Abstract
Introduction: The autonomic nervous system (ANS) and hypothalamic pituitary adrenal-axis (HPA-axis), part of the endocrine system, comprise the peripheral stress response. The stress response functions to maintain homeostasis in response to physical, physiological, or psychological stressors. Dysfunction of the stress response may present as altered baseline levels or reactivity in response to stressors. A dysfunctional stress response may be part of the pathophysiology underlying the persistence and maintenance of persistent post-concussion symptoms (PPCS). Manual therapy is an intervention that can modulate the stress response. Manual therapy has also been shown to differentially modulate the stress response in healthy males depending on whether the upper or lower cervical spine is mobilised. No study has investigated whether cervical spine mobilisations can differentially modulate the stress response in individuals with a dysfunctional stress response, such as PPCS.
Aim: The purpose of this trial is to investigate whether mobilisation of the upper or lower cervical spine elicits different responses of the ANS and HPA-axis in males with PPCS by comparing (1) HPA-axis response measured with salivary cortisol (sCOR) and (2) the ANS response measured with heart rate variability (HRV). Cortisol is the primary stress hormone and end- product of the HPA-axis, and HRV is a proxy measure of ANS activity, specifically the parasympathetic nervous system (PSNS).
Methods: This trial employed a randomised, controlled, parallel design. The primary outcome was sCOR concentration. The secondary outcome was the HRV metric, rMSSD, measured with a smartphone application. Nineteen males diagnosed with PPCS, aged 19-35 years, were included. Participants were randomly assigned at a 1-1 ratio with a block length of six into either intervention group: upper (n=10) or lower (n = 9) cervical spine mobilisation. Each outcome was collected at different time points, pre-and post-intervention. Under controlled conditions, the same operator performed all interventions in the same location. Statistical analyses were performed using the Friedman’s Two-Way ANOVA, Mann-Whitney U test, and Wilcoxon Signed Rank Test.
Results: Thirty minutes following lower cervical spine mobilisations, there was a statistically significant within-group reduction in SCOR concentration. Thirty minutes following upper cervical spine mobilisations, there was a statistically significant increase in rMSSD. The night following the intervention, there was a non-significant increase in SCOR concentration tollowing lower cervical spine mobilisation and a non-significant decrease in SCOR concentration following upper cervical spine mobilisation.
Conclusion: Lower cervical spine mobilisations led to a reduction in HPA-axis activity, and upper cervical spine mobilisations led to an increase in PSNS activity 30 min following the intervention. Although non-significant, a differential response to cervical spine mobilisations was shown the night following the intervention, with lower cervical spine mobilisation increasing and upper cervical spine mobilisation decreasing HPA-axis activity.
Implications: The results of this trial provide preliminary evidence for cervical spine mobilisations to differentially modulate the stress response at specific time points. Understanding the mechanisms of effect of cervical spine mobilisations and relating them to the underlying pathophysiology of PPCS provides a novel rationale for using cervical spine mobilisations to rehabilitate individuals with PPCS.