Blood Pressure Measurement
Poor Reliability of Wrist Blood Pressure
Self-Measurement at Home
A Population-Based Study
Edoardo Casiglia, Valérie Tikhonoff, Federica Albertini, Paolo Palatini
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Abstract—The reliability of blood pressure measurement with wrist devices, which has not previously been assessed under
real-life circumstances in general population, is dependent on correct positioning of the wrist device at heart level. We
determined whether an error was present when blood pressure was self-measured at the wrist in 721 unselected subjects
from the general population. After training, blood pressure was measured in the office and self-measured at home with
an upper-arm device (the UA-767 Plus) and a wrist device (the UB-542, not provided with a position sensor). The upperarm−wrist blood pressure difference detected in the office was used as the reference measurement. The discrepancy
between office and home differences was the home measurement error. In the office, systolic blood pressure was 2.5%
lower at wrist than at arm (P=0.002), whereas at home, systolic and diastolic blood pressures were higher at wrist than
at arm (+5.6% and +5.4%, respectively; P<0.0001 for both); 621 subjects had home measurement error of at least ±5
mm Hg and 455 of at least ±10 mm Hg (bad measurers). In multivariable linear regression, a lower cognitive pattern
independently determined both the systolic and the diastolic home measurement error and a longer forearm the systolic
error only. This was confirmed by logistic regression having bad measurers as dependent variable. The use of wrist
devices for home self-measurement, therefore, leads to frequent detection of falsely elevated blood pressure values likely
because of a poor memory and rendition of the instructions, leading to the wrong position of the wrist. (Hypertension.
2016;68:896-903. DOI: 10.1161/HYPERTENSIONAHA.116.07961.) Online Data Supplement
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Key Words: blood pressure
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epidemiology
B
lood pressure (BP) independently predicts cardiovascular risk in affluent countries.1–5 However, several studies
have shown that awareness of hypertension and BP control is
still suboptimal,1 and thus effective strategies should be developed to improve BP control and adherence to therapy. One
of the methods used to achieve these goals is represented by
self-measurement of BP at home by automatic devices. Many
studies have shown that BP self-measurement at home allows
a better BP control in hypertension and has a greater prognostic value than office BP.6,7 In addition, self BP measurement is
more appealing to the patient than the customary procedure in
the physician’s surgery often causing long waits.6
Upper-arm automatic devices gave fresh impetus to home
self-measurement because of their user friendliness,8 the only
conditions to be respected being adequate cuff dimensions and
correct positioning of the cuff on the patient’s arm.9–14
For reasons of market penetration and following a general tendency to miniaturization, many wrist devices recently
appeared on the market15 having the advantage of being smaller
and easier to fit than upper-arm monitors,16 and today wrist
devices are used by a large portion of people who measure their
BP at home.17 However, in spite of technical improvement,
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heart
■
methods
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wrist
their reliability in real-life conditions is not unanimously
accepted.18–20 Accuracy of BP measurement at wrist largely
depends on the difference in height between the wrist and the
heart because of the confounding effect of the hydrostatic pressure caused by the limb blood column.21–23 Wrists kept at a
higher level in comparison with the heart lead to a false lower,
and wrists at a lower level lead to a false higher BP values.
Very rarely do patients receive appropriate training from family doctors or other healthcare personnel. Instructions attached
to commercial packages require a certain degree of personal
discernment, i.e., a good cognitive pattern. Only a few models
have a position sensor to verify that the wrist is placed properly
at heart level,24 but even for these devices, no study has evaluated their reliability in real-life conditions.
The aim of the present study was to ascertain whether wrist
home BP is performed reliably or an error is present in measurement, and to identify the determinants of this error if any.
To verify the reliability of wrist BP self-measurement,
we determined at a population level the upper-arm−wrist BP
difference in the office under a doctor’s supervision and then
verified whether this difference was maintained during home
self-measurement.
Received June 5, 2016; first decision June 16, 2016; revision accepted July 12, 2016.
From the Department of Medicine, University of Padua, Italy.
The online-only Data Supplement is available with this article at http://hyper.ahajournals.org/lookup/suppl/doi:10.1161/HYPERTENSIONAHA.
116.07961/-/DC1.
Correspondence to Edoardo Casiglia, Department of Medicine, University of Padua, Via Giustiniani, 2, Padua, Italy. E-mail [email protected]
© 2016 American Heart Association, Inc.
Hypertension is available at http://hyper.ahajournals.org
DOI: 10.1161/HYPERTENSIONAHA.116.07961
896
Casiglia et al Unreliable Wrist Home BP 897
Methods
Study Population and General Protocol
The analysis involved in the frame of the GOLDEN study (Growing
Old With Less Disease Enhancing Neurofunctions), 721 unselected
subjects were recruited from an Italian general population (response
rate to call 73%), aged 49.3±15.4 (range, 18.0–89.8) years, living in an area of ≈107 km2 and sharing homogeneous lifestyle.25
At screening, all underwent anthropometrics and a questionnaire.26
Education was defined as years of schooling based on the highest
educational qualification achieved. Height (in m) and weight (in kg)
were recorded without shoes with the subjects wearing light indoor
clothing.27 Biceps skinfold thickness28 was measured (in mm) with
a plicometer (Holtain Ltd, Crymych, United Kingdom) applying a
caliper pressure of 10 g mm−2. At the screening, no subjects had atrial
fibrillation that could decrease the accuracy of automatic BP measurement, so that no one was excluded because of this reason.
Devices
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The AND device Model UA-767 Plus was used for upper-arm BP
measurement and the AND device Model UB-542 for wrist measurement (A&D Company, Tokyo, Japan). The UA-767 Plus was validated for BP measurement by the British Hypertension Society (A/A
grading),29 and the UB-542 was validated according to the European
Society of Hypertension International Protocol revision 2010.30 For
the upper-arm measurement, a standard cuff was used for arm circumferences of up to 32 cm and a large cuff for circumferences of
>32 cm. For the wrist measurement, the wrist circumference had to be
within the 13.5- to 21.5-cm range as recommended by the manufacturer. No subject had a wrist circumference outside this range.
