Estimating Blood Pressure from Photoplethysmogram Signal and Demographic Features using Machine Learning Techniques

Hypertension is a potentially unsafe health ailment, which can be indicated directly from the Blood pressure (BP). Hypertension always leads to other health complications. Continuous monitoring of BP is very important; however, cuff-based BP measurements are discrete and uncomfortable to the user. To address this need, a cuff-less, continuous and a non-invasive BP measurement system is proposed using Photoplethysmogram (PPG) signal and demographic features using machine learning (ML) algorithms. PPG signals were acquired from 219 subjects, which undergo pre-processing and feature extraction steps. Time, frequency and time-frequency domain features were extracted from the PPG and their derivative signals. Feature selection techniques were used to reduce the computational complexity and to decrease the chance of over-fitting the ML algorithms. The features were then used to train and evaluate ML algorithms. The best regression models were selected for Systolic BP (SBP) and Diastolic BP (DBP) estimation individually. Gaussian Process Regression (GPR) along with ReliefF feature selection algorithm outperforms other algorithms in estimating SBP and DBP with a root-mean-square error (RMSE) of 6.74 and 3.59 respectively. This ML model can be implemented in hardware systems to continuously monitor BP and avoid any critical health conditions due to sudden changes.Comment: Accepted for publication in Sensor, 14 Figures, 14 Table

Dual-path TokenLearner for Remote Photoplethysmography-based Physiological Measurement with Facial Videos

Remote photoplethysmography (rPPG) based physiological measurement is an emerging yet crucial vision task, whose challenge lies in exploring accurate rPPG prediction from facial videos accompanied by noises of illumination variations, facial occlusions, head movements, \etc, in a non-contact manner. Existing mainstream CNN-based models make efforts to detect physiological signals by capturing subtle color changes in facial regions of interest (ROI) caused by heartbeats. However, such models are constrained by the limited local spatial or temporal receptive fields in the neural units. Unlike them, a native Transformer-based framework called Dual-path TokenLearner (Dual-TL) is proposed in this paper, which utilizes the concept of learnable tokens to integrate both spatial and temporal informative contexts from the global perspective of the video. Specifically, the proposed Dual-TL uses a Spatial TokenLearner (S-TL) to explore associations in different facial ROIs, which promises the rPPG prediction far away from noisy ROI disturbances. Complementarily, a Temporal TokenLearner (T-TL) is designed to infer the quasi-periodic pattern of heartbeats, which eliminates temporal disturbances such as head movements. The two TokenLearners, S-TL and T-TL, are executed in a dual-path mode. This enables the model to reduce noise disturbances for final rPPG signal prediction. Extensive experiments on four physiological measurement benchmark datasets are conducted. The Dual-TL achieves state-of-the-art performances in both intra- and cross-dataset testings, demonstrating its immense potential as a basic backbone for rPPG measurement. The source code is available at \href{https://github.com/VUT-HFUT/Dual-TL}{https://github.com/VUT-HFUT/Dual-TL

A Survey of AI-based Approaches for Processing Photoplethysmography Signals

Photoplethysmography (PPG) is a non-invasive optical technique that measures physiological parameters like heart rate, blood oxygen saturation, and blood volume. However, PPG signals are often noisy and contaminated with artifacts, posing challenges to inaccurate measurements. To address this, artificial intelligence (AI) techniques have been employed by many researchers to improve  PPG signal processing. This paper presents a comprehensive survey of AI-based approaches for processing PPG signals in recent years. Various AI techniques, including machine learning, deep learning, and natural language processing, are discussed in relation to their application in PPG signal analysis.  The limitations and challenges associated with AI-based approaches in this context are also explored. Furthermore, future research directions are highlighted to leverage AI’s potential for revolutionizing PPG signal processing and expanding its applications. By examining the latest advancements, this survey aims to guide researchers and practitioners in understanding and harnessing AI-based methods for enhanced PPG signal processing, contributing to improved healthcare monitoring and diagnosis

