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Validation of non-invasive central blood
pressure devices: ARTERY Society task
force consensus statement on protocol
standardization
James E. Sharman
1
*, Alberto P. Avolio
2
, Johannes Baulmann
3
, Athanase Benetos
4
,
Jacques Blacher
5
, C. Leigh Blizzard
1
, Pierre Boutouyrie
6
, Chen-Huan Chen
7
,
Phil Chowienczyk
8
, John R. Cockcroft
9
, J. Kennedy Cruickshank
10
, Isabel Ferreira
11
,
Lorenzo Ghiadoni
12
, Alun Hughes
13
, Piotr Jankowski
14
, Stephane Laurent
6
,
Barry J. McDonnell
9
, Carmel McEniery
15
, Sandrine C. Millasseau
16
,
Theodoros G. Papaioannou
17
, Gianfranco Parati
18,19
, Jeong Bae Park
20
,
Athanase D. Protogerou
21
, Mary J. Roman
22
, Giuseppe Schillaci
23
, Patrick Segers
24
,
George S. Stergiou
25
, Hirofumi Tomiyama
26
, Raymond R. Townsend
27
,
Luc M. Van Bortel
28
, Jiguang Wang
29
, Siegfried Wassertheurer
30
, Thomas Weber
31
,
Ian B. Wilkinson
15
, and Charalambos Vlachopoulos
32
1
Menzies Institute for Medical Research, University of Tasmania, Hobart, Australia;
2
Faculty of Medicine and Health Sciences, Department of Biomedical Sciences, Macquarie University,
Sydney, Australia;
3
Clinic of Internal Medicine II, University Hospital Schleswig-Holstein, Luebeck, Germany;
4
De´partement de Me´decine Ge´riatrique, CHRU de Nancy and
INSERM U1116, Universite´ de Lorraine, Vandoeuvre-les-Nancy, France;
5
Hypertension and Cardiovascular Prevention Unit, Hoˆtel-Dieu University Hospital, Assistance Publique-
Hoˆpitaux de Paris, University Paris Descartes, Paris, France;
6
Departments of Pharmacology, European Georges Pompidou Hospital, Assistance Publique Hoˆpitaux de Paris,
Inserm UMR 970, University Paris Descartes, Paris, France;
7
Faculty of Medicine, Department of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC;
8
Department of
Clinical Pharmacology, King’s College London British Heart Foundation Centre, London, UK;
9
Department of Biomedical Sciences, School of Health Sciences, Cardiff
Metropolitan University, Cardiff, UK;
10
Cardiovascular Medicine Group, Division of Diabetes and Nutritional Sciences, King’s College, London, UK;
11
School of Public Health, The
University of Queensland, Herston, Brisbane, Australia;
12
Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy;
13
Institute of Cardiovascular Science,
University College London, London, UK;
14
First Department of Cardiology and Hypertension, Institute of Cardiology, Jagiellonian University Medical College, Krak
ow, Poland;
15
Division of Experimental Medicine and Immunotherapeutics, Department of Medicine, University of Cambridge, Cambridge, UK;
16
Pulse Wave Consulting, Saint Leu la Foret,
France;
17
Biomedical Engineering Unit, First Department of Cardiology, Hippokration Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece;
18
Department of Cardiology, S. Luca Hospital, Istituto Auxologico Italiano, Milan, Italy;
19
Department of Medicine and Surgery, University of Milano-Bicocca, Milan, Italy;
20
Department of Medicine/Cardiology, Cheil General Hospital, Dankook University College of Medicine, Seoul, Korea;
21
Department of Pathophysiology, Cardiovascular
Prevention and Research Unit, ‘Laiko’ Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece;
22
Division of Cardiology, Department of
Medicine, Weill Cornell Medical College, New York, NY, USA;
23
Dipartimento di Medicina, Universit
a di Perugia, Unit
a di Medicina Interna, Ospedale ‘S. Maria’, Terni, Italy;
24
IBiTech-bioMMeda, Ghent University, Ghent, Belgium;
25
Hypertension Center STRIDE-7, National and Kapodistrian University of Athens, Third Department of Medicine,
Sotiria Hospital, Athens, Greece;
26
Department of Cardiology, Tokyo Medical University, Tokyo, Japan;
27
Perelman School of Medicine, University of Pennsylvania, Philadelphia,
PA, USA;
28
