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 filipovsky@fnplzen.cz

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.

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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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14

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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