Insomnia in Chinese Medicine: The Heart of the Matter

Abstract

Chronic insomnia affects a significant proportion of the general population worldwide, and is associated with several serious medical conditions. From the Western scientific literature, hyper-arousal (on the cognitive–emotional, behavioral, autonomic, or central nervous system level) is a final common pathway involved in its pathogenesis. However, from a Chinese medicine (CM) perspective, it is the Heart, capitalized to denote the functional system as described in CM theory, that is the key organ involved in insomnia due to its role as the “seat of consciousness.” This article explores how insomnia is understood from the CM perspective, in particular the role of the Heart, and some of the neurophysiological evidence that supports these ancient theoretical understandings. The potential role of the vagus nerve and its relationship with the (biomedical) heart and CM Heart is also examined. Finally, some of the evidence in association with mechanisms of action of acupuncture in insomnia, in particular its impact on cardiovascular variables associated with insomnia, is presented, along with findings of systematic reviews.

Introduction

Chronic insomnia is defined as difficulties falling asleep, maintaining sleep, and/or early morning awakening occurring at least three times per week over three months plus at least one related daytime impairment (fatigue, attention impairment, mood disturbance, impaired performance).¹ It affects 9–15% of the general population worldwide, with a prevalence of approximately 6% in countries of high income.² There can be a genetic component to chronic insomnia, with hereditary coefficients of 42–57%.¹ Women are more likely to suffer from insomnia than men at a ratio of 1.4:1,² which increases to 1.7:1 after 45 years of age.¹

Chronic insomnia interacts with other medical conditions.³ Research indicates a relationship between insomnia and anxiety disorders,⁴ depression,^4
–6 suicide ideation,⁷ cognitive decline,⁸ cortical atrophy,⁹ decreased immune functioning,¹⁰ hypertension,³ and cardiovascular disease.^1,3,11 Prospective longitudinal studies indicate that people with insomnia have an increased risk of myocardial infarction (relative risk [RR] = 1.5; 95% confidence interval [CI] 1.2–1.8),¹² which may be mediated by short sleep duration.¹ Anxiety and insomnia are both associated with cardiovascular disease, and insomnia has been found to modulate the association of cardiovascular symptoms with anxiety substantially, indicating that insomnia plays a critical role in development of cardiovascular symptoms in women with anxiety.¹³ Incident insomnia has also been found to be associated with fair to poor perceived health and physical disability. In multivariate analyses, these risk factors explained the higher incidence of insomnia among those with medical conditions such as heart disease, stroke, and diabetes.¹⁴

Insomnia is associated with anxiety and depression.^4
–6,15 Chronic insomnia is a risk factor for the development of psychiatric disorders, including depression, as well as a prodrome of major depressive episodes. Although insomnia usually disappears as depression is treated, it may persist, indicating heightened vulnerability to depressive relapse or recurrence.¹⁶ For example, a meta-analysis found that insomnia is associated with a 2.6 times greater risk of developing depression.⁵ Taylor et al.⁶ found that people with insomnia were 9.8 and 17.4 times more likely to have clinically significant depression and anxiety, respectively. Konstam et al.¹⁷ found both depression and anxiety have been implicated in contributing independently to the poor outcomes seen in patients with heart failure, and Strik et al. found symptoms of depression and anxiety were associated with cardiac events.¹⁸

From a Chinese medicine (CM) perspective, the Heart (“Xin” in Chinese, and capitalized in this paper to distinguish it from the anatomically described organ) is the central Zang-Fu organ involved in the pathogenesis and treatment of insomnia by virtue of its role as the “seat of consciousness,” the place where the “Shen” or spirit or mind is housed. Consciousness is ascribed to the Heart, not the brain as it is in Western medicine.¹⁹ The Heart is also a central organ involved in the etiology and pathogenesis of anxiety and depression. In the treatment of insomnia with CM, addressing the imbalance associated with the Heart is a key strategy, and there is scientific evidence that indicates that acupuncture, for example, is able to effect physiological changes on the heart that are involved in the pathophysiology of insomnia from a Western scientific perspective. Although this traditional concept appears at first examination incoherent by modern physiological understandings, it does make sense when viewed within the function of the vagal nervous system. The vagus nerve (10th cranial nerve) is predominantly afferent, informing the brain of visceral experience. Could the ancient Chinese have been correct, at least in part, when they ascribed consciousness and mind to the Heart? And does the vagus nerve provide the connection and therefore physiological basis for this?

This article will explore how insomnia is understood from a CM perspective, in particular the role of the Heart, and some of the neurophysiological evidence that supports these ancient theoretical understandings. The potential role of the vagus nerve and its relationship with the heart (in the biomedical sense) and CM Heart is also examined. Finally, some of the evidence in association with mechanisms of action of acupuncture in insomnia, in particular its impact on cardiovascular variables associated with insomnia is presented. In exploring this information, it attempts to lead the reader to consider where there may be convergences in understanding between the two medical systems, CM and Western medicine, with respect to this condition, and in particular draws attention to emerging scientific evidence that supports the notion of interdependence between organ systems, espoused in CM theory and increasingly embraced in Western medicine.

Insomnia from a Western Medical Perspective

From the Western medicine perspective, the pathophysiology of insomnia is complex. According to the two-process model of sleep–wake regulation, two processes control sleep–wake rhythms: a circadian process (controlled by an internal clock in the suprachiasmic nucleus) and a homoeostatic process (the need for sleep, driven by time since last adequate sleep).¹ The circadian process is controlled by an internal clock within the suprachiasmic nucleus, and is synchronized to the time of day by predominantly the light–dark/day–night cycle. Melatonin is an important hormone involved in the circadian process: secretion by the pineal gland is suppressed by light and peaks in the middle of the night.

It has been suggested that orexin is a master regulator of the sleep–wake cycle. Orexin A and B are expressed in a few thousand cells located in the lateral hypothalamus. However, receptors are widely distributed throughout the brain.²⁰ Orexin cells are highly active when awake and inactive during sleep. On the basis of their actions, orexin antagonists have been developed, including the new drug Surexant.²⁰

Adenosine is another important factor. This is a neuropeptide hypothesized to be associated with the homeostatic system. It promotes sleep by inhibiting the orexin system (which induces arousal), and its production is linked to the amount of time spent awake.¹ The parts of the brain mostly responsible for controlling the sleep–wake cycle are “the ascending reticular activating system, the ventrolateral preoptic nucleus, the median preoptic nuclei, and a group of orexinergic neurons in the lateral hypothalamus.”¹ ^(p549)

According to Riemann et al.,¹ hyper-arousal (involving the autonomic [ANS] and central nervous systems [CNS]) appears to be involved as the final common pathway in insomnia. This is caused by an imbalance of sleep–wake regulation due to either hypo-activity of the sleep-inducing systems or over-activity of the arousal systems or both.^1,3 Potential mechanisms underpinning insomnia include a misalignment of the circadian process, and dysfunction of the homeostatic process, lesions in the area of the brain associated with sleep regulation, and changes at the neurochemical level, such as reduced GABA-ergic activity (weakening the sleep-promotion system) or over-activity of the orexin activity (strengthening the arousal system).¹ Inhibition of the usual activity decline in various brain regions that normally occurs in the switch from being awake to asleep has been found on positron emission tomography scans in insomniacs, which Riemann et al. suggest lends support to the idea that there is general over-activity of the arousal, emotion-regulating, and cognitive systems in the pathophysiology of insomnia. This has then led to insomnia being understood as a “disorder of corticolimbic overactivity that interferes with sleep-promoting brain structures.”¹ ^(p554)

There is also a genetic component to insomnia, with heritability coefficients of 42–57%, and epigenetic mechanisms are also likely to be involved in its development and maintenance. Stress is hypothesized to alter activity of the hypothalamic–pituitary–adrenal (HPA) axis (stress regulatory system), inducing changes in parts of the brain that are particularly neuroplastic and vulnerable to stress and stress hormones, such as the hippocampus.¹

Research suggests heritability for insomnia and reactivity of sleep patterns of stressful events, which explains why insomnia may occur in response to stressful events.⁴ Stressful life events have been found to be closely associated with the onset of chronic insomnia, and this appears to be mediated by predisposing personality traits.²¹

Gene loci contributing to sleep characteristics and variability have been identified, though little is known about the genetic background of insomnia.²² Epigenetic gene–environment interactions identified recently may contribute to the understanding of the genetic control of sleep. It has been hypothesized that insomnia may be influenced by epigenetic control processes involving sleep mechanisms and stress-response related gene–environment interactions that impact on brain plasticity.²² For more detail, the reader is referred to Palagini et al.'s summary.²²

The hyperarousal model of insomnia has underpinned much of the research into the pathophysiology of insomnia, based on findings that people with insomnia show signs of hyperarousal, either on the cognitive–emotional, behavioral, ANS, or CNS level. Objective sleep measures, electroencephalogram (EEG) activity, HPA axis activity, inflammation markers (e.g., cortisol), and other physiological outcome variables suggest that insomnia is a disorder of hyperarousal present during the day and at night.²¹

Much CNS research has focused on the HPA axis, using (stress hormone) cortisol levels as a major outcome variable indicating increased arousal.¹ ANS research indicates that heart rate is elevated and heart rate variability (HRV; the beat-to-beat variation in either the heart rate or the duration of the R-R interval, the heart period) is decreased in those with insomnia before sleep and during Stage 2 non-REM sleep, reflective of increased sympathetic nervous system activity.²³ Decreased HRV has been found to be associated with increased mortality following myocardial infarctions, and has been used to assess risk of cardiovascular mortality.²⁴ For a comprehensive exploration of the mechanisms underpinning insomnia, readers are referred to Riemann et al.¹

Budhirajo et al. found that the odds of having insomnia were significantly elevated in people with heart disease, hypertension, diabetes, stomach ulcers, and other medical disorders. They argue that while medical disorders may result in sleep disturbances, the sleep disorders themselves may increase the severity of such medical disorders—that is, it is bidirectional. Both alteration in immune function and inflammation may underlie the association between insomnia and other medical disorders, as may psychosocial stress.²⁵

