Suboccipital Decompression Enhances Heart Rate Variability Indices of Cardiac Control in Healthy Subjects Journal of Alternative and Complementary Medicine 2013, Vol. 19, No. 2, pp. 92–96

Paul D. Giles, DO, MS, Kendi L. Hensel, DO, PhD, Christina F. Pacchia, PhD, MichaelL. Smith, PhD: From the Department of Integrative Physiology, University of NorthTexas Health Science Center. BACKGROUND FROM DAN MURPHY: Heart rate variability (HRV) is the variation in the time interval between heartbeats.It is largely under the control of the autonomic nervous system.The parasympathetic influence lengthens HRV via the release of acetylcholine bythe vagus nerve (slowing the heart rate).The sympathetic influence shortens HRV via the release of epinephrine andnorepinephrine (accelerating the heart rate). Vagal and sympathetic nerve activity constantly interact; under resting conditions,vagal tone prevails. KEY POINTS FROM THIS STUDY: 1) Osteopathic manipulative treatment (OMT) focusing on the upper cervicalspine is theorized to affect the function of the vagus nerve and thereby influencethe parasympathetic branch of the autonomic nervous system. 2) This study was designed to determine the acute effect of upper cervical spinemanipulation on cardiac autonomic control as measured by heart rate variability. Itused 19 healthy, young adult subjects underwent cervical osteopathic manipulationand sham manipulation. Six minutes of electrocardiographic data were collectedbefore and after each intervention, and heart rate variability was assessed. 3) Study exclusion factors included:hypertension, caffeine consumption within 4 hours, tobacco use within 48 hours,history of cardiovascular disease, neuropathic disorders, unexplained episodes ofsyncope, and any musculoskeletal signs/symptoms. 4) The anatomical relationship of the efferent vagus nerve to the musculoskeletal structures at the occiput lends credence to the hypothesis thatosteopathic manipulative treatment at this location, such as suboccipitaldecompression, could affect vagal functions. 5) Previous studies have shown that manual therapies can affect vagal function. 6) Cervical manipulation may have direct effects on the parasympatheticnervous system. 7) Decompression of the occipito-atlantal junction, a technique that focuses ontreating an articular compression between the occiput and the atlas, may improveconditions relating to the path of the vagus as it exits the skull. 8) Because of the proximity of the vagus to the musculoskeletal structures inthe suboccipital region, it is plausible that local inflammation, edema, musclehypertonicity or spasm, or other somatic dysfunctions could cause either a chemicalor compressive effect on the vagus, thereby affecting its optimum function. 9) Since the vagus plays a significant role in the autonomic control of heartrate, it is therefore also plausible that if optimum performance of the vagus isimpeded by dysfunction in the surrounding structures, its ability to contributeeffectively to the autonomic control of heart rate might also be affected. 10) The manipulation protocol involved the treatment of the subjects posteriorcervical musculature by using kneading and stretching. The kneading force wasapplied perpendicular to the long axis of the muscle. The stretching was aseparation of the origin and insertion of a muscle. This soft tissue treatment wasperformed for about 5 minutes. Then occipital-atlas decompression was applied for 2 – 3 minutes by using the index fingers to contact the occiput as near to theoccipital condyles. The sham treatment placed the fingers near the occipitalcondyles, but no tension was applied in any direction, for about 8 minutes. 11) Heart rate variability is used to assess changes in autonomic control of heartrate under a variety of conditions including with manual therapies. Heart ratevariability was measured as an index of autonomic control. 12) The changes in the frequency domain indices of heart rate variability wereconsistent with an enhanced parasympathetic control associated with the OMTtreatment. 13) These data demonstrate that suboccipital decompression, a soft tissuemanipulative technique, can affect indices of heart rate variability. 14) Many forms of manipulative medicine have been theorized to affect theautonomic nervous system, and it has been espoused that this can include bothstimulatory and inhibitory effects on the respective branches of the autonomicnervous system. 15) The data in our study consistently point to an effect of suboccipitaldecompression to moderately enhance parasympathetic control of heart rate and/orshift the sympatho-vagal balance to a more predominant vagal control. These 3effects were associated with a slowing of heart rate accompanying suboccipital decompression. 16) This study shows changes in the heart rate variability indices relating to areduced sympathetic and enhanced parasympathetic control. [Key Point] 17) The suboccipital decompression used in this study caused significant changesconsistent with an enhanced parasympathetic control of heart rate. 18) This study demonstrates that suboccipital manipulative decompression canaffect heart rate variability. This effect is consistent with potential changes in thecontrol of heart by the parasympathetic nervous system. These data support the hypothesis that upper cervical spine manipulation can acutely affect measures ofheart rate variability in healthy individuals. COMMENTS FROM DAN MURPHY The bottom-line conclusion of this study is that upper cervical spine mechanicalfunction is influenced by upper cervical spine manipulation, which in turn influencesthe vagus parasympathetic control of the heart.These authors suggest that the mechanism whereby upper cervical spinalmanipulation influences the vagus nerve and therefore the balance ofparasympathetic and sympathetic control of the heart is mechanical.We have reviewed 2 other articles with the same conclusions (upper cervical spinemechanical function is influenced by upper cervical spine manipulation, which inturn influences the vagus parasympathetic control of the heart), but with a differentmechanism. Their mechanism is that upper cervical spine mechanoreceptorsneurologically fire to the medullary Nucleus Intermedius which then fires to theNucleus Tractus Solitarius (a sensory nucleus of the vagus nerve in the medulla),which in turn influences cardiorespiratory function. Interestingly, both studies favorably mention chiropractic upper cervical adjusting to influence blood pressure: Article Review #13-08 The Neurochemically Diverse Intermedius Nucleus of the Medulla as a Source ofExcitatory and Inhibitory Synaptic Input to the Nucleus Tractus SolitariiThe Journal of Neuroscience; August 1, 2007; 27(31); pp. 8324-8333.Ian J. Edwards, Mark L. Dallas, Sarah L. Poole, Carol J. Milligan, Yuchio Yanagawa,Gabor Szabo, Ferenc Erdelyi, Susan A. Deuchars, and Jim Deuchars Article Review #3-11: The intermedius nucleus of the medulla: A potential site for the integration ofcervical information and the generation of autonomic responses.Journal of Chemical Neuroanatomy; November 2009, 38, pp. 166 – 175.Ian J. Edwards, Susan A. Deuchars, Jim Deuchars