Brian Budgell

Reflex effects of subluxation: the autonomic nervous system*

BACKGROUND The collective experience of the chiropractic profession is that aberrant stimulation at a particular level of the spine may elicit a segmentally organized response, which may manifest itself in dysfunction within organs receiving autonomic innervation at that level. This experience is at odds with classic views of neuroscientists about the potential for somatic stimulation of spinal structures to affect visceral function. OBJECTIVE To review recent findings from basic physiologic research about the effects of somatic stimulation of spinal structures on autonomic nervous system activity and the function of dependent organs. DATA SOURCE Findings were drawn from a major recent review of the literature on the influences of somatic stimulation on autonomic function and from recent original physiologic studies concerning somatoautonomic and spinovisceral reflexes. CONCLUSIONS Recent neuroscience research supports a neurophysiologic rationale for the concept that aberrant stimulation of spinal or paraspinal structures may lead to segmentally organized reflex responses of the autonomic nervous system, which in turn may alter visceral function.

Review of methods used by chiropractors to determine the site for applying manipulation

BackgroundWith the development of increasing evidence for the use of manipulation in the management of musculoskeletal conditions, there is growing interest in identifying the appropriate indications for care. Recently, attempts have been made to develop clinical prediction rules, however the validity of these clinical prediction rules remains unclear and their impact on care delivery has yet to be established. The current study was designed to evaluate the literature on the validity and reliability of the more common methods used by doctors of chiropractic to inform the choice of the site at which to apply spinal manipulation.MethodsStructured searches were conducted in Medline, PubMed, CINAHL and ICL, supported by hand searches of archives, to identify studies of the diagnostic reliability and validity of common methods used to identify the site of treatment application. To be included, studies were to present original data from studies of human subjects and be designed to address the region or location of care delivery. Only English language manuscripts from peer-reviewed journals were included. The quality of evidence was ranked using QUADAS for validity and QAREL for reliability, as appropriate. Data were extracted and synthesized, and were evaluated in terms of strength of evidence and the degree to which the evidence was favourable for clinical use of the method under investigation.ResultsA total of 2594 titles were screened from which 201 articles met all inclusion criteria. The spectrum of manuscript quality was quite broad, as was the degree to which the evidence favoured clinical application of the diagnostic methods reviewed. The most convincing favourable evidence was for methods which confirmed or provoked pain at a specific spinal segmental level or region. There was also high quality evidence supporting the use, with limitations, of static and motion palpation, and measures of leg length inequality. Evidence of mixed quality supported the use, with limitations, of postural evaluation. The evidence was unclear on the applicability of measures of stiffness and the use of spinal x-rays. The evidence was of mixed quality, but unfavourable for the use of manual muscle testing, skin conductance, surface electromyography and skin temperature measurement.ConclusionsA considerable range of methods is in use for determining where in the spine to administer spinal manipulation. The currently published evidence falls across a spectrum ranging from strongly favourable to strongly unfavourable in regard to using these methods. In general, the stronger and more favourable evidence is for those procedures which take a direct measure of the presumptive site of care– methods involving pain provocation upon palpation or localized tissue examination. Procedures which involve some indirect assessment for identifying the manipulable lesion of the spine–such as skin conductance or thermography–tend not to be supported by the available evidence.

The effect of spinal manipulative therapy on experimentally induced pain: a systematic literature review

BackgroundAlthough there is evidence that spinal manipulative therapy (SMT) can reduce pain, the mechanisms involved are not well established. There is a need to review the scientific literature to establish the evidence-base for the reduction of pain following SMT.ObjectivesTo determine if SMT can reduce experimentally induced pain, and if so, if the effect is i) only at the level of the treated spinal segment, ii) broader but in the same general region as SMT is performed, or iii) systemic.DesignA systematic critical literature review.MethodsA systematic search was performed for experimental studies on healthy volunteers and people without chronic syndromes, in which the immediate effect of SMT was tested. Articles selected were reviewed blindly by two authors. A summary quality score was calculated to indicate level of manuscript quality. Outcome was considered positive if the pain-reducing effect was statistically significant. Separate evidence tables were constructed with information relevant to each research question. Results were interpreted taking into account their manuscript quality.ResultsTwenty-two articles were included, describing 43 experiments, primarily on pain produced by pressure (n = 27) or temperature (n = 9). Their quality was generally moderate. A hypoalgesic effect was shown in 19/27 experiments on pressure pain, produced by pressure in 3/9 on pain produced by temperature and in 6/7 tests on pain induced by other measures. Second pain provoked by temperature seems to respond to SMT but not first pain. Most studies revealed a local or regional hypoalgesic effect whereas a systematic effect was unclear. Manipulation of a “restricted motion segment” (“manipulable lesion”) seemed not to be essential to analgesia. In relation to outcome, there was no discernible difference between studies with higher vs. lower quality scores.ConclusionsThese results indicate that SMT has a direct local/regional hypoalgesic effect on experimental pain for some types of stimuli. Further research is needed to determine i) if there is also a systemic effect, ii) the exact mechanisms by which SMT attenuates pain, and iii) whether this response is clinically significant.