Western medical treatment includes cognitive–behavioral therapy (first-line therapy and found to be more effective than drugs in long-term treatment of insomnia) and the prescribing of benzodiazapines and benzodiazepine-receptor agonists. These drugs are unsuccessful in achieving sustained remission in a significant proportion of patients and are associated with serious side effects and dependency. Antihistamines and tricyclic antidepressants, which work by blocking the wake-promoting aminergic and cholinergic transmission, also have serious side effects. The drug Suvorexant, an orexin receptor antagonist, suppresses the wake stimulatory network of sleep–wake regulation. Novel therapies currently being investigated include transcranial magnetic and electrical brain stimulation.¹

The Heart , Shen 神, Consciousness, and Insomnia

In ancient China, when the guiding theories of CM originated at least 2000 years ago, theories were based largely on observations of the body, and signs and symptoms in illness, and analogies were drawn between these and characteristics of natural phenomenon to explain the physiological functioning of the body and pathological changes in disease. Unlike early Greek medicine, dissection of the body did not occur until much later. The concept of the Heart (“Xin” in Chinese) in CM is broader than its role in the cardiovascular system, and in fact a distinction was not made between the Heart and mind/consciousness. The Heart is understood to “house the Shen” or “house the mind.” Shen or spirit (or vitality) refers, in the broad sense, to the exterior manifestation of physiological functioning of the body and, in the narrower sense, to mental consciousness or activities, including memory, perception, and thinking.^26,27 Matsumoto and Birch²⁸ state that the “Xin” is both “heart” and “mind” and that it is not possible to say categorically whether classical CM scholars made a distinction between the two or if there were acknowledged differences between the two depending on context. From a systems biology point of view, Xin and Shen are not “objects” but multilevel functions only peripherally associated with anatomical organs. Given that CM theory was based largely on observations of the human, one could speculate that it is likely that they observed the relationship between, for example, intense emotional experiences and palpitations and/or what was termed “Chest Bi” (chest pain, which in modern times could “correlate” with angina or heart attack), which may have informed their theories of the role of emotions in the pathogenesis of heart-related conditions. Certainly, both palpitations and angina/heart attack are clinical entities within CM, and the role of the Heart and emotions in the pathogenesis of these is recognised and described in CM texts.

The concept of “Shen” is seen as a rarified form of qi that resides in the Heart. Thus, the Heart is seen as the “seat of counsciousness.” The Shen is easily unsettled and requires the anchoring of the more material Jing or Blood or yin, vital substances that provide the material basis of the body.²⁹ The basis of insomnia is that the Shen is in some way disturbed. Although the etymological origin of Shen is uncertain, Schuessler³⁰ notes a possible Sino-Tibetan etymology when comparing the Chepang gliŋh “spirit of humans.” The character , or as traditionally written , suggests the sun rising over the sea, meaning radiance. The glyph can, among many meanings, suggest a mouth, as in chanting or speaking. Another interpretation is a pictograph of a “lightning bolt,” semantically suggesting both “lightning” and “spirits” coming down from the heavens. Perhaps this might indicate inspiration, enthusiasm, or psychological engagement?

The association of the Heart with consciousness is captured in chapter 8 of the Huang Di Nei Jing Su Wen, one of the oldest guiding CM texts, which says: “The heart is the sovereign of all organs and represents the consciousness of one's being. It is responsible for intelligence, wisdom, and spiritual transformation.”³¹ ^(p34) This is in contrast with Western thought that would ascribe consciousness and intelligence to the mind and brain.

As the “Commander of Blood” and the seat of consciousness, the Heart controls emotional activities: qi, Blood (Xue), and essence (Jing) are understood to be the material basis for emotional and mental processes, though the Liver is responsible for harmonizing the emotions via its action in regulation of the flow of qi (and therefore blood) in the body.^26,27,32 According to tradition, Jing () is stored in the kidneys and is the most dense physical matter within the body (as opposed to Shen, which is the most volatile and refined).²⁹ The Heart is connected to the other four Zang-Fu organs (Liver, Kidney, Spleen, and Lung) via interdependent relationships described by various theories, including Five Phase/Element Theory, Meridian Theory, Zang-Fu Theory, and others. Thus, imbalance in the other organ systems can impact on the Heart and vice versa. Importantly, such imbalances in other organ systems do form part of the understanding of the etiology and pathogenesis of insomnia (as well as any other disorder) and are addressed in treatment with acupuncture and Chinese herbal medicine. In CM, diseases or disorders typically have several underlying patterns of disharmony, each characterised by particular signs and symptoms reflective of the underlying pathogenesis of a disorder at that point in time. The number of underlying patterns of disharmony of insomnia varies between textbooks, with seven and nine being described by two publications.^33,34 These patterns include insomnia due to Heart Fire/Kidney Water disharmony: the Kidney yin (water) is deficient and fails to “cool” the Heart “fire,” which then disturbs the Shen/spirit. This pattern is therefore reflective of disharmony between the Heart and Kidney Zang-Fu organs. Another pattern involves Heart, Blood, and Spleen qi deficiency. According to theory, the Spleen produces qi and therefore Blood for the body, and the Shen requires the yin Blood to nourish and quiet it or anchor it at night. If this Heart Blood is deficient, the Shen is unsettled. This pattern is therefore reflective of a disharmony between the Heart and Spleen Zang-Fu organs. The reader is referred to other sources for a more in-depth explanation of the patterns of disharmony of insomnia.^33,34 Suffice to say, the underlying patterns of disharmony are reflective of the interrelationship between the five Zang organs (Heart, Spleen, Liver, Lung, and Kidney). These patterns are also not unique to insomnia, and underpin many different conditions, for example palpitations, depression, and anxiety, conditions that in CM also relate to the Heart and Shen or spirit. Unlike in Western medicine, in CM, the different patterns of disharmony are treated using different treatment principles and different Chinese herbal formulae and acupuncture points (acupoints). In essence, however, it is the Shen that is being addressed when insomnia is treated.

