How does acupuncture work?

Physiological Effects and Mechanisms of Acupuncture

Leah Friend Heartwood, L.Ac.⼁May, 2020

Acupuncture is utilized as a therapeutic modality of Chinese and East Asian medicine. The practice has been developed over thousands of years. Acupuncture uses single-use, sterile needles inserted into the skin to stimulate and cause local or systemic change. Simply put, needles are used to communicate with the body to achieve a desired effect. As with all medicine, there is still much to learn about acupuncture, however research continues to further our understanding of its effects. The following areas of research help describe some of the observable physiological effects of acupuncture and electroacupuncture.

Pain Relief and Decreased Inflammation

Acupuncture stimulates the peripheral and central nervous systems and is associated with the release of a number of endogenous opioids (and other neurotransmitters) that are widely known for their analgesic effect (1,2). Electroacupuncture has been shown to activate nervous system fibers that help migrate opioid-containing cells to the site. Electroacupuncture stimulation has also been shown to result in the inhibited expression of an enzyme (COX2) that can lead to inflammation (3,4). Inflammation is a necessary immune response to injury and infection that can become chronic under certain circumstances, contribute to a number of diseases, and has been consistently linked with acute and chronic pain conditions. 

While inflammation is known to cause pain, painful stimuli may also be associated with the production of inflammation in a process called neurogenic inflammation. This pathway is thought to be mediated by the release of certain neuropeptides (including Calcitonin Gene Related Peptide and Substance P) by sensory nerves in response to painful stimuli. Elevated levels of certain neuropeptides like Substance P can be found in the affected tissues of patients with inflammatory bowel disease and rheumatoid arthritis, for example (5). The primary goal in treating many pain syndromes is the regulation of inflammatory mediators and, in some studies, electroacupuncture has been demonstrated to downregulate these substances (6,7)

The Nervous System and Stress

Bodily functions are inhibited or stimulated by sensory information to the autonomic nervous system. The parasympathetic division is correlated with a relaxed and restful state, while the sympathetic division prepares the body for emergency, action, and a fight or flight response. Both responses have important physiological functions and while not all stress is harmful or negative, chronically activated sympathetic responses to long term stress may have negative health effects (8). 

Acupuncture stimulation may affect the autonomic nervous system via signaling and mediation of the central nervous system. This is thought to be through the modulation of neurotransmitters and the stimulation of brain regions that control the autonomic nervous system such as the hypothalamus (9,10,11). Acupuncture stimulation has been correlated with increased parasympathetic nervous system activity as measured by a lowered heart rate and changes to heart rate variability, pupil size, blood pressure, and skin temperature (9,12). 

Additionally, EEG data measuring brain activity shows an increase in all spectral bands (except gamma) with acupuncture stimulation, which is positively correlated with high frequency of heart rate variability (13). High heart rate variability may be associated with a more parasympathetic state and more resilience to stress (12,14,15). 

Neural Injury Recovery

Electroacupuncture has been studied and used in the context of stroke recovery and has been shown to increase blood flow, reduce inflammatory injury, increase growth factor, and inhibit cell death, which may alleviate the symptoms of neurological deficits due to ischemic brain injury (16,17). 

The vagus nerve is the most extensive cranial nerve and is associated with the parasympathetic control of the heart, lungs, and digestive system and innervation of the skin of the concha of the ear (18). One study showed an increase in vagus nerve activity with auricular/ear electroacupuncture. Stimulation of the vagus nerve could be neuroprotective in the context of acute ischemic stroke due to its association with decreased inflammation (via cholinergic anti-inflammatory pathway activation) (17,19). 

Multiple studies have also shown that acupuncture, with and without electrical stimulation, is more effective in improving motor impairment post stroke than rehabilitation therapy alone (20,21). One study found that motor function improvement with electroacupuncture treatment also correlated with a reduction in serum levels of substances associated with the presence of neuronal injury and ischemic stroke (specifically NSE, S-100B and ET) (22). Further information on the use of acupuncture to treat hemiplegia and symptoms associated with ischemic stroke can be found in my case study.

Connective Tissue: a possible mechanism of acupuncture

There is a growing pool of research regarding the intricate web of connective tissue in the body called fascia. Fascia connects muscle to bone, secures and stabilizes organs, surrounds all muscles, nerves, and blood vessels, and spans the entire body. Fascia is remarkably full of sensory nerves and is highly linked to our nervous system.  

Acupuncture may be uniquely able to access and communicate with the fascia via needle stimulation. Consider the analogy of fascia spanning the entire body as a spider web. A web is able to transmit information via the smallest of movements on the periphery. Similarly, acupuncture may be able to cause changes in the body by interacting with the web of fascia. The study of mechanotransduction may help explain this. 

Mechanotransduction is how physical stimulation and sensory information can cause biochemical and biological changes in the body. Mechanoreceptors are a type of sensory neuron that make these responses possible, some of which are found in fascia (23). Gentle stimulation of an acupuncture needle may cause a winding or pulling of the fascia. The pulling of this connective tissue can generate a mechanical signal that is transmitted into connective tissue cells such as fibroblasts. Mechanical stimulation of fibroblasts can activate a signaling cascade and cause a variety of cellular responses with potentially therapeutic physiological effects (24,25,26). Some of these effects may be local or peripheral and may include the amplification of signaling along connective tissue planes, modification of sensory input, and the secretion of chemical substances from cells with measurable changes to “tissue perfusion, pH, cytokines, or growth factors”(24).

In summary, some possible physiological effects of acupuncture and/or electroacupuncture:

  1. The release endogenous opioids causing pain relief
  2. The inhibition of enzyme COX2 causing a decrease in inflammation
  3. Downregulation of inflammation-causing peptides CGRP and SP
  4. The inhibition of cell death and inflammatory injury and a decrease in serum levels of markers associated with ischemic brain injury
  5. An increase in parasympathetic nervous system activity (a restful state) associated with a decreased heart rate and higher heart rate variability 
  6. The mechanical stimulation of the fascia resulting in a plethora of cellular responses, some of which may have therapeutic effects 

There are many more observable effects of acupuncture and research findings than are listed here. There is a high potential of therapeutic value to low risk, non-habit forming therapies such as acupuncture. There is much to be gained by incorporating the insights of both eastern and western practices into our framework of medicine. Continued data collection and acupuncture research is a benefit to the medical community and helps to deepen our understanding of physiology, pathology, and medicine.

Acupuncture should be performed by a licensed acupuncturists and acupuncture approaches and styles may vary widely among practitioners.

Reference List

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