Mechanism of the Acupuncture Effect

Western physicians as a group remain skeptical as to the effectiveness of acupuncture therapy and doubtful about the practicality of incorporating it into the main body of acceptable Western medical practice. Acupuncture analgesia is a case in point. Most Western physicians are of the opinion that any success in controlling pain can be attributed to a number of psychological factors, particularly when surgical intervention is involved. A relationship between successful acupuncture and patient susceptibility to hypnosis has been demonstrated by Katz and colleagues. Some physicians believe that the Chinese are conditioned by their culture to bear pain with considerably more stoicism than is possible for Westerners to do and that their apparent tolerance to it is, therefore, much greater. The acknowledged skill of Chinese surgeons, when combined with such presumed conditioning, hypnosis, and successful distraction of the patients from the procedure itself, are considered sufficient in themselves to produce the good results described by the eyewitnesses and reported on in the growing literature on the subject. This now includes reports that should help contradict these conservative attitudes. These describe a wide variety of surgical emergencies which require procedures to be undertaken without patients being “prepared” psychologically beforehand.

Similarly, dental extractions acceptable to patients are commonplace. The successful treatment of enuresis in small children is also reported. Veterinarians have found many uses for acupuncture in treating domestic and laboratory animals such as rabbits, rats, and mice. Wheeler and colleagues have mapped body acupuncture points used by veterinarians for treating goats, pigs, cows, and chickens and have confirmed that these correspond to low resistance points as measured by skin con tact resistance. Despite these findings, it has not yet been possible to identify any anatomical rationale to explain the basic system of 14 meridians used in classical acupuncture therapy.

It is assumed that successful acupuncture must depend on the integrity of nerve function. About half of all known acupunture points are in some way directly related to the peripheral nerve, and about 35% are located close to peripheral nerves. This leaves only 15% of known acupuncture points apparently not located on or close to any nerve structure. The Teh Chi sensation of heaviness, soreness, and numbness is assumed to result from the effects of acupuncture at peripheral nerve endings. Injection of procaine near Ho Ku (84, CO 4) and Tsu San Li (178, ST 36) inhibits Teh Chi from occurring, and decreases the pain threshold to potassium iontophoresis as well. Most studies on this question have been concentrated on the Ho Ku point, since 50-60% of all clinical cases require acupuncture at this point. Ho Ku is used to control pain in the head, neck, trunk, and upper extremities. Many dental patients in whom Ho Ku (84, CO 4) was the point of choice showed a threefold increase in their pain threshold, while their temperature and sensitivity to pressure remained unchanged. Bressler also obtained an analgesic effect lasting 12 hr in squirrel monkeys, using the Ho Ku (84, CO 4) point.

Acupuncture classics have always emphasized the importance of the Teh Chi response for successful acupuncture, the premise being that the stronger this is, the better the results of treatment. It has not been possible to demonstrate either Teh Chi or any therapeutic effect of acupuncture either in paralytic patients or in those with procaine nerve blocks. The numbness noted when Hsiao Hai (131, SI 8) is used is considered to be due to pressure on the ulnar nerve. The Teh Chi obtained by using Ho Ku (84, CO4) is associated with contraction of the first dorsal osseus muscle which is innervated by the spinal nerves at C8 and T1. When other points, such as Huan Tiao (217, GB 30), Feng Shih (218, GB 31), Yang Ling Chuan (221, GB 34), Tsu San Li (178, ST 36), and Tai Chung (322, LI 3) are used, Teh Chi is usually obtained. The Acupuncture Anesthesia Group of the Shanghai Institute of Physiology recorded muscle potentials in 32 healthy adults, using Ho Ku (84, CO 4), Chu Chih (91, CO 11), and Tsu San Li (178, ST 36).

The group observed a good correlation between intensity of muscle activity noted by manual palpation and the subjective Teh Chi response. These disappear entirely in patients under spinal anesthesia and are greatly reduced when intravenous sodium thiopentol is used. It is still far from clear precisely how such muscle activity or nerve conduction presumably brought about by the Teh Chi response is related to successful acupuncture treatment.

No one knows exactly how acupuncture blocks pain, nor are we certain of the precise physiological and biochemical mechanisms of pain involved. Pain appears to involve multiple systems, including the peripheral nerve endings, brainstem, midbrain reticular formation, thalamus, and prefrontal cortex. The role of midbrain reticular formation in acupuncture analgesia has been studied in guinea pigs. When electric pulses were passed through Tsu San Li (178, ST 36) and Yang Ling Chuan (221, GB 34), or when the Achilles tendon was compressed manually, no pain response could be recorded at the medial reticular formation. Intravenous morphine produces the same effect. Chang  at the Shanghai Institute of Physiology found that pain discharge at the thalamic neurons persisted after the dorsal column in rats and rabbits had been sectioned, but disappeared immediately following either an intravenous injection of morphine, squeezing of the Achilles tendon, or needling at Tsu San Li (178, ST 36) and Shang Chu Hsu (179, ST 37).

