Design: A pre- post-test study design. Setting: An acute laboratory-based study that examined the effect of application of a brief mechanical stimulus (simulating a chiropractic adjustment using an Activator® Instrument) to the neck on cardiac autonomic nervous and cardiovascular function.
Participants: Eleven (11) young healthy adults completed this study. Intervention: A single mechanical impulse (“sham” or “authentic” manipulation procedure) was applied to the neck.
Main Outcome Measures: Heart rate (HR), heart rate variability (HRV) and non-invasive beat-to-beat blood pressure (BP) were measured.
Results: There were significant reductions in BP after application of the mechanical stimulus in the supine posture (p < .05). Particularly, the reductions peaked at 20 sec post-stimulation. Changes in HR and HRV parameters, however, were not significant in either supine or sitting posture (p > .05). Also there were no significant differences in responses between authentic and sham manipulation procedures.
Conclusion: Our results showed that a mechanical stimulus applied to the upper cervical region is capable of acutely influencing cardiovascular function in young adults. The sham spinal manipulative procedure chosen for this study appeared to be contaminated with unspecified factors that had interventional effects, or the response might be due to an arousal reaction. This issue is being addressed in further investigations.
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