Neurovertebral Influence Upon the Autonomic Nervous System:
Some of the Somato-Autonomic Evidence to DateThis section is compiled by Frank M. Painter, D.C.
Send all comments or additions to: Frankp@chiro.org
FROM: Chiropractic Journal of Australia 2009 (Mar); 39 (1): 2–17 ~ FULL TEXT
Thanks to the Chiropractic Journal of Australia, and the Editor Rolf E. Peters, DC, MCSc, FICC, FACC for permission to reproduce this full-text article, exclusively at Chiro.Org!Peter L. Rome
Private practice of chiropractic
Mount Waverley,
Victoria 3149
Objective: To present a broad overview of the literature in relation to the volume and variety of published material referring to spine-related neural reflexes upon organic symptoms, signs and conditions - the somato-autonomic influence. This presentation particularly emphasises somato-autonomic reflexes and to a degree, somato-autonomic-visceral reflexes mediated through the spinal influence of the neuraxis. It seeks to catalogue the evidence of the potential for further influence upon the function of internal anatomical structures - that is, other than those which may be regarded as purely musculoskeletal. The study further highlights the significant formal original neurophysiology research activities by chiropractors and medical researchers. These activities tend to explain the phenomena of this neurovertebral influence upon autonomic and internal function.
Data Sources: Citations were extracted from a number of sources including: The Index to Chiropractic Literature, PubMed, Reference lists of previously published papers and textbooks, and two osteopathic electronic indexes. Over 500 papers were assessed and in a few cases only the abstracts were obtainable.
Data Synthesis: There appears to be a developing interest in the influence of the autonomic nervous system (ANS) as depicted by the number of medical texts currently emerging. The most extensive work to date has been by Sato et al, where their studies correlate with spine-related concepts so pertinent to this presentation. The volume, variety and depth of material listed does not appear to have been presented previously. The inter-professional co-operative research projects are noted.
Conclusion: It is noted that the volume of material presented tends to further define the neurological basis of the many clinical observations, and may provide additional explanation for the subjective patient reports of positive responses to manual manipulative intervention. Effectively at this stage, this both underpins and builds upon a long-established empirically based rationale.
INDEX TERMS: MeSH: AUTONOMIC NERVOUS SYSTEM; CHIROPRACTIC; MANIPULATION, SPINAL. (OTHER):SOMATO- AUTONOMIC REFLEX; SOMATO-VISCERAL REFLEX; ORGANIC CONDITIONS; VISCERAL DYSFUNCTION; VERTEBRAL ADJUSTMENT.
From the FULL TEXT Article:
Introduction
Gray’s Anatomy states that the “...function (of the nervous system) is to control and coordinate all the other organs and structures and to relate the individual to its environment.” [1]
Gray’s statement emphasises the all-encompassing, integrative role of the nervous system – a continuing concept effectively expounded by Sherrington in 1906. [2]
This paper seeks to survey the literature relating to somatic impact upon the autonomic nervous system, and the effect that has on internal organic function or dysfunction. That aim would also assess evidence relating to aberrant somatic neural input, be that stimulatory or suppressive, and in turn assess, modify, or normalise such influences upon neural physiology and neuropathophysiology.
Various hypotheses exist on this matter of spine-related neural dysfunction. These range from involvement of massive irritation due to bombardment of noxious mechanoreceptors brought on by localised pathomechanics, to irritation and inflammatory response at the radicular level – or a combination of these various factors. [3–7] Carrick, in his significant original research has demonstrated, [8] and Terrett through an hypothesis, [9] have proposed concepts of neural influence at a more central level.
In reference to segmental neurospinal dysfunction, it is important to appreciate that at least for the purpose of this paper, a vertebral subluxation is not just a strict mechanical displacement of a vertebra. It is more accurately termed a vertebral subluxation complex (VSC) to encompass all the involved elements including functions and structures. A significant component in this complex is intersegmental articular mechanical dysfunction. This may comprise aberrant movement, fixation (hypomobility) or hypermobility between adjacent facets, as well as articular muscular and ligamentous changes triggering neural firing of mechanoreceptors, proprioceptors, effectively nociceptive noxious input. The VSC would then include disturbances of these structures and their function, especially their effect upon articular physiology (function) and the integral neurophysiology. Inflammatory and circulatory disturbances of the articular environment could also be associated. It is this total pathophysiological complex that would provide the opportunity through which manual intervention by way of a vertebral adjustment may be directed in order to influence internal body physiology. [10] It is submitted again that segmental dysfunction more than osseous displacement, may be the primary physical-mechanical feature involving any associated neural aberration in this situation but, that is only one part of the complex. Only a dry skeleton could have osseous disruption without more complex involvement.
