Validation of the Omron MX3 Plus oscillometric blood pressure ...

Devices and technology 165
Validation of the Omron MX3 Plus oscillometric blood
pressure monitoring device according to the European
Society of Hypertension international protocol
Andrew Coleman a , Paul Freeman a , Stephen Steel a and Andrew Shennan b
Background Demand for devices that allow the
self-assessment of blood pressure continues to rise.
Few self-assessment devices, however, have been
validated against recognised protocols. The aim of this
study was to validate the Omron MX3 Plus (model
HEM-742-E) oscillometric blood pressure measuring
device in accordance with the international protocol of the
European Society of Hypertension. This automated
device is currently available to the public in the UK through
high-street chemists and other outlets.
Design The European Society of Hypertension’s
international protocol for validation of blood pressure
measuring devices in adults divides validation into two
phases. The first phase is performed on 15 individuals,
five in each of three specific blood pressure categories.
If the device passes the first phase then a further 18
patients are recruited, making a total of 33 individuals
on which the final validation is based. All subjects are aged
30 years or above.
Methods The automated device was connected in
parallel to two reference mercury sphygmomanometers.
Nine sequential same-arm measurements were taken
from each subject by two trained observers, alternating
between the mercury sphygmomanometers and the test
device.
Results The Omron MX3 Plus passed both phases of the
ESH validation process. The mean (standard deviation)
of the difference between the observer and the device
measurements was – 1.15 (5.7) mmHg for systolic
and – 1.61 (4.7) mmHg for diastolic pressures, respectively.
Conclusions The Omron MX3 Plus can be recommended
for home and professional use in an adult population.
Blood Press Monit 10:165–168 c 2005 Lippincott Williams
& Wilkins.
Blood Pressure Monitoring 2005, 10:165–168
Keywords: blood pressure monitoring, oscillometric measurement,
validation studies, self-measurement, automated devices
a Medical Physics Department, Guy’s & St Thomas’ NHS Foundation Trust
and b Division of Reproductive Health, Endocrinology and Development, Kings
College School of Medicine, St Thomas Campus, London, UK.
Sponsorship:Sponsorship: The study was funded by Omron Healthcare Europe
B.V. Kruisweg 577, 2132 NA Hoofddorp, The Netherlands.
Correspondence and requests for reprints to Andrew Coleman, Medical Physics
Department, The Rayne Institute, Guy’s & St Thomas’ NHS Foundation Trust,
London SE1 7EH, UK.
Tel: + 44 (0)20 7188 3811; fax: + 44 (0)20 7188 0735;
e-mail: Andrew.Coleman@gstt.nhs.uk
Received 26 October 2004 Revised 20 December 2004
Accepted 20 December 2004
Introduction
There are currently estimated to be more than 40
companies actively involved in the supply of more than
90 different models of automated blood pressure (BP)
monitors in the United Kingdom (UK). This level of
diversity is partly the result of increased demand, driven
by the decommissioning of professional-use mercury
sphygmomanometers, and partly due to the growth in
the market for self-measurement devices [1,2]. Although
such diversity may be good for competiton and prices, few
of these devices have had any formal validation of their
accuracy. Indeed, there is insufficient evidence to be
confident about the clinical use of the majority of the
self-measurement devices on the UK market [3].
Medical device agencies, faced with recommending
suitable BP monitors as a replacement for mercury
sphygmomanometers, are increasingly relying on results
of technology assessments in the form of clinical
1359-5237 c 2005 Lippincott Williams & Wilkins
validations against published British, European or US
protocols [4–6]. Validation against these protocols provides
evidence of the degree of agreement between
clinical readings from the automated monitor and those
on a mercury sphygmomanometer, still widely accepted as
the gold standard for non-invasive BP measurement.
This paper presents a study of a relatively new automated
BP monitor (Omron MX3 Plus; Omron Healthcare
Europe B.V. Hoofddorp, The Netherlands) that is widely
marketed to the public in the UK. This device was
validated using the European Society of Hypertension
International protocol [5].
Methods
The tested device
The Omron MX3 Plus (Model HEM742E) is an
electronic oscillometric device with a capacitive pressure
sensor designed to measure blood pressure in the range
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166 Blood Pressure Monitoring 2005, Vol 10 No 3
0–299 mmHg and pulse rates in the range 40–180 beats
per min. The specified device accuracy for these two
measurements is ± 3 mmHg and ± 5% of the display
reading respectively. Systolic blood pressure, diastolic
blood pressure and pulse rate are all displayed on a digital
readout. The inflation is by automatic pumping system
and deflation is controlled by automatic pressure release
valve.
The unit is powered by an AC adaptor or four 1.5 V
alkaline batteries (type LR6 AA) and weighs 350 g
(without batteries). It measures 118 mm 90 mm
130 mm (width, height and depth, respectively) and is
supplied with a cuff of dimensions 145 mm 480 mm
(width and length respectively). The standard cuff is
applicable to arm circumferences in the range 220–
320 mm. An optional additional large cuff of dimensions
174 mm 617 mm is available for arm circumferences in
the range 320–420 mm.
