Autonomic Nervous System and Chiropractic Theories of Nerve Interference

The central chiropractic concept of nerve interference posits that spinal joint dysfunctions, known as vertebral subluxations, can disrupt nerve signaling and adversely affect autonomic nervous system (ANS) function, thereby impacting organ health [3]. This theory has been a cornerstone of chiropractic since its inception and remains a subject of intense debate regarding its validity and clinical relevance [10]. The concept originated with Daniel David Palmer in 1895, who proposed that "a subluxated vertebra...is the cause of 95 percent of all diseases" [1]. In his writings, Palmer theorized that spinal misalignments created pressure on nerves, altering their "tone" by making them too tense or too slack, and that the resulting disease was determined by which specific nerves were affected by this interference [1, 23].

The original "bone-on-nerve" model was refined by Palmer's son, B.J. Palmer, who focused on the upper cervical spine. His 'Hole-in-One' (HIO) technique proposed that misalignments of the atlas (C1) and axis (C2) were the primary "true subluxation" disrupting the flow of information from the brainstem to the rest of the body's organs [2, 25]. In the mid-to-late 20th century, the theory evolved into the more complex vertebral subluxation complex (VSC) model.¹ This model expanded the proposed mechanisms of neurological interference beyond simple nerve compression [3]. It included dysafferentation, a neurophysiological concept where abnormal signals from dysfunctional spinal joints alter central sensory processing, and dysautonomia, a direct disturbance of autonomic nerve regulation [3, 15]. This modern interpretation differs from the Palmerian idea of a physical nerve pinch [15].

Contemporary research investigates these proposed links through measurable physiological markers of ANS activity. One proposed mechanism is the somatoautonomic reflex, where mechanical stimulation of spinal joints is hypothesized to modulate the output of preganglionic autonomic neurons in the spinal cord [14]. Some studies have reported transient changes in autonomic function following spinal manipulative therapy (SMT). For instance, a 1997 study by Brennan et al. reported a temporary increase in skin conductance after SMT, suggesting a brief activation of the sympathetic nervous system [6]. A 2008 study by Welch & Boone found that cervical adjustments might induce a parasympathetic response, as indicated by a drop in diastolic blood pressure, while thoracic adjustments could elicit a sympathetic response [5]. Other research has noted a significant decrease in pupil diameter (miosis) immediately after cervical manipulation, indicating a shift toward parasympathetic activity [8], and a decrease in salivary cortisol levels, suggesting an effect on the hypothalamic-pituitary-adrenal (HPA) axis [7].

Despite these findings, the clinical relevance and validity of the nerve interference theory are heavily disputed. Critics point to the transient nature of the observed effects and the low quality of much of the research. A 2018 systematic review by De-la-Llave-Rincón et al. examined the effect of SMT on heart rate variability (HRV), a key indicator of autonomic balance, and concluded that while some studies suggest an influence, the overall evidence is of low quality and too heterogeneous to permit firm conclusions [4]. Furthermore, major systematic reviews have failed to find evidence supporting the use of chiropractic for the systemic diseases originally targeted by the subluxation theory. A 2021 review by Gyer et al. found no evidence that manual therapy is effective for non-musculoskeletal disorders such as asthma, infantile colic, or hypertension [9]. In line with this criticism, the National Center for Complementary and Integrative Health (NCCIH) states that the chiropractic theory of subluxation causing or contributing to disease is not supported by evidence [10]. This position is echoed in a 2009 critical review by Mirtz et al., which concluded that "No supportive evidence is found for the chiropractic subluxation being associated with any disease process" and called the concept "unsupported speculation" [11].

Historical development of nerve interference theory

The concept of nerve interference as a primary cause of disease is foundational to chiropractic and originates with its founder, Daniel David Palmer. In the late 19th century, Palmer developed a theory based on his initial chiropractic adjustment in 1895. He posited that a misaligned or "subluxated" vertebra created pressure on spinal nerves, thereby interfering with the normal transmission of nerve impulses ². In his writings, Palmer made the expansive claim that "a subluxated vertebra... is the cause of 95 percent of all diseases" ³. According to his model, this mechanical pressure altered the "tone" of the nerve, making it either too tense or too slack. The specific organ or tissue that became diseased was determined by which particular nerve was being compressed by the spinal misalignment ³. This early model, detailed in Palmer’s posthumously published book The Chiropractor ⁴, presented a relatively straightforward mechanical explanation for disease, linking spinal structure directly to systemic health and pathology.

