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Cited by 250Non-Invasive Vital Sign MonitoringCardiovascular Health and Disease PreventionHeart Rate Variability and Autonomic Control

Wearable Photoplethysmography for Cardiovascular Monitoring

Open access
Charlton, Peter H., Kyriacou, Panicos A., Mant, Jonathan, Marozas, Vaidotas, Chowienczyk, Phil, Alastruey, Jordi·2022·Proceedings of the IEEE
DOI 10.1109/jproc.2022.3149785PMC PMC7612541
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Abstract

Smart wearables provide an opportunity to monitor health in daily life and are emerging as potential tools for detecting cardiovascular disease (CVD). Wearables such as fitness bands and smartwatches routinely monitor the photoplethysmogram signal, an optical measure of the arterial pulse wave that is strongly influenced by the heart and blood vessels. In this survey, we summarize the fundamentals of wearable photoplethysmography and its analysis, identify its potential clinical applications, and outline pressing directions for future research in order to realize its full potential for tackling CVD.

AI snapshot

Written from the paper’s full text.

TL;DR

Wearable photoplethysmography (PPG) is widely used for heart-rate monitoring and is being developed for broader cardiovascular monitoring, including blood pressure, respiratory rate, oxygen saturation, atrial fibrillation, and vascular risk. This narrative review summarizes PPG fundamentals, signal processing, clinical applications, and research directions, concluding that accuracy, validation, and clinical integration remain key challenges.

Key findings

  • Wearable PPG can already estimate HR, but accuracy falls during exercise: summary MAE 2.15 bpm at rest vs 7.70 bpm during treadmill exercise and 10.64 bpm during cycling.
  • In a community smartwatch study, possible AF notifications from 1-min PPG recordings had a PPV of 0.84; sensitivity and specificity were not assessed.
  • Computational modeling of PPG in healthy subjects aged 25–75 found stiffness index increased with age and d/a decreased with age; both indices were predominantly influenced by arterial properties (large artery diameter, PWV, peripheral vascular resistance), with SI also strongly influenced by stroke volume and d/a by HR.
  • The review identifies AF detection as perhaps nearest to clinical use, while BP, RR, SpO2, arterial stiffness, sleep, stress, sepsis, HF, and preeclampsia applications need further validation.

Methods

  • Narrative review summarizing key literature on wearable PPG fundamentals, signal processing, physiological parameter estimation, clinical applications, future research, and resources; includes tables of further reading, PPG datasets, and wearable devices.
  • No systematic search, meta-analysis, or formal risk-of-bias assessment is described.
  • A computational model simulated PPG for healthy subjects aged 25–75 under varied cardiovascular conditions using the PWDB; SI and d/a were extracted and assessed via relative sensitivity to cardiovascular properties.

Limitations

  • The paper states it is a narrative review; it notes that mechanisms underlying PPG pulse wave shape are not fully understood, it is not clear which pulse-wave detection approaches perform best, and many clinical applications require further validation.
  • The paper notes that most wearable BP devices are not validated, and SpO2 measurements from conventional pulse oximeters have been found less accurate and less reliable in black patients than white patients.
  • Evident from the text: the modeling findings use synthetic/simulated data from healthy adults aged 25–75, not daily-life wearable recordings, and the review does not provide a systematic synthesis of evidence quality.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1109/jproc.2022.3149785

Cites

303 of 303 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 172 cited sources checked · 0 supported · 0 flagged

  • Findingcitation

    Many PPG datasets contain finger PPG signals, whereas only a few contain wrist PPG signals.

    “Many datasets contain finger PPG signals, whereas only a few contain wrist PPG signals: pulse wave morphology may differ between these sites [58].”
    Quote in the paperNot a substantial claim
  • Findingcitation

    Very few PPG datasets have been acquired in daily life conditions.

    “Furthermore, very few datasets have been acquired in daily life conditions (the PPG-DaLiA Dataset is a notable exception [295]), making it difficult to compare wearable PPG analysis techniques [28], [72].”
    Quote in the paperNot a substantial claim
  • Findingown data

    Both indices were predominantly influenced by arterial properties: large artery diameter, PWV, and peripheral vascular resistance.

    “Both indices were predominantly influenced by arterial properties: large artery diameter, PWV, and peripheral vascular resistance.”
    Quote in the paperSubstantial claim
  • Premisecitation

    The shape of the PPG pulse wave is influenced by the incident wave transmitted through the arteries from the heart and by reflected waves from a range of arterial sites.

    “The shape is influenced not only by the incident wave transmitted through the arteries from the heart but also by reflected waves from a range of arterial sites [6].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [6] source

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  • Premisenone given

    The shape of a PPG pulse wave is determined primarily by the heart and blood vessels.

    “The shape of a PPG pulse wave is determined primarily by the heart and blood vessels.”
    Quote in the paperNot a substantial claim
  • May combine two claims. 62
  • Classified as probably not a substantial claim. 44

  • May combine two claims.