Neurophysiological Support for CM Concepts

The role of the (biomedically defined) heart in mind, emotions, consciousness, and memory is increasingly finding support within Western medicine. The field of “neurocardiology” envisages the heart as a sensory organ that is capable of processing and encoding information that functions not only in concert with the brain but also independently of it.³⁵ Several experiments have demonstrated that in addition to affecting autonomic regulatory centers, cardiac afferent neurological input can also affect higher brain centers involved in emotional processing and perception. Changes in both afferent and efferent autonomic activity have been found to be associated with changes in heart rhythm patterns; for example, positive emotions have been found to be associated with increased coherence of heart rhythm, while negative emotions have been found to be associated with disordering of the heart rhythm.³⁵

The interdependent relationship between the Heart and other Zang-Fu organs, espoused in CM theories is also supported when one considers the neuroanatomical connections that have been found to exist between the heart organ and other organs.³⁶ Clusters of ANS neurons that regulate the organs such as the heart, lung, gastrointestinal tract, kidney, and bladder lie near the organs and communicate with each other, forming networks that facilitate information exchange. For example, the neurons controlling the heart and respiratory tract communicate with each other.³⁶ One could postulate that this might be the anatomical basis for the relationship between the Heart and Lung in CM.

There are almost as many afferent fibers (going toward the brain) as there are efferent in the nerve pathways connecting most of the organ systems to the brain. The abdominal vagus nerve, for example, is composed of up to 90% afferent fibers, and there is more neural traffic from heart to brain than the other way.³⁷ Scientific research has established the presence of bidirectional signaling between the gastrointestinal tract (GIT) and brain, which is regulated at the neuronal (CNS and enteric nervous system), hormonal, and immunological levels, termed the enteric microbiota–gut–brain axis.³⁸ It has also been established that there is an association between stress-related conditions such as anxiety and various GIT disorders, including irritable bowel syndrome.³⁸ In CM, the GIT includes the Spleen and Stomach, as well as the Small Intestine and Large Intestine. It could be argued that the Heart, as the “king of organs,” is involved in the pathogenesis of anxiety, regardless of the pattern of disharmony. The establishment of these nervous system connections adds neurophysiological support for the interconnectedness between the Zang-Fu organ systems as set out in various theories, including Zang-Fu Theory and Five Element Theory.

In addition, the regulation of the internal environment of the body by the peripheral ANS occurs in conjunction with CNS neurons that sense the external environment.³⁶ This neuroanatomical interdependence could be seen as providing some support from the biomedical perspective of the notion of holism that underpins CM, that is, of the interdependence of human and environment.

Support for the role of the heart in insomnia

Support for a role of the heart in insomnia in the scientific literature also includes changes in HRV and heart rate in people with chronic insomnia (discussed previously), and the association between insomnia and cardiovascular disease. Prospective longitudinal studies indicate an increased risk of acute myocardial infarction (RR = 1.5; 95% CI 1.2–1.8) in those with insomnia. Psychoneuroimmunologist Dr Paul Pearsall's accounts of heart-transplant patients who have taken on memories and other characteristics (such as fondness for certain foods) of the heart donor³⁹ raise questions about the possibility of cellular memory and the integral role of the heart.

Of the many neuronal connections between brain and organ systems within the body, the vagus nerve is of particular interest. From an anatomical point of view, the vagus nerve originates in the brain stem and projects, independently of the spinal cord, to many organs in the body cavity, including the heart and the digestive system. The vagus is not a single neural pathway but rather a complex bidirectional system with myelinated branches linking the brain stem and various target organs.⁴⁰ These neural pathways allow direct and rapid communication between brain structures and specific organs. Because the vagus nerve contains both efferent (i.e., motor) and afferent (i.e., sensory) fibers, it promotes dynamic feedback between brain control centers and the target organs to regulate homeostasis.