This foundational theory was significantly refined, and in many ways narrowed, by his son, Bartlett Joshua (B.J.) Palmer, who became known as the "Developer" of chiropractic. B.J. Palmer assumed leadership of the Palmer School of Chiropractic and directed the profession’s intellectual development for decades ¹. While D.D. Palmer considered subluxations throughout the spine, B.J. Palmer eventually focused his attention almost exclusively on the upper cervical spine. Through extensive research at his facilities, he concluded that the most significant nerve interference occurred at the level of the atlas (C1) and axis (C2) vertebrae. This led to his development of the 'Hole-in-One' (HIO) technique, a system that advocated for adjusting only these top two spinal bones ⁵.

The rationale for the HIO technique was that misalignments in this specific area were the primary or "true subluxation" capable of disrupting the flow of nerve information from the brainstem down the spinal cord and out to the entire body ⁵. B.J. Palmer theorized that an atlas or axis misalignment could impinge upon the brainstem and upper spinal cord, disrupting the transmission of what he termed "mental impulses" from the brain to the body’s organs. By correcting this single, pivotal subluxation, he believed the body’s innate intelligence could restore normal function and health throughout the entire system, rendering adjustments elsewhere unnecessary ¹. This shift represented a move from D.D. Palmer’s more generalized "pinched nerve" model to a more specific, top-down theory of neurological control centered on the craniocervical junction.

Proposed neurophysiological mechanisms

Modern attempts to explain how spinal dysfunction might influence autonomic function have moved beyond early mechanical pressure models. A proposed operational model for assessing the neurological effects of vertebral subluxation includes four components: dysafferentation (abnormal afferent input), dyskinesia (abnormal movement), dysponesis (errors in action potential output), and dysautonomia (dysfunction of the autonomic nervous system). ⁶.⁷ Three primary mechanisms are often proposed: the somatoautonomic reflex, dysafferentation, and the modulation of nociceptive input.

The somatoautonomic reflex hypothesis suggests a direct link between somatic (body frame) and autonomic nervous systems. According to this model, mechanical stimulation of somatic afferent fibers in spinal joint capsules, ligaments, and muscles can modulate the activity of preganglionic autonomic neurons ⁸. These somatic afferents travel to the spinal cord and synapse within the intermediolateral cell column, where the cell bodies of sympathetic preganglionic neurons are located. As proposed by Budgell in a 2000 paper, this input can either excite or inhibit autonomic outflow, providing a plausible mechanism for how a spinal manipulation could induce physiological changes ⁸. Some clinical research provides findings consistent with this model. For instance, a 2008 study by Welch and Boone reported that cervical adjustments were associated with a parasympathetic response (a drop in diastolic blood pressure), whereas thoracic adjustments were linked to a sympathetic response ⁹. Similarly, a 2016 study by D'Alessandro et al. observed a significant, transient decrease in pupil diameter (miosis) following cervical manipulation, indicating a shift toward parasympathetic activity ¹⁰¹¹. A 2019 systematic review found moderate-certainty evidence that oscillatory spinal mobilization techniques probably produce an immediate, short-term increase in skin sympathetic nerve activity, reflected by a rise in skin conductance. ¹².

A second proposed mechanism is dysafferentation, a concept distinct from the Palmerian nerve-pinch theory ³. As described by Seaman in 1998, dysafferentation refers to an alteration in the quality and quantity of afferent information sent from mechanoreceptors in dysfunctional spinal joints to the central nervous system ¹³. According to this hypothesis, joint restriction or aberrant motion generates abnormal patterns of sensory input. This sustained, corrupted stream of information is theorized to alter central sensory processing in the spinal cord, brainstem, and higher centers, potentially leading to inappropriate or dysfunctional autonomic output ¹³. This model shifts the focus from direct nerve compression to a disruption in neurological information processing.

