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Cited by 348Non-Invasive Vital Sign MonitoringHeart Rate Variability and Autonomic ControlHemodynamic Monitoring and Therapy

Sources of inaccuracy in photoplethysmography for continuous cardiovascular monitoring

Open access
Fine, Jesse, Branan, Kimberly L., Rodriguez, Andres J., Boonya-ananta, Tananant, Ajmal, Ramella-Roman, Jessica C., McShane, Michael J., Coté, Gerard L.·2021·Biosensors
DOI 10.3390/bios11040126PMC PMC8073123
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Abstract

Photoplethysmography (PPG) is a low-cost, noninvasive optical technique that uses change in light transmission with changes in blood volume within tissue to provide information for cardiovascular health and fitness. As remote health and wearable medical devices become more prevalent, PPG devices are being developed as part of wearable systems to monitor parameters such as heart rate (HR) that do not require complex analysis of the PPG waveform. However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability. Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces. A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin). Here, we present a comprehensive review of the literature that aims to summarize these noise sources for future PPG device development for use in health monitoring.

AI snapshot

Written from the paper’s full text.

TL;DR

This review synthesizes literature on sources of inaccuracy in photoplethysmography (PPG) for continuous cardiovascular monitoring, grouping them into individual variation, physiological processes, and external perturbations. It argues that advanced PPG parameters require accounting for these noise sources across diverse populations and real-world conditions, not just controlled fitness/heart-rate settings.

Key findings

  • Noise sources are divided into three main categories: individual variation (skin tone, obesity, age, gender), physiology (respiration, venous pulsation, body site, local body temperature), and external perturbation (motion artifact, ambient light, applied pressure).
  • Skin tone: a 535 nm wrist device showed error of 1.04 BPM for “fair” skin vs 10.90 BPM for “dark” skin; Polar OH1 bias increased with darker skin (p < 0.001), while Bent et al. found no statistically significant skin-tone relationship but a mean absolute error of approximately 9 BPM across all skin tones.
  • Obesity: Monte Carlo simulations predicted a 40% loss of PPG signal amplitude on the wrist as simulated radial artery depth increased from 2.5 to 3.5 mm; obesity is also linked to changes in capillary density, blood flow, SpO2, trans epidermal water loss, and skin thickness.
  • Motion and pressure: Basis Peak vs Fitbit Charge HR correlations were r = 0.92 vs r = 0.83 overall, and during high-intensity events r = 0.77 vs r = 0.58; Apple Watch 4 had MAE of 2.7 BPM at rest and 4.6 BPM while walking. Applied pressure from 0–15 kPa produced over 300% variation in the b/a ratio, dropping to less than 5% at optimal pressure; a force regulator reduced coefficient of variation from 50.9% to 1.8%.

Methods

  • Design: comprehensive literature review; no new experimental data are reported.
  • Data/sample: synthesizes published human studies, in silico modeling, commercial and FDA-cleared/approved PPG devices, and prior reviews; examples include studies with 256 subjects for skin tone, 70 subjects for Polar OH1, 56 patients for wearable comparison, and 93 individuals for age-related PPG features.
  • Main analysis: narrative synthesis categorizing noise sources into individual variation, physiology, and external factors, with summary tables for age-induced PPG changes, temperature effects, and adaptive filters for motion artifacts.

Limitations

  • The paper states that few noise sources had a comprehensive solution, understanding of how conditions such as obesity affect skin and cardiovascular monitoring is still developing, and future research should incorporate larger studies inclusive of diverse populations.
  • Evident from the text: as a narrative review, it does not report a systematic search strategy or quantitative meta-analysis; many cited studies are small, some lack statistical analyses, and findings conflict (e.g., Bent et al. vs other skin-tone studies; inconsistent skin thickness data).

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

Integrity signals

Registry

Crossref · 10.3390/bios11040126

Cites

210 of 210 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 283 cited sources checked · 0 supported · 0 flagged

  • Findingnone given

    PPG-based RCIM devices that are FDA cleared or approved and can accurately and consistently record clinical parameters in a sufficiently diverse population for true health monitoring are scarce.

    “PPG-based RCIM devices that are U.S. Food and Drug Administration (FDA) cleared or approved and can accurately and consistently record clinical parameters in a sufficiently diverse population for true health monitoring are scarce.”
    Quote in the paperSubstantial claim
  • Findingnone given

    Publications that experimentally and explicitly demonstrate the effect of obesity or BMI on the PPG waveform are limited.

    “While, to the authors’ knowledge, publications that experimentally and explicitly demonstrate the effect of obesity or BMI on the PPG waveform are limited, we will explore works which suggest that there would be a substantial effect [56,59,60,61,62,63,64,65,66,67,68,69,70].”
    Quote in the paperNot a substantial claim0 of 10 sources checked
    • cites [56] Gibney, 2010, Skin and subcutaneous adipose layer thickness in adults with diabetes at sites used for insulin injections: Implications for needle length recommendations, Curr. Med. Res. Opin. source

      Not checked in the free run.

    • cites [59] Elgendi, 2012, On the analysis of fingertip photoplethysmogram signals, Curr. Cardiol. Rev. source

      Not checked in the free run.

    • cites [60] Iacopi, 2020, Using Skin Bioengineering to Highlight How Weight and Diabetes Mellitus Modify the Skin in the Lower Limbs of Super-Obese Patients, Diabetes Metab. Syndr. Obes. Targets Ther. source

      Not checked in the free run.

    • cites [61] Chin, 1999, Increased cutaneous blood flow but impaired post-ischemic response of nutritional flow in obese children, Atherosclerosis source

      Not checked in the free run.

    • cites [62] Francischetti, 2011, Skin capillary density and microvascular reactivity in obese subjects with and without metabolic syndrome, Microvasc. Res. source

      Not checked in the free run.

    • cites [63] Czernichow, 2010, Microvascular dysfunction in healthy insulin-sensitive overweight individuals, J. Hypertens. source

      Not checked in the free run.

    • cites [64] Debbabi, 2006, Increased skin capillary density in treated essential hypertensive patients, Am. J. Hypertens. source

      Not checked in the free run.

    • cites [65] Ijzerman, 2004, Impaired microvascular function in obesity: Implications for obesity-associated microangiopathy, hypertension, and insulin resistance, Circulation source

      Not checked in the free run.

    • cites [66] Kapur, 2013, Obesity is associated with a lower resting oxygen saturation in the ambulatory elderly: Results from the cardiovascular health study, Respir. Care source

      Not checked in the free run.

    • cites [67] Petrofsky, 2015, The effect of BMI on oxygen saturation at rest and during mild walking, J. Appl. Med. Sci.

      Not checked in the free run.

  • Findingreasoning

    While many sources of noise had documented potential solutions, few had a comprehensive solution.

    “While many sources of noise had documented potential solutions, few had a comprehensive solution and even our understanding of how conditions such as obesity affect the skin and cardiovascular monitoring are still developing.”
    Quote in the paperSubstantial claim
  • Findingreasoning

    A review of the literature shows that the difficulty in creating an RCIM PPG device partially originates from the many sources of noise that researchers encounter.

    “A review of the literature shows that the difficulty in creating such a device partially originates from the many sources of noise that researchers encounter.”
    Quote in the paperSubstantial claim
  • Findingown data

    Sources of noise can be divided primarily into three categories: individual variation, physiological processes, and external perturbation.

    “As shown in Table 7, we found that sources of noise can be divided primarily into three categories: individual variation, physiological processes, and external perturbation.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim. 40
  • May combine two claims. 102
  • The quote only partly states this claim. 1

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

    Findingnone given

    All six identified devices with FDA status appear to be able to provide patients and providers with data for oxygen saturation (SpO2), respiration rate, and pulse rate.

    “All six identified devices with FDA status appear to be able to provide patients and providers with data for oxygen saturation (SpO2), respiration rate, and pulse rate.”
    Quote in the paperNot a substantial claim

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

    Findingnone given

    In some cases, FDA approval is only for when the wearable is used within a software suite or healthcare framework, as with the Samsung Gear S2.

    “In some cases, FDA approval is only for when the wearable is used within a software suite or healthcare framework. This is the case with the Samsung Gear S2, which is FDA cleared to monitor heart rate toward detecting atrial fibrillation when done with the LIVMOR Halo™ Detection System.”
    Quote in the paperNot a substantial claim

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

    Findingnone given

    To the authors' knowledge, there is no work that comprehensively summarizes the literature surrounding these sources of noise and how they affect the waveform of the PPG and its derivatives.

    “To the authors’ knowledge, there is no work that comprehensively summarizes the literature surrounding these sources of noise and how they affect the waveform of the PPG and its derivatives.”
    Quote in the paperNot a substantial claim

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

    Findingnone given

    To the authors' best knowledge, literature does not exist that demonstrates the relationship between skin thickness and obesity for the finger, a common location for pulse oximeters.

    “To the authors’ best knowledge, literature does not exist that demonstrates this relationship for the finger, a common location for pulse oximeters.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingnone given

    The temperature of the body site where PPG data are collected can influence the resultant waveform amplitude and the time between waveforms.

    “It has been shown that the temperature of the body site where PPG data are being collected can influence the resultant waveform amplitude, and even the time between waveforms. This is summarized in Table 5.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

    Findingnone given

    Our understanding of how conditions such as obesity affect the skin and cardiovascular monitoring is still developing.

