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294 World J Emerg Med, Vol 4, No 4, 2013 Li et al
Discrepancy of blood pressure between the brachial
artery and radial artery
Wen-yuan Li
1
, Xiao-hai Wang
2
, Li-chong Lu
3
, Hao Li
4
1
Department of Anesthesiology, Second Afliated Hospital of Nanjing Medical University, Nanjing, China
2
Department of Anesthesiology, Afliated Drum-Tower Hospital of Medical College of Nanjing University, Nanjing, China
3
Department of Cardio-Thoracic Surgery, Affiliated Drum-Tower Hospital of Medical College of Nanjing University,
Nanjing, China
4
Department of Anesthesiology, First People's Hospital of Yancheng, Yancheng, China
Corresponding Author: Xiao-hai Wang, Email: wxh32@jlonline.com
Original Article
INTRODUCTION
Blood pressure (BP) is a vital sign indicating
general health of critically ill patients and guiding their
treatment. It is well known that the accurate method for
monitoring BP is passing a transducer connected to a
catheter directly into the ascending aorta. However, this
technique is invasive and not suitable for all patients.
In general, non-invasive blood pressure monitoring is
commonly used in the clinic. Systemic blood pressure
is usually estimated by conventional measurements of
brachial artery blood pressure with a brachial cuff using
oscillometric devices.
However, when patients have some difficulties in
monitoring BP on the upper arm, such as the wound on
the skin or infection of subcutaneous tissues of the upper
arm, brachial blood pressure (bBP) is not suitable for
measurement. Meanwhile, looking for another way to
monitor BP will be necessary. Under this condition, we
found that in many patients with intact forearms, the radial
blood pressure (rBP) on the wrist is easy to be measured.
Therefore, we investigated the relationship between bBP
and rBP using appropriate cuffs and intended to nd that
whether rBP can substitute bBP clinically.
2013 World Journal of Emergency Medicine
BACKGROUND: In this study, we attempted to nd the relations between blood pressure (BP)
measured on the brachial artery (bBP) and BP assessed on the radial artery (rBP) in the right arm.
METHODS: Three hundred and fifteen patients were enrolled in this study. Those who had
peripheral vascular disease, wounds of arm skin or subcutaneous tissue infection were excluded.
After a 15-minute equilibration and stabilization period after inducation of anesthesia, three bBP and
rBP records were obtained sequentially using an oscillometric device with an adult cuff and infant cuff,
respectively. Order for each BP was randomized.
RESULTS: The bBP was signicantly lower than the rBP (P<0.05). The difference between the
two values varied from 13 to 18 mmHg in systolic BP (SBP), diastolic BP (DBP) and mean blood
pressure (MAP) respectively. And the rBP was positively correlated with the bBP (r=0.872, 0.754,
0.765; P<0.001, <0.001, <0.001; SBP, DBP, MAP, respectively).
CONCLUSION: The bBP value can be evaluated by the noninvasive measurements of rBP
using an appropriate cuff in clinical practice.
KEY WORDS: Blood pressure; Brachial artery; Radial artery; Correlation; Linear regression
World J Emerg Med 2013;4(4):294297
DOI: 10.5847/ wjem.j.19208642.2013.04.010
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295 World J Emerg Med, Vol 4, No 4, 2013
bSBP (mmHg) 9099 100109 110119 120129 130139 140149 90149
rSBP-bSBP 1713 1710 177 189 1711 2111 1810
n 22 42 74 63 69 45 315
Table 2. Absolute differences of SBP between rBP and bBP in different intervals
t=0.929, P=0.462.
Location SBP DBP MAP
Upper arm 127.919.5 79.612.6 94.614.9
Forearm 145.222.7 92.113.3 108.417.0
P <0.001 <0.001 <0.001
Table 1. BP values of the two measuring locations (mmHg)
Data are given as meanSD; *Paired t test.
bDBP (mmHg) 5059 6069 7079 8089 9099 100109 50109
rDBP-bDBP 1713 158 136 126 105 1413 137
n 16 61 99 98 34 7 315
Table 3. Absolute differences of DBP between rBP and bBP in different intervals
t=2.176, P=0.057.
bMAP (mmHg) 6069 7079 8089 9099 100109 110119 120129 60129
rMAP-bMAP 147 1511 156 157 157 138 148 157
n 6 38 106 75 66 22 2 315
Table 4. Absolute differences of MAP between rBP and bBP in different intervals
t=0.311, P=0.931.
METHODS
This study was approved by the Institutional Ethics
Committee at Drum-Tower Hospital. A total of 315
patients, 149 males and 166 females, aged 1879 years,
were enrolled in this study. They all provided the written
informed consent.
Participants were excluded if they had upper limb
amputation, cuts or bruising of the skin at measurement
sites. In addition, those with hypertension, arrhythmia,
aortic coarctation, aortic dissection, peripheral vascular
disease, congenital heart disease, and vasculitis were all
excluded.
Under the condition of general anesthesia, the right
upper limbs of all patients (in a supine position) were
exposed. The upper arm and forearm were kept at heart
level. Appropriate-sized cuffs were chosen according to
the circumferences measured at the midpoint of the upper
arm and forearm. Then we placed the two cuff bladders
over the arterial pulsation and wrapped the cuffs snugly
around the patients' upper arm and forearm with the
cuff bladders encircling at least 80 % of circumferences,
because too small a cuff size leads to false high BPs
and too large leads to false low BPs.
[1,2]
After induction
of anesthesia and a 15-minute stabilization period, BP
was recorded sequentially on the upper arm and forearm
using two automated oscillometric BP monitors (Datex-
Ohmeda, Madison, WI, USA). Order for site to be
measured was first decided randomly, measurement
should be repeated twice at intervals of at least 1 minute,
and the 2 readings were averaged. When the two readings
at the same site differed by >4 mmHg, the recording was
removed, and additional readings should be obtained.
[3]
Statistical analysis
Data were presented as mean and standard deviations
(meanSD). Statistical analysis was performed using
SPSS v.13 (SPSS, Inc. Chicago, IL, USA.). bBP and
rBP were compared using paired t-test. The association
between bBP and rBP was evaluated using the intraclass
correlation coefficient. We used one-way analysis of
variance (ANOVA) to compare BPs of each interval. A P
value of <0.05 was considered statistically signicant.
RESULTS
Mean BMI was 23.23.5 kg/m
2
(range 18.530.7
kg/m
2
), mean circumference of arm and forearm was
25.32.8 cm (range 2234 cm) and 16.31.4 cm (range
1320 cm), respectively. An infant cuff (appropriate
circumference 1020 cm) was used to measure rBP. We
used various sizes of adult cuffs to measure bBP (12
cm22 cm, for arm circumference of 22 to 26 cm; 16
cm30 cm, for arm circumference of 27 to 34 cm).
We obtained 1890 valid pressure readings from 315
patients. The mean BP value for each measurement of
location is shown in Table 1. The mean SBP and DBP in
the upper arm were both significantly higher than those
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296 World J Emerg Med, Vol 4, No 4, 2013 Li et al
Figure 1. Scatterplots of rSBP, rDBP, and rMAP between rBP and bBP
after general anesthesia. The x-axis indicates the mean of two readings
of the bronchial artery; y-axis, the mean of BP values of the radial
artery. Linear regression analysis showed a significant correlation
between rBP and bBP.
rSBP (mmHg)
0 50 100 150 200 250
200
180
160
140
120
100
80
60
40
20
0
b
S
B
P