Device validation
A validation team was appointed for the study. This team
consisted of a medically qualified expert, who provided
clinical oversight and supervision, along with two clinical
scientists and a technician, who recruited patients and
acted as observers, undertaking the intercomparison
between the automated and mercury devices. The team
members were full-time hospital staff and operate
validations as part of their designated duties. A healthcare
assistant was employed to act as an additional observer
when required. All those involved as observers were
trained using the CD-ROM tutorial on the British
Hypertension Society Website [7]. Their competence
was assessed as described in the British Hypertension
Society protocol [4].
Approval for the study was obtained from the local
research ethics committee. The subjects, aged 30 years
and above, were recruited from patients attending routine
hypertension clinics at Guy’s & St Thomas’ Hospital
NHS Trust. Some subjects were recruited from staff
groups within the hospital. Written consent was obtained
from all subjects. Exclusion criteria included the presence
of atrial fibrillation or frequent extra systoles, and those
who had sufficiently weak Korotkoff sounds such that
auscultation was impossible. A total of 43 subjects were
recruited.
Four new Accoson Dekamet Mk3 mercury sphygmomanometers
(A C Cossor & Son Ltd., London, UK) were
purchased as references devices for this study. These
were tested for absolute static pressure scale accuracy by
intercomparison of the pressure scales with an automated
digital pressure calibrator (Druck DPI 520; Druck Ltd,
Leicester, UK). This automated device provides a static
pressure calibration accuracy of ± 0.01 mmHg and has an
absolute calibration traceable to the UK national standard
for pressure. The mercury sphygmomanometers were
checked against the absolute pressure accuracy specification
(better than ± 3 mmHg) and leakage rate specification
( < 4 mmHg/min at 250 mmHg) in the European
Standard [8]. Having replaced the plastic columns with
glass, it was possible to select two reference sphygmomanometers
providing pressure scales accurate to within
1 mmHg.
Thesubjectswereseatedinaroomclosetotheclinic,and
measurements started after consent was obtained, allowing
5–10 min rest. Arm circumferences were measured and
recorded to allow the appropriate cuff size to be selected.
Patients were asked if they had kidney problems or
diabetes, and if they were on hypertension medication.
Their responses were recorded on a standard form to allow
retrospective analysis of results against these indicators, if
required. Blood pressure was measured simultaneously with
the two reference mercury sphygmomanometers by the two
trained observers. Care was taken to ensure that observers
were blinded to each other’s readings. This was achieved by
positioning the reference devices so that the scales were not
simultaneously visible to either observer. All pressures were
measured and recorded with the patient seated, with the
upper arm at heart level. The mean (standard deviation) of
the observed measurement in 33 participants was
139 mmHg (22), with a range 102–178 mmHg, for SBP,
and 85 mmHg (15) with a range of 58–112 mmHg for DBP.
Measurements were carried out and recorded in the
protocol-specified sequence:
BPa Mercury (entry value used to categorize subjects)
BPb Device (to check the automated device, not included
in the analysis)
BP1 Mercury (observers 1 and 2)
BP2 Device (supervisor with test device)
BP3 Mercury (observers 1 and 2)
BP4 Device (supervisor with test device)
BP5 Mercury (observers 1 and 2)
BP6 Device (supervisor with test device)
BP7 Mercury (observers 1 and 2)
Subjects were allocated into BP categories on the basis of
measurement BPa. Measurement BPb was discarded, and
served only to confirm that the automated test device was
capable of registering a reading. The measurements BP1
to BP7 were analysed to assess accuracy of the test
device.
Data analysis
The published protocol describes the data analysis in
detail. In summary, the mean of each pair of observer
measurements is calculated, and this value is subtracted
from the BP measurements made by the test device. The
sign is ignored. These values (in mmHg) are referred to as
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Validation of Omron MX3 Plus Coleman et al. 167
the ‘device–observer comparison values’. As there are three
device measurements (BP2, BP4, BP6) then three device–
observer comparison values can be generated for each
individual. Obviously, small comparison values represent
good agreement between the device and the observer.
The data from 15 individuals, from Phase 1, generate a total
of 45 (3 15) ‘device–observer comparison values’, which
are categorized to determine the number of comparison
values falling within the 5, 10 and 15 mmHg error
categories.Thisanalysisisdoneseparatelyforbothsystolic
(SBP) and diastolic (DBP) blood pressures. The protocol
specifies the minimum number of ‘device–observer comparisonvalues’allowedwithinthesecategories.Atleastone
of these categories must have more than the protocolspecified
number of comparisons for a pass.
A further 18 individuals are then recruited (Phase 2) if
the device passes Phase 1. The data collection and
analysis proceeds in the same way, using data from all 33
subjects, and generating, in this case, 99 (3 33) device–
observer comparison values for both SBP and DBP. The
data is categorized, as before, and the device passes or
fails against a second, protocol-specified requirement for
the minimum number of device-observer comparison
values in each category (Phase 2.1).