The third hypothesis involves the modulation of nociceptive input and its effect on central sensitization. In states of chronic pain or joint dysfunction, a constant barrage of nociceptive afferent signals can sensitize neurons in the central nervous system, leading to a state of hyperexcitability ¹⁴. This central sensitization is often accompanied by an increase in resting sympathetic tone. It is theorized that spinal manipulative therapy, as described in texts like Bergmann and Peterson's Chiropractic Technique, may reduce this nociceptive barrage by improving joint mechanics and stimulating mechanoreceptors that inhibit pain pathways ¹⁴. By quieting this peripheral nociceptive noise, manipulation could help down-regulate central sensitization and, in turn, reduce the associated elevated sympathetic activity. Some evidence, such as a 2011 study by Plaza-Manzano et al. that found a significant decrease in salivary cortisol levels after cervical manipulation, suggests a potential modulatory effect on the hypothalamic-pituitary-adrenal (HPA) axis and the broader stress response ¹⁵. However, it is important to contextualize these proposed mechanisms with the overall state of the evidence. A 2018 systematic review by De-la-Llave-Rincón et al. examining the effect of spinal manipulation on heart rate variability, a key indicator of autonomic balance, concluded that the available evidence is of low quality and too heterogeneous to permit firm conclusions about clinical relevance ¹⁶¹⁷.

Research on transient autonomic effects

Investigations into the immediate physiological consequences of spinal manipulative therapy (SMT) have sought to identify objective, transient changes in the autonomic nervous system. These studies, however, have produced a complex and often contradictory body of evidence. For instance, research has suggested that the anatomical region of the adjustment may determine the nature of the autonomic response. A 2008 study by Welch and Boone published in the Journal of Manipulative and Physiological Therapeutics observed that specific adjustments appeared to elicit opposing effects. The study found that a cervical spine adjustment was associated with a significant decrease in diastolic blood pressure, a change indicative of a parasympathetic or vagal response ⁹. Conversely, when the manipulation was applied to the thoracic spine, the researchers noted a trend toward a sympathetic response, suggesting that the site of stimulation is a key variable in the resulting autonomic outcome ⁹.

The measurement of skin conductance, an indicator of sympathetic sudomotor activity, has also yielded ambiguous results. One report on a 1997 study by Brennan et al. indicated that spinal manipulation was linked to a brief, measurable increase in skin conductance, implying a short-term activation of the sympathetic nervous system ¹². However, another analysis of the same research project concluded that there were no significant changes in skin conductance when comparing spinal manipulation at the T4 or L4 levels to a sham intervention, leaving the effect on this sympathetic marker unclear ¹⁸. In contrast, pupillometry has provided more consistent, though still transient, evidence for an autonomic shift. A 2016 study by D'Alessandro et al. observed a statistically significant decrease in pupil diameter, a condition known as miosis, immediately after a cervical spine manipulation ¹⁰¹¹. This constriction of the pupil is regulated by parasympathetic fibers, and the finding suggests a rapid, temporary shift away from sympathetic tone and toward parasympathetic dominance following the adjustment ¹¹.

The effects of SMT on the hypothalamic-pituitary-adrenal (HPA) axis, a major component of the body's stress response system, have been similarly inconsistent. One notable example of this is seen in conflicting findings regarding the stress hormone cortisol. A 2011 study by Plaza-Manzano and colleagues, published in The Spine Journal, reported that a single cervical thrust manipulation led to a significant decrease in salivary cortisol levels in healthy subjects at 10 and 20 minutes post-intervention when compared to a control group ¹⁵. This result would suggest that the manipulation had a down-regulating effect on the HPA axis. However, a subsequent study in 2014 by the same lead author, published in the Journal of Orthopaedic & Sports Physical Therapy, found precisely the opposite effect. A 2014 randomized controlled study on asymptomatic subjects found that cervical spinal manipulation triggered a significant increase in serum cortisol levels immediately after the intervention, while thoracic manipulation did not. ¹⁹. This later study also identified concurrent increases in the plasma levels of neurotensin and oxytocin, suggesting a more complex neuroendocrine response to the mechanical stimulus of an adjustment ¹⁹. Taken together, these individual experimental studies demonstrate that while spinal adjustments can induce measurable, short-lived physiological changes, the direction, reproducibility, and clinical significance of these autonomic effects remain highly debated.

