Photoplethysmogram Analysis and Applications: An Integrative Review

Abstract

Beyond its use in a clinical environment, photoplethysmogram (PPG) is increasingly used for measuring the physiological state of an individual in daily life. This review aims to examine existing research on photoplethysmogram concerning its generation mechanisms, measurement principles, clinical applications, noise definition, pre-processing techniques, feature detection techniques, and post-processing techniques for photoplethysmogram processing, especially from an engineering point of view. We performed an extensive search with the PubMed, Google Scholar, Institute of Electrical and Electronics Engineers (IEEE), ScienceDirect, and Web of Science databases. Exclusion conditions did not include the year of publication, but articles not published in English were excluded. Based on 118 articles, we identified four main topics of enabling PPG: (A) PPG waveform, (B) PPG features and clinical applications including basic features based on the original PPG waveform, combined features of PPG, and derivative features of PPG, (C) PPG noise including motion artifact baseline wandering and hypoperfusion, and (D) PPG signal processing including PPG preprocessing, PPG peak detection, and signal quality index. The application field of photoplethysmogram has been extending from the clinical to the mobile environment. Although there is no standardized pre-processing pipeline for PPG signal processing, as PPG data are acquired and accumulated in various ways, the recently proposed machine learning-based method is expected to offer a promising solution.

Quality Assessment and Morphological Analysis of Photoplethysmography in Daily Life

“…Besides the several sources of inaccuracy the PPG can be subjected to, it is worth remembering that different physiological activities can also influence PPG waveform parameters: in particular, for the time parameters ( RT, PT , Δ T ), changes in cardiac activity have a significant impact on the timing of the events reflected in the PPG waveform ( 11 ); respiration can induce variations affecting both the pulsatile and non-pulsatile components of the PPG signal ( 62 ); lastly, PPG is strongly affected by the autonomic nervous system, leading to significant changes especially in the time domain ( 63 ).…”

“…The resulting signal is quasi-periodic, consisting of a stereotyped waveform called “PPG pulse,” which occurs with each heartbeat ( 10 ). Each PPG pulse contains several fiducial points, each of them corresponding to a cardiac event ( 11 ), as shown in Figure 1 :…”

“…The resulting signal is quasi-periodic, consisting of a stereotyped waveform called "PPG pulse, " which occurs with each heartbeat (10). Each PPG pulse contains several fiducial points, each of them corresponding to a cardiac event (11), as shown in Figure 1: • Systolic foot: represents the minimum of the pulse and corresponds to the beginning of the systolic phase of the heart; • Systolic peak: represents the maximum of the pulse and corresponds to the maximum blood volume during the systolic phase of the heart; • Dicrotic notch: a local minimum corresponding to the aortic valve closure; • Diastolic peak: represents the second maximum of the pulse and corresponds both to the diastolic phase of the heart and wave reflection in the periphery.…”

Multimodal Finger Pulse Wave Sensing: Comparison of Forcecardiography and Photoplethysmography Sensors

“…Pulse waves (PW) or sphygmic waves are mechanical waves that propagate from the ventricles through the whole vascular system as brisk enlargements of the blood vessels’ lumens, caused by sudden increases in local blood pressure [ 1 , 2 , 3 ]. Photoplethysmography (PPG) is one of the most widely used techniques for PW sensing, owing to its ability to measure blood oxygen saturation when both red and infrared light sources are used simultaneously.…”

“…Photoplethysmography (PPG) is one of the most widely used techniques for PW sensing, owing to its ability to measure blood oxygen saturation when both red and infrared light sources are used simultaneously. PPG is commonly used both in clinical and non-clinical settings, and it has been integrated in a variety of consumer electronics products to enable wearable, unobtrusive monitoring of heart rate and arrhythmias [ 1 , 2 , 3 ].…”