Journal of Human Hypertension (2000) 14, 423–427
 2000 Macmillan Publishers Ltd All rights reserved 0950-9240/00 $15.00
www.nature.com/jhh
ORIGINAL ARTICLE
Accuracy of the OMRON M4 automatic
blood pressure measuring device
JE Naschitz1, L Loewenstein1, R Lewis1, D Keren1, L Gaitini2, A Tamir3 and
D Yeshurun1
Departments of 1Internal Medicine A, 2Anesthesiology and 3Epidemiology, Bnai Zion Medical Center and
the Bruce Rappaport Faculty of Medicine, Technion Israel Institute of Technology, Haifa, Israel
Despite widespread use of the automatic blood pressure
(BP) measuring device OMRON M4, there is little formal
validation on its accuracy. A study was conducted to
assess the accuracy of the OMRON M4 compared with
the true indirect BP measured by mercury sphygmomanometer (MS). A rapid method for the evaluation of
automatic blood pressure measurement devices (READ)
was applied for this study. The READ is based on
numerous BP measurements at rest and during a standardised postural challenge in a small number of subjects who exhibit a wide range of BPs. Blood pressure
measurements were done in supine position for 10 min
followed by head-up tilt for 30 min and again supine for
10 min. The automatic device (AU) and the MS were connected to one arm-cuff by means of a T connector. A
stethoscope with dual sets of ear-pieces was used for
duplicate MS measurements (MS1 and MS2). The MS1,
MS2 and AU measurements were taken simultaneously
in a blinded manner. Three units of the automatic instrument were evaluated. An average of 111 measurements
per unit were performed, every BP category being
present in ⭓15 MS measurements. The differences
between MS1 and MS2 measurements (⌬BP: MS1–MS2)
were utilized to assess the consistency of true indirect
BP and the differences between AU and MS measurements (⌬BP:AU-MS2) were utilized to assess the accuracy of the AU. The following characteristics of the
OMRON M4 were assessed: (1) grade of accuracy,
(2) aberration pattern, (3) consistency of the aberrationpattern, and (4) correlation between levels of BP and
⌬BP: AU-MS. For MS paired readings, 92–100% of systolic and 99–100% of diastolic readings fell within 5
mm Hg difference range, that is consistent with a British
Hypertension Society grade A of both. For AU compared
to MS2, 29–64% of systolic and 73–94% of diastolic
readings fell within 5 mm Hg and 49–86% of systolic and
86–99% of diastolic readings fell within 10 mm Hg and
the devices qualified C, D and C, respectively. All
devices exhibited irregular and inconsistent aberration
patterns, making the design of correction formulas
impractical. In conclusion, the OMRON M4 device did
not meet the requirements of the British Hypertension
Society and, therefore, cannot be recommended for
clinical use.
Journal of Human Hypertension (2000) 14, 423–427
Keywords: validation; blood pressure measurement; tilt test
Introduction
The diagnosis and management of hypertension is
traditionally based on casual blood pressure (BP)
readings taken at the physician’s office. Although
casual BP is easy to obtain, several studies have
shown that patients with an elevated BP in the office
may have lower BP if measured by the patients
themselves at home.1,2 A greater number of readings
can be obtained leading to a greater accuracy3 and
the absence of the white-coat effect.4 Also, these
measurements are free of observer bias.5 It would
seem appropriate to encourage the widespread use
of self-recorded BP as an important adjunct to the
clinical care of the patient with hypertension.6,7
Particular attention must be paid to ensure the
accuracy of the devices used.8 Ideally, rec-
Correspondence: Dr Jochanan E Naschitz, Department of Internal
Medicine A, Bnai Zion Medical Center, P.O. Box 4940, 31048
Haifa, Israel
Received 19 October 1999; revised and accepted 3 February 2000
ommended devices should have been subjected to
standard validation procedures.
Validation of automatic BP measuring devices
(AU) is a relatively new field of research. Most validation procedures assess the accuracy of the test
device compared with the true indirect BP measured
by mercury sphygmomanometer (MS). At present
validation of automatic BP measurement devices is
very cumbersome, time-consuming and expensive
because a large number of subjects, a wide range of
BPs, and many well trained observers are required
for validation.9–11 We proposed a rapid method for
the evaluation of automatic blood pressure measurement devices (READ).12 The READ is based on
numerous BP measurements at rest and during a
standardised postural challenge in a small number
of subjects who exhibit a wide range of BPs. It could
serve as a pre-validation test, disclosing inadequacies in automatic BP measuring devices which
may be amenable to correction by the manufacturer
and thus prevent them needlessly going through
cumbersome validation protocols. Second, the
READ could be useful as a post-validation test to
Accuracy of the OMRON M4 automatic BP measuring device
JE Naschitz et al
424
examine whether or not accurate devices preserve
their accuracy in field. Third, the READ could be
helpful for testing automatic devices which are to
be used in scientific studies.
