2: Dynamic Pathophysiology of Acupoints

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CHAPTER 2 Dynamic Pathophysiology of Acupoints

INTRODUCTION

Acupoints in different parts of the human body have different anatomic characteristics. All acupoints, however, have one element in common: they are able to become sensitive, tender, or even painful when exposed to a pathologic disorder. The process of sensitizing is still a puzzle to scientists and clinicians. Recent research data and clinical observations related to muscle pain ¹ help to explain more clearly some of the characteristics of acupoints.

It is important to clarify confusion regarding the differences between acupoints and trigger points.

1. The definition of acupoints is neurogenically oriented, whereas the definition of trigger points is myofascially defined. A trigger point is classically defined as an exquisitely tender spot in the muscle.² By contrast, an acupoint can form anywhere in the body. In this book a tender acupoint is defined as any anatomic structure associated with sensitized sensory nerves. This neurogenic definition suggests that acupoints may appear on any part of the body where there is a sensory nerve. Sensory nerves are distributed all over the body, which means that acupoints may appear anywhere in the body, such as in the muscles, tendons, joints, at bone foramina, and in the suture lines of the skull. About 70% of classic acupoints are also trigger points because muscles constitute a large proportion of the body. Acupuncture therapy and trigger point therapy are different by both definition and clinical practice.

2. Tender acupoints gradually develop when homeostasis declines. These tender acupoints, therefore, are defined as homeostatic acupoints (HAs) in this book. As a rule, homeostatic acupoints develop symmetrically in the human body because the distribution of peripheral nerves is bilaterally symmetrical. By contrast, most trigger points are activated directly by the pain symptoms and are not necessarily symmetrical. Trigger points share some, but not all, characteristics of acupoints, which means that trigger points have some inclusive but not exclusive parameters of acupoints. Acupoints share all the characteristics of trigger points. Thus not all acupoints are trigger points, but all trigger points are acupoints. Note that trigger points correspond to symptomatic acupoints in our Integrative Neuromuscular Acupoint System (INMAS).

One of the most important concepts of acupuncture is that acupoints are pathophysiologically dynamic entities. The degree of their sensitivity changes when homeostasis (the yin-yang balance) changes. Most acupoints show practically no sensitivity when the homeostasis is optimal. Acupoints become tender when homeostasis declines or the body is insulted by pathologic factors. Thus the number of tender HAs can be the quantitative indicator of the homeostasis status of the body. The more tender the HAs detected in the body, the more imbalanced the homeostasis is. Once the homeostasis declines, the health deteriorates.

Then the chain reaction follows: the immune function is suppressed, self-healing capability is impaired, and different pathological disorders may be developed. Patients with more tender acupoints in their bodies need more treatments than those with less tender acupoints.

An understanding of acupoint physiology is important for clinical practice because at the practical level such understanding enables a practitioner to perform quantitative acupuncture evaluation to obtain a reliable prognosis of acupuncture treatment, to predict how many treatment sessions will be needed, and to achieve maximal pain relief in more than 90% of pain patients.

DYNAMIC PHASES OF ACUPOINTS

Dr. H.C. Dung described three phases of acupoints: latent, passive, and active.³ Generally in healthy people some acupoints are neither sensitive nor tender. These nonsensitive acupoints are referred to as latent acupoints.

Under the influence of pathophysiologic disturbances, such as chronic pain or disease, nonsensitive (latent) acupoints are gradually transformed into sensitive or passive acupoints. Almost everyone has a number of passive (tender) acupoints, but people are not consciously aware of them until an experienced practitioner palpates these acupoints with a certain amount of pressure, at which acupoint a person may feel tender or sore at the palpated locations. Most acupoints encountered in acupuncture practice are passive acupoints.

As pathologic disturbances continue to insult the body, pain becomes more intense, and finally passive acupoints become active acupoints. Patients feel painful active acupoints without any palpation and are able to show the precise location of these points and areas to their doctors.