BP Measurement and Training
During the initial visit, after a 5-minute rest in the sitting posture, all
subjects had their BP measured at upper-arm and wrist by a physician in triplicate to minimize alert reaction. The last 2 readings were
averaged and considered as upper-arm office BP and wrist office BP.
Subjects then received an individual training about the use of the 2
devices, teaching theory and answering questions, if any. For upperarm BP, they were trained to undress their nondominant arm, to rest
in the sitting position for 5 minutes, to apply the cuff taking care of
the position on the artery, to keep the elbow on a desk and the forearm
horizontal, and to proceed with automatic BP measurement without
moving from their seat. Then, they had to remove the cuff, to apply
the wrist device on the same arm, to keep the elbow on the desk with
the forearm bent to place the wrist at heart level (Figure 1A), and to
measure wrist BP, once more without moving from their seat. The
waiting times were the same for all measurements. Then, the subject had to self-measure upper-arm and wrist BP under a physician’s
supervision.
It was decided to measure first the upper-arm and then the wrist
BP both at home and in the office to avoid confusion, as a random
protocol seemed to be too difficult to pursue in uncontrolled home
conditions.
Home Self-Measurement
Subjects were asked to self-measure the upper-arm and then the wrist
BP at home every morning and evening at the same time of the day
for 7 consecutive days by means of the 2 devices cited above, following the instructions received during training. After getting the BP
reports back, the arm and wrist BP values self-measured in the 7 days
were averaged separately for systolic and diastolic BP and considered
as upper-arm home BP and wrist home BP in data analysis.
Presumptive Error in Home Self-Measurement
The difference between BP recorded at the upper arm and BP measured
at the wrist was calculated (separately for systolic and diastolic) both
in the office and at home. At home, self-measured BP on each morning and evening were averaged, obtaining for each day a systolic and
a diastolic mean value. The differences between upper-arm BP−wrist
BP day 1, upper-arm BP−wrist BP day 2, and so on, for each day were
calculated for systolic and diastolic BP and averaged to obtain the
mean home upper-arm−wrist BP difference for systolic and diastolic,
respectively. The upper-arm−wrist BP difference obtained in the office
under doctor’s supervision was considered as the reference value. To
evaluate how much the upper-arm−wrist BP difference measured by
the study participant at home deviated from the office reference value,
we calculated the discrepancy between the office and home differences,
separately for systolic and diastolic BP, as (office upper-arm−office
wrist BP difference) −(home upper-arm−home wrist difference), and
defined this discrepancy as home measurement error. According to
most authorities considering as tolerable a mean difference between
2 measurements up to 5 mm Hg when automatic devices are used,31
subjects showing a home measurement error greater than ±5 mm Hg
were labeled as bad measurers and subjects with home measurement
error within ±5 mm Hg as good measurers. As this limit might be considered too restrictive, the same operation was then performed using
±10 instead of ±5 mm Hg as boundaries. Both the continuous variable
home measurement error (in mm Hg) and the categorical variable bad
measurer (0=no, 1=yes) were separately used in data analysis.
Neuropsychological Assessment
At the initial visit, cognitive assessment was performed by a MiniMental State Examination32 and by a comprehensive neuropsychological battery of validated paper-and-pencil tests standardized for
Italian people33 administered in a single session lasting ≈2 hours.
Details are described Cognitive Pattern Assessment section of onlineonly Data Supplement and in Table S1 in the online-only Data
Supplement.
Ethics
The investigation conformed to the Declaration of Helsinki and institutional guidelines, and was approved by the Ethics Committees of
the University of Padua, of the University Hospital of Verona, and of
the Local Health Units No. 4 and No. 20 of the Veneto Region (Italy).
Each subject gave and signed informed consent.
Statistics
Sample size
As to our knowledge, no experience is available about arm and wrist
BP self-measured at home at a population level in epidemiological
setting, it was assumed a priori a plausible difference between arm
and wrist BP at home around 10±10 mm Hg for systolic and 5±10 for
diastolic BP. Power analysis showed that 148 subjects per group in
equality for the 2 proportions test were sufficient to show effects with
a power of 0.90 and a test level of 0.10 for β error and of 0.20 for α
error. Therefore, the cohort of 721 subjects recruited for the present
study seemed to be adequate even after stratifying by upper-arm and
wrist and by office and home measurements.
General and Descriptive Statistics
Linearity assumption was ascertained for each variable by the residuals method and normality assumption by the Kolmogorov–Smirnov
1-sample test. Continuous variables were expressed as mean and SD
and compared between groups with ANOVA and the Bonferroni post
hoc test. In a first model, crude values were considered to describe
BP values. Then the analysis was adjusted for age, sex, highest educational level achieved, hypertension, forearm length, upper-arm
circumference, and the cognitive tests cited in Cognitive Pattern
Assessment section of online-only Data Supplement. Categorical
variables were expressed as percent rate and compared with the χ2
test. To show the discrepancies between upper-arm and wrist BP measurements in the 2 settings, the Bland–Altman approach was used.
Multiple Regression Analysis
The hypothesis was advanced that the home measurement error could
depend on an erroneous position of the forearm at home with the
wrist at a lower level than the heart, because of imperfect comprehension, memorization, or practical execution of instructions. To test
898 Hypertension October 2016
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Figure 1. Correct (A) and incorrect (B–D) forearm positions in wrist blood pressure measurement. Dashed line indicates heart level.
Position B (wrist higher than heart level) leads to falsely lower values. Positions C and D (forearm in horizontal position or vertical close to
the body) lead to falsely higher values.
this hypothesis, home systolic and diastolic errors as defined above
were separately used as dependent variables in regression analyses
adjusted for the confounders listed above, having forearm length and
cognitive assessment variables as putative independent determinants.
The item bad measurer was used as dependent variable in logistic regression adjusted for the confounders listed above. Coefficients
were shown with 95% confidence intervals. The null hypothesis was
rejected for P<0.05.
Results
Descriptive Analysis
The characteristics of the cohort are summarized in Table 1.
