically assessing the electrical characteristics of acupoints (15).

The biomolecules effected by acupoints:
Stimulation of acupoints may release biomolecules, which create an analgesic effect or neuromodulation. A variety of studies have shown increased release of adenosine (16), nitric oxide, cyclic guanosine monophosphate (17), and/or norepinephrine (18) with acupuncture. As well, a more recent study has shown higher partial oxygen pressure and higher levels of calcium, iron, copper, and zinc in acupoints when compared to nearby tissues (19).

Acupoint sensitization:
In cases of pathology, some acupoints appear to show changes in heat-sensitization and pain-sensitization (21), with different diseases showing different pain-sensitive points. Acupoints appear to be sensitized by noxious stimuli from viscera, as the degree of sensitization of acupoints seems to be affected by the level of malfunction of the internal organs (20).

Myofascial trigger points (MTrPs) have been proposed as a mechanism to explain musculoskeletal pain (5) and have been found to correspond to classical acupoints in 99.5% of cases (22). MTrPs have previously been found to be biochemically distinct from surrounding tissues and contain substances associated with pain and inflammation (23). Thus, it could be reasonably assumed that MTrPs are best matched to the “ah-shi” (tender) points for pain (24).

Systemic Effects of Stimulating Acupoints

Visceral and organ function:
Acupuncture is thought to cause adjustments to viscera and organs via the neuroendocrine-immune network (16). In a study where neuroanatomical tracers were injected into an acupuncture point (ST36) in rats, labeled neurons were found in tractus solitarius and the spinal cord, indicating a connection between the acupoint and the central nervous system (25).

Maintenance of homeostasis:
Traditional Chinese Medicine (TCM) presumes the existence of two opposing and complementary forces in nature, known as “Yin” and “Yang”. These forces purportedly work together to regulate the flow of vital energy, or ”Qi”. A person who is in good health is thought to have Yin and Yang in balance and a smooth flow of Qi. The meridian system is a network of channels thought to bring Qi from the internal organs to the surface. Acupoints are defined as specific points along the meridians where stimulation can infuse or diffuse Qi. However, there is no convincing evidence to date to support this theory. Instead, it seems that the relationship between the traditional theory and the modern understanding of acupuncture is based on a complex interaction of multiple physiological functions, which involve the nervous, circulatory, endocrine, and immune systems (9).

Acupuncture likely effects homeostasis through the somato-autonomic reflex (26) and modulates any imbalance between the sympathetic and parasympathetic systems (6). It also stimulates somatic afferent nerves in the skin and muscles, leading to somatic sensory information being carried to the cortex of the brain and various nuclei in the brainstem and hypothalamus (27). This afferent input significantly affects autonomic functions (26) and modulates various biomechanical responses (27).

Acupuncture-induced analgesic effects have been used to alleviate a wide variety of painful conditions. Acupuncture induces afferent nerve signals that modulate spinal signal transmission and pain perception in the brain (3), while activating areas of the brain that contribute to inhibitory modulation of descending pain pathways (28). Acupuncture also activates afferent nociceptive nerve fibers, spinal and complex brain neural pathways, and various signal molecules (3).

Verum Acupoints and Sham Acupuncture:

Several RCTs have shown superior results from acupuncture at verum (traditional) acupoints when compared to sham acupoints. However, a growing body of evidence suggests that sham acupoints may also have therapeutic effects and that there is no significant difference between verum and sham acupoints (29). A study of 23 commonly used acupoints found significant variability in point size, ranging from 2.7 to 41.4 cm2 (31). This suggests that the term “acupuncture field” may be more accurate than acupuncture point, and that the 1 cun distance that is standard between sham points and verum points may not be far enough for clinical trials (this may be part of the reason many trials comparing traditional/verum points to sham points often show little difference!). It is also possible that positive effects from sham acupuncture may be due to positive patient expectations, the patient-practitioner interaction, the experience of invasive needling techniques, and/or specific biological effects of skin palpation and needling (30).

Clinical Application & Conclusions:

Acupoints may release certain substances or cause neurophysiological changes that affect the function of organs, maintain homeostasis, or treat disease. However, the research evidence is insufficient at this point to draw specific conclusions regarding the existence of acupoints as distinct, physiological entities, or be certain of their clinical relevance. Further, well-designed studies are required to investigate the complex factors involved in the definition of acupoints and allow appropriate control procedures for clinical studies to be developed.

Study Methods:

No study methods were provided as this was a narrative literature review.

Study Strengths / Weaknesses:

Strengths:
  • The authors attempted to explore a wide variety of theories and vast body of research on acupuncture.
  • The authors considered both traditional acupuncture and biomedical acupuncture for this review.
Weaknesses:
  • This was a narrative literature review, therefore no study methods were provided, so it is unclear how the authors gathered or evaluated the research they reviewed.