As stated previously, the vagus nerve is 80–90% afferent,^37,41 and cardiovascular afferents send more signals to the brain than to the other major organs.³⁷ According to McCraty, research has demonstrated that brain rhythms exhibit various degrees of synchronized activity with the heart; for example, the activity and amplitude of brain waves tends to increase with an increase in heart rate. When the heart rhythm is coherent, there tends to be an increase in heart–brain synchronization. These occurrences reflect the intercommunication occurring between different biological rhythms.³⁷ The term “physiological coherence” or “heart coherence,” measured by HRV analysis, is the state in which the person's heart rhythm patter becomes more ordered.³⁷ He states that there is evidence that the heart plays a special role in synchronizing activity across multiple systems and levels of organization, and via its generation of rhythmic information patterns in the body, it is in constant communication with the brain and body via multiple pathways. These include via the ANS, via hormones, biophysically via pressure and sound waves, and energetically via electromagnetic field interactions. McCraty believes that “the heart is well positioned to act as the ‘global coordinator’ in the body's symphony of functions to bind and synchronize the system as a whole.”³⁷ ^(p14) The heart's extensive nervous system is sophisticated enough to qualify as a “heart brain” according to neurocardiologist Armour.³⁶ A study found that the heart and brain were capable of receiving and processing information about future events before the event happened, and that the heart receives such “intuitive” information before the brain, and sends a different pattern of afferent signals to the brain, which modulates the frontal cortex.⁴² For further information on neurophysiological and energetic medicine research in relation to the heart and heart coherence, the reader is directed to the HeartMath Institute (www.heartmath.org).

Relationship between the heart and cardiac vagal tone

In considering the centrality of the Heart in both insomnia and depression according to CM, via its role in housing the Shen/consciousness/mind, it is of interest that cardiac vagal tone, as indexed by abnormalities in the level and/or reactivity of respiratory sinus arrhythmia (RSA), has been related to psychiatric impairment, including risk for depression. Longitudinal studies of depression have focused on RSA levels and have found mixed support for the hypothesis that low RSA levels predict a more pernicious course of depression.⁴³

Acupuncture and its effect on vagal activity

Acupuncture is able to affect the vagal activity and autonomic functions of the cardiovascular, respiratory, and gastrointestinal systems. Studies of hypertension, diabetes, epilepsy, and depression have shown that the mechanism of auricular vagus nerve stimulation (VNS) may be comparable with the cervical VNS in terms of pathways.⁴⁴ Mechanism studies suggest that afferent projections, especially from the auricular branch of the vagus nerve to the nucleus of the solitary tract, form the anatomical basis for the vagal regulation of auricular acupuncture.⁴⁵ Acupuncture stimulation of the auricular branch of the vagus nerve (the only branch to connect to the cerebral cortex) through needling at the concha (ear) has been found to lower arterial blood pressure (BP), inhibit heart-rate acceleration, and improve epilepsy in animal models.⁴⁴ Auricular electro-acupuncture in patients suffering with depression has been found to increase HRV, as well as improve quality of life.⁴⁴ This seems to support a role for the vagus nerve in connecting to the heart, via its impact on HRV, known to be decreased in insomnia.²² Auricular acupuncture has been found to exert an antidiabetic effect via modulation of melatonin.⁴⁴ Given the role of melatonin secretion in sleep and the fact that its production is disturbed in insomnia, the investigation of auricular acupuncture's impact on vagus-nerve activity and melatonin production in insomniacs would be worth investigating.

Evidence linking vagus-nerve activity, emotions, and insomnia

Evidence linking vagus-nerve activity, emotions, and insomnia includes El-Sheikh and Buckhalt's study, which examined the role of children's emotional intensity and vagal functioning in predicting sleep problems in healthy elementary school-aged children.⁴⁶ Children's vagal regulation was assessed via RSA during a baseline and a reaction time (RT) task. Dispositional emotionality was examined via parent report, and sleep problems were examined through child reports and home monitoring with wrist actigraphs. Increased emotional intensity was predictive of a decreased amount of sleep and increased night activity. Poorer vagal regulation, characterized by lower levels of RSA suppression to the RT task, predicted increased sleep problems. The authors concluded that these results indicate that children's emotionality and vagal regulation predict unique variance in the amount and quality of children's sleep, and are suggestive that this may underlie, at least in part, sleep disturbances in healthy children.⁴⁶ More research is needed in order to understand the role that vagus-nerve activity might play in sleep disturbances such as insomnia.

Another study found that stimulation of the vagus nerve in seven treatment-resistant people suffering from depression resulted in a significant overall improvement in sleep architecture, with decreased awake time, decreased Stage 1 sleep, and increased Stage 2 sleep, and the strength of the ultradian sleep EEG rhythms being restored to within normal range.⁴⁷

Expansion of CM theory

The ascribing of consciousness to the Heart by ancient CM theorists may not have been inaccurate and may have merit. Armour's concept of the “heart brain” and the research of the HeartMath Institute certainly provide some support from neurophysiology. It is time to expand CM theory to encompass both Heart and brain, and to extend the understanding of the brain beyond its early conceptualization as the “sea of marrow,” given the passage of time and increased knowledge since Five Element Theory and other guiding CM theories were initially developed. For example, in classical CM theory, it is said of “marrow” that if Kidney Jing is weak, the brain (marrow) may be undernourished, leading to poor memory and poor concentration, and an “empty” feeling in the head with dizziness and lassitude.⁴⁸ Development of CM theory might, for example, involve the broadening of the concept of the Heart as the seat of consciousness and Shen to include the brain's role as understood in biomedicine.