The OMRON M4 is an automatic BP measurement
device particularly designed for self-monitoring of
the BP. This device is relatively inexpensive. Its precision is ±3 mm Hg according to the manufacturer,
yet there is little formal validation in the literature
concerning its accuracy. The aim of the present
study was to assess the accuracy of the OMRON M4
according to the grading system of the British Hypertension Society.10
having been utilized before. The cuff automatic
inflation time is approximately 25 sec and the
deflection time is 30 to 80 sec, depending on the
measure of the systolic BP. Each device was calibrated before the study.
READ protocol
Informed consent was obtained from all patients and
controls under an investigational protocol approved
by the institutional review board for clinical studies.
For evaluation of each of the three OMRON M4
devices, the HUTT was performed in four subjects,
each subject representing a different category of the
sitting BPs: optimal-normal BP, mild hypertension,
moderate hypertension, and severe hypertension.
The differences between MS1 and MS2 measurements (⌬BP: MS1–MS2) were determined to evaluate the consistency of the ‘true indirect BP’. The differences between AU and MS2 measurements (⌬BP:
AU-MS2) were calculated to assess the parameters
of accuracy of the automatic device.
Patients
READ parameters
Adult patients of both sexes with a mean age of 51
years (range 20 to 75 years) and mean body mass
index 23 (range 21 to 24.8) were assigned to the
study. All patients exhibited sinus rhythm during
the test. According to their sitting BPs the patients
were classified to the following categories:13 optimal
BP and normal BP, mild hypertension, moderate
hypertension, and severe hypertension.
The following parameters of each of the OMRON M4
units were determined: (1) grade of accuracy according to the British Hypertension Society grading system,10 (2) the pattern of aberration, (3) consistency
of the aberration-pattern, and (4) correlation
between ⌬BP: AU-MS and levels of BP.
Patients and methods
The head-up tilt test (HUTT)
The tilt test comprises phases of supine rest and postural challenge.14 The patient lay supine on the tilt
table, secured to the table at chest, hips and knees
using adhesive girdles, the cuff of the BP recording
device attached to the left arm which was supported
at heart level at all times during the study. The automatic device (AU) and the MS were connected to
one arm-cuff by means of a T connector. Stethoscopes with dual sets of ear-pieces permitted duplicate MS measurements (MS1 and MS2). The MS1,
MS2 and AU measurements were taken simultaneously in a blinded manner. The MS measurements were done with a standard Baumanometer
(Standby Model 0661–0250) by two physicians certified in the BP measurement technique according to
the American Heart Association recommendations.15 The BP was measured initially in the
supine position for 10 min. This was followed by
slowly (during 30 sec) tilting the patient to 70°C
head-up position. The tilt phase lasted 30 min and
was followed by another supine phase of 10 min
duration. The BP measurements were performed at
2-min intervals. On the average, 28 BP measurements were obtained in each patient. During the
course of the tilt test an electrocardiogram was
recorded continuously.
Instruments tested
Three OMRON M4 devices were evaluated, two of
them having been in clinical use (approximately 150
and 200 measurements, each) and one device not
Journal of Human Hypertension
The grade of accuracy: The test devices were
evaluated by calculating the percentage of readings
that pertain within the ⌬BP: AU-MS2 ⭐5 mm Hg,
⭐10 mm Hg and ⭐15 mm Hg. The data for each test
device were referred to the grading chart of the British Hypertension Society.10 According to the latter,
a test device is acceptable for clinical practice when
at least 65% of the readings fall within the 5 mm Hg,
85% within 10 mm Hg, and 95% within 15 mm Hg
of the MS. In a similar way, the differences between
MS1 and MS2 measurements permitted to assess the
consistency of the ‘true indirect BP’ referred to the
grading chart of the British Hypertension Society.
