Mechanistic Basis of Acupuncture - Literature review Example

Mechanistic Basis of Acupuncture – A Scientific Review This article summarizes the various theories proposed to explain the mechanism of action of acupuncture. Method Literature pertaining to research and information about mechanism of action of acupuncture was searched from relevant databases like PUBMED, MEDLINE, etc. The MESH key words used were “acupuncture” and “mechanism”. Also, relevant literatures in Google Search without restriction for language of publication were searched. The literature was then narrowed down to few selected articles of interest. The main issues and concepts were identified and discussed in relation to the broader literature. Introduction Acupuncture is one of the oldest complementary and alternative therapies and one of the most commonly used medical procedures in the world. It originated in China more than 3,000 years ago. It is commonly practiced as a routine treatment in China, Japan, Korea, and Taiwan. Since 1970s, its popularity has spread world wide (Ernst “desktop guide”). The procedures in acupuncture involve stimulation of anatomical points called ‘acupuncture points’ on the body with thin needles by a variety of techniques which range from manipulation by hands to electrical stimulation. Acupuncture is effective for relieving dental pain, chronic pain in joints (osteoarthritis), chronic back pain, and recurrent headache. It reduces nausea and vomiting after surgical procedures and chemotherapy. Cancer patients on chemotherapy and radiotherapy treatment, who develop intolerable pain and nausea, may get relief from acupuncture. It also reduces nausea associated with pregnancy (Kaptchuk 374-383). The puzzle that is hunting the researchers is that how an unmedicated needle, inserted at a site remote from its desired application can produce desired results. A point on the lower leg produces desired effects on the gastric function and a point on the hand cures headache. It is not fully known as to what is the mechanism of action behind these effects. Various theories have been put forward by researchers. The term acupuncture is used to describe a variety of treatments that differ in many important aspects, both theoretical and technical and hence there is difficulty in drawing conclusion from existing literature (Langevin 167-75). Proposed theories discussing the mechanism of action of acupuncture The Traditional Chinese Medicine theory: According to this theory, both wellness and illness result from an imbalance of yin and yang. ‘Yin’ refers to the feminine aspect of life. It is nourishing, lower, cool, deficient, inside, receptive, protective, soft and yielding. ‘Yang’ refers to the masculine aspect of life. It is considered to be upper, hot, hard, dominant, energetic, dynamic, excessive, outside and creative. Wellness is a result of movement between these opposite forces. This movement is called Qi and is considered to be the essential element in the healing system of acupuncture (TCM, “tcm.health-info.org”). Acupuncture is basically effected through acupuncture points and meridians. The meridians connect the surface of the body to internal organs and these meridians represent channels through which energy or "meridian qi" flows and involves electrical activity. . It is because of this assumption that electrical point locators are commonly used in clinical practice. However, there is no research supporting this theory despite the fact that the acupuncture is executed based on this theory. Also, the associations between acupuncture points or meridians and certain electrical properties have remained controversial. Most of the studies were actually limited by small sample sizes, poor research design, poor procedural descriptions, lack of rigorous statistical analyses and use of surface electrodes which were confounded by various factors including pressure, skin moisture, electrode contact and abrasion of the stratum corneum (Ahn 5-10). Placebo theory: Some researchers state that acupuncture acts by placebo effect. This hypothesis was considered because acupuncture meridians and their energy, as described in the traditional Chinese Medicine theories could not be visualized or proved by any method. The researchers argued that the acupuncture points are located at sites that have a high density of neurovascular structures and are generally between or at the edges of muscle groups and that these locations are actually less painful than random needle sticks into a muscle groups (Helms 1996). The Endorphin release theory: As early as 1974, a research group from Peking studied the mechanism on rabbits. They found that infusion of cerebrospinal fluid from a rabbit that had undergone acupuncture into a naive rabbit resulted in significant increase in the pain threshold of the rabbit that received the cerebrospinal fluid.  So the researchers thought that some substances are released from the central nervous system during acupuncture and these mediate the acupuncture-induced analgesia.  