The above-mentioned research adds only limited support for a neuroanatomical basis for what the ancient Chinese theorized in terms of the interrelationship between Zang-Fu organs. Nonetheless, it bears consideration. Could the nervous system (CNS and peripheral nervous system) be a sixth Element that sits at the center of the Five Element Theory diagram, like an overarching meta-system that interrelates with the five Zang and six Fu organs?

Acupuncture Treatment of Insomnia: Mechanisms of Action and Evidence of Efficacy

A World Health Organization Review of Acupuncture in 2002 lists insomnia as one of several diseases for which there has been shown to be a therapeutic effect, but further proof was needed.⁴⁹ Various attempts have been made to understand the mechanisms by which acupuncture exerts an effect using biomedical physiological variables, by necessity. There is, after all, no medical scientific evidence that qi or yin and yang exist. Rather, these concepts are metaphors that capture an experiential reality that can be married to specific treatment protocols.

Mechanisms of action of acupuncture in pain relief

The mechanisms by which acupuncture induces analgesia have been reasonably well studied. Andersson and Lundeberg⁵⁰ hypothesized that acupuncture produces affects via sympathetic regulation in the same way as other forms of sensory stimulation or strong muscle contractions.⁵¹ Increases in endogenous opioids in the cerebrospinal fluid, including met-enkephalin, beta endorphin, and dynorphin, have been found following acupuncture, which can be reversed by the opiate blocker naloxone. These opioids not only mediate analgesia, but they are also involved in the stress response: increased levels of plasma beta endorphin has been found to be correlated with severe stress in depressed patients, as well as in anxious patients before and after social and cognitive stressors.⁵² Spence et al. argue that there is a reasonable basis to infer that acupuncture might also be able to mediate anxiety via the endogenous opiate system.⁵²

Acupuncture and its effect on the ANS

Acupuncture has been shown to influence indicators of ANS activity, including BP, pupil size, skin conductance, thermography-recorded skin temperature, microneurography-recorded muscle sympathetic activities, heart rate, and HRV.^51,53 Stimulation of specific acupoints has created different effects on the ANS; for example, stimulation of the acupoint Quchi (Large Intestine 11, LI11) can co-activate parasympathetic and sympathetic activities.⁵¹ Acupuncture can modulate the nervous system to achieve a desired balance; for example, it can be used to treat both hyper- and hypotension, and hyper- and hypofunction of gastrointestinal motility.⁵¹

Acupuncture and its physiological effect in insomnia

When considering how acupuncture may impact physiologically in insomnia, acupuncture has been shown to regulate various neurotransmitters and hormones, such as endorphins, serotonin, norepinephrine, adrenocorticotrophic hormone, cortisol, acetylcholine, melatonin, substance P, gamma-aminobutyric acid, and nitric oxide, known to be involved in sleep regulation.⁵¹ Acupuncture can also regulate higher cortical function, the HPA axis, and somato-visceral reflexes.⁵¹ In an open pre–post clinical study of 18 adults with anxiety, five weeks of acupuncture (two sessions per week, though no further detail of acupuncture treatment including acupoints is available) was found to increase the production of melatonin significantly at midnight and decrease its production between 8:00am and 3:00pm in insomniacs. Sleep onset latency and arousal index significantly decreased, total sleep time and sleep efficiency significantly increased, and percentage of time spent in Stage 3 slow wave sleep increased from 4.2% before acupuncture to 6.1% (normal mean 7%) after acupuncture. There was also a significant improvement in state and trait anxiety and the CESD Depression Inventory.⁵² This result is interesting but not surprising when one considers that the underlying pathogenesis of conditions such as depression and anxiety often share common pathways with insomnia, according to CM.

Some studies have found an effect of acupuncture on HRV, specifically that acupuncture can increase HRV.^53,54 Huang et al.⁵³ found that acupuncture at acupoint Shenmen (Heart 7, Ht7) was associated with a significantly higher high-frequency (HF) component of HRV (thought to be mediated by cardiac parasympathetic activation), and a significantly higher very-low-frequency component (thought to reflect the activity of the sympathetic nervous system) and higher low-frequency (LF) component (reflecting both sympathetic and parasympathetic systems plus other unidentified factors), leading the authors to suggest that Shenmen acupuncture may activate both cardiac sympathetic and parasympathetic systems.⁵³ An earlier systematic review of sham-controlled randomized controlled trials (RCTs) concluded there was no consistent evidence of an effect on HRV;⁵⁵ however, a more recent systematic review found that there was support for an effect of acupuncture in modulating the low frequency (LF) component of HRV in healthy and unhealthy subjects⁵⁶. Acupressure and acupuncture have been found to decrease heart rate in some studies in humans;^54,57,58 however, another study found acupuncture did not cause any significant change.⁵³

Kung et al. found that auricular acupressure in women with postmenopausal insomnia (five auricular points every night for four weeks before sleep) was associated with increased total sleep duration and sleep efficiency, decreased sleep latency, increased parasympathetic activity, and decreased sympathetic activity (as measured by HRV).⁵⁹