In addition to these changes, brain concentrations of some neurotransmitters can also be altered by acupuncture. For example, electric stimulation at Feng Lung (182, ST 40) and Yang Fu (225, GB 38) has been found to increase the amount of 5-hydroxytryptamine in the medulla and thalamus and to decrease glutamic acid in the thalamus. However, this has not been accompanied by any significant alteration of norepinephrine and Y-aminobutyric acid in the cortex, hippocampus, thalamus, midbrain, or medulla. It is of interest to note that intraventricular injection of 5-hydroxytryptamine or sodium glutamate may also increase the pain threshold to radiant heat. An increase in the pain threshold can also be demonstrated in rats when cross-circulation or perfusion of cerebrospinal fluid from acupuncture-treated rabbits to the lateral ventricles of recipient animals is performed. The analgesic effect of acupuncture appears to be different from that of morphine. The effect of morphine can be suppressed by intraventricular administration of reserpine, whereas acupuncture at Kun Lun (291, BL 60) augments the analgesic effect. On the other hand, intraventricular injection of atropine greatly reduces the acupuncture effect but does not alter that of morphine. An important milestone will have been reached when more research is done to duplicate these animal data and it becomes possible to establish an unequivocal relationship between modem neuroscience and the ancient art of acupuncture.

Over the past few years, pituitary opiate-like substances have been identified and purified. Cyclic trypsin- and chrymotrypsinsensitive peptides bind opiate receptors, and thus presumably attenuate intense pain in experimental animals. More recently, these peptides have been identified as endorphins with amino acid sequences corresponding to the residues of ,6-lipotropin, MSH, or ACTH. The acupuncture-endorphin link is under active investigation at a number of research centers in the United States and Canada. Direct evidence of an acupuncture-endorphin interaction was recently demonstrated by Goldstein of Stanford and Pomeranz of Toronto. If their findings can be confirmed, acupuncture would seem to induce pituitary release of endorphin which, in turn, modulates tolerance to pain. It can be expected that studies such as these will in time clarify the precise nature of the role endorphins play in acupuncture-induced analgesia or anesthesia.

Decreasing the intensity of felt pain.

The small fibers transmit impulses more evenly and continuously on the target cells in the substantia gelatinosa, thus heightening the intensity of pain experienced. In patients with selective degeneration of the large peripheral fibers, as in cases of herpes zoster and similar neuropathies, the gate opens because of the relative dominance of the opposing small fibers. This often causes these patients to experience a more intense type of pain. Stimulating the large fibers at a site of pain by rubbing, massaging, scratching, or with a Pifco stimulator used in short bursts, or by the use of acupuncture may increase large fiber discharge and thereby diminish the intensity of pain experienced. Although unequivocal confirmation of the gate theory of pain is not yet available, the concept does seem to offer the best explanation to date of how acupuncture can block or alleviate pain.

The perception of pain and its transmission depend on involvement of the dorsal root, the lateral spinothalamic tract, the thalamus, and the pre-frontal cortex. The brainstem’s reticular formation provides an important link between the levels of pain perception and exerts an inhibitory effect upon its transmission. There are at least three central regulatory mechanisms involved. The midbrain transmits the first warning of impending pain. The nerve impulses involved are purely adrenergic and can be inhibited by commonly used analgesics, such as salicylates and imipramine. The next level is mediated mainly by the cholinergic nerve fibers of the thalamus. It is more specific for pain, and can be aroused by strong stimuli and inhibited by narcotics such as morphine or Demerol. The third level is mediated by the prefrontal cortex which is responsible for intellectual alertness. Pain is a complicated, finely integrated process, and is greatly influenced not only by a patient’s physiological and pathological states, but also by his or her race, sex, age, personality, and emotional makeup.

The incoming information from the sites of noxious stimuli is, therefore, filtered through a set of intermediate cells including those in the substantia gelatinosa and other laminae in the dorsal horns and even in the thalamic centers, or is modulated by the recently proposed nocioceptive circuit at the marginal neurons of the spinal cord. Stimulation by acupuncture involves preferential excitation of large fibers, thus blocking the noxious impulses transmitted from the small fibers. Electrical stimulation with high frequencies or rapid manual twirling of needles may excite the low threshold, fast-conducting fibers before the continuous, slow rate impulses. The gate control theory cannot, however, explain the acupuncture effect on remote pain which can occur on the contralateral side or at anatomically completely unrelated sites. Moreover, the gate theory offers no explanation of other observed physiological effects unrelated to pain control such as blood pressure regulation or gastric secretion and motility.