Patterns of aberration: The aberration pattern of
automatic measurements was evaluated by observation of the time-curves of systolic ⌬BP (AU-MS2)
and diastolic ⌬BP (AU-MS2) (Figure 1). We proposed that the aberration is regular and ‘positive’
when ⬎90% of ⌬BPs (AU-M2) in a subject are positive values. The aberration is regular and ‘negative’
when ⬎90% of ⌬BPs (AU-MS2) in a subject are
negative values. The 90% cut-off was proposed taking in consideration that inconsistency of a competent examiner should not exceed 10% of measurements.10,16 A ‘regular biphasic’ aberration was
diagnosed when positive and negative aberrations
succeed in a predictable order. An ‘irregular’ aberration was diagnosed when serial AU-MS2 measurements were irregularly positive and negative.
Consistency of aberration: The consistency of the
aberration pattern is assessed by observing similarity or dissimilarity of aberration patterns on several tests performed with a device. An instrument’s
aberration pattern is ‘consistent’ when the aber-
Accuracy of the OMRON M4 automatic BP measuring device
JE Naschitz et al
425
Figure 3 Correlation between diastolic sphygmomanometric BP
and ⌬BP: AU-MS2.
ration is either positive or negative in each patient
examined.
Correlations between levels of BP and ⌬BP: AUMS2: The differences ⌬BP:AU-MS2, systolic and
diastolic, were correlated with the values of MS2,
systolic and diastolic, respectively. For statistical
analysis the t-test and Bland-Altman plots were utilized as appropriate.
Results
Figure 1 Blood pressure differences on serial measurements during the tilt test recorded in a patient with mild systolic and diastolic hypertension. (a) systolic BP differences. (b) diastolic BP differences. The paired sphygmomanometric measurements MS1
and MS2 were similar, attesting the consistency of ‘true indirect
BP’. The paired automatic versus manual measurements AU and
MS2 showed discrepancies that often exceeded 10 mm Hg, thus
demonstrating inaccuracy of automatic device.
Figure 2 Correlation between systolic sphygmomanometric BP
and ⌬BP: AU-MS2.
An average of 27.6 simultaneous AU and MS
measurements (range 24 to 36) were performed per
patient, and an average of 111 measurements (range
106 to 116) were performed per device tested. For
each device, every BP category of the JNC VI13 was
met in at least 15 manual BP measurements. Differences between paired BP measurements are shown
in Table 1, demonstrating overlap of paired MS
measurements (⌬BP: MS1–MS2) and considerable
discrepancy of AU and MS measurements (⌬BP:
AU-MS2).
Consistency of the true indirect BP was tested
according to the standards of the British Hypertension Society (Table 2). For paired MS readings, 92–
100% of systolic and 99–100% of diastolic readings
fell within 5 mm Hg difference range, that is consistent with a British Hypertension Society grade A of
both.10 The grade of accuracy of the OMRON M4
was evaluated based on the same principle (Table
2). For AU compared to MS2, 29–64% of systolic
and 73–94% of diastolic readings fell within 5
mm Hg and 49–86% of systolic and 86–99% of diastolic readings fell within 10 mm Hg. Based on both
systolic and diastolic ⌬BP: AU-MS2, the automatic
devices classified C, D and C, respectively, according to the British Hypertension Society grading
chart.
Patterns of aberration and their consistency are
shown in Table 3. Formulas for correction of
aberrant BP values could not be proposed for the
OMRON M4 device since there was no apparent rule
commanding the instrument’s deviation from true
indirect BP. Weak correlation was found between
⌬BP: AU-MS2 and levels of the sphygmomanometric BP. Systolic BP differences ⌬BP: AU-MS2
correlated positively to values of sphygmomanoJournal of Human Hypertension
Accuracy of the OMRON M4 automatic BP measuring device
JE Naschitz et al
426
Table 1 Differences between paired BP measurements: ⌬BP: MS1-MS2 and ⌬BP: AU-MS2
⌬BP: MS1-MS2 (mm Hg)
mean (s.d.)
OMRON M4
Systolic
a
Diastolic
−1.10 (2.31)
−0.28 (1.52)
0.02 (1.96)
Device 1
Device 2
Device 3
⌬BP: AU-MS2 (mm Hg)
mean (s.d.)
Systolic
−1.12 (2.01)
−0.58 (1.52)
0.19 (1.58)
Diastolic
−5.46 (7.01)
−14.5 (12.28)a
−2.44 (6.41)
−3.71 (8.27)a
−0.65 (5.33)
0.28 (3.03)
Not satisfying requests of accuracy of the American National Standard.11
Table 2 Percentage of BP differences ⭐5 ⭐10 and ⭐15 mm Hg
⌬BP: MS1–MS2
(mm Hg)
Device
1
2
3
a
⌬BP: AU-MS2
(mm Hg)
BHSa
⭐5
⭐10
⭐15
Systolic 92%
Diastolic 99%
Systolic 100%
Diastolic 99%
Systolic 98%
Diastolic 100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
A
A
A
A
A
A
BHSa
⭐5
⭐10
⭐15
57%
75%
29%
73%
64%
94%
77%
86%
49%
95%
86%
99%
92%
99%
58%
99%
97%
100%
C
C
D
B
C
A
British Hypertension Society grading system.