Research has investigated the efficacy of particular acupoints in treating insomnia. For example, intradermal needles for three days at acupoints Shenmen (Ht7) and Neiguan (PC6) was associated with a significant improvement in insomnia-related scales compared with sham acupuncture.²³ When diurnal variation of BP was examined, the number of “non-dippers” (those whose systolic BP and/or diastolic BP nocturnal decrease was <10% of their daytime BP, generally as a result of sympathetic nervous system hyperactivity) decreased significantly more in the acupuncture group than in the sham group. The LF/HF ratio decreased significantly more in the acupuncture group than it did in the sham group at the end of treatment.²³ Their results back up findings of other studies, which have found that Shenmen and Neiguan have an inhibitory effect on the sympathetic nervous system.²³

T'ai chi and sleep quality

Although not directly related to acupuncture, a study has demonstrated the benefits of t'ai chi, a form of exercise therapy, in enhancing parasympathetic activity and improving sleep quality in patients with chronic heart insufficiency.⁶⁰ T'ai chi, not unlike acupuncture, emphasizes harmony between the organ systems, and the promotion of circulation of qi in the meridian system (pathways in which qi is believed to flow in the body).

Systematic reviews

Several systematic reviews have been conducted to investigate the efficacy of acupuncture in its various forms in treating insomnia.^{11,61

–65} The results of several of these are presented in Table 1. In general, the results of the systematic reviews indicate that many of the studies suffered from methodological flaws.⁶⁵ Despite these limitations, it appears that there is some evidence that acupuncture may be useful in the treatment of insomnia.

Table 1.

Systematic Reviews of Acupuncture Treatment of Insomnia

Reference	No. studies	Interventions	Results	Comments
Yeung et al. (2009)¹¹	20 studies, 1956 subjects	N = 18 studies TNA vs. diazepines N = 1 study TNA vs. sleep hygiene N = 1 study TNA vs. non-invasive acupuncture	Results suggest TNA superior to benzodiazapines, sleep hygiene counseling, and sham acupuncture in treatment of insomnia. In the two of reasonable quality: TNA (individualized) was found to be significantly better at improving insomnia compared with sleep hygiene in one study of pregnant women. In stroke patients, one study found evidence that acupuncture at Shenmen (Ht 7) and Neiguan (PC 6) was found to be associated with significant improvement of ISI and AIS over sham acupuncture.	Treatment protocol standardized in n = 10 studies. Poor methodology for most studies (only 2 had Jadad score ≥3); 13/20 used “effective rate” as only outcome measure. Evidence of publication bias.
Bezerra et al. (2015)⁶¹	12 studies of acupuncture (Acu) in postmenopausal women with sleep disorders (3 case reports, 8 RCTs, 1 cohort study)	8 used exclusively body Acu based on TCM; 1 used ear acupuncture; 2 used a mixed protocol	Unable to perform meta-analysis due to heterogeneity of studies. Nine studies found improvements in sleep complaints; three showed non-significant effects. Of the eight RCTs, one had treatment of sleep disorders as a primary outcome; three failed to show significant effect of acupuncture on sleep disorders.	Satisfactory compliance with STRICTA criteria; low risk of bias. Data insufficient to conclude that acupuncture is a reliable treatment of menopausal sleep disorders.
Yeung et al. (2012)⁶²	227 studies, 17,916 subjects. 57 examined Acu; 89 examined CHM; 40 examined combination of two different Acu modalities; 24 examined combination of CHM and Acu	Study focused on patterns of disharmony, acupoints, and CHM prescriptions prescribed for insomnia	Limited consistency of pattern based treatment across practitioners. Total of 87 different underlying patterns of disharmony were identified, with 10 patterns constituting 73% of the diagnoses. Deficiency of the Heart and Spleen was the most commonly diagnosed pattern. The following acupoints were used regardless of pattern: Shenmen (Ht 7), Yintang (EX), Sanyinjiao (Sp 6), Baihui (EX), Anmian (EX), Sishencong (EX).	Treatment principles underlying selection of herbs was seldom reported.
Huang et al. (2009)⁶³	30 studies: n = 12 RCTs (3 double-blinded, 5 used sham controls)	Half the studies used ear treatments, the other half used body Acu either alone or in combination with adjunct therapies. All except four reported individualized treatment protocols.	RCTs: of the five that used sham controls, four found Acu to more effective than sham. However, none evaluated the adequacy of the sham treatments.	Considerable heterogeneity of the studies made it difficult to integrate results. Methodological problems in many. Very few studies used a sham control. There were inconsistencies in choosing location of sham acupoints, which may have led to inconsistent results.
Cheuk et al. (2012)⁶⁴	33 RCTs with 2293 participants with insomnia (15–98 years of age), some with medical conditions contributing to insomnia (stroke, end-stage renal disease, perimenopause, pregnancy, psychiatric conditions)	RCTs evaluating any form of Acu (needle acupuncture, EA, acupressure, or magnetic acupressure) for insomnia, comparing acupuncture with/without additional treatment against placebo or sham or no treatment or same additional treatment.	Compared with no treatment (two studies) or sham/placebo (two studies), acupressure resulted in more people with improvement in sleep quality (compared with no treatment: OR = 13.08, 95% CI 1.79–95.59; compared to sham/placebo: OR = 6.62, 95% CI 1.78–24.55), but when assuming that dropouts had a worse outcome in sensitivity analysis the beneficial effect of Acu was inconclusive. Some evidence that Acu as an adjunct to “other treatment” (compared with “other treatment” alone) increases the proportion of people with improved sleep quality (13 studies, 883 participants, OR = 3.08, 95% CI 1.93–4.90), though on subgroup analysis, only needle acupuncture (not EA) demonstrated benefits.	Due to poor methodological quality, high levels of heterogeneity, and publication bias, the current evidence is insufficient to support or refute the role of acupuncture in treating insomnia.