(
m
m
H
g
)
y=0.749x+19.13
r=0.872
P<0.001
y=0.673x+21.51
r=0.765
P<0.001
rMAP (mmHg)
0 50 100 150 200
160
140
120
100
80
60
40
20
0
b
M
A
P

(
m
m
H
g
)
y=0.712x+13.96
r=0.754
P<0.001
rDBP (mmHg)
0 20 40 60 80 100 120 140 160
140
120
100
80
60
40
20
0
b
D
B
P

(
m
m
H
g
)
in the forearm respectively (P<0.001).
Scatterplots of BP between the upper arm and
forearm rSBP and bSBP were significantly correlated
(r=0.872, P<0.001), and rDBP and bDBP were also
signicantly correlated (r=0.754, P<0.001) in addition to
rMAP and bMAP (r=0.765, P<0.001) (Figure 1). Linear
regression analysis showed a significant correlation
between rBP and bBP.
The absolute differences between rBP and bBP in
SBP, DBP and MAP are shown in Tables 24. We divided
bBP into several intervals for every 10 mmHg. There
were no signicant differences in absolute difference of
rBP and bBP between the intervals (P=0.462, P=0.057,
P=0.931). bBP could be obtained by subtracting 18, 13,
13 mmHg from rBP in SBP, DBP, and MAP, respectively.
DISCUSSION
Usually, the BP of the brachial artery is measured
using an oscillometric device with an appropriate cuff in a
clinic. But in some patients, BP can't be monitored on their
upper arms because of the wound of skin or infection.
Some studies
[4,5]
considered oscillometric devices for wrist
measurement, but most studies have shown that these
devices are inaccurate.
[68]
BPs at the wrist measured by
oscillometric devices generally overestimate BP compared
with conventional sphygmomanometry on the upper arm,
and the differences could be substantial.
[3]
It was reported
that systemic pressure increased as the measurement
location was moved toward the periphery of the body
away from the heart, whereas diastolic pressure was not
different.
[9]
Nevertheless, our study showed that rDBP was
much higher than bDBP. We thought this disparity might
be due to the patients' state. In Lee's study,
[9]
the patients
were measured before the induction of anesthesia, but
our patients were measured during the maintainence of
anesthesia.
Researchers
[10,11]
reported that there were marked
differences between SBP of the radial artery and that
of the brachial artery, and they were also correlated
significantly with BMI. In our study, we found the
differences between rBP and bBP, and also a strong
linear relationship between them. Therefore, we can
calculate bBP from the linear equation. Obviously, it is
impractical to calculate bBP in the clinic. According to
the absolute differences of BP values in the two sites, we
could estimate dSBP, dDBP and dMAP by subtracting
18, 13, 13 mmHg from rSBP, rDBP, rMAP, respectively.
And there was no significant difference between the
calculated values and the measured values.
To avoid these inuences of "white coat effect", cold,
tension, movement of arms, muscle fasciculation, blood
pressure was measured in the maintenance of general
anesthesia with room temperature at 2426 C during
the experiment.
[12,13]
The position of the measured site
could affect the values, i.e. the BP readings would be
high if the arm was below the right atrium, whereas the
readings would be low when the arm was above the heart
level. These differences might be attributed to the effects
of hydrostatic pressure and could be about 2 mmHg for
every inch above or below the heart level.
[2]
Hence the
midpoint of both upper arm and forearm was placed at
the level of the heart in this study.
[2,14]
From this study, we conclude that when BP value
is difficult to be measured from the upper arm, it can
be estimated by the measurement of the forearm as rBP
using an appropriate cuff in clinical practice.
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297 World J Emerg Med, Vol 4, No 4, 2013
Funding: None.
Ethical approval: This study was approved by the Institutional
Ethics Committee at Drum-Tower Hospital, Nanjing, China.
Conicts of interest: The authors state that there is no conict of
interest invoving the study.
Contributors: All the authors contributed to the concept of the
study, performance of the study, data collection, and writing of the
manuscript.
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Received April 7, 2013
Accepted after revision July 20, 2013