In Table S2, data are stratified by arterial hypertension and in
Table S3 by normalization of arterial hypertension. In Tables
S4, subjects are stratified according to the trait of bad measurer.
All subjects had Mini-Mental State Examination >25 and
were classified as having no patent clinical cognitive impairment. As shown in Figure 2, office systolic BP was lower at
the wrist than at the arm, whereas office diastolic BP showed
a negligible difference (−2.5%; P=0.002 for systolic; −0.7%
for diastolic, nonsignificant). In contrast, at home both systolic and diastolic BPs were higher at the wrist than at the
arm (+5.6%, P<0.0001 for systolic; +5.4%, P<0.0001 for diastolic). The corresponding values adjusted for the confounders
listed above are shown in Figure S1.
These discrepancies were also present within the subgroup
of people with hypertension, both in crude and adjusted analysis (Figures S2 and S3). The upper-arm−wrist BP differences
in the office and at home are presented in Figure 3. Bland–
Altman plots for the office and home systolic BP measurements are shown in Figure 4. A greater dispersion around the
mean was present at office (SD, 13.0 mm Hg) than at home
(8.1 mm Hg). The average systolic measurement error was
9.6±15.1 mm Hg and the diastolic measurement error was
4.6±10.0 mm Hg.
Casiglia et al Unreliable Wrist Home BP 899
Table 1. Characteristics of the Cohort, Also Showing Stratification by Sex
Items
Whole Cohort (n=721)
Men (n=310)
Women (n=411)
P Value
Age, y
49.3±15.4
49.9±15.6
48.8±15.3
0.3
Forearm length, cm
23.8±3.0
24.8±3.2
23.0±2.6
0.0001
Upper-arm length, cm
36.9±16.0
38.4±17.0
35.9±15.1
0.04
Upper-arm circumference, cm
28.9±3.2
29.3±3.0
28.5±3.1
0.0005
Office upper-arm SBP, mm Hg
131.2±19.0
135.9±17.2
127.6±19.5
0.0001
Office upper-arm DBP, mm Hg
82.5±10.8
85.0±10.5
80.7±10.7
0.0001
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Office wrist SBP, mm Hg
127.9±18.7
134.3±17.4
123.1±18.1
0.0001
Office wrist DBP, mm Hg
81.9±12.0
85.5±12.0
79.1±11.2
0.0001
Heart rate, bpm
65.7±10.6
63.3±11.1
67.5±9.8
0.0001
Serum LDL-C, mg/dL
126.6±30.2
130.9±30.3
123.4±29.9
0.001
Serum triglycerides, mg/dL
105.1±69.8
124.6±87.5
90.3±47.6
0.0001
Serum HDL-C, mg/dL
59.4±16.7
52.7±13.7
64.6±17.0
0.0001
Smoking (0: no; 1: yes)
106 (14.7%)
50 (16.1%)
56 (13.6%)
0.3
Alcohol intake (0: no; 1: yes)
325 (45.1%)
204 (65.8%)
121 (29.4%)
20 (2.8%)
14 (4.5%)
6 (1.5%)
353 (49.0%)
184 (59.4%)
169 (41.1%)
12 (1.7%)
6 (1.9%)
6 (1.5%)
Diabetes mellitus (0: no; 1: yes)
Hypertension (0: no; 1: yes)
COPD (0: no; 1: yes)
0.0001
0.02
0.0001
0.7
Systolic and diastolic blood pressures (SBP and DBP) are those measured at the screening, before the individual training. COPD indicates
chronic obstructive pulmonary disease; HDL-C, high-density-lipoprotein cholesterol; and LDL-C, low-density-lipoprotein cholesterol.
According to the ±5 mm Hg cutoff, 100 subjects (13.9%)
turned out to be good measurers (home measurement error
within ±5 mm Hg) and 621 (86.1%) to be bad measurers
(home measurement error outside the ±5-mm Hg interval);
among the latter, 508 (81.8% of the bad measurers and
70.4% of the entire cohort) had higher wrist than upper-arm
home BP and 113 had lower wrist than upper-arm home BP
(18.2% of the bad measurers and 15.7% of the entire cohort).
The same analysis for ±10-mm Hg home measurement error
is shown in the Results for ±10 mm Hg Home Measurement
Error section of online-only Data Supplement.
Among the good measurers (within the ±5-mm Hg interval), the correlation between office and home measurement
Figure 2. Upper-arm and wrist blood pressures in the office and
at home. P<0.0001, *vs upper-arm systolic home blood pressure
(BP), †vs wrist systolic home BP, ‡vs upper-arm diastolic home
BP, §vs wrist diastolic home BP.
was 0.854 (P<0.0001) for upper-arm systolic BP and was
0.868 (P<0.0001) for wrist systolic BP (z statistics, −0.62;
P=0.6 between the 2). Within the bad measurers with home
measurement error <−5 mm Hg (presumably those who kept
the wrist at a lower level than the heart), the correlation
between office and home measurement was 0.655 (P<0.0001
versus good measurers) for upper-arm systolic BP and 0.591
(P<0.0001 versus good measurers) for wrist systolic BP.
Multivariable Regression Analysis
In multivariable linear regression (Table 2), lower praxic abilities were determinants of both systolic and diastolic errors.
Lower memory with interference was also a determinant of
Figure 3. Differences between arm and wrist blood pressure
(BP) values in the office and at home. P<0.0001, *vs upper-arm
systolic home blood pressure (BP), †vs wrist systolic home BP,
‡vs upper-arm diastolic home BP, §vs wrist diastolic home BP.
900 Hypertension October 2016
Figure 4. Bland–Altman plot of upperarm−wrist blood pressure differences
measured in the office and at home. Lines
depict mean and 95% limits of agreement.