    Findingown data

    Several CV properties were found to have similar effects on the pulse wave: changes in arterial stiffness, mean BP, and peripheral compliance all impacted the portion of the pulse wave between systolic and diastolic peaks; HR and arterial diameter impacted the height of the diastolic peak.

    “several CV properties were found to have similar effects on the pulse wave: changes in arterial stiffness, mean BP, and peripheral compliance all impacted the portion of the pulse wave between systolic and diastolic peaks; HR and arterial diameter impacted the height of the diastolic peak.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    The PPG signal is susceptible to motion artifact, and good skin contact is required to obtain high-quality signals.

    “The PPG signal is susceptible to motion artifact, as shown in Fig. 1(e), and good skin contact is required to obtain high-quality signals [7].”
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    • cites [7] source

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    Premisenone given

    The pulsatile portion of the PPG is primarily determined by the volume of arterial blood in the tissue bed, which increases and decreases with each heartbeat.

    “The pulsatile portion of the PPG is primarily determined by the volume of arterial blood in the tissue bed, which increases and decreases with each heartbeat.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The mechanisms underlying the PPG pulse wave shape are not yet fully understood.

    “The mechanisms underlying the PPG pulse wave shape are not yet fully understood [6].”
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    • cites [6] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    PPG signals can be expressed in Volts, with the pulsatile component of the order of 1 mV in amplitude, although lower amplitudes can be caused by technical factors such as inappropriate gain control or physiological factors such as vasoconstriction.

    “In this case, the pulsatile component of the PPG can be of the order of 1 mV in amplitude [55] although lower amplitudes can be caused by technical factors, such as inappropriate gain control, or physiological factors, such as vasoconstriction [9].”
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  • Classified as probably not a substantial claim.

    Premisereasoning

    Signal processing techniques have been developed to extract additional physiological parameters from the PPG.

    “Consequently, signal processing techniques have been developed to extract additional physiological parameters from the PPG.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationreasoning

    If PPG signal processing techniques could be refined and validated for use in daily life, then wearables could potentially be used for cardiovascular monitoring and to inform clinical decisions.

    “If these techniques could be refined and validated for use in daily life, then potentially wearables could be used for CV monitoring and to inform clinical decisions.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The PPG signal consists of a baseline component and a pulsatile portion.

    “As shown in Fig. 1(d), it consists of a baseline component and a pulsatile portion.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [47] source

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    Premisereasoning

    The choice of PPG measurement site influences both user acceptability and the usefulness of PPG signals.

    “The choice of PPG measurement site influences both user acceptability and the usefulness of PPG signals.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Photoplethysmography has already had a profound impact on clinical care through its use in pulse oximeters, which are routinely used to assess blood oxygen saturation in a wide range of clinical settings.

    “Photoplethysmography has already had a profound impact on clinical care through its use in pulse oximeters, which are routinely used to assess blood oxygen saturation in a wide range of clinical settings.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [35] source

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  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    The PPG contains information on the cardiac, vascular, respiratory, and autonomic nervous systems.

    “The PPG also contains information on the cardiac, vascular, respiratory, and autonomic nervous systems.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    PPG and arterial blood pressure pulse waves have similarities but their shapes differ because the signals are produced by different physiological mechanisms.

    “While there are similarities between PPG and arterial blood pressure (BP) pulse waves, their shapes differ [54] because the signals are produced by different physiological mechanisms.”
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    • cites [54] source

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  • May combine two claims.

    Interpretationreasoning

    The upper wrist PPG may be dominated by microvascular blood, whereas the finger PPG is more strongly influenced by blood flow in the digital arteries.

    “This may be because the upper wrist PPG is dominated by microvascular blood, whereas the finger PPG is more strongly influenced by blood flow in the digital arteries [see Fig. 1(a) and (c)].”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The PPG is influenced by temperature, the use of reflected or transmitted light, and the anatomical measurement site.

    “Other factors that influence the PPG include the temperature [48], [49], the use of reflected or transmitted light, and the anatomical measurement site [50].”
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    • cites [48] source

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    Premisenone given

    Fluctuations in venous blood volume also affect the PPG signal.

    “Fluctuations in venous blood volume also affect the signal.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    There is no widely accepted measurement unit for the PPG signal.

    “There is no widely accepted measurement unit for the PPG signal.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationcitation

    Approaches to identify individuals at risk of cardiovascular disease could prompt interventions and help reduce CVD-associated mortality and morbidity.

    “Approaches to identify individuals at risk of CVD could prompt these interventions and help reduce CVD-associated mortality and morbidity.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [2] source

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  • May combine two claims.

    Premisecitation

    The photoplethysmogram (PPG) signal is an optical measure of arterial blood volume that fluctuates with each heartbeat and is strongly influenced by the heart and blood vessels.