    “While many sources of noise had documented potential solutions, few had a comprehensive solution and even our understanding of how conditions such as obesity affect the skin and cardiovascular monitoring are still developing.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    PPG can fill the gap in preventative cardiovascular monitoring if a sufficiently accurate and precise device is developed.

    “PPG can fill this gap if a sufficiently accurate and precise device is developed.”
    Quote in the paperSubstantial claim

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

    Premisenone given

    PPG systems developed for remote and wearable use are typically for general wellness and fitness, which precludes them from being prescribed for medical use at home.

    “PPG systems developed for remote and wearable use are typically for general wellness and fitness. This precludes it from being prescribed for medical use at home.”
    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.

    Interpretationnone given

    The indications for use in these devices are very significant advancements in remote monitoring, but still lag in the potential prognostic capabilities of the PPG.

    “The indications for use in these devices are very significant advancements in remote monitoring, but still lag in the potential prognostic capabilities of the PPG.”
    Quote in the paperNot a substantial claim

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

    Premisecitation

    RCIM has proven to be a promising route to deliver preventative care by reducing both the death rate and burdens placed on the healthcare system.

    “Remote and continuous/intermittent monitoring (RCIM) has proven to be a promising route to deliver preventative care by reducing both the death rate and burdens placed on the healthcare system [1,2,3].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [1] Wilkoff, 2008, HRS/EHRA expert consensus on the monitoring of cardiovascular implantable electronic devices (CIEDs): Description of techniques, indications, personnel, frequency and ethical considerations: Developed in partnership with the Heart Rhythm Society (HRS) and the European Heart Rhythm Association (EHRA); and in collaboration with the American College of Cardiology (ACC), the American Heart Association (AHA), the European Society of Cardiology (ESC), the Heart Failure Association of ESC (HFA), and the Heart Failure Society of America (HFSA). Endorsed by the Heart Rhythm Society, the source

      Not checked in the free run.

    • cites [2] Roger, 2011, Heart disease and stroke statistics—2011 update: A report from the American Heart Association, Circulation source

      Not checked in the free run.

    • cites [3] Jencks, 2009, Rehospitalizations among patients in the Medicare fee-for-service program, N. Engl. J. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The blood pressure cuff, ECG patch, and Holter monitor are not often used for long-term remote monitoring.

    “The blood pressure cuff, ECG patch, and Holter monitor are also not often used for long-term remote monitoring [24].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [24] Bansal, 2018, Portable out-of-hospital electrocardiography: A review of current technologies, J. Arrhythmia source

      Not checked in the free run.

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

    Premisenone given

    Hardware and software within the device itself can contribute to the noise.

    “In addition, the hardware and software within the device itself can contribute to the noise.”
    Quote in the paperNot a substantial claim

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

    Premisecitation

    These tests are rarely administered preventatively, despite research which concludes that preventative testing could reduce deaths by up to 25%.

    “Additionally, these tests are rarely administered preventatively, despite research which concludes that preventative testing could reduce deaths by up to 25% [1].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [1] Wilkoff, 2008, HRS/EHRA expert consensus on the monitoring of cardiovascular implantable electronic devices (CIEDs): Description of techniques, indications, personnel, frequency and ethical considerations: Developed in partnership with the Heart Rhythm Society (HRS) and the European Heart Rhythm Association (EHRA); and in collaboration with the American College of Cardiology (ACC), the American Heart Association (AHA), the European Society of Cardiology (ESC), the Heart Failure Association of ESC (HFA), and the Heart Failure Society of America (HFSA). Endorsed by the Heart Rhythm Society, the source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Premisenone given

    These sources of error pertain to variation within and across individuals (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin).

    “These sources of error pertain to variation within and across individuals (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin).”
    Quote in the paperNot a substantial claim

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

    Premisecitation

    PTT, used to determine PWV and estimate blood pressure without a cuff, requires extraction of the time delay from two PPG waveforms or from an ECG and PPG waveform.

    “Additionally, some parameters in the literature such as pulse transit time (PTT), which is used to determine pulse wave velocity (PWV) and estimate blood pressure without a cuff, requires extraction of the time delay from two PPG waveforms or from an ECG and PPG waveform [31,32].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [31] Nabeel, 2018, Arterial blood pressure estimation from local pulse wave velocity using dual-element photoplethysmograph probe, IEEE Trans. Instrum. Meas. source

      Not checked in the free run.

    • cites [32] Nabeel, P., Karthik, S., Joseph, J., and Sivaprakasam, M. (2017, January 8–10). Experimental validation of dual PPG local pulse wave velocity probe. Proceedings of the 2017 IEEE International Symposium on Medical Measurements and Applications (MeMeA), Rochester, MN, USA. source

      Not checked in the free run.

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

    Premisenone given

    Numerous non-FDA cleared/approved fitness devices exist and can estimate heart rate by quantifying the number of systolic peaks in a period of time, but a single parameter limits the amount of extractable information.

    “Numerous non-FDA cleared/approved fitness devices exist and can estimate heart rate by quantifying the number of systolic peaks in a period of time, but a single parameter limits the amount of extractable information.”
    Quote in the paperNot a substantial claim

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

    Premisenone given

    Complex analyses of the PPG waveform yield valuable clinical information such as blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability.

    “However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisenone given

    The literature has demonstrated the potential diagnostic and prognostic strength for the PPG; however, the PPG features can only be utilized if the waveform is of a high quality with high signal-to-noise ratio (SNR).

    “Overall, the literature has demonstrated the potential diagnostic and prognostic strength for the PPG; however, the PPG features can only be utilized if the waveform is of a high quality with high signal-to-noise ratio (SNR).”
    Quote in the paperSubstantial claim

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

    Premisecitation

    Beyond fitness and heart rate monitoring, the primary medical use of PPG has been focused on obtaining information about the cardiovascular system towards cardiovascular disease (CVD) diagnosis and treatment.

    “Beyond fitness and heart rate monitoring, the primary medical use of the PPG has been focused on obtaining information about the cardiovascular system towards cardiovascular disease (CVD) diagnosis and treatment [17,18].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [17] Elgendi, 2019, The use of photoplethysmography for assessing hypertension, NPJ Digit. Med. source

      Not checked in the free run.

    • cites [18] Vakily, 2017, A system for continuous estimating and monitoring cardiac output via arterial waveform analysis, J. Biomed. Phys. Eng.

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to,

    “A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    These results indicate that overall, mean modulation goes down with increasing Fitzpatrick scale, and with exercise one would expect greater blood volume changes causing a higher signal for the more absorbing blue/green wavelengths, at least for the source to detector distances used in the study.

    “These results indicate that overall, the mean modulation goes down with increasing Fitzpatrick scale, and with exercise one would expect greater blood volume changes causing a higher signal for the more absorbing blue/green wavelengths, at least for the source to detector distances used in the study.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Mohapatra et al. found that with a multiwavelength PPG device, perfusion index, pulsatile strength, and SNR all increased when data collected with the 590 nm LED were analyzed.

    “With 20 subjects ranging from Fitzpatrick II to Fitzpatrick IV, the perfusion index (AC/DC), pulsatile strength, and SNR were all found to increase when data collected with the 590 nm LED were analyzed.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [51] Mohapatra, P., Preejith, S., and Sivaprakasam, M. (2017, January 22–25). A novel sensor for wrist based optical heart rate monitor. Proceedings of the 2017 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), Torino, Italy. source

      Not checked in the free run.

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

    Premisecitation

    Obesity, determined by having a body mass index greater than 30, affects 40% of the United States and leads to cardiovascular disease, hypertension, and type 2 diabetes.

    “Obesity, determined by having a body mass index greater than 30, affects 40% of the United States and leads to cardiovascular disease, hypertension, and type 2 diabetes [57].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [57] Poirier, 2006, Obesity and cardiovascular disease: Pathophysiology, evaluation, and effect of weight loss: An update of the 1997 American Heart Association Scientific Statement on Obesity and Heart Disease from the Obesity Committee of the Council on Nutrition, Physical Activity, and Metabolism, Circulation source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    The wavelength range needs to be optimized for both skin tone and blood absorption, particularly as more advanced parameters are derived from PPG signals, because absorption of green light by melanin in individuals with a darker skin tone limits light penetration to the subcutaneous tissue where the blood is located.

    “However, the wavelength range needs to be optimized for both skin tone and blood absorption, particularly as more advanced parameters are derived from PPG signals, as the absorption of green light by melanin in individuals with a darker skin tone limits the light penetration to the subcutaneous tissue where the blood is located.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    Mendelson et al. found that relative amplitude of the AC component to the entire signal (AC + DC) increased as LED/photodiode spacing increased from 4 to 11 mm, although no statistical analyses were presented.

    “It was found that relative amplitude of the AC component to the entire signal (AC + DC) increased as LED/photodiode spacing increased from 4 to 11 mm, although no statistical analyses were presented.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [53] Mendelson, 1988, Noninvasive pulse oximetry utilizing skin reflectance photoplethysmography, IEEE Trans. Biomed. Eng. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Preejith et al.'s device had an error of 1.04 BPM for 'fair' skinned individuals and 10.90 BPM for 'dark' skinned participants, a greater than 10 times increase in absolute error.

