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IoT and Wearable Sensors for Health Monitoring
Published in Rashmi Gupta, Arun Kumar Rana, Sachin Dhawan, Korhan Cengiz, Advanced Sensing in Image Processing and IoT, 2022
Radhika G. Deshmukh, Akanksha Pinjarkar, Arun Kumar Rana
Photoplethysmography (PPG) is the method used by most wearables with heart rate monitors nowadays to measure heart rate. The term PPG refers to shining light into the skin and measuring the amount of light dispersed by blood flow. PPG sensors work on the principle that light entering the body scatters in a predictable manner as blood flow dynamics change, such as with variations in blood pulse rates (heart rate) or blood volume (cardiac output). Heart rate can be measured using a variety of techniques and sensors. The electrode (sensor) and the skin are idealised as two portions of a standard capacitor in one method, which uses capacitive sensing. PPG is a method of measuring blood flow volume variations using light. Fitbit and other fitness trackers use a photodiode to achieve this. A constant green light is supplied to the wearer's skin, which measures the photodiode's light absorption. This data is passed on so that the pulse can be calculated. The more blood that flows through the user's veins, the more light the diodes absorb. A heart rate sensor is shown in Figure 7.5.
Deep Learning for IoT-Healthcare Based on Physiological Signals
Published in Jacques Bou Abdo, Jacques Demerjian, Abdallah Makhoul, 5G Impact on Biomedical Engineering, 2022
Joseph Azar, Raphaël Couturier
Photoplethysmography (PPG) is a non-invasive optical technique to track vital signs, including heart rate, heart rate variability, and blood oxygenation. The PPG waveform reveals blood volume variations and includes important features useful for studies such as cycle period, baseline, and amplitude. Fortunately, wearable health monitoring devices, including smartwatches and fitness trackers, can now collect PPG signals and track cardiac activity by deriving the heart rate variability features from PPG the same as the electrocardiogram (ECG) [43]. One of the main fields using PPG today is affective computing, where this signal was used for tasks such as stress detection [30].
Biomedical Sensors and Data Acquisition
Published in Rajarshi Gupta, Dwaipayan Biswas, Health Monitoring Systems, 2019
Photoelectric plethysmography, commonly known as photoplethysmography (PPG), is an optical technique for measuring blood volume changes in peripheral body parts (fingertips, toe, earlobes, and forehead). The commonest use of PPG is in pulse oximetry, the measurement of blood oxygen saturation in ICUs. Over the last 20 years, research of PPG has shown its great potential toward various physiological functions like cardiac output, blood pressure, respiratory functions, heart rate, and many more [13]. There are two basic sensing techniques for PPG, viz., reflection mode and transmission mode [14]. Both use a matched pair or LED–photodiode (PD) combination attached to body part to illuminate a small portion of skin tissue and sense the blood volume information based on difference of absorbance of light radiation between blood-full and bloodless skin at near infrared (IR) wavelengths. The transmission mode, LED (operating in 0.8–1 µm wavelength), and PD are attached to opposite surface of skin, and the PD captures the light after passing through the bones, tissues, and blood capillaries. Under this wavelength, light is least absorbed by water content of the tissue. The PPG waveform shows a steady (DC) and a pulsatile component. The steady part represents thermoregulation and autonomic functions. The pulsatile component, as shown in Figure 2.13, is related to blood volume changes and consists of two phases, anacrotic (relates to ventricular systole) and catacrotic (relates to ventricular diastole), represented by four major fiducial points, viz., foot (F), systolic peak (SP), dicrotic notch (DN), and diastolic peak (DP). During ventricular systole, there is a momentary rise in blood volume in the peripheral capillaries, and in the mentioned wavelength, the received light intensity at the PD is less. The absorption of light by blood is quantitatively expressed by Beer–Lambert’s law: I=I0e−dαc,
A review of medical wearables: materials, power sources, sensors, and manufacturing aspects of human wearable technologies
Published in Journal of Medical Engineering & Technology, 2023
Mohammad Y. Al-Daraghmeh, Richard T. Stone
Photoplethysmography (PPG) sensors are optical detection to measure the volumetric variations of blood circulation, which include a light source and a detector, with red and infra-red light-emitting diodes commonly used as the light source. The PPG sensor monitors alterations in the light intensity through reflection from or transmission through the tissue for heart rate monitoring purposes [94]. PPG sensors have become more popular recently due to the limitations of ECG sensors, which require at least three electrodes positioned at certain anatomical positions, ECG electrodes may irritate the patient's skin, and ECG tools are inappropriate for daily use at home [95]. Castaneda et al. [96] reviewed some of the recent developments of wearable PPG sensors and discussed that light with longer wavelengths such as infra-red penetrates more deeply into the tissue than green light. However, infra-red light is more susceptible to motion artefacts. Therefore, a green LED that has a shorter wavelength may be a better option for specific applications.
The potential for photoplethysmographic (PPG)-based smart devices in atrial fibrillation detection
Published in Expert Review of Medical Devices, 2020
Stephanie L. Harrison, Deirdre A. Lane, Yutao Guo, Gregory Y. H. Lip
Photoplethysmography (PPG) involves optically measuring changes in tissue blood volume through the skin. PPG-based technologies detect the typical AF rhythm by monitoring heart rhythm intervals. This is different to ECG which measures electrophysiological events during cardiovascular contractions. Usually, to detect AF with ECG, significant clinical time and expertise is required to interpret and analyze the results. Initial screening with PPG-based smart devices linked with automated complex algorithms, which detect suspected AF have the potential to reduce clinical input and time. However, it is still unclear which features of the signal produced using PPG-based technologies should be utilized to develop algorithms for detection of AF. A recent study developed an algorithm for detection of AF with up to 97.2% sensitivity and 99.6% specificity but noted increased demands for signal quality were required to achieve this [5].
Heart rate measures from the Apple Watch, Fitbit Charge HR 2, and electrocardiogram across different exercise intensities
Published in Journal of Sports Sciences, 2019
Elizabeth A. Thomson, Kayla Nuss, Ashley Comstock, Steven Reinwald, Sophie Blake, Richard E. Pimentel, Brian L. Tracy, Kaigang Li
Wearable physical activity monitors (or fitness trackers) have improved greatly with the increased convenience and access of many features associated with physical activity (Lewis, Lyons, Jarvis, & Baillargeon, 2015). Numerous studies have examined many consumer based devices for validation of some variables (e.g., steps, distance, activity duration, and estimate energy expenditure) (Ferguson, Rowlands, Olds, & Maher, 2015; Gusmer, Bosch, Watkins, Ostrem, & Dengel, 2014; Imboden, Nelson, Kaminsky, & Montoye, 2017). However, HR assessment is a newer feature of these wearable physical activity monitors. The technology of photoplethysmography (PPG) measures HR using green and infra-red lights and photodetector(s) to detect changes in blood volume just below the skin surface (Kamal, Harness, Irving, & Mearns, 1989). This technology is used in both the Apple Watch (Apple Support, 2017) and the Fitbit Charge HR 2 (Fitbit, 2017) to measure HR.