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the systolic error, and clock drawing test was a determinant
of diastolic error. Forearm length was a direct determinant
of the systolic error only (Table 2). Arterial hypertension
was a direct confounder for both errors, whereas the systolic
error was also directly confounded by older age, greater arm
circumference, higher systolic or pulse pressure. In sensitivity analysis, taking selectively into consideration the 508
bad measures presumably keeping the wrist lower than the
heart level, the association between forearm length and the
systolic error was greater (coefficient, 7.22; SE, 1.46; confidence interval, 1.20–8.31; P=0.0005), without any significant
changes in the rest of the model. The multivariable linear
analysis stratified by sex is shown in Tables S5 and S6: in
men, lower memory was a determinant of both systolic error
and diastolic error and lower praxic abilities and clock drawing test of the diastolic error only. Among the women, lower
memory, lower praxic abilities, and longer forearm were
determinant of the systolic error and clock drawing test of
the diastolic error.
In multivariable logistic regression, lower praxic abilities (odds ratio, 0.167; P=0.0005), memory with interference
(odds ratio, 0.921; P=0.007), and abstraction (odds ratio,
Table 2. Whole Cohort
Dependent Variable: Home Systolic Error
Dependent Variable: Home Diastolic Error
Coefficient (SE)
95% CI of the
Coefficient
P Value
Coefficient (SE)
95% CI of the
Coefficient
P Value
Praxic abilities (score)
−7.67 (3.75)
−15.02 to −0.32
0.04
−5.94 (2.50)
−10.84 to −1.05
0.02
MI 10 (score)
−2.20 (0.82)
−3.81 to −0.59
0.007
−3.94 (0.91)
−5.72 to −2.15
0.0001
5.94 (2.74)
0.56 to 11.32
0.03
−0.69 (0.55)
−1.76 to 0.38
0.2
Independent Covariables
Determinants
Forearm length, cm
Forearm length,* cm
Clock drawing test (score)
7.22 (1.46)
1.20 to 8.31
−2.25 (1.36)
−4.92 to 0.42
0.0005
0.1
0.95 (1.83)
−5.94 (2.50)
−2.64 to 4.53
0.6
−10.84 to −1.05
0.02
Confounders
Age, y
0.10 (0.03)
0.04 to 0.16
0.001
0.03 (0.02)
−0.01 to 0.07
0.1
Sex (0: women; 1: men)
−1.28 (0.75)
0.19 to 2.74
0.1
−0.94 (0.50)
−1.91 to 0.04
0.1
Arm circumference, cm
13.35 (3.03)
7.41 to 19.28
0.0001
−0.02 (2.02)
−3.97 to 3.94
1.0
2.02 (0.85)
0.36 to 3.68
0.02
1.17 (0.56)
0.06 to 2.28
0.04
Systolic blood pressure, mm Hg
9.81 (4.27)
1.45 to 18.18
0.02
4.89 (2.84)
−0.60 to 10.46
0.1
Pulse pressure, mm Hg
3.23 (1.58)
0.14 to 6.33
0.04
1.57 (1.05)
−0.48 to 3.63
0.1
Abstraction (score)
−0.80 (0.91)
−2.58 to 0.97
0.4
−1.05 (0.60)
−2.24 to 0.13
0.1
Digit span (score)
0.72 (1.89)
−2.99 to 4.42
0.7
0.73 (1.26)
−1.74 to 3.20
0.6
Hypertension (1: yes)
IPM (score)
−0.48 (0.91)
−2.27 to 1.31
0.6
0.11 (0.61)
−1.08 to 1.31
0.9
Education, y
1.78 (1.19)
−0.56 to 4.12
0.1
0.36 (0.80)
−1.20 to 1.92
0.7
Multiple linear regression. Systolic and diastolic errors as dependent variable, respectively. Age, sex, hypertension, arm circumference, forearm length, systolic blood
pressure, educational level, memory with interference at 10 s test (MI 10), immediate prose memory (IPM), praxic abilities, clock drawing, abstraction, and digit span
tests as independent variables. Pulse pressure was used in alternative to systolic and diastolic blood pressure. CI indicates confidence interval.
*Selectively in the 508 subjects keeping the wrist higher than the heart level.
Casiglia et al Unreliable Wrist Home BP 901
0.870; P=0.02) were negatively associated, and forearm length
(odds ratio, 1.066; P=0.03) was positively associated with ±5
bad measurers (complete analysis is available in Table S7).
Discussion
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The main finding of our study is that the relationship between
BP measured at the upper-arm and at the wrist varied according to whether BP measurements were made in the office
under a doctor’s supervision or at home in a real-life situation. When BP was taken in the office, the values measured
at the wrist were, as shown by others,18–25 slightly lower than
those measured at the upper-arm. In contrast, when BP was
self-measured at home by the study participants, higher BP
values were obtained at the wrist than at the arm. In the large
majority of the participants classified as bad measurers, the
home measurement error was because of a disproportionately high wrist BP.
The discrepancy between the upper-arm−wrist BP difference obtained in the 2 settings is probably because of an error
in home self-measurement despite appropriate training. It is
likely that many subjects, when left free to measure their BP
at home, did not follow the instructions received during the
training session because of a deficit in memory or in executive
functions, a limitation that persisted after adjustment for age
and was not prevented by years of schooling.
Inability to follow the instructions for poor memorization
and carelessness were likely to affect wrist BP rather than
upper-arm BP measurement because of the important effect of
an incorrect forearm position on wrist BP. Accurate measurement of BP at the wrist requires that the heart and the wrist are
kept at the same level to avoid the effects of hydrostatic pressure. If the forearm is kept horizontal on the supporting desk
(Figure 1C), leaning or even vertical along the subject’s side
(Figure 1D), the hydraulic pressure caused by the upper limb
blood column mass is added to the hemodynamic pressure and
their sum is recorded by the wrist device. Based on the difference between density of human blood and mercury, in the
present study, the magnitude of the home measurement error
would translate into an average level discrepancy between the
heart and the wrist of 10±11 cm (confidence interval, 9.1–
11.5). According to this extrapolation, in our experience, the
range of the error was from 10 over to 65 cm under the heart
level. Obviously, part of the upper-arm−wrist BP difference
may be because of random BP variability between 1 measurement and the other or to unreliable upper-arm BP measurements, and thus the differences in level reported above can
only be considered as indicative. This interpretation was confirmed by significant effect of forearm length in multivariable
linear analyses for the systolic home measurement error. When
the wrist is kept at a lower level than the elbow (Figure 1D), a
longer forearm magnifies the hydrostatic effect of the wrong
arm position,34 an effect that is notoriously more pronounced
for systolic than for diastolic BP.35–37
The reason for the wrong position of forearm in a high
number of subjects was probably because of a worse cognitive pattern, as shown by the inverse association of the
measurement error with memory, praxic abilities, visuospatial, and executive functions, as shown for instance by
the clock drawing test. It is presumable that subjects having
worse cognition were those more prone to make a mistake in
wrist self-measurement. This interpretation is corroborated
by previous observations that wrist devices provided with
a position sensor, helping subjects to keep the wrist at heart
level, usually give lower values than those without a sensor.24
In the present study, it was decided to use wrist monitors
without a sensor because these are the devices mostly used
in the real world.