Table 3 Patterns of aberration of the OMRON M4
Device
Aberration pattern
Systolic
⌬BP: AU-MS2
Consistency of
aberration
pattern
Diastolic ⌬BP: ⌬BP
⌬BP: AU-MS2
1
Negative, negative,
irregular, negative
Irregular, irregular,
positive, negative
inconsistent
2
negative, negative,
negative, negative
Negative, positive,
positive, negative
inconsistent
3
Negative, negative,
irregular, negative
negative, irregular,
irregular, irregular
inconsistent
metric systolic BP (r = 0.4256). Diastolic BP differences ⌬BP: AU-MS2 correlated negatively to values
of sphygmomanometric diastolic BP (r = −0.34198)
(Figures 2 and 3).
Discussion
Because of the demand for long-term antihypertensive treatment, the involvement of the patient in BP
control is desirable. Such involvement is feasible if
user-friendly and precise automatic BP measurement devices are available. Trained patients are able
to provide reliable self-measured BP with automatic
devices. Such measurements could be adequate for
clinical and for research purposes as well.6,7 However, it should be emphasised that the accepted standard for non-invasive BP measurements is the MS.
An automatic device may be a convenient surrogate
for self-measurement of BP for those patients who
have difficulty in achieving skill and accuracy in
self-measuring BP with a MS. When using an autoJournal of Human Hypertension
matic instrument, preference should be given to
devices which have been authorised by a regular
validation procedure. Also, the automatic devices
need to be periodically re-calibrated. For research
purposes, in addition to re-calibration the validity
of each automatic device should be periodically
reassessed.
The accuracy of various models of OMRON
devices has been evaluated, their precision ranging
from excellent to bad.17–22 We could not find in the
literature data on validation of the OMRON model
M4. In the present study, the OMRON M4 device
invariably underestimated the diastolic BP and
unpredictably over- or underestimated the systolic
BP. Each of the three devices evaluated by us qualified within category C or D of the British Hypertension Society grading system.10 A similar category of
error can be understood if the automatic device is
grossly inaccurate. Alternatively, the possibility that
the MS—the gold standard with which automatic
devices are compared23—was inaccurate has been
excluded since differences between manual
measurements by blinded observers were insignificant. The automatic BP measurements were inaccurate in all ranges of BP, whether normal, high-normal
as well as mild, moderate and severe hypertension.
Beyond establishing the degree of accuracy of an
automatic BP measuring device, identification of the
pattern of aberration of an instrument could be the
basis for the ‘diagnosis’ of a faulty device as well as
for calculating a formula for correction of the measured BP. Such formula must be tailored for each
inadequate unit. The OMRON M4 units exhibited
irregular aberration patterns, therefore making proposition of correction formulas impossible.
For our investigation we have used a recently
introduced test for the rapid evaluation of automatic
Accuracy of the OMRON M4 automatic BP measuring device
JE Naschitz et al
BP measurement devices, the READ.12,16 Conventional procedures for validation of automatic BP
measurement devices are very cumbersome, timeconsuming and expensive because a large number
of subjects are tested across a wide range of BPs, and
employment of many well trained observers.11 There
is a need to simplify the validation of automatic BP
measurement devices by enlisting fewer subjects,
with a more restricted range of BPs and carrying out
numerous BP measurements in each subject. For the
READ, we utilized the setting of the head-up tilt test.
The major purpose of tilting in the present study
was to increase the range in BP values for each subject, thereby permitting to restrict the number of
patients enlisted. The preliminary power analysis
for READ takes advantage of the established principles utilized for validation methods.10 The total
number of BP measurements for both the READ and
for validation studies is comparable, and covers the
spectrum of low, medium and high BP in similar
proportions for both methods.10,12,24 Since discrepancies between automatic devices and the mercury
standard are influenced by age,25 subjects covering
a spectrum of ages from 20 to 75 years were examined in this study.
In conclusion, our investigation showed that the
OMRON M4 automatic BP measuring device for selfmeasurement of the BP is inaccurate and cannot be
recommended for clinical use.
9
10
11
12
13
14
15
16
17
18
References
1 Mancia G, Bertinieri G, Grassi G et al. Effects of blood
pressure measurement by the doctor on patient’s blood
pressure and heart rate. Lancet 1983; 2: 695–698.