    “There was an error of 1.04 beats per minute (BPM) for “fair” skinned individuals and an error of 10.90 BPM for “dark” skinned participants, citing the lack of usability of their device for dark skinned individuals.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [40] Preejith, S., Alex, A., Joseph, J., and Sivaprakasam, M. (2016, January 12–14). Design, development and clinical validation of a wrist-based optical heart rate monitor. Proceedings of the 2016 IEEE International Symposium on Medical Measurements and Applications (MeMeA), Benevento, Italy. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Blood flow regulation and oxygen saturation are both known to deviate with respect to obesity and BMI.

    “Blood flow regulation and oxygen saturation are both known to deviate with respect to obesity and BMI [71].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [71] Limberg, 2016, Peripheral Blood Flow Regulation in Human Obesity and Metabolic Syndrome, Exerc. Sport Sci. Rev. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Preejith et al. found a significant direct correlation between SNR of heart rate and skin tone using a 535 nm LED, indicating that a darker skin tone yields higher error in the measurement.

    “Preejith et al. confirmed that skin tone matters when using green light only. The analysis of their PPG biosensor (single source 535 nm LED) showed a significant direct correlation SNR of the heart rate with skin tone, indicating that a darker skin tone yields higher error in the measurement [40].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [40] Preejith, S., Alex, A., Joseph, J., and Sivaprakasam, M. (2016, January 12–14). Design, development and clinical validation of a wrist-based optical heart rate monitor. Proceedings of the 2016 IEEE International Symposium on Medical Measurements and Applications (MeMeA), Benevento, Italy. source

      Not checked in the free run.

  • May combine two claims.

    Premisereasoning

    Many PPG devices use green light (~550 nm), primarily driven by the relatively high absorption spectrum of hemoglobin in this range, which can give a strong pulsatile signal with changes in blood volume.

    “However, many PPG devices use green light (~550 nm). The decision to use green light in most PPG systems is primarily driven by the relatively high absorption spectrum of hemoglobin in this range (Figure 3b), which is the main absorber in blood and thus can potentially give a strong pulsatile signal with changes in blood volume.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Obesity can lead to changes in skin thickness, blood flow, and oxygen saturation, affecting the optical properties of skin and the distance light has to travel to reach a target vessel.

    “In particular, obesity can lead to changes in skin thickness, blood flow, and oxygen saturation. This affects the optical properties of skin in addition to the distance light has to travel to reach a target vessel or vessels [48,59,60].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [48] Jacques, 2013, Optical properties of biological tissues: A review, Phys. Med. Biol. source

      Not checked in the free run.

    • cites [59] Elgendi, 2012, On the analysis of fingertip photoplethysmogram signals, Curr. Cardiol. Rev. source

      Not checked in the free run.

    • cites [60] Iacopi, 2020, Using Skin Bioengineering to Highlight How Weight and Diabetes Mellitus Modify the Skin in the Lower Limbs of Super-Obese Patients, Diabetes Metab. Syndr. Obes. Targets Ther. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Individuals with obesity experience increased cutaneous blood flow to meet the oxygenation needs of tissue, but the blood flow of adipose tissue generally decreases with obesity both after a meal and during a fasting state.

    “Individuals with obesity experience increased cutaneous blood flow to meet the oxygenation needs of tissue. However, the blood flow of adipose tissue generally decreases with obesity both after a meal and during a fasting state [61,72].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [61] Chin, 1999, Increased cutaneous blood flow but impaired post-ischemic response of nutritional flow in obese children, Atherosclerosis source

      Not checked in the free run.

    • cites [72] Altintas, 2016, In vivo reflectance-mode confocal microscopy assessments: Impact of overweight on human skin microcirculation and histomorphology, J. Biomed. Opt. source

      Not checked in the free run.

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

    Premisecitation

    These often-overlooked disparities with diversity (e.g., skin tone and obesity) are now becoming more documented in the literature.

    “These often-overlooked disparities with diversity (e.g., skin tone and obesity) are now becoming more documented in the literature [34,35,36].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [34] Colvonen, P.J., DeYoung, P.N., Bosompra, N.-O.A., and Owens, R.L. (2020). Limiting Racial Disparities and Bias for Wearable Devices in Health Science Research, Oxford University Press US. source

      Not checked in the free run.

    • cites [35] Hidalgo, 2021, Critical care trainees call for pulse oximetry reform, Lancet Respir. Med. source

      Not checked in the free run.

    • cites [36] Rodriguez, 2021, Synthetic Photoplethysmography (PPG) of the radial artery through parallelized Monte Carlo and its correlation to Body Mass Index (BMI), Sci. Rep. source

      Not checked in the free run.

  • May combine two claims.

    Premisenone given

    Eumelanin has high absorbance with a peak in the ultraviolet wavelength (220 nm) and a steady decay through the visible wavelength region.

    “This is due to the high absorbance of eumelanin with a peak in the ultraviolet wavelength (220 nm) and a steady decay through the visible wavelength region.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisereasoning

    The absorption of epidermal melanin is much higher in the visible region of light and much lower in the near infrared region (NIR), so NIR light will travel further through pigmented skin.

    “Since the absorption of epidermal melanin is much higher in the visible region of light and much lower in the near infrared region (NIR), the NIR range of light will travel further through pigmented skin.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Hermand et al. found that bias (mean difference between the Polar OH1 and ground truth) increased with darker skin (p < 0.001), and heart rate accuracy was positively correlated to skin tone (p < 0.05).

    “In determining heart rate, it was found that bias (defined as the mean difference between the OH1 and ground truth) increased with darker skin (p < 0.001), and heart rate accuracy was positively correlated to skin tone (p < 0.05).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [41] Hermand, 2019, Validation of a photoplethysmographic heart rate monitor: Polar OH1, Int. J. Sports Med. source

      Not checked in the free run.

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

    Premisecitation

    The wearable devices used in Bent et al. utilized red and near infrared light, which can more easily penetrate the epidermis.

    “Additionally, the wearable devices used in this study utilized red and near infrared light, which can more easily penetrate the epidermis.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [46] Bent, 2020, Investigating sources of inaccuracy in wearable optical heart rate sensors, NPJ Digit. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    For Fitzpatrick IV individuals, the perfusion index increased between 1.2 and 7.1 times with the use of 590 nm light, pulsatile strength increased by 1.1 to 3.1 times, and SNR increased by 1.3 to 2.6 times, although no statistical significance analyses were performed.

    “For Fitzpatrick IV individuals, the perfusion index increased between 1.2 and 7.1 times with the use of the 590 light, while pulsatile strength increased by 1.1 to 3.1 times and SNR increased by 1.3 to 2.6 times, although no statistical significance analyses were performed [51].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [51] Mohapatra, P., Preejith, S., and Sivaprakasam, M. (2017, January 22–25). A novel sensor for wrist based optical heart rate monitor. Proceedings of the 2017 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), Torino, Italy. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    In the resting condition, green light had larger mean modulation (p < 0.001) than other wavelengths, and after exercise, blue and green had greater SNR ratios than red or infrared (p < 0.001).

    “In the resting condition, green light had larger mean modulation (p < 0.001) than other wavelengths, and after exercise, blue and green had greater SNR ratios than red or infrared (p < 0.001).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [52] Fallow, 2013, Influence of skin type and wavelength on light wave reflectance, J. Clin. Monit. Comput. source

      Not checked in the free run.

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

    Interpretationreasoning

    The lack of increase in error observed by Bent et al. may be due to the already large error present in the results (mean absolute error approximately 9 BPM across all skin tones).

    “It is possible that the lack of increase in error observed is due to the already large error present in the results reported—the mean absolute error is approximately 9 BPM across all skin tones.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    Most of the listed changes are due to the cardiovascular system, as arteries change how they respond to a cardiac pulse as the vessel ages.

    “Most of the listed changes are due to the cardiovascular system, as arteries change how they respond to a cardiac pulse as the vessel ages.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Skin thickness is directly correlated to BMI and can dampen PPG signal amplitude.

    “Perhaps most detrimental to the PPG waveform is skin thickness, as it is directly correlated to BMI and can dampen PPG signal amplitude [56,70].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [56] Gibney, 2010, Skin and subcutaneous adipose layer thickness in adults with diabetes at sites used for insulin injections: Implications for needle length recommendations, Curr. Med. Res. Opin. source

      Not checked in the free run.

    • cites [70] Derraik, J.G., Rademaker, M., Cutfield, W.S., Pinto, T.E., Tregurtha, S., Faherty, A., Peart, J.M., Drury, P.L., and Hofman, P.L. (2014). Effects of age, gender, BMI, and anatomical site on skin thickness in children and adults with diabetes. PLoS ONE, 9. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The ratio b/a has been found to correlate positively to age, while c/a, d/a and e/a have all been correlated negatively to age.

    “The ratio b/a has been found to correlate positively to age, while c/a, d/a and e/a have all been correlated negatively to age [29,59].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [29] Takazawa, 1998, Assessment of vasoactive agents and vascular aging by the second derivative of photoplethysmogram waveform, Hypertension source

      Not checked in the free run.

    • cites [59] Elgendi, 2012, On the analysis of fingertip photoplethysmogram signals, Curr. Cardiol. Rev. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Keratinocytes become shorter, water content decreases, lipid content decreases, and collagen synthesis and turnover decrease with age.