Later, several researches pointed to the stimulation of secretion of endogenous morphine-like substances called endorphins (Kaptchuk 374-383). The studies hypothesized that these endorphins act on the opiate receptor sites and inhibit the transmission of pain signals. The evidence to support this action was that endorphin levels in blood and cerebrospinal fluid increased in response to acupuncture and opiate receptor antagonists like naloxone blocked this effect. Also, loss of opiate receptors in genetically altered mice resulted in suppression of this effect. Stimulation of afferent nerve fibers theory: Some other studies have shown that acupuncture stimulates type 3 small afferent fibers within muscle tissue (Stux 187: 209). These fibers which are connected to the hypothalamus-pituitary axis act locally through the spinal cord. They also act systemically through the release of certain neurochemicals. The local and distal pain suppressing effects of acupuncture is dependent upon electrical stimulation of the acupuncture needle. Different frequency and intensity of electrical stimulation determines whether the effect is local, i.e., within the region of the body innervated by a single spinal nerve tract or through the systemic secretion of certain neurochemicals. Recent studies have concentrated on functional magnetic resonance imaging. The data resulting from these studies suggest the ability of acupuncture to regulate more complex physiological processes and that acupuncture has regionally specific, quantifiable effects on relevant brain structures (Kaptchuk 374-383). Acupuncture may also stimulate gene expression of neuropeptides. Some of the recent theories have suggested connective tissue mediated mechanisms and electromagnetic mechanisms as mechanistic basis of acupuncture. Connective tissue mediated mechanism theory: In 2002, Langevin and Yandow reported in their study about a hypothesis which proposed that the network of acupuncture points and meridians can be viewed as a representation of the network formed by interstitial connective tissue. The ultrasound images showing connective tissue cleavage planes at acupuncture points in normal human subjects supported this hypothesis. Acupuncture points in serial gross anatomical sections through the human arm were mapped and found that there was 80% correspondence between the sites of acupuncture points and the location of intermuscular or intramuscular connective tissue planes in postmortem tissue sections. Hence, the anatomical relationship of acupuncture points and meridians to connective tissue planes is probably relevant to acupunctures mechanism of action. The researchers thus suggested a potentially important integrative role for interstitial connective tissue (Langevin and Yandow 257-265). In another study in 2002, Langevin and colleagues demonstrated that the thin acupuncture needles become coupled with connective tissue underlying the dermis. They proposed that this mechanical event then gets transformed into a biochemical signal through a process called mechano-transduction. This mechanical signal is postulated to act both locally (near the site of needling) and at a distance via the hypothesized connective tissue planes (Langevin “connective tissue involvement” 872-874). This hypothesis comes in view of the fact that needle manipulation gives rise to a bio-mechanical phenomenon which is characterized by an increase in the force necessary to pull the needle out of the tissue. This force is more when compared to the force necessary to instill the needle. This is known as needle grasp. Langevin and colleagues investigated whether this needle grasp was due to winding of connective tissue or due to contraction of muscle. In their research, they found that increased needle penetration of muscle does not result in greater pull out force than increased penetration of subcutaneous tissue and it is actually the acupuncture needle rotation that increases pullout force. Also, acupuncture needle rotation results in deformation of subcutaneous tissue which is characterized by increase in periodic architectural order and increase in subcutaneous tissue volume in the vicinity of the needle. These findings supported the fact that connective tissue winding is the mechanism responsible for increase in the pullout force induced by needle rotation and not muscle contraction. Thus, these investigations pointed to the involvement of subcutaneous tissue in needle grasp and the potential role of interstitial connective tissue in neuro-modulation. The researchers also suggested that the mechanism of action of acupuncture also involves extra neural tissues. The idea of involvement of only neural or neuro-chemical mechanisms in the function of acupuncture was thus gradually abandoned. Acupuncture acts not simply via neural stimulation but also by producing changes in the connective tissue milieu surrounding sensory afferent nerve fibers. These connective tissue changes may be long lasting and hence can have prolonged therapeutic effects (Langevin “connective tissue involvement” 872-874). In one of the studies by Ahn and others, they hypothesized that segments of acupuncture meridians that are associated with loose connective tissue planes between the muscles or between the muscle and bone and which are visible by ultrasound have greater electrical conductance than non-meridian, parallel control segments. In their study, the electrical properties of connective tissue planes associated with meridians were examined by combined ultrasound evaluation and tissue impedance measurements. The results of the study concluded that tissue impedance was lower along the pericardium meridian but not