Historical
In his 1910 text, Palmer founded what became the chiropractic profession on the basis of the importance of a neurospinal influence upon physiology. He cited the “nervous system known as the automatic functions” [11] – now known as the ANS. In 1954, Müller produced a text entitled “Autonomics in Chiropractic”, again highlighting the importance of the ANS to the profession. His text noted that “The essential role of the autonomic nervous system as an integrator and controller of body functions is a fact all are agreed upon. That structure or function is disturbed, sometimes seriously, however this correlation is deranged from any cause is becoming more widely recognized by all schools of healing. It is the very bedrock upon which the premise of chiropractic is based.” [12] More recent research has become much more intensive, with sophisticated studies and advanced neurophysiology research into such topics concerning the critical interaction between the musculoskeletal system and the autonomic nervous system. [13–20]
Interestingly, as if aware of complex neural physiology through noxious stimulation, Palmer maintained that rather than nerves being “squeezed or pinched”, neural energy was “...accelerated, (and)...the volume and force is augmented.” [21] It seems he was apparently aware of the bombardment of noxious impulses from disturbed proprioceptors or mechanoreceptors at that time, well before the complexities of such reflexes was appreciated as deeply as they are today.
For some 50 years early last century, the neurophysiologist Sherrington pioneered studies of neural reflexes. He stated that “To describe the action of nerve (sic) as integrative is, although true, hardly sufficient for a definition” – implying that neural influence was extensive. [2]
In the 1930’s, Cannon addressed the issue of a relationship between the sympathetic division of the ANS with homeostasis, [22] and Huber and Crosby explored the “Somatic and visceral connections of the diencephalon.” [23] A theme followed by Sollman in Germany in 1958. [24]
Other early authors such as Alverez, Breig, Pottenger, Kuntz and Sachs published significant texts for their time on the topic of neurovisceral disorders. [25–29] But their concepts now seem to receive less emphasis.
In Russia, Speransky conducted extensive research in neurophysiology, his text was translated and published in 1935 entitled, A Basis for the theory of Medicine... He cites Charcot as noting “that not every injury to a nerve results in dystrophic lesions of the tissues, and that these lesions are connected not with the cessation of the functioning of the nerve, but with its irritation.” He also cites Mitchell et al as stating that “partial injury to nerves is more dangerous in this respect than complete severance.” [30]
More recently, the medical specialists Bannister (1988), Korczyn (1990), Appenzeller (1995), Goldstein (2001) Jänig (2006) have made significant contributions in the field of the autonomic nervous system. [31–35]
Currently, there are journals based on the ANS. One entitled Autonomic Neuroscience: Basic and Clinical, is produced by Elsevier and edited by Geoffrey Burnstock. This was previously published under the title of The Journal of the Autonomic Nervous System until the year 2000. Clinical Autonomic Research is the official journal of the Clinical Autonomic Research Society. There are also a number of other journals on the topic of neurophysiology and neurology. To this writer’s knowledge, there is no specific journal based on the somatic-autonomic-visceral complex.
Burnstock has authored and co-authored many papers on neurophysiology as listed on Pubmed
(http: //www.ncbi.nlm.nih.gov/entrez/query.fcgi). His curriculum vitae would be one of the most extensive in this respect. His discovery of a “third nervous system” – the purinergic, in addition to the adrenergic and the cholinergic, was a most significant contribution to neurophysiology. [36, 37]
Earlier, Johnston et al in particular explored clinical aspects of the ANS in some depth. Their exploration of the underlying role of the ANS has been highlighted in at least two pioneering scientific texts. From the mid-1960’s to the mid-1980’s, they were some of the earliest to broaden the importance of the clinical aspects of autonomic dysfunction. [38, 39]
Seminal Work
This author is convinced however, that the most notable work in this field is that conducted by Akio Sato and colleagues in Japan. Their widely published works culminated in a text The Impact Of Somatosensory Input On Autonomic Functions, published over 328 pages in the Reviews of Physiology, Biochemistry and Pharmacology in 1997. [16] These extensive studies in neurophysiology conducted through the laboratories at the Department of the Autonomic Nervous System at the Metropolitan Institute of Gerontology, in Tokyo, Japan, provide a contemporary foundation for understanding clinically observed phenomena noted by manual practitioners. Sato has also been involved in the publications of numerous papers and at least two texts.
It should be noted that both familial and trauma induced dysautonomia (also called autonomic dysfunction syndrome, [40] usually refers to a more serious form of autonomic breakdown, as does the term partial dysautomia, [41] or sympathetic dysfunction (Reflex Sympathetic dystrophy). [42] However, there can be milder versions of the traumainduced autonomic symptoms.