Heymans Institute of Pharmacology, Ghent University, Ghent, Belgium;
29
The Shanghai Institute of Hypertension, Ruijin Hospital, Shanghai Jiaotong University School
of Medicine, Shanghai, China;
30
Health & Environment Department, Austrian Institute of Technology, Vienna, Austria;
31
Cardiology Department, Klinikum Wels-Grieskirchen,
Wels, Austria; and
32
First Department of Cardiology, Hippokration Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece
Received 17 September 2016; revised 8 November 2016; editorial decision 7 December 2016; accepted 8 December 2016; online publish-ahead-of-print 30 January 2017
Introduction
The original Riva-Rocci method to measure blood pressure (BP)
using a cuff at the upper arm assumed the pressure obtained by this
technique was a good proxy for central aortic BP.
1,2
The clinical
(prognostic) importance of brachial cuff BP is undeniable for both the
assessment of cardiovascular risk associated with elevated BP and the
benefits of treatment-induced BP reduction.
3
However, it is also
The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology.
* Corresponding author. Tel: þ61 3 62264709, Fax: þ61 3 6226 7704, Email: james.sharman@utas.edu.au
V
C
The Author 2017. Published by Oxford University Press on behalf of the European Society of Cardiology.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/),
which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact
journals.permissions@oup.com
European Heart Journal (2017) 38, 2805–2812
CURRENT OPINION
doi:10.1093/eurheartj/ehw632
Hypertension
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generally appreciated that peripheral artery systolic BP (SBP; brachial
or radial artery) may be an inaccurate substitute for central SBP.
4
This has been reported in human studies using intra-arterial catheter-
ization of peripheral and central arteries.
5–8
There may also be a dis-
crepancy between peripheral and central BP responses to vasoactive
drugs.
9
These findings are corroborated in larger studies using non-
invasive central aortic BP methods,
10–13
and, while yet to be fully
adopted in clinical practice, an independent prognostic value of cen-
tral BP has been demonstrated.
14–16
Altogether, there is a growing
interest among clinicians towards improving risk estimates by using
devices that provide more accurate measures of central aortic BP
than those provided by current brachial cuff BP methods.
Many non-invasive devices have been developed that purport to
estimate central BP from different peripheral artery sites (e.g. radial,
brachial, carotid arteries) using different principles of recording the
pressure or surrogate signals (e.g. applanation tonometry, oscillome-
try, ultrasound, or magnetic resonance imaging) and different calibra-
tion methods to derive central BP. Since upper arm cuff-based
devices to estimate central BP are more clinically appealing, in recent
years several companies have developed such devices using a variety
of techniques (e.g. oscillometric sub-diastolic or supra-systolic wave-
form analysis with generalized transfer functions), which employ a
variety of signal processing steps to estimate central BP from periph-
eral signals.
17,18
Yet, with no standardized guidelines,
17
the accuracy
testing of these new devices (as well as the preceding devices) has
not been undertaken in a uniform fashion with comparable protocols,
emphasizing the need for guidance in this field.
19–22
An international
task force was convened to address this situation.
Task force aims
(1) To identify issues that need to be addressed and reach consensus
relating to methods for assessing and reporting the accuracy of cen-
tral BP devices.
(2) To provide recommendations regarding appropriate protocols to
assess and report the evaluation of accuracy (validation) of central
BP devices.
