Chiropractic adjustments of the upper neck- shown to lower blood pressure by 27 overall points (more powerful on average than 2 doses of blood pressure lowering medications) without having prior experience of neck or back pain.

-Journal of Human Hypertension May 2007;21(5):347-52. Epub 2007 Mar 2.

Research proves that chiropractic adjustments directly affect the autonomic nervous system, improving heart rate variability and increasing the heart's ability to recognize and adapt to stressors. 

-Journal of Manipulative and Physiological Therapeutics - May 2006.