Gazit et al concluded that“ ...autonomic nervous system-related symptoms of the patients have a pathophysiological basis, which suggests that dysautonomia is an extraarticular manifestation in the joint hypermobility syndrome.” [43]
A number of authors have noted a connection between joint hypermobility and autonomic nervous system dysfunction (ANSD). [44] ANSD usually refers to a more acute and serious clinical situation, even though it is hypothesised to involve joint proprioception. [45] In the manual therapies however, interest in articular integrity is normally concerned with hypomobility or joint fixations and its potential to affect the ANS. [3]
This historical section was included to show that a degree of recognition, and supportive evidence for the somatoautonomic concepts have existed for some years. But it is the more subtle clinical presentations which this paper seeks to focus upon.
Method
This overview seeks to assess somato-autonomic topics in neurophysiology published by chiropractic and osteopathic researchers, and medical authors in chiropractic and other journals. (Table 1) [cits 46–106] While not a meta-analysis, this paper summarises the dates and themes of these papers, their authors’ professions, and the professions associated with journals of publication. This paper is offered in a manner which would encourage the reader to view the references as an integral part of a study of the hypotheses concerned.
It has also been the intention of this study to present examples of the wide variety of areas researched, and to portray the numerical volume of published items. Consequently, an atypical format (tabular) was adopted to cover such broad factors.
Many early journals were published before the advent of the MeSH terms and the ‘Key Words’ adjunct. Currently, some medical as well as some chiropractic journals still do not uniformly utilise these systems. A selection of early citations have been included along with the more recent references to note the fact that a degree of relevant physiological research had been in evidence for many years although it is only chiropractors, osteopaths as well as a limited number of medical doctors and physiotherapists who appear interested in this aspect of clinical care.
In both PubMed and Google, a search was made under the terms somato autonomic, somatic autonomic, somato autonomic visceral and dysautonomia. While there were quite a number of papers on these topics, interest seems to have been renewed more recently. During this search it was noted that there was a direct interest between acupuncture and somato-autonomic-visceral reflexes – a connection also noted by Sato et al. [107]
A search of library sources revealed considerable published material concerning neurospinal-related visceral physiology and pathophysiology. In recent years more formal papers have been appearing, together with original physiological research studies which tend to clarify the rationale of these spine-related-ANS somatovisceral concepts. In particular, three electronic avenues which were employed were,The Index to Chiropractic Literature (www.chiroindex.org) and,
The Osteopathic Index (www.osteopathic-research.com).
http://ostmed.hsc.unt.edu/ostmed/index.htmlThe primary source of material for this paper was from the examination of the reference lists of previously published material. Citations have been gleaned from these sources as well as PubMed (http://www.ncbi.nlm.nih.gov/entrez/ query.fcgi), Index Medicus and textbooks. The four volumes of the Chiropractic Research Archive Collection (CRAC) index series published by the Canadian Memorial Chiropractic College between circa 1980 and 1990, were also a valuable resource of data for this purpose. [108–111] Copies of original papers were obtained where possible, and abstracts where this was not feasible.
The electronic Index to Chiropractic Literature was examined, while another electronic index MANTIS, also has an extensive electronic reference base of the manual spinal sciences, but was not drawn upon at this time – The Chiropractic Index – MANTIS (www.healthindex.com/MANTIS) – (ex-Chirolars).
The PubMed index on CAM was found not to be of assistance on this issue. (The CAM Citation Index (Complementary and Alternative Medicine Citation Index) (www.nlm.nih.gov/nccam/camonpubmed.htm#),
The author’s own database collected over some years comprises more than 1,200 citations on specified spine-related conditions. It also includes neurophysiology references on spine-related conditions. These are further divided into the different professions, and list some 127 different pathophysiological organic conditions. As an example of the volume of the material in the general literature – albeit at different standards of evidential levels, at least 21 chiropractic and 8 osteopathic papers concerning respiratory conditions have been located. In addition, there are at least a further 35 medical references also published in relation to spine-related respiratory conditions, these date from 1925 to 1995.
It also notes supportive medical neurophysiological research which has been cited in relevant papers and which report neurospinal influence upon organic function and dysfunction. (Table 2) [cits 112–172]
The nature of this presentation has been to highlight the variety, volume and depth of available evidence. It especially seeks to explicate the neurophysiological research conducted by chiropractors as well as that in chiropractic institutions and that sponsored by chiropractic research organisations. Where it is possible, it also notes inter-professional joint authorship and inter-professional co-operative research projects involving chiropractors as well as medical and osteopathic researchers in the neurosciences. However, this is not always clear in the publications.