Task force process
Initiation of the task force emanated from issues raised at an
organized debate relating to central BP at the ARTERY Society
Meeting, Maastricht, The Netherlands in October 2014. Task force
members were invited to provide feedback on a draft document of
intent prior to the first meeting at the ESH Meeting, Milan, Italy, June
2015. At this meeting, terms of reference, principal issues, and topics
were refined. A second meeting to discuss outstanding issues was
held at the 2015 ARTERY Society meeting, Krakow, Poland, with
communication of upgraded documents to members for input, and
with disagreements settled by majority consensus.
Identified issues and recommendations (a glossary of terms is pro-
vided in Table 1):
(1) Disparity of non-invasive central BP devices as to what is being meas-
ured. Most central BP devices claim to produce an estimated central
BP relative to cuff brachial BP with brachial SBP usually higher than
central SBP. This can be achieved by a variety of techniques including:
(a) Brachial forearm or radial applanation tonometry and a peripheral
waveform-aorta transfer function
23
or the radial waveform second
systolic peak.
24
(b) Local derivation of carotid BP on the assumption that with appropri-
ate waveform calibration (i.e. mean arterial pressure [MAP] and dia-
stolic BP [DBP]) carotid BP represents central aortic BP. This can be
achieved by non-invasive carotid artery tonometry or ultrasound/
magnetic resonance imaging of the carotid diameter/area wave-
form.
25–27
(similar techniques are also being applied on aortic disten-
sion waveforms).
28
However, for practical applications, the radial or
brachial artery waveform is more readily recorded where waveforms
are registered with more consistent reproducibility and repeatability,
and are less prone to noise introduced by incorrect vessel applana-
tion or respiration as can occur with carotid waveforms.
(c) Calculated central BP through transfer function and modified calibra-
tion of peripheral pressure waveforms.
26,29,30
Methods (b) or (c) may produce central SBP estimates higher than
brachial cuff SBP (discussed within issue 2).
(i) Recommendations: Device manufacturers should clearly state the
purported measurement function of their device. While recognizing
wide variety in devices, these can be broadly categorized into two
types based on their function:
Type I—device purports to give an estimate of central BP rela-
tive to measured brachial BP (i.e. relatively accurate pressure
difference between central and peripheral sites).
Type II—device purports to estimate the intra-arterial central
BP (i.e. relatively accurate absolute central BP value despite in-
accuracy at the peripheral site).
Both function types may be available within a single device. A
summary of differences between device types in comparison to
intra-arterial brachial and central aortic BP are presented in
Figure 1.
(2) Calibration of peripheral artery signals using brachial cuff BP.
Accuracy of non-invasive central BP methods depends on the accur-
acy of methods used to calibrate the peripheral artery (radial, bra-
chial, or carotid) waveform. Central BP estimations can be acquired
with reasonable accuracy if peripheral waveforms are calibrated with
invasive BP.
23,30,31
However, brachial cuff BP is commonly used for
calibration purposes and this introduces error
32,33
as a consequence
of the recognized underestimation of intra-arterial brachial SBP to-
gether with overestimation of intra-arterial brachial DBP.
34–36
Therefore, calibrating the waveform to brachial cuff SBP and DBP is
likely to result in underestimation of central SBP and central pulse
pressure, but overestimation of central DBP relative to intra-arterial
central DBP. Furthermore, amplification of SBP from brachial to ra-
dial arteries may compound the error in underestimation of central
SBP and central pulse pressure when radial artery waveforms are cali-
brated using brachial SBP and DBP.
37–40
The magnitude of
calibration-induced error may often exceed 10 mmHg for each of
SBP, pulse pressure, and DBP, irrespective of brachial cuff BP meth-
ods (e.g. auscultation or oscillometry).
41
Despite these issues, calibration of peripheral waveforms with bra-
chial SBP and DBP still results in the estimation of a central SBP that is
relative to, and usually lower than, the measured brachial cuff SBP
(device Type I). This information is important to know because bra-
chial cuff SBP is used clinically and the proportional difference with
2806 J.E. Sharman et al.
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central SBP (degree of SBP amplification) may be relevant to hyper-
tension management decisions, including monitoring the effects of
drug treatment in which responses may differ between the brachial
artery and the aorta.