Arterial tonometry in the measurement of the effects of innocuous mechanical stimulation of the neck on heart rate and blood pressure.

Arterial tonometry was used to continuously monitor the effects on heart rate and blood pressure of a series of innocuous mechanical stimuli applied to the neck in conscious humans. The stimuli used were derived from procedures commonly employed in clinical examination and physical therapy of the neck. In alert subjects, the stimuli used generally caused small and sometimes statistically significant decreases in heart rate, systolic pressure and diastolic pressure. In alert subjects, statistically significant decreases in systolic and diastolic pressure were particularly associated with stimuli which involved full rotation of the neck. In the course of the prolonged series of stimuli, some subjects slept or reported being on the verge of sleep. In these subjects, the same stimuli produced mixed effects on heart rate and increases in systolic and diastolic pressure which were significantly different from the effects obtained in fully alert subjects.

The effect of spinal manipulative therapy on spinal range of motion: a systematic literature review.

BackgroundSpinal manipulative therapy (SMT) has been shown to have an effect on spine-related pain, both clinically and in experimentally induced pain. However, it is unclear if it has an immediate noticeable biomechanical effect on spinal motion that can be measured in terms of an increased range of motion (ROM).ObjectiveTo assess the quality of the literature and to determine whether or not SMT is associated with an immediate increase in ROM.DesignA systematic critical literature review.MethodSystematic searches were performed in Pubmed, the Cochrane Library and EMBASE using terms relating to manipulation, movement and the spine. Selection of articles was made according to specific criteria by two independent reviewers. Two checklists were created based on the needs of the present review. Articles were independently reviewed by two reviewers. Articles were given quality scores and the data synthesized for each region treated in the literature. Findings were summarized in tables and reported in a narrative fashion.ResultsFifteen articles were retained reporting on experiments on the neck, lumbar spine, hip and jaw. The mean quality score was 71/100 (ranges 33/100 - 92/100). A positive effect of SMT was reported in both studies where mouth opening was assessed after cervical manipulation. In five of the nine studies on cervical ROM a positive effect was reported, whereas the remaining four studies did not show improvement. None of the three studies of the lumbar spine showed an effect of SMT on lumbar ROMs and one study of sacroiliac manipulation reported no effect on the ROM of the hip joint.In relation to the quality score, the seven highest ranked studies, showed significant positive effects of SMT on ROM. Continuing down the list, the other studies reported no significant differences in the outcomes between groups.ConclusionSMT seems sometimes to have a small effect on ROM, at least in the cervical spine. Further research should concentrate on areas of the spine that have the potential of actually improving to such a degree that a change can be easily uncovered.

Visceral responses to spinal manipulation

While spinal manipulation is widely seen as a reasonable treatment option for biomechanical disorders of the spine, such as neck pain and low back pain, the use of spinal manipulation to treat non-musculoskeletal complaints remains controversial. This controversy is due in part to the perception that there is no robust neurobiological rationale to justify using a biomechanical treatment of the spine to address a disorder of visceral function. This paper therefore looks at the physiological evidence that spinal manipulation can impact visceral function. A structured search was conducted, using PubMed and the Index to Chiropractic Literature, to construct of corpus of primary data studies in healthy human subjects of the effects of spinal manipulation on visceral function. The corpus of literature is not large, and the greatest number of papers concerns cardiovascular function. Authors often attribute visceral effects of spinal manipulation to somato-autonomic reflexes. While this is not unreasonable, little attention is paid to alternative mechanisms such as somato-humoural pathways. Thus, while the literature confirms that mechanical stimulation of the spine modulates some organ functions in some cohorts, a comprehensive neurobiological rationale for this general phenomenon has yet to appear.

Responses of dorsal spinal cord blood flow to innocuous cutaneous stimulation in anesthetized rats

In urethane-anesthetized, artificially-ventilated rats, alterations in dorsal spinal cord blood flow (SCBF) were measured with a laser Doppler flowmeter in response to innocuous mechanical cutaneous stimulation. SCBF recorded at the T12-L1 level increased with brushing of the ipsilateral, but not contralateral, upper back, lower back or proximal hindlimb. Brushing of the forepaw, proximal forelimb or hindpaw had no effect on T12-L1 SCBF. SCBF recorded at the L4-6 level increased with brushing of the ipsilateral, but not contralateral, proximal hindlimb and hindpaw. Brushing of the forepaw, proximal forelimb, upper back or lower back had no effect on SCBF at the L4-6 level. None of these brushing stimuli produced significant changes in systemic arterial blood pressure or heart rate. Pretreatment with phenoxybenzamine, an alpha adrenoceptor blocking agent, resulted in a small but statistically significant attenuation in the response of SCBF to brushing. However, pretreatment with propranolol, a beta adrenoceptor blocking agent, or atropine, a muscarinic cholinergic receptor blocking agent, produced no such effect. These results indicate that innocuous mechanical cutaneous input can produce a segmentally-organized increase in regional SCBF, which may be mediated in part, by alpha adrenergic receptors.