Systematic reviews and evidence synthesis

To assess the collective strength and consistency of primary research, multiple systematic reviews and evidence syntheses have been published. These higher-level analyses generally find that the research investigating the autonomic effects of spinal manipulation is of low quality and too heterogeneous to permit firm conclusions about clinical relevance ¹⁶²⁰. A 2018 systematic review by De-la-Llave-Rincón and colleagues, published in Complementary Therapies in Medicine, specifically evaluated the effect of spinal manipulative therapy (SMT) on heart rate variability (HRV), a common proxy for autonomic balance. The authors analyzed the available randomized controlled trials but found the collective body of evidence to be of low to moderate quality and filled with conflicting results ¹⁷. They concluded that this heterogeneity, combined with methodological weaknesses in the primary studies, prevented any definitive conclusion regarding the effectiveness of SMT for modulating autonomic function or its clinical importance ¹⁶.

This critique of evidence quality is amplified in reviews examining clinical outcomes for non-musculoskeletal disorders, which are theoretically linked to the autonomic dysfunction proposed in chiropractic theory ⁶. A comprehensive 2021 systematic review by Gyer et al. A 2021 systematic review in Chiropractic & Manual Therapies covering six randomized controlled trials found no evidence of effect for spinal manipulative therapy in the management of non-musculoskeletal disorders, including infantile colic, childhood asthma, and hypertension. ²⁰. After synthesizing the available evidence, the review found no support for a clinically relevant effect for manual therapy in treating these or other evaluated non-musculoskeletal disorders ²⁰²¹. A 2021 systematic review of evidence from a global summit of researchers concluded that for the non-musculoskeletal conditions of colic, asthma, hypertension, dysmenorrhea, and migraine, spinal manipulation performed no better than a sham intervention. ²¹. These findings directly challenge the clinical application of theories tracing organic disease to spinal nerve interference, a foundational concept in chiropractic originating with D.D. Palmer ³.

Beyond clinical outcomes, critical reviews have also examined the core theoretical construct of the vertebral subluxation itself. A 2009 critical review by Mirtz and colleagues in the journal Chiropractic & Osteopathy evaluated the evidence for the chiropractic subluxation concept as a causative factor in disease. Their analysis concluded, "No supportive evidence is found for the chiropractic subluxation being associated with any disease process or of creating suboptimal health conditions requiring intervention" ²². The authors characterized the concept as remaining in the "realm of unsupported speculation" ²³. This position is consistent with that of major health organizations, such as the U.S. The National Center for Complementary and Integrative Health describes chiropractic as a licensed health profession that emphasizes the body's ability to heal itself, with treatment typically involving manual therapy like spinal manipulation for problems related to the musculoskeletal system. ²⁴. In aggregate, these high-level evidence syntheses indicate that while individual studies may report transient physiological changes post-manipulation, the overall research base is considered too low in quality and inconsistent to support claims that chiropractic adjustments can reliably modulate autonomic function to produce clinically significant health benefits for systemic diseases.

Variants and related techniques

The general chiropractic theory of nerve interference has given rise to specific techniques heavily predicated on modulating autonomic nervous system (ANS) function. A prominent historical example is the 'Hole-in-One' (HIO) technique developed by B.J. Palmer, the son of chiropractic's founder ¹. Departing from his father's concept that subluxations causing disease could occur anywhere in the spine ³, B.J. Palmer theorized that the primary site of nerve interference was at the craniocervical junction ⁵. His HIO technique, detailed in chiropractic texts ⁷, involved adjusting only the atlas (C1) and axis (C2) vertebrae. The rationale was that misalignments in this area uniquely disrupted the flow of information from the brainstem down the spinal cord, thereby affecting the function of the body's organs ⁵. Modern upper cervical specific techniques, such as the National Upper Cervical Chiropractic Association (NUCCA) and Atlas Orthogonal methods, evolved from this HIO foundation, maintaining a focus on the C1-C2 region.