    “The photoplethysmogram (PPG) signal is a measure of arterial blood volume, which fluctuates with each heartbeat and is used by many wearables to monitor heart rate (HR).”
    • Also stated in: § PPG Signal · plain
      “The shape of a PPG pulse wave is determined primarily by the heart and blood vessels.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [6] source

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  • May combine two claims.

    Premisecitation

    Alternative measurement sites such as the arm, ear, chest, or face can have advantages over the wrist, including being less prone to motion artifact or vasoconstriction and providing more accurate heart rate measurements.

    “These alternative sites can have advantages over the wrist, such as being less prone to motion artifact [63] or vasoconstriction [62], and providing more accurate HR measurements [64].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [63] source

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    • cites [62] source

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    • cites [64] source

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  • May combine two claims.

    Premisecitation

    The attractor's shape in phase-space analysis is determined by the shape of the pulse waves, and its density is determined by variability in pulse wave shape.

    “The attractor’s shape is determined by the shape of the pulse waves, and its density is determined by variability in pulse wave shape [117], [118].”
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    • cites [117] source

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    • cites [118] source

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  • May combine two claims.

    Premisenone given

    Approaches to identify individual pulse waves in the PPG seek to overcome two key challenges: pulse waves can exhibit two peaks, particularly in young subjects, and artifacts can create spurious peaks.

    “Approaches to identify individual pulse waves in the PPG seek to overcome two key challenges: 1) pulse waves can exhibit two peaks, particularly in young subjects [see Fig. 1(g)] and 2) artifacts can create spurious peaks [see Fig. 1(e)].”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    A low-pass cutoff frequency as low as 2.25 Hz may be suitable for heart rate estimation, whereas higher cutoff frequencies are required for analyses of pulse wave timing (such as 5 Hz for interbeat interval calculation) and pulse wave shape (such as 20 Hz for feature extraction).

    “A low-pass cutoff frequency as low as 2.25 Hz may be suitable for HR estimation [75], whereas higher cutoff frequencies are required for analyses of pulse wave timing (such as 5 Hz for interbeat interval (IBI) calculation [76]) and pulse wave shape (such as 20 Hz for feature extraction [77]) [11].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [75] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Novel techniques have been developed to determine whether derived respiratory rates are accurate.

    “Similarly, novel techniques have been developed to determine whether derived RRs are accurate [89].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [89] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisereasoning

    Derivatives are typically derived from the PPG after eliminating high-frequency noise, which can otherwise greatly obscure the derivatives.

    “Derivatives are typically derived from the PPG after eliminating high-frequency noise, which can otherwise greatly obscure the derivatives.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Reference motion signals that can be used for motion artifact removal include accelerometry, the gyroscope signal, or a PPG signal of a different wavelength.

    “Reference motion signals that can be used include accelerometry [81], [82], the gyroscope signal [83], or a PPG signal of a different wavelength (such as using an infrared PPG to remove motion artifact from a green PPG) [84].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [81] source

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  • May combine two claims.

    Premisecitation

    Contact pressure resulting from attachment can influence pulse wave shape and timing, so it should ideally be kept constant or calibrated when performing analyses using these signal characteristics.

    “Second, the contact pressure resulting from the attachment can influence pulse wave shape and timing, meaning that it should ideally be kept constant or calibrated when performing analyses using these signal characteristics [70].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [70] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationreasoning

    Some approaches, such as analyzing the local maxima scalogram, use minimal heuristic information, which may make them more suitable for use across settings, although heuristics may be useful for ensuring high performance in particular settings.

    “Some approaches, such as analyzing the local maxima scalogram, use minimal heuristic information, which may make them more suitable for use across settings, although heuristics may be useful for ensuring high performance in particular settings.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

    Premisereasoning

    It is important to only use high-quality signals for pulse wave analysis, as pulse wave features can be distorted in the presence of noise.

    “It is important to only use high-quality signals for pulse wave analysis, as pulse wave features can be distorted in the presence of noise.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisenone given

    It is not yet clear which approaches for identifying individual pulse waves perform best nor whether a single approach can be used for all patient groups and recording settings.

    “It is not yet clear which approaches perform the best nor whether a single approach can be used for all patient groups and recording settings.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing). May combine two claims.

    Premisereasoning

    It is important to select a signal quality threshold suitable for the intended application, as a very high-quality signal might be required for analysis of pulse wave shape, whereas a lower quality signal could be acceptable for heart rate monitoring.

    “It is important to select a threshold suitable for the intended application, as a very high-quality signal might be required for analysis of pulse wave shape, whereas a lower quality signal could be acceptable for HR monitoring.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    For heart rate estimation, the high-pass cutoff should be less than the heart rate (e.g., 0.4 Hz) to ensure that even the lowest plausible heart rate of 30 bpm is preserved.

    “For HR estimation, the high-pass cutoff should be less than the HR (e.g., 0.4 Hz [75], ensuring that even the lowest plausible HR of 30 bpm is preserved).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [75] source

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  • May combine two claims.

