On photoplethysmography artifact reduction and applications

181 Pages·2017·6.82 MB·English

On photoplethysmography artifact reduction and applications
Citation for published version (APA):
Wijshoff, R. W. C. G. R. (2016). On photoplethysmography artifact reduction and applications. [Phd Thesis 1
(Research TU/e / Graduation TU/e), Electrical Engineering]. Technische Universiteit Eindhoven.
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Published: 06/09/2016
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On photoplethysmography artifact
reduction and applications
proefschrift
ter verkrijging van de graad van doctor aan de Technische Universiteit
Eindhoven, op gezag van de rector magnificus prof.dr.ir. F.P.T. Baaijens,
voor een commissie aangewezen door het College voor Promoties, in het
openbaar te verdedigen op dinsdag 6 september 2016 om 16:00 uur
door
Ralph Wilhelm Christianus Gemma Rosa Wijshoff
geboren te Sittard
Dit proefschrift is goedgekeurd door de promotor en de samenstelling van de
promotiecommissie is als volgt:
voorzitter: prof.dr.ir. A.B. Smolders
1e promotor: prof.dr. R.M. Aarts
copromotor: dr.ir. M. Mischi
leden: dr. J. Allen (Newcastle University)
prof.dr.ir. W. Steenbergen (Universiteit Twente)
prof.dr.ir. F.N. van de Vosse (TU Eindhoven)
prof.dr.ir. P.F.F. Wijn (TU Eindhoven)
adviseur: dr. G.J. Noordergraaf (Elisabeth-Tweesteden Ziekenhuis Tilburg
& Radboud UMC Nijmegen)
Hetonderzoekdatinditproefschriftwordtbeschrevenisuitgevoerdinovereen-
stemming met de TU/e Gedragscode Wetenschapsbeoefening.
On photoplethysmography artifact
reduction and applications
Ralph Wijshoff
Doctorate committee:
prof.dr. R.M. Aarts TU Eindhoven, promotor
dr.ir. M. Mischi TU Eindhoven, copromotor
prof.dr.ir. A.B. Smolders TU Eindhoven, chairman
dr. J. Allen Newcastle University
prof.dr.ir. W. Steenbergen Universiteit Twente
prof.dr.ir. F.N. van de Vosse TU Eindhoven
prof.dr.ir. P.F.F. Wijn TU Eindhoven
dr. G.J. Noordergraaf Elisabeth-Tweesteden Ziekenhuis Tilburg
& Radboud UMC Nijmegen
This work was supported by NL Agency, IOP Photonic Devices, IPD083359
HIP, Hemodynamics by Interferometric Photonics.
Cover design: Romy van Geffen, Echt, the Netherlands.
Reproduction: CPI Koninklijke Wöhrmann, Zutphen, the Netherlands.
A catalogue record is available from the Eindhoven University of Technology
Library. ISBN: 978-90-386-4113-3.
Copyright © 2016, Ralph Wijshoff.
All rights reserved. Copyright of the individual chapters belongs to the pub-
lisher of the journal listed at the beginning of each respective chapter. Repro-
duction in whole or in part is prohibited without the written consent of the
copyright owner.
Summary
On photoplethysmography artifact reduction and applications
Photoplethysmography (PPG) is a non-invasive and easy-to-use optical tech-
nology which is nowadays widely applied to monitor the cardiovascular and res-
piratory systems. By emitting light through tissue, PPG can measure variations
intissueblood-volumeviatheresultingvariationsinopticalabsorptionandscat-
tering. PPG is mostly used in the application of pulse oximetry where cardiac-
induced variations in a red and a near-infrared PPG signal are used to measure
pulse rate (PR) and peripheral arterial functional-hemoglobin oxygen-saturation
(SpO ). TheuseofPPGiscurrentlyalsospreadinginambulatorysettings. PPG
2
is for instance applied in optical heart rate watches. Ambulatory PPG measure-
ments could also be valuable for the detection of epileptic seizures and atrial fib-
rillation. Ambulatory oximetry measurements could be of relevance for improved
management of long-term oxygen-therapy.
PPGsignalsarehighlysusceptibletomotion. MotionartifactsinPPGsignals
arespuriousfluctuationswhichcomplicatethedetectionofthecardiaccomponent.