2 Hoegholm A, Kristensen KS, Madsen NH, Svendsen
TL. White coat hypertension diagnosed by 24-hour
monitoring: examination of 159 newly diagnosed
hypertensive patients. Am J Hypertens 1992; 5: 64 –70.
3 Pickering T, for the American Society of Hypertension
Ad Hoc Panel. Recommendations for the use of home
(self) and ambulatory blood pressure monitoring. Am
J Hypertens 1995; 9: 1–11.
4 Fagard R, Staessen J, Thijs L. Ambulatory blood pressure during antihypertensive therapy guided by conventional pressure. Blood Press Monit 1996; 1: 279–
281.
5 Stergiou GS, Voutsa AV, Achimastos AD, Mountokalakis TD. Home self-monitoring of blood pressure: is
fully automated oscillometric technique as good as
conventional stethoscopic technique? Am J Hypertens
1997; 10: 428– 433.
6 Thijs L et al. Reference values for self-recorded blood
pressure. A meta-analysis of summary data. Arch
Intern Med 1998; 158: 481– 488.
7 Vidt DG. Self-recorded blood pressures. Arch Intern
Med 1998; 158: 425.
8 Jones D, Engelke MK, Brown ST, Swanson M. A com-
19
20
21
22
23
24
25
parison of two noninvasive methods for blood pressure
measurement in the triage area. J Emerg Nurs 1996; 22:
111–115.
O’Brien E, Atkins N, Staessen J. Factors influencing
validation of ambulatory blood pressure measuring
devices. J Hypertens 1995; 13: 1235–1240.
O’Brien E et al. British Hypertension Protocol: evaluation of automatic and semi-automatic blood pressure
measuring devices with special reference to ambulatory systems. J Hypertens 1990; 8: 607–619.
White WB et al. National standard for measurement of
resting and ambulatory blood pressures with automated sphygmomanometers. Hypertension 1993; 21:
504 –509.
Naschitz JE et al. Rapid estimation of automatic blood
pressure measuring devices (READ). J Hum Hypertens
(in press).
The sixth report of the Joint National Committee on
Prevention, Detection, and Treatment of High Blood
Pressure. NIH Publication, 1997, p 11.
Naschitz JE et al. Comparison of the 10-minute supine
30-minute-tilt test with 24-hour ambulatory blood
pressure monitoring for diagnosis of diastolic and systemic hypertension. Am J Cardiol 1995; 76: 366–369.
Curb JD et al. Training and certification of blood pressure observers. Hypertension 1983; 5: 610–614.
Naschitz JE et al. In-field validation of automatic blood
pressure measuring devices. J Hum Hypertens 2000;
14: 37–42.
Watson S et al. Accuracy of a new wrist cuff oscillometric blood pressure device: comparisons with
intraarterial and mercury manometer measurements.
Am J Hypertens 1998; 12: 1469–1474.
Mengden T et al. Reliability of self-measured blood
pressure values by hypertensive patients. Am J Hypertens 1998; 12: 1413–1417.
Brown MA, Robinson A, Buddle ML. Accuracy of
automated blood pressure recorders in pregnancy.
Aust N Z J Obstet Gynecol 1998; 38: 262–265.
Stergiou GS. Voutsa AV, Achimastos AD, Moutokalakis TD. Home self-monitoring of blood pressure: is
fully automated oscillometric technique as good as
conventional stethoscopic technique? Am J Hypertens
1997; 10: 428– 433.
Bald M, Westhues R, Bonzel KE. Blood pressure monitoring at the wrist: is it reliable in children and adolescents? Z Kardiol 1996; 85 (Suppl 3P): 106–108.
Walma EP et al. Accuracy of an oscillometric automatic blood pressure device: the OMRON HEM 403C.
J Hum Hypertens 1995; 9: 169–174.
Association for the Advancement of Medical Instrumentation. American National Standard for Electronic
or Automatic Shygmomanometers. Arlington, Va:
Association for Advancement of Medical Instrumentation, 1987.
Polk BF, Rosner B, Feudo R, Vandenburgh M. An
evaluation of the Vita-Stat automatic blood pressure
measurement device. Hypertension 1980; 2: 221–227.
Miller ST, Elam JT, Graney MJ, Applegate B. Discrepancies in recording systolic blood pressure of elderly
persons by ambulatory blood pressure monitor. Am J
Hypertens 1992; 5: 16–21.
427
Journal of Human Hypertension