    Premisecitation

    Green light in reflectance mode results in higher quality PPG signals, greater robustness to temperature changes, and more accurate heart rate monitoring.

    “In contrast, green is often used in reflectance mode, resulting in higher quality PPG signals [67], greater robustness to temperature changes [48], and more accurate HR monitoring [68].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [67] source

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    Premisecitation

    Longer wavelengths penetrate to deeper depths and are influenced by different levels of the vasculature.

    “Longer wavelengths penetrate to deeper depths [47] and are, thus, influenced by different levels of the vasculature.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [47] source

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    Premisenone given

    Typically, signal segments are deemed to be either high or low quality through the use of empirical thresholds.

    “Typically, signal segments are deemed to be either high or low quality through the use of empirical thresholds.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Several approaches have been proposed for PPG signal quality assessment, including statistical analysis of pulse wave shape, perfusion index, template matching, dynamic time warping, and deep learning.

    “Several approaches have been proposed, including statistical analysis of pulse wave shape [56], assessing the level of perfusion through the perfusion index (the ratio of the amplitude of the pulsatile component of the PPG to its baseline) [56], assessing the similarity of successive pulse wave shapes using template matching [86] or dynamic time warping [87], and deep learning [88].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
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  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    Individual pulse waves must be identified in order to obtain interbeat intervals and extract pulse wave features from individual waves.

    “Individual pulse waves must be identified in order to obtain IBIs (the time between consecutive pulse waves) and extract pulse wave features from individual waves.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Motion artifact removal is particularly helpful for facilitating heart rate monitoring during exercise, although in many situations it is preferable to only estimate parameters from high-quality signals to increase accuracy.

    “Motion artifact removal is particularly helpful for facilitating HR monitoring during exercise [13] although, in many situations, it is preferable to only estimate parameters from high-quality signals to increase accuracy.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [13] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    There are benefits to acquiring other signals simultaneously with the PPG, such as ECG for pulse arrival time measurement and accelerometry, gyroscope, or a second PPG signal for motion artifact removal.

    “There are also benefits to acquiring other signals simultaneously with the PPG, such as the electrocardiogram (ECG) (for pulse arrival time (PAT) measurement), and an accelerometry, gyroscope, or second PPG signal (for motion artifact removal—see Section III-A2).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    SpO2 can be measured from two PPG signals acquired using different wavelengths of light (typically red and infrared) using the modulation ratio R, which is related to SpO2 through an empirically determined calibration curve.

    “SpO2 can be measured from two PPG signals acquired using different wavelengths of light”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [135] source

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  • May combine two claims.

    Premisenone given

    There is a fundamental difference between heart rate variability and pulse rate variability: HRV is obtained from the timings of electrical impulses causing ventricular contraction, whereas PRV is obtained from the timings of pulse waves arriving at the periphery.

    “There is a fundamental difference between HRV and PRV: HRV is obtained from the timings of electrical impulses causing ventricular contraction, whereas PRV is obtained from the timings of pulse waves arriving at the periphery.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Heart rates from wrist-worn devices have been found to be acceptably accurate during rest (summary mean absolute error of 2.15 bpm) although they are less accurate during exercise (mean absolute error of 7.70 bpm during treadmill exercise and 10.64 bpm during cycling).

    “HRs have been found to be acceptably accurate during rest [e.g., summary mean absolute error (MAE) of 2.15 beats per minute (bpm)] although they are less accurate during exercise (e.g., MAE of 7.70 bpm during treadmill exercise and 10.64 bpm during cycling) [14].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [14] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Machine learning is often used to create a model relating pulse wave features to BP.

    “Often machine learning is used to create a model relating pulse wave features to BP”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [23] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given

    Heart rate is already widely measured by wearable PPG devices.

    “HR is already widely measured by wearable PPG devices.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Several models relating BP to PTT or PAT have been proposed, including models that incorporate additional variables such as HR.

    “Several models relating BP to PTT or PAT have been proposed [156], including models that incorporate additional variables, such as HR [157].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [156] source

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  • May combine two claims.

    Premisecitation

    SpO2 measurement is now being incorporated into smart wearables, requiring two PPG signals at different wavelengths.

    “SpO2 measurement is now being incorporated into smart wearables [139], requiring two PPG signals at different wavelengths.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [139] source

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  • May combine two claims.

    Premisecitation

    BP has been estimated from the PPG using a single PPG, a proximal and distal PPG to measure PPT, or a distal PPG and a signal indicating ventricular contraction to measure PAT.

    “BP has been estimated from the PPG using the following inputs [26]: a single PPG [19]; a proximal and a distal PPG to measure PPT [21], [22]; or a distal PPG signal and a signal indicating the time of ventricular contraction (e.g., ECG, phonocardiogram) to measure PAT [20], [21], [150].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
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    • cites [21], [22]

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  • May combine two claims.

    Premisecitation

    An alternative approach proposed in [138] provides greater accuracy when using low-quality PPG signals, although at greater computational cost.