Motion artifacts can be caused by motion of the PPG sensor relative to the skin,
acceleration-induced sloshing of blood, and deformation of the illuminated tissue
volume by dynamic variations in sensor contact-pressure. Furthermore, motion
cancausethePPGsensortovariablyloosecontactwiththeskin,whichcancause
variations in the amount of ambient light reaching the photodiode.
This thesis deals with the processing and analysis of PPG signals which have
been corrupted by motion artifacts. We focused on applications where motion
artifacts are (quasi-)periodic and could therefore be modeled and removed. Mo-
tion artifacts were estimated via motion reference signals. Quasi-periodic motion
artifactscanoccurduringactivitiesofdailyliving(ADL)andarerelevantincar-
diopulmonary exercise testing (CPX) and cardiopulmonary resuscitation (CPR).
We furthermore focused on explicitly removing the motion artifacts to recover
artifact-reduced PPG signals for further beat-to-beat analysis.
i
ii Summary
We first investigated artifacts caused by motion of the PPG sensor relative
to the skin (Chapter 2). We developed a convenient method to measure relative
sensor motion via a laser diode and self-mixing interferometry (SMI). Via SMI,
the monitor diode of a laser diode could measure the Doppler frequency-shift of
laser-light which was back-scattered by a moving object and re-entered the laser
cavity. The motion of the laser diode could be derived from the Doppler frequen-
cies. Via SMI we could conveniently use a single component as a light source
for the PPG measurement and as a sensor for the relative motion measurement.
We also developed an in-vitro skin perfusion phantom to investigate the effect
of relative sensor motion on PPG signals. We used a laser diode as PPG light
source to illuminate the perfusion phantom, and we generated artifacts in-vitro
bydynamicallyvaryingthedistancebetweenthelaserdiodeandthePPGphoto-
diode. We showed that SMI could accurately measure displacement of the laser
diode relative to the diffusely-scattering skin phantom. In-vitro, we found good
correlation between the laser displacement and the resulting artifacts.
Subsequently,weperformedastudyonhealthyvolunteerstotestSMI-derived
relative sensor motion in a more realistic scenario (Chapter 3). Red and near-
infrared PPG signals were measured on the forehead of healthy volunteers with a
commercially available PPG sensor. Quasi-periodic motion artifacts were gener-
ated by walking on a treadmill. We measured sensor motion relative to the skin
byaugmentingthePPGsensorwithalaserdiodeandusingSMI.Forcomparison,
wepositionedanaccelerometerontopofthePPGsensortomeasureheadmotion.
Both motion measurements were used to estimate the fundamental frequency of
motion. WefoundthattheaccelerometeroutperformedtheSMImeasurementby
providing a motion reference signal which had a better signal-to-noise ratio and
moreconsistentlycontainedafrequencycomponentatthefundamentalfrequency
of motion. This may have been the result of limited relative sensor motion. We
therefore recommend using an accelerometer to obtain a motion reference signal
in this scenario. We furthermore used these data to develop a generic algorithm
to estimate and remove the motion artifacts from the measured PPG signals
(Chapter 3). The resulting artifact-reduced PPG signals provided more stable
measurements of inter-beat-intervals and SpO , which can be of relevance for
2
applications in ADL, CPX and CPR.
We have also investigated the potential value of using PPG during CPR. The
goal of CPR is achieving return of spontaneous circulation (ROSC). Detection of
ROSCinvolvesassessingwhetherthehearthasresumedbeating,whichistypically
performed by manual palpation. Manual palpation is unreliable, time-consuming
and interrupts the chest compressions. As a result, manual palpation can lead
to long interruptions in the chest compressions, which reduce the compression-
generated blood flow and can thereby negatively impact CPR outcome. An ob-
jective, non-invasive and easy-to-use method which can support the detection of
ROSC, preferably during compressions, would therefore be a valuable asset.
Inapre-clinicalautomated-CPRstudywefoundthatPPGcanpotentiallyde-
tectwhentheheartresumesbeatingduringCPR(Chapter4). PPGcoulddetect
Summary iii
absence and presence of a spontaneous pulse in few-second pauses in compres-
sions and during ongoing compressions. When the spontaneous pulse rate and
compression rate were different, PPG could detect the spontaneous pulse rate.
