Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

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Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice.

We extract heart rate and beat lengths from videos by measuring subtle head motion caused by the Newtonian reaction to the influx of blood at each beat. Our method tracks features on the head and performs principal component analysis (PCA) to decompose their trajectories into a set of component motions. It then chooses the component that best corresponds to heartbeats based on its temporal frequency spectrum. Finally, we analyze the motion projected to this component and identify peaks of the trajectories, which correspond to heartbeats. When evaluated on 18 subjects, our approach reported heart rates nearly identical to an electrocardiogram device. Additionally we were able to capture clinically relevant information about heart rate variability.

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Detecting Pulse from Head Motions in Video

In the past decade, there has been a resurgence in the field of unobtrusive cardiomechanical assessment, through advancing methods for measuring and interpreting ballistocardiogram (BCG) and seismocardiogram (SCG) signals. Novel instrumentation solutions have enabled BCG and SCG measurement outside of clinical settings, in the home, in the field, and even in microgravity. Customized signal processing algorithms have led to reduced measurement noise, clinically relevant feature extraction, and signal modeling. Finally, human subjects physiology studies have been conducted using these novel instruments and signal processing tools with promising results. This paper reviews the recent advances in these areas of modern BCG and SCG research.

/pdf/ballistocardiography-and-seismocardiography-a-review-of-1qwmaxt19u.pdf

Ballistocardiography and Seismocardiography: A Review of Recent Advances

A sensor system is adapted for use with an article of footwear and includes an insert member including a first layer and a second layer, a port connected to the insert and configured for communication with an electronic module, a plurality of force and/or pressure sensors on the insert member, and a plurality of leads connecting the sensors to the port.

Footwear having sensor system

Recent studies in computer vision have shown that, while practically invisible to a human observer, skin color changes due to blood flow can be captured on face videos and, surprisingly, be used to estimate the heart rate (HR). While considerable progress has been made in the last few years, still many issues remain open. In particular, state of-the-art approaches are not robust enough to operate in natural conditions (e.g. in case of spontaneous movements, facial expressions, or illumination changes). Opposite to previous approaches that estimate the HR by processing all the skin pixels inside a fixed region of interest, we introduce a strategy to dynamically select face regions useful for robust HR estimation. Our approach, inspired by recent advances on matrix completion theory, allows us to predict the HR while simultaneously discover the best regions of the face to be used for estimation. Thorough experimental evaluation conducted on public benchmarks suggests that the proposed approach significantly outperforms state-of the-art HR estimation methods in naturalistic conditions.

/pdf/self-adaptive-matrix-completion-for-heart-rate-estimation-34gc3nht50.pdf

Self-Adaptive Matrix Completion for Heart Rate Estimation from Face Videos under Realistic Conditions

The ballistocardiogram (BCG) measures the reaction of the body to cardiac ejection forces, and is an effective, non-invasive means of evaluating cardiovascular function. A simple, robust method is presented for acquiring high-quality, repeatable BCG signals from a modified, commercially available scale. The measured BCG waveforms for all subjects qualitatively matched values in the existing literature and physiologic expectations in terms of timing and IJ amplitude. Additionally, the BCG IJ amplitude was shown to be correlated with diastolic filling time for a subject with premature atrial contractions, demonstrating the sensitivity of the apparatus to beat-by-beat hemodynamic changes. The signal-to-noise ratio (SNR) of the BCG was estimated using two methods, and the average SNR over all subjects was greater than 12 for both estimates. The BCG measurement was shown to be repeatable over 50 recordings taken from the same subject over a three week period. This approach could allow patients at home to monitor trends in cardiovascular health.

https://iopscience.iop.org/article/10.1088/0967-3334/30/2/005/pdf

Robust ballistocardiogram acquisition for home monitoring.

The field of ballistocardiography seems to be enjoying a recent resurgence, most notably through the development of novel technologies and signal processing methods for measurement and analysis. After the method almost vanished in the late 80's and 90's, it is reasonable to wonder what is different this time, and if the technique has now more chances of becoming what its pioneer always wanted — a widespread clinical tool. This paper is an effort to compare and contrast this novel wave of research (notably in the context of the authors' own work). It also suggests that the new approaches have several key differences with past embodiments that place them in a good position to address some specific issues such as cardiac resynchronization therapy device optimization or congestive heart failure monitoring. This optimism is largely fed by the recent technological advances enabling the measurement of the BCG unobtrusively, frequently, at home or in a hospital, and by a re-focus on monitoring and trending applications.

/pdf/ballistocardiography-a-method-worth-revisiting-52mpck69vo.pdf

Ballistocardiography — A method worth revisiting

In accordance with embodiments of the present disclosure, a ballistocardiogram (BCG) sensor is used to detect heart and vascular characteristics of a user, and provide a BCG output indicative of the detected cardiovascular characteristics. The BCG output can be used for various purposes, such as detecting arterial aging. Secondary sensors can be used in conjunction with the BCG and can be used to determine the central arterial blood pressure, when used in conjunction with a peripheral blood pressure measurement.

Systems and methods for monitoring the circulatory system

Characteristics of a user's heart are detected. In accordance with an example embodiment, a ballistocardiogram (BCG) sensor is used to detect heart characteristics of a user, and provide a BCG output indicative of the detected heart characteristics. The BCG output is further processed using data from one or more additional sensors, such as to reduce noise and/or otherwise process the BCG signal to characterize the user's heart function.

Systems and methods for monitoring heart function

The ballistocardiogram (BCG) signal represents the movements of the body in response to cardiac ejection of blood. Recently, many groups have developed low-cost instrumentation for facilitating BCG measurement in the home. The standard method used in the literature for estimating the BCG pulse response has generally been ensemble averaging over several beats. Unfortunately, since the BCG pulse response is likely longer than a typical heartbeat interval, this standard approach does not yield a full-length estimate of the response. This paper describes a simple, novel algorithm for estimating the full-length BCG pulse response using the R-wave timing of a simultaneously acquired electrocardiogram (ECG). With this pulse response, the full signal can be reconstructed, enabling the analysis of slow transient effects in the BCG signal, and of the measurement noise. Additionally, while this paper focuses only on the BCG signal, the same algorithm could be applied to other biomedical signals such as the phonocardiogram or impedance cardiogram, particularly when the heartbeat interval is shorter than the duration of the cpulse response.

Richard M. Wiard

Papers

Robust ballistocardiogram acquisition for home monitoring.

Ballistocardiography — A method worth revisiting

Systems and methods for monitoring the circulatory system

Systems and methods for monitoring heart function

Novel methods for estimating the ballistocardiogram signal using a simultaneously acquired electrocardiogram