Review“There is increasing evidence that manual therapies may trigger a cascade of cellular, biomechanical, neural and/or extra-cellular events as the body adapts to the external stress. Collectively (the research suggests) that spinal manipulation can alter the activity of nearby mechanical sensitive neurons...and in turn can lead to responses by the central and autonomic nervous systems...(which) may in turn lead to observed changes in circulating levels of various neuropeptides and regulatory proteins.” [173]
Studies of somato-autonomic function and dysfunction are steadily emerging with quality research which continues to be carried out. Chiropractic neurophysiologists in conjunction with medical neurophysiologists are conducting much of this. (Tables 1 & 2) Some authors may have a number of papers on a particular topic, a limited selection only was adopted in this paper.
While recognising that articular adjustments – a localised and specific form of SMT, do have potential for certain physiological effects, further substantiation of spinal manipulative influence upon visceral conditions is steadily emerging. [174] That is, initial clinical and anecdotal observations are being explored by more extensive and formal studies. A wider acceptance of such concepts has probably developed to the same stage as that of the evidential literature support for manipulative approaches to mechanical lumbar spine conditions of thirty to forty years ago, and now also adopted by other professions.
This growing volume of elucidating scientific research on spine-related neuro-autonomic conditions has been summarised by Slosberg when he reports:“...that repetitive stimulation of small myelinated and unmyelinated somatic afferents can dramatically increase reflex pre- and post-ganglionic sympathetic discharge.” And notes further that “...electrically stimulated articular nerves from knee joints of anesthetized cats (led to) two sympathetic responses of different latencies in the inferior cardiac nerves resulting in increases of heart rate and blood pressure.” He states further that “...studies suggest that the alteration of afferent articular input due to joint dysfunction and nociception excitation, in conditions of noxious mechanical deformation or chemical irritation, may provoke significant changes in efferent and autonomic responses.” [175]
Much of this research is centred around major noxious stimulation of the autonomic nervous system from vertebrogenic (somato-autonomic) sources into the spinothalamic tract. Due to the integrative nature of the neuraxis, this is now known to fire into the tractus solitarius, interomedial lateral cell column (IML) of the spinal cord, other spinal cord tracts, through the brain stem nuclei and into the cortical areas. [72] (Tables 1 & 2)
Edwards and colleagues suggest that“...the InM (Intermedius Nucleus) contains neurochemically diverse neurons and sends both excitatory and inhibitory projections to the NTS (Nucleus Tractus Solitarii). These data provide a novel pathway that may underlie possible reflex changes in autonomic variables after neck muscle spindle afferent activation.” While somato-autonomic mechanisms are recognised, there is currently only limited evidence exploring the long-term neurological effects of more minor traumatic effects emanating from spinal structures under such adverse conditions. [77]
Jinkins further clarifies the concepts by stating that
“The clinical state of neurogenic spinal radiculopathy accompanying nerve root spinal nerve, and dorsal root ganglion injury, may be associated with definite somatic and autonomic syndromes.” He notes further that “The combined clinical complex includes “autonomic reflex dysfunction...and ...”generalized alterations in autonomic viscerosomatic tone.” [135]
Medical texts vary in their depth of commitment to the concept of somatovisceral disorders. Bourdillon states tentatively that,
“If autonomic reflex activity is accepted as a vehicle for many of the manifestations of joint and somatic dysfunction, then one can postulate that coronary vasospasm might be a result of somatic dysfunction and, if so, that it might respond to manual management.” [176]
An interesting study by De Landsheere et al incorporating PET monitoring found that stimulating the spinal cord (electrically), reduced exercise induced angina in patients, without conventional drugs or surgery. They found that the stimulation resulted in decreased ECG signs of myocardial ischemia, but not myocardial perfusion. [177]
It could be argued that if disturbances of the spine through such trauma as cervical whiplash (in its varying degrees), has recognisable neurological consequences, it is reasonable and possible to assume that normalising such a disturbed cervical spine should then also tend to ameliorate the neurological sequelae.
Whiplash injuries in particular can result in a number of neurological disturbances. (Table 3) [cits 178–193] In her text, Jackson mentions various autonomic symptoms which could result from disturbances to the cervical spine and cervical sympathetic supply. [194] They include:A sensation of exophthalmos
Blurring of vision ‘Dazed and addled’
‘Drop attacks’
Dysphagia
Nausea
Palpitations
Paresthesias
Tachycardia
Tinnitus
Vertigo
Vomiting
Weakness of extremitiesThese citations provide evidence which tends to suggest that trauma of the cervical spine in particular, can have distinct neurological sequelae. It would seem logical that mechanical amelioration of mechanical trauma as in cervical facet hypomobility, hypermobility and noxious sensory input from related soft tissue scarring and damage, as well as joint irritation and inflammation, may well ameliorate or alleviate at least some of the associated neurological sequelae. It would seem reasonable to extend these same principles to other levels of injury in the spine. It is reasoned here, that there are varying degrees of whiplash other than the more extreme forms of trauma, less severe mechanical insult or indeed irritation, particularly of a chronic nature which would also have neurologically noxious input, and may explain a number of different insidious signs, symptoms and conditions.
