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Int J Clin Exp Med 2016;9(1):209-218
www.ijcem.com /ISSN:1940-5901/IJCEM0015739
Original Article
Comparison of atlanto-axial artery hemodynamics
during cervical spine manipulation with doppler
ultrasound in rhesus macaques
Kai-Qi Cui1,3*, Yuan Jiang1,3*, Yuan-Yi Zheng2, Xiao Zheng2, Ze-Sha Ling1,3, Gong-Wei Jia1, Lang Jia1, Wei
Jiang1, Le-Hua Yu1,3
1Department of Rehabilitation Medicine and Physical Therapy, The Second Afliated Hospital of Chongqing Medi-
cal University, Chongqing, P. R. China; 2Department of Ultrasonography, The Second Afliated Hospital of Chongq-
ing Medical University, Chongqing, P. R. China; 3School of Rehabilitation Medicine and Physical Therapy, Chongq-
ing Medical University, Chongqing, P. R. China. *Co-rst authors.
Received September 7, 2015; Accepted November 23, 2015; Epub January 15, 2016; Published January 30,
2016
Abstract: Background: The vulnerability of atlanto-axial vertebral artery (C1-C2 VA) to cervical spine manipulation
(CSM), resulting in compromised blood ow and possible cerebrovascular accident, is well recognized. It needs to
build animal model for further investigate the blood ow changes in the vertebral arteries during cervical spine
manipulation (CSM). Methods: Peak systolic velocity (PSV), end diastolic velocity (EDV), resistance index (RI) and
lumen diameter of bilateral VAs were measured using duplex Doppler ultrasound in 6 healthy rhesus monkeys
with the cervical spine in eight cervical positions used in CSM. Results: The mean PSV and EDV of both VAs were
decreased signicantly in contralateral rotation, extension-ipsilateral and -contralateral rotation, and extension-
ipsilateral and -contralateral rotation with traction (P < 0.05). A signicant increase (P < 0.05) in RIs with left rota-
tion and extension-left rotation-traction was demonstrated in right VA. Doppler waveforms revealed that blood ow
followed a dampened systolic waveform during contralateral rotation and extension-contralateral rotation, and a
near occlusion in combined extension-contralateral rotation with traction. Conclusion: The VA of rhesus monkey is
subjected to forces that are sufcient to reduce blood ow velocity in positions involving in contralateral rotation,
extension-ipsilateral and -contralateral rotations as well as combined extension- rotation with manual traction. The
study of hemodynamics of the vertebral artery in rhesus monkey, which apply to biologic and mechanical research,
is need to further conduct.
Keywords: Atlanto-axial joint, vertebral artery, Doppler ultrasound, rhesus macaques
Introduction
Cervical spine manipulation (CSM) is a thera-
peutic intervention and has increasingly admin-
istrated by physicians, physical therapists, and
chiropractors around the world [1-6]. Some evi-
dence in literature reviews to support the use
of manipulation techniques for the treatment of
neck pain and headache [7-11]. A conservative
estimate of approximately 193 million of CSMs
is performed each year in the United States
and Canada [5-12]. This growing acceptance
has, in turn, advocated the necessity to evalu-
ate its potential side effects and complications
that include cerebrovascular accidents such as
stroke, paralysis, and even death [13-17], most
commonly due to arterial dissection of the ver-
tebral artery (VA) at atlanto-axial joint (C1-C2)
[18-20]. It is estimated that the incidence of
vertebral artery dissection (VAD) ranges from 1
to 1.7 in 100,000 person years in the United
States [21], and the stoke resulting from VAD
happened in 0.75 to 1.12 per 100,000 person
years [22]. Despite this relatively rare occur-
rence, the clinical relevance of changes in VA
blood ow associated with cervical spine move-
ments have been the main focus of consider-
able researches.
Several studies were conducted that measure
VA blood ow velocity using Doppler ultrasonog-
raphy. However, the results of such studies
have provided conicting evidence, for instance,
some studies suggested that there was dimin-
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
210 Int J Clin Exp Med 2016;9(1):209-218
ished blood ow in the contralateral VA during
cervical rotation whether extension was added
or not [23, 24], whereas other authors have
reported that ow velocity in VAs decreased sig-
nicantly during both ipsilateral and contralat-
eral rotation [25-27], or no changes [28-30].