    “An alternative approach proposed in [138] has been found to provide greater accuracy when using low-quality PPG signals, although at greater computational cost”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [138] Goldman, 2000, Masimo signal extraction pulse oximetry, J. Clin. Monitor. Comput. source

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    • cites [137] source

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  • May combine two claims.

    Interpretationcitation

    Potential explanations for pulse rate variability not being a surrogate of heart rate variability during exercise or stress include motion artifact in the PPG rendering PPG-derived interbeat intervals less accurate, a lack of motion artifact removal in PRV studies, and variability in preejection period and pulse transit time causing additional variability in PPG-derived interbeat intervals.

    “Potential explanations for this include [17]: 1) motion artifact in the PPG rendering PPG-derived IBIs less accurate; 2) a lack of motion artifact removal in PRV studies; and 3) variability in preejection period and PPT causing additional variability in PPG-derived IBIs.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [17] source

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  • Classified as probably not a substantial claim.

    Premisenone given

    The time difference between the electrical impulses and pulse wave arrival consists of the preejection period and the pulse transit time.

    “The time difference between the electrical impulses and pulse wave arrival consists of the preejection period (the time between the impulses and ejection of blood into the aorta) and the pulse transit time (PPT) (the time taken for the pulse wave to propagate from the heart to the measurement site).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Both the preejection period and pulse transit time are variable, potentially causing differences between heart rate variability and pulse rate variability.

    “Both of these components are variable, potentially causing differences between HRV and PRV.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Conventional pulse oximeters have been found to be less accurate and less reliable in black patients than white patients.

    “they have been found to be less accurate and less reliable in black patients than white patients”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [144]–[147]

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  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    PPG-based approaches usually cannot be considered as a replacement for clinical tests often due to their inferior performance.

    “However, they usually cannot be considered as a replacement for clinical tests often due to their inferior performance.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The volume-clamp method is an alternative PPG-based approach for measuring BP.

    “The volume-clamp method is an alternative PPG-based approach for measuring BP”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [160] source

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  • May combine two claims.

    Interpretationreasoning

    Deep learning approaches have advantages over traditional feature extraction approaches: they are hypothesis-free and do not require pulse wave analysis algorithms.

    “Deep learning approaches have the following advantages over traditional feature extraction approaches: 1) they are hypothesis-free, i.e., there is no need to hypothesize the pulse wave features of interest and 2) they do not require pulse wave analysis algorithms”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The PPG has been used to assess perfusion, hemoglobin concentration, and haemorheology.

    “The PPG has also been used to assess perfusion [179], [180], hemoglobin concentration [181], and haemorheology [182].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [179] source

      Not checked in the free run.

    • cites [180] source

      Not checked in the free run.

    • cites [181] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    It may be possible to identify changes in BP from a single PPG without calibration, which could have utility in detecting clinical deteriorations such as sepsis.

    “it may be possible to identify changes in BP from a single PPG without calibration [159], which could have utility in detecting clinical deteriorations, such as sepsis.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [159] source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Arterial stiffness can be assessed using similar techniques to those used to estimate BP because it is related to BP.

    “Since it is related to BP, it can be assessed using similar techniques to those used to estimate BP.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The potential role of PPG-based approaches is likely to be in the early detection of CVD and ubiquitous measurement of risk factors, which could trigger a further clinical assessment.

    “Therefore, the potential role of PPG-based approaches is likely to be in the early detection of CVD and ubiquitous measurement of risk factors, which could trigger a further clinical assessment.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    It can be difficult to identify AF as it may not produce symptoms and may occur only intermittently.

    “However, it can be difficult to identify AF as it may not produce symptoms and may occur only intermittently”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [190] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The performance of techniques for detecting AF from the PPG has been assessed in several studies, although further work is required to determine which approach is most suitable for clinical use.

    “The performance of techniques for detecting AF from the PPG has been assessed in several studies [76], [193]–[196] although further work is required to determine which approach is most suitable for clinical use”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [76] source

      Not checked in the free run.

    • cites [193]–[196]

      Not checked in the free run.

    • cites [28] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Standards have been developed for the validation of wearable, cuffless BP devices, although further work is required to refine validation standards to account for issues presented by PPG-based devices.

    “Standards have been developed for the validation of wearable, cuffless BP devices [168], [169] although further work is required to refine validation standards to account for the issues presented by PPG-based devices [170].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [168] source

      Not checked in the free run.

    • cites [169] source

      Not checked in the free run.

    • cites [170] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    While frequent calibration may be necessary to accurately estimate absolute BP values from a single PPG, less frequent calibration may be required when estimating BP from certain PAT measurements.

    “While frequent calibration may be necessary to accurately estimate absolute BP values from a single PPG, less frequent calibration may be required when estimating BP from certain PAT measurements”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [158] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Statistical modeling and machine learning can be used to develop models to analyze PPG signals.