9,12
Different calibration modes have been suc-
cessfully employed in an attempt to derive more accurate estimations
of central SBP (device Type II);
8,29,30,42
however, in doing so, the po-
tentially confusing impression may be given that central SBP is sub-
stantially higher than brachial SBP (reverse amplification), which is
likely to be non-physiological under normal conditions and arises
from the combination of underestimated brachial SBP by cuff, to-
gether with more accurate (higher) central SBP estimation.
Nonetheless, random scatter or measurement error could also con-
tribute to reverse amplification, particularly among older arterial age-
ing phenotypes where the difference between central and brachial
SBP may be small. Although improved accuracy of central SBP using a
Type II device is desirable in terms of better risk stratification related
to BP, determination of the true degree of aorta-to-brachial SBP
amplification will be lost unless a recalibrated estimation of brachial
SBP is provided, along with the details of how this is derived.
Notwithstanding the complex interaction of calibration and wave
propagation phenomena relating central and peripheral SBP, it still
needs to be determined if the recalibrated brachial SBP derived by
this process is an accurate estimate of intra-arterial brachial SBP.
Data from meta-analysis indicate that using MAP and DBP could
be a preferred calibration option to provide a relatively more accur-
ate non-invasive estimation of central SBP.
43
Several methods may be
used to derive MAP, including by calculation from potentially inaccur-
ate brachial cuff BP [e.g. DBP þ 1/3 (or 40%) pulse pressure,
44
or
from integration of the pressure waveforms calibrated to cuff BP], or
estimation from the peak oscillometric signal,
45
but information re-
garding the accuracy of these approaches is limited. Central BP indi-
ces derived from oscillometric MAP and DBP calibrated peripheral
waveforms show stronger associations with hypertension-related
end organ disease and outcomes than either brachial BP or central
BP derived by calibration using brachial oscillometric SBP and
DBP.
46–50
These data come from independent investigators that have
used the same device,
46–50
and it remains to be clarified if the findings
may be more widely generalizable or if this is a device-specific phe-
nomenon. The observation that much of the inaccuracy in estimated
central BP lies with poor calibration from inaccurate brachial cuff BP,
implies that better BP risk stratification might be achieved with more
accurate brachial cuff BP per se. Indeed, calls have been made for
more rigorous brachial BP accuracy criteria.
51,52
(ii) Recommendations. To achieve accurate non-invasive assessment
of true central BP, more accurate non-invasive estimates of intra-
arterial brachial BP are needed. Establishing more rigorous accuracy
criteria for brachial BP is desirable. Current evidence suggests that
calibration with MAP and DBP may provide a more accurate assess-
ment of central BP than calibration with SBP and DBP, although
Table 1 Glossary of terms
Intra-arterial (invasive) blood pressure Direct measurement of blood pressure within the artery using an in-dwelling catheter-based pres-
sure transducer
Peripheral (non-invasive) blood pressure Blood pressure at a site distal from the aorta. This most often refers to brachial or radial artery
blood pressure, but for the purpose of this paper also includes carotid blood pressure even
though local derivation is regarded as a surrogate of central blood pressure
Central (aortic) blood pressure Blood pressure in the proximal ascending aorta
Systolic blood pressure amplification The increase in systolic blood pressure from proximal to peripheral arterial vessels (e.g. aorta-to-
brachial, or brachial-to-radial arteries)
Transfer function Signal processing step to estimate central blood pressure waveforms from peripherally recorded
waveforms
Calibration Process of scaling a waveform using units of pressure
Figure 1 Illustration of the differences in systolic (SBP) and dia-
stolic (DBP) blood pressure (BP) between intra-arterial brachial and
central BP, brachial cuff BP, and non-invasive central BP devices
Types I and II (BP ranges of different methods represented by the
double arrows). Red shaded area A, represents the true (intra-ar-
terial) level of central-to-brachial SBP amplification, and red shaded
area B represents the non-invasive estimated central-to-brachial
SBP amplification (A and B may be similar in magnitude). The non-
invasive central SBP estimated using central BP device Type II may
be higher than non-invasive brachial cuff SBP, but this is due to
underestimation of true (intra-arterial) brachial SBP with the cuff
device and, therefore, does not reflect physiological amplification.
The hatched areas denote that there will be a degree of variability in
estimated BP between devices.
Validation of non-invasive central blood pressure devices 2807
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further validation is required across cohorts with different character-
istics (e.g. age, sex, levels of BP).
(3) Disparity in validation standards. Multiple reference standards
and calibration methods have been used among previous ‘validation’
studies, often including:
a. Comparison of estimated central BP (by non-invasive device) with in-
vasive central BP (by fluid filled or micromanometer-tipped intra-
arterial catheter), and calibration of the non-invasive waveforms with
invasive MAP and DBP on the assumption of minimal difference in
MAP and DBP between central to peripheral large arteries (i.e. 1–
3 mmHg). This assesses accuracy of the mathematical process of
transforming peripheral into central pressure per se and not the ac-
curacy of the device as used in clinical practice.
b. Comparison of estimated central BP with invasive central BP, and cali-
bration of the non-invasive waveforms with non-invasive BP (typically
brachial SBP and DBP or MAP and DBP). This assesses accuracy of
the central BP estimation as may be used in clinical practice.
c. Comparison of estimated central BP from one non-invasive device
with another non-invasive device as the reference standard (usually
the SphygmoCor device),
17
and calibration of both devices with the
same non-invasive brachial BP, to assess inter-device concordance.
(3) Recommendations. The reference standard against which device
accuracy of central BP estimation is gauged should be intra-arterial
catheter in the ascending aorta [expanded details within section enti-
tled ‘Invasive (intra-arterial) central BP reference standard’]. The calibra-
tion mode may vary depending on the operating principles of the
device, but in all cases, details of the calibration method developed by
the manufacturer should be provided (see Issues 1 and 2). If the bra-
chial BP waveform undergoes recalibration to produce a ‘new’ bra-
chial BP (as per two Type II devices already using this method),
29,42
then the recalibrated brachial BP values (and the method to derive
them) should also be provided so that the level of estimated aorta-
to-brachial SBP amplification can be gauged.
(4) Limitations in performing invasive validation studies. The accepted
central BP reference standard is intra-arterial measurement by cath-
eter,
4,53
but this method still requires careful handling by experienced
operators to avoid measurement error. The technique is only rou-
tinely and necessarily performed in selected clinical populations (i.e.
patients with suspected coronary artery disease or children with con-
genital heart disease), thus rendering data potentially non-
generalizable to other patient populations or healthy people in
whom non-invasive central BP devices may be clinically applied.
Validation against the invasive standard among people for whom cen-
tral artery catheterization is not clinically indicated is a matter for re-
view by ethical boards.
(4) Recommendations. Whilst acknowledging that an intra-arterial
validation standard is less practical, currently there are no non-
invasive alternatives. In any case, with appropriate sample size it
should still be possible to recruit participants from the catheteriza-
tion laboratory of different age, sex, BP range, heart rate range, body
habitus (e.g. body mass index, arm size), and disease status (e.g. þ/-
coronary artery disease, þ/- diabetes). In future, it may be reasonable
to use non-invasive central BP devices as reference standards for
comparison among different subject populations. The acceptance cri-
teria for such devices are yet to be determined, but may include ap-
propriate validation by comparison with the intra-arterial standard, as
well as proved clinical prognostic value. Currently such a device is
not available. A summary of issues and recommendations is provided
in Table 2.
Validation protocol requirements
Several scientific bodies have developed validation protocols for
non-invasive peripheral BP monitors,
54–59
yet they differ on proced-
ural features such as sample size and selection criteria, number of as-
sessment phases, acceptable margin of error, BP range and pass/fail
criteria.
