An Experimental Study of the Effects of External Physiological Parameters on the Photoplethysmography Signals in the Context of Local Blood Pressure (Hydrostatic Pressure Changes)
Abstract:A comprehensive study of the effect of a wide range of controlled human subject motion on Photoplethysmographic signals is reported. The investigation includes testing of two separate groups of 5 and 18 subjects who were asked to undertake set exercises whilst simultaneously monitoring a wide range of physiological parameters including Breathing Rate, Heart Rate and Localised Blood Pressure using commercial clinical sensing systems. The unique finger mounted PPG probe equipped with miniature three axis acceler… Show more
“…In high-acceleration environments of tactical flight, peripheral sensors cannot be used effectively because of blood pooling and altered blood pressure at the extremities. [ 31 ].…”
An increasing proportion of occupational mishaps in dynamic, high-risk operational environments have been attributed to human error, yet there are currently no devices to routinely provide accurate physiological data for insights into underlying contributing factors. This is most commonly due to limitations of commercial and clinical devices for collecting physiological data in environments of high motion. Herein, a novel Photoplethysmography (PPG) sensor device was tested, called SPYDR (Standalone Performance Yielding Deliberate Risk), reading from a behind-the-ear location, specifically designed for high-fidelity data collection in highly dynamic high-motion, high-pressure, low-oxygen, and high-G-force environments. For this study, SPYDR was installed as a functional ear-cup replacement in flight helmets worn by rated US Navy aircrew. Subjects were exposed to reduced atmospheric pressure using a hypobaric chamber to simulated altitudes of 25,000 feet and high G-forces in a human-rated centrifuge up to 9 G acceleration. Data were compared to control devices, finger and forehead PPG sensors, and a chest-mounted 12-lead ECG. SPYDR produced high-fidelity data compared to controls with little motion-artifact controls in the no-motion environment of the hypobaric chamber. However, in the high-motion, high-force environment of the centrifuge, SPYDR recorded consistent, accurate data, whereas PPG controls and ECG data were unusable due to a high-degree-motion artifacts. The data demonstrate that SPYDR provides an accurate and reliable system for continuous physiological monitoring in high-motion, high-risk environments, yielding a novel method for collecting low-artifact cardiovascular assessment data important for investigating currently inaccessible parameters of human physiology.
“…In high-acceleration environments of tactical flight, peripheral sensors cannot be used effectively because of blood pooling and altered blood pressure at the extremities. [ 31 ].…”
An increasing proportion of occupational mishaps in dynamic, high-risk operational environments have been attributed to human error, yet there are currently no devices to routinely provide accurate physiological data for insights into underlying contributing factors. This is most commonly due to limitations of commercial and clinical devices for collecting physiological data in environments of high motion. Herein, a novel Photoplethysmography (PPG) sensor device was tested, called SPYDR (Standalone Performance Yielding Deliberate Risk), reading from a behind-the-ear location, specifically designed for high-fidelity data collection in highly dynamic high-motion, high-pressure, low-oxygen, and high-G-force environments. For this study, SPYDR was installed as a functional ear-cup replacement in flight helmets worn by rated US Navy aircrew. Subjects were exposed to reduced atmospheric pressure using a hypobaric chamber to simulated altitudes of 25,000 feet and high G-forces in a human-rated centrifuge up to 9 G acceleration. Data were compared to control devices, finger and forehead PPG sensors, and a chest-mounted 12-lead ECG. SPYDR produced high-fidelity data compared to controls with little motion-artifact controls in the no-motion environment of the hypobaric chamber. However, in the high-motion, high-force environment of the centrifuge, SPYDR recorded consistent, accurate data, whereas PPG controls and ECG data were unusable due to a high-degree-motion artifacts. The data demonstrate that SPYDR provides an accurate and reliable system for continuous physiological monitoring in high-motion, high-risk environments, yielding a novel method for collecting low-artifact cardiovascular assessment data important for investigating currently inaccessible parameters of human physiology.
“…However, the estimation of these attributes is influenced by several factors, which can be classified into three categories: cardiovascular, biological, and acquisition [ 9 , 10 , 11 ]. Acquisition factors are related to the properties and intensity of the emitted light [ 12 ], ambient light [ 13 ], photo-detector sensitivity [ 14 ], measurement point [ 15 ], temperature [ 16 ], motion artifacts [ 17 ], and contact force (CF) between the sensor and the skin [ 18 ], among others. Temperature fluctuations can cause changes in blood flow and alterations in the PPG waveform [ 16 , 19 , 20 , 21 ].…”
Photoplethysmography (PPG) is widely used to assess cardiovascular health. However, its usage and standardization are limited by the impact of variable contact force and temperature, which influence the accuracy and reliability of the measurements. Although some studies have evaluated the impact of these phenomena on signal amplitude, there is still a lack of knowledge about how these perturbations can distort the signal morphology, especially for multi-wavelength PPG (MW-PPG) measurements. This work presents a modular multi-parametric sensor system that integrates continuous and real-time acquisition of MW-PPG, contact force, and temperature signals. The implemented design solution allows for a comprehensive characterization of the effects of the variations in these phenomena on the contour of the MW-PPG signal. Furthermore, a dynamic DC cancellation circuitry was implemented to improve measurement resolution and obtain high-quality raw multi-parametric data. The accuracy of the MW-PPG signal acquisition was assessed using a synthesized reference PPG optical signal. The performance of the contact force and temperature sensors was evaluated as well. To determine the overall quality of the multi-parametric measurement, an in vivo measurement on the index finger of a volunteer was performed. The results indicate a high precision and accuracy in the measurements, wherein the capacity of the system to obtain high-resolution and low-distortion MW-PPG signals is highlighted. These findings will contribute to developing new signal-processing approaches, advancing the accuracy and robustness of PPG-based systems, and bridging existing gaps in the literature.
“…On the other hand, SpO 2 response measured on the peripheral parts of the body (such as the fingers or the wrist) has several disadvantages compared to measuring on the forehead or on the ears. These drawbacks include 1) a time lag in blood oxygen level changes compared to the head (especially forehead and earlobes), [ 2–4 ] