Automated compared to manual office blood pressure and to home blood
pressure in hypertensive patients
Short title: Automated pressure in treated subjects
Jan FILIPOVSKÝ a,b, Jitka SEIDLEROVÁ a,b, Zdeněk KRATOCHVÍL a, Petra
KARNOSOVÁ a,b, Markéta HRONOVÁ a, Otto MAYER jr. a,b
a Department of Internal Medicine II, Charles University, Medical Faculty in Pilsen,
Czech Republic
b Biomedical Centre, Charles University, Medical Faculty in Pilsen, Czech Republic
Corresponding author / requests for reprints
Professor Jan Filipovský, MD, PhD
Department of Internal Medicine II, Charles University Medical Faculty in Pilsen
E. Beneše 13, 305 99 Pilsen, Czech Republic
phone +420 377 402 591, fax +420 377 402 374, e-mail [email protected]
Word count: 3436
Number of tables: 3
Number of figures: 4
Online supplement: number of tables: 3
2
Abstract
Objective: We studied the relationships of automated blood pressure (BP),
measured in the health care centre, to manual office BP and to home BP.
Methods: Stable outpatients treated for hypertension were measured
automatically, being seated alone in a quiet room, six times after a five-minute rest
with the BpTRU device, and immediately afterwards using auscultatory method.
Home BP was measured in a subgroup during seven days preceding the visit.
Results: The automated, office and home BP values were 131.2±21.8/77.8±12.1,
146.9±20.8/85.8±12.4, and 137.7±17.7/79.4±8.2 mm Hg, respectively. Limits of
agreement between office and automated BP (2 SDs in the Bland Altman plot)
were +42.6 to -12.6/+22.6 to -6.6 mm Hg for systolic/diastolic BP; for home and
automated BP, they were +45.8 to -25.8/+20.8 to -12.6 mm Hg. For patients with
two visits, intraclass correlation coefficients of BP values measured during the first
and second visit were 0.66/0.72 for systolic/diastolic automated BP and 0.68/0.74
for systolic/diastolic office BP.
Conclusions: Automated BP was lower than home BP and was not related to
home BP more closely than to office BP. It did not show better repeatability than
office BP. Whether automated BP and “white coat effect”, calculated as office BP –
automated BP difference, is of clinical and prognostic importance, deserves further
studies.
Keywords: blood pressure measurement; automated office blood pressure; home
blood pressure; white-coat effect
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Introduction
Automated BP measurement, which consists of multiple fully automated blood
pressure (BP) measurements done in the health care centre without presence of a
physician or a nurse, has been developed during the last 10-15 years. Compared
with routine manual office BP measurement, automated BP may correlate more
strongly with awake ambulatory BP measurement, be more consistent from visit to
visit, and virtually eliminate office-induced hypertension. Some data show that it
correlates better with left ventricular mass index and carotid intima-medial
thickness (1-3). Automated BP might also eliminate drawbacks of the out-of-office
BP measurement, ambulatory BP monitoring (ABPM) or home BP self-
measurements (HBP). These BP measurements are better predictors of
cardiovascular events than office BP (4). However, ABPM is relatively expensive
and may be poorly tolerated by the patient, while it is difficult to control the quality
of HBP measurement. Manual office BP measurement in routine clinical practice
often does not follow the recommendations stated in the guidelines (4); the routine
office BP being on average by 10/7mmHg higher than research study BP (1).
Thus, automated BP provides an attractive option how to quickly and easily obtain
BP values that show all the advantages mentioned above. In Canada, more than
25% of primary care physicians are now using automated BP measurement in
their office practices (5).
Automated BP can be measured with the BpTRU device which passed
successfully the validation study (6). It conforms to the standard of the Association
for the Advancement of Medical Instrumentation and got the ‘A/A’ grade according
to the British Hypertension Society protocol. Moreover, it is relatively easy to
perform.
4
There are several studies about the relationship of automated BP to daily ABPM
(1,7,8); the majority of them, though not all, showed a good agreement. However,
the relationships between automated and home BP were to our knowledge
analyzed only in one paper published recently (9). The questions arise (1) to what
extent the automated BP values are related to out-of-office measurements and (2)
whether they are more stable than BP measured manually in the office.
Therefore, in our study, we investigated the associations between automated
BP and manual office BP in stable treated hypertensive patients, and we
compared the values measured during repeated visits. Furthermore, in a subgroup
of patients with home BP available, we studied the relationships of all the three BP
measurement methods.