Research ndings for the sustained extension-
rotation are equally equivocal with signicant
decreases in blood ow [31, 32], or no effect
noted on VA blood ow [25, 27]. In addition,
other positions such as extension and the
application of manual traction have been limit-
edly investigated with no consensus conclusion
on the ndings [24, 27, 31].
On the basis of the inconsistency of the evi-
dence, it is need to develop experimental ani-
mal model for investigate the blood ow chang-
es in the vertebral arteries during cervical
spinal manipulation or/and pre-manipulative
testing of these vessels, for instance, clinical
studies are usually complicated by uncontrolled
variables such as age, gender, nutrition, hyper-
tension, alcohol, tobacco, and drug abuse, data
derived from clinical trials measuring blood ow
velocity are difcult to interpret and generally
require large sample size for relevant informa-
tion [33, 34]. To investigate whether end-range
cervical movements produce signicant chang-
es in VA blood ow velocity, resistance index,
and lumen diameter, the rhesus macaque
(Macaca mulatta), a member of the Old-world
Primate, was selected as the study subject to
provide some evidence on which to base the
treatment of humans.
Materials and methods
Animals
A total of 6 adult rhesus macaques, 3 male, 3
female, approximate age 4.3 ± 0.6 yrs.; weight
4.5 ± 0.6 kg; height 51.5 ± 2.1 cm (Macaca
mulatta, Chongqing Medical University Animal
Research Center, Chongqing, P. R. China) were
involved in the current study. All experimental
protocol was approved by the Institutional
Animal Care and Use Committee of Chongqing
Medical University. Before participation in the
experimental study all animals underwent a
routine physical examination, ensured they are
one group of healthy rhesus macaques without
any neurological, cardiovascular and musculo-
skeletal diseases. A prior Doppler examination
ensured that there was no any abnormality in
cervical spine and neck vasculature. Animals
were singled-housed in cages (121 × 68 × 81
cm) located in a clean and quiet single room.
The lights were on 12 hours daily from 7:00 am
to 7:00 pm, and the temperature was main-
tained at 22°C. A pelleted diet was fed twice
daily (Lab Diet, Chongqing, P. R. China) with
fresh fruits/vegetables, and water was avail-
able ad libitum.
Pre-test preparation
All rhesus monkeys were intramuscularly anes-
thetized with Xylazine Hydrochloride (0.1 mL/
kg) and handled humanely for all procedures.
Postoperative analgesia with Buprenorphine
Hydrochloride (0.1 mg/kg) was given as need-
ed. Postoperative evaluations for behaviors,
food and water consumption, and urine and
feces production were done. Under sterile cir-
cumstances the rhesus monkey were placed in
supine position on an insulating mat, and the
region of interest was washed and cleaned
accordingly. A thorough examination of the cer-
vical spine was performed prior to the Doppler
test.
Cervical spine manipulation maneuvers
Eight spinal manipulation maneuvers were cho-
sen that incorporate all of the maximum pas-
sive arthrokinematic facet motions and per-
formed bilaterally with the animal placed in
supine position. All cervical movements were
performed by a single qualied physical thera-
pist with extensive experience in manual thera-
py and joint manipulation. The procedure com-
menced with a 10 minutes rest period to allow
for a period of hemodynamic stability. Systolic
blood pressure (SBP, mmHg), diastolic blood
pressure (DBP, mmHg) and pulse rate (PR,
beats/min) were measured in the resting posi-
tion and during cervical manipulations with a
digital Blood Pressure Monitor (model DS-145,
ALPK2, Japan; ± 3 mmHg for BP and ± 5% for
PR). Eight spinal manipulation maneuvers as
follow:
Flexion 60o
For the C1-C2 facet joint exion shown in Figure
1B, the examiner manually stabilized C1 with a
bilateral laminar contact between the thumb
and index nger of the stabilizing hand while
placing the manipulating hand against the infe-
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
211 Int J Clin Exp Med 2016;9(1):209-218
rior nuchal line, and then passively introduced
exion to 60o.
Extension 60o
With the animal’s head extending over the edge
of the examination table, the examiner manu-
ally stabilized C1 with a bilateral laminar con-
tact between the thumb and index nger of the
stabilizing hand while placing the manipulating
hand against the inferior nuchal line, and then
passively introduced extension to 60o (Figure
1C).
Rotation 90o
The examiner encircled the animal’s head, with
index nger on the ipsilateral lamina of C1,
Figure 1. Cervical positions of rhesus macaque during duplex Doppler ultrasound examination.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
212 Int J Clin Exp Med 2016;9(1):209-218
spanned the arch of C2 with the thumb and
passively introduced 90o rotation either away
from the US evaluation side or toward the US
evaluation side (Figure 1D, 1G).