Basedonthepre-clinicaldata,wedevelopedanalgorithmtodetectcardiogenic
output in a PPG signal during CPR, intended to support clinicians in detecting
ROSC (Chapter 5). The algorithm could estimate and reduce the compression
componentinthePPGsignal,torecoveracompression-reducedPPGsignalwhich
contained an estimate of the underlying spontaneous pulse component. Visual
inspection of such a signal can support detecting whether the heart has resumed
beatingand,ifso,whethertheheartisbeatingatregularintervals. Thealgorithm
could track the spontaneous pulse rate via spectral analysis of the compression-
reduced PPG signal. The algorithm could also detect a pronounced decrease in
the baseline of the PPG signal, which occurred when the heart resumed beating
and was presumably caused by a redistribution of blood volume to the periphery.
Detection ofa decreasein the baselineaccommodated forcoinciding spontaneous
pulse rate and compression rate, at which occurrence the compression reduction
algorithmandthespectralanalysiscouldnotbeusedtodetectcardiogenicoutput.
The algorithm indicated cardiogenic output when a spontaneous pulse rate or a
pronounced decrease in the baseline were detected. The indication of cardiogenic
outputbythealgorithmshowedgoodagreementwiththeoccurrenceofROSCas
annotatedbyclinicians. Therefore,weconcludedthatthealgorithmmaysupport
clinicians in the detection of ROSC during CPR.
PPG-basedsupportforROSCdetectionmayofferimprovementsinCPR.Ob-
jectivedetectionoftheabsenceofcardiogenicoutputcouldshortenorpreventun-
necessary interruptions in compressions for ROSC assessment. This can increase
thefractionoftimethatcompressionsaredeliveredduringCPRtogenerateblood
flow, and may therefore increase the chance of achieving ROSC. Objective detec-
tion of the presence of cardiogenic output could guide stopping CPR, which may
reducerefibrillationwhichisassociatedwithsustainedcompressionsonabeating
heart. Detection of the presence of cardiogenic output could also guide adminis-
tration of vasopressors, which may have detrimental effects if administered when
the heart has just resumed beating.
iv Summary
Contents
1 Introduction 1
1.1 Photoplethysmography and pulse oximetry . . . . . . . . . . . . . 2
1.2 The PPG signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Oxygen saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Theoretical determination of oxygen saturation . . . . . . . 6
1.3.2 Practical determination of oxygen saturation . . . . . . . . 8
1.3.3 Oxygen saturation levels . . . . . . . . . . . . . . . . . . . . 9
1.4 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4.1 Pulse rate and pulse interval . . . . . . . . . . . . . . . . . 9
1.4.2 Heart rate variability and pulse rate variability . . . . . . . 9
1.4.3 Heart rate turbulence and pulse rate turbulence. . . . . . . 10
1.4.4 Pulse arrival time and pulse transit time . . . . . . . . . . . 10
1.4.5 Ambulatory oximetry monitoring . . . . . . . . . . . . . . . 10
1.4.6 Cardiopulmonary exercise testing . . . . . . . . . . . . . . . 11
1.4.7 Cardiopulmonary resuscitation . . . . . . . . . . . . . . . . 11
1.4.7.1 Introduction to CPR . . . . . . . . . . . . . . . . 11
1.4.7.2 PPG and pulse oximetry during CPR . . . . . . . 13
1.5 Motion artifact handling . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5.1 Origins of motion artifacts in PPG . . . . . . . . . . . . . . 14
1.5.2 Recovery of artifact-reduced PPG signals . . . . . . . . . . 15
1.5.3 Motion-robust extraction of parameters . . . . . . . . . . . 15
1.5.4 Detection of artifact-free PPG signal segments . . . . . . . 16
1.6 Scope and objectives of the thesis . . . . . . . . . . . . . . . . . . . 16
1.6.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.6.2 Objectives of Part I . . . . . . . . . . . . . . . . . . . . . . 17
1.6.3 Objectives of Part II . . . . . . . . . . . . . . . . . . . . . . 18
v