    “Statistical modeling and machine learning can be used to develop models to analyze PPG signals”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [23] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    AF is often not recognized in clinical practice because gold-standard ECG assessments may not be indicated due to a lack of symptoms, and intermittent episodes may be missed as 12-lead ECG assessments are usually conducted at a single time point in a clinic rather than over several days.

    “Consequently, it is often not recognized in clinical practice [191], where gold-standard ECG assessments may not be indicated due to a lack of symptoms, and intermittent episodes of AF may be missed as 12-lead ECG assessments are usually conducted at a single time point in a clinic, rather than over several days during daily life.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [191] 2015

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Most wearable PPG BP devices are not validated, although some have recently been certified for medical use.

    “Most devices are not validated [163] although some have recently been certified for medical use [164]–[166].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [163] source

      Not checked in the free run.

    • cites [164]–[166]

      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationnone given

    The potential utility of wearable PPG in clinical applications lies in its convenience: existing clinical tests can be invasive and more time-consuming, are conducted at a specific time rather than continuously, and often require a clinical operator and more expensive equipment.

    “The potential utility of wearable PPG in these applications lies in its convenience: existing clinical tests can be invasive and more time-consuming, are conducted at a specific time rather than continuously in daily life, and often require a clinical operator and more expensive equipment.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    The rate of HR recovery (HRR) after exercise has been associated with CV events and mortality, and postoperative morbidity.

    “The rate of HR recovery (HRR) after exercise has been associated with CV events and mortality [244], and postoperative morbidity [245].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [244] source

      Not checked in the free run.

    • cites [245] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    It has been observed that stress tends to increase HR and increase PRV.

    “While it has been observed that stress tends to increase HR and increase PRV”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [230] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    HR, RR, and SpO2 have previously been derived from the PPG to identify deteriorations in health, including changes prior to cardiac arrests.

    “HR, RR, and SpO2 have previously been derived from the PPG to identify deteriorations in health [239], including changes prior to cardiac arrests [46].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [239] source

      Not checked in the free run.

    • cites [46] Charlton, 2017

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    A desaturation of 4% is often used as an (imperfect) indicator of apnea.

    “a desaturation of 4% is often used as an (imperfect) indicator of apnea”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [207] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    In a community study, a smartwatch was used to identify possible AF in 1-min PPG recordings, and the positive predictive value of notifications was found to be 0.84, indicating that wearables may have utility for identifying possible AF.

    “The positive predictive value (PPV) of notifications was found to be 0.84, indicating that wearables may have utility for identifying possible AF.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [29] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    It is difficult to measure stress frequently in everyday life: salivary cortisol swab tests are often used as a reference marker of stress.

    “However, it is difficult to measure stress frequently in everyday life: salivary cortisol swab tests are often used as a reference marker of stress”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [229] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The utility of PRV for assessing stress has been investigated in several studies, including a study of PRV metrics derived from short recordings.

    “The utility of PRV for assessing stress has been investigated in several studies [230]–[232], including a study of PRV metrics derived from short recordings [233].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [230]–[232]

      Not checked in the free run.

    • cites [233] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    It has been proposed that the PPG could be used to assess vascular age.

    “It has been proposed that the PPG could be used to assess vascular age”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [26] source

      Not checked in the free run.

    • cites [32] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Three broad approaches have been proposed to identify apnea events from the PPG: detecting desaturations from SpO2 values, detecting reductions or cessations in breathing from changes in PPG-derived respiratory modulations, and estimating the apnea-hypopnea index from the PPG.

    “Three broad approaches have been proposed to identify apnea events from the PPG.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [206]–[211]

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Studies have demonstrated the potential utility of smartwatch data for improving detection of COVID-19 beyond that provided by symptom data alone and for presymptomatic detection of COVID-19.

    “Studies have demonstrated the potential utility of smartwatch data for improving detection of COVID-19 beyond that provided by symptom data alone [215] and for presymptomatic detection of COVID-19 [216].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [215] source

      Not checked in the free run.

    • cites [216] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Some of these indices have been found to be independent predictors of CV risk and mortality, demonstrating their potential utility for risk prediction.

    “Some of these indices have been found to be independent predictors of CV risk and mortality [33], [238], demonstrating their potential utility for risk prediction.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [33] source

      Not checked in the free run.

    • cites [238] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Vascular age may have particular utility for CV risk prediction since aortic PWV has been found to be predictive of CV events and all-cause mortality.

    “Vascular age may have particular utility for CV risk prediction since aortic PWV has been found to be predictive of CV events and all-cause mortality”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [171] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationreasoning

    This provides an incentive for using wearables to monitor stress and assist with stress management.

    “This provides an incentive for using wearables to monitor stress and assist with stress management.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    PPG-based wearables can facilitate remote physiological monitoring in the acute care setting, reducing the staff contact required to monitor patients with infectious diseases such as COVID-19.