In an extensive study, Hinoko noted that whiplash disturbed ‘proprio-autonomic reflexes’, not only of the cervical sympathetic nerves, but also that of cervical and lumbar proprioceptors. [195] Others have also noted proprioceptive disturbance in the form of vertigo and head re-positioning aberrations following whiplash. [184, 196–197]
Grimm and colleagues highlighted ‘interaction between cutaneous and vasomotor sympathetic neuron’ response to acute musculoskeletal injury. [20] They monitored “cardiovascular modulation, baroreceptor sensitivity, sudomotor response (skin conduction) and peripheral skin temperature.” Their findings were indicative of changes to somato-autonomic function.
The physiotherapy profession has more recently also become interested in the neurological aspects of manual therapy as a treatment of non-musculoskeletal conditions. [198] Grieve [199] acknowledges ‘autonomic nerve involvement’ in such signs and symptoms as:Dyspnoea
Flushing
Nausea
Pallor
Pulse alterations
Reduced respiratory excursion
Sweating
VomitingIn considering neurospinal influence, it is worth noting the rather wide range of research papers which assess the chiropractic profession’s interest in biochemical markers as well as exploring connections between spinal manipulation and this measurable biochemistry. These have been monitored in a number of studies, many of which are related to the immune system. Nevertheless, they reflect rather dynamic interest in measurable biochemistry markers. (Table 4) [cits 200–234] Apart from the immunological interest in a number of these chiropractic papers, [216, 226] a neuroimmunological relationship through the ANS has been recognised. [127, 146, 165, 187, 235]
Some acknowledgement should also be placed on research into the effects of spine-related physiology, pathomechanics, and pathophysiology in an animal model. Two of the earliest studies on this topic were conducted by Cleveland (Circa 1965) and Burns et al in 1948. [236, 237] More recent research by Brennan et al amongst others utilising mammalian subjects, has been particularly extensive.
(Table 5) [cits 238–239]
Another paper of interest was that by Kimura and Sato entitled “Somatic regulation of autonomic functions in anaesthetised animals – neural mechanisms of physical therapy including acupuncture”, depicts extensive somatoautonomic circuits. [138]
A recent landmark study by Bakkum et al., found that “preliminary data suggest that chronic vertebral hypomobility at L4–L6 in the rat affects synaptic density and morphology in the superficial dorsal horn of the L2 spinal cord level.” [240] This finding would fit within the chiropractic model of segmental fixation within the VSC.
Physical postural distortions, anomalies, and dysfunction of the spine have also been attributed to adverse influence on the function of visceral structures innervated from disturbed vertebral levels. (Table 6) [cits 241–257]
Over almost fifty years between 1905 and 1952, Goldthwaite and medical colleagues in particular, espoused the postural implications and complications of visceroptosis and vascular stasis associated with a wide range of visceral conditions. In their extensively referenced text Goldthwaite et al., stated that “It is through this autonomic system that disturbances or improvements in visceral function are mediated by changes in the mechanics of the body.” [245] A number of mechanisms contribute to significant proprioceptive input, with direct structural influence through the centralised neural channels. This would suggest that a significant change in posture and postural mechanics may influence neuropathophysiology. Lennon et al summarise this aspect as follows:“Observations of the striking influence of postural mechanics on function and symptomatology have led to our hypothesis that posture affects and moderates every physiologic function from breathing to hormonal production. Spinal pain, headache, mood, blood pressure, pulse, and lung capacity are among the functions most easily influenced by posture.”
“The most significant influences of posture are upon respiration, oxygenation, and sympathetic function. Ultimately, it appears that homeostasis and autonomic regulation are intimately connected with posture. [249]In addition, cutaneous and vasomotor autonomic reflexes can provide further examples of spine-related somatoautonomic activity.