Influence of innocuous cervical vertebral movement on the efferent innervation of the adrenal gland in the rat

In general, in central nervous system intact anesthetized animals, adrenal sympathetic efferent nerve activity and catecholamine secretion increase in response to noxious somatic stimulation, and decrease in response to innocuous somatic stimulation. In anesthetized rats, noxious chemical stimulation of the thoracic and lumbar interspinous tissues is associated with large increases in adrenal sympathetic efferent nerve activity and catecholamine secretion, with a clear segmental organization to the reflex apparent in spinalized animals. However, the adrenal sympathetic nerve responses to mechanical stimulation in the form of pressure applied laterally to the lower thoracic and lower lumbar vertebrae do not display segmental organization, and the depressor response is more characteristic of responses to innocuous somatic stimulation despite the use of large forces (up to 3.0 kg). Therefore, we sought to determine whether innocuous movements of the mechanoreceptor-rich deep tissues of the neck modulate the sympathetic outflow to the adrenal gland. We performed experiments in 14 anaesthetised (Urethane 1 g/kg and Chloralose 0.1 g/kg) adult rats. Rats were intubated and breathed spontaneously. A computer driven small animal manipulator was used to impose ramp and hold rotational displacements (12 degrees /s, hold duration 2 s) of the 2nd cervical vertebra (range 2-30 degrees ) while recording multi-unit activity from sympathetic nerves innervating the adrenal gland. While noxious forepaw pinch elicited an increase in sympathetic nerve activity to the adrenal gland, there was no significant change in sympathetic nerve activity with small (2 degrees or 6 degrees ) rotations. Significant changes (P<0.05) in sympathetic activity were observed in only 7% (n=21) of all trials at larger displacements (12 degrees , 20 degrees , 25 degrees , 30 degrees n=287 trials). Our data suggest that although noxious stimuli may modulate sympathetic outflow, it is rare for afferents signalling innocuous cervical vertebral movements to modulate sympathetic nerves innervating the adrenal gland.

Contribution of supraspinal and spinal structures to the responses of dorsal spinal cord blood flow to innocuous cutaneous brushing in rats.

Responses of dorsal spinal cord blood flow (SCBF) to innocuous mechanical cutaneous stimulation were investigated in anesthetized central nervous system intact (CNS-intact) and C2 spinalized rats. SCBF was recorded at the L4-L6 level with a laser Doppler flowmeter. SCBF increased with brushing of the ipsilateral proximal hindlimb and hindpaw, and there were no significant differences in the magnitudes of the responses in CNS-intact and spinalized animals. Brushing of the lower back had no effect on SCBF at the L4-L6 level in either cohort. Brushing stimulation produced no significant changes in systemic arterial blood pressure. The responses of SCBF to brushing in CNS-intact animals were diminished by pretreatment with phenoxybenzamine, an alpha-adrenoceptor blocking agent, but no such effects were seen in spinalized animals. These results indicate that innocuous mechanical cutaneous input can produce a segmentally-organized increase in regional SCBF, and that the responses are modulated, in part at least, by alpha-adrenergic receptors via supraspinal structures.

Cerebrospinal Fluid Pressure Response to Upper Cervical Vertebral Motion and Displacement in the Anesthetized Rat

OBJECTIVE This study examined whether aligned or off-axis (subluxated) static and dynamic vertebral displacement within normal physiological ranges modulated cerebrospinal fluid pressure (CSF) as is considered to occur by some chiropractic theories. METHODS Cerebrospinal fluid pressure pressure was measured via a subarachnoid catheter implanted at the lumbar level in 12 anesthetized adult male Wistar rats. A computer-driven manipulator was used to impose 3 motion patterns on the C2 vertebra: (i) dynamic oscillatory displacement (24 degrees peak-to-peak 1.0 and 2.0 Hz), (ii) static rotary (ramp 20 degrees at 10 degrees per second and hold for 4 minutes) displacement about both the normal and an offset axis of rotation, and (iii) a spinal manipulative thrust displacement (200 degrees per second; 12 degrees peak-to-peak). RESULTS The CSF pressure at rest for all rats ranged from 4.5 to 9.1 mm Hg, with a mean (+/- SD) of 6.3 +/- 1.4 mm Hg. Of the imposed movements, only an offset ramp and hold displacement resulted in a significant (P < .05) difference between the CSF pressure before (6.1 +/- 0.7 mm Hg) and during the imposed movement (6.6 +/- 0.7 mm Hg). None of the interventions were associated with significant changes in the powers of the principal peaks of the CSF pressure power spectrum. CONCLUSIONS The results of this study suggest that static or dynamic displacement of an upper cervical vertebra within the limits of tissue integrity do not induce physiologically important changes in absolute CSF pressure or pressure dynamics in anesthetized rats.