Methods
A total number of 353 patients were examined in the hypertension centre by one of
three participating physicians (JS, JF, ZK). During the visit, the patient was first
seated alone in a separate room. After five minutes of rest measured with the
stopwatch, the patient alone started the measurements with the BpTRU device by
pressing the START button (Figure 1 illustrates the settings). Immediately after
these measurements, he/she proceeded to the office where auscultatory BP
measurements were done by the physician; the number of measurements was left
at the physician´s decision (twice in majority of patients). Of these patients, 62 had
two visits with both automated BP and manual office BP measurements; the
patients were examined by the same physician during the two visits with the
treatment unchanged. The mean interval between visits was about three months.
One hundred fourteen patients measured their BP at home. These patients
were accustomed to measure their HBP regularly; before the study, they were
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instructed both verbally and in writing that BP must be measured after a five-
minute rest, in a sitting position, with forearm supported – and they got a special
form where they filled the BP measurements done during seven days preceding
the visit, two measurements in the morning before taking the drugs and two in the
evening.
The BpTRU device was set to measure BP six times in one-minute intervals.
The BPM 200 model discards the first measurement and calculates the mean of
the second to the sixth measurement. The sphygmomanometers used for
auscultatory measurements were Nissei DM-1000 and Riester N desk model. All
sphygmomanometers, including BpTRU, were calibrated before the study.
For statistical analysis, we used the SAS software version 9.3 (SAS Institute
Inc., Cary, North Carolina, USA). The results are presented as an arithmetic mean
± standard deviation or as a proportion (percentage). We applied usual statistical
methods: Pearson and intraclass correlation coefficients and multiple regression
analysis. We constructed Bland Altman plots to compare automated BP with
manual office BP and home BP, and home BP with manual office BP.
Results
Basic characteristic of the sample is shown in Table I. Majority of patients (82%)
took ≥ 2 antihypertensive drugs, 55% were on hypolipidemic therapy and 27% had
diabetes mellitus. Means of the second to the sixth automated BP measurements
are shown in Table SI (online supplement); the mean values dropped from 135/79
(2nd measurement) to 129/77 mm Hg (6th measurement). In Table II, the
differences between office BP, automated BP and home BP and their correlations
are shown. Automated BP was the lowest BP value, being by 15/8 mm Hg lower
than office BP and by 10/4 mm Hg lower than home BP; the Pearson correlation
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coefficients of automated BP to office BP were slightly higher than to home BP for
both systolic (0.79 and 0.65, respectively) and diastolic BP (0.82 and 0.68,
respectively). Individual differences are shown in Bland – Altman plots (Figure 2:
automated BP vs office BP, automated BP vs home BP, Figure 3: home BP vs
office BP).
Multiple regression of the difference between systolic office BP and automated
BP, which can be considered a “white coat effect” (WCE), was further calculated
(Table SII, online supplement). WCE was predicted by the office BP value
(positive association) and by the duration of the follow-up: the patients followed
more than six months in the centre had significantly larger differences in systolic
BP, but there was no difference in diastolic BP (Table SIII, online supplement).
Furthermore, we studied repeatability of office BP in 62 patients who had data
available from two consecutive visits. Table III summarizes the associations of
different BP measurements. The intraclass correlation coefficients of the BP
values from visit 1 and 2 were of similar magnitude for office BP and for automated
BP. In Figure 4, individual “white coat effects” (= differences between office BP
and automated BP during visits 1 and 2 are shown.
Discussion
The key finding of our study is that automated BP in hypertensive patients was
significantly lower than both office BP (by 15/8 mm Hg) and home BP (by 10/4 mm
Hg). Moreover, we observed large individual differences between office and
automated BP.
In our group, the limit for hypertension of 140/90 mm Hg according to office BP
corresponded to 125/82 mm Hg with automated BP. Generally, higher office BP
values may be caused by improper measurements; this is, however, not the case
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of our study where special attention was paid to high quality measurements. They
were done by three physicians, all of them with clinical experience in internal
medicine/cardiology >10 years. Therefore, higher office BP in our study was
mainly due to white coat effect. Indeed, Saladini et al. (10) studied the white coat
effect in untreated hypertensive subjects; they found that BP increased by 12/6
mm Hg when a physician only entered the examination room, without physical
contact with the patient. Our results are in accordance with this finding.
In repeatability analysis, the intraclass correlation coefficients (ICC) were 0.66
and 0.72 for automated SBP and DBP, respectively. These values were lower than
those found by Myers et al. (11): they reported ICCs for automated SBP/DBP
measured at three visits 0.896/0.873. We found the ICCs to be practically identical
for office and automated BP. This was surprising because we expected that
automated BP, measured in very standardized conditions, would be more stable.