Cardiovascular assessment by imaging photoplethysmography – a review

AbstractOver the last few years, the contactless acquisition of cardiovascular parameters using cameras has gained immense attention. The technique provides an optical means to acquire cardiovascular information in a very convenient way. This review provides an overview on the technique’s background and current realizations. Besides giving detailed information on the most widespread application of the technique, namely the contactless acquisition of heart rate, we outline further concepts and we critically discuss the current state.</jats:p

Constrained independent component analysis for non-obtrusive pulse rate measurements using a webcam

Assessment of cardiac function of a patient is very important for understanding a patient\u27s physiological state. Remote measurements of the cardiac pulse can provide comfortable physiological assessment by minimizing the amount of wires and cables and allowing for near continuous measurements. It has been found that state-of-the-art algorithms based on independent component analysis (ICA) suffer from a sorting problem which hinders their performance. This effect is demonstrated in this work. The automated pulse detection techniques are applied to RGB color video recordings of the facial region of a person being monitored for cardiac function in a remote sensing environment. Automated face tracking is employed to locate the region of interest and address motion artefacts. This work proposed and evaluates a novel algorithm based on constrained source separation, aka, constrained independent source separation (cICA) to accurately estimate the pulse rate of a patient by solving the sorting problem observed in the ICA based approach. The constrained optimization problem incorporates prior information and additional requirements in the form of constraints. A reference signal with a single tone frequency corresponding to a possible heart rate is fed to the cICA algorithm. This forces the output signal to match the reference signal embodying prior knowledge about an underlying IC. It is also shown that with this algorithm a near photoplethysmography (PPG) signal corresponding to the variations in blood volume in the body can be extracted. An IRB approved study encompassing 45 subjects resulted in Bland-Altman analysis with an FDA-approved finger blood volume pulse (BVP) sensor demonstrating that the proposed algorithm provides significantly improved accuracy

Cuffless Blood Pressure in clinical practice: challenges, opportunities and current limits.

Background: Cuffless blood pressure measurement technologies have attracted significant attention for their potential to transform cardiovascular monitoring.Methods: This updated narrative review thoroughly examines the challenges, opportunities, and limitations associated with the implementation of cuffless blood pressure monitoring systems.Results: Diverse technologies, including photoplethysmography, tonometry, and ECG analysis, enable cuffless blood pressure measurement and are integrated into devices like smartphones and smartwatches. Signal processing emerges as a critical aspect, dictating the accuracy and reliability of readings. Despite its potential, the integration of cuffless technologies into clinical practice faces obstacles, including the need to address concerns related to accuracy, calibration, and standardization across diverse devices and patient populations. The development of robust algorithms to mitigate artifacts and environmental disturbances is essential for extracting clear physiological signals. Based on extensive research, this review emphasizes the necessity for standardized protocols, validation studies, and regulatory frameworks to ensure the reliability and safety of cuffless blood pressure monitoring devices and their implementation in mainstream medical practice. Interdisciplinary collaborations between engineers, clinicians, and regulatory bodies are crucial to address technical, clinical, and regulatory complexities during implementation. In conclusion, while cuffless blood pressure monitoring holds immense potential to transform cardiovascular care. The resolution of existing challenges and the establishment of rigorous standards are imperative for its seamless incorporation into routine clinical practice.Conclusion: The emergence of these new technologies shifts the paradigm of cardiovascular health management, presenting a new possibility for non-invasive continuous and dynamic monitoring. The concept of cuffless blood pressure measurement is viable and more finely tuned devices are expected to enter the market, which could redefine our understanding of blood pressure and hypertension

Exploring remote photoplethysmography signals for deepfake detection in facial videos