    “PPG-based wearables can also facilitate remote physiological monitoring in the acute care setting, reducing the staff contact required to monitor patients with infectious diseases, such as COVID-19”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [240] Wehrly, 2019

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationnone given

    There are several approaches to integrate wearable PPG-based devices into clinical pathways, each of which has different performance requirements.

    “There are several approaches to integrate wearable PPG-based devices into clinical pathways, each of which has different performance requirements.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Pulse wave morphology may differ between finger and wrist PPG measurement sites.

    “pulse wave morphology may differ between these sites [58].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [58] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    In [29], an irregular pulse notification was generated if an irregular pulse was identified in at least five out of six PPG recordings in a 48-h period.

    “In [29], an irregular pulse notification was generated if an irregular pulse was identified in at least five out of six PPG recordings in a 48-h period [29].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [29] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

    Interpretationnone given

    Even though photoplethysmography has been used clinically for 40 years in pulse oximeters, there is still much opportunity to exploit the technology for further benefit, aided by the widespread use of photoplethysmography in wearable devices.

    “Even though photoplethysmography has been used clinically for 40 years in pulse oximeters, there is still much opportunity to exploit the technology for further benefit, aided by the widespread use of photoplethysmography in wearable devices.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationnone given

    Key signal processing challenges include the estimation of blood pressure, respiratory rate, and arterial blood oxygen saturation (using reflectance photoplethysmography), each of which could be of great value clinically.

    “Key signal processing challenges include the estimation of BP, RR, and arterial blood oxygen saturation (using reflectance photoplethysmography), each of which could be of great value clinically.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    The performance of wearable devices varies and can have a considerable impact on the success of a study, influencing the proportion of time for which data are captured, whether data capture is biased toward particular subjects, and the quality of data in different activities.

    “The performance of these devices varies and can have a considerable impact on the success of a study, influencing the proportion of time for which data are captured, whether data capture is biased toward particular subjects, and the quality of data in different activities [72].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [72] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationnone given

    Further development of the technology will be aided by freely available datasets, particularly those acquired in daily living with reference labels, and open-source algorithms against which to compare new signal processing techniques.

    “Further development of the technology will be aided by freely available datasets, particularly those acquired in daily living with reference labels, and open-source algorithms against which to compare new signal processing techniques.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    It has been proposed that the PPG could be used to identify possible preeclampsia, particularly in resource-constrained settings.

    “it has been proposed that the PPG could be used to identify possible preeclampsia, particularly in resource-constrained settings”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [264] source

      Not checked in the free run.

  • May combine two claims.

    Interpretationnone given

    The PPG signal contains a wealth of information on the cardiovascular system although there are several confounders that can either obscure this information (such as motion artifact) or alter it (such as contact pressure).

    “The PPG signal contains a wealth of information on the CV system although there are several confounders that can either obscure this information (such as motion artifact) or alter it (such as contact pressure).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    In [46], algorithms to detect clinical deteriorations in hospital patients generated an alert if at least 50% of the data acquired within a 30-min period were outside of normal ranges.

    “Similarly, in [46], algorithms to detect clinical deteriorations in hospital patients generated an alert if at least 50% of the data acquired within a 30-min period were outside of normal ranges.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [46] Charlton, 2017

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The speed of HRR in response to standing is reduced in HF and is predictive of mortality.

    “the speed of HRR in response to standing is reduced in HF and is predictive of mortality”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [257] source

      Not checked in the free run.

    • cites [258] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    The detection of an irregular pulse to prompt further assessment for atrial fibrillation is, perhaps, nearest to being ready for clinical use.

    “The detection of an irregular pulse to prompt further assessment for AF is, perhaps, nearest to being ready for clinical use.”
    Quote in the paperNot a substantial claim
92 of 92

  • The paper relies on this without support.

    A diagnosis of atrial fibrillation requires ECG verification.

    “Currently, a diagnosis of AF requires ECG verification, so the potential role of PPG-based devices is limited to initial assessment.”

  • The paper relies on this without support.

    Subsequent anticoagulant treatment for atrial fibrillation has the side effect of increased bleeding risk.

    “This is particularly important in the case of AF because subsequent anticoagulant treatment has the side effect of increased bleeding risk.”

  • The paper relies on this without support.

    A wide range of consumer devices is available with varying performance levels and no universal standards.

    “Second, a wide range of consumer devices is available with varying performance levels and no universal standards.”

  • The paper relies on this without support.

    At present, there is little evidence for the long-term health benefits of self-directed cardiovascular health monitoring.

    “At present, there is little evidence for the long-term health benefits of this approach.”

  • The paper relies on this without support.

    Even the best consumer devices may not perform sufficiently well to avoid excessive resource utilization.

    “First, even the best devices may not perform sufficiently well to avoid excessive resource utilization.”
5 of 5

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • There is high variance in PPG signal quality across different devices, such that a device-specific consideration seems appropriate.

    “Naturally, the signal quality of PPG data in general is often discussed in other work as it is highly susceptible to motion artifacts57, however, there is also a high variance in PPG signal quality across different devices67, such that a device-specific consideration seems appropriate.”

