The effect of spinal manipulative therapy on heart rate variability and pain in patients with persistent or recurrent neck pain

OBJECTIVE: Persistent or recurrent neck pain is a common reason to seek healthcare. Manual therapy in combination with exercises is recommended by clinical guidelines for this patient group. Autonomic dysregulation with reduced parasympathetic activity, increased sympathetic activity, and impaired conditioned pain modulation is seen in a range of chronic pain conditions such as persistent or recurrent neck pain. An immediate response to spinal manipulative therapy of the autonomic nervous system has been observed, but the evidence is of very low to moderate quality and the underlying mechanisms are unknown. Examining the long-term effect of spinal manipulative therapy on the autonomic nervous system, pain, and disability is thus relevant, and measures of heart rate variability can provide an objective measure of this relationship. The aim of this project was to examine the effects on pain, disability, and heart rate variability of adding spinal manipulative therapy to home stretching exercises over a period of two weeks. Further, an explorative investigation into the relationship between changes in pain and changes in heart rate variability was undertaken. In addition the temporal stability and responsiveness of the conditioned pain modulation measurements was also investigated. METHOD: A randomized controlled clinical trial was carried out in multidisciplinary primary care clinics. One group received home stretching exercises and spinal manipulative therapy, and the other group received home stretching exercises only. The subjective pain experience was investigated by assessing pain intensity (NRS-11) and the affective quality of pain (McGill questionnaire). Neck disability (NDI) and health status (EQ-5D) were also measured. Heart rate variability at rest was measured using a portable heart monitor. CPM was measured using a universal “clamp” from Clas Ohlson and a coldwater bath (0-2 ℃). The subjects received four treatments over two weeks. Linear mixed models were used to investigate the group by time interaction. Multivariate analysis of variance (MANOVA) was used to investigate the temporal stability of the CPM test. The study was approved by the Regional Ethical Review Board (Stockholm) (ref: 2018/2137-31). RESULTS: No statistically significant group effect was found for pain, disability, or any of the heart rate variability indices. No statistically significant association was found between changes in pain (NRS-11) and changes in HRV. The CPM test appears to be moderately stable over time for both subjects who experienced a clinically important difference and those who did not over a two-week treatment period. CONCLUSION: Adding spinal manipulative therapy to a two-week stretching protocol did not significantly improve heart rate variability, pain or disability in this well-controlled RCT. Further investigations found no significant association between treatment response from spinal manipulative therapy and home stretching exercises and HRV over two weeks. Further research on pain, disability and HRV should focus on subjects with higher pain intensity and a longer intervention period. Also, further investigation of the relationship between pain and HRV is warranted. The CPM utilized showed moderate temporal stability for this patient group. Changes in persistent or recurrent neck pain over two weeks were not associated with changes in the CPM test response