    “Keratinocytes become shorter, water content decreases, lipid content decreases, and most notably, collagen synthesis and turnover decrease [93].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [93] Farage, 2013, Characteristics of the aging skin, Adv. Wound Care source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    This change in skin thickness decreases the necessary propagation of light to obtain a PPG signal, which can contribute to an increase in PPG signal strength, along with capillary depletion.

    “This change in skin thickness decreases the necessary propagation of light to obtain a PPG signal, which can contribute to an increase in PPG signal strength, along with capillary depletion.”
    Quote in the paperNot a substantial claim

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

    Interpretationnone given

    The increased absorption of deoxygenated hemoglobin compared to that of oxygenated hemoglobin in the far-red region could decrease SNR of PPG measurements that use those wavelengths of light.

    “The increased absorption of deoxygenated hemoglobin compared to that of oxygenated hemoglobin in the far-red region could decrease SNR of PPG measurements that use those wavelengths of light.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisereasoning

    PPG principally measures the response/elasticity of arteries to blood flow, and thus will change if the properties governing artery compliance change.

    “PPG principally measures the response/elasticity of arteries to blood flow, and thus will change if the properties governing artery compliance changes.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    Leveque et al. found a decrease in skin thickness and a positive, direct relationship between PPG amplitude and age, which they attribute to capillary depletion.

    “A Holtain skin caliper applied to the dorsal forearm found a decrease in skin thickness, and an infrared PPG was used to determine PPG amplitude. The authors attribute the positive, direct relationship between PPG amplitude and age to capillary depletion, due to similar skin thicknesses observed between older participants and children, despite an increased PPG amplitude in the older participants.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [94] Leveque, 1984, In vivo studies of the evolution of physical properties of the human skin with age, Int. J. Dermatol. source

      Not checked in the free run.

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

    Premisecitation

    Ahn et al. extracted features from fingertip-based PPG and the second derivative PPG (APG) and correlated them to chronological age to determine what they defined as the vascular age index.

    “Using data from 93 individuals of various ages, Ahn et al. extracted features from fingertip-based PPG and the second derivative PPG, acceleration plethysmography (APG, Figure 4), and correlated them to chronological age in order to determine what they defined as the vascular age index [83].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [83] Ahn, 2017, New aging index using signal features of both photoplethysmograms and acceleration plethysmograms, Healthc. Inform. Res. source

      Not checked in the free run.

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

    Premisecitation

    Hartmann et al. determined that there is no statistically significant change in PPG amplitude as a function of age.

    “Another study by Hartmann et al. determined that there is no statistically significant change in PPG amplitude as a function of age; however, this work featured 36 individuals ranging in age from only 33 to 58.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [95] Hartmann, 2019, Quantitative comparison of photoplethysmographic waveform characteristics: Effect of measurement site, Front. Physiol. source

      Not checked in the free run.

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

    Premisenone given

    The integumentary system also responds to aging.

    “However, the integumentary system also responds to aging.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Suzuki and Oguri used artificial intelligence to determine blood pressure from a cuffless monitor and incorporated age into their algorithm.

    “Suzuki and Oguri similarly used artificial intelligence to determine blood pressure from a cuffless monitor and incorporated age into their algorithm [96].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [96] Suzuki, S., and Oguri, K. (2009, January 2–6). Cuffless blood pressure estimation by error-correcting output coding method based on an aggregation of adaboost with a photoplethysmograph sensor. Proceedings of the 2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Hilton Minneapolis, MI, USA. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Gender differentiation in average blood pressure and average heart rate indicate that baseline differences in vascular and cardiovascular parameters must be considered to determine cardiovascular health between males and females, which also extends into analyses of the PPG waveform.

    “Phuong and Maibach noted that gender differentiation in average blood pressure and average heart rate indicate that baseline differences in vascular and cardiovascular parameters must be considered to determine cardiovascular health between males and females, which also extends into analyses of the PPG waveform [98].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [98] Phuong, C., and Maibach, H.I. (2016). Gender differences in skin. J. Textb. Aging Skin, 1729–1755. source

      Not checked in the free run.

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

    Interpretationreasoning

    This leads to dramatic changes in PWV and subsequently PTT.

    “This leads to dramatic changes in PWV and subsequently PTT.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Proctor et al. reported that the average heart rate for males was 70-72 BPM and the average for females was 78-85 BPM in 16 endurance-trained men and 14 endurance-trained women.

    “Proctor et al. reported that the average heart rate for males was 70–72 BPM and the average for females was 78–85 BPM in 16 endurance-trained men and 14 endurance-trained women [99].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [99] Proctor, D.N., Beck, K.C., Shen, P.H., Eickhoff, T.J., Halliwill, J.R., and Joyner, M.J. (1998). Influence of age and gender on cardiac output-V o 2 relationships during submaximal cycle ergometry. J. Appl. Physiol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Artificial intelligence and machine learning have been used to determine blood pressure from PPG and mitigate the effects age have on the estimate.

    “Artificial intelligence and machine learning have been used to determine blood pressure from PPG and mitigate the effects age have on the estimate.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [92] 2011, Non-invasive estimate of blood glucose and blood pressure from a photoplethysmograph by means of machine learning techniques, Artif. Intell. Med. source

      Not checked in the free run.

    • cites [96] Suzuki, S., and Oguri, K. (2009, January 2–6). Cuffless blood pressure estimation by error-correcting output coding method based on an aggregation of adaboost with a photoplethysmograph sensor. Proceedings of the 2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Hilton Minneapolis, MI, USA. source

      Not checked in the free run.

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

    Premisecitation

    An algorithm that incorporates age into systolic and diastolic blood pressure determination was created.

    “An algorithm that incorporates age into systolic and diastolic blood pressure determination was created.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [92] 2011, Non-invasive estimate of blood glucose and blood pressure from a photoplethysmograph by means of machine learning techniques, Artif. Intell. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Skin thickness is a gender-dependent variable known to affect signal strength, and is observed to be higher in men than women across all age ranges.

    “Skin thickness is another gender-dependent variable known to affect signal strength (as mentioned previously), and is observed to be higher in men than women across all age ranges [97,103].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [97] Dao, 2007, Gender differences in skin: A review of the literature, Gend. Med. source

      Not checked in the free run.

    • cites [103] Shuster, 1975, The influence of age and sex on skin thickness, skin collagen and density, Br. J. Dermatol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Significant differences in artery diameter lead to significantly different radial artery flow rates, with a flow rate of 21 ± 4 and 10 ± 1 mL/min for males and females, respectively.

    “These significant differences in artery diameter lead to significantly different radial artery flow rates as well, with a flow rate of 21 ± 4 and 10 ± 1 mL/min for males and females, respectively [102].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [102] Joannides, 2002, Influence of vascular dimension on gender difference in flow-dependent dilatation of peripheral conduit arteries, Am. J. Physiol. Heart Circ. Physiol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Post-menopausal females have higher blood pressure than males, which can be attributed to arterial stiffness.

    “However, post-menopausal females have higher blood pressure than males, which can be attributed to arterial stiffness [101].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [101] Reckelhoff, 2001, Gender differences in the regulation of blood pressure, Hypertension source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Males have a 15-30% increase in heart mass compared to females resulting in females' hearts having to beat faster to maintain the same output.

    “Males have a 15–30% increase in heart mass compared to females resulting in females’ hearts having to beat faster to maintain the same output [100].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [100] Prabhavathi, 2014, Role of biological sex in normal cardiac function and in its disease outcome—A review, J. Clin. Diagn. Res. JCDR

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Physiological differences between men and women extend into cardiovascular health and are noticeable in the PPG waveform.

    “The physiological differences between men and women extend into cardiovascular health and are thus noticeable in the PPG waveform [97,98].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [97] Dao, 2007, Gender differences in skin: A review of the literature, Gend. Med. source

      Not checked in the free run.

    • cites [98] Phuong, C., and Maibach, H.I. (2016). Gender differences in skin. J. Textb. Aging Skin, 1729–1755. source

      Not checked in the free run.

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

    Premisecitation

    Shuster et al. measured skin thickness in 90 Caucasian men and 107 women and found that forearm skin thickness is greater in men than women, but no statistics were presented to explore statistical significance.

    “Shuster et al. measured skin thickness in 90 Caucasian men and 107 women and found that forearm skin thickness is greater in men than women, but no statistics were presented to explore statistical significance [103].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [103] Shuster, 1975, The influence of age and sex on skin thickness, skin collagen and density, Br. J. Dermatol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Post-puberty, both males and females have an increase in arterial compliance, determining no gender-dependent differences between the measurement.

    “Post-puberty, both males and females have an increase in arterial compliance, determining no gender-dependent differences between the measurement.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [104] Ahimastos, 2003, Gender differences in large artery stiffness pre-and post puberty, J. Clin. Endocrinol. Metab. source

      Not checked in the free run.

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

    Premisecitation

    For respiratory measurements, respiratory synchronous variation in the PPG signal is irrespective of gender, and thus no action is required.