Extension 60o and rotation 90o
With the animal’s head extending over the
examination table, C1 was rst passively pre-
positioned in 60o extension, and then was
either 90o rotated away from the US evaluation
side or rotated toward the US evaluation side
(Figure 1E, 1H).
Extension 60o, rotation 90o and traction
For the C1-C2 facet joint distraction, C1 was
rst passively pre-positioned with a combina-
tion of 60o extension and 90o rotation either
away from the US evaluation side or rotation
toward the US evaluation side; then the exam-
iner passively distracted C1 with approximately
1/3 the animal’s body weight to achieve 1-2
mm of vertebral separation in a cranial direc-
tion (Figure 1F, 1I).
Ultrasonographic examination
A standard, duplex Doppler ultrasound device
(Mylab 50, Esaoto Corporation, Genoa, Italy)
was applied to measure peak systolic velocity
(PSV, cm/s), end diastolic velocity (EDV, cm/s),
resistance index (RI) and lumen diameters (LD,
cm). The machine possesses a color ow map-
ping capability, and a high frequency 12-5 MHz
broadband linear array transducer. All scanning
was performed by a single qualied ultrasonog-
rapher with extensive experience in musculo-
skeletal US imaging and the examination of the
extra-cranial vasculature. Measurement of
PSV, EDV, RI and LD were recorded three times
in each position for both left and right VAs using
the same order of sampling. Each of the posi-
tions was sustained passively for at least 30
seconds. Ranges of motion (ROM, degree) for
exion, extension and left/right rotation were
measured with a goniometer. The animal was
then rested in a neutral position for 10 seconds
and was observed for neurological signs before
re-positioning for the next movement. Following
the test procedure, the ultrasonographer
reviewed all scans for any artery pathology or
abnormal discrepancy.
Statistical analysis
The software package SPSS version 20.0
(SPSS Inc., Chicago, Illinois, USA) was used for
statistical analysis. The mean (± SD) blood ow
PSVs and EDVs, RIs, and LDs were calculated
for the right and left VA with the cervical spine
in all the different positions. Hemodynamic sta-
bility was evaluated by comparing SBP, DBP,
and PR measurements taken before and during
the ultrasound examination, using paired sam-
ples t-tests. The consistency between mea-
surements of ROM was also determined using
paired samples t-test. One-way ANOVA with
repeated measures on the PSV, EDV, RI, and LD
measurements were performed to identify any
statistically signicant change between the
neural position and each different head move-
ment. Post hoc tests were calculated with
Table 1. Values of blood ow velocities and lumen diameters taken at the C1-C2 region of the right
and left vertebral artery in rhesus monkeys
Position PSV-LVA
(cm/s)
PSV-RVA
(cm/s)
EDV-LVA
(cm/s)
EDV-RVA
(cm/s) RI-LVA RI-RVA LD-LVA
(cm)
LD-RVA
(cm)
N 16.71 ± 3.21 16.65 ± 5.45 7.43 ± 2.03 7.77 ± 2.16 0.56 ± 0.07 0.52 ± 0.08 0.10 ± 0.01 0.11 ± 0.02
F 14.24 ± 0.84 13.45 ± 1.25 5.70 ± 0.21 5.27 ± 1.35 0.60 ± 0.02 0.61 ± 0.09 0.08 ± 0.01 0.10 ± 0.01
E 14.69 ± 2.73 14.56 ± 2.76 5.42 ± 3.77 6.37 ± 3.77 0.66 ± 0.17 0.58 ± 0.15 0.11 ± 0.01 0.10 ± 0.01
LR 14.51 ± 1.86 11.90 ± 3.43*5.93 ± 1.38 4.02 ± 1.34*0.60 ± 0.09 0.65 ± 0.12*0.11 ± 0.01 0.10 ± 0.02
RR 10.38 ± 1.15*14.88 ± 4.00 4.50 ±0.83*6.10 ± 1.56 0.57 ± 0.05 0.58 ± 0.04 0.10 ± 0.02 0.10 ± 0.01
ELR 10.67 ± 1.09*11.07 ± 0.87*4.54 ± 1.33*4.86 ± 0.97*0.58 ± 0.11 0.56 ± 0.08 0.10 ± 0.02 0.10 ± 0.02
ERR 9.75 ± 1.79*11.6 ± 2.55*4.02 ± 0.77*5.91 ± 1.93 0.59 ± 0.03 0.51 ± 0.07 0.10 ± 0.02 0.10 ± 0.02
ELRT 10.47 ± 2.30*9.48 ± 1.28*4.20 ± 1.68*3.03 ± 0.72*0.61 ± 0.10 0.68 ± 0.09*0.11 ± 0.02 0.10 ± 0.02
