Of all systems in the body perhaps the autonomic nervous system (ANS) best demonstrates the essence of the yin-yang theory. The sympathetic (SNS) division of the ANS is representative of the activity, heat, and intensity of yang, while the parasympathetic (PNS) divisions calming, healing, and soothing influences correspond to yin qualities.
In the ANS stress and tension act like yang to boost the body into fight or flight mode with increased releases of norepinephrine (NE) and adrenaline (EP/epinephrine). When speaking of stress it is useful to recognize three basic forms:
1. Acute/mild stress
2. Chronic/moderate stress
3. Traumatic stress
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Understanding the body's various stress responses and how they activate the ANS can teach us many things about how acupuncture produces therapeutic results. Let's start with how the ANS responds to acute or mild stress.
Acupuncture as a Mild Stressor
In mild stress, the SNS becomes more active and prepares the body for the fight or flight response. The heart rate will increase, the pupils and bronchioles dilate, and the muscles become more tense and ready for activity and exertion. As the mild stressor diminishes the SNS activity decreases and the parasympathetic activity increases. When the PNS activity increases it rises above its baseline and produces a rebound effect.
This rebound effect is important and it is one reason why many patients feel more relaxed during acupuncture. This also explains why patients often fall asleep during acupuncture.
Figure Source: Somatic experiencing: using interoception and proprioception as core elements of trauma therapy; P. Payne, P. Levine, M. Crane-Godreau; https://www.frontiersin.org/articles/10.3389/fpsyg.2015.00093/
When a patient receives acupuncture it acts as a mild stressor as the needle pierces the skin and elicits a mild painful stress response. However, when the initial discomfort from the needle subsides, and when the needle stimulation stops, the SNS activity starts to decline, and PNS activity increases. Over time and with a series of sessions this can help to modulate the ANS and restore balance and homeostasis to the SNS and PNS. This has wide-ranging implications for many disorders.
As the ANS regulates all the major organs in the thorax and abdomen, we can expect acupuncture (as a mild stressor) to have effects on various systems. Many of the internal disorders that acupuncture has shown to be effective for such as hypertension, cardiovascular disease, inflammation, pain, digestive, and reproductive conditions work in part by balancing the ANS.
While there are other mechanisms at work with acupuncture, such as endorphins release, effects on the myofascial system, spinal reflexes, etc, the role it plays on the ANS is vital.
Moderate and Chronic Stress
While mild and acute stress is short-lived and evokes a parasympathetic rebound, medium-grade stressors and chronic stress can cause an increased amount of SNS activity over time. Additionally, chronic stress can lead to a higher baseline of sympathetic tone and this may lead to various symptoms and diseases.
The build-up of stress over time is called allostatic load, and this represents the cumulative nature of stress within various physiological systems. Since the ANS is connected to major organ systems, the limbic system, and emotional processing, the build-up of stress can affect our bodies and minds in a variety of adverse ways.
It is important for acupuncturists and other therapists and doctors to understand stress responses, as decreasing high baseline sympathetic activity, while increasing parasympathetic tone is crucial in the treatment of many chronic conditions.
Applying treatments that balance the yin-yang nature of the ANS can be useful for treating insomnia, anxiety, hypertension, headaches, chronic pain, IBD (inflammatory bowel disease), and more. While acupuncturists and other doctors have various point combinations to use based on the diagnosis and patterns, less attention has been given to needle techniques and the individual patient's unique response to therapy. This is something I elaborate on in my newest class Acupuncture, Stress, and ANS Responses.
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