Acupuncture is a traditional practice involving the insertion of fine needles into specific points on the body. Modern scientific investigation confirms that this technique stimulates measurable changes in both local and systemic blood flow. The physical act of needling initiates a cascade of neurological and biochemical events that result in the widening of blood vessels, a process known as vasodilation. This effect on circulation is a significant mechanism underlying the therapeutic benefits of the practice.
The Scientific Verdict on Blood Flow
Research employing advanced imaging technologies has demonstrated that acupuncture affects the body’s circulatory system. Techniques like Color Doppler Imaging (CDI) measure blood flow velocity, providing quantitative evidence of circulatory changes. Studies using CDI show that stimulating certain acupoints can cause a significant increase in blood flow volume in peripheral arteries shortly after the needle is removed.
The effects are not limited to the immediate site of insertion; they can be both localized and systemic. Functional Magnetic Resonance Imaging (fMRI) and Transcranial Doppler (TCD) ultrasonography have revealed that acupuncture can influence blood flow in the brain. TCD studies report an increase in mean cerebral blood flow velocity following acupuncture in post-stroke patients. Furthermore, acupuncture can affect blood supply to internal organs, with certain point stimulations increasing flow through the superior mesenteric artery, which supplies the intestines.
Biological Mechanisms of Vasodilation
The vasodilation observed after needle insertion is primarily driven by a neurogenic response involving small diameter sensory nerve fibers. Mechanical stimulation from the needle activates these nerve endings, which triggers a localized reaction called the axon reflex. This reflex bypasses the central nervous system, causing the sensory neuron to send a signal backward along its own branches in the periphery.
This antidromic signaling causes the release of potent vasoactive neuropeptides into the surrounding tissue. The most prominent of these are Calcitonin Gene-Related Peptide (CGRP) and Substance P. CGRP is a strong vasodilator that directly causes the smooth muscle to relax, widening the blood vessel. Substance P also contributes to vasodilation and increases vascular permeability, which facilitates the movement of fluid and immune cells.
In addition to this local reflex, acupuncture modulates the overall balance of the Autonomic Nervous System (ANS). The ANS is composed of the sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) divisions. Acupuncture stimulation tends to decrease sympathetic activity and increase parasympathetic dominance.
This shift toward parasympathetic control contributes to systemic vasodilation, easing tension in blood vessel walls throughout the body. The effect is further amplified by the release of Nitric Oxide (NO) from endothelial cells lining the blood vessels. Nitric Oxide is a gas signaling molecule that acts as a powerful muscle relaxant, allowing blood vessels to expand and accommodating greater blood flow. The combined action of the local axon reflex, neuropeptide release, and systemic ANS modulation accounts for the widespread circulatory improvements seen with acupuncture.
Clinical Relevance of Improved Circulation
The enhanced blood flow resulting from acupuncture provides several therapeutic advantages. Increased circulation ensures an accelerated supply of oxygen and nutrients required for tissue metabolism and energy production. Better blood flow also enhances the delivery of hormones and immune cells, supporting the healing of injured or inflamed areas.
Improved circulation assists the body in clearing metabolic waste products that accumulate in tissues, which contribute to localized pain and inflammation. The enhanced vascular permeability caused by neuropeptide release also aids in the removal of excess fluid from the interstitial space. This helps reduce localized edema and swelling, which often accompany injuries and chronic inflammatory conditions.