52
A ‘universal’ brachial BP validation protocol is under devel-
opment through collaboration of the American Association for the
Advancement of Medical Instrumentation (AAMI), the International
Organization for Standardisation (ISO), and the ESH Working Group
on Blood Pressure Monitoring and Cardiovascular Variability, and
projected to be in effect in 2018. This harmonized protocol is ex-
pected to inform many aspects of central BP validation protocols that
equally apply to brachial BP (e.g. age, gender, BP range), but an inter-
nationally accepted central BP protocol directed by regulatory
authorities is still required, as distinct from the forthcoming brachial
BP protocol.
Recommendations below focus on central BP specific protocol re-
quirements, with some relevant features drawn from existing valid-
ation guidelines.
54–56
For unambiguous interpretation of
requirements, facets of the protocol have been listed as proposed in
the revised Australian Code for the Responsible Conduct of
Research, in terms of ‘must’, ‘should’ and ‘may’. ‘Must’ indicates a ne-
cessary component for highest quality, ‘should’ indicates a strong rec-
ommendation, but may not be the only way that the component can
be achieved, and ‘may’ is used to provide further guidance.
60
Protocol requirements are summarised in Table 3 as a pro-forma
guide for investigators. Less attention is given to protocol features
equally relevant to brachial BP (i.e. sample characteristics, results re-
porting and pass criteria) but some proposed direction is also pro-
vided based on existing guidelines
54–56
for interim guidance (and to
highlight outstanding issues) prior to development of an accepted
international central BP validation protocol. A list of issues in need of
resolution in the future development of such a protocol is provided
in Table 4.
Study setting. The isolated room should be without disturbing influ-
ences of excessive ambient noise from monitoring devices.
Non-invasive central BP device measurement standards. The manufac-
turer, model, software version, and description of operating prin-
ciples, including the signal processing step/s (averaging, filtering) and
complete calibration processes (including methods to derive calibra-
tion points such as SBP, DBP, and MAP) must be provided. The time
taken to complete the measurement of BP, including the time points
at which brachial BP and central BP are estimated and the cuff defla-
tion speed should be reported. This is relevant to the timing of non-
invasive BP measurements with respect to intra-arterial monitoring
because there may be substantial beat-to-beat variation in intra-
arterial BP that may not be captured using a non-invasive BP device.
56
The appropriate cuff size must be defined and used. The dimensions
of the inflatable bladder for all cuff sizes available with the device
should be reported, as well as the process to determine appropriate
cuff size (e.g. measurement of upper arm and/or fitting within pre-
scribed range indicated on the cuff). A process of familiarization with
2808 J.E. Sharman et al.
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the equipment, involving test measurements before starting the valid-
ation study should be performed and reported. If there are additional
or optional features or functions, separate validation studies must be
performed. Any process used to gauge quality control of waveform
or BP measures, and the process used to delineate acceptable quality
for analysis must be reported. For example if runs of bigeminy, trige-
miny, atrial fibrillation, or isolated premature beats and the following
compensatory beats have been removed from analysis.
54
The num-
ber of readings deemed unacceptable must be reported, together
with the reason/s for exclusion.
Invasive (intra-arterial) central BP reference standard.
Micromanometer-tipped catheters are the preferred instruments to
use, but meticulously handled fluid-filled catheters may also be ac-
ceptable for accurately measuring intra-arterial BP.
