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European
recommendations validation of cuffless blood
pressure European Society of
Hypertension on Blood Pressure
Monitoring Variability
Palatini
c
, Konstantinos G. Kyriakoulis
a
,
Kollias
a
, Gianfranco Parati
f,g
, Roland Asmar
h
,
Asayama
j
, Paolo Castiglioni
k
,
Kario
n
, Richard J. McManus
o
, Martin Myers
p
,
Tan
r
, Jiguang Wang
s
, Yuanting Zhang
t
,
Mukkamala
w
Journal of Hypertension 2023, 41:000–000
a
Hypertension Center STRIDE-7, National and Kapodistrian University of Athens,
School of Medicine, Third Department of Medicine, Sotiria Hospital, Athens, Greece,
b
Macquarie Medical School, Faculty of Medicine, Health and Human Sciences,
MacquarieUniversity, Sydney, New South Wales, Australia,
c
Department of Medicine,
University of Padova, Padova, Italy,
d
School of Population Health, University of New
South Wales, The George Institute for Global Health, Sydney, New South Wales,
Australia,
e
Physikalisch-Technische Bundesanstalt, Berlin, Germany,
f
Department of
Medicine and Surgery, University of Milano-Bicocca,
g
Istituto Auxologico Italiano,
IRCCS, Cardiology Unit and Department of Cardiovascular, Neural and Metabolic
Macquarie Medical School, Faculty of Medicine, Health and Human Sciences, Mac-
s
ESH Paper
recalibration test (cuff calibration stability over time). Not
all these tests are required for a given device. The necessary
tests depend on whether the device requires individual user
calibration, measures automatically or manually, and takes
measurements in more than one position.
Conclusion: The validation of cuffless BP devices is
complex and needs to be tailored according to their
functions and calibration. These ESH recommendations
present specific, clinically meaningful, and pragmatic
validation procedures for different types of intermittent
cuffless devices to ensure that only accurate devices will be
quarie University, Sydney, New South Wales, Australia, The Shanghai Institute of
Hypertension, Ruijin Hospital, Shanghai Jiaotong University School of Medicine,
Shanghai,
t
Hong Kong Centre for Cerebro-Cardiovascular Health Engineering
(COCHE), Hong Kong, China,
u
CharitC19e - Universit€atsmedizin Berlin, Freie Universit€at
Berlin, Humboldt-Universit€at zu Berlin, Berlin Institute of Health, Department of
Clinical Pharmacology & Toxicology, CharitC19e University Medicine, Berlin, Germany,
v
The Conway Institute, University College Dublin, Dublin, Ireland and
w
Department of
Bioengineering and Department of Anesthesiology and Perioperative Medicine,
University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Correspondence to Professor George S. Stergiou, MD, PhD, FRCP, Hypertension
Center STRIDE-7, National and Kapodistrian University of Athens, School of Medicine,
Third Department of Medicine, Sotiria Hospital, 152 Mesogion Avenue, Athens
11527, Greece. Tel: +30 2107763117; fax: +30 2107719981;
e-mail: stergiougs@gmail.com
Received 21 May 2023 Accepted 22 May 2023
J Hypertens 41:000–000 Copyright ? 2023 Wolters Kluwer Health, Inc. All rights
(BP decrease accuracy); awake/asleep test (BP change
accuracy); exercise test (BP increase accuracy); and
Hypertension (ESH) Working Group on BP Monitoring and
Cardiovascular Variability recommends procedures for
validating intermittent cuffless BP devices (providing
measurements every >30sec and usually 30–60min, or
upon user initiation), which are most common.
Validation procedures: Six validation tests are defined
for evaluating different aspects of intermittent cuffless
devices: static test (absolute BP accuracy); device position
test (hydrostatic pressure effect robustness); treatment test
Sciences, S. Luca Hospital, Milan, Italy,
h
Foundation-Medical Research Institutes,
Geneva, Switzerland,
i
Department of Hygiene, Epidemiology & Medical Statistics,
National and Kapodistrian University of Athens, School of Medicine, Athens, Greece,
j
Department of Hygiene and Public Health, Teikyo University School of Medicine,
Tokyo, Japan,
k
IRCCS Fondazione Don Carlo Gnocchi Onlus, Milan, Italy; Department
of Biotechnology and Life Sciences (DBSV), University of Insubria, Varese, Italy,
l
Department of Internal Medicine, Hospital Mutua Terrassa, University of Barcelona,
Catalonia, Spain,
m
Department of Mechanical Engineering, University of Maryland,
College Park, Maryland, USA,
n
Division of Cardiovascular Medicine, Department of
Medicine, Jichi Medical University School of Medicine, Tochigi, Japan,
o
Nuffield
Department of Primary Care Health Sciences, University of Oxford, Oxford, UK,
p
Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario,
Canada,
q
Department of Bioengineering and Department of Medicine, University
of Pittsburgh, Pittsburgh, Pennsylvania, USA,
r
The George Institute for Global Health,
Journal
Society of Hypertension
for the
measuring devices:
Working Group
and Cardiovascular
George S. Stergiou
a
, Alberto P. Avolio
b
, Paolo
Aletta E. Schutte
d
, Stephan Mieke
e
, Anastasios
Nikos Pantazis
i
, Achilleas Stamoulopoulos
i
, Kei
Alejandro De La Sierra
l
, Jin-Oh Hahn
m
, Kazuomi
Takayoshi Ohkubo
j
, Sanjeev G. Shroff
q
, Isabella
Reinhold Kreutz
u
, Eoin O’Brien
v
, and Ramakrishna
Background: There is intense effort to develop cuffless
blood pressure (BP) measuring devices, and several are
already on the market claiming that they provide accurate
measurements. These devices are heterogeneous in
measurement principle, intended use, functions, and
calibration, and have special accuracy issues requiring
different validation than classic cuff BP monitors. To date,
there are no generally accepted protocols for their
validation to ensure adequate accuracy for clinical use.
Objective: This statement by the European Society of
used in the evaluation and management of hypertension. reserved.
DOI:10.1097/HJH.0000000000003483
of Hypertension www.jhypertension.com 1
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JH-D-23-00362
Keywords: accuracy, blood pressure measurement,
on what to recommend against the background of some
1.2 Objective
Stergiou et al.
favorable reports encouraging their use and the fact that
someofthemhavereceivedformalregulatoryapproval(e.g.,
U.S.FDAclearance,EuropeanUnionCEmarking).However,
this does not guarantee that these devices are accurate for
clinical use [3]. Thus, there is urgent demand expressed by
the scientific community [1–3,8,10,11] to establish standards
whicharespecifictocufflessBPdevicesandcanensuretheir
accuracy and usefulness in detecting and managing individ-
uals with elevated BP in clinical practice.
validation of different types of cuffless BP devices, many
published studies claiming reasonable accuracy of such
devices suffer from inadequate and heterogeneous testing
and reporting [1,8]. Healthcare professionals are uncertain
cuffless, monitoring, smartphone, smartwatch, validation,
wearable, wristband
Abbreviations: AAMI, Association for the Advancement
of Medical Instrumentation; ABPM, Ambulatory blood
pressure monitoring; BP, Blood pressure; ESH, European
Society of Hypertension; IEEE, Institute of Electrical and
Electronics Engineers; ISO, International Organization for
Standardization; PPG, Photoplethysmography
1. INTRODUCTION
1.1 Background
S
everal novel cuffless blood pressure (BP) measuring
devices, typically in the form of a wearable for
automated or manual use, have appeared on the
market, and few gained formal clearance by some regula-
tory organizations [1–3]. These devices are attractive for
individuals with hypertension, but also for apparently
healthy people who wish to monitor their BP as part of
wider ‘wellness’ monitoring [1].
For cuff BP devices, which are widely used for hyper-
tension diagnosis and management in clinical practice,
several protocols for their clinical validation have been
developed, and a Universal Standard has been published
in 2018 by the U.S. Association for the Advancement of
Medical Instrumentation (AAMI), the European Society of
Hypertension (ESH) Working Group on BP Monitoring and
Cardiovascular Variability and the International Organiza-
tion for Standardization (ISO) for global use (AAMI/ESH/
ISO Universal Standard - ISO 81060-2:2018, from now on
referred to as ‘Universal Standard’) [4–6]. However, it is
recognized that the validation protocols for cuff BP devices
are inadequate for cuffless devices [1,4–9]. The primary
reason is that many cuffless devices require individual user
calibration and thereby actually measure intra-person BP
changes rather than absolute BP levels. A secondary reason
is that many cuffless devices offer unique functions. For
example, typical devices are automated yet positioned at
the wrist and may thus be susceptible to significant error
due to hydrostatic pressure effects. Therefore, cuffless
devices necessitate different and more complex procedures
for their validation.
Because of the absence of a standard protocol for the
2 www.jhypertension.com
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The ESH Working Group on BP Monitoring and Cardiovas-
cular Variability responded to this need to have clinically
relevant and feasible procedures for the validation of cuff-
less BP devices intended for screening, diagnosing, treat-
ing, and following hypertension. This statement presents
the background, rationale, principles, procedures, and
requirements for the validation of ‘intermittent’ cuffless
BP measuring devices (see definition below), which are
most common [3]. The primary objective of this work is
to establish essential requirements for such devices taking
into consideration their special functions and calibration,
so that they may be confidently used in clinical practice
for hypertension management. ‘Continuous’ cuffless BP
devices (see definition below) are not addressed here, as
an ISO standard for such devices was recently published
(ISO 81060-3:2022) [12].
1.3 Development process
An international panel of 26 scientists was appointed by the
ESH Working Group on BP Monitoring and Cardiovascular
Variability. The panel included clinicians, bioengineers,
physiologists, and biostatisticians with expertise in clinical
hypertension, BP measurement research, BP device clinical
validation, and BP and cardiovascular measurement tech-
nologies. For developing this ESH statement, several virtual
meetings were conducted, with exchange of opinions and
proposals among the contributing scientists, and several
draft versions were prepared within 1 year, until consensus
was eventually reached.
2. CUFFLESS BLOOD PRESSURE
MEASURING DEVICES
2.1 Cuffless blood pressure measuring device
types and terminology
2.1.1 Measurement principles
Thereareseveraldifferentprinciplesunderlying cufflessBP
measuring devices [7]. However, pulse wave analysis with
or without pulse arrival time is by far the most popular
measurement principle. Pulse wave analysis devices obtain
a peripheral arterial waveform typically with a photople-
thysmography (PPG, optical) or tonometry (force) sensor
and apply machine learning to extract features from the
waveform and calibrate the features to BP. Pulse wave
analysis - pulse arrival time devices are similar except that
an ECG waveform is also measured to extractthetimedelay
between the ECG and peripheral arterial waveforms, and
possibly other ECG waveform features. The calibration
(sometimes referred to as initialization) for these devices
is achieved with periodic (e.g., monthly) cuff BP measure-
ments (cuff-calibrated), or with demographics such as age,
BMI, and sex, which are known to correlate with BP
(demographic-calibrated). Cuffless BP measurement prin-
ciples have been proposed that do not require individual
user calibration (calibration-free). These devices have been
much less investigated but could become available in
the future.
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2.1.2 Intended uses
Cuffless BP measuring devices have different intended uses
(Table 1). The classic cuff BP monitors (oscillometric or
manual auscultatory) provide intermittent BP measure-
ments (snapshots) upon device activation by the user on
each occasion. Classic 24-h ambulatory BP monitoring
(ABPM) obtains intermittent but automated BP readings
in prespecified time intervals, usually every 20–30min for
24h. Cuffless BP devices can provide continuous (e.g.,
beat-to-beat) or intermittent measurements (e.g., several
readings per 24h taken automatically or manually) [13].
In the intensive care, anesthesia, or operating room
setting, where very short-termBP fluctuationsare of clinical
significance, continuous BP monitoring by a cuffless device
would be of value and might replace to some extent more
invasive methods if found to be accurate. On the other
hand, for the diagnosis and management of clinical hyper-
tension, very short-term BP estimations are probably of
limited value. The intended use of cuffless BP monitors
monitor BP (vital sign) continuously and should be validat-
ed against reference invasive intra-arterial BP measure-
ment, as the manual auscultatory method cannot track
very short-term beat-to-beat fluctuations [12]. On the other
hand, for a cuffless BP monitor which will be used
for hypertension screening, diagnosis, and management,
manual auscultatory BP measurement should be the refer-
ence, as this method is the basis for defining diagnostic
and intervention BP thresholds for treatment decisions in
clinical hypertension [1].
2.1.3 Functions and calibration
Cuffless BP measuring devices can be different in function
and calibration. The various functions and modes of cali-
bration establish important terminology in this document
(Table 2). Cuffless BP measuring devices are primarily
categorized as: Continuous: cuffless BP devices, which
report BP readings every C2030s (definition introduced
in ISO 81060-3:2022) [12] or Intermittent: cuffless BP
TABLE 1. Intended uses of cuffless blood pressure measuring devices
Intended use (Users)
Clinical index
(Clinical assessment)
Blood pressure
measurement
Reference
measurement
Hypertension screening (Apparently healthy people) Cardiovascular risk factor (Hypertension) Intermittent Manual auscultatory
Hypertension diagnosis and long-term follow-up (Patients) Cardiovascular risk factor (Hypertension) Intermittent Manual auscultatory
Intensive care - Anesthesia (Healthcare professionals) Vital sign (Hemodynamic condition) Continuous Intra-arterial
Modified from [1].
very
in IS
very
, we
via
le d
rtphone
en
i
tc) e
Validation of cuffless blood pressure devices
needs to be considered, as different procedures and criteria
may be required for their validation [1]. For example, a
cuffless device developed for use in the ICU would ideally
TABLE 2. Function and calibration of cuffless blood pressure measuring
Device function/calibration
BP output
frequency
Continuous
Outputs BP readings e
(definition introduced
Intermittent
Outputs BP readings e
will and initiation.
Measurement
mode
Automated
Measures BP for days
for each measurement
Manual
Measures BP in a sing
(e.g., user holds a sma
still to take a measurem
Sensor
Wearable
Obtains BP with sensor f
glasses, chest device, e
Heart-level Obtains BP with sensor pos
Calibration
Cuff-
calibrated
Reports BP readings after
readings and requires perio
Demographic-
calibrated
Reports BP readings after
(e.g., sex, age, height, wei
Calibration-
free
Reports BP readings withou
(i.e., cuff BP, demographi
Journal of Hypertension
Copyright ? 2023 Wolters Kluwer Health, Inc. Unauthorized
devices, which report BP readings every >30s (usually
30–60min), or upon user initiation. The present document
addresses the principles, procedures, and requirements for
devices – Terminology
Definition
≤30 seconds
O 81060-3:2022 [12]).
>30 seconds (usually 30-60 min), or upon user’s own
eks, or months without requiring any action by the user
a wearable device (see below).
evice position via user activation
, smartwatch, or portable device at heart level while
t).
tted on the user (e.g., wristband, smartwatch, ring, on
ither automatically, manually, or both.
itioned at/near heart level (e.g., a chest device).
initial individual-user input of one or more cuff BP
dic recalibration with cuff BP measurements.
initial input of individual user demographics
ght, or other).
t any additional individual user information
cs, or other).
www.jhypertension.com 3
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the clinical validation of intermittent cuffless BP devices
reporting absolute BP readings (values) intended for
screening, diagnosis, and monitoring of hypertension.
‘Trending’ BP cuffless devices, which provide BP changes
relative to an unknown user-specific baseline value (e.g.,
for a BP increase from 100mmHg at baseline to 115mmHg
after some time, a trending device would aim to report
0mmHg and then 15mmHg instead of the absolute BP
values) [12], are not considered in this statement, as they
may not be useful in clinical hypertension diagnosis
and management.
Intermittent cuffless devices may be Automated or
Manual (initiated or activated by the user). Automated
devices come in the form of a Wearable and report BP
readings without any action of the user, whereas manual
devices can come in a wearable or nonwearable (e.g.,
smartphone) form and take BP measurements in a single
device position relative to the heart (defined by the manu-
facturer) upon user initiation. Automated devices may be
further categorized as a wearable sensor at Heart-level or
invasive intra-arterial method directly ‘measures’ BP. All
noninvasive cuff BP methods (including standard reference
manual auscultatory and also automated oscillometric
methods) indirectly ‘estimate’ BP using different methodol-
ogies and assumptions rather than making a true ‘measure-
ment’ofthe arterialBP. Thisis also the case with cuffless BP
devices not requiring individual-user calibration. On the
otherhand,cuff-calibratedcufflessdeviceseffectively‘track
changes’ in BP relative to the preceding cuff BP measure-
ment for calibration, but do output ‘absolute BP values’ by
using the cuff BPmeasurement obtained during calibration.