Latent acupoints represent normal tissues. Neurologically passive acupoints have a lower mechanical threshold than normal tissues do and start to fire impulses to the spinal cord and brain under normal mechanical pressure. The same amount of pressure will not induce impulses on latent points. Active acupoints have the lowest mechanical threshold; they may continuously fire impulses to the brain, even without being submitted to external mechanical pressure, and may finally sensitize the neurons in the spinal cord and brain. As the mechanical threshold decreases, the physical size of a sensitized acupoint increases. The phase transition from latent to passive or from passive to active is a continuous process without any clear demarcation; so there is no quantitative measurement for differentiating acupoints of different phases. Table 2-1 provides some criteria, based on our clinical experience, to differentiate the three phases of acupoints. The pressure used to palpate the acupoints is about 2 or 3 pounds. In the clinic we use the thumb to press the points. The pressure is about 2 or 3 pounds when the thumbnail turns from pinkish to whitish. The pressure used to palpate may need to be adjusted because some patients tolerate less pressure if their acupoints are very sensitive or even painful.

Table 2-1 Three Pathophysiologic Phases of an Acupoint

Physiologic Phase	Physiologic Feature	Physical Features (Size)
Latent	Nonsensitive	Normal tissue
Passive	Sensitive on palpation	Diameter <2 cm
Active	Painful without palpation	Diameter usually >2 cm

We postulate that because passive and active acupoints have different mechanical or pain thresholds, they have different neurophysiologic characteristics. For example, passive acupoints will increase electrical signals to the brain only on palpation or needling stimulation. Active acupoints, which continuously fire electrical signals to the brain, will reduce electrical signals to the brain on or after needling stimulation. In other words, acupuncture needling increases impulses from passive acupoints but calms signals from active acupoints. This electrophysiologic difference between passive and active acupoints has been confirmed by experimental data in rats (Y.-T. Ma, unpublished data).

We also believe that chronic pain becomes “wired” or “programmed” into the spinal cord and possibly the brain centers to build up “pain memory.” This occurs partly because the active acupoints continuously fire impulses to the central nervous system (CNS), thus activating the silent synapses (connections) between the neurons in the CNS to form the “pain circuitry.” This “pain memory” could explain the difficulties in treating chronic pain because the practitioner needs to erase the pain memory in the CNS in addition to healing peripheral injuries.

Clinical cases show that there are direct and indirect events that stimulate or activate the transition of acupoints from latent to passive and from passive to active phases. Acute injuries, overuse fatigues, repetitive motions, compression of nerves such as radiculopathy, and joint dysfunctions such as arthritis directly turn the local (symptomatic) acupoints tender. Chronic disorders, fever, cold, visceral diseases (such as those of the heart, lung, gallbladder, stomach), and emotional distress indirectly sensitize both homeostatic (systemic) and symptomatic (local) acupoints. In the latter cases, the tender symptomatic acupoints often appear neurosegmentally related to the disturbed organs, possibly through neural viscerocutaneous reflex.

PHYSICAL PROPERTIES OF ACUPOINTS

Physical properties of acupoints refer to the physical representation of acupoints on the body surface in terms of quality (sensitivity) and quantity (size of each tender acupoint and total number of tender acupoints in the body). Physical properties of acupoints include three parameters: sensitivity, specificity, and sequence.³ These physical properties of acupoints indicate the severity or chronicity of pain symptoms.

Sensitivity

Passive acupoints may ache or feel tender, sore, or painful when palpated with adequate pressure (about 2 or 3 pounds at fingertip, as previously discussed). The amount of sensitive intensity is termed sensitivity. Some patients describe their reaction on palpation of passive acupoints as “a little bit tender,” whereas others cry out with pain. The latter patients clearly feel more pain from the same palpation during examination and their symptoms are either more severe or more chronic. Thus these patients may need more treatments to achieve pain relief than patients with less sensitive acupoints. In other words the amount of sensitivity of an acupoint is proportional to the amount of pain: the more sensitive the acupoint, the more pain the patient feels.