This means that automated BP also shows important inter-visit variability which
can be caused by patient´s mental state, time from drug administration and also by
external influences, e.g. weather. Due to the fact that both manual and automated
BPs are variable between visits, their difference (“white coat effect”) is variable as
well.
Furthermore, we compared home BP with automated BP. We expected that the
mean values would be similar, but home BP was much higher. When comparing
office and home BP, we observed that there was a large number of patients with
masked treated hypertension in our sample. For the analysis of home BP, we took
all the measurements taken during the seven days preceding clinical visit. The
data were also recalculated after the exclusion of the first day measurement– as
recommended by the European guidelines for home BP (12) – and the results
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were practically identical (data not shown). These data show that compared to
automated office BP, home measurements may be associated with a certain
stress, either social (presence of family members), or due to the procedure of BP
self-measurement. Individual differences between home and automated BP values
were again very variable, and the standard deviations of automated BP – home
BP differences were slightly larger than those of automated BP – office BP
differences (Figure 2).Therefore, we do not think that automated office BP could
predict home BP measurements.
There are several studies showing that automated office BP value is close to
the mean of daily ambulatory BP: it differs usually by two to four mm Hg for both
systolic and diastolic BP (1). The correlations between automated BP and mean
ABPM are, however, not very close: Pearson correlation coefficients range from
0.34 to 0.6 (7). One study, performed in 329 hypertensive subjects, showed that
the association of automated BP to daily ABPM was not better than that of office
BP (Edwards et al. 448-53): the 95% limits of agreement were similarly large for
both comparisons (-31 mm Hg to +33 mm Hg for systolic automated BP vs ABPM
and -27.8 mm Hg to +37.4 mm Hg for office BP vs ABPM); the mean systolic office
BP was by 4.9 mm Hg higher and automated BP by 3.2 mm Hg lower than the
mean systolic ABPM. Large limits of agreement between automated BP and
ABPM were also found in the CAMBO trial (13).
Our study had several limitations which are mainly the consequence of the fact
that it was an observational study done in usual patients of the hypertension
centre. We performed repeated visits in order to evaluate repeatability of WCE, but
they were done only in a subsample. Moreover, more than two visits would be
better in order to know the long-term stability of WCE, and this should be done in
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future studies. Another limitation concerns the home BP. The patients measured it
with their own devices, which may bring some imprecision. Only those patients,
however, who measured their home BP regularly before the study, were included
into analysis. When the patient starts monitoring his home BP, he is asked to bring
his device into the office, he is instructed how to measure it and the device is
checked in the office towards auscultatory BP measurements.
In conclusion, automated BP may become important in the future, because its
measurement is relatively easy, it is more comfortable for the patient than ABPM
and more reliable than home BP. As it is done in the absence of a physician or a
nurse, it might serve – in combination with office BP – for the quantification of
WCE. Quantification of WCE or correct diagnosis of white-coat hypertension is
important. Although there is no direct evidence about how to treat white-coat
hypertension (4), it is clear that it is associated with increased probability of having
subclinical organ damage (14), and of developing sustained hypertension (15) or
diabetes (16). Moreover, some studies have shown that white coat hypertension is
also associated with higher incidence of cardiovascular events (17,18).
A lot of research is, however, needed for determining the role of automated BP.
Limited data are available about automated BP and subclinical organ damage
(2,3), we have no data about the association of automated BP to cardiovascular
mortality, and standardization of the procedure (time interval before the beginning
of the automated measurements, time intervals between the automated
measurements, and level of intimacy) is not yet sufficient. Once the measurement
procedure is standardized, limits of normal values, probably different from those
for office BP, would be necessary.
10
The standardization of blood pressure measurement becomes especially
relevant now in the light of the recently published results of the SPRINT trial which
showed that intensive BP lowering in non-diabetic hypertensive subjects (systolic
BP <120 mm Hg) is beneficial as compared with <140 mm Hg (19). It is stated in
the main publication that “dose adjustment was based on a mean of three blood-
pressure measurements at an office visit while the patient was seated and after 5
minutes of quiet rest; the measurements were made with the use of an automated
measurement system (Model 907, Omron Healthcare).” The comments on
SPRINT state that “automated manometer was preset to wait for 5 minutes before
measurement” (20) and even that the subjects were measured “3 times
unobserved” (21). However, whether this was done systematically in all 102
participating clinical sites, is not clear as neither the protocol, nor the publication
on design and rationale (22) specified the method of BP measurement sufficiently.