Demographic-calibrated cuffless devices may be inter-
preted to ‘predict’ the BP level from basic user information
and likewise track BP changes but in comparison to the
predicted BP level. Despite the fundamental differences in
how BP readings are generated with different technologies,
in this document the term BP ‘measurement’ will be used
for all the above instances to represent the ‘BP determina-
tion’ in general, irrespective of the method used.
3. VALIDATION
PRESSURE
3.1
cuffless
Alt
level,
6 and
Stergiou et al.
elsewhere on the body. Heart-level devices are not affected
by hydrostatic pressure changes in different body postures.
Most automated devices are wrist devices and do not fall in
this category. Automated and manual devices may be Cuff-
calibrated, Demographic-calibrated,orCalibration-
free. A cuff-calibrated device may also take demographics
as additional input for determining BP. The manner of
calibration which a cuffless device utilizes is most relevant
for determining a validation protocol. There may be nine
types of intermittent cuffless BP measuring devices based
on the different combinations of their functions and cali-
bration (Table 3). Finally, some cuffless BP devices may
offer multiple functions (e.g., a cuffless BP technology
implemented in a smartwatch device may operate both
automatically and manually).
2.2 Blood pressure measurement, estimation,
change tracking, and prediction
BP measurement is a widely used term to describe a BP
value provided by any device, whereas in fact only the
TABLE 3. Nine possible types of intermittent cuffless blood pressure
Each of these device types requires a different set of validation tests (see Table
4 www.jhypertension.com
Copyright ? 2023 Wolters Kluwer Health, Inc. Unauthorized
periodic calibrations with cuff devices, and/or provide
automated BP measurements with sensors not positioned
at the level of the heart. As a result, clinical validation for
cuffless BP monitors is necessarily more difficult [1,7,8].
Unique aspects in the validation of cuffless BP measuring
devices include testing the following:
1. Ability to track BP changes such as short-term, diur-
nal, treatment-induced, seasonal, or other variations
(for devices requiring individual-user calibration).
2. Impact of different device positions relative to
the heart (for automated devices with sensors not
at heart level).
devices according to their function and calibration
Fig. 1).
hough
aspects for clinical validation of
blood pressure measuring devices
classic cuff devices measure absolute BP at heart
many cuffless devices measure BP changes, require
Unique
OF CUFFLESS BLOOD
MEASURING DEVICES
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3. Impact of body movement and physical activity (for
automated wearable devices).
4. Stability of cuff calibration accuracy over time (for
devices requiring periodic cuff calibration).
3.2 Current validation protocols for blood
pressure measuring devices
3.2.1 AAMI/ESH/ISO Universal Standard for cuff
blood pressure devices (ISO 81060-2:2018)
In the last 30years, several protocols have been developed
by scientific organizations for the validation of cuff BP
devices [9]. In 2018, AAMI, ESH, and ISO agreed on a
Universal Standard (AAMI/ESH/ISO - ISO 81060-2:2018)
for global use [4,5]. According to this standard, a general
population study is required with at least 85 subjects
fulfillingprespecifiedcriteria(e.g.,age,sex,BPdistribution,
cuff size, etc.) and using manual auscultatory BP as the
reference method. In 2020, an amendment was published
to address issues regarding limb size distribution [6]. How-
ever, this standard is not appropriate for the validation of
cuffless BP devices [1,4,5]. The most important limitation is
3.2.2 Institute of Electrical and Electronics Engineers
(IEEE) standard for cuffless wearable devices
In2014,theIEEEpublishedthefirststandardforassessingthe
accuracy of ‘cuffless wearable BP devices’ (IEEE 1708-2014)
[18]. An amendment to the protocol was published in 2019
(IEEE1708a-2019)[19](Table4).Thisstandardisalandmark
contributionintheeraofcufflessBPdevices,asfundamental
issuesandmethodologicalconsiderationswhicharespecific
to these devices were addressed for the first time. The IEEE
standard was designed to test the accuracy of both continu-
ous and intermittent cuffless BP devices using manual aus-
cultatoryBPasreference.Thecomparisonsaremadeinstatic
conditions immediately following cuff calibration, after in-
ducingBPincreasesanddecreasesofspecificmagnitude(up
to30mmHg),andbeforecuffrecalibrationisrecommended.
A sample size of C2185 individuals is required, and the pass
criteria are based on the mean absolute error of the test
measurements against the reference measurements [18,19].
Although the IEEE standard addresses key aspects of
cuffless BP device validation, it did not always provide
adequate solutions. An important limitation is that methods
for inducing the BP changes were not specified, rendering
this standard to be more theoretical than implementable.
blood
ISO
cont
depending
tion
Test and reference BP measurement Simultaneous or sequential Simultane
10 mmHg
a
See
Validation of cuffless blood pressure devices
Journal
Copyright
3.Table
requirements (BP difference) C207 mmHg (mean absolute
difference)
C206C6Pass
that the Universal Standard does not include procedures to
test the ability of devices to track BP changes. Such pro-
cedures are not necessary for cuffBP devicesbut are of vital
importance for cuffless devices requiring individual-user
calibration. It has been demonstrated that a cuffless BP
device immediately post cuff-calibration can easily pass the
Universal Standard for cuff BP devices, which is performed
in static conditions and excludes cases with clinically im-
portant BP variability [1]. However, such a device may be
grossly inaccurate in its actual purpose of tracking changes
in BP (e.g., acutely induced in a laboratory environment,
duringsleep,orbyBP-loweringdrugs).Thus,thevalidation
ofcufflessBPdevicesusingprotocolsdevelopedforcuffBP
devices (which has been done in several published studies
[14–17]) is inadequate and misleading [1].
TABLE 4. Key aspects of validation procedures developed for cuffless
Electronics Engineers [18,19], the International Organizat
Hypertension Working Group on BP Monitoring and Cardiov
IEEE Standard
1708–2014 [18] &
1708a–2019 [19] 81060-3
Device type Cuffless wearable BP devices Cuffless
Number of subjects C2185 30–120
correla
Reference method Manual auscultatory
Validation tests
A. Immediately post calibration Yes
B. In different device positions Yes
C. After inducing BP change Yes
Laboratory setting: acute
(procedures not specified)
Clinica
(routine
D. Before recalibration Yes
of Hypertension
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Indeed, few studies have attempted to implement this
standard, and they failed to properly address the key step
of inducing BP changes (especially BP lowering) [20,21].
Thus, it is crucial to explicitly define methods for inducing
BP changes which are reproducible and applicable for all
device types and feasible for many validation centers.
3.2.3 ISO 81060-3:2022 standard for cuffless
continuous devices
In 2022, ISO published itsfirststandard (ISO 81060-3:2022)
that is specific for ‘continuous noninvasive sphygmoman-
ometers’ (Table 4), defined as devices ‘estimating BP from
each cardiac cycle without arterial puncture and providing
a continual series of BP parameters’ [12]. Such devices
provide BP values with an output period (period of time
pressure measuring devices by the Institute of Electrical and
ion for Standardization [12], and by the European Society of
ascular Variability. Modified from [1]
Standard
:2022 [12]
ESH Recommendations 2023
(current document)
inuous BP devices Cuffless intermittent BP devices (9 types – cf. Table 3)
on intraclass
for each BP parameter
85–175 depending on the device type
Intra-arterial Manual auscultatory; 24-h oscillometric
Yes Yes, for some device types
a
Yes Yes, for some device types
a
Yes
l setting: acute
in-hospital care)
Yes, for some device types
a
Laboratory setting: short-term (exercise)
Clinical setting: longer-term (prepost treatment;
awake/asleep)
Yes Yes, for some device types
a
ous Sequential (24-h BP simultaneous)
(meanC6SD of
difference)
C205C68 mmHg (meanC6SD of difference)
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after which updated BP values are provided) C2030s. This
means that the protocol is inappropriate for devices with an
output period >30s, which is the case for most cuffless
devices [12]. Note that although a continuous cuffless
devicemayanalyzeeachheartcycle,outputofBPestimates
may not occur for every cycle.
