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arxiv: 2401.04560 · v4 · submitted 2024-01-09 · 💻 cs.CV

Phase-shifted remote photoplethysmography for estimating heart rate and blood pressure from facial video

Pith reviewed 2026-05-24 04:37 UTC · model grok-4.3

classification 💻 cs.CV
keywords remote photoplethysmographyheart rate estimationblood pressure estimationfacial videodeep learningphase discrepancynon-contact monitoringrPPG
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The pith

Phase discrepancy between acral and facial rPPG signals extracted from video enables estimation of both heart rate and blood pressure.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents a two-stage deep learning framework that first extracts remote photoplethysmography signals from facial and acral video regions and then uses their phase difference to predict blood pressure values. This approach aims to provide contact-free monitoring of heart rate and blood pressure, which could allow continuous tracking without cuffs or electrodes. The method incorporates data augmentation via frame interpolation and a bounded output layer to keep predictions within physiological ranges. On standard datasets it reports lower errors for heart rate than prior video methods.

Core claim

The paper establishes a 2-stage deep learning framework where DRP-Net infers phase-shifted rPPG signals from acral and facial regions to estimate heart rate, and BBP-Net analyzes the phase discrepancy along with temporal features to estimate SBP and DBP within bounded ranges using a scaled sigmoid. Data augmentation via frame interpolation is used to improve heart rate accuracy. On the MMSE-HR dataset, this yields a heart rate MAE of 1.78 BPM, a 34.31% reduction over the recent method, with SBP and DBP MAEs of 10.19 mmHg and 7.09 mmHg; on V4V the corresponding errors are 3.83 BPM, 13.64 mmHg, and 9.4 mmHg.

What carries the argument

The phase discrepancy between acral and facial rPPG signals, which BBP-Net analyzes to regress systolic and diastolic blood pressure beyond heart rate correlation.

If this is right

  • Heart rate can be estimated from facial video with reduced mean absolute error using dual-region rPPG extraction.
  • Systolic and diastolic blood pressure can be inferred from the same video signals without contact sensors.
  • A scaled sigmoid activation constrains blood pressure outputs to predefined physiological ranges.
  • Frame interpolation augmentation improves rPPG signal quality for more accurate heart rate tracking.
  • The framework shows consistent results on both the MMSE-HR and V4V datasets.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The method could support continuous monitoring in telehealth or driver-assist scenarios where contact sensors are impractical.
  • Phase timing differences might be further analyzed to derive additional cardiovascular metrics such as pulse transit time.
  • Performance on larger and more diverse populations would be required to establish broader reliability.
  • Smartphone-camera deployment could increase accessibility of frequent checks but would need robustness to variable lighting and motion.

Load-bearing premise

The phase discrepancy between acral and facial rPPG waveforms supplies independent information sufficient to regress continuous SBP and DBP values rather than merely correlating with heart rate.

What would settle it

Train BBP-Net without the phase discrepancy input between the two rPPG signals and measure whether blood pressure estimation error rises to match or exceed a heart-rate-only baseline.

Figures

Figures reproduced from arXiv: 2401.04560 by Gyutae Hwang, Sang Jun Lee.

Figure 1
Figure 1. Figure 1: Overview of the training pipeline of the proposed method. Red and blue texts indicate ground truth and predicted physiological information, [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Data augmentation process of bradycardia and tachycardia samples. [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Architecture of DRP-Net. D. Dual remote photoplethysmography network (DRP-Net) In this paper, we propose DRP-Net to estimate phase-shifted rPPG signals from image sequences, and [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Architecture of BBP-Net. In (2), BPd is the estimated blood pressure, and BP max and BP min are heuristic parameters that represent upper and lower bounds of blood pressure. The symbol BP can be either SBP and DBP, and the upper and lower bounds of SBP [ are set to 155 mmHg and 85 mmHg. On the other hand, the upper and lower bounds of DBP \ are set to 95 mmHg and 45 mmHg. In (2), σ, z and τ denote the sigm… view at source ↗
Figure 5
Figure 5. Figure 5: Visualization of rPPG signals (left) and their PSD (right). The upper [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Bland-Altman plot of predicted and reference blood pressure on the [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Predicted heart rate computed from facial rPPG signals and their reference heart rate. In subfigures (a)–(f), Pearson correlation between the predicted [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Cross skin tone testing. The horizontal axis represents the Fitzpatrick [PITH_FULL_IMAGE:figures/full_fig_p011_8.png] view at source ↗
Figure 10
Figure 10. Figure 10: Visualization of spatial attention αs. The highlighted areas illustrate regions with higher attention scores. [2] S. Aggarwal and K. Pandey, “Early identification of pcos with commonly known diseases: obesity, diabetes, high blood pressure and heart disease using machine learning techniques,” Expert Systems with Applications, vol. 217, p. 119532, 2023. [3] O. Faust, W. Hong, H. W. Loh, S. Xu, R.-S. Tan, S… view at source ↗
read the original abstract