    “For respiratory measurements, Nilsson et al. have reported that respiratory synchronous variation in the PPG signal is irrespective of gender, and thus no action is required [111].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [111] Nilsson, 2006, Age and gender do not influence the ability to detect respiration by photoplethysmography, J. Clin. Monit. Comput. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Dehghanojamahalleh et al. demonstrated variations in PPG morphology attributed to gender differences, with direct influence of gender variation only significantly different at the upper peripheral measurement site such as the hand and fingers as opposed to lower extremities such as the ankle and feet.

    “Dehghanojamahalleh et al. demonstrated variations in PPG morphology attributed to gender differences [105]. Interestingly, direct influence of gender variation was only significantly different at the upper peripheral measurement site such as the hand and fingers as opposed to lower extremities such as the ankle and feet.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [105] Dehghanojamahalleh, 2019, Sex-Related Differences in Photoplethysmography Signals Measured From Finger and Toe, IEEE J. Transl. Eng. Health Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    For females, PWV stayed roughly the same, while there was an increase in PWV for males.

    “However, for females, PWV stayed roughly the same, while there was an increase in PWV for males.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [104] Ahimastos, 2003, Gender differences in large artery stiffness pre-and post puberty, J. Clin. Endocrinol. Metab. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    During prepuberty, females have lower arterial compliance and higher central and peripheral PWV yielding stiffer arteries compared to males.

    “It was discovered during prepuberty, females have lower arterial compliance and higher central and peripheral PWV yielding stiffer arteries compared to males.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [104] Ahimastos, 2003, Gender differences in large artery stiffness pre-and post puberty, J. Clin. Endocrinol. Metab. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The finger is arterially dominated while the forearm has a larger venous component.

    “The finger is arterially dominated while the forearm has a larger venous component [120].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [120] Ysehak Abay, T., Shafqat, K., and Kyriacou, P.A. (2019). Perfusion Changes at the Forehead Measured by Photoplethysmography during a Head-Down Tilt Protocol. Biosensors, 9. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Pulse wave propagation delay between the genders indicates baseline differences in arterial stiffness with women displaying lower degrees of pulse arrival latency delay indicating higher vascular stiffness.

    “Pulse wave propagation delay between the genders indicates baseline differences in arterial stiffness with women displaying lower degrees of pulse arrival latency delay indicating higher vascular stiffness [106,107].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [106] Mukkamala, 2015, Toward ubiquitous blood pressure monitoring via pulse transit time: Theory and practice, IEEE Trans. Biomed. Eng. source

      Not checked in the free run.

    • cites [107] Guajardo, 2018, Sex differences in vascular dysfunction and cardiovascular outcomes: The cardiac, endothelial function, and arterial stiffness in ESRD (CERES) study, Hemodial. Int. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The venous system contributes periodicity to the PPG signal, but this is often considered noise.

    “The venous system similarly contributes periodicity to the PPG signal, but this is often considered noise.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [116] Shelley, 1993, The detection of peripheral venous pulsation using the pulse oximeter as a plethysmograph, J. Clin. Monit. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Shelley et al. and Sami et al. both demonstrated the influence of the venous signal on SpO2, showing that forehead and earlobe pulse oximeters produced a significantly biased variable component of the PPG determined to originate from central venous pressure (CVP).

    “Shelley et al. and Sami et al. both demonstrated the influence of the venous signal on SpO2, showing that forehead and earlobe pulse oximeters (respectively) produced a significantly biased variable component of the PPG determined to originate from central venous pressure (CVP) [125,127].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [125] Shelley, 2005, The effect of venous pulsation on the forehead pulse oximeter wave form as a possible source of error in Spo2 calculation, Anesth. Analg. source

      Not checked in the free run.

    • cites [127] Sami, 1991, Central venous pulsations associated with a falsely low oxygen saturation measured by pulse oximetry, J. Clin. Monit. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Venous pulsations have been shown to artificially inflate the systolic peak amplitude and interfere with the rising systolic edge of the typical PPG waveform.

    “They have been shown to artificially inflate the systolic peak amplitude and interfere with the rising systolic edge of the typical PPG waveform; an important parameter used in cardiovascular health determination [116].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [116] Shelley, 1993, The detection of peripheral venous pulsation using the pulse oximeter as a plethysmograph, J. Clin. Monit. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Nijland et al. confirmed in fetal lambs that reflectance pulse oximetry SpO2 readings were significantly lower than fiberoptic SaO2 values, and when the vessel was coagulated, this difference became negligible.

    “Nijland et al. also confirmed these results in fetal lambs, where reflectance pulse oximetry SpO2 readings were significantly lower than fiberoptic SaO2 values. However, when the vessel was coagulated, this difference became negligible [128].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [128] Nijland, 1996, Reflectance pulse oximetry in fetal lambs: Subcutaneous vessels and vasoconstriction affect its reliability, J. Clin. Monit. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Dicrotic notch duration at the finger was not significantly different from measurements under the wrist and forehead, but was different from the earlobe, arm, and wrist.

    “Dicrotic notch duration at the finger was not significantly different from measurements under the wrist and forehead, but was different from the earlobe, arm, and wrist.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [95] Hartmann, 2019, Quantitative comparison of photoplethysmographic waveform characteristics: Effect of measurement site, Front. Physiol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Eliminating venous contributions to PPG by application of contact pressure may eliminate the arterial pulsation in hypotensive patients as well as increase pressure-induced injury risk to the measurement site.

    “However, it is possible that this will eliminate the arterial pulsation in hypotensive patients as well as increase pressure-induced injury risk to the measurement site [125].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [125] Shelley, 2005, The effect of venous pulsation on the forehead pulse oximeter wave form as a possible source of error in Spo2 calculation, Anesth. Analg. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    For silicon photodiodes, the absorption coefficient increases with temperature, so the detectors absorb less light at higher temperatures, inducing an apparent shift in PPG amplitude.

    “For silicon photodiodes, the absorption coefficient increases with temperature, and thus the detectors will absorb less light at higher temperatures, inducing an apparent shift in PPG amplitude [161].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [161] Optoelectronics, O. (2020, August 06). Temperature and Bias Effects. Available online: http://www.osioptoelectronics.com/technology-corner/frequently-asked-questions/temperature-bias-effects.aspx.

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The back of the ear and earlobe yielded significantly higher PPG signal amplitude than the hand and postauricular region, but LDV values and comparisons to the fingertips and the rest of the face were not significant.

    “The back of the ear and earlobe yielded significantly higher PPG signal amplitude than the hand and postauricular region (i.e., neck behind the ear), but LDV values and comparisons to the fingertips and the rest of the face were not significant.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [144] Tur, 1983, Basal perfusion of the cutaneous microcirculation: Measurements as a function of anatomic position, J. Investig. Dermatol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The fingertips have the thinnest skin, followed by the forearm, dorsal hand, cheek, and forehead.

    “Overall, the literature has shown that the fingertips have the thinnest skin, followed by the forearm, dorsal hand, cheek, and forehead [139].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [139] Dahlqvist, 2018, Vibrotactile and thermal perception and its relation to finger skin thickness, Clin. Neurophysiol. Pract. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Allen et al. reported a 2.6-times increase in PPG amplitude, 93% decrease in LDF flux, and median decrease of 0.089 degrees Celsius following a deep inspiratory gasp of air.

    “They reported a 2.6-times increase in PPG amplitude, 93% decrease in LDF flux, and median decrease of 0.089 degrees Celsius [150].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [150] Allen, 2002, Microvascular blood flow and skin temperature changes in the fingers following a deep inspiratory gasp, Physiol. Meas. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    All these motions range between 0.1 and 20 Hz, which is within the frequency range for heart rate (1-4 Hz).

    “All these motions range between 0.1 and 20 Hz, which is within the frequency range for heart rate (1–4 Hz) [163].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [163] Zong, C., and Jafari, R. (2015, January 25–29). Robust heart rate estimation using wrist-based PPG signals in the presence of intense physical activities. Proceedings of the 2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Milan, Italy. source

      Not checked in the free run.

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

    Premisecitation

    For all wavelengths of light, the forehead is superior to the cheeks and the whole face for determining heart rate.

    “Fallet et al. found via iPPG that for all wavelengths of light, the forehead is superior to the cheeks and the whole face for determining heart rate.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [146] Fallet, S., Moser, V., Braun, F., and Vesin, J.-M. (2016, January 11–14). Imaging photoplethysmography: What are the best locations on the face to estimate heart rate?. Proceedings of the 2016 Computing in Cardiology Conference (CinC), Vancouver, BC, Canada. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Both micro-motions and macro-motions cause more significant fluctuations to the PPG signal than sedentary motions.

    “Adjusting positions or tapping a finger can be considered a micro-motion, while a macro-motion is performing an exercise such as walking or jogging—both types of motion cause more significant fluctuations to the signal than sedentary motions.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: Motion artifacts are picked up by PPG sensors and cause fluctuations within the collected signal.

  • May combine two claims.

    Premisecitation

    The amount of pressure applied is often underreported and can manipulate the resultant PPG waveform.

    “Grabovskis et al. noted that the amount of pressure applied is often underreported and can manipulate the resultant PPG waveform [132].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [132] Grabovskis, 2013, Effect of probe contact pressure on the photoplethysmographic assessment of conduit artery stiffness, J. Biomed. Opt. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    PTT is also similar bilaterally at the ears and finger, while a small difference exists at the toes.