The ISO 81060-3:2022 standard is intended for ‘measur-
ingcontinuousBPchangesinclinicalsettingswherechanges
in BP have therapeutic consequences’ [12] (e.g., ICU and
operating rooms where BP needs to be continuously
assessed as a vital sign). Thus, this standard is not applicable
for BP devices intended for screening, diagnosing, and
ABPM values calculated using different hourly BP samples
within the same 24-h period, the meanC6SD of the awake/
asleep SBP/DBP difference was -0.1C63.7/0.4C62.7mmHg,
which may ensure high power for studies comparing two
24-h BP monitoring methods applied simultaneously (G.S.
Stergiou, K.G. Kyriakoulis, unpublished data). However,
oscillometric cuffBPdevicesalsoyieldsomemeasurements
with appreciable error, and different brands of validated
oscillometric devices will not produce identical BP values
[32]. Averaging the many BP measurements over the awake
and asleep periods and comparing the awake/asleep BP
changes rather than absolute BP values may mitigate these
l
etc.
Stergiou et al.
managingclinicalhypertensionwherefastchangesrequiring
measurement frequency C2030s is probably of limited value.
The ISO 81060-3:2022 standard requires the use of an
intra-arterial reference for the validation of continuous
cuffless BP monitors. However, intra-arterial BP values
differ from those obtained by manual auscultation, which
is the reference method for the diagnosis and management
of clinical hypertension. Moreover, the intra-arterial refer-
ence restricts recruitment to patients having an intra-arterial
line, which limits its applicability and the generalizability of
the results to healthy people and special populations.
3.3 Clinical field studies of automated wearable
intermittent devices versus oscillometric cuff
devices
A pragmatic and clinically meaningful approach which has
been used in several studies for testing the accuracy of
automated wearable intermittent cuffless devices is the
evaluation versus simultaneous 24-h ABPM using validated
oscillometricupperarmcuffdevices[22–27].Thisapproach
is important especially for individual-user calibrated devi-
ces to assess whether they can track awake/asleep BP
changes(whichisahighlyrelevanttestforclinicalpractice);
are robust to different device and body positions; and are
effective during different daily activities. Although the im-
pact of each one of these factors cannot be separately
assessed, several studies have shown that 24-h ABPM is
very useful for demonstrating that some commercially
available cuff-calibrated cuffless devices cannot track the
awake/asleep BP change, which was evident even with
relatively small sample sizes [26,28–30].
The reproducibility of ABPM is known to be superior to
that of the office BP measurements [31]. Moreover, the
reproducibility of ABPM based on different hourly BP
samples within the same 24-h period is superior to that
reported in published studies that compared ABPM record-
ings performed on different days [31]. In a comparison of
TABLE5. Availableproceduresforassessingtheaccuracyofindividua
BP changes Setting Procedure
Short-term (minutes) Laboratory BP change via bicycle, treadmill, handgrip,
mental arithmetic, cold-pressor, slow
breathing, fast-acting drug (e.g.,
nitroglycerin), Valsalva maneuver,
Mid-term (24h) Clinical field Awake/asleep BP change
Long-term (days/weeks) Clinical field Antihypertensive drug-induced BP change
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issues [32]. Thus, a comparison of the awake/asleep BP
change reported by wearable automated devices with that
by a reference 24-h ABPM cuff device appears to be a valid
and pragmatic validation approach.
Home BP monitoring using validated oscillometric up-
per arm cuff BP devices may also be useful in assessing the
ability of cuffless BP devices to track BP changes induced
by drug treatment (assessment before and days/weeks after
treatment change) [26]. This is a clinically relevant and
practical experiment with direct implications for using
cuffless BP devices in practice. However, whenever possi-
ble manual auscultation is the preferred reference method.
3.4 Available procedures for assessing the
ability of cuffless devices to track blood
pressure changes
The assessment of the ability to track BP changes is crucial
and the most problematic part of the validation of common
individual user-calibrated cuffless BP devices [8]. The
abovementioned IEEE and ISO standards for cuffless devi-
ces highlight the need to incorporate BP changes in the
validation procedure [12,18,19]. The current IEEE standard
does not present specific interventions for inducing BP
changes [18,19], while the ISO standard leverages natural
BP changes occurring in the hospital environment [12]. It
should be noted that for cuffless devices providing BP
readings without requiring any individual user-specific
input before use, there is no reason to require validation
for their ability to track BP changes [8].
It is important to define protocols for standardized
procedures to induce BP changes, which are feasible for
many research centers, well tolerated and acceptable by
many subjects/patients, and provide reproducible results,
allowingthecomparisonoffindingsbydifferentstudies.BP
changes can be acute, diurnal, or long-term (Table 5). As
mentioned above, acute (very short-term) BP changes may
not be meaningful in clinical hypertension diagnosis and
user-calibratedcufflessdevicesintrackingbloodpressurechanges
Key points
C15 Interventional procedure
C15 Potential risks for some patients
C15 Reference: manual auscultatory BP measurement pre and post/
during procedure
C15 Observational procedure
C15 Specifically for automated wearable cuffless BP devices
C15 Reference: automated 24-h ambulatory cuff BP measurement
C15 Observational procedure
C15 Reference: manual auscultatory or automated home cuff BP
measurement pre- and post-treatment
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Validation of cuffless blood pressure devices
management, whereas diurnal (awake/asleep) and long-
term (weeks-months) BP changes are routinely assessed.
BP changes (increases or decreases) could potentially be
induced in the laboratory setting, or in the pragmatic
context of clinical care (Table 5) [1].
In the laboratory setting, BP changes can be induced via
different physiological mechanisms, including via physical
exercise (bicycle, handgrip, treadmill, legs up-down, etc.),
mental arithmetic test, cold pressor test, slow breathing,
Valsalva maneuver, neck chamber technique, or short-
acting drugs such as nitroglycerin [1]. Applying these pro-
cedures would transform the classic validation procedure
from observational (as with cuff BP device validation) to
interventional, potentially raising safety issues for some
subjects (patients), as well as issues related to feasibility,
reproducibility, consistency, resources, cost, and other
factors. BP responses of different interventions are not
uniformly predictable among different individuals and
could induce severe hypotension or hypertension. Further-
more, some interventions are short acting, making auscul-
tation a less suitable reference. Thus, most of these
interesting experimental procedures may not be appropri-
ate for validation protocols designed to be applied in
different research centers for formally approving or reject-
ing a device for clinical use. Some interventions can satisfy
these requirements with limited risks for most patients.
Submaximal physical exercises (bicycle and handgrip) in
particular are generally well studied interventions which
can be used in many centers for inducing short-term and
relatively steady BP increases [33–35].
Inthe pragmatic context ofclinical care, investigations to
test the abilityof a cufflessdevice to track BP changes might
include standard validation sessions of the cuffless device
before and several days/weeks after up- or down-titration
of BP lowering drug treatment to assess the treatment-
induced BP change, or simultaneous cuffless wearable
BP monitoring with a validated upper-arm cuff oscillomet-
ric ABPM device for 24h to assess awake/asleep BP change
[1].Clinicalfieldstudiesmayinvolvetheuseofoscillometric
cuff devices as the reference BP method (office, ambulato-
ry, or home). In this case, the BP changes rather than
absolute BP values should be assessed, and several meas-
urements of the reference (and thus test) device should be
averaged to mitigate the impact of reference BP measure-
ment error.
4. EUROPEAN SOCIETY OF
HYPERTENSION RECOMMENDATIONS
FOR VALIDATING CUFFLESS BLOOD
PRESSURE MEASURING DEVICES
4.1 Rationale
Automated cuff devices determine BP from only the arterial
(oscillometric cuff pressure) waveform at the time of mea-
surement. By contrast, many cuffless devices determine BP
from a hemodynamic measurement and other information
that is known to be predictive of the prevailing BP. This
extra information is often a preceding cuff BP measurement
or demographic data, and is invoked for individual
user calibration. However, the other information can be
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dynamic, such as the time of day, which has been shown to
help track BP at night [3], silent accelerometer to similarly
indicate nighttime, and heart rate, which could be obtained
withanECG,ratherthanahemodynamicmeasurement[3].It
is ideal to assess cuffless devices in relation to ‘baseline
models’. Baseline models determine BP without the hemo-
dynamic‘measurement’andonlyfromtheotherinformation
(calibration or dynamic data). If a cuffless device is not
significantly more accurate than the baseline model, then
there is no need to have a device at all. For example, the
Microsoft Research Aurora Project concluded that several
cuff-calibrated cuffless devices were not able to provide
greater BP measurement accuracy than a suitable baseline
model[3].However,arrivingatappropriatebaselinemodels,
especially for demographic-calibrated devices, may be diffi-
cultatpresent.Furthermore,fromaclinicalpointofview,the
bottom line is that the device provides data useful for man-
aging hypertension, irrespective of how it determines BP.