Contemporary explanations for how these techniques might influence the ANS have moved beyond a simple mechanical nerve pinch. Instead, they often incorporate the vertebral subluxation complex model, which posits mechanisms like dysautonomia (direct disturbance of autonomic regulation) and dysafferentation ⁶. The concept of dysafferentation suggests that abnormal sensory input from dysfunctional spinal joints, particularly the highly innervated joints of the upper cervical spine, alters central sensory processing in the brainstem and spinal cord ¹³. This differs from the original Palmerian model of direct nerve compression ¹³. Another proposed mechanism is the somatoautonomic reflex, where mechanical stimulation of spinal structures is thought to activate afferent nerve fibers that synapse within the spinal cord, thereby modulating the output of preganglionic autonomic neurons ⁸.

Research investigating these proposed mechanisms has focused on measuring objective physiological markers of ANS activity following spinal manipulation. Some studies have reported transient shifts toward parasympathetic activity. For example, a 2016 study by D'Alessandro et al. observed a significant decrease in pupil diameter (miosis) immediately after a cervical spine manipulation, a change indicative of a shift toward parasympathetic activity ¹¹. Similarly, a 2008 study by Welch & Boone reported that cervical adjustments were associated with a significant drop in diastolic blood pressure, which they interpreted as a parasympathetic response, whereas thoracic adjustments appeared to elicit a sympathetic response ⁹. However, the evidence base is not consistent. Research on the hypothalamic-pituitary-adrenal (HPA) axis, a key stress-response system linked to the ANS, has produced conflicting results. A 2011 study by Plaza-Manzano et al. found a significant decrease in salivary cortisol levels after a cervical thrust manipulation ¹⁵, while a separate 2014 study by the same lead author reported an increase in blood cortisol levels following spinal manipulation ¹⁹. This heterogeneity is a recurring theme in systematic reviews, with one 2018 review concluding that while some studies suggest spinal manipulation can influence heart rate variability, the evidence is of low to moderate quality and conflicting, preventing definitive conclusions ¹⁷. Ultimately, high-level reviews have found no convincing evidence that these observed transient physiological changes translate into clinically relevant effects for non-musculoskeletal disorders such as asthma or hypertension ²⁰²¹.

Clinical claims for non-musculoskeletal disorders

The historical basis for claims of treating non-musculoskeletal disorders originates with the founder of chiropractic, D.D. Palmer, who proposed that "a subluxated vertebra... is the cause of 95 percent of all diseases" ³. This concept, detailed in works like The Chiropractor ⁴, posited that vertebral misalignments apply pressure to spinal nerves, altering their "tone" and causing disease in the organs supplied by those nerves ³. This framework led to the practice of treating visceral conditions such as asthma, infantile colic, or hypertension by adjusting specific spinal segments. Later theories, like B.J. Palmer's 'Hole-in-One' technique, focused exclusively on the upper cervical spine as the primary site of interference for all disease processes ⁵. More contemporary models, such as the vertebral subluxation complex, have attempted to update this idea with modern neurophysiological language, suggesting mechanisms like dysautonomia (direct disturbance of autonomic nerve regulation) as the link between spinal dysfunction and organ health ⁶.

Despite the persistence of these claims, rigorous scientific evaluation has consistently failed to validate them. Multiple high-level systematic reviews have concluded that chiropractic care and other forms of manual therapy are not effective for treating non-musculoskeletal conditions. A comprehensive 2021 systematic review by Gyer et al. published in Chiropractic & Manual Therapies analyzed evidence for a wide range of organic and visceral disorders. The authors found no evidence of a clinically relevant effect for manual therapy in treating asthma, infantile colic, and hypertension, among others ²⁰²¹. They concluded that claims of effectiveness for these conditions are not supported by evidence from randomized controlled trials ²¹.

This finding echoes an earlier critical review from 2009 by Mirtz et al. in Chiropractic & Osteopathy, which examined the evidence for the subluxation concept itself. The review concluded, "No supportive evidence is found for the chiropractic subluxation being associated with any disease process," describing the concept as remaining in the "realm of unsupported speculation" ²³²². This scientific consensus is reflected by major health organizations. The National Center for Complementary and Integrative Health (NCCIH), for example, states that the chiropractic theory of subluxation causing or contributing to disease is not supported by evidence ²⁴. The discrepancy between the observed transient autonomic effects, such as a short-term activation of the sympathetic nervous system ¹² or a shift toward parasympathetic activity ⁹¹⁰, and the lack of durable clinical outcomes remains a central point of criticism. The evidence indicates that while spinal manipulation may induce temporary physiological responses, these changes do not translate into effective treatments for systemic diseases as originally theorized ²⁰²¹.