Human health can be critically affected by cardiovascular diseases, such as hypertension, arrhythmias, and stroke. Heart rate and blood pressure are important biometric information for the monitoring of cardiovascular system and early diagnosis of cardiovascular diseases. Existing methods for estimating the heart rate are based on electrocardiography and photoplethyomography, which require contacting the sensor to the skin surface. Moreover, catheter and cuff-based methods for measuring blood pressure cause inconvenience and have limited applicability. Therefore, in this thesis, we propose a vision-based method for estimating the heart rate and blood pressure. This thesis proposes a 2-stage deep learning framework consisting of a dual remote photoplethysmography network (DRP-Net) and bounded blood pressure network (BBP-Net). In the first stage, DRP-Net infers remote photoplethysmography (rPPG) signals for the acral and facial regions, and these phase-shifted rPPG signals are utilized to estimate the heart rate. In the second stage, BBP-Net integrates temporal features and analyzes phase discrepancy between the acral and facial rPPG signals to estimate SBP and DBP values. To improve the accuracy of estimating the heart rate, we employed a data augmentation method based on a frame interpolation model. Moreover, we designed BBP-Net to infer blood pressure within a predefined range by incorporating a scaled sigmoid function. Our method resulted in estimating the heart rate with the mean absolute error (MAE) of 1.78 BPM, reducing the MAE by 34.31 % compared to the recent method, on the MMSE-HR dataset. The MAE for estimating the systolic blood pressure (SBP) and diastolic blood pressure (DBP) were 10.19 mmHg and 7.09 mmHg. On the V4V dataset, the MAE for the heart rate, SBP, and DBP were 3.83 BPM, 13.64 mmHg, and 9.4 mmHg, respectively.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper proposes a two-stage deep learning framework for non-contact estimation of heart rate (HR) and blood pressure (BP) from facial video. DRP-Net extracts phase-shifted remote photoplethysmography (rPPG) signals from acral and facial regions to estimate HR (with data augmentation via frame interpolation), while BBP-Net analyzes temporal features and the phase discrepancy between these signals to regress systolic (SBP) and diastolic (DBP) blood pressure values, using a scaled sigmoid to bound outputs. On the MMSE-HR dataset it reports HR MAE of 1.78 BPM (34.31% reduction vs. a recent method), SBP MAE 10.19 mmHg and DBP MAE 7.09 mmHg; on V4V the corresponding MAEs are 3.83 BPM, 13.64 mmHg and 9.4 mmHg.

Significance. If the phase-discrepancy cue can be shown to carry BP information independent of HR correlation, the approach would offer a concrete advance in vision-based cardiovascular monitoring by avoiding contact sensors. The reported MAEs are competitive with prior rPPG work, but the absence of any ablation isolating the phase component or external validation leaves the incremental contribution unverified.