Table 7) [cits 250–262]
Wilson noted that “static contraction of skeletal muscle activates small-diameter afferent nerve fibres which evoke a reflex increase in sympathetic nerve activity and cardiovascular function.” They cite others as making the same observation. [271]
As highlighted by D’Aubigne in the preface to Kapandji’s text (and in the text’s title), is the term central to this subject – the term ‘physiology of a joint’. It comprises not only the cell physiology of all associated articular tissue, but also the biomechanical aspects of normal articular movements – joint physiology, structures and function. [272] Physiology can be defined as the “a branch of biology that deals with the functions and activities of life or of living matter (as organs, tissues, or cells) and of the physical and chemical phenomena involved.” Pathophysiology of a joint then is some abnormality of the function of associated tissues, including especially neural tissues and articular mechanics – a derangement of function or “the physiology of abnormal states; specifically : the functional changes that accompany a particular syndrome or disease.” [273]
Whatmore and Kohli define the term dysponesis and that “most diseases consist of physiologic reactions that lead to organic dysfunction. These physiologic reactions constitute the response of the organism to some noxious agent, whether microbial, chemical, or mechanical.” [274]
In another component of the subluxation complex (myopathology or myopathophysiology), Edwards et al proposed that autonomic variables can be influenced by afferent muscle spindle activation, particularly from the posterior muscles of the neck. Further, that cardiorespiratory variables rely on interaction between the somatic and autonomic systems, essentially somato-sympathetic reflexes. [70]
Hyngstrom et al, found further that “intrinsic electrical properties of spinal motoneurons vary with joint angle(s)...” and that “dendrites of spinal motoneurons amplify inputs to a marked degree through persistent inward currents (PICs)...(where) dendritic amplification is subject to neuromodulatory control from the brainstem.” [134]
It is submitted that if autonomic influence can be so readily disturbed locally, it would seem reasonable that associated visceral function could also be influenced, and that the material presented would tend to support that hypothesis. Inasmuch as the correction (vertebral adjustment) of a physically and physiologically disturbed spinal element (a VSC) may provide an acknowledged physiological mechanism to ameliorate or normalise the connected autonomic disturbance and linked organic dysfunction, that hypothesis could then be reasonably supported.
Discussion‘The autonomic nervous system is intimately responsive to changes in the somatic activities of the body and while its connections with the somatic elements are not always clear in anatomical terms, the physiological evidence of visceral reflex activities stimulated by somatic events is abundant.” [275]
Central to this discussion is the fact that the autonomic nervous system “is a visceral and largely involuntary sensory and motor system (where) virtually all visceral reflexes are mediated by local circuits in the brain stem or spinal cord” [276] As stated, much of this activity is interceded through the spinal cord neurologically and the intervertebral foramina anatomically. If it is accepted that the ANS effectively influences all functions in the body, then there are six key elements to be addressed on this topic of external manual influence and spine-related pathophysiology. They are:
Neural dysfunction. Whether within the vertebral subluxation complex (segmental dysfunction) there can be influence, irritation, interference or modulation (stimulation or inhibition) with afferent and/or efferent neural transmission – Dorlands Dictionary defines such a role as reflexogenic – producing or increasing reflex action. [277]
Organic dysfunction. Whether any resultant altered neural transmission can adversely alter or influence innervated structural or organic physiology;
The degree to which any neural-induced pathophysiology of viscera may take place;
Neural Pathophysiology. Whether subsequent manual spinal adjustment (SMT) can positively influence neuropathophysiology of neural dysfunction;
Organic pathophysiology. Whether manual adjustment may influence the innervated visceral dysfunction or other structures by that positive influence, and if so;
How that influence may be monitored and modified to best effect for a particular patient’s response.
It is submitted that if a spinal, or indeed a peripheral articular adjustment does not affect, influence or have input upon the nervous system in any way, then effectively, manual manipulative therapy professions would not have a raison d’être in advancing such a neurospinal model. The reduction by articular adjustment of a bombardment of noxious neural stimuli from aberrant articular or associated soft tissue nociceptive [152, 166, 270, 278] input, could be deemed an example of a positive influence. Clinical examples would be in the cases of resolution of the vascular component of cervicogenic headaches, [65] or the positive influence upon a dysfunctional lumbar spinal segment associated with PMT or dysmenorrhea. – conditions that are a dysfunction (pathophysiological) rather than pathological. [279, 280]
If neural disturbance (Table 8) [various cits + 281] via hyperstimulation, suppression, or irritation is present within a subluxation complex, and deliberate neutralisation or normalisation of such aberrations through a vertebral segmental adjustment takes place, then the vertebral adjustment would be deemed to have had a positive neural influence. The differentiation and degree of a VSC affecting a somatic-somatic or a somatovisceral reflex (or both at once), must be the subject of interesting future research.
Another area of research interest could involve differentiating the variation in biological response to the VSC. For example, one response might be somato-somatic and another somato-visceral, even though by definition both would have a segmental neurological factor at the same vertebral level. A more specific example would be why a C1/C2 VSC in one patient produces headaches, in another migraines, and in yet another, no headache at all – just localised facet or muscle pain.
Extensive research currently being undertaken by the chiropractic neuroscientist Bolton et al, seems to corroborate the hypothesis of definitive compromise of neural physiology due to articular facet disturbance. [282, 283] Their research involves complex neurological aspects of both the VSC and the vertebral adjustment.