Significance, debate, and scientific status

The concept of nerve interference, originating with the vertebral subluxation, is central to the historical and philosophical identity of chiropractic. The profession’s founder, D.D. Palmer, proposed in his 1895 writings that "a subluxated vertebra... is the cause of 95 percent of all diseases" by impeding nerve function ³⁴. This foundational idea was further developed by his son, B.J. Palmer, whose 'Hole-in-One' (HIO) technique posited that misalignments of the atlas (C1) and axis (C2) vertebrae were the most critical disruptions to the nervous system's control over the body ⁵¹. This belief, that correcting spinal misalignments restores health by removing nerve interference, has remained a core, albeit highly controversial, tenet for a segment of the profession, distinguishing chiropractic from other manual therapies.

Despite its historical significance, the theory that vertebral subluxations cause organic disease is scientifically unsubstantiated and a primary source of internal debate and external criticism ²⁴²². A 2009 critical review by Mirtz et al. published in Chiropractic & Osteopathy is frequently cited for its conclusion that "No supportive evidence is found for the chiropractic subluxation being associated with any disease process" and that the concept exists in the "realm of unsupported speculation" ²³. Modern proponents have moved away from Palmer's simplistic bone-on-nerve model, proposing more complex neurophysiological mechanisms such as the "vertebral subluxation complex" ⁶. This model includes concepts like dysafferentation, where abnormal signaling from dysfunctional spinal joints alters central processing, and dysautonomia, a direct disturbance of autonomic regulation ⁶¹³. However, these models also lack robust evidentiary support linking them to specific systemic diseases.

Research investigating the effects of spinal manipulation on the autonomic nervous system has produced a body of inconsistent and low-quality evidence. While some isolated studies have observed transient physiological changes, they fail to form a coherent picture or demonstrate clinically relevant outcomes for non-musculoskeletal conditions. For example, a 1997 study by Brennan et al. reported a temporary increase in skin conductance post-manipulation, suggesting sympathetic activation ¹², but a separate 1997 study by the same lead author found no significant changes in this same measure compared to a sham intervention ¹⁸. Similarly, a 2011 study by Plaza-Manzano et al. found a decrease in salivary cortisol after cervical manipulation ¹⁵, whereas a 2014 study from the same research group reported an increase in blood cortisol levels following spinal manipulation ¹⁹.

Systematic reviews have consistently highlighted these evidentiary weaknesses. A 2018 review by De-la-Llave-Rincón et al. on spinal manipulation’s effect on heart rate variability, a key indicator of autonomic balance, concluded that the evidence was low quality and too heterogeneous to allow for firm conclusions ¹⁶. Reinforcing this lack of clinical translation, a 2021 systematic review by Gyer et al. found no evidence to support the use of manual therapy for non-musculoskeletal disorders like asthma, infantile colic, or hypertension ²⁰²¹. Consequently, the broad scientific consensus is that the chiropractic theory of nerve interference causing systemic disease remains a speculative doctrine, unproven by the standards of evidence-based medicine ²⁴²².

Sources

1. John P. Stiga, The vertebral subluxation complex, research insights (1982) - https://openlibrary.org/works/OL11214161W

2. The Chiropractor (Classic Reprint) by Daniel David Palmer (2018, Forgotten Books) - https://books.google.com/books/about/The_Chiropractor_Classic_Reprint.html?hl=&id=alw1vAEACAAJ

3. D.D. Palmer proposed that "a subluxated vertebra... is the cause of 95 percent of all diseases" by creating pressure on nerves, which alters their "tone" (too tense or too slack), and that the specific disease depends on which nerves are affected. - https://www.google.com/books/edition/The_Chiropractor_s_Adjuster/h384AQAAMAAJ?hl=en

4. Textbook of Chiropractic Technique by F. P. DeGiacomo (1981) - https://books.google.com/books/about/Textbook_of_Chiropractic_Technique.html?hl=&id=0QGtAAAACAAJ