Specificity

Specificity refers to the size and precise location of a passive acupoint. In the beginning of the passive phase, the area or surface size of a tender acupoint is relatively small, about 0.5 cm (1/5 inch) in diameter, and difficult to locate. This means the sensitized acupoint is related only to a limited tissue structure and restricted to a particular anatomic location. This condition is referred to as higher specificity. When symptoms become more severe, the sensitivity of the acupoint spreads to surrounding tissues, and consequently the surface size of the acupoint grows. The surface size of the acupoint may grow by up to or even more than 3 to 4 cm (1.5 inches) in diameter, and the acupoint becomes more easily palpable. This condition is referred to as lower specificity. Some practitioners ⁴ found that careful palpation reveals large, tender regions varying from 16 to 200 cm² (about 1.5 to 5 inches in diameter) surrounding a tender point.

It is more difficult to locate a smaller, less sensitive acupoint than a larger, more sensitive acupoint. Therefore the smaller acupoint is defined as being more specific. An acupoint is more specific when it is limited to a small area and less specific when it is larger and covers a broader area. Specificity is inversely proportional to sensitivity: specificity decreases when sensitivity increases and vice versa.

Sequence

Acupoints appear in the human body according to two models: systemic or symptomatic.³ A physically healthy person always has from a few to about 20 passive acupoints in the body. More passive acupoints will appear symmetrically all over the body when the healthy person gradually develops chronic problems, such as chronic diseases, and degenerative problems related to age, poor diet, bad posture, lack of exercise, or persisting physical or emotional stress. This phenomenon is referred to as the systemic model of acupoint formation, which indicates that passive acupoints appear all over the body systemically when homeostasis declines. Most important, in the systemic model all passive acupoints are formed in predictable locations and in a predictable sequence. The predictable sequence shows which acupoint becomes sensitive first and which acupoint will be sensitized next. This predictability in all people, healthy or sick, provides a quantitative basis for evaluation of a patient’s health status and allows the development of a standardized treatment protocol for acupuncture therapy aimed to restore homeostasis (see Chapter 6). We call these predictable acupoints homeostatic acupoints because they are related to homeostatic decline. Once homeostasis is restored, some HAs are gradually desensitized and eventually the tenderness disappears.

If a healthy person sustains an acute injury, such as in vehicular accidents or sports-related injury, or is afflicted with an acute disease, such as a cold or muscle sprain, tender points will appear around the injured area or in related skin or muscle segments. These local tender points are termed symptomatic acupoints (SAs). An acute injury is an example of the symptomatic model of acupoint formation. The local appearance of SAs reflects the personal nature of the acute injury or disease. Each patient may present particular symptomatic acupoints.

In physically healthy bodies HAs are transformed from latent phase into passive phase following a highly predictable pattern. For example, the H1 deep radial acupoint (located on the deep radial nerve where the nerve enters the lateral side of the forearm to supply the extensor muscles of the wrist and fingers) is always first to become tender in everyone (refer to the figure on the inside cover).

The number of tender HAs in the body serves as a quantitative indicator of the patient’s health status. Usually a healthier person has less tender acupoints in his or her body. If a healthy person has acute pain, a few acupuncture sessions will relieve the pain. Less healthy people have more tender acupoints, and such patients will need more acupuncture sessions to achieve relief of even minor acute pain. Thus the number of tender HAs in the body is the quantitative indicator of (1) health status, (2) self-healing capacity (healthy persons heal better and faster), and (3) the number of acupuncture treatments that may be needed to achieve pain relief. This quantitative indicator provides us with a reasonably objective method to evaluate patients and to predict the prognosis of treatments (see Chapter 6).

Suppose two patients complain about similar symptoms of low back pain, but patient A has 20 passive acupoints on the body, whereas patient B has more than 40 passive acupoints on the body. Clinically patient A is likely to need two to four treatments to achieve pain relief, whereas patient B may need eight treatments to achieve similar relief. Moreover patient A is likely to enjoy long-term or permanent relief from pain after these two to four treatments, but there is a high possibility that patient B will experience a relapse of the symptoms a few months after the initial eight treatments. Because the homeostasis of patient A indicates that the patient is healthier than patient B and has a stronger healing potential, patient A (1) will experience faster therapeutic results with fewer acupuncture treatments, (2) will enjoy longer and complete pain relief, and (3) is less likely to experience a relapse of the same pain symptom.