The home measurement error was also associated with
higher BP levels or the diagnosis of hypertension. A higher
BP is likely to affect the magnitude of the measurement error.
In addition, in keeping with previous study,38 the hypertensive
participants had a much worse cognitive pattern, as shown in
Table S2. However, the measurement error was also present
among the normotensives.
Clinical Relevance
An upper-arm−wrist difference greater than ±5 or ±10 mm Hg
was reached at home by the majority of the participants, presumably for an improper use of wrist BP monitors. This is
alarming as it is estimated24 that wrist devices for self-measurement have gained 30% to 50% of the market share of the
BP measuring devices sold in affluent countries, and most
people use them without any preliminary training from healthcare personnel.
Limitations
The main limitation is that we had no gold standard for establishing the reliability of wrist self-measurement at home. We
could not use office wrist BP as the reference because, as shown
by our results, home BP is generally lower than office BP and
is devoid of the alarm reaction. For this reason, we used the
difference between upper-arm and wrist office BP as a reference presuming that, although at a different BP level, the upperarm−wrist BP difference would not vary in the 2 settings. A
further limitation is that we assumed that the home measurement
error was mainly because of misuse of the wrist rather than the
arm device because of the well known problems inherent to the
use of wrist devices. However, the relationship of the forearm
length with the home measurement error lends support to our
assumption. It was also decided to measure first upper-arm and
then wrist BP both at home and in the office to avoid confusion,
as it appeared that a random protocol was too difficult to pursue
by subjects free to act in uncontrolled home conditions. This
is not a major problem, because at home, wrist BP was higher
than upper-arm BP. Finally, in our study, a remarkable whitecoat effect was found, probably because of the epidemiological
setting in the office; however, a similar white-coat effect was to
be expected with upper-arm and wrist measurement.39
Strengths of the study are general population setting, the
large sample size, taking into consideration both morning and
evening measurements as home BP, and the use of the same
2 devices in each subject for the office and home measurements, thereby avoiding the confounding effect of different
BP monitors.
Perspectives
At a population level, the use of wrist devices for self BP
measurement often leads to detection of falsely elevated BP
902 Hypertension October 2016
values. This is likely to be because of poor comprehension
and/or to incorrect application of instructions leading to incorrect position of the arm during self-measurement, a problem
that for hydraulic reasons can be magnified by longer forearms. This represents a public health problem because of the
overestimation of people with hypertension, with increase in
costs for the community and deterioration of quality of life
for the patient. A worse cognitive pattern is a key factor in
this chain of events. It is thus prudent to discourage the use
of wrist devices in patients in whom cognitive deterioration is
likely to be present.
Sources of Funding
This study was funded by the Italian Ministry of Health (RF2009-1469148, GOLDEN study [Growing Old With Less Disease
Enhancing Neurofunctions]).
Disclosures
Downloaded from http://hyper.ahajournals.org/ by guest on June 14, 2017
None.
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Novelty and Significance
What Is New?
Summary
• Reliability of self-measurement at home with wrist devices was tested
Self blood pressure measurement at home with wrist devices is
often unreliable, a phenomenon favored by impaired cognitive
function that leads to wrong wrist position and detection of falsely
elevated blood pressure. Self-use of wrist devices should be discouraged, especially in people in whom cognitive deterioration is
likely to be present.
for the first time in a general population.
Downloaded from http://hyper.ahajournals.org/ by guest on June 14, 2017
What Is Relevant?
• At home, most wrist self-measurements overestimated upper-arm mea-
surements, probably because of the wrist being kept lower than the
heart, thereby adding the pressure due to the blood column to the clinical
pressure, a phenomenon magnified by longer forearms.
Poor Reliability of Wrist Blood Pressure Self-Measurement at Home: A Population-Based
Study
Edoardo Casiglia, Valérie Tikhonoff, Federica Albertini and Paolo Palatini
Downloaded from http://hyper.ahajournals.org/ by guest on June 14, 2017
Hypertension. 2016;68:896-903; originally published online August 22, 2016;
doi: 10.1161/HYPERTENSIONAHA.116.07961
Hypertension is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 2016 American Heart Association, Inc. All rights reserved.
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Data Supplement (unedited) at:
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ONLINE SUPPLEMENT
POOR RELIABILITY OF WRIST BLOOD PRESSURE
SELF-MEASUREMENT AT HOME.
A POPULATION-BASED STUDY
Edoardo Casiglia, Valérie Tikhonoff, Federica Albertini, Paolo Palatini
Department of Medicine, University of Padua, Italy
Running title: Unreliable wrist home BP
Supplemental material: 2 paragraphs; 7 tables; 3 figures
Corresponding Author
Prof. Edoardo Casiglia
Department of Medicine
University of Padua
Via Giustiniani, 2 – Padua – Italy
Tel +39-049-8212277
Fax +39-049-8754179
e-mail [email protected]
1
Cognitive pattern assessment
The praxic abilities were evaluated through the tests summarized in Table S1 below, giving a final score
ranging from 0 to 6. In the test of memory with interference at 10 seconds (scoring 0 to 9) the
participants had to recall a consonant trigram after an interval delay during which they had to count
backward starting from a 3-digit random number presented by the examiner immediately after the
trigram, and, at the end of the interval delay of 10 seconds, to recall the trigram.1,2 The verbal fluency
test3 (scoring 0 to 34 in 3 tasks averaged) required to generate appropriate names in a fixed period of
time. The digit span4 (scoring 0 to 8) consisted of memorization and repetition of a series of numbers. In
the immediate prose memory test (scoring 0 to 28), a prose passage of 30 words was presented on a
one-to-one basis, asking for immediate verbatim recalls. The test of abstraction (scoring 0 to 6) required
inclusion in the same category of words having common elements. In the clock drawing test the
participant was instructed to draw a clock indicating 2:45 h, setting the hands and numbers on the face
«so that a child could read them».