Abstract. With the advent of deep learning-based facial forgeries, also called "deepfakes", the feld of accurately detecting forged videos has become a quickly growing area of research. For this endeavor, remote photoplethysmography, the process of extracting biological signals such as the blood volume pulse and heart rate from facial videos, offers an interesting avenue for detecting fake videos that appear utterly authentic to the human eye. This thesis presents an end-to-end system for deepfake video classifcation using remote photoplethysmography. The minuscule facial pixel colour changes are used to extract the rPPG signal, from which various features are extracted and used to train an XGBoost classifer. The classifer is then tested using various colour-to-blood volume pulse methods (OMIT, POS, LGI and CHROM) and three feature extraction window lengths of two, four and eight seconds. The classifer was found effective at detecting deepfake videos with an accuracy of 85 %, with minimal performance difference found between the window lengths. The GREEN channel signal was found to be important for this classifcationEtäfotoplethysmografian hyödyntäminen syväväärennösten tunnistamiseen. Tiivistelmä. Syväväärennösten eli syväoppimiseen perustuvien kasvoväärennöksien yleistyessä väärennösten tarkasta tunnistamisesta koneellisesti on tullut nopeasti kasvava tutkimusalue. Etäfotoplethysmografa (rPPG) eli biologisten signaalien kuten veritilavuuspulssin tai sykkeen mittaaminen videokuvasta tarjoaa kiinnostavan keinon tunnistaa väärennöksiä, jotka vaikuttavat täysin aidoilta ihmissilmälle. Tässä diplomityössä esitellään etäfotoplethysmografaan perustuva syväväärennösten tunnistusmetodi. Kasvojen minimaalisia värimuutoksia hyväksikäyttämällä mitataan fotoplethysmografasignaali, josta lasketuilla ominaisuuksilla koulutetaan XGBoost-luokittelija. Luokittelijaa testataan usealla eri värisignaalista veritilavuussignaaliksi muuntavalla metodilla sekä kolmella eri ominaisuuksien ikkunapituudella. Luokittelija pystyy tunnistamaan väärennetyn videon aidosta 85 % tarkkuudella. Eri ikkunapituuksien välillä oli minimaalisia eroja, ja vihreän värin signaalin havaittiin olevan luokittelun suorituskyvyn kannalta merkittävä

Facial Video-based Remote Physiological Measurement via Self-supervised Learning

Facial video-based remote physiological measurement aims to estimate remote photoplethysmography (rPPG) signals from human face videos and then measure multiple vital signs (e.g. heart rate, respiration frequency) from rPPG signals. Recent approaches achieve it by training deep neural networks, which normally require abundant facial videos and synchronously recorded photoplethysmography (PPG) signals for supervision. However, the collection of these annotated corpora is not easy in practice. In this paper, we introduce a novel frequency-inspired self-supervised framework that learns to estimate rPPG signals from facial videos without the need of ground truth PPG signals. Given a video sample, we first augment it into multiple positive/negative samples which contain similar/dissimilar signal frequencies to the original one. Specifically, positive samples are generated using spatial augmentation. Negative samples are generated via a learnable frequency augmentation module, which performs non-linear signal frequency transformation on the input without excessively changing its visual appearance. Next, we introduce a local rPPG expert aggregation module to estimate rPPG signals from augmented samples. It encodes complementary pulsation information from different face regions and aggregate them into one rPPG prediction. Finally, we propose a series of frequency-inspired losses, i.e. frequency contrastive loss, frequency ratio consistency loss, and cross-video frequency agreement loss, for the optimization of estimated rPPG signals from multiple augmented video samples and across temporally neighboring video samples. We conduct rPPG-based heart rate, heart rate variability and respiration frequency estimation on four standard benchmarks. The experimental results demonstrate that our method improves the state of the art by a large margin.Comment: IEEE Transactions on Pattern Analysis and Machine Intelligenc

The 2023 wearable photoplethysmography roadmap

Photoplethysmography is a key sensing technology which is used in wearable devices such as smartwatches and fitness trackers. Currently, photoplethysmography sensors are used to monitor physiological parameters including heart rate and heart rhythm, and to track activities like sleep and exercise. Yet, wearable photoplethysmography has potential to provide much more information on health and wellbeing, which could inform clinical decision making. This Roadmap outlines directions for research and development to realise the full potential of wearable photoplethysmography. Experts discuss key topics within the areas of sensor design, signal processing, clinical applications, and research directions. Their perspectives provide valuable guidance to researchers developing wearable photoplethysmography technology