ERRT 9.49 ± 1.26*10.96 ± 2.93*3.19 ± 1.24*4.22 ± 1.35*0.66 ± 0.11 0.62 ± 0.07 0.10 ± 0.01 0.11 ± 0.01
Abbreviations: PSV-peak systolic velocity; EDV-end diastolic velocity; RI-resistive index; LD-lumen diameter; LVA-left vertebral artery; RVA- right
vertebral artery. N-neutral; F-exion; E-extension; LR-left rotation; RR- right rotation; ELR-extension-left rotation; ERR-extension-right rotation; ELRT-
extension-left rotation-traction; ERRT- extension-right rotation-traction. All values are mean ± standard deviation, n = 6 rhesus macaque monkeys,
*P < 0.05.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
213 Int J Clin Exp Med 2016;9(1):209-218
Bonferroni correction for multiple comparisons
(P < 0.05). One additional paired sample t-tests
was used to identify any signicant hemody-
namic difference (P < 0.05) between the left
and right VA in each different position. P values
< 0.05 were considered to indicate a trend
towardstatistical signicance.
Results
Ultrasonographic examination was successful-
ly performed in all positions on both left VA
(LVA) and right VA (RVA). No animal showed any
alteration in BP, PR, and ROM as a result of the
experimental procedure that was statistically
signicant in relation to the ndings of this
study. No abnormalities were reported by the
ultrasonographer upon reviewing the ultra-
sound scans.
Comparison of VA blood ow in various cervi-
cal positions
The mean (± SD) blood ow PSVs, EDVs, RIs as
well as LDs for neutral and each of different
cervical spine positions are shown in Table 1.
Typical patterns of change in blood ow for both
VAs are illustrated in Figure 2. The mean PSV of
LVAs tended to decrease signicantly in sus-
tained contralateral rotation (RR) (P < 0.05),
extension -left/right rotation (ELR, ERR) (P <
0.01), and extension-left/right rotation with the
application of traction (ELRT, ERRT) (P < 0.01).
The similar patterns of change was also found
in RVA, a signicant decrease in blood ow
velocities with contralateral cervical spine rota-
tion (LR) (P = 0.01), ELR and ERR (P < 0.05),
ELRT and ERRT (P < 0.01) (Figure 2A). The
mean EDV of LVAs and RVAs decreased signi-
cantly during contralateral rotation (P < 0.05),
ELR and ERR (P < 0.05), ELRT and ERRT (P <
0.01) as compared with the neutral position
(Figure 2B). A signicant increase in RIs with
left rotation (LR) (P < 0.05) and extension-left
rotation-traction (ELRT) was demonstrated in
RVAs (P = 0.003). For the LVA there were similar
changes in the RIs, but were not signicant
(Figure 2C).
Comparison of VA blood ow between left and
right VAs
On comparing the mean PSVs between the left
and right VAs with the cervical spine in neutral
position, no statistically signicant difference
Figure 2. Changes in A. Mean peak systolic velocity (PSV); B. Mean end diastolic velocity (EDV); C. Mean resistance
index (RI); and D. Mean lumen diameter (LD) of left and right vertebral artery in rhesus monkeys. *P<0.05 in LVA;
oP < 0.05 in RVA.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
214 Int J Clin Exp Med 2016;9(1):209-218
was found between LVA and RVA (P = 0.769)
and during the positioning sequence (P =
0.290). The similar no signicant difference
was also found between the mean EDVs of LVA
and RVA in neutral position (P = 0.164) and in
each different position (P = 0.262). RIs of LVA
were not statistically different from RVA in neu-
tral cervical spine position (P = 0.329) and no
signicant differences (P = 0.307) in each cer-
vical position. In addition, no signicant differ-
ence was found in the mean lumen diameters
between the left and right sides in neutral posi-
tion (P = 0.222) and during different cervical
movements (P = 0.551).