    “Additionally, PTT is also similar bilaterally at the ears and finger, while a small difference exists at the toes [91].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [91] Allen, 2002, Age-related changes in peripheral pulse timing characteristics at the ears, fingers and toes, J. Hum. Hypertens. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    Physiological temperature changes due to thermoregulation may impact a signal, and studies detailing changes caused by external temperatures also illustrate significant PPG impact.

    “Thus, while physiological temperature changes due to thermoregulation may impact a signal, studies detailing changes caused by external temperatures also illustrate significant PPG impact.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    PPG quality is improved with warm temperatures.

    “The authors conclude that PPG quality is improved with warm temperatures, yet do not mention the effect of thermoregulatory responses [155].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [154] Khan, 2015, Investigating the effects of temperature on photoplethysmography, IFAC Pap. Online source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Motion artifacts within a PPG signal can skew results for SpO2, heart rate, and other PPG-dependent measurements, creating false alarms or inaccurate readings.

    “With the addition of motion artifacts within a PPG signal, results for SpO2, heart rate, and other PPG dependent measurements can be skewed. This can create false alarms or inaccurate readings.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Motion artifacts are picked up by PPG sensors and cause fluctuations within the collected signal.

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

    Premisecitation

    There is a consistent increase in signal amplitude in the wrist PPG compared to the finger PPG.

    “Additionally, the authors noted a consistent increase in signal amplitude in the wrist PPG compared to the finger PPG.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [26] Rajala, 2018, Comparison of photoplethysmogram measured from wrist and finger and the effect of measurement location on pulse arrival time, Physiol. Meas. source

      Not checked in the free run.

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

    Premisecitation

    The appropriate amount of pressure is such that the b/a ratio of the SDPPG is equal to 0.70, meaning that the external pressure on the arterial wall is equal to the mean arterial pressure.

    “They determine that the appropriate amount of pressure is such that the b/a ratio of the SDPPG is equal to 0.70. This means that the external pressure on the arterial wall is equal to the mean arterial pressure [132].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [132] Grabovskis, 2013, Effect of probe contact pressure on the photoplethysmographic assessment of conduit artery stiffness, J. Biomed. Opt. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Green was the best option due to its higher correlation coefficient, but blue is an alternative due to its significantly similar ΔSNR as green.

    “It was determined that green was the best option due to its higher correlation coefficient, but blue is an alternative option due to its significantly similar ΔSNR as green.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [164] Lee, J., Matsumura, K., Yamakoshi, K.-I., Rolfe, P., Tanaka, S., and Yamakoshi, T. (2013, January 3–7). Comparison between red, green and blue light reflection photoplethysmography for heart rate monitoring during motion. Proceedings of the 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Osaka, Japan.

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Red and IR have deeper penetration depths than blue and green, making them prone to more motion artifacts such as factors that directly affect the DC baseline.

    “With their longer wavelengths, red and IR have deeper penetration depths compared to blue and green, making them prone to more motion artifacts such as the factors that directly affect the DC baseline [162,164].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [162] Maeda, 2011, Relationship between measurement site and motion artifacts in wearable reflected photoplethysmography, J. Med. Syst. source

      Not checked in the free run.

    • cites [164] Lee, J., Matsumura, K., Yamakoshi, K.-I., Rolfe, P., Tanaka, S., and Yamakoshi, T. (2013, January 3–7). Comparison between red, green and blue light reflection photoplethysmography for heart rate monitoring during motion. Proceedings of the 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Osaka, Japan.

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The Apple Watch had the best MAPE (1.14-6.70%), while Fitbit Charge HR and Garmin Forerunner 225 had MAPE of 2.38-16.99% and 7.87-24.38%, respectively.

    “In another study, performed by Dooley et al., the comparison was made between the Apple Watch (AP), FB, and Garmin Forerunner 225 (GF), where the AP was considered the best in terms of MAPE (1.14–6.70%), while the FB and the GF had a MAPE of 2.38–16.99% and 7.87–24.38%, respectively [167].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [167] Dooley, 2017, Estimating accuracy at exercise intensities: A comparative study of self-monitoring heart rate and physical activity wearable devices, JMIR mHealth uHealth source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The Apple Watch (p = 0.84) and Garmin Forerunner 225 (p = 0.35) had no significant difference in HR readings from the ECG during vigorous intensity.

    “The AP (p = 0.84) and GF (p = 0.35) had no significant difference in HR readings from the ECG during vigorous intensity.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [167] Dooley, 2017, Estimating accuracy at exercise intensities: A comparative study of self-monitoring heart rate and physical activity wearable devices, JMIR mHealth uHealth source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Sukor et al.'s algorithm had an accuracy of 83 ± 11%, a sensitivity of 89 ± 10%, and a specificity of 77 ± 19%.

    “They found their algorithm to have an accuracy of 83 ± 11%, a sensitivity of 89 ± 10 %, and a specificity of 77 ± 19%.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [169] Sukor, 2011, Signal quality measures for pulse oximetry through waveform morphology analysis, Physiol. Meas. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    When comparing their algorithm to an ECG, Sukor et al. were able to lower the error in heart rate readings to 0.49 ± 0.66 bpm, whereas without the algorithm, the error was 7.23 ± 5.78 bpm.

    “When comparing their algorithm to an ECG, they were able to lower the error in heart rate readings to 0.49 ± 0.66 bpm, whereas without the algorithm, the error was 7.23 ± 5.78 bpm.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [169] Sukor, 2011, Signal quality measures for pulse oximetry through waveform morphology analysis, Physiol. Meas. source

      Not checked in the free run.

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

    Interpretationreasoning

    Depending on the exercise, each tracker will have a different accuracy, which could be attributed to the different noise-canceling algorithms used on board.

    “This shows that, depending on the exercise, each tracker will have a different accuracy, which could be attributed to the different noise-canceling algorithms used on board.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The Apple Watch 4 had the highest accuracy with an MAE of 2.7 BPM at rest and 4.6 BPM during the walking phase.

    “This study also showed that the Apple Watch 4 had the highest accuracy with an MAE of 2.7 BPM at rest and 4.6 BPM during the walking phase,”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [46] Bent, 2020, Investigating sources of inaccuracy in wearable optical heart rate sensors, NPJ Digit. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    During low-intensity events, the Basis Peak provided accurate heart rate readings (r = 0.84, p < 0.05), while the Fitbit Charge HR had a moderate correlation (r = 0.73, p < 0.05).

    “During the low-intensity events, the BP provided accurate heart rate readings (r = 0.84, p < 0.05), while the FB had a moderate correlation (r = 0.73, p < 0.05).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [165] Jo, 2016, Validation of biofeedback wearables for photoplethysmographic heart rate tracking, J. Sports Sci. Med.

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    When going from a resting phase to a low-intensity walking phase, the correlation coefficient went down but slowly rebounded when moved into a more intense walking phase.

    “When going from a resting phase to a low-intensity walking phase, they found that the correlation coefficient went down but had slowly rebounded when moved into a more intense walking phase.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [166] Stahl, 2016, How accurate are the wrist-based heart rate monitors during walking and running activities? Are they accurate enough?, BMJ Open Sport Exerc. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    High-intensity events caused the Basis Peak to have a weaker correlation (r = 0.77, p < 0.05), whereas the Fitbit Charge HR had the weakest correlation (r = 0.58, p < 0.05).

    “High-intensity events caused the BP to have a weaker correlation (r = 0.77, p < 0.05), whereas the FB had the weakest correlation (r = 0.58, p < 0.05).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [165] Jo, 2016, Validation of biofeedback wearables for photoplethysmographic heart rate tracking, J. Sports Sci. Med.

      Not checked in the free run.

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

    Interpretationnone given

    Aside from location and wavelength, the intensity of motion plays a role in how accurate heart rate monitoring is.

    “Aside from location and wavelength, the intensity of motion also plays a role in how accurate heart rate monitoring is.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The mean absolute percentage error (MAPE) of the Basis Peak and Fitbit Charge HR were 3.6% and 6.2%, respectively.

    “These results align with an assessment done by Stahl et al., where they measured the mean absolute percentage error values (MAPE) of BP and the FB to be 3.6% and 6.2%, respectively [166].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [166] Stahl, 2016, How accurate are the wrist-based heart rate monitors during walking and running activities? Are they accurate enough?, BMJ Open Sport Exerc. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisereasoning

    Accelerometers and gyroscopes are the standards, but when trying to measure micro motions such as finger tapping, they do not always pick up on the motion because the wrist remains still.

    “Accelerometers and gyroscopes are the standards, but when trying to measure micro motions such as finger tapping, accelerometers and gyroscopes do not always pick up on the motion because the wrist remains still.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [179] Casson, 2016, Gyroscope vs. accelerometer measurements of motion from wrist PPG during physical exercise, ICT Express source

      Not checked in the free run.

    • cites [180] Lee, 2018, Motion artifact cancellation in wearable photoplethysmography using gyroscope, IEEE Sens. J. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Chong et al. achieved an accuracy of 93.7% during a daily motion experiment and saw a significant reduction in error for SpO2 and heart rate measurements.

    “They were able to achieve an accuracy of 93.7% during a daily motion experiment, and they saw a significant reduction in error for SpO2 and heart rate measurements.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [170] Chong, 2014, Photoplethysmograph signal reconstruction based on a novel hybrid motion artifact detection–reduction approach. Part I: Motion and noise artifact detection, Ann. Biomed. Eng. source

      Not checked in the free run.