A final test (Phase 2.2) is applied to the same data set to
determine how accurate the device will be for individual
subjects. At least 22 of the 33 individuals must have two
of their three ‘device–observer comparison values’ lying
within 5 mmHg. No more than three of the 33 subjects
can have all three comparison values over 5 mmHg. If the
device passes both Phase 2.1 and Phase 2.1 tests, it is
considered suitable for clinical use.
Results
The mean age of the 33 participants was 50 ± 10.6 years
(range 31–73 years). Eighteen of the individuals were
male and fifteen female. The mean arm circumference
was 30 ± 3.1 cm, with a range of 24–37 cm. Seven males
and eight females were included in Phase 1 of the study.
Table 1 shows the results from Phase 1, and illustrates
the minimum number of ‘device–observer comparison’
values within the three error categories required by the
protocol for a ‘pass’, along with measured ‘device–
observer comparison values’ obtained on the Omron
MX3 Plus. The number of device–observer comparison
values exceeded the required amount in all three error
categories. This indicated that the Omron MX3 Plus
device was unlikely to fail Phase 2. Based on these
results, the study moved to Phase 2.
Table 2a shows the number of ‘device–observer comparison
values’ obtained with the full subject number
Table 1 The number of ‘device-observed comparison values’ for
systolic (SBP) and diastolic (DBP) blood pressures falling within
specified error categories in Phase 1 (number of individuals 15,
total number of ‘device–observer comparison values’ 45).
Error categories
r 5 mmHg r 10 mmHg r 15 mmHg
Required to pass Phase 1 one of Z 25 Z 35 Z 40
SBP 34 41 45
DBP 39 44 45
Table 2a The number of ‘device-observed comparison values’ for
systolic (SBP) and diastolic (DBP) blood pressures falling within
specified error categories in Phase 2.1 (number of individualsts 33,
total number of ‘device-observed comparison values’ 99).
Error categories
r 5 mmHg r 10 mmHg r 15 mmHg
Required to pass Phase 2.1 two of Z 65 Z 80 Z 95
all of Z 60 Z 75 Z 90
Omron MX3 Plus SBP 68 90 97
DBP 75 96 98
Table 2b The number of participants having the specified fraction
of ‘device-observed comparison values’ for systolic (SBP) and
diastolic (DBP) blood pressures in the r 5mmHg error category
(number of participants 33).
Specified fraction of comparison
values
2/3 within
5 mmHg
0/3 within
5 mmHg
Required to pass Phase 2.2 both Z 22 r 3
Omron MX3 Plus SBP 28 3
DBP 28 3
(n = 33). The protocol requirements are more stringent
for Phase 2.1, and are shown in this table together with
the measured ‘device–observer comparison values’ for the
Omron MX3 Plus. Again, agreement was obtained in all
three error categories, and the device was judged as
having passed this test. The data for systolic and diastolic
pressures are presented in Figures 1a and 1b, respectively.
These Bland–Altman plots demonstrate acceptable
agreement between the test and reference devices over
the required pressure range.
Finally, the same data was analysed by individual subject
to check that at least two of the three device-observer
comparison values lie within 5 mmHg in at least 22 of the
33 subjects, and that three or less of the subjects show
device–observer comparison values in which none of the
three values was less than 5 mmHg. The data is shown in
Table 2b. Agreement was obtained and the device was
judged as passing this test. The overall mean (standard
deviation) of the difference between the observer and
the device measurements for the 33 patients was – 1.15
(5.7) mmHg for SBP and – 1.61 (4.7) mmHg for the DBP
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168 Blood Pressure Monitoring 2005, Vol 10 No 3
Fig. 1
(a)
Device pressure-mean observer
pressure (mmHg)
(b)
Device pressure-mean observer
pressure (mmHg)
15
10
5
0
−5
−10
−15
−20
30 50 70 90 110 130 150 170 190
Mean of device and two observers pressure (mmHg)
15
10
5
0
−5
−10
−15
−20
30 50 70 90 110 130 150 170 190
Mean of device and two observers pressure (mmHg)
Plots of the pressure difference (mmHg) between the mean of the two
observers and the Omron MX3 Plus device and the mean pressure
(mmHg) for the mean of the two observers and the Omron MX3 Plus
device in 33 subjects: (a) systolic blood pressure values and (b)
diastolic blood pressure values.
respectively. The Omron MX3 Plus, therefore, fulfilled
the criteria set by the Association for the Advancement of
Medical Instrumentation (AAMI) [6] (mean < 5 mmHg
and standard deviation < 8 mmHg), albeit for a sample
size smaller than that specified in the AAMI protocol.
Discussion
The SBP and DBP of 33 subjects were measured using
the Omron MX3 Plus (HEM-742-E) and two reference
mercury sphygmomanometers. Differences in the values
obtained with the automated device and mercury
sphygmomanometer were analysed, and the device was
found to pass the published international (ESH) validation
protocol requirements. The Omron MX3 Plus can,
therefore, be recommended for home and professional
use in an adult population.
Acknowledgement
Appreciation is expressed to Anne-Marie Reinders for
advice on the implementation of the European Hypertension
Society international protocol.
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