Doppler waveforms of blood ow
Upon reviewing spectral Doppler waveforms of
blood ow velocity measurements, the results
revealed that blood ow followed a low resis-
tance pattern in the neutral position, which is a
wide peak systolic and high diastolic ow in the
VA (Figure 3A); a dampened systolic waveform,
which is an indication of a turbulence distal to
the point of sampling during positions such as
end-range contralateral rotation and extension-
contralateral rotation (Figure 3B, 3C); then the
waveform indicated a near occlusion in com-
bined extension-contralateral rotation with
traction, where blood ow velocity was slower
than the usual ow velocity in the neutral posi-
tion, and diastolic ow velocity reached zero
and extended beyond the baseline (Figure 3D).
Discussion
CSM can ease the neck pain and headache,
however, it could cause some iatrogenic dam-
ages. Although the probability of the iatrogenic
damages is very low, the adverse effect will be
great in some case. Atlanto-axial joint is the
most agility and weakest as well as the most
dangerous movement segment as it has com-
plex structures and special functions in occipi-
to-cervical migration department. The charac-
teristic of rotary motion of atlanto-axial joint
initiated from atlas: 1) rotary motion from 0° to
30°, the axis remains immovable; 2) rotary
motion from 30° to 60°, the axis begins move,
but at a slower speed compared with atlas; 3)
rotary motion from 60° to maximumrotation,
rotation of atlas and axis have reached to maxi-
Figure 3. Ultrasound spectral images of blood ow velocities during different head positions.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
215 Int J Clin Exp Med 2016;9(1):209-218
mum, the rotation of the neck occurs exclusive-
ly at segments below the axis. The segment of
VAs adjacent to atlanto-axial joint is considered
to be the most vulnerable to the stimuli to cervi-
cal vertebra, such as rotation, stretch and com-
pression [35]. Sim et al. [36] suggested that
the VA is elongated by approximately 5 mm dur-
ing contralateral rotation with 50-90% of cervi-
cal rotation attributed to movement at the
atlanto-axial joint. Therefore, the adversely
inuence of intracranial blood ow would occur-
rence during CSM, even likely deteriorate the
symptom of verterbral-basilar artery ischemia,
particularly if atherosclerosis or other vascular
disorders simultaneous in VAs.
Recently, some scholars suggested that many
of side effects (vertebral artery dissection,
stroke, etc.) are unlikely to be the result of cer-
vical manipulation. Even a drastic debate
between David Cassidy and Benedict, argued
whether abandon CSM for security reasons [37,
38]. It was documented that CSM is safe for
normal and healthy VAs from a mechanical
point [39]. Healthy adults who experience vari-
ous head positions and CSM have no signi-
cant change in blood ow in the VAs using
Duplex ultrasound with colour Doppler imaging
[40]. Another research measured blood ow
and velocity at the atlanto-axial artery using
phase-contrast magnetic resonance imaging,
and no signicant change in blood ow have
been found [41]. However, those results are
inconsistent with previous study [26]. By the
way, the relationship between vertebral artery
lesion and CSM in humans is still difcult con-
rm as the integrity of vessel is typically
unknown before using CSM. Some scholars
focus on using animals to study the changes in
VA blood ow associated with cervical spine
movements or simulating a pre-existing vascu-
lar lesion within the VAs of animals prior to CSM
application [42-44]. Comparison with adult pigs
or dogs, rhesus monkey as a kind of non-human
primates has the unique dominant position
depend upon genetic and genomic similarity,
anatomic and physiologic closeness to humans
[45, 46]. Moreover, the 3D-CTA imaging data of
cervical artery of rhesus monkeys, which was
obtained from our prior subject, shown that ver-
tebral artery of rhesus monkey was similar with
anatomic structure of human. We speculate
this investigation of atlanto-axial artery in rhe-
sus monkey would have been capable of pro-
viding quantify VAs hemodynamics during CSM.
The ndings of this present study demonstrat-
ed that the blood ow of the VAs of rhesus
macaque was signicantly affected by cervical
positions especially involving with contralateral
rotation, extension-rotation and a combined
extension-rotation with manual traction.