major comments (2)
  1. [BBP-Net description] Description of BBP-Net and the scaled-sigmoid bound: the central premise that phase discrepancy between acral and facial rPPG streams supplies information usable for continuous SBP/DBP regression beyond what HR alone provides is invoked to motivate the second-stage network, yet no ablation (e.g., single-stream input, time-shifted streams to null lag, or direct HR-regressor baseline for the BP task) is reported; without such a controlled comparison the end-to-end MAEs cannot be attributed to the phase cue.
  2. [Experimental results] Results on MMSE-HR and V4V: the claimed 34.31 % MAE reduction and the absolute MAEs for HR/SBP/DBP are presented without error bars, subject-wise cross-validation protocol, or re-implementation details of the baseline method, rendering the quantitative claims difficult to interpret or reproduce.
minor comments (2)
  1. [Abstract] Abstract contains the typo 'photoplethyomography' (should be photoplethysmography) and refers to the work as 'this thesis' while the submission is an arXiv paper.
  2. [Methods] Notation for the scaled sigmoid bound and the precise definition of 'phase discrepancy' feature fed to BBP-Net should be formalized with an equation rather than left descriptive.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive feedback on our manuscript. We address the major comments point by point below, agreeing where the manuscript requires strengthening and outlining the specific revisions we will implement.

read point-by-point responses
  1. Referee: [BBP-Net description] Description of BBP-Net and the scaled-sigmoid bound: the central premise that phase discrepancy between acral and facial rPPG streams supplies information usable for continuous SBP/DBP regression beyond what HR alone provides is invoked to motivate the second-stage network, yet no ablation (e.g., single-stream input, time-shifted streams to null lag, or direct HR-regressor baseline for the BP task) is reported; without such a controlled comparison the end-to-end MAEs cannot be attributed to the phase cue.

    Authors: We agree that the absence of ablation studies isolating the contribution of the phase discrepancy is a limitation in the current manuscript. To address this, the revised version will include new experiments: (1) BBP-Net with only temporal features from a single rPPG stream, (2) a variant with artificially time-shifted streams to remove phase information, and (3) a direct baseline regressing SBP/DBP from the estimated HR alone. These controlled comparisons will quantify the incremental value of the phase cue and support the motivation for the two-stage design. revision: yes

  2. Referee: [Experimental results] Results on MMSE-HR and V4V: the claimed 34.31 % MAE reduction and the absolute MAEs for HR/SBP/DBP are presented without error bars, subject-wise cross-validation protocol, or re-implementation details of the baseline method, rendering the quantitative claims difficult to interpret or reproduce.

    Authors: We acknowledge that the experimental reporting can be improved for reproducibility and statistical rigor. In the revision we will: add error bars (standard deviations across folds or subjects) to all MAE results; provide a detailed description of the subject-wise cross-validation protocol (including number of folds and how subjects are partitioned); and clarify the source of the baseline numbers (re-implementation details or values taken from the original publication) along with any hyperparameter or preprocessing differences. revision: yes

Circularity Check

0 steps flagged

No significant circularity in claimed derivation chain.

full rationale

The paper proposes an empirical two-stage supervised deep learning pipeline (DRP-Net for dual rPPG extraction followed by BBP-Net for BP regression) and reports MAEs obtained by training and testing on the MMSE-HR and V4V datasets. No first-principles mathematical derivation, uniqueness theorem, or parameter-free prediction is asserted that reduces by construction to its own inputs or to a self-citation. The phase-discrepancy premise is introduced as an architectural design choice rather than a derived result, and the scaled-sigmoid bound is a simple output-range constraint. Standard ML evaluation on held-out splits does not constitute the enumerated circularity patterns; therefore the score is 0 and the steps list remains empty.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

Only abstract available; the approach rests on standard rPPG domain assumptions plus a large number of fitted neural-network weights and an ad-hoc bounding function whose range is chosen rather than derived.

free parameters (2)
  • DRP-Net and BBP-Net weights
    All network parameters are fitted during supervised training on video datasets.
  • BP range bounds and sigmoid scaling factors
    Predefined numeric interval and scaling constants used to constrain BBP-Net outputs.
axioms (2)
  • domain assumption Subtle skin color variations in video faithfully encode pulsatile blood volume changes (rPPG principle)
    Invoked by the definition of DRP-Net and the use of its outputs for both HR and BP.
  • domain assumption Phase and shape discrepancy between acral and facial rPPG waveforms contains usable information about arterial blood pressure
    Central modeling choice for BBP-Net; if false the second stage has no signal.

pith-pipeline@v0.9.0 · 5899 in / 1676 out tokens · 29108 ms · 2026-05-24T04:37:42.139557+00:00 · methodology

discussion (0)

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