Chiropractic + Naturopathic Doctor

Research Review Corner: June 2014

Shawn Thistle   

Features Research

Study Title: Changes in vertebral artery blood flow following various head positions and cervical spine manipulation

Study Title: Changes in vertebral artery blood flow following various head positions and cervical spine manipulation

Authors: Quesnele J, Triano J, Noseworthy M, Wells G


Publication Information: Journal of Manipulative & Physiological Therapeutics 2014; 37(1): 22-31.

Vertebral artery (VA) dissection leading to vertebrobasilar artery (VBA) stroke is rare in the general population. However, it is an important cause of nonatherosclerotic stroke in young adults.

Exactly what precipitates VBA stroke is unknown, although it has been suggested that there may be an underlying genetic predisposition in some people that can be triggered by various risk factors. One such risk factor is trivial trauma (e.g. unusual head positions, including cervical manipulation). Nevertheless, many VBA strokes occur in the absence of any of the supposed risk factors.

Few studies have investigated the effects of cervical spinal manipulation (CSM) on VA blood flow, and those that have reported inconsistent results, likely due to poor methodology. This milieu casts doubt on whether apparently healthy individuals can actually experience altered cervical blood flow as a result of these maneuvers.

The purpose of this study was to observe VA blood flow after manipulation and various head positions in order to determine the extent head/neck motion interacts with VA blood flow.

Pertinent results
Ten males aged 24 to 30 years participated in the study, all were right-handed. Data collection sessions lasted approximately two hours for each participant and they all completed the full testing protocol.

There appeared to be a small side-to-side difference between ipsilateral and contralateral VA flow and VA velocities, with the contralateral side being lower than the ipsilateral. However, this difference was not statistically significant for either flows (P = .19) or velocities (P = .14). There were no other interactions, nor trends toward differences for any of the other blood flow or velocity variables.

Conclusions, practical applications
Based on this small but pertinent study, and others that have measured blood flow after head movements, practitioners who use manual methods can be reasonably confident there is little or no evidence that various head motions, including CSM, produce significant cerebrovascular hemodynamic effects in the VAs.

Some researchers have suggested the VA theoretically may be stretched and/or compressed during head rotation, but this mechanism was not tested in this study. However, it has been shown in cadaveric studies that strain forces sustained by the VAs during CSM are lower than those associated with physiologic neck rotation.

A recent study by Thomas et al. used very similar methodology to the current one (i.e. they used MRI to evaluate blood-flow during CSM and head positions) and came to nearly the same conclusion. The study investigated the effects of manual therapy interventions for mechanical neck pain on vertebral and internal carotid arterial blood flow, as well as cerebral inflow. They found the average inflow of blood to the brain was not significantly changed by any of the test positions as compared to neutral. Also, there were no flow differences between any of the four arteries in any tested head position. However, they did report that there were large blood flow variations in some individuals.

Two other previous studies have investigated the effects of CSM on VA blood flow in humans, both conducted by Licht et al. One of the studies examined peak velocity in the VA after CSM in a randomized controlled trial that used Doppler ultrasound, whereas the other study used colour-coded duplex. Similar to the current study, they found no change in VA blood flow or peak velocity with different head positions or after CSM. The consistent findings of these studies lend support to the conclusion that blood velocity and flow through the VA was not significantly changed by head rotations or CSM.

It is important to consider that all participants in these studies have been healthy, so the conclusions that a healthy artery should have the capacity to withstand the mechanical stresses of CSM may not apply to persons with weakened arteries. Some evidence has accumulated which indicates that arteries can become weakened due to underlying arteriopathy that renders the artery friable, which can be caused by conditions such as infection, pro-inflammatory factors and connective tissue disorders.

Dr. SHAWN THISTLE is the founder and president of Research Review Service, an online, subscription-based service to help busy practitioners integrate current, relevant, scientific evidence into their practice ( ).

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