These ESH recommendations therefore do not directly
include assessment of baseline models, but focus on testing
individual user-calibrated devices in terms of measuring
clinically meaningful BP changes with a level of accuracy
that facilitates hypertension management. The required BP
changes may be large enough to prevent the cuff BP
measurement at calibration alone from trivially passing
the tests. In addition, even if a device can measure absolute
BPfrom static demographicinformation alone, itwouldstill
have to be proven to track BP changes over time through
some dynamic measurement. An important and related
point of these ESH recommendations is that the procedures
for changing BP are specific and balance practicality with
assurance that only adequate devices will be used in
clinical practice.
In these ESH recommendations, the number of tests
required for a given device naturally increases with increas-
ing functions of the device as well as its calibration require-
ments.Ontheotherhand,iftechnicalhurdlesareovercome
such that a cuffless device is calibration-free like an auto-
mated cuff device, then it should likewise undergo a single
test. The net effect of the ESH recommendations may be
that the timeline from development through validation of a
cuffless device is comparable for all device types.
As much as possible, these ESH recommendations are
based on the principles of the Universal Standard for
automated cuff devices [4,5], which has been extensively
used and globally accepted. The ESH recommendations
also take inspiration from the IEEE 1708-2014 & 1708a-2019
[18,19] and the ISO 81060-3:2022 [12] standards for
cuffless devices.
4.2 Validation tests – Overview
These ESH recommendations include six different valida-
tion tests: static test (absolute BP accuracy); device position
test (hydrostatic pressure effect robustness); treatment test
(BP decrease accuracy); awake/asleep test (BP change
accuracy); exercise test (BP increase accuracy); and recali-
bration test (cuff calibration stability over time) (Fig. 1,
Boxes 1–6). These tests are intended to address all of
the accuracy concerns of different intermittent cuffless
devices with varying functions and calibration (Table 2).
There are nine types of cuffless BP devices (Table 3), and
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Stergiou et al.
each device shall undergo a different subset of the tests
according to its type (Table 6). To be recommended for
clinical use, a cuffless BP device must pass all required tests
(Table 6).
FIGURE 1 Summary of validation tests for cuffless blood pressure devices.
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Cuffless BP devices which do not require any individual
user calibration (calibration-free) shall be validated in an
85-subject general population study according to the Uni-
versal Standard (ISO 81060-3:2022) (Table 6). Automated
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different from the position used for calibration. For demographic-calibrated
devices which require a 35-subject static test, the 35-subject position test shall
be performed independently from the static test in a different device position.
- Age 18–80years.
- Males C2130%, females C2130%.
-Reference BP distribution: As in the Universal Standard (C215%/C215%/C2120% of
the reference SBP readings shall beC20100/C21160/C21140mmHg respectively, and
C215%/C215%/C2120% of the reference DBP readings shall be C2060/C21100/
C2185mmHg) respectively [4,5].
Procedure: This test shall use the same arm sequential reference-test BP
measurement procedure of the Universal Standard [4,5] in at least one
different position compared to a standard position. There shall be three
valid paired reference-test BP measurements per patient for C21105 total
measurement pairs, and the vertical distance between the standard and
nonstandard positions must be C2120cm (and ideally as large as practically
possible). For cuff-calibrated devices calibration shall be performed at least one
Validation of cuffless blood pressure devices
wearable calibration-free devices must also undergo the
exercise test according to the Universal Standard for ABPM
cuff devices [5]. If the device sensors are not placed at heart
level, they must additionally undergo the device position
Box 1 STATIC TEST
Rationale: This test shall be used for calibration-free and demographic-
calibrated cuffless BP devices (Table 6). This test assesses the absolute BP
measurement accuracy of the cuffless device and is equivalent to the Universal
Standard for validation of an automated cuff device against reference dual-
observer manual auscultation [4,5]. Cuff-calibrated BP devices shall not
undergo a static test, provided that the cuff BP device used for calibration
has been validated according to the Universal Standard [4,5].
Sample size - Subjects:
- Sample size: C2185 subjects for calibration-free devices; C2135 subjects for
demographic-calibrated devices.
- Age 18–80years.
- Males C2130%, females C2130%.
- Reference BP distribution: As in the Universal Standard for 85-subject and
35-subject studies (C215%/C215%/C2120% of the reference SBP readings shall be
C20100/C21160/C21140mmHg respectively, and C215%/C215%/C2120% of the
reference DBP readings shall be C2060/C21100/C2185mmHg) respectively [4,5].
Procedure: This test shall use the same arm sequential reference-test BP
measurement procedure of the Universal Standard for a general population
[4,5]. There shall be three valid paired reference-test BP measurements per
subject (C21255 or C21105 total measurement pairs for 85-subject or 35-subject
study, respectively).
Data analysis - Reporting:
- According to the Universal Standard [4,5,36].
- Bland–Altman plots of the test-reference BP differences against their average
values [36].
Pass criteria: Criterion 1 of the Universal Standard (mean and SD of theC21255
(or C21105) BP errors [test BP measurement minus reference BP measurement]
within 5 and 8mmHg, respectively). For an 85-subject study, also Criterion 2
(SD of C2185 average BP errors [subject average test BP measurement minus
subject average reference BP measurement) within levels dependent on the
mean BP error from Criterion 1) [4,5].
test (Box 2). Calibration-free devices do not need to under-
go tests for assessing BP changes.
Cuffless BP devices which require individual-user cali-
bration (cuff-calibrated or demographic-calibrated) should
commence validation with a ‘primary’ test. The primary test
iseitherthetreatmenttest(Box3)formanualdevices,orthe
awake/asleep test (Box 4) for automated wearable devices.
If this test is successful, then all the additional required tests
shall be performed sequentially (Table 6). For manual
devices, the exercise test should be performed second.
For automated wearable devices, the treatment test should
be performed second, followed by the exercise test.
Some cuffless devices may require special programming
by the manufacturer to be able to undergo testing. For
example, an automated wearable cuffless BP device that
doesnot display the BPmeasurement inreal timeshouldbe
reprogrammed accordingly.
4.3 Validation tests – Sample sizes
A Monte Carlo simulation analysis was performed to calcu-
late the pass probabilities of cuffless devices with different
levels of accuracy for each test (Fig. 1) using different
sample sizes (see Supplemental Digital Content, Suppl.
Tables 1–6, http://links.lww.com/HJH/C212). The analysis
was extensive and included a total of 1000 simulations for
each combination of 15 different sample sizes and 13
different accuracy level hypothetical devices for each vali-
dation test (see Supplemental Digital Content, Suppl.
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Box 2 DEVICE POSITION TEST
Rationale: This test shall be used for automated wearable cuffless BP devices
with sensors not worn at heart level (Table 6). This test assesses the robustness
of the cuffless device against hydrostatic pressure effects on BP measurement.
As an example, for a wrist device and a typical arm length, local BP is about
40mmHg higher when the hand is fully lowered than when it is at heart level,
despite no change in systemic BP. When the sensor is at heart level (e.g., classic
arm cuff device, chest patch), hydrostatic pressure effects are avoided. For
manual cuffless devices, the user is expected to always take the measurement
in a standard position according to manufacturer specification and thereby
obviate hydrostatic pressure effects (as well as movement artifact). Devices
requiring the position test shall be validated against reference dual-observer
manual auscultation in a standard position (e.g., sitting position with arm
restingonthetableastypicallyappliedforcalibration)andatleastonedifferent
vertical position with respect to the heart. Examples of the alternate position
may be:
- Sitting posture with arm hanging free on the side for a cuffless wrist or finger
device;
- Supine posture for a cuffless device embedded in glasses; and
- Supine posture for a cuffless device embedded in a foot accessory/band.
