Photoplethysmography (PPG) technology has been used to develop small, wearable, pulse rate sensors. These devices, consisting of infrared light-emitting diodes (LEDs) and photodetectors, offer a simple, reliable, low-cost means of monitoring the pulse rate noninvasively. Recent advances in optical technology have facilitated the use of high-intensity green LEDs for PPG, increasing the adoption of this measurement technique. In this review, we briefly present the history of PPG and recent developments in wearable pulse rate sensors with green LEDs. The application of wearable pulse rate monitors is discussed.

Wearable Photoplethysmographic Sensors—Past and Present

A monitoring device configured to be attached to the ear of a person includes a base, an earbud housing extending outwardly from the base that is configured to be positioned within an ear of a subject, and a cover surrounding the earbud housing. The base includes a speaker, an optical emitter, and an optical detector. The cover includes light transmissive material that is in optical communication with the optical emitter and the optical detector and serves as a light guide to deliver light from the optical emitter into the ear canal of the subject wearing the device at one or more predetermined locations and to collect light external to the earbud housing and deliver the collected light to the optical detector.

Light-guiding devices and monitoring devices incorporating same

Methods and apparatus for qualifying and quantifying excitation-dependent physiological information extracted from wearable sensors in the midst of interference from unwanted sources are provided. An organism is interrogated with at least one excitation energy, energy response signals from two or more distinct physiological regions are sensed, and these signals are processed to generate an extracted signal. The extracted signal is compared with a physiological model to qualify and/or quantify a physiological property. Additionally, important physiological information can be qualified and quantified by comparing the excitation wavelength-dependent response, measured via wearable sensors, with a physiological model.

Noninvasive physiological analysis using excitation-sensor modules and related devices and methods

A photoplethysmograph (PPG) is a simple medical device for monitoring blood flow and transportation of substances in the blood. It consists of a light source and a photodetector for measuring transmitted and reflected light signals. Clinically, PPGs are used to monitor the pulse rate, oxygen saturation, blood pressure, and blood vessel stiffness. Wearable unobtrusive PPG monitors are commercially available. Here, we review the principle issues and clinical applications of PPG for monitoring oxygen saturation.

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Current progress of photoplethysmography and SPO2 for health monitoring.

The calculation of arterial oxygen saturation (SpO2) relies heavily on the amplitude information of the high-quality photoplethysmographic (PPG) signals, which could be contaminated by motion artifacts (MA) during monitoring. A new method combining temporally constrained independent component analysis (cICA) and adaptive filters is presented here to extract the clean PPG signals from the MA corrupted PPG signals with the amplitude information reserved. The underlying PPG signal could be extracted from the MA contaminated PPG signals automatically by using cICA algorithm. Then the amplitude information of the PPG signals could be recovered by using adaptive filters. Compared with conventional ICA algorithms, the proposed approach is permutation and scale ambiguity-free. Numerical examples with both synthetic datasets and real-world MA corrupted PPG signals demonstrate that the proposed method could remove the MA from MA contaminated PPG signals more effectively than the two existing FFT-LMS and moving average filter (MAF) methods. This paper presents a new method which combines the cICA algorithm and adaptive filter to extract the underlying PPG signals from the MA contaminated PPG signals with the amplitude information reserved. The new method could be used in the situations where one wants to extract the interested source automatically from the mixed observed signals with the amplitude information reserved. The results of study demonstrated the efficacy of this proposed method.

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Motion artifact removal from photoplethysmographic signals by combining temporally constrained independent component analysis and adaptive filter

Reduction the motion artifact from photo plethysmograph (PPG) signals can improve the precision of the measurement of heart rate or arterial oxygen saturation in movement state. This paper presents a new wristband PPG/ACC sensor device, which utilizes the adaptive filter technique to reduce the motion artifact of the original PPG signals. A 3-axis MEMS accelerometer sensor is attached to the PPG sensor to detect the wrist movement. A fast transversal RLS algorithm is performed to reduce the computed complexity of the adaptive filter. Experiment results show that this device can provide more reliable and stable signals against motion artifact corruption under the typical types of movement, such as swinging arms.

Pengfei Wei

Papers

A new wristband wearable sensor using adaptive reduction filter to reduce motion artifact