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

    Interpretationreasoning

    The discussed detection methods are all real-time ways to detect and eliminate sections of acquired PPG signals that contain corrupted areas due to motion artifacts.

    “The discussed detection methods are all real-time ways to detect and eliminate sections of acquired PPG signals that contain corrupted areas due to motion artifacts.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Selvaraj et al. used kurtosis and Shannon Entropy to determine motion artifacts and achieved an accuracy of 88.8% in a laboratory setting.

    “Kurtosis and Shannon Entropy were the measurements used by Selvaraj et al. to determine motion artifacts, and they were able to perform an accuracy of 88.8% in a laboratory setting [174].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [174] Selvaraj, N., Mendelson, Y., Shelley, K.H., Silverman, D.G., and Chon, K.H. (September, January 30). Statistical approach for the detection of motion/noise artifacts in Photoplethysmogram. Proceedings of the 2011 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Boston, MA, USA. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    With the use of adaptive filters and secondary sensors, motion artifacts can be identified and eliminated, or identified and reconstructed to restore the original PPG signal void of all motion artifacts.

    “With the use of adaptive filters and secondary sensors, motion artifacts can be identified and eliminated, or they can be identified and reconstructed to restore the original PPG signal, void of all motion artifacts.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Krishnan et al. discovered that skew and kurtosis measurements in the time domain were higher when there was corruption, and frequency-domain kurtosis was smaller when there was corruption.

    “They discovered skew and kurtosis measurements in the time domain to be higher when there was corruption, and the frequency-domain kurtosis was smaller when there was corruption.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [173] Krishnan, R., Natarajan, B., and Warren, S. (April, January 31). Analysis and detection of motion artifact in photoplethysmographic data using higher order statistics. Proceedings of the 2008 IEEE International Conference on Acoustics, Speech and Signal Processing, Las Vegas, NV, USA. source

      Not checked in the free run.

  • May combine two claims. The quote only partly states this claim.

    Premisecitation

    Coucerio et al. achieved a specificity of 92.7% and a sensitivity of 82.7% using time-domain and period domain analysis of 26 features.

    “They were able to achieve a specificity of 92.7% and a sensitivity of 82.7%.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [172] Couceiro, R., Carvalho, P., Paiva, R.P., Henriques, J., and Muehlsteff, J. (September, January 28). Detection of motion artifacts in photoplethysmographic signals based on time and period domain analysis. Proceedings of the 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, San Diego, CA, USA. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Karlen et al. achieved a positive predictive value of 96.68% and a sensitivity of 98.93% for mobile PPG measurements.

    “They were able to achieve a positive predictive value of 96.68% and a sensitivity of 98.93%.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [171] Karlen, W., Ansermino, J.M., and Dumont, G. (September, January 28). Adaptive pulse segmentation and artifact detection in photoplethysmography for mobile applications. Proceedings of the 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, San Diego, CA, USA. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Both the piezoelectric transducer and another wavelength of light can pick up finer motions such as finger tapping.

    “Both the piezoelectric transducer and another wavelength of light can pick up these finer motions [181,182].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [181] Lee, 2019, Motion artifact identification and removal from wearable reflectance photoplethysmography using piezoelectric transducer, IEEE Sens. J. source

      Not checked in the free run.

    • cites [182] Zhang, Y., Song, S., Vullings, R., Biswas, D., Simões-Capela, N., van Helleputte, N., van Hoof, C., and Groenendaal, W. (2019). Motion artifact reduction for wrist-worn photoplethysmograph sensors based on different wavelengths. Sensors, 19. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Without force regulation, the coefficient of variation between five posture stages was 50.9%; the addition of the force regulator dropped the coefficient of variation to 1.8%.

    “Without force regulation, the coefficient of variation between five posture stages was calculated at 50.9%. The addition of the force regulator dropped the coefficient of variation to 1.8%.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [212] Sim, 2018, A contact-force regulated photoplethysmography (PPG) platform, AIP Adv. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    With an applied pressure range of 0-15 kPa, there was a variation of over 300 percent in the b/a ratio; when an optimal pressure was reached, the variation coefficient dropped to less than 5 percent.

    “Grabovskis et al. reported with an applied pressure range of 0–15 kPa, there was a variation of over 300 percent in the b/a ratio [209]. When an optimal pressure was reached, the variation coefficient dropped to less than 5 percent.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [209] Grabovskis, A., Marcinkevics, Z., Rubenis, O., Rubins, U., and Lusa, V. (2012, January 16–19). Photoplethysmography system for blood pulsation detection in unloaded artery conditions. Proceedings of the Biophotonics: Photonic Solutions for Better Health Care III, Brussels, Belgium. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    For shorter wavelengths, the occlusion pressure was lower, as more superficial arterioles with low mean arterial pressure were in the light path at these wavelengths.

    “For shorter wavelengths, the occlusion pressure was lower, as more superficial arterioles with low MAP were in the light path at these wavelengths.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [210] Spigulis, J., Gailite, L., Erts, R., and Lihachev, A. (2007, January 17–19). Contact probe pressure effects in skin multi-spectral photoplethysmography. Proceedings of the European Conference on Biomedical Optics, Munich, Germany. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    The change in these fundamental features can affect other measurements such as the b/a ratio, the relationship between the frequency response of a PPG signal and a blood pressure signal, or the pulse transit time (PTT).

    “The change in these fundamental features can affect other measurements such as the b/a ratio, derived from the a and b peaks of the second derivative of a PPG signal, used to characterize arterial stiffness [132], the relationship between the frequency response of a PPG signal and a blood pressure signal [207], or the pulse transit time (PTT) which is used as an indicator for fluctuating stiffness”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [132] Grabovskis, 2013, Effect of probe contact pressure on the photoplethysmographic assessment of conduit artery stiffness, J. Biomed. Opt. source

      Not checked in the free run.

    • cites [207] Hsiu, 2011, Effects of different contacting pressure on the transfer function between finger photoplethysmographic and radial blood pressure waveforms, Proc. Inst. Mech. Eng. Part H J. Eng. Med. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    As external pressure exceeds the point where transmural pressure is no longer zero, the vessel begins to occlude, and the AC amplitude begins to decrease until there is no longer a signal where the vessel is occluded.

    “As the external pressure exceeds the point where the transmural pressure is no longer zero, the vessel begins to occlude, and the AC amplitude begins to decrease until there is no longer a signal where the vessel is occluded.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    At 60 mmHg, there were the greatest R2 values for four out of five harmonics, and with different applied pressures, the R2 values ranged from 0.13 to 0.77 for the first harmonic.

    “At 60 mmHg, there were the greatest R2 values for four out of five harmonics, and with the different applied pressures, the R2 values ranged from 0.13 to 0.77 for the first harmonic.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [207] Hsiu, 2011, Effects of different contacting pressure on the transfer function between finger photoplethysmographic and radial blood pressure waveforms, Proc. Inst. Mech. Eng. Part H J. Eng. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    With an applied force at the finger of 0.2-1.8 N, there was an increase in AC amplitude and AC/DC ratio until the parameters reached a peak and then decreased, while the pulse area decreased, and the DC offset increased.

    “As reported by Teng and Zhang, with an applied force at the finger of 0.2–1.8 N, there was an increase in AC amplitude and AC/DC ratio until the parameters reached a peak and then decreased, while the pulse area decreased, and the DC offset increased [206].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [206] Teng, 2004, The effect of contacting force on photoplethysmographic signals, Physiol. Meas. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    For the PTT calculated at 90% of the pulse amplitude, there was a similar increasing trend for the PTT but without a significant difference (p = 0.107), and the PTT leveled out to a constant value for a transmural pressure of around 0.1 N.

    “Lastly, for the PTT calculated at 90% of the pulse amplitude, there was a similar increasing trend for the PTT but without a significant difference (p = 0.107). The PTT leveled out to a constant value for a transmural pressure of around 0.1 N.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [208] Teng, 2006, The effect of applied sensor contact force on pulse transit time, Physiol. Meas. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Rhee et al.'s finger-ring system applied a skin pressure of about 75 mmHg and, due to its compliance, held steady the applied pressure while the finger was in different positions.

    “This band would apply a skin pressure of about 75 mmHg and, due to its compliance, it would hold steady the applied pressure while the finger was in different positions.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [213] Rhee, 2001, Artifact-resistant power-efficient design of finger-ring plethysmographic sensors, IEEE Trans. Biomed. Eng. source

      Not checked in the free run.

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

    Interpretationnone given

    Various attempts are made in PPG sensing circuitry to effectively reject DC photocurrent.

    “Various attempts are also made in the PPG sensing circuitry level to effectively reject DC photocurrent.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    PPG signals are low-amplitude signals and have a normal pulse frequency within the range of 0.5 to 4 Hz.

    “PPG signals are low-amplitude signals and have a normal pulse frequency within the range of 0.5 to 4 Hz [195,196].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [195] Wong, 2005, A near-infrared heart rate measurement IC with very low cutoff frequency using current steering technique, IEEE Trans. Circuits Syst. I Regul. Pap. source

      Not checked in the free run.