along the spleen meridian. The researchers argued that the lack of difference at the spleen location might have been due to both control and meridian needles penetrating connective tissue and the tissue impedance might have been influenced by needle penetration of connective tissue, whether meridian-associated or not (Ahn 5-10). Electro-magnetic mechanism theory: Some researchers, in the recent times have proposed that acupuncture may work via an electromagnetically based mechanism. They hypothesized that acupuncture points have increased conductivity and decreased resistance compared to the surrounding skin and hence, acupuncture points conduct electrical current better than elsewhere on the body. Acupuncture needles create an electrical difference (voltage) between the end of the needle that is outside the body and the point of needle that is inside the body. This voltage is actually created by thermo-coupling, bimetallic effects and other methods. This voltage promotes the conduction of current along the needle shaft and creates an electromagnetic field around the needle. The shaft of the needle that remains outside the body will receive and transmit electromagnetic signals from the environment. Reichmanis and others investigated and proved that the electrical resistance of acupuncture points varies with disease states, sleep, urination, meals, birth and delivery, physical exercise, and changes in external environment such as temperature, time of day and season (Reichmanis 69-72). Researchers have proposed that endogenous electro-magnetic fields signal and regulate physiologic states, biologic and circadian rhythms, and immune and endocrine functions (Fedorowski 765-773). These fields are at low-level, low-frequency, and low-intensity, similar to those generated in the body by acupuncture, and hence can stimulate and regulate physiological processes such as bone mending, cell division, and wound healing. Bioelectromagnetics has now become one of the established and important components of acupuncture therapy (Milburn 53-63). Research There yet a lot to be studied and evaluated as far as the basis of acupuncture is concerned. Also, research concerning the methods to improve the techniques of acupuncture is going on. The new aspect of interest in acupuncture is Biomagnetics. The Bioelectromagnetics research is divided into three areas: 1) basic mechanisms of electromagnetic-biochemical interaction; 2) systemic properties of electromagnetic regulation; 3) interaction between organism and (electromagnetic) environment. This field needs further studies and evidence. Conclusion The medical benefits of acupuncture, especially the pain relief aspects are now well recognized by all countries in the world. Acupuncture has emerged as an important alternative medicine. Whatever is the mechanism of action, the fact still remains that it is effective in treating chronic pain and has been a source of relief to millions who have gone fed up with conventional medications and their side effects. A clear picture of the biological basis of acupuncture is only now emerging as a result of research in recent years. Despite 20 years of research, the efficacy of acupuncture in general is not established and the exact cause of its effect is not known. So far, the connective tissues mediated mechanisms theory and electromagnetic mechanisms theory have emerged as the most successful theories of mechanistics of acupuncture. References Ahn, Andrew, Wu, Junru, Badger, Gary, Hammerschlag, Richard and Langevin, Helene "Electrical impedence along connective tissue planes associated with acupuncture meridians." BMC Complementary and Alternative Medicine  (2005): 5-10. Ernst E. The Desktop Guide to Complementary and Alternative Medicine: An Evidence Base Approach. New York: Mosby, 2001. Fedorowski Artur, Steciwko Andrzej and Rabczynki Jerzy. "Influence of low-frequency electromagnetic field on growth of endogenous Morris hepatoma and its metastatic ability." Med Sci Monit 4. 5 (1998): 765-773. Helms J. Acupuncture Energetics. Berkeley, CA: Medical Acupuncture Publishers, 1996. Kaptchuk, Ted. “Acupuncture: Theory, Efficacy, and Practice.” Annals of Internal medicine 136. 2 (March 2002): 374-383. Langevin Helene, Churchill David, Wu Junru. et. al " Evidence of connective tissue involvement in acupuncture." The FASEB Journal 16 (June 2002): 872-874. Langevin HM, Vaillancourt PD. "Acupuncture: does it work and, if so, how?" Seminar in  Clinical Neuropsychiatry 4. 3(July 1999):167-75. Langevin Helene and Yandow Jason. " Relationship of acupuncture points and meridians to connective tissue planes." The Anatomical record 269. 6 (Dec. 2002): 257-265. Milburn, MP." Emerging relationships between the paradigm of oriental medicine and acupuncture." American Journal of Acupuncture 23(1994):53-62. Peking Medical College, Research Group of Acupuncture Anaesthesia. “The role of some neurotransmitters of brain in finger acupuncture analgesia.” Scientia Sinica 17. 1 (1974): 112-130. Reichmanis M, Marino AA, Becker RO. “D.C. skin conductance variation at acupuncture loci.” American Journal of Chinese Medicine 4.1(1976):69-72. Stux, G and Hammerschlag, R. Clinical acupuncture: Scientific Basis Verlag: Springer, 2001. Traditional Chinese Medicine (TCM)/Acupuncture. Accessed on 4th August, 2007. Available at: http://tcm.health-info.org. Read More