References
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individuals at risk for cardiovascular disease: the «clock-in-the-box» screening test. Int J Geriatr
Psychiat. 2011; 26: 969-975.
2. Peterson LR, Gentile A. Proactive interference as a function of time between tests. J Exp Psychol.
1965; 70: 473-478.
3. Lezak MD. Neuropsychological assessment. Oxford University Press, Oxford, 1995.
4. Wechsler D. The measurement of adult intelligence. Williams and Witkins, Baltimore, 1939.
2
Results for ±10 mmHg home measurement error
According to the definition based on ±10 mmHg cut-off, 266 subjects (36.9%) turned out to be good
measurers (home measurement error within 10 mmHg) and 455 (63.1%) to be bad measurers; among
the latter, 382 (84.0% of the bad measurers, 53.0% of the entire cohort) kept wrist lower than heart
level, and 73 (16.0% of the bad measurers, 10.1% of the entire cohort) kept wrist higher than heart
level.
Within the good measurers for the category ±10 mmHg, the correlation between office and home
measurement was 0.812 (p<0.0001) for upper-arm systolic BP and was 0.832 (p<0.0001) for wrist
systolic BP. Within the corresponding bad measurers with home measurement error under -10 mmHg
the correlation between office and home measurement was 0.563 (p<0.0001; z-statistic 6.366,
p<0.0001 vs. good measures) for upper arm and 0.434 (p<0.0001; z-statistic 9.373, p<0.0001 vs. good
measurers) for wrist systolic BP.
3
Table S1. Test aimed at verifying the praxic abilities, consisting in mimicking some movements or
gestures.
Instruction
score
Pantomime of use of objects
Please, show which movement you would
perform having in your hand …………………
Show ………………………………………………
a hammer
0 or 1
a toothbrush
0 or 1
the sign of the Cross
0 or 1
the gesture to say «he’s
crazy»
0 or 1
Copy of gestures without a definite meaning
middles finger bended on
index finger
Please, copy the gestures I am making ……………
a forearm extended
forwards, open palm
outwards; the other
forearm bended with the
fist on the shoulder
0 or 1
0 or 1
4
Table S2. General characteristics of the cohort at the screening, showing stratification by arterial hypertension.
Items
Age (years)
Body mass index (kg/m2)
Biceps skinfold thickness (mm)
Forearm length (cm)
Upper-arm length (cm)
Upper-arm circumference (cm)
Office upper-arm SBP (mmHg)
Office upper-arm DBP (mmHg)
Heart rate (bpm)
Serum LDLC (mmol˖l-1)
Serum triglycerides (mmol˖l-1)
Serum HDLC (mmol/l-1)
Cardiac index (l˖min-1˖m-2)
Smoking (0: no; 1: yes)
Alcohol intake (0: no; 1: yes)
Diabetes (0: no; 1: yes)
COPD (0: no; 1: yes)
MMSE (score)
MI 10 (score)
Praxic abilities (score)
Clock drawing test (score)
Abstraction (score)
Digit span (score)
Immediate prose memory (score)
Education (years)
Normotensives
(n=368)
41.9 ± 14.1
23.9 ± 3.7
9.7 ± 6.0
23.8 ± 2.9
37.7 ± 2.9
27.8 ± 3.0
119.7 ± 11.9
76.9 ± 8.7
65.1 ± 10.3
3.2 ± 0.8
0.9 ± 0.7
1.6 ± 0.5
2.6 ± 1.2
70 (19.0%)
134 (36.4%)
4 (1.1%)
4 (1.1%)
29.3 ± 1.7
6.9 ± 2.2
5.9 ± 0.1
9.5 ± 1.3
5.0 ± 1.3
6.6 ± 1.2
12.8 ± 4.6
11.7 ± 4.0
Hypertensives
(n=353)
57.0 ± 12.6
27.6 ± 4.5
11.3 ± 6.9
23.8 ± 3.1
36.1 ± 16.2
30.0 ± 3.2
143.2 ± 17.5
88.4 ± 9.7
66.4 ± 10.8
3.4 ± 0.8
1.4 ± 0.9
1.4 ± 0.4
3.1 ± 1.4
36 (10.2%)
191 (54.1%)
16 (4.5%)
8 (2.3%)
28.3 ± 2.9
6.1 ± 2.5
5.8 ± 0.1
8.6 ± 2.5
4.1 ± 1.9
6.1 ± 1.2
10.1 ± 4.2
9.0 ± 3.6
p value
0.0001
0.0001
0.0001
0.9
0.1
0.0001
0.0001
0.0001
0.1
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.001
0.3
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; LDLC, low-density-lipoprotein
cholesterol, HDLC, high-density-lipoprotein cholesterol; COPD, chronic obstructive pulmonary disease; MMSE,
mini mental state examination test; MI10, memory with interference at 10 seconds test.
5
Table S3. General characteristics of the cohort showing stratification by controlled and uncontrolled
hypertension.