However, there was no signicant reduction in
blood ow during exion and extension of the
cervical spine. Variations in BP and PR were
unlikely to contribute to the changes observed
because these measurements were not signi-
cantly different in each different cervical posi-
tion. Based on the anatomic structures with
regard to the cervical arteries, the sustained
rotation and extension-rotation tests have
been clinically used to determine the presence
of vertebrobasilar artery dysfunction. We found
that full range of cervical rotation at C1-C2
stressed the VAs sufciently to demonstrate
reduction of blood ow. Although no signicant
difference was found between the diameters of
the left and right VAs in either the neutral posi-
tion or cervical spine rotation, mean PSV and
EDV tended to decrease below resting values in
the both left and right VAs during contralateral
rotation. Extension-rotation has also been
investigated extensively with controversial
results, and combined extension- rotation
mechanically stressed the contralateral artery
more than rotation alone. It is possible that
when attempting to combine full extension with
rotation, the vertebral artery is more vulnerable
to shear and tensile forces at the region, where
it exits C2 and runs vertically and laterally to
C1. Additional traction applied to the cervical
spine while it is in an extended and rotated
position produced the maximal mechanical
stress to the contralateral VA as compared to
any other position.
In addition, the RI increased signicantly in
right VA during left rotation and combined
extension-left rotation-traction, suggesting that
the resistance encountered by the blood ow
was actually increased. This nding was consis-
tent with the expectation of vessel narrowing
and associated increased resistance to ow.
The RI is based on the premise that diastolic
velocity is likely to be reduced to a greater
extent by higher resistance than is systolic
velocity, leading to a rise in the index [32].
However, the measurements of this study indi-
cate that both the PSVs and the EDVs of VAs
are reduced in these positions, albeit the PSVs
to a proportionally greater degree.
Comparison of atlanto-axial artery hemodynamics during CSM with doppler ultrasound
216 Int J Clin Exp Med 2016;9(1):209-218
Limitations
As with any study, there are a number of limita-
tions in the current study. First of all, the study
is based on maneuvers of cervical spine manip-
ulation, the order of movement progression
was the same for all animals. This method was
chosen in order to gradually adding further
stress to the arterial system. However, because
combined extension-rotation-traction was the
last movements in the sequence and demon-
strated the greatest ow decrease, it is not
completely clear if the order of testing may
have affected the results and further investiga-
tion is required before such claims can be justi-
ed. Also, a convenience sample of young,
healthy, and asymptomatic monkeys was used
in this study. Since no attempt was made to
investigate whether positional maneuvers have
a greater hemodynamic effect in those mon-
keys with symptomatic vertebrobasilar insuf-
ciency, it is therefore not possible to generalize
the results to the symptomatic population. In
addition, although Doppler ultrasound has
advantages in terms of patient comfort, non-
invasiveness and relative time of performance
in comparison to angiography, there are a num-
ber of potential problems associated with its
use. For instance, the reliability of Doppler sam-
pling is highly dependent on the skill of the
technician to accurately locate and identify the
VA, particularly when measuring in the extreme
neck positions such as combined extension
and rotation. Another major shortcoming of
ultrasound is the lack of specicity, ultrasound
often shows nonspecic hemodynamics signs
of VA occlusion.
Conclusions
On the basis of the reference data presented in
this study, the VA of rhesus monkey was sub-
jected to forces that was sufcient to reduce
blood ow velocity in positions involving in con-
tralateral rotation, combined extension with
ipsilateral and contralateral rotations, and
combined extension-rotation with manual trac-
tion of the cervical spine seems to have a par-
ticularly signicant effect in reducing the maxi-
mum blood ow in the contralateral VA. Given
the comparison with the recently research of
atlanto-axial artery hemodynamics during CSM
in healthy human from other scholars [39, 40],
the different results between rhesus monkey
and humans implicate that furtherbiologic and
mechanical research of vertebral artery in rhe-
sus monkey need to investigate, even though
rhesus monkey has lots of similarities in ana-
tomic structure of vertebral artery.
Acknowledgements
This research received nancial support from
National Natural Science Foundation of China,
No: 81171859 and Chongqing Municipal
Healthcare Department Medical Research
Grant, No. 2010-1-20: 2. We also express our
sincere thanks to Dr. Yi Yuan, Dr. Lei Yuan
and Miss Zunzhen Zhou for their helpful
assistance.
Disclosure of conict of interest
None.
Address correspondence to: Dr. Le-Hua Yu, Depar t-
ment of Rehabilitation Medicine and Physical Ther-
apy, The Second Afliated Hospital of Chongqing
Medical University, Chongqing, P. R. China; School of
Rehabilitation Medicine and Physical Therapy,
Chongqing Medical University, Chongqing, P. R.
China. Tel: +86 13896179179; E-mail: yulehua@
cqmu.edu.cn
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