In relation to other spinal levels, there are a number of symptoms which can reflect spine-related neurological involvement. [284] Common examples would include pain as in vertebrogenic sciatica and brachial plexus neuropathy. [285, 286] Symptomatically, these conditions may be associated with various other neural symptoms including paresthesias, formication, muscle weakness, hyporeflexia, hyperalgesia and hypalgesia, through to muscle atrophy and trophic changes. [287] In osteopathic research, Karason and Drysdale demonstrate a somatovisceral reflex involving increased cutaneous circulation at the L5/S1 level, following administration of spinal adjustments (high-velocity low-amplitude – HVLA). These were conducted ‘outside the region of the sympathetic outflow.’ [288]
Further examples would be spinogenic dyspepsia. [289–292] Another could be the ciliospinal reflex, which incorporates both elements of a transient basic somatovisceral reflex. Chusid and McDonald classify the ciliospinal reflex as a visceral reflex. They also note that in the presence of Horner’s Syndrome which involves the T1 and T2 sympathetic segment, the ciliospinal reflex is lost. [293]
It may be a rudimentary example, but if it is noted that just a sharp stimulating slap on the back can affect neural activity (nociceptive, mechanoceptive) and invoke sympathetic responses such as pupillary dilation, increased pulse rate and adrenal secretion, then a somato-autonomic neural mechanism would be demonstrated. If that slap on the back can produce a generalised somato-autonomic response, then a controlled, specific, neuromechanical stimulation via a specific vertebral adjustment to a mechanically disturbed spinal segment may have the potential towards a more localised and predictable physiological response. It is noted that other factors such as psychological aspects, may also be involved in this example.
Physical therapy techniques including exercises, and at times manual manipulative musculoskeletal techniques, have also been employed in the management of a variety of visceral conditions involving the sympathetic nervous system. These include respiratory and cardiovascular rehabilitation. [294]
Recognition of the existence of neural and visceral pathophysiology or physiological dysfunction are central to this model. While consideration is given to the possibility of vertebrogenic visceral dysfunction and vertebrogenic visceral symptoms, the advent of actual vertebrogenic visceral pathology needs additional research. The possibility of simulated symptoms of visceral conditions has been discussed elsewhere. [295]
Even with a diagnosis of a simulated organic condition, the patient’s complaint is likely to be present in a symptomatic form. Unless the symptom is recognised as simulation, then previous diagnoses, treatments, or medication are likely to be based on those symptoms and not necessarily directed at the condition itself. That is, a treatment may well have been based in error on an actual organic condition, but one that is only simulated. One wonders if this could be a potential shortcoming in some Cochrane Collaboration studies, which appear to be based on the assumption of an accurate diagnosis in the first place – followed by treatment based on that diagnosis.
On the other hand there is a need for much more fundamental research to fully substantiate the spinovisceral role, even though reasonable evidence does exist. Conversely, there is a far greater paucity of evidence which would contradict claims by patients that they subjectively experience benefit from SMT. There seems to be a notable lack of double-blind controlled studies which negate positive claims regarding autonomic symptoms by patients under chiropractic care. Indeed, to justify the more recent adoption by manipulative medicine and manipulative physiotherapy of manual spinal therapy in relation to musculoskeletal conditions, there would appear to be a lack of evidential studies which provide the legitimacy for and justification of that involvement.
A connection has been discussed between mechanical spinal disturbance and resultant influence upon autonomic function. [13] This has been further depicted by way of highlighting sensory and mechanical disturbance from lumbar and cervical spinal facet changes (Table 1), and from whiplash (Table 3). It is also seen neurologically through the autonomic symptoms associated with migraine and other headaches, [296–298] and pain. (Table 9) [cits 299–310] There does however seem to be only limited research into the ANS effects from the varying durations and severities of more minor chronic pain situations. Although Johnston [38, 39] and Bannister31 have discussed the finding that autonomic function, autonomic dysfunction and degrees of autonomic failure can be of varying degrees of severity. Carrick has shown that specific influence on cervical spinal structures has led to a reasonable hypothesis regarding spinal influence upon brain function, as monitored by blind-spot mapping. [8] Disturbance of specific aspects of the extensive autonomic network may also explain some visceral symptoms and pathophysiological conditions of organic dysfunction as listed in this paper.
Summary“Health practices such as acupuncture and spinal manipulation frequently employ stimulation of somatic tissues in the treatment of visceral symptomology. The efficacy of these practices may well be based in somato-autonomic reflexes. An understanding of how afferent input modulates autonomic function, therefore, has considerable meaning beyond its academic interest.” [14]
Traditionally, medical interest in neural function in man has been centred on the more serious expressions of ANS dysfunction. [31, 311] However it is in relation to the more subtle signs and symptoms which this paper sought to illustrate – and especially, to look at the neurospinal connections – even in infants. [312]
It is a stimulating chore to attempt to differentiate between the papers mentioned. The cited extensive writings in the referenced literature by Bolton, Brennan, Budgell, Burns, Carrick, Pickar, Korr, Patterson, Swenson and particularly Sato et al., do provide a deeper awareness and appreciation of neuro-vertebral concepts. Their contribution has been significant in providing greater insight into the wide influence of disturbed somato-autonomic-visceral reflexes.
