Background: The notion that spinal manipulation has an effect upon visceral function has existed since the early history of the chiropractic profession. Patients have reported incidental changes such as improved function of the respiratory and digestive systems. Over the past two decades the use of Heart Rate Variability to assess sympathovagal balance has expanded from the fields of cardiology and obstetrics to a broad array of disciplines, including, but not limited to, acupuncture, psychology, exercise physiology, and manual therapy. The effect on the autonomic nervous system may be a factor in the therapeutic effects of these varied interventions.
Objective: The purpose of this paper is to systematically review all peer-reviewed, published studies regarding the use of Heart Rate Variability to assess changes in the autonomic nervous system resulting from spinal manipulative therapy.
Data Sources: Several online databases, including Medline, MANTIS, OVID, ICL, CINHAL, and Cochrane were searched using keywords spinal manipulation and/or chiropractic manipulation, combined with heart rate, heart rate variability, autonomic nervous system. Articles from 1996 forward were included.
Study Selection: English and non-English articles were included in this review. Randomized clinical trials and prospective observational trials on heart rate variability and spinal manipulation were included. No unpublished material or non-peer reviewed literature were included in this research.
Data Extraction: Each of the studies was critically reviewed. The following were extracted from each paper and entered into a Microsoft Excel spreadsheet: author; study design; sample size, intervention, outcomes.
Data Synthesis: A critical evaluation list of 20 methodological items and their operational definitions was
used to assess each paper. This evaluation list is based on work done by Bronfort and colleagues, as well as by Owen. A validity score resulting from the 20-point critical evaluation was calculated for each paper.
Results: Nine papers met criteria for inclusion. One of the studies was a randomized clinical trial, and eight of the nine studies were prospective observational studies. The validity scores ranged from 27% to 83%.
Conclusion: There is evidence demonstrating an effect of spinal manipulation on sympathovagal balance. There is also evidence supporting a regional effect of manipulation of the thoracic and lumbar spine. This review also revealed the need for a rigorous protocol to be followed in order to obtain valid recordings.
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