ELECTROPHYSIOLOGY OF ACUPOINTS

Muscles and nerves are excitable tissues that generate electrical signals when stimulated. When not disturbed, that is, in the so-called healthy state, muscles and nerves are electrically silent at rest. Dr. David G. Simmons and his colleagues investigated the electrical activity in trigger points.¹ They found two significant components of electrical activity in trigger points:

1. Intermittent and high amplitude spike potentials

2. Continuous lower-amplitude noise-like recordings, which they named spontaneous electrical activity (SEA)⁵

Dr. Y.-T. Ma also discovered similar electrical activities of the neurons in the spinal cord and the midbrain (periaqueductal gray matter [PAG]) in responding to induced pain in animal experiments. In normal tissues the activities of the neurons in the spinal cord and the PAG are silent at rest. When pain or inflammation is introduced into the muscles, the spikes and SAE appear in both the spinal cord and the PAG. As the pain intensity increases, the frequency and amplitude of spikes increase and the frequency may reach more than 200 spikes a second. Electrophysiologically the pain intensity is translated into spike frequency in the nervous signaling system.

ACUPUNCTURE NEEDLING RESTORES NORMAL ENERGY METABOLISM OF ACUPOINTS

Dr. David G. Simmons has shown that muscular contraction knots are the histopathologic characteristics of trigger points.⁵ Dr. C. Chan Gunn also suggests a similar histologic structure of the shortened muscles with palpable tender or painful bands or points (Figure 2-1).

Figure 2-1 A trigger point contains shortened muscle fibers, which may present as palpable tender or painful knots or bands. The entire muscle may become shortened and tight if it harbors trigger point(s) and resists stretching. The shortened muscle constantly pulls the tendons and causes tendinitis.

(From Filshie J, White A: Medical acupuncture: a Western scientific approach, Edinburgh, 1998, Churchill Livingstone.)

Careful examination of pathologic activity of passive or active acupoints and the muscles harboring these tender acupoints shows that, in addition to pronounced pain symptoms, at least two other abnormal phenomena are present:

1. The surface temperature of most acupoints is a little higher than that of normal tissues

2. The affected muscles are tight and resist stretching

In 1950 medical scientist Y. Nakatani (see Chapter 1) from Japan’s Kyoto University discovered that acupoints on the skin have a high level of electrical conductivity. Moreover the electrical conductivity of some acupoints increased significantly during sickness. He found 370 such points, incorporated them into the classic meridians system, and called these acupoints Ryodoraku points,⁶ which in both Japanese and Chinese languages means meridian point with good electrical conductivity.

In 1977 Nakatami noted that Ryodoraku points were situated on areas containing sweat glands and inferred that the higher electrical conductivity of Ryodoraku is due to the high electrical conductivity of the sweat glands. Modern Ryodoraku theory focuses on interactions between the sympathetic and somatic nervous systems.⁶ There is no doubt that abnormal energy metabolism is actively involved in the formation of passive and active acupoints related to soft tissue metabolism, as discussed below.

First we briefly review the process of normal energy metabolism in the muscles. After receiving electrical signals (motor-unit action potentials) from a motor neuron in the spinal cord, a muscle cell (muscle fiber) will release calcium into its cytoplasm from its storage pool, the cellular organelle called sarcoplasmic reticulum (SR). This higher cytoplasmic concentration of calcium triggers cellular contractile activity

After contraction the cellular machine pumps calcium from cytoplasm back to the SR to reduce the concentration of cytoplasmic calcium. Once the concentration of cytoplasmic calcium declines, muscle fibers immediately relax, so the muscles are able to prepare for the next signal-induced contraction. Normal muscle fibers contract only when they receive a signal (motor-unit potential) from the spinal cord.

The contraction and relaxation of the muscles require energy to move calcium back and forth between cytoplasm and the SR. If muscle fibers are injured or deprived of energy supply, the cellular machine stops pumping calcium from the cytoplasm to the SR, which results in a persistent high concentration of cytoplasmic calcium. This persistent high concentration of cytoplasmic calcium leads to sustained contraction of muscle fibers.