5. B.J. Palmer's 'Hole-in-One' (HIO) technique involved adjusting only the atlas (C1) and axis (C2), based on his theory that misalignments in this specific area were the primary "true subluxation" disrupting the flow of information from the brain down the spinal cord and out to the body's organs. - https://juniperpublishers.com/jojnhc/pdf/JOJNHC.MS.ID.555857.pdf

6. Kent, 2019 - https://www.vertebralsubluxationresearch.com/2019/08/02/proposed-neurobiological-processes-associated-with-models-of-vertebral-subluxation-dysafferentation-dyskinesia-dysponesis-dysautonomia-neuroplasticity-and-ephaptic-transmission/

7. Sheldon T. Sharpe, Neurology of the Vertebral Subluxation Complex in Chiropractic (2020) - https://openlibrary.org/works/OL21896014W

8. Seaman DR, Journal of Manipulative and Physiological Therapeutics (1998) - https://www.researchgate.net/publication/13600570_Dysafferentation_A_novel_term_to_describe_the_neuropathophysiological_effects_of_vertebral_subluxation_syndrome_in_women

9. The 2008 Welch & Boone study in the 'Journal of Manipulative and Physiological Therapeutics' suggested that cervical adjustments may elicit a parasympathetic response (indicated by a significant drop in diastolic pressure) while thoracic adjustments may elicit a sympathetic response. - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2686395/

10. A 2021 systematic review by Gyer et al. in 'Chiropractic & Manual Therapies' found no evidence of a clinically relevant effect for manual therapy in treating non-musculoskeletal disorders like asthma, infantile colic, and hypertension, among others. - https://chiromt.biomedcentral.com/articles/10.1186/s12998-021-00384-x

11. Briggs L, Boone WR, 1988 - https://www.ncbi.nlm.nih.gov/pubmed/3392474

12. Wirth, B., Gassner, A., de Bruin, E.D. et al., 2019 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6417274/

13. Plaza-Manzano G, et al., Journal of Orthopaedic and Sports Physical Therapy (2014) - https://www.jospt.org/doi/10.2519/jospt.2014.4996

14. Gyer G, et al., Chiropractic & Manual Therapies (2021) - https://chiromt.biomedcentral.com/articles/10.1186/s12998-021-00402-y

15. A 2011 study by Plaza-Manzano et al. in 'The Spine Journal' found a significant decrease in salivary cortisol levels in healthy subjects 10 and 20 minutes after a cervical thrust manipulation compared to a control group, suggesting an effect on the HPA axis. - https://www.thespinejournalonline.com/article/S1529-9430(10)01053-1/fulltext

16. The 2018 systematic review by De-la-Llave-Rincón et al. in 'Complementary Therapies in Medicine' concluded that while some studies suggest spinal manipulative therapy can influence HRV, the evidence is of low quality and heterogeneous, preventing firm conclusions about its clinical relevance. - https://www.sciencedirect.com/science/article/abs/pii/S096522991730537X

17. Hawk C, Khorsan R, Lisi AJ, Ferrance RJ, Evans MW (2007) - https://www.liebertpub.com/doi/10.1089/acm.2007.7088

18. Nicholson GG, A study to determine the effect of spinal manipulation on skin conductance, 1996 - https://www.ncbi.nlm.nih.gov/pubmed/8896033

19. Plaza-Manzano G, et al., 2014 - https://pubmed.ncbi.nlm.nih.gov/24582413/

20. Côté et al., 2021 - https://doi.org/10.1186/s12998-021-00362-9

21. Mirtz TA, et al., Chiropractic & Osteopathy (2009) - https://chiromt.biomedcentral.com/articles/10.1186/1746-1340-17-13

22. Mirtz, T. et al., 2009 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2786226/

23. De-la-Llave-Rincón AI, et al., Complementary Therapies in Medicine (2018) - https://www.researchgate.net/publication/323385210_Effect_of_Spinal_Manipulative_Therapy_on_Heart_Rate_Variability_A_Systematic_Review

24. National Center for Complementary and Integrative Health, 2019 - https://www.nccih.nih.gov/health/chiropractic-in-depth