Wearable Photoplethysmography for Cardiovascular Monitoring

Abstract

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

Detecting beats in the photoplethysmogram: benchmarking open-source algorithms

“…It exhibits a pulse wave for each heartbeat, caused by the ejection of blood from the heart into the circulation. A wealth of physiological information can be deduced from the timing and shape of PPG pulse waves (Charlton et al 2022 ). Consequently, a fundamental step in analysing the PPG is to detect individual pulse waves, corresponding to individual heartbeats.…”

“…It is important to assess the performance of beat detectors in different use cases where PPG signals can have different morphologies and levels of artifact (Charlton et al 2022 ). Specifically, pulse oximeters acquire PPG signals at the finger close to major arteries, often with little motion artifact.…”

Establishing best practices in photoplethysmography signal acquisition and processing

“…Despite the widespread use of photoplethysmography, best practices have not yet been established for acquiring and processing photoplethysmography signals. This may in part be due to the diversity of photoplethysmography device designs, ranging from smartwatches to earbuds, and applications, ranging from oxygen saturation measurement in clinical practice to heart rate monitoring during exercise (Charlton et al 2022 ). Potentially, the best approach to signal acquisition and signal processing could differ between each device design and application.…”

“…Firstly, wearable devices which provide the raw PPG signal are invaluable for such research, as demonstrated through the use of the Empatica E4 wristband in many research studies (McCarthy et al ). Whilst several research devices can provide the raw PPG signal (Charlton et al 2022 ), large-scale studies could be conducted more easily in daily life if consumer devices were similarly able to provide raw PPG signals. Secondly, freely available datasets allow researchers to benchmark their own PPG signal processing algorithms against others on a common dataset.…”

“…Secondly, freely available datasets allow researchers to benchmark their own PPG signal processing algorithms against others on a common dataset. Several such datasets are available (Charlton et al 2022 ), including: the WeSAD and PPG-DaLiA datasets, acquired using an Empatica E4 device in healthy subjects (Schmidt et al , Reiss et al 2019 ); and the VitalDB and the MIMIC Waveform databases, acquired from critically-ill patients (Johnson et al 2016 , Lee and Jung 2018 ). However, there are limitations to current datasets: they are often collected from either healthy volunteers or a particular patient population, rather than a broad cross-section of society; they often contain PPG signals acquired by only one device, rather than signals acquired using different hardware configurations; and they are often recorded in either laboratory or clinical settings, but few are recorded in daily life.…”