Items
Age (years)
Body mass index (kg/m2)
Biceps skinfold thickness (mm)
Forearm length (cm)
Upper-arm length (cm)
Upper-arm circumference (cm)
Office upper-arm SBP (mmHg)
Office upper-arm DBP (mmHg)
Heart rate (bpm)
Serum LDLC (mmol˖l-1)
Serum triglycerides (mmol˖l-1)
Serum HDLC (mmol˖l-1)
Smoking (0: no; 1: yes)
Alcohol intake (0: no; 1: yes)
Diabetes (0: no; 1: yes)
COPD (0: no; 1: yes)
Controlled
hypertensives
(n=133)
56.6 ± 13.5
27.4 ± 4.4
11.8 ± 7.5
24.0 ± 3.4
37.8 ± 16.5
29.2 ± 3.0
127.5 ± 8.5
81.2 ± 6.0
65.3 ± 10.5
3.3 ± 0.8
1.5 ± 0.8
1.4 ± 0.3
13 (9.8%)
67 (50.4%)
11 (8.3%)
3 (2.3%)
Uncontrolled
hypertensives
(n=220)
57.4 ± 12.1
27.7 ± 4.7
10.9 ± 6.4
23.6 ± 2.9
35.2 ± 16.0
30.8 ± 3.3
152.7 ± 14.4
92.7 ± 8.9
67.1 ± 11.0
3.4 ± 0.8
1.4 ± 0.9
1.5 ± 0.4
23 (10.5%)
124 (56.4%)
5 (2.3%)
5 (2.3%)
p value
0.6
0.5
0.2
0.2
0.1
0.0001
0.0001
0.0001
0.1
0.053
0.3
0.0005
0.9
0.3
0.02
1.0
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; LDLC, low-density-lipoprotein
cholesterol; HDLC, high-density-lipoprotein cholesterol; COPD, chronic obstructive pulmonary disease.
*In sensitivity analysis, selectively in the 508 subjects keeping the wrist lower than the heart level.
6
Table S4. General characteristics of the cohort at the screening, showing stratification by good and bad
measurers according to the ±5 mmHg cut-off.
Items
Age (years)
Body mass index (kg/m2)
Biceps skinfold thickness (mm)
Forearm length (cm)
Forearm length (cm)
Upper-arm length (cm)
Upper-arm circumference (cm)
Upper-arm SBP (mmHg)
Upper-arm DBP (mmHg)
Heart rate (bpm)
Serum LDLC (mmol˖l-1)
Serum triglycerides (mmol˖l-1)
Serum HDLC (mmol˖l-1)
Cardiac index (l˖min-1˖m-2)
Smoking (0: no; 1: yes)
Alcohol intake (0: no; 1: yes)
Diabetes (0: no; 1: yes)
Hypertension (0: no; 1: yes)
COPD (0: no; 1: yes)
Good measurers
(n=100)
47.6 ± 15.7
26.2 ± 4.8
10.6 ± 6.1
23.5 ± 3.1
23.5 ± 3.1
36.9 ± 16.0
28.8 ± 3.5
126.3 ± 15.9
81.4 ± 9.4
66.1 ± 11.1
3.3 ± 0.9
1.2 ± 0.7
1.5 ± 0.4
2.8 ± 1.2
10 (10.0%)
42 (42.0%)
4 (4.0%)
50 (50.0%)
3 (3.0%)
Bad measurers
(n=621)
49.6 ± 15.4
25.6 ± 4.5
10.4 ± 6.6
23.8 ± 3.0
24.9 ± 3.3*
36.9 ± 16.0
28.9 ± 3.2
132.0 ± 19.3
82.7 ± 11.0
65.7 ± 10.5
3.3 ± 0.8
1.2 ± 0.8
1.5 ± 0.4
2.8 ± 1.3
96 (15.5%)
283 (45.6%)
16 (2.6%)
303 (48.8%)
9 (1.4%)
p value
0.2
0.2
0.8
0.4
0.001
1.0
1.0
0.005
0.3
0.8
0.7
0.5
0.2
1.0
0.2
0.6
0.6
0.9
0.4
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; LDLC, low-density-lipoprotein
cholesterol; HDLC, high-density-lipoprotein cholesterol; COPD, chronic obstructive pulmonary disease.
*In sensitivity analysis, selectively in the 508 subjects keeping the wrist lower than the heart level.
7
Table S5. Multiple linear regression in men, having systolic and diastolic measurement error in whole cohort as dependent variable, respectively, and age,
hypertension, arm circumference, forearm length, systolic BP, educational level, memory with interference at 10 seconds test, immediate prose memory
test, praxic abilities, clock drawing test, abstraction test and digit span test as independent variables. Pulse BP was used in alternative to systolic.
Independent
covariables
Coefficient
(SE)
95% CI of the
coefficient
p
value
Dependent variable: home systolic error
Coefficient
(SE)
95% CI of the
coefficient
p
value
Dependent variable: home diastolic error
Praxic abilities (score)
MI 10 (score)
Forearm length (cm)
Forearm length* (cm)
Clock
drawing
test
(score)
1.46 (8.10)
-4.97 (1.30)
0.17 (4.24)
7.40 (1.22)
-2.38 (1.98)
Determinants
-14.44 to 17.37
-7.53 to -2.42
-8.14 to 8.49
0.09 to 6.18
-6.28 to 1.51
0.9
0.0001
1.0
0.01
0.2
-14.47 (5.45)
-2.46 (0.88)
-1.70 (2.85)
-1.11 (2.16)
-2.62 (1.34)
Determinants
-25.18 to -3.76
-4.18 to -0.074
-7.29 to 3.90
-4.33 to 2.75
-5.25 to -0.01
0.01
0.005
0.6
0.4
0.049
Age (years)
Arm circumference (cm)
Hypertension (1: yes)
Systolic BP (mmHg)
Pulse BP (mmHg)
Abstraction (score)
Digit span (score)
IPM (score)
Education (years)
0.09 (0.05)
25.94 (5.42)
1.00 (1.32)
16.43 (6.93)
5.86 (2.63)
1.25 (1.47)
2.03 (3.14)
2.53 (1.46)
0.56 (1.90)
Confounders
0.01 to 0.19
15.29 to 36.58
-1.58 to 3.58
2.83 to 30.03
0.70 to 11.01
-1.63 to 4.16
-4,13 to 8.20
-0.33 to 5.40
-3.18 to 4.30
0.046
0.0001
0.4
0.02
0.03
0.4
0.5
0.1
0.8
0.04 (0.03)
-2.34 (3.65)
2.26 (0.89)
1.38 (4.67)
0.67 (1.76)
-1.50 (0.99)
-0.57 (2.11)
1.17 (0.98)
-0.34 (1.29)
Confounders
-0.02 to 0.11
-9.50 to 4.83
0.63 to 4.00
-7.78 to 10.54
-2.79 to 4.13
-3.44 to 0.44
-4.72 to 3.58
-0.76 to 4.10
-2.86 to 2.17
0.2
0.5
0.01
0.8
0.7
0.1
0.8
0.2
0.8
BP indicates blood pressure; MI 10, memory with interference at 10 seconds test; IPM, immediate prose memory test.