Additional References:

  1. Fung PC. Probing the mystery of Chinese medicine meridian channels with special emphasis on the connective tissue interstitial fluid system, mechanotransduction, cells durotaxis and mast cell degranulation. Chin Med 2009; 34(10): 1-6.
  2. Cabyoglu MT, Ergene N, Tan U. The mechanism of acupuncture and clinical applications. Int J Neurosci 2006; 116(2): 115-125.
  3. Wang AM, Kain ZN, White P. Acupuncture analgesia: I. The scientific basis. Anesth Analg 2008; 106(2): 602-610.
  4. Furlan AD, van Tulder MW, Cherkin DC, et al. Acupuncture and dry-needling for low back pain. Cochrane Database Syst Rev 2005; 25(1): CD001351.
  5. Melzack R, Stillwell DM, Fox EJ. Trigger points and acupuncture points for pain: Correlations and implications. Pain 1977; 3(1): 3-23.
  6. Ernst E. Acupuncture – A critical analysis. J Intern Med 2006; 259(2): 125-137.
  7. Zhang D, Ding G, Shen X, et al. Role of mast cells in acupuncture effect: A pilot study. Explore 2008; 4(3): 170-177.
  8. Wang YS, Zhang JB, Jiang JF, et al. Research on effects of the thermal stimulation by moxibustion at different temperatures on cardiac function in rats and on mast cells in the local site of moxibustion. Evid Based Complement Altern Med 2013; 545707.
  9. Zhao ZQ. Neural mechanism underlying acupuncture analgesia. Prog Neurobiol 2008; 85(4): 355-375.
  10. Kuo TC, Lin CW, Ho FM. The soreness and numbness effect of acupuncture on skin blood flow. Am J Chin Med 2004; 32(1): 117-129.
  11. Lee BC, Ogay V, Kim KW, et al. Acupuncture muscle channel in the subcutaneous layer of rat skin. J Acupunct Meridian Stud 2008; 1(1): 13-19.
  12. Cheng KJ. Neuroanatomical basis of acupuncture treatment for some common illnesses. Acupunct Med 2009; 27(2): 61-64.
  13. Zhang WB, Jeong DM, Lee YH, et al. Measurement of subcutaneous impedance by four electrode method at acupoints located with single-power alternative current. Am J Chin Med 2004; 32(5): 779-788.
  14. Ngai SP, Jones AY, Cheng EK. Lung meridian acupuncture point skin impedance in asthma and description of a mathematical relationship with FEV1. Respir Physiol Neurobiol 2011; 179(2-3): 187-191.
  15. Ahn AC, Martinsen OG. Electrical characterization of acupuncture points: Technical issues and challenges. J Altern Complement Med 2007; 13(8): 817-824.
  16. Wang Y, Yin LM, Xu YD, et al. The research of acupuncture effective biomolecules: Retrospect and prospect. Evid Based Complment Altern Med 2013; 608026.
  17. Jou NT, Ma SX. Responses of nitric oxide-cGMP release in acupuncture point to electroacupuncture in human skin in vivo using dermal microdialysis. Microcirculation 2009; 16(5): 434-443.
  18. Chen JX, Ibe BO, Ma SX. Nitric oxide modulation of norepinephrine production in acupuncture points. Life Sci 2006; 79(23): 2157-2164.
  19. Yan X, Zhang X, Liu C, et al. Do acupuncture points exist? Phys Med Biol 2009; 54(9): N143-150.
  20. Li L, Yu L, Rong P, et al. Visceral nociceptive afferent facilitates reaction of subnucleus reticularis dorsalis to acupoint stimulation in rats. Evid Based Complement Altern Med 2013; 931283.
  21. Kwon YD, Lee JH, Lee MS. Increased temperature at acupuncture points induced by weight reduction in obese patients: A preliminary study. Int J Neurosci 2007; 117(5): 591-595.
  22. Dorsher PT. Can classical acupuncture points and trigger points be compared in the treatment of pain disorders? Birch’s analysis revisited. J Altern Complement Med 2008; 14: 353-359.
  23. Sikdar S, Shah JP, Gebreab T, et al. Novel applications of ultrasound technology to visualize and characterize myfascial trigger points and surrounding soft tissue. Arch Phys Med Rehabil 2009; 90(11): 1829-1838.
  24. Birch S. Trigger point – Acupuncture point correlations revisited. J Altern Complement Med 2003; 9(1): 91-103.
  25. Lee CH, Jung HS, Lee TY, et al. Studies of the central neural pathways to the stomach and Zusanli (ST36). Am J Chin Med 2001; 29: 211-220.
  26. Anderron S, Lundeberg T. Acupuncture – From empiricism to science: Functional background to acupuncture effects in pain and disease. Med Hypotheses 1995; 45(3): 271-281.
  27. Takahashi T. Mechanism of acupuncture on neuromodulation in the gut – A review. Neuromodulation 2011; 14(1): 8-12.
  28. Millan MJ. Descending control of pain. Prog Neurobiol 2002; 66(6): 355-474.
  29. Kong JC, Lee MS, Shin BC, et al. Acupuncture for functional recovery after stroke: A systematic review of sham-controlled randomized clinical trials. CMAJ 2010; 182(16): 1723-1729.
  30. Habib AS. Do we really understand what constitutes an acupuncture point?: Commentary on a paper by Molsberger et al. (this issue). Eur J Pain 2012; 16(9): 1207-1208.
  31. Molsberger AF, Manickavasagan J, Abholz HH, et al. Acupuncture points are large fields: The fuzziness of acupuncture point localization by doctors in practice. Eur J Pain 2012; 16(9): 1264-1270.