Acu, acupuncture; CI, confidence interval; CHM, Chinese herbal medicine; EA, electroacupuncture; EX, extra points; Ht, Heart; PC, Pericardium; Sp, Spleen (in reference to meridians); OR, odds ratio; TNA, traditional needle acupuncture.

The large number (87) of patterns of disharmony of insomnia in the systematic review by Yeung et al.⁶² is in sharp contrast to the relatively small number of patterns set out in modern textbooks.^32,33 This is not unlike the finding of O'Brien et al. who identified a much greater range of patterns of disharmony of hypercholesterolemia in a study of hypercholesterolemic Australians than what are commonly found in textbooks.⁶⁶ Future empirical studies of the patterns of disharmony of insomnia are required.

Intersections of Knowledge

Clearly the CM perspective of the pathophysiology of insomnia, in particular the centrality of the Heart, is very different to that of biomedicine. The very idea of the Heart as the seat of consiousness, the place of residence of the “Shen” or “mind,” is certainly foreign to Western thinking, which still firmly places “mind” and mental processes as a function of the brain. It wasn't always this way, and thinking is once again changing. The assignation of the role of the mind to the heart was supported in early Greek medicine. Around 55 bc, Lucretius in the treatise “On the Nature of Things, Book III” said:

The dominant force in the whole body is that guiding principle which we term mind or intellect. This is firmly lodged in the midregion of the breast. Here is the place where fear and alarm pulsate. Here is felt the caressing touch of joy. Here, then, is the seat of the intellect and the mind.³⁶

CM has a model of explaining the interrelationships between the various organ systems in disease/illness. In CM, the Heart is central in the pathogenesis of insomnia, anxiety, and depression, and there are some common underlying patterns of disharmony and pathomechanisms. Western medicine is now grappling with the interrelationship of a range of diseases/conditions and pathomechanisms, with the immune system and inflammation linking many. The neurological basis for relationships between organ systems, in the biomedical sense, lends some support to the interdependent relationships between the Zang-Fu organs, as espoused in CM theory. Research into heart and heart coherence suggests that the heart behaves like a brain.

Western medicine needs to embrace a more holistic notion of the human being, and scientific research at the cellular, tissue, and system level is starting to bear out the criticality of this holistic approach. CM, on the other hand, is being put under the scientific microscope, where the evidence-based approach is being applied. At first glance, these two medical systems might seem incommensurate. However, there might be more points of intersection than previously thought. Applying scientific research methods to a system of medicine such as CM underpinned by a very different set of metaphysics, notions of what constitutes the nature of reality, may not be ideal, but within the inherent limitations, it is worthwhile, as it facilitates dialogue across medical disciplines that might just spark new understanding.

Conclusion

The pathogenesis of insomnia from a Western biomedical perspective is complex, and involves hyperarousal in both the CNS and ANS. The heart is involved, with changes to HRV and heart rate, and there is evidence of a relationship between insomnia, anxiety, and depression in the Western medical literature. The vagus nerve plays an important part in communication between the brain and other systems, including the heart, and may play a role in insomnia. In CM, the Heart, where consciousness is seen to reside, is involved in the pathogenesis of insomnia as well as anxiety and depression, and the interdependent relationships between the organ systems explains this association. There is evidence that acupuncture is able to effect physiological changes in the treatment of insomnia via its impact on the Heart and the heart. Despite apparent differences in how the body is understood, there appear to be some points of intersection between the two medical systems.

The ascribing of the Heart as the seat of consiousness or mind in CM is finding some support within the scientific literature and may not be as far fetched an idea as would initially appear. As the neurophysiological connections and relationships between the brain, gut, heart, and, no doubt in the future, other organs are elucidated, we may begin to see further support for the interdependence of the organs in the body that is espoused within ancient CM literature. We may also see further emerging evidence of the role of the heart in memory and consciousness, which challenges the Cartesian duality of mind and body and the centrality of the brain as the location of mind and consiousness. CM theory also needs to develop. With all the knowledge at our disposal from a biomedical perspective, it is perhaps time to further develop CM theory to encompass knowledge of the brain beyond its limited concept as the “sea of marrow.” The concept of a sixth element in Five Element Theory may sound heretical. However, theory does need to move forward in any system of medicine.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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