The mechanisms underlying pain and its perception are still incompletely understood. It is known that Meissner’s corpuscles are responsible for tactile sensation, the Pacinial corpuscles for pressure, the Ruffini corpuscles for heat, the Krause corpuscles for cold, and free nerve endings for pain. When noxious stimuli are present, whether initiated mechanically, by changes in temperature, or by local elaboration of chemical substances such as bradykinin, prostaglandin E, histamine, acetylcholine, 5-hydroxytryptamine, adrenalin, noradrenalin, or an abnormal concentration of hydrogen or potassium ion, pain is produced and is transmitted by the well-rnyelinated A fibers, about 45 µmin diameter, at a speed of 6-30 m/sec, and also by the unmyelinated or finely covered C fibers, about 1.8 µmin diameter, at a speed of 0.5-2 m/sec.

A fibers are responsible for fast, intermittent pain impulses. The sensation of pain conveyed by the slow-speed C fiber is continuous. These fibers accept different types of impulses with little receptor specificity. The differences between various types of pain impulses are related to the speed of transmission through either A or C fibers. In nerve ischemia, conduction of pain through A fibers is suppressed before conduction through the C fibers, whereas local analgesics block conduction through the C fibers first. Neurons spread up and down the length of the spinal cord, with many integrated networks all over the long fibers in the spino-spinal or spino-reticular pathways.

Melzack and Wall postulate that a gate control mechanism is present in the substantia gelatinosa. The different pain impulses from noxious stimuli are stransmitted by the small myelinated and nonmyelinated fibers, whereas blunted mechanical stimuli, such as pressure, are transmitted by large fibers. The preferential excitation of large fibers blocks the noxious effect of input from small fibers. The activity in the large fibers is inhibitory, and the impulses occur in bursts to keep the gate partially closed, thus decreasing the intensity of felt pain. The small fibers transmit impulses more evenly and continuously on the target cells in the substantia gelatinosa, thus heightening the intensity of pain experienced. In patients with selective degeneration of the large peripheral fibers, as in cases of herpes zoster and similar neuropathies, the gate opens because of the relative dominance of the opposing small fibers. This often causes these patients to experience a more intense type of pain. Stimulating the large fibers at a site of pain by rubbing, massaging, scratching, or with a Pifco stimulator used in short bursts, or by the use of acupuncture may increase large fiber discharge and thereby diminish the intensity of pain experienced. Although unequivocal confirmation of the gate theory of pain is not yet available, the concept does seem to offer the best explanation to date of how acupuncture can block or alleviate pain.

The perception of pain and its transmission depend on involvement of the dorsal root, the lateral spinothalamic tract, the thalamus, and the pre-frontal cortex. The brainstem’s reticular formation provides an important link between the levels of pain perception and exerts an inhibitory effect upon its transmission. There are at least three central regulatory mechanisms involved. The midbrain transmits the first warning of impending pain. The nerve impulses involved are purely adrenergic and can be inhibited by commonly used analgesics, such as salicylates and imipramine. The next level is mediated mainly by the cholinergic nerve fibers of the thalamus. It is more specific for pain, and can be aroused by strong stimuli and inhibited by narcotics such as morphine or Demerol. The third level is mediated by the prefrontal cortex which is responsible for intellectual alertness. Pain is a complicated, finely integrated process, and is greatly influenced not only by a patient’s physiological and pathological states, but also by his or her race, sex, age, personality, and emotional makeup.

The incoming information from the sites of noxious stimuli is, therefore, filtered through a set of intermediate cells including those in the substantia gelatinosa and other laminae in the dorsal horns and even in the thalamic centers, or is modulated by the recently proposed nocioceptive circuit at the marginal neurons of the spinal cord. Stimulation by acupuncture involves preferential excitation of large fibers, thus blocking the noxious impulses transmitted from the small fibers. Electrical stimulation with high frequencies or rapid manual twirling of needles may excite the low threshold, fast-conducting fibers before the continuous, slow rate impulses. The gate control theory cannot, however, explain the acupuncture effect on remote pain which can occur on the contralateral side or at anatomically completely unrelated sites. Moreover, the gate theory offers no explanation of other observed physiological effects unrelated to pain control such as blood pressure regulation or gastric secretion and motility.

It is well known that injecting procaine or inserting a needle into a trigger point may relieve referred pain and even pain at its point of origin. Counterirritation by means of mustard plasters, ice packs, hot water bottles, or cupping has a long history of usefulness. Mild irritation at a site of pain can often bring about substantial relief of a more severe pain. What the precise effect of acupuncture is cannot be answered as yet. Electrical discharges can be demonstrated at acupuncture points when needles are inserted into ear or body points. Activation of the large fibers with discharges at frequencies of about 800-1,000 sec? has been demonstrated at the acupuncture point, Yu Chi (61, LU 10), in an abductor pollicis brevis muscle.