Based on the indications presented, it would be fair to suggest that to date, the neurological implications of SMT may be more intricate, extensive and sophisticated than even DD Palmer may have believed. [313] However, more research is required for further understanding and to elucidate the complex of neurovisceral-pathophysiological phenomena. It is hoped that true scientists would thoroughly consider all material before drawing conclusions on the role of chiropractic in this somato-autonomic area.
As indicated, basic scientific evidence does exist in support of a spine related influence upon the ANS. It suggests distinctly possible vertebrogenic factors in affecting such autonomic activity in the disturbance of some forms of heart rate, blood pressure and neural activity in renal, adrenal and gastrointestinal function. The potential for a possible physical, as opposed to a chemical form of intervention, is exciting. Given the volume, variety and indeed depth of the material mentioned here, one could be regarded as ultra-conservative if one concluded meekly that there does appear to be at least some potential in support of an hypothesis of spine-related neuro-autonomic pathophysiological dysfunction. Sato et al stated that “...the decreases in blood pressure and renal nerve activity during manipulation of the spine are thought to be supraspinal reflexes.” [314]
Conclusion“In contrast to the impressive body of knowledge concerning the effects of visceral afferent activity on autonomic functions, there is, generally speaking, much less information available on the reflex regulation of visceral organs by somatic afferent activity from skin, the skeletal muscle and their tendons, and from joints and other deep tissues. The elucidation of the neural mechanisms of somatically induced autonomic reflex responses, usually called somato-autonomic reflexes, is, however, essential to developing a truly scientific understanding of the mechanisms underlying most forms of physical therapy, including spinal manipulation and traditional as well as modern forms of acupuncture and moxibustion.” – Sato A et al [315]
In essence, this has been an attempt to highlight the published literature surrounding the hypotheses appropriate to the manual manipulative therapies in general, and the science of chiropractic in particular. It draws connections between the effect upon the autonomic nervous system due to pain, postural disturbance, and the mechanical disruption of trauma, with whiplash being the most easily demonstrated. There are indications in some of the references that trauma does not have to be extreme to produce such symptoms. It has attempted further, to look at the reflexogenic effects of factors affecting the ANS. It then follows the next association – that of the effect of ANS irritation upon the physiology of structures innervated by an ANS modified by such changes, especially those regarded as spine-related.
It would seem reasonable to hypothesise that if disturbance or mechanical insult to the spine can lead to ANS-related dysfunction or symptoms, then alleviation of that disturbance or insult should also tend to ameliorate those same symptoms, and thereby encourage disturbed physiology in involved structures to return towards normal function.
The volume and variety of evidence presented in this cursory overview, would tend to suggest there should be open mindedness when considering the possibilities of manual management of a number of somatovisceral conditions. An attitude of outright rejection may tend to limit chiropractic within a musculoskeletal field. This could deny science a whole area of opportunity, and deprive certain patients of options for a potential source of minimally invasive natural health management. Once all the available evidence is considered, and further research has had the opportunity to explain the clinically observed phenomenon of positive outcomes, proper assessment can then take place. Despite the material presented here, one is still reticent in making broad claims.
To consider the historical base for chiropractic, without the vital inherent correlations with the nervous system, is essentially to not fully appreciate chiropractic as it was originally intended – and where it is currently pioneering this natural model of health care.
Co-operation between the health professions, together with a serious, constructive and unbiased research effort into this topic, would raise the potential for a more effective, non-invasive means of influencing internal physiology and potentially, pathophysiology.
It would seem appropriate to be able to influence the nervous system and physiological dysfunction through the least invasive intervention possible and through readily accessible neural procedures. If that potential is through SMT, then it behoves the scientific community to explore that potential and develop it to its extreme. Rejecting the concept without thorough investigation is unscientific and close-minded.
While much research is currently underway, many areas remain to be explored in order to further develop the somato-autonomic-visceral hypothesis. To this author, the weight of the evidence so far is such that a significant neurospinal connection cannot be ignored or discounted. Beyond the basic neurophysiological research, the positive clinical indications so far suggest quite inspiring promise.“The human nervous system is the most complex physical system known to mankind: it consists of many billions of interactive units whose constantly changing patterns of activity are reflected in every aspect of human behaviour and experience.” Gray’s Anatomy [316]
REFERENCESAn extensive list of references is available by contacting the author on cadaps@bigpond.net.au
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