    From Data quality evaluation in wearable monitoring (2022) · cites this paper as [57]

  • BVP data is dependent on measuring reflected light from a light-emitting diode (LED), and this signal can be heavily skewed by contamination from external light sources and motion artifacts, sometimes to the point of being irrecoverable through retrospective data processing.

    “BVP data is dependent on measuring reflected light from a light-emitting diode (LED), and this signal can be heavily skewed by contamination from external light sources and motion artifacts, sometimes to the point of being irrecoverable through retrospective data processing40,57,58.”

    From Data quality evaluation in wearable monitoring (2022) · cites this paper as [57]

  • BVP's low quality underlines its high susceptibility to measurement artifacts.

    “underlining its high susceptibility to measurement artifacts57.”

    From Data quality evaluation in wearable monitoring (2022) · cites this paper as [57]

  • For reflectance measurements used for heart rate monitoring, green light is usually used as this provides high quality PPG signals and is less affected by temperature changes and accuracy.

    “For reflectance measurements used, for example, for heart rate monitoring, green light is usually used as this provides high quality PPG signals and is less affected by temperature changes and accuracy.132”

    From Effect of skin color on optical properties and the implications for medical optical technologies: a review (2024) · cites this paper as [132]

Cites

2 retracted

Flagged first, then by citations

Research works printed but not linked: 9

  1. 2019, Cisco Visual Networking Index (VNI) Global Mobile Data Traffic Forecast Update, 2017–2022 White Paper
  2. 2021, Gartner Forecasts Global Spending on Wearable Devices to Total $81.5 Billion in 2021
  3. 10.7717/peerj.6947/table-1 · DOI
  4. Charlton, 2017, Continuous Respiratory Rate Monitoring to Detect Clinical Deteriorations Using Wearable Sensors
  5. 2015, Atrial fibrillation prevalence estimates in England: Application of recent population estimates of AF in Sweden
  6. 2020, What Should I Know About the Fitbit Heart Study?
  7. Charlton, 2021, A Study of the Acceptability and Performance of Wearables for Atrial Fibrillation Screening in Older Adults
  8. Petersen, 2002, Coronary heart disease statistics: Heart failure supplement
  9. Healey, 2000, Wearable and Automotive Systems for the Recognition of Affect From Physiology

Cited by

Sorted by citations

Related

Authors
Charlton, P. H., Kyriacou, P. A., Mant, J., Marozas, V., Chowienczyk, P., & Alastruey, J.
Affiliations
  • University of London (GB)
  • University of Cambridge (GB)
  • Kaunas University of Technology (LT)
  • King's College London (GB)
Corresponding author
Charlton, Peter H.
ORCID
Venue
Proceedings of the IEEE
Publisher
Institute of Electrical and Electronics Engineers (IEEE)
Published
2022-03
Volume
110
Issue
3
Pages
355-381
ISSN
  • 0018-9219 (ISSN-L)
  • 1558-2256
DOI
10.1109/jproc.2022.3149785
PMC
PMC7612541
OpenAlex
W4220840763
Semantic Scholar
e2397a66794ee73ff264acb1b40c4a1ceffd871b
Cited by
250
References
296
Citations by year
2026: 108 · 2025: 62 · 2024: 37 · 2023: 33 · 2022: 10
FWCI
10.32
Type
journal article
Language
en
Open access
Licence
Locations
  • Proceedings of the IEEE (publishedVersion, cc-by-sa)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • City Research Online (City University London) (acceptedVersion)
  • Research Portal (King's College London) (submittedVersion, cc-by)
Funders
  • Wellcome Trust
  • National Institute for Health and Care Research (203148/Z/16/Z)
  • British Heart Foundation (WT203148/Z/16/Z, PG/15/104/31913, FS/20/20/34626, SP/14/8/31352)
  • University of Cambridge
  • King's College London (WT203148/Z/16/Z)
  • European Cooperation in Science and Technology (CA18216)
  • Lietuvos Mokslo Taryba (01.2.2-LMT-K-718, 01.2.2-LMT-K-718-01-0030)
  • Engineering and Physical Sciences Research Council ([WT203148/Z/16/Z], WT 203148/Z/16/, 203148/ Z/16/Z)
  • European Regional Development Fund (01.2.2-LMT-K-718, 01.2.2-LMT-K-718-01-0030)
  • Centre For Medical Engineering, King’s College London (203148/Z/16/Z, WT 203148/Z/16/Z)
Topics
  • Physical Sciences › Engineering › Biomedical Engineering › Non-Invasive Vital Sign Monitoring
  • Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Cardiovascular Health and Disease Prevention
  • Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Heart Rate Variability and Autonomic Control
Keywords
cardiovascular monitoring, cardiovascular disease detection, smartwatches, fitness bands, arterial pulse wave, optical pulse measurement

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-09.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-09.

Statistics and arithmetic are recomputed, not judged.

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