Sample size - Subjects:
- Sample size: C2135 subjects. For calibration-free devices which require an 85-
subject static test, the 35-subject position test can be part of the static test with
validation in the standard position in 50 subjects and in at least one different
position in 35 subjects. For cuff-calibrated devices the 35-subject device
position test shall be performed only in a nonstandard position, which is
Tables 1–6, http://links.lww.com/HJH/C212). Criterion 1
of the Universal Standard was generally employed
(see below). Low, moderate, and high accuracy cuffless
devices were defined according to the meanC6SD of their
BP errors against the reference method for all tests [4]. A
high accuracy device yields meanC6SD of the test-reference
BP differences of 0–3C60–5mmHg; a moderate accuracy
device, 3–5C65–8mmHg; and a low accuracy device,
>5C6>8mmHg [4] (see Supplemental Digital Content,
Suppl. Tables 1–6, http://links.lww.com/HJH/C212).
For the novel awake/asleep test, BP error refers to the
test-reference awake/asleep BP change difference. For this
test, meanC6SD limits of 5C68mmHg were adopted as pass
criteria. For a cuffless device with a mean of 0mmHg and a
SD of 8mmHg, about 80% of the errors would lie within
10mmHg, which may be a reasonable requirement. On the
other hand, for a device with mean of t5 or -5mmHg and
an SD of 8mmHg, about 70% of the errors would lie within
10mmHg, which may also be acceptable. In these extreme
cases, about 30% of the errors would be C2110mmHg.
day before the test.
Data analysis - Reporting:
- According to the Universal Standard [4,5,36].
- Bland-Altman plots of the test-reference BP differences against their average
values [36].
Pass criteria: Criterion 1 of the Universal Standard for N C21 35 subjects with
device in alternate position.
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Sample size - Subjects:
- Sample size: C2135 subjects.
- Age 18–80years.
- Males C2130%, females C2130%.
- Reference BP distribution: C2130% of the subjects shall have average 24-h
ambulatory cuff SBP C21130mmHg and C2130% shall have average 24-h
ambulatory cuff DBP C2180mmHg; C2130% of the subjects shall have average
Stergiou et al.
Box 3 TREATMENT TEST
Rationale:Thistestshallbeusedforcuff-calibratedordemographic-calibrated
cuffless BP devices (Table 6). This is a ‘primary’ test for manual devices and
should be performed first. If the test is successful, then the other required tests
(Table 6) shall be performed. This test assesses the ability of the cuffless device
to track long-term and clinically important BP decreases in the context of
routine clinical care. The device is calibrated according to the manufacturer
instructions in subjects with uncontrolled hypertension, then antihypertensive
drug treatment is initiated or up-titrated, and after 1–4weeks the device
accuracy is tested against reference dual-observer manual auscultation before
re-calibration.
Sample size - Subjects:
- Sample size: C2135 subjects.
- Age 18–80 years
- Males C2130%, females C2130%.
- Untreated or treated for hypertension, with uncontrolled BP and medical
indication for antihypertensive drug treatment initiation or up-titration.
- At least 35% of the subjects shall have a diuretic drug added (thiazide or
thiazide-like, not received at baseline) andC2135% of the subjects should have a
A correlation coefficient between the awake/asleep BP
change of the cuffless device versus the reference device
of0.70wasalsoadoptedasafurtherpasscriteriontoensure
BP change tracking ability in individuals. A correlation
coefficient of 0.70 means that a cuffless device accounts
for about 50% of the variance in the reference measure-
ments. Although useful for assessing BP change tracking
ability, the correlation coefficient was not utilized for the
treatment and exercise tests, because it greatly increased
the probability of a moderate accuracy device to fail.
Todefinetheoptimalsamplesizeforeachtest,focuswas
put on moderate accuracy devices with the aim of ensuring
that the selected sample size would give a reasonable pass/
failure probability [4] (see Supplemental Digital Content,
Suppl. Tables 1–6, http://links.lww.com/HJH/C212).
long-acting dihydropyridine calcium channel blocker added (e.g., amlodipine,
not received at baseline) as monotherapies or on top of other drugs. Treatment
choices will be exclusively made according to the individual’s clinical indication.
These drugs reduce BP through very different physiological mechanisms (blood
volume reduction in the case of a diuretic, and vasodilation in the case of a
calcium channel blocker) and consequently change the PPG waveform for
example in distinct ways. Therefore, the pair of drugs constitutes a necessarily
challenging test for cuffless devices requiring individual user calibration.
- At least 60% of the subjects shall have reference SBP decrease C2110mmHg
and C2160% of the subjects shall have reference DBP decrease C215mmHg. At
least 30% of the subjects shall have reference SBP decrease <10mmHg and
C2130% of the subjects shall have reference DBP decrease <5mmHg. BP
decrease here is defined as the average post-treatment (validation session)
reference BP minus the average pre-treatment (baseline session) reference BP.
- Subjects may be recruited from those who performed the static and/or device
position tests. This test can be combined with the recalibration test (see below)
if the post-treatment validation is performed at the time when recalibration is
recommended by the manufacturer (e.g., 4weeks).
Procedure: Baseline BP will be assessed by three sequential auscultatory BP
measurements (two observers) after 5 min sitting rest and with 30s between
measurements. The average of the last two readings will be used. Then the
treatment change shall be performed, and the validation test shall be applied
some days or weeks after the drug treatment change (usually 1–4weeks later
and before the test device requires re-calibration) [4,5]. The same arm
sequential procedure of the Universal Standard will be applied with three
valid paired reference-test BP measurements obtained per patient for a total of
C21105 pairs. For cuff calibrated devices, the calibration shall be performed at
least one day before measuring baseline BP and applying treatment changes
and recalibration shall not be performed before the validation session.
Data analysis - Reporting:
- According to the Universal Standard [4,5,36].
- Pre- and post-treatment reference BP (meanC6SD).
- Bland–Altman plots of the test-reference BP differences against their average
values [36].
- Correlation plots of the test post-pre treatment BP changes against the
referencepost-pretreatmentBPchangesalongwiththecorrelationcoefficient.
Pass criteria: Criterion 1 of the Universal Standard [4,5].
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Box 4 AWAKE/ASLEEP TEST
Rationale: This test shall be used for automated wearable cuffless BP devices
that are cuff-calibrated or demographic-calibrated (Table 6). This is a ‘primary’
test forautomatedwearable devices andshould beperformedfirst. Ifthetestis
successful, then the other required tests (Table 6) shall be performed. This test
assesses the ability of the cuffless device to track clinically important BP
decreases during sleep. The test is based on comparison of the cuffless
device with classic 24-h ABPM and could be performed in the context of
routine clinical care. It will not compare individual BP values but rather the
average awake/asleep BP changes of the cuffless device versus ABPM. This test
will also indirectly assess accuracy under varying device position, activity,
and motion.
An acceptable probability for a moderate accuracy device
(e.g.,with errorof4C67mmHg)to failwasgenerally consid-
ered to be about 20%. This approach is in line with the
justification of the 85-subject sample size for the Universal
Standard [4]. Furthermore, there was no reason to focus on
highandlowaccuracydevices,asthesedeviceshadeitheran
adequately low, or an adequately high probability to fail,
respectively (see Supplemental Digital Content, Suppl.
Tables 1–6, http://links.lww.com/HJH/C212). The simula-
tionwasconductedusingR(Rversion4.2.2),andthecodeis
24-h ambulatory cuff SBP <120mmHg and C2130% shall have average 24-h
ambulatory cuff DBP <70mmHg.
Procedure: The cuffless BPdevice shallbecomparedtoclassic 24-h ABPMona
routine day. For cuff- calibrated devices, calibration shall be performed at least
one day before the test. Reference 24-h ABPM shall follow the ESH guidelines
[37] with an upper-arm cuff device validated via the Universal Standard [4,5].
Measurements shall be taken at 20min intervals during the entire 24-h period.