Therefore, we do not know whether BP measurement in SPRINT was similar to
the automated BP in our study.
The 2013 ESC/ESC Guidelines for the management of arterial hypertension (4)
state that “if feasible, automated recording of multiple BP readings in the office
with the patient seated in an isolated room ... might be considered as a means to
improve reproducibility and make office BP values closer to those provided by
daytime ABPM or home BP”. Our data show, however, that automated BP is very
different from office BP and from home BP as well, and literary data show that the
agreement between automated BP and ABPM is not, in our opinion, very high
either. Therefore, automated BP at present should not be used instead of other BP
measurements, but as a supplementary tool, along with the well established
methods, including classic manual office BP.
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Acknowledgements
The study was supported by the Charles University Research Fund (project
number P36).
Conflicts of interest
The authors declare no conflict of interest.
12
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Table I. Characteristics of the patients
Number 353
Females, n (%) 175 (49.6%)
Age, years 61.4±13.1
Number of antihypertensives, n (%)
0 9 (2.5%)
1 56 (15.9%)
2 86 (24.4%)
3 69 (19.5%)
>4 133 (37.7%)
Number of manual BP measurements, n (%)
1 23 (6.5%)
2 272 (77.1%)
3 58 (16.4%)
Coronary heart disease, n (%) 61 (17.2%)
Stroke, n (%) 18 (5.1%)
Diabetes mellitus, n (%) 97 (27.4%)
Hypolipidemic treatment, n (%) 194 (55.0%)
Oral glucose-lowering agents, n (%) 73 (20.7%)
Treatment with insulin, n (%) 27 (7.7%)
Values are means ± standard deviation or number (percentage).
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Table II. Automated, manual office and home blood pressure values, their differences and correlations
Total sample (n = 353)
Automated BP
(mm Hg)
Office BP
(mm Hg)
Δ office BP –
automated BP
(mm Hg)
Automated BP
vs office BP
r
Systolic BP 131.2±21.8 146.9±20.8 15.0±13.8 0.79
Diastolic BP 77.8±12.1 85.8±12.4 8.0±7.3 0.82
continues on the next page
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Home BP available (n = 114)
Automated
BP
(mm Hg)
Office BP
(mm Hg)
Home BP
(mm Hg)
Δ home BP –
automated BP
(mm Hg)
Home BP vs
Automated BP
r
Δ home BP –
office BP
(mm Hg)
Home BP vs
office BP
r
Systolic BP 127.7±22.0 143.5±21.9 137.7±17.7 10.0±17.9 0.65 -5.8±17.6 0.62
Diastolic BP 75.2±11.2 82.1±11.4 79.4±8.2 4.2±8.3 0.68 -2.7±9.2 0.60
Means ± SD and Pearson correlation coefficients are shown; all coefficients were significant at p<0.0001.
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Table III Correlations of blood pressure measurements (n=62)
Intraclass correlation coefficient 90% confidence interval
1st vs 2nd visit
Manual office SBP 0.68 0.56-0.79
Manual office DBP 0.74 0.65-0.84
Automated SBP 0.66 0.54-0.78
Automated DBP 0.72 0.62-0.82
Manual office vs automated BP during one visit
SBP 1st visit 0.65 0.52-0.77
SBP 2nd visit 0.59 0.45-0.73
DBP 1st visit 0.68 0.56-0.79
DBP 2nd visit 0.69 0.58-0.80
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Legend to the Figures
Figure 1. Use of BpTRU in our study
Figure 2 Bland – Altman plots for automated vs manual office BP (upper
panel) and for automated vs home BP (lower panel). Mean differences in solid
lines and 2 SDs in dashed lines are shown.
Figure 3. Bland – Altman plots for manual office vs home BP. Mean
differences in solid lines and 2 SDs in dashed lines are shown.
Figure 4. Individual differences between office BP and automated BP (“white-
coat effect”) in 62 patients who had two visits. Of 32 patients who had their systolic
office BP – automated BP difference above median during the first visit (high
systolic WCE, median = 16 mm Hg), 23 (72%) were also above median during the
second visit; of 29 patients whose had their diastolic office BP – automated BP
difference above median (= 6 mm Hg) during the first visit, 17 (59%) were also
above median during the second visit.
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Figure 1
21
Figure 2 upper panel
22
Figure 2 lower panel
23
Figure 3
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Figure 4