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Lascurain-Aguirrebeña I1,2, Newham DJ3, Galindez-Ibarbengoetxeac X1, Casado-Zumeta X4, Lertxundi A5, Critchley DJ2
1University of the Basque Country (UPV/EHU), Physiology, Leioa, Spain, 2Kings College London, Division of Health and Social Care Research, Faculty of Life Sciences & Medicine, London, United Kingdom, 3Kings College London, Centre of Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, London, United Kingdom, 4Atlas Fisioterapia, Donostia, Spain, 5University of the Basque Country (UPV/EHU), Leioa, Spain
Background: Activation of the brain's dorsal periaqueductal gray (dPAG) may be responsible for the hypoalgesic effects of mobilisations. Electrical stimulation in animals produces analgesia and sympathoexcitation, and mobilisations cause increased sympathetic nervous system (SNS) activity, in some cases concurrently with hypoalgesia, although this has mostly been tested in asymptomatic people. Evidence of an association between symptomatic change and sympathoexcitation is very limited. Previous studies have not separated the different tonic and phasic contributors to the signal, which limits understanding of the effects.
Purpose: To investigate the effects of cervical mobilisations on sympathoexcitation by skin conductance (SC) in participants with neck pain using separated tonic and phasic SC activity analysis; and, to explore the relationship between symptomatic improvement and changes in SC.
Methods: In a double blind randomised controlled trial 40 participants with mechanical neck pain (20-69 years; 25 female; 34 chronic) were randomly allocated to either cervical mobilisations or placebo (same head position and hand contact but no oscillation). SC was measured in the fingers before, during, and after intervention. Participants were classified as responders if they reported to be at least “somewhat better” on the global rating of change scale. Participant blinding was assessed with a treatment credibility scale.
Results: 65% and 30% of those in the mobilisation and placebo group respectively were classified as responders (adjusted odds ratio: 4.33; p=0.03). During the intervention mobilisations demonstrated greater change (p0.05) in skin conductance level (SCL) (41% vs 6%) and frequency of skin conductance responses (SCR) (0.6 vs 0.2 per minute), and greater time to 50% of all SCRs (4.5 mins vs 2.2 mins). There were no differences in the maximum amplitude SCR. There were no differences between groups from during to after the intervention. There was no association between any SC changes and symptomatic improvement. Mobilisations and placebo were equally credible. Regardless of intervention, participants with a higher SCR frequency at baseline were more likely to be classified as responders following the intervention (odds ratio: 4.97; p=0.037).
Conclusion(s): Mobilisations cause sympathoexcitation, however changes are most likely produced by an orienting response where the presentation of novel and significant stimuli causes increased skin conductance level and frequency of SCRs. Absence of differences in maximum amplitude SCR suggests that both interventions provide a similar initial sympathoexcitatory stimulation. However, significant differences in the frequency of SCRs during intervention suggests that the ever-changing stimuli provided by mobilisations e.g. variation in force, are capable of providing a novel stimulus for a longer duration. This is further supported by the greater time to 50% of all SCRs observed with mobilisations suggesting lower habituation to the stimulus. SCR frequency has previously been associated with different personality traits and emotional states; it is possible that these may affect the placebo effect.
Implications: this study provides an alternative explanation for the sympathoexcitatory changes observed with mobilisations. Concurrent sympathoexcitatory and hypoalgesic changes may not have a causal relationship but represent the occurrence of two parallel processes. Sympathoexcitation may not be a maker of dPAG involvement in mobilisations.
Keywords: neck pain, mobilisations, sympathetic nervous system
Funding acknowledgements: None.
Purpose: To investigate the effects of cervical mobilisations on sympathoexcitation by skin conductance (SC) in participants with neck pain using separated tonic and phasic SC activity analysis; and, to explore the relationship between symptomatic improvement and changes in SC.
Methods: In a double blind randomised controlled trial 40 participants with mechanical neck pain (20-69 years; 25 female; 34 chronic) were randomly allocated to either cervical mobilisations or placebo (same head position and hand contact but no oscillation). SC was measured in the fingers before, during, and after intervention. Participants were classified as responders if they reported to be at least “somewhat better” on the global rating of change scale. Participant blinding was assessed with a treatment credibility scale.
Results: 65% and 30% of those in the mobilisation and placebo group respectively were classified as responders (adjusted odds ratio: 4.33; p=0.03). During the intervention mobilisations demonstrated greater change (p0.05) in skin conductance level (SCL) (41% vs 6%) and frequency of skin conductance responses (SCR) (0.6 vs 0.2 per minute), and greater time to 50% of all SCRs (4.5 mins vs 2.2 mins). There were no differences in the maximum amplitude SCR. There were no differences between groups from during to after the intervention. There was no association between any SC changes and symptomatic improvement. Mobilisations and placebo were equally credible. Regardless of intervention, participants with a higher SCR frequency at baseline were more likely to be classified as responders following the intervention (odds ratio: 4.97; p=0.037).
Conclusion(s): Mobilisations cause sympathoexcitation, however changes are most likely produced by an orienting response where the presentation of novel and significant stimuli causes increased skin conductance level and frequency of SCRs. Absence of differences in maximum amplitude SCR suggests that both interventions provide a similar initial sympathoexcitatory stimulation. However, significant differences in the frequency of SCRs during intervention suggests that the ever-changing stimuli provided by mobilisations e.g. variation in force, are capable of providing a novel stimulus for a longer duration. This is further supported by the greater time to 50% of all SCRs observed with mobilisations suggesting lower habituation to the stimulus. SCR frequency has previously been associated with different personality traits and emotional states; it is possible that these may affect the placebo effect.
Implications: this study provides an alternative explanation for the sympathoexcitatory changes observed with mobilisations. Concurrent sympathoexcitatory and hypoalgesic changes may not have a causal relationship but represent the occurrence of two parallel processes. Sympathoexcitation may not be a maker of dPAG involvement in mobilisations.
Keywords: neck pain, mobilisations, sympathetic nervous system
Funding acknowledgements: None.
Topic: Musculoskeletal: spine; Musculoskeletal
Ethics approval required: Yes
Institution: Univerisity of the Basque Country
Ethics committee: CEISH
Ethics number: M10/2016/095.
All authors, affiliations and abstracts have been published as submitted.