Awake and asleep time intervals will be defined using each subject’s reported
in-bed and out-of-bed times during the 24-h period. At least 25 awake and 12
asleep BP readings indicated by the device as valid, and at least one valid BP
reading every 2h of the 24-h period are required for an acceptable ABPM
recording. The minimum requirements for valid BP monitoring via the cuffless
device should be specified by manufacturer instructions. The cuffless device
may be applied for 24-h simultaneously with reference ABPM, or for more days
also per manufacturer instructions. However, the cuffless BP measurements
shall be compared to a single valid 24-h reference ABPM session. The cuffless
and reference devices may be applied on the same limb, or on opposite limbs if
cuff inflation interferes with cuffless device functioning. In the latter case, the
interarm BP difference shall be checked using the ISO 81060-3:2022
procedure [12]. This procedure involves two observers taking sequential BP
measurementsonthetwoarms(60sintervals)andalternatingthestartingarm.
The procedure will be repeated until three valid BP readings on the right arm
and the left arm are obtained. Subjects with average absolute difference
between the two arms >15mmHg for SBP and/or >10mmHg for DBP shall
beexcluded.BPdataselectionprotocolshallbeperformedaccordingtotheISO
81060-3:2022 [12].
Data analysis - Reporting:
- Participant age, sex, weight, height, and average 24-h, awake, and asleep
SBP/DBP reported by the reference (cuff) device and the test (cuffless) device
(meanC6SD).
- Participant average awake-asleep SBP/DBP change (meanC6SD, mmHg)
reported by the reference device and the test device.
-Participantaverage awake-asleep SBP/DBP change reported by the test device
minus average awake-asleep SBP/DBP change reported by the reference device
(meanC6SD, mmHg).
- Bland–Altman plots of the differences between the test awake-asleep BP
changes and the reference awake/asleep BP changes against their average
values [36].
- Correlation plots of the test awake-asleep BP changes against the reference
awake-asleep BP changes.
Pass criteria: Mean C205mmHg and SD C208mmHg for the difference between
the awake-asleep SBP/DBP change from the test and reference devices, and
correlation coefficient C210.70 between the test awake-asleep BP changes and
the reference awake-asleep BP changes (for both SBP and DBP).
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provided (see Supplemental Digital Content, Suppl. Text
Document 1, http://links.lww.com/HJH/C212).
With this approach, it was evident that for all tests a
moderate accuracy device (with error of 4C67mmHg)
appears to have an acceptable failure probability of about
20%usingasampleofatleast35subjects(seeSupplemental
Digital Content, Suppl. Tables 1–6, http://links.lww.com/
HJH/C212). Thus, a sample size of at least 35 subjects per
test was deemed appropriate for cuffless devices requiring
multiple tests for their validation (Table 6). Increasing the
samplesizeofanyvalidationtestincreasesthestudypower,
which is particularly important for moderate accuracy
devices as their probability to pass is increased. (see Sup-
plemental Digital Content, Suppl. Tables 1–6, http://links.
lww.com/HJH/C212).
Box 5A. EXERCISE TEST – BICYCLE EXERCISE TEST (Standard Procedure)
Rationale:Thistestshallbeusedforcuff-calibratedordemographic-calibrated
cuffless BP devices (Table 6). It assesses the ability of the cuffless device to track
physiological BP increases and is essentially the same as the Universal Standard
for the validation of classic ABPM devices against manual auscultation during
exercise [5]. It will also show whether the cuffless device can provide accurate
BP measurements under some motion (similar to what may be encountered in
daily life). Submaximal cycling, which has limited risks for subjects, will be
employedto inducesubstantial,short-termbut steady(fora coupleof minutes)
BP increases.
Sample size - Subjects:
- Sample size: C2135 subjects.
- Age 18–65years.
- Males C2130%, females C2130%.
- Reference BP distribution: C2130% of the subjects shall have baseline (pre-
exercise) reference SBP C21140 mmHg.
- Exclusion criteria: baseline SBP C21160mmHg and/or baseline DBP
C21100mmHg, high total cardiovascular risk, or any other clinical condition
possibly associated with any risk to the subject in this test.
- At least 30% of the subjects shall have a reference SBP increase C218mmHg
during exercise. There is no DBP change requirement, yet both SBP and DBP
measurements will be assessed. SBP increase is defined as the average
reference SBP during exercise minus the average reference SBP at baseline.
Procedure: This test shall be performed according to the ISO 81060-2:2018
[5] for validation of classic ABPM devices. For cuff-calibrated devices, the
calibration shall be performed at least one day before measuring baseline BP
and performing the test. Baseline (pre-exercise) BP will be assessed by three
sequential auscultatory BP measurements (two observers) after 5min sitting
rest and with 30s between measurements. The average of the last two
readings will be used. Dynamic (aerobic) exercise will be performed
immediately after baseline measurements on a bicycle ergometer with the
aim of increasing heart rate by at least 20%. During the procedure, the
subject’s elbow and forearm shall be supported. The cuff shall be at heart
level during the reference reading. When the target heart rate is achieved, the
subject will maintain stable cycling pace and the validation session will be
performed. There shall be three valid paired reference-test BP measurements
per patient for C21105 total measurement pairs. If any two sequential reference
readings differ in SBP by >8mmHg or in DBP by >6mmHg, the pair of
reference and test BP readings shall be excluded but more readings can be
obtained in the subject (maximum of two additional pairs of readings) [5,36].
Data analysis - Reporting:
- According to the Universal Standard [5,36].
- Baseline and exercise reference BP and pulse rate readings (meanC6SD).
- Bland–Altman plots of the test-reference BP differences against their average
values [36].
- Correlation plots of the test post-pre exercise BP changes against the
reference post-pre exercise BP changes along with the correlation coefficient.
Pass criteria: Criterion 1 of the Universal Standard for SBP and DBP [4,5].
Box 5B. EXERCISE TEST – HANDGRIP EXERCISE TEST (Alternative Procedure)
Rationale: If the cuffless BP device requires the user to stay still (e.g., for 30s)
to take a measurement, then a ‘handgrip exercise test’ shall instead be
performed to induce a BP increase without body motion. This test includes
an ISO 81060-2:2018 validation session using the same arm sequential
measurement method, with handgrip exercise performed intermittently and
immediately before each test or reference BP measurement (Supplemental
Digital Content, Suppl. Figure 1, http://links.lww.com/HJH/C212).
Sample size - Subjects: As for the bicycle exercise test (see above).
Procedure:
- For cuff-calibrated devices, the calibration shall be performed at least one day
before measuring baseline BP and performing the test. Baseline (resting) BP will
be assessed by three sequential auscultatory BP measurements (two observers)
after5minsittingrestandwith30sbetweenmeasurements(seeSupplemental
Digital Content, Suppl. Figure 1, http://links.lww.com/HJH/C212). The average
of the last two readings will be used.
- Immediately after the baseline measurements, the maximum grip strength of
the dominant arm will be quantified using a grip strength dynamometer.
Handgrip exercise will then be performed using resistance set to 30% of the
maximum grip strength (using a device with adjustable grip strength).
- Participantswillperforman‘initial exercisesession’toinduce BPincreasevia12
setsof8repetitivehandgripsalternatingbetweenhands(6setsperhand,starting
with the dominant one) (see Supplemental Digital Content, Suppl. Figure 1,
http://links.lww.com/HJH/C212). Then, the first reference BP measurement will
be obtained to start an ISO 81060-2:2018 validation session [5] using the same
armsequentialmeasurementmethod (seeSupplemental Digital Content,Suppl.
Figure 1, http://links.lww.com/HJH/C212).
- Participants will perform ‘maintenance exercise sessions’ immediately before
eachtestandeachreferenceBPmeasurementsvia4setsof8repetitivehandgrips
alternatingbetweenhands(2setsperhand,startingwiththedominantone)(see
SupplementalDigital Content,Suppl. Figure 1, http://links.lww.com/HJH/C212).
- There shall be 3 valid paired reference-test BP measurements per patient for
C21105 total measurement pairs. If any two sequential reference readings differ
in SBP by >8mmHg or in DBP by >6mmHg, the pair of reference and test BP
readings shall be excluded but more readings can be obtained in the subject
(maximum of two additional pairs of readings) [5,36].
Data analysis - Reporting: As for the bicycle exercise test (see above).
Pass criteria: As for the bicycle exercise test (see above).