One of the consequences of this sustained contraction of muscle fibers is the tenderness of acupoints. Note that this sustained contractile activity happens without any signals (motor-unit potentials) from the spinal cord.

The sustained contraction significantly increases the demand for energy and leads to “energy crises.” Sustained muscle contraction shuts the capillary network that supplies the region with nutrition and oxygen and therefore generates a low-oxygen environment (hypoxia). Without energy and oxygen, the cellular machine cannot pump calcium from cytoplasm back to its storage pool (SR), which results in sustained high calcium concentration in the cytoplasm and the consequent persistent sustained muscle contraction. Thus the vicious cycle is built and perpetuated (Figure 2-2).

Figure 2-2 Energy metabolism and the cellular process of muscle fiber contracture in a tender acupoint. The energy crisis hypothesis is suggested by Dr. David G. Simons.

(Redrawn from Simons DG, Travell JG, Simons LS: Travell & Simons’ myofascial pain and dysfunction: the trigger point manual, vol 1, Upper half of body, Philadelphia, 1999, Lippincott–Williams & Wilkins.)

Here we briefly discuss the molecular mechanism of muscle contraction. In healthy skeletal muscle fibers (cells), calcium is stored in a cellular organelle, the SR. When the motor nerve fiber sends impulses to the muscles, the impulses initiate the action potential in the membrane of the muscle fiber. This action potential spreads into the SR (whose membrane is a continuum of the muscle membrane), resulting in the release of calcium into cytoplasm. The high concentration of cytoplasmic calcium triggers the coupling between two linear proteins (actin and myosin). After coupling, these two linear proteins slide against each other, thus leading to shortening of the muscle fiber. This coupling and sliding between the two protein molecules consume a large amount of energy in the form of ATP. If there are no further impulses from the motor nerve fiber after the initial shortening, the SR will reuptake the calcium back to storage, causing the concentration of cytoplasmic calcium to drop. The low cytoplasmic calcium decouples the contractile proteins actin and myosin, resulting in the relaxing of the muscle fiber.

If a muscle fiber is damaged, SR is unable to reuptake the cytoplasmic calcium back for storage, which creates a persistent high concentration of cytoplasmic calcium. The two contractile protein molecules cannot decouple because of this high concentration of cytoplasmic calcium. This results in persistent contraction of the muscle fiber, even without any impulse from the motor nerve. If this energy-consuming process (the energy crisis) continues, tender muscle bands or acupoints will be formed and the tender bands will become a permanent contracture if the energy crisis persists a long time. Finally, this energy crisis may cause chronic inflammation in the involved soft tissues. Both energy crisis and inflammation increase the local temperature.

Acupuncture needling creates a tiny lesion and bleeding in the contractile muscle and surrounding tissues. As a result of the needling, the tight contracted muscle immediately relaxes and blood circulation improves. Thus acupuncture needling breaks the vicious cycle of energy crises in trigger points inside the muscle.

The needled lesion disturbs the surrounding tissue and generates a small electrical current of up to 500 mA/cm,⁷ which we call the lesion current. The needle lesion causes a tiny local bleeding, which stimulates secretion of numerous growth factors, such as platelet-derived growth factors and neurotrophic factors.

The electrical current generated by the lesion and the bleeding caused by needling promote healing and regeneration of damaged tissues and induce DNA synthesis of new proteins and collagens, which repair damaged cellular organelles and restore normal functions. A needle-induced lesion may last at least 2 days or longer before the body heals it, which means that lesion-induced stimulation may last as long. During the healing period, the lesioned cells are digested and replaced by the same types of tissue cells. This explains why acupuncture needling can achieve longer-lasting results. After the needles are removed, the needle-induced lesions keep working for at least 48 hours.

Another important feature is that needling and needle-induced lesions also trigger the local and systemic immune and antiinflammatory reaction that controls the inflammation in the area of needle-induced lesions (see Chapter 4). This explains the antiinflammatory function of acupuncture therapy.