Acupuncture may stimulate a number of systemic effects related to hormonal homeostasis, as well as autonomic nervous functions. Acupuncture at Tsu San Li (178, ST 36), Feng Chi (207, GB 20), or Nei Kuan (68, HG 6) can lower blood pressure when it is elevated and normalize it when the value is low. It has been reported that 58% of 206 hypertensive patients showed a definite decrease of their blood pressure which was also associated with a decrease in cholesterol and lipoprotein levels, neutrophilia, and lymphocytopenia. It has also been reported that acupuncture at Jen Chung (Shui Kou) (2, VG 26) or Su Liao (3, VG 25) prolongs survival in animals with artificial pneumothorax or suffering from hemorrhagic shock. Acupuncture at Tsu San Li (178, ST 36) can increase lung volume and oxygen consumption. Stimulation at Tsu San Li (178, ST 36) or Wei Shu (25 2, BL 21) has been found to increase gastric motility and acid secretion in animals.

More recently, Matsumoto et al. conducted studies in 100 rabbits and 45 humans which demonstrated an increased amplitude and frequency of intestinal motility, as measured by balloon catheter, when sine wave stimulus was applied at Tsu San Li (178, ST 36). Despite increased intestinal peristalsis, no change was noted either on electrocardiograms or in blood pressure measurements. An increased alpha wave was also noted on electroencephalograms similar to that obtained in patients given sedatives. Many interesting biochemical and hematological phenomena have been observed such as changes in neutrophils, lymphocytes, gamma globulin levels, and specific immune substances. Tsu San Li (178, ST 36) and Lan Wei (EM) are said to be effective in combating the inflammatory process manifested in acute appendicitis. Tsu San Li (178, ST 36), Ta Chu (14, VG 14), and Ming Men (24, VG 4) are useful for increased urinary excretion of 17-hydroxyendothelial system in animals. How important these changes may be when related to the recent findings of increased urinary excretion of 17-hydroxy-corticosteroid and decreased excretion and adrenalin is unknown. We believe that more basic research into the physiological effects of acupuncture will shed further light on our understanding of this rejuvenated art.

In 1961, Chinese scientists reported on work they had done demonstrating the biological and immunological activities of insulin following its resynthesis from its beta and alpha chains. Many Western physicians at that time cast doubts upon this scientific achievement. This attitude should not now be repeated. It is clear that a great deal more work has to be accomplished before Western societies can fully accept acupuncture as a useful form of treatment. It would be useless as a therapeutic procedure if it were only effective in treating Oriental people or could only be successfully performed by Oriental acupuncturists. More research has to be undertaken by competent investigators trained in the West using modern physiological and biochemical equipment to determine if acupuncture does in fact work, and if so, how.

There are many guidelines recommended by the NIH Ad Hoc Committee on Acupuncture and by several state medical societies and acupuncture study groups. At present, no one considers acupuncture a workable substitute for conventional anesthesia in surgery. However, the impossibility of ensuring complete absence of pain during surgery together with our present lack of understanding of the mechanisms involved in acupuncture should not prevent us from using this potentially helpful modality for patients unable to tolerate general anesthesia or when the use of specific analgesics or narcotics is contraindicated. Keeping in mind the many complications that can result from the use of general anesthetic agents and the prolonged postoperative course associated with their use, as well as the many untoward effects of drugs, cardiorespiratory complications, electrolyte imbalance, and infections resulting from prolonged intravenous feedings, we must seriously consider the alternative of such a mild, completely physical, easily controlled, and relatively noninvasive modality, even though end results may not always be quite as effective.

We have large numbers of potent analgesics and narcotics available that stop pain temporarily in many of our patients. However, we are still frequently unable to deal with intractable or chronic pain. A considerable number of pain clinics in this country are actively engaged in acupuncture research in an attempt to meet this challenge. There are usually two types of pain in patients with malignant disease. The continuous, unrelenting type of low-intensity pain is believed to be transmitted through the C fibers and presumably is due to low-grade tumor infiltration and tissue damage. The episodic, intermittent, unbearable type of pain is transmitted through the A fibers. It is often the most agonizing kind of pain for the patient, and since there is a limit to the effectiveness of narcotics and analgesics to deal with this, acupuncture can most probably provide a useful alternative means for lessening its intensity.

More research is badly needed on the selection of acupuncture points, frequency of treatment, and methods of stimulation, as well as on the development of suitable analytical tools for objective evaluation of clinical responses. Studies on the effectiveness of acupuncture for anesthesia and analgesia, as compared to that obtained with the commonly used analgesics and narcotics, must also be undertaken if acupuncture is to gain any substantial acceptance by Western physicians.

Leave a comment

Your email address will not be published. Required fields are marked *