Box 5B. (Continued)
Validation of cuffless blood pressure devices
Journal of Hypertension
Copyright ? 2023 Wolters Kluwer Health, Inc. Unauthorized
For each validation test, the minimum sample size re-
quired to evaluate the accuracy of a cuffless BP device is
presented. It is important to stress that while having a
smaller sample size hardly impacts the evaluation of low
Box 6 RECALIBRATION TEST
Rationale: This test shall be used for cuff-calibrated cuffless BP devices
requiring periodic recalibration (Table 6). This test assesses the stability of
thecuffcalibrationovertimetoprovidesomeconfidencethatBPmeasurement
accuracy is maintained between successive cuff calibrations. This test shall be
performedimmediatelybeforerecalibrationisrequiredaccordingtomanufacturer
instructions (e.g., maximum recommended time until recalibration is 4weeks).
In the time interval between cuff calibration and this test, treatment changes
can be performed if indicated in people with uncontrolled BP.
Sample size - Subjects:
- Sample size: C2135 subjects.
- Age 18–80years.
- Males C2130%, females C2130%.
- Cuff BP for calibration distribution (BP used to calibrate the device taken by
manual auscultatory measurement, or an upper arm cuff oscillometric device
validated according to the Universal Standard): As in the Universal Standard
(C215%/C215%/C2120% of the reference SBP readings shall be C20100/C21160/
C21140mmHg, respectively, and C215%/C215%/C2120% of the reference DBP
readings shall be C2060/C21100/C2185mmHg), respectively [5].
- Subjects recruited for other tests can be included (e.g., treatment test).
Procedure: The same arm sequential measurement procedure of the Universal
Standard [4,5] shall be applied immediately before manufacturer-
recommended recalibration. There shall be 3 valid paired reference-test BP
measurements per subject forC21105 total measurement pairs. The original cuff
calibration for the cuffless device shall be used, and no recalibration is allowed
prior to the test.
Data analysis - Reporting:
- According to the Universal Standard [4,5,36].
- Bland–Altman plots of the test-reference BP differences against their average
value [36].
Pass criteria: Criterion 1 of the Universal Standard [4,5].
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presuure
Stergiou et al.
TABLE 6. Validation tests required for intermittent cuffless blood
and high accuracy devices, it does make it tougher for a
moderateaccuracydevicetopass(seeSupplementalDigital
Content, Suppl. Tables 1–6, http://links.lww.com/HJH/
C212). Thus, increasing the sample size of any of the tests
maybedecided,aiming atincreasingthepassprobabilityof
amoderateaccuracydevice,aswellasbetterunderstanding
of the performance of the device.
The overall pass probability will decrease as the number
of required tests to pass increases. All the probability
calculations (see Supplemental Digital Content, Suppl.
Tables 1–6, http://links.lww.com/HJH/C212) assume that
each test is independent from the other tests. However, as
considerablepopulationoverlapmayoccurinpractice(i.e.,
same subjects recruitedfor morethan onetest) andbecause
the tests are not completely distinct (e.g., three tests assess
BP changing tracking ability), a cuffless device with high
chance to pass one test may be expected to also have high
probability of passing other tests. In other words, for a
device undergoing several tests, the product of the indi-
vidual probabilities for passing each one of them may
represent a significant underestimation of the overall pass
probability for the device.
5. STRENGTHS AND LIMITATIONS AND
IMPLEMENTATION
These ESH recommendations build upon previous well
established principles, definitions, and procedures by the
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devices according to their type (cf. Table 3)
IEEE, ISO, AAMI, and ESH [4–6,9,12,18,19,38]. The unique
strengths of these ESH recommendations are mainly in
addressing the validation of various types of cuffless devi-
ces intended for use in hypertension management and
defining specific procedures (i.e., a recipe) for testing the
devices. Notably, the validation procedures are highly
relevant to clinical practice and largely observational and
pragmatic rather than experimental or interventional, and
include the assessment of the accuracy of the devices in
measuring absolute BP, BP under different device posi-
tions, and BP changes induced by drug treatment, sleep,
and exercise.
The validation procedures are designed to be conducted
in clinical settings with personnel experienced in BP mea-
surement research. The overall evaluation of some devices
may be demanding and rather complex and might be
performed in different research centers as a multicenter
project. A stepwise validation approach is recommended,
with a primary test for each device type that should be
performed first. The other required tests can then be
performed in decreasing order of difficulty, and with inter-
im analyses performed per test. The sample size should be
increased from the minimum requirement if higher study
power is needed (e.g., for moderate accuracy devices).
An important issue is that cuffless devices may occasion-
ally be modified by the manufacturers, with the changes
applied through software updates. Although these modifi-
cations are likely to improve the accuracy of the BP
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Validation of cuffless blood pressure devices
measurements, it is important to stress that if the device
software is updated, then the validation procedures should
be repeated. Moreover, when reporting on the validation
procedure, the exact version of the software used must
be stated.
The ESH recommendations have limitations as well.
Although considerable effort was put into simplifying the
validation process and reducing the sample sizes, the
validation of most cuffless BP devices is still necessarily
demanding and complex, with the purpose of ensuring that
only accurate devices will be used in clinical practice. The
validation procedures are not appropriate for all cuffless BP
measuring devices and particularly those intended for
continuous monitoring in critical care. The Universal Stan-
dard for cuff devices defines special populations (e.g.,
children, pregnant women) requiring separate validation,
as the accuracy of these devices may be different in these
populations compared to the general population [4,5,39].
While special populations are anticipated for cuffless devi-
ces (e.g., people with dark skin for PPG-based technolo-
gies), the particular populations and the device types that
are impacted are still unknown. The validation procedures
also do not include requirements according to the environ-
ment, such as ambient temperature, which may likewise
impact the accuracy of certain cuffless devices. Future
iterations of the validation procedures could include such
requirements. Lastly, some of the recommended tests,
especially those for assessing the accuracy of tracking BP
changes, may sometimes be challenging to perform. How-
ever, gaining experience in implementing the tests is nec-
essary to guide future revisions to these recommendations.
CONCLUSION
These ESH recommendations present specific, clinically
meaningful, and pragmatic procedures for assessing the
accuracy of common and various intermittent cuffless BP
measuring devicesintendedforhypertensionmanagement.
Cuffless devices that pass the required validation tests are
expected to be helpful in diagnosing hypertension, guiding
antihypertensive therapy, and monitoring hypertension
over time. Conversely, cuffless devices that do not pass
the required validation tests may not be useful or could
even be harmful to hypertension management. The ESH
recommendations areintended to preventinadequate devi-
ces from being used in patient care while fostering the
development of future cuffless devices that are designed to
pass the required validation tests.
ACKNOWLEDGEMENTS
Conflicts of interest
G.S.S., P.P., and E.O.B. conducted clinical development and
validation studies for various manufacturers of blood pres-
sure measurement technologies and advised manufacturers
ondeviceandsoftwaredevelopment.A.P.A.hascontributed
to validation studies by various manufacturers of blood
pressure measurement technologies. K.G.K. and A.K. par-
ticipated in several validation studies funded by manufac-
turers of blood pressure measurement technologies with
payments to their institution. A.E.S. received speaker
Journal of Hypertension
Copyright ? 2023 Wolters Kluwer Health, Inc. Unauthorized
honoraria from Omron Healthcare and Aktiia. G.P. has
received honoraria for lectures by Omron and Somnomed-
ics, and financial support by the Italian Ministry of Health
(Ricerca Corrente). R.A. has served as consultant for several
manufacturers of blood pressure monitors and speaker in
sponsored symposia and has performed validation of blood
pressuremonitors.K.A.isaconsultantofOmronHealthcare.
P.C. is funded by the Italian Ministry of Health (Ricerca
Corrente). J.O.H. has National Institutes of Health grants
on cuff-less blood pressure measurement and has received
research funding from Samsung Advanced Institute of Tech-
nology. He has patents on cuffless blood pressure measure-
ment,andsomehavebeenlicensedtoDigitouchHealthand
Samsung Advanced Institute of Technology. K.K. received
research grants from Omron healthcare, A&D, and Fukuda
Denshi Inc. R.J.M. has worked with Omron and Sensyne.
Consultancyand/orlicensingpaidtohisinstitution.T.O.has
receivedresearchgrantandconsultantfeefromOmron.S.G.
S. holds pending patents on cuffless blood pressure mea-
surement methods. I.T. was previously employed by AtCor
Medical. J.W. has received grants from Omron. R.M. holds
NIHgrantsandissuedandpendingpatentsoncufflessblood
pressure measurement methods, and some of the patents
have been licensed or optioned to Digitouch Health and
Samsung Advanced Institute of Technology.
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