    • cites [196] Moraes, J.L., Rocha, M.X., Vasconcelos, G.G., Vasconcelos Filho, J.E., de Albuquerque, V.H.C., and Alexandria, A.R. (2018). Advances in photopletysmography signal analysis for biomedical applications. Sensors, 18. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    With the change in transmural pressure, there is a related compliance change in the affected vessel, and the vessel reaches maximum compliance when the transmural pressure is zero.

    “With the change in transmural pressure, there is also a related compliance change in the affected vessel. The vessel reaches maximum compliance when the transmural pressure is zero [205].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [205] Forster, 1986, Oscillometric determination of diastolic, mean and systolic blood pressure—A numerical model, J. Biomech. Eng. source

      Not checked in the free run.

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

    Interpretationreasoning

    With a low bandwidth of around 5 Hz, PPG signals can be extracted from high frequency noise using a low-pass filter and from low frequency noise using a high-pass filter.

    “With a low bandwidth of around 5 Hz, PPG signals can be extracted out from high frequency noise using a low-pass filter and from low frequency noise using a high-pass filter (e.g., to reject 60 Hz room lights and to reject DC sunlight).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Wang et al.'s ear-worn sensor method was effective in shielding from noise due to ambient light, as the DC level of the PPG signal was less than 2 nA when the LEDs were switched off.

    “This method was found to be effective in shielding from noise due to ambient light, as the DC level of the PPG signal was considerably low (measured to be less than 2 nA) when the LEDs were switched off.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [200] Wang, 2007, Multichannel reflective PPG earpiece sensor with passive motion cancellation, IEEE Trans. Biomed. Circuits Syst. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    Several characteristics of the PPG waveform are affected by changes in contact force, including the AC amplitude, the DC offset amplitude, the ratio of AC/DC amplitudes, and the normalized pulse area.

    “Several characteristics of the PPG waveform are affected by changes in contact force, including; the AC amplitude, the DC offset amplitude, the ratio of AC/DC amplitudes, and the normalized pulse area.”
    Quote in the paperSubstantial claim
126 of 126

  • The paper relies on this without support.

    The findings of the cited studies on specific PPG devices and populations are applicable to PPG-based continuous cardiovascular monitoring devices in general.

    “Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces.”

  • The paper relies on this without support.

    The Fitzpatrick scale is a valid proxy for skin pigmentation relevant to PPG light-tissue interactions.

    “The most common way to characterize skin tone is via the Fitzpatrick Scale [37].”

  • The paper relies on this without support.

    The physiological changes associated with obesity measured in the cited studies are present in the target population of PPG users.

    “The variation of BMI across individuals is thus a potential source of variation for PPG measurements.”

  • The paper relies on this without support.

    Gender is binary.

    “While the wide spectrum of ages can make it a difficult parameter to incorporate into models, gender is binary, making it easier to incorporate.”

  • The paper relies on this without support.

    PWV is highly dependent on vascular stiffness and is observable through PPG.

    “PWV is highly dependent on vascular stiffness and is observable through PPG.”

  • The paper relies on this without support.

    Pulse pressure is dependent on both arterial stiffness and cardiac output.

    “Pulse pressure is dependent on both arterial stiffness and cardiac output.”

  • The paper relies on this without support.

    Motion artifacts are picked up by PPG sensors and cause fluctuations within the collected signal.

    “Within all settings, motion artifacts are picked up by the sensor and cause fluctuations within the collected signal.”

  • The paper relies on this without support.

    Ambient light intensity is generally multiple orders of magnitude larger than the pulsatile (AC) component of the PPG, which can lead to signal saturation.

    “The ambient light intensity can be a zero frequency (e.g., DC), such as sunlight, or at a variable frequency, as from room lights (e.g., 60 Hz in the US) and is generally multiple orders of magnitude larger than the pulsatile (AC) component of the PPG, which can lead to signal saturation.”

  • The paper relies on this without support.

    Only a limited number of RCIM PPG devices have FDA approval.

    “However, only a limited number of RCIM PPG devices have FDA approval.”
9 of 9

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?

  • Technological limitations are primarily sensor-related (LED wavelength, light intensity, placement), while algorithmic limitations stem from biased datasets, poor calibration, and underrepresentation of darker skin in training cohorts.

    “Technological limitations are primarily sensor-related - such as LED wavelength, light intensity, and placement - while algorithmic limitations stem from biased datasets, poor calibration, and underrepresentation of darker skin in training cohorts.”

    From Photoplethysmography in Diverse Skin Tones: Evaluating Bias in Smartwatch Health Monitoring (2025) · cites this paper as [28]

    Section 2.1 (Skin Tone; page unavailable) links PPG accuracy to LED wavelength and source–detector placement, and reports greater error for darker skin tones. The Introduction also acknowledges hardware and software sources of noise. However, the cited passages do not establish that technological limitations are primarily sensor-related or that algorithmic limitations stem from biased training datasets, poor calibration, or underrepresentation of darker skin in training cohorts; the study with fewer dark-skinned participants is described as a device validation, not a training cohort. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

  • Statistically reliable patterns tied to phenotype, particularly adiposity, and to a lesser extent skin pigmentation, were evident and align with optical and physiological mechanisms described in prior work.

    “Nonetheless, statistically reliable patterns tied to phenotype, particularly adiposity, and, to a lesser extent, skin pigmentation, were evident and align with the optical and physiological mechanisms described in prior work [13,43].”

    From PPG-Based Heart Rate Accuracy in Hispanic Adults with Fitzpatrick III–V Skin Tones: An Evaluation of Body Composition and Skin-Tone Effects (2026) · cites this paper as [43]

  • Melanin attenuates the wavelength of incident light and limits penetration to subcutaneous tissue because it is highly light-absorbing.

    “Melanin attenuates the wavelength of the incident light and limits the penetration to the subcutaneous tissue because is high light-absorbing [80,101].”

    From Skin pigmentation influence on pulse oximetry accuracy: a systematic review and bibliometric analysis (2022) · cites this paper as [101]

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Pulse wave velocity is said to both decrease and increase with age

    Minor

    The text says pulse wave velocity (PWV) decreases with age, but later says it increases with age. Table 3 also lists an increase.

  • Hartmann study's mean age conflicts with its stated age range

    Minor

    The same 36-person Hartmann study is described as having ages from 33 to 58 and a mean age of 33. If 33 is the minimum and at least one participant is 58, the mean must be greater than 33-even when rounded to the nearest year.

  • Photodiode absorption is said to increase while absorbed light decreases

    Minor

    The text says the absorption coefficient increases with temperature, then concludes that the detectors absorb less light at higher temperatures. Those statements point in opposite directions under the stated explanation.

3 of 3

Cites

1 retracted

Flagged first, then by citations

2 of the 212 references couldn’t be matched to a known paper.

Research works printed but not linked: 3

  1. Hasan, 2015, A New First-Derivative Related Index to Assess Pulse Wave Transit Time from a Photoplethysmographic Waveform: Age Dependence and Agreement with Normative Data, Int. J. Bioinform. Biomed. Eng., 1, 276
  2. Goepfert, L., Petersen, C.L., Ansermino, J.M., and Gorges, M. (2018, January 10–13). Evaluation of a Combined PPG/MPG Sensor in Healthy Volunteers. Proceedings of the Anesthesia and Analgesia, Miami, FL, USA.
  3. Sazonov, E. (2014). Wearable Sensors: Fundamentals, Implementation and Applications, Elsevier.

Cited by

Sorted by citations

Related

Authors
Fine, J., Branan, K. L., Rodriguez, A. J., Boonya-ananta, T., Ajmal, Ramella-Roman, J. C., McShane, M. J., & Coté, G. L.
Affiliations
  • Texas A&M University (US)
  • Florida International University (US)
  • Department of Biomedical Engineering, Florida International University, Miami, FL 33174, USA
  • Texas A&M Engineering Experiment Station (US)
Corresponding author
  • McShane, Michael J.
  • Coté, Gerard L.
ORCID
Venue
Biosensors
Publisher
MDPI AG
Published
2021-04-16
Volume
11
Issue
4
Pages
126
ISSN
2079-6374 (ISSN-L)
DOI
10.3390/bios11040126
PMC
PMC8073123
OpenAlex
W3155015885
Cited by
348
References
212
Citations by year
2026: 80 · 2025: 74 · 2024: 70 · 2023: 74 · 2022: 40 · 2021: 10
FWCI
4.09
Type
journal article
Language
en
Open access
Licence
Locations
  • Biosensors (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Florida International University Digital Commons (Florida International University) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
National Science Foundation (1648451)
Topics
  • Physical Sciences › Engineering › Biomedical Engineering › Non-Invasive Vital Sign Monitoring
  • Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Heart Rate Variability and Autonomic Control
  • Health Sciences › Medicine › Surgery › Hemodynamic Monitoring and Therapy
Keywords
photoplethysmography, wearable health monitoring, cardiovascular monitoring, motion artifacts, ambient light interference, skin tone, body temperature, heart rate variability, blood pressure estimation, respiration, venous pulsation
MeSH terms
Wearable Electronic Devices, Blood Pressure, Heart Rate, Humans, Monitoring, Physiologic, Respiration, Signal Processing, Computer-Assisted, Artifacts, Photoplethysmography

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.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

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