61–63
For measure-
ment of waveform features, in which minor inflection points need to
be identified (i.e. augmented pressure), high frequency,
micromanometer-tipped catheters with high-frequency acquisition
systems should be used as signal-dampening will alter waveform fea-
tures. A full description of the type, make and model of catheter, the
frequency response and handling procedures must be provided. This
should include: the process to determine frequency response; cath-
eter French size; tubes length and number of taps and connectors,
flushing protocol, sensor/s position on the catheter; how the mani-
fold position was maintained at heart level (for fluid-filled devices
where hydrostatic pressure may influence BP data); calibration/zero-
ing steps performed together with details of additional equipment
used for this process where relevant (note: zero drift may still be a
cause of imprecision when using micromanometer-tipped catheters);
details of how positioning in the central aorta was confirmed in each
case (e.g. fluoroscopy); sampling rate at which waveforms were re-
corded and all waveform data processing steps together with details
of equipment/software used for this purpose; process by which
waveform period for comparison with non-invasive central BP device
was confirmed (e.g. marking relevant time points). As the recording
unit and A/D converter also have their frequency characteristics, the
frequency response of the overall acquisition system from fluid-filled
catheter or micromanometer-tip to the end-recording unit (graph-
plotter or digital data recorded) should be provided. Procedures
such as the ‘pop test’ may be used to evaluate the overall acquisition
system natural frequency and damping coefficient.
62
Alternatively,
the performance of the fluid filled catheter systems may be assessed
by comparison with micromanometer-tipped catheter (including
challenging the fluid filled system across different heart rates).
Data acquisition at rest. By necessity, subjects will be supine during
catheterization. Before recording resting values, the subject should
be allowed a period of undisturbed rest (e.g. without talking or move-
ment for at least 5 min
54,64
) and must be free from the acute effects
of interventions causing hemodynamic changes (e.g. vasoactive
drugs,
65
contrast dye
66
). There must be no talking whilst BP measures
are being recorded. Medications used during the procedure should
be reported. The non-invasive central BP values must be compared
with the intra-arterial central BP (reference) values averaged over a
time-period matching the deflation cycle of the non-invasive device
and recorded under stable conditions, ideally simultaneously, or as
contemporaneous as possible. If simultaneous measurement is not
possible, a complete description of the protocol and the interval be-
tween intra-arterial and non-invasive BP measures must be provided,
and ideally with the order between measures randomised. The time
difference between measures should be in the immediate vicinity and
without possibility of disturbing influences such as subject positional
changes, drugs, or other interventions. The average intra-arterial
monitoring period will vary between devices being tested due to dif-
ferent operating characteristics (e.g. range 10 s to 1 min) and should
be reported. Comparison of single beat intra-arterial BP with non-
invasive central BP is not acceptable due to potential for selective
bias, but also because of the aforementioned issues of beat-to-beat
variation of intra-arterial BP, which can be influenced by respiration
(2–4 mmHg lower BP with inspiration) under normal circumstances,
.............................................................. ................... .................................................................................................... ...............................
Table 2 Summary of issues in the assessment and reporting of central blood pressure (BP) monitors and
recommendations
Issue Recommendation
1. Disparity of non-invasive central
BP devices as to what is being
measured
Device manufacturers should clearly state the purported measurement function of their device. These can be
broadly categorized into two types based on function: Type I—estimates central BP relative to measured bra-
chial BP; Type II—estimates intra-arterial central BP
Both function types may be available within a single device
2. Calibration of peripheral artery
signals using brachial cuff BP
To achieve accurate non-invasive assessment of true central BP, more accurate non-invasive estimates of intra-
arterial brachial BP are needed. Establishing more rigorous accuracy criteria for brachial BP is desirable.
Current evidence suggests that calibration with MAP and DBP may provide a more accurate assessment of
central BP than calibration with SBP and DBP
3. Disparity in validation standards The reference standard against which device accuracy of central BP estimation is gauged should be intra-arterial
catheter in the ascending aorta. Details of the calibration method should be provided. If the brachial BP wave-
form undergoes recalibration to produce a ‘new’ brachial BP, then the recalibrated brachial BP values (and
the method to derive them) should also be provided so that the level of estimated aorta-to-brachial systolic
BP amplification can be gauged
4. Limitations in performing invasive
validation studies
In future, it may be reasonable to use non-invasive central BP devices as reference standards, but the acceptance
criteria for this are yet to be determined
Validation of non-invasive central blood pressure devices 2809