*In sensitivity analysis, selectively in the 221 men keeping the wrist lower than the heart level.
8
Table S6. Multiple linear regression in women, having systolic and diastolic measurement error in whole cohort as dependent variable, respectively, and age,
hypertension, arm circumference, forearm length, systolic BP, educational level, memory with interference at 10 seconds test, immediate prose memory test,
praxic abilities, clock drawing test, abstraction test and digit span test as independent variables. Pulse BP was used in alternative to systolic BP.
Independent
covariables
Coefficient
(SE)
95% CI of the
coefficient
p
value
Dependent variable: home systolic error
Coefficient
(SE)
95% CI of the
coefficient
p
value
Dependent variable: home diastolic error
Praxic abilities (score)
MI 10 (score)
Forearm length (cm)
Forearm length* (cm)
Clock drawing test (score)
-11.81 (4.08)
-2.40 (1.18)
12.40 (3.78)
14.62 (2.11)
-0.54 (1.92)
Determinants
-19.81 to -3.81
-4.72 to 0.08
4.98 to 19.82
4.80 to 18.76
-4.30 to 3.22
0.004
0.04
0.001
0.0005
0.8
-2.80
0.83
4.79
5.11
-4.75
Determinants
-8.10 to 2.50
-0.53 to 2.20
-0.13 to 9.70
-0.03 to 9.50
-7.24 to -2.25
0.3
0.2
0.1
0.1
0.0002
Age (years)
Arm circumference (cm)
Hypertension (1: yes)
Systolic BP (mmHg)
Pulse BP (mmHg)
Abstraction (score)
Digit span (score)
IPM (score)
Education (years)
0.10 (004)
2.77 (3.79)
2.28 (1.11)
4.65 (5.63)
1.25 (2.93)
-1.90 (1.14)
-1.03 (2.33)
0.16 (1.05)
1.04 (1.59)
Confounders
-0.01 to 0.09
-1.51 to 8.32
-1.53 to 1.35
3.04 to 17.67
0.28 to 5.56
-2.37 to 0.61
-0.64 to 5.53
-2.84 to 0.23
-0.57 to 3.56
0.1
0.2
0.9
0.01
0.03
0.2
0.1
0.1
0.2
0.04 (0.3)
3.40 (2.51)
-0.09 (0.73)
10.3 (3.73)
2.92 (1.34)
-0.88 (0.76)
2.40 (1.55)
-1.30 (0.78)
1.49 (1.05)
Confounders
-0.01 to 0.09
-1.51 to 8.32
-1.53 to 1.35
3.04 to 17.67
0.28 to 5.56
-2.37 to 0.61
-0.64 to 5.53
-2.84 to 0.23
-0.57 to 3.56
0.1
0.2
0.9
0.01
0.03
0.2
0.1
0.1
0.2
BP indicates blood pressure; MI 10, memory with interference at 10 seconds test; IPM, immediate prose memory test.
*In sensitivity analysis, selectively in the 287women keeping the wrist lower than the heart level.
9
Table S7. Logistic regression having «bad measurers» as dichotomic dependent variable (0: good measures; 1: bad measurers) and age, hypertension, arm
circumference, forearm length, systolic BP, educational level, memory with interference at 10 seconds test, immediate prose memory test,
praxic abilities, clock drawing test, abstraction test and digit span test as independent variables.
Independent
covariables
Odds ratio
(SE)
95% CI of the
odds ratio
p
value
0.0005
0.007
0.005
0.5
0.1
0.001
0.7
0.03
0.002
0.7
0.6
0.0002
Praxic abilities (score)
MI 10 (score)
Forearm length (cm)
Clock drawing test (score)
0.167 (0.086)
0.921 (0.028)
1.066 (0.024)
0.979 (0.034)
Determinants
0.061 to 0.457
0.868 to 0.978
1.020 to 1.114
0.915 to 1.048
Age (years)
Arm circumference (cm)
Hypertension (1: yes)
Systolic BP (mmHg)
Abstraction (score)
Digit span (score)
IPM (score)
Education (years)
1.009 (0.006)
1.110 (0.022)
1.064 (0.177)
1.010 (0.005)
0.870 (0.040)
1.020 (0.064)
0.909 (0.150)
0.923 (0.020)
Confounders
0.997 to 1.021
1.068 to 1.154
0.769 to 1.473
1.001 to 1.019
0.796 to 0.951
0.901 to 1.154
0.658 to 1.256
0.885 to 0.963
BP indicates blood pressure; MI 10, memory with interference at 10 seconds test;
IPM, immediate prose memory test.
10
Figure S1. Upper-arm and wrist blood pressure in the office and at home. Values are adjusted for age (years),
sex (0=women, 1=men), highest educational level achieved (years), arterial hypertension (0=no, 1=yes),
forearm length (cm), upper-arm circumference (cm), memory with interference at 10 seconds test, immediate
prose memory test, praxic abilities, clock drawing test, abstraction test and digit span test. Using systolic and
diastolic BP (mmHg) instead of arterial hypertension did not change significantly the model.
11
Figure S2. Upper-arm and wrist blood pressure in the office and at home in hypertensive subjects only.
Unadjusted data.
12
Figure S3. Upper-arm and wrist blood pressure in the office and at home in hypertensive subjects only.
Values are adjusted for age (years), sex (0=women, 1=men), highest educational level achieved (years),
arterial hypertension (0=no, 1=yes), forearm length (cm), upper-arm circumference (cm), memory with
interference at 10 seconds test, immediate prose memory test, praxic abilities, clock drawing test, abstraction
test and digit span test. Using systolic and diastolic BP (mmHg) instead of arterial hypertension did not change
significantly the model.
13