Research Review By Dr. Joshua Plener©

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Date Posted:

May 2021

Review Title:

Vertebral Artery Blood Flow & Chiropractic Procedures – Research Updates

Studies Reviewed:

  1. Leenaerts L, Molenaar W & Cattrysse E. Changes in Vertebral Arterial Blood Flow During Premanipulative Tests in Participants With Upper Cervical Spine Motion Restriction. Journal of Manipulative and Physiological Therapeutics 2020; 43: 134-43.
  2. Yelverton C, Wood J, Petersen D & Peterson C. Changes in Vertebral Artery Blood Flow in Different Head Positions and Post-Cervical Manipulative Therapy. Journal of Manipulative and Physiological Therapeutics 2020; 43: 144-51.
  3. Mahmoud W, Kamel E, Mahmoud M & Ahmed AS. The Hemodynamic Response of the Vertebral Artery to 3 Time Durations of the Static Stretching Exercise in the End Position of Contralateral Cervical Rotation. Journal of Manipulative and Physiological Therapeutics 2020; 43: 152-9.

Background Information:

Common treatments for neck pain include manual therapy interventions such as spinal manipulation and stretching. As approximately 50% of cervical rotation occurs at the atlantoaxial joint (1, 2), it has been suggested that there is the possibility of a reduction of vertebral artery blood flow during cervical spine manipulation or other manual therapy procedures (3-5). The possible mechanism contributing to this includes stretching of the contralateral vertebral artery and compression of the ipsilateral vertebral artery over the bony landmarks in the region.

In the current literature, some studies have found a decrease in blood flow velocity in the contralateral vertebral artery associated with cervical spine rotation (6), while other studies have suggested that the natural tortuosity of the vertebral artery prevents these distortions from occurring (7, 8). Furthermore, it has been reported that the vertebral artery strain during spinal manipulation is lower than the strain induced during range of motion (ROM) testing, thereby decreasing the likelihood of a disruption of the vertebral artery during spinal manipulation. One limitation of the current literature is that studies completed to date have mostly examined healthy participants, not taking into account individuals with upper cervical spinal restrictions, or even neck pain (the very patients we see in practice!) (6). These restrictions may further reduce the potential for compression or stretching forces of the vertebral artery due to a reduction in the available range of motion (6).

Static stretching is another common treatment approach used for neck pain that has shown beneficial clinical results. It has been suggested that sustained end-range cervical rotation for 60 seconds or longer should be avoided, in order to help prevent any potential compromise of the vertebral artery (6, 9). Similar to spinal manipulation, studies using pulsed-wave Doppler sonography have produced contradicting results, with some studies showing significant reduction in the contralateral vertebral artery blood flow, while others found no significant reduction during these maneuvers (10-12). There is minimal literature assessing the duration of stretching and its impact on blood hemodynamics.

The aim of this Research Review is to briefly summarize three studies investigating the hemodynamics of the vertebral arteries during manual therapy set-ups and procedures. The purpose of the first study by Leenaerts et al. was to measure changes in blood flow velocity and volume flow rate in the contralateral vertebral artery during end-range rotation and pre-manipulative hold, and to compare these measurements between participants with and without C1-2 range of motion restriction. The purpose of the second study by Yelverton et al. was to examine the blood flow through the vertebral arteries during different rotary head positions and post-cervical spinal manipulation. The aim of the third study by Mahmoud et al. was to investigate the effect of sustained end-range cervical rotation using 3 different time durations.

Pertinent Results:

Leenaerts L, Molenaar W & Cattrysse E. Changes in Vertebral Arterial Blood Flow During Premanipulative Tests in Participants With Upper Cervical Spine Motion Restriction. JMPT 2020; 43: 134-43.

Thirty participants were included in this study, which found no significant differences between the test positions and the presence or absence of C1-2 range of motion restrictions for peak systolic velocity and volume flow rate in the vertebral arteries. They found that on the contralateral left vertebral artery in end range rotation, peak systolic velocity decreased significantly compared with the neutral position (p = 0.49), and on the contralateral left vertebral artery with the cervical spine in pre-manipulative hold, peak systolic velocity, time-averaged peak velocity and volume flow rate decreased significantly compared with neutral position. However, there were no significant differences between the test position and C1-2 rotational range of motion restriction for the above parameters.

Yelverton C, Wood J, Petersen D & Peterson C. Changes in Vertebral Artery Blood Flow in Different Head Positions and Post-Cervical Manipulative Therapy. JMPT 2020; 43: 144-51.

25 subjects participated in the study between 20-30 years of age. There were no statistically significant differences for peak systolic flow velocity, end diastolic flow velocity, and mean flow velocity across the 4 head and neck positions (neutral, 45 degrees of rotation, maximum rotation and neutral post-manipulation). In addition, there were no statistically significant differences for vessel diameter and flow rate across the 4 head and neck positions.

Mahmoud W, Kamel E, Mahmoud M & Ahmed AS. The Hemodynamic Response of the Vertebral Artery to 3 Time Durations of the Static Stretching Exercise in the End Position of Contralateral Cervical Rotation. JMPT 2020; 43: 152-9.

The study found that a period of 60 seconds of sustained end-range cervical rotation had the highest percentage of change in peak systolic volume, end diastolic volume, and resistive index in the contralateral vertebral artery. Furthermore, as expected, a period of 10 seconds of sustained rotation had the lowest effect on hemodynamics of the vertebral arteries.

Clinical Application & Conclusions:

Overall, these studies support the notion that manual therapy interventions and maneuvers are safe with regards to the blood flow in the vertebral arteries.

Leenaerts et al. demonstrated that despite a change in vertebral artery hemodynamics as compared to neutral position, there were no significant differences between participants with and without a C1-2 dysfunction.

Yelverton et al. demonstrated that across the 4 head positions, hemodynamic blood flow parameters were not significantly different. In fact, the authors found that at post manipulation, the end diastolic flow velocity increased. This increase in blood flow and vessel diameter post manipulation could indicate that the natural tortuosity of the vessel prevents the distortions to the blood flow that some have proposed (13). Research into this concept is limited, and therefore further research is required to better understand this potential mechanism.

Finally, Mahmoud et al. found a significant effect on blood flow velocities on the contralateral vertebral artery regardless of the period used, with greater reductions the longer the time was held. However, despite temporary alterations in hemodynamics during the stretching exercises, there were no clinical symptoms reported. A previous review concluded that the absence of symptoms during cervical spine rotation may indicate enough cerebral collateral circulation to counter act any potential temporary decrease of flow velocity occurring as a result of compression or stretching of the contralateral vertebral artery. As this current study found a similar reduction of peak systolic volume for both the 30 and 60 seconds of sustained end range rotation, therapists treating patients who may be at risk for vertebral artery insufficiency, may wish to only consider conducting stretches involving cervical end range rotation at 30 seconds or less (14).

Study Methods:

Leenaerts L, Molenaar W & Cattrysse E. Changes in Vertebral Arterial Blood Flow During Premanipulative Tests in Participants With Upper Cervical Spine Motion Restriction. JMPT 2020; 43: 134-43.
 
Participants were recruited who were 18 to 65 years of age and assessed with the flexion-rotation test to identify if a C1-2 restriction was present (15). Ultrasound measurements were taken with the participants supine and the cervical spine in neutral position, as well as 4 different test postures consisting of maximum passive rotation to the right and to the left and pre-manipulative hold with passive rotation to the right and to the left. Pre-manipulative hold was performed by placing the C1-2 joint into side flexion combined with contralateral rotation with digital pressure on C1-2, just short of a manipulative thrust. A general linear model of repeated measures was used with neutral and test postures as the within-participants factor, and the C1-C2 dysfunction, regional cervical left and right rotation greater than 69 degrees, vertebral artery side, sex, age older than 50 and NDI score higher than 4 as the between-participants factors.

Yelverton C, Wood J, Petersen D & Peterson C. Changes in Vertebral Artery Blood Flow in Different Head Positions and Post-Cervical Manipulative Therapy. JMPT 2020; 43: 144-51.

Twenty-five healthy participants between 20-30 years of age presenting with an upper cervical rotary restriction determined by motion palpation were included in the study. Following all 25 participants being screened for at least one upper cervical spine restriction, the technician placed the transducer head of the Doppler ultrasound onto the upper portion of the vertebral artery on the contralateral side of contact as close to C1-2 as possible. Each participant was positioned in 4 head positions consisting of neutral, 45 degrees of rotation, maximum rotation and neutral post-manipulation. At each position the peak systolic flow velocity, end diastolic flow velocity, mean flow velocity, vessel diameter and flow rate hemodynamic parameters were recorded. The hemodynamic variables across all 4 cervical positions according to the level manipulated were assessed.

Mahmoud W, Kamel E, Mahmoud M & Ahmed AS. The Hemodynamic Response of the Vertebral Artery to 3 Time Durations of the Static Stretching Exercise in the End Position of Contralateral Cervical Rotation. JMPT 2020; 43: 152-9.

Thirty asymptomatic male participants between 20-50 years of age were included in this study. Participants were required to actively rotate their neck to at least 45 degrees, regardless of a history of neck pain or injury. Both vertebral arteries were scanned in neutral positions to ensure no significant differences between the 2 sides were present. The participants were asked to actively rotate their neck until maximum rotation was reached, allowing the therapist to maintain the end range cervical rotation. Vertebral artery scans were recorded at 3 time points, consisting of the cervical spine in the position of sustained end range cervical rotation for 10 seconds, 30 seconds and 60 seconds. Between each recording, the cervical spine was returned to neutral position for 60 seconds. Peak systolic velocity and end diastolic velocity were measured in centimetres per second while the resistance index was measured as a ratio. A paired t-test was used to determine any variations between the 2 sides of the vertebral arteries in the neutral position of the cervical spine. A one-way reported measures analysis of variance was used to assess significant effects determined by the neutral position, 10 seconds, 30 seconds and 60 seconds of cervical rotation.

Study Strengths / Weaknesses:

Strengths:
  • These three studies add to the body of literature regarding vertebral artery hemodynamic properties during manual therapy.
  • These studies help fill current knowledge gaps in the literature such as the effect of upper cervical dysfunction on the vertebral arteries.
Weaknesses:
  • The accuracy of the Doppler ultrasound is dependent on the user/operator.
  • Small sample sizes were used in each study, therefore the generalizability of the findings may be questioned.
  • Locating the vertebral artery is difficult and may require measuring below the C1-2 region.

Additional References:

  1. Mitchell J. Vertebral artery blood flow velocity changes associated with cervical spine rotation: a meta-analysis of the evidence with implications for professional practice. J Manipulative Physiol Ther 2009; 17(1): 46-57.
  2. Arnold C, Bourassa R, Langer T, et al. Doppler studies evaluating the effect of a physical therapy screening protocol on vertebral artery blood flow. Man Ther 2004; 9(1): 13-21.
  3. Haldeman S, Carey P, Townsend M, et al. Arterial dissections following cervical manipulation: the chiropractic experience. Can Med Assoc J 2001; 165(7): 905-906.
  4. Herzog W, Leonard TR, Symons B, et al. Vertebral artery strains during high-speed, low-amplitude cervical spinal manipulation. J Electromyogr Kinesiol 2012; 22(5): 740-746.
  5. Cassidy JD, Boyle E, Cote P. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case-crossover study. J Manipulative Physiol Ther 2009; 32(2 suppl 1): S201-S208.
  6. Mitchell J. Vertebral artery blood flow velocity changes associated with cervical spine rotation: a meta-analysis of the evidence with implications for professional practice. J Man Manip Ther 2009; 17(1): 46-57.
  7. Haynes M, Milne N. Color duplex sonographic findings in human vertebral arteries during cervical rotation. J Clin Ultrasound 2001; 29(1): 14-24.
  8. Thiel HW. Gross morphology and pathoanatomy of the vertebral arteries. J Manipulative Physiol Ther 1991; 14(2): 133-141.
  9. Thomas LC, Rivett DA, Bateman G, et al. Effect of selected manual therapy interventions for mechanical neck pain on vertebral and internal carotid arterial blood flow and cerebral inflow. Phys Ther 2013; 93(11): 1563-1574.
  10. Rossitti S, Volkmann R. Changes of blood flow velocity indicating mechanical compression of the vertebral arteries during rotation of the head in the normal human measured with transcranial Doppler sonography. Arquivos Neuropsiquiatria 1995; 53(1): 26-33.
  11. Licht PB, Christensen HW, Hojgaard P, et al. Triplex ultrasound of vertebral artery flow during cervical rotation. J Manipulative Physiol Ther 1998; 21(1): 27-31.
  12. Mitchell J, Keene D, Dyson C, et al. Is cervical spine rotation, as used in the standard vertebrobasilar insufficiency test, associated with a measureable change in intracranial vertebral artery blood flow? Man Ther 2004; 9(4): 220-227.
  13. Haynes M, Milne N. Color duplex sonographic findings in human vertebral arteries during cervical rotation. J Clin Ultrasound 2001; 29(1): 14-24.
  14. Kerry R, Taylor AJ. Cervical arterial dysfunction assessment and manual therapy. Man Ther 2006; 11(4): 243-253.
  15. Hall TM, Robinson KW, Fujinawa O, et al. Intertester reliability and diagnostic validity of the cervical flexion-rotation test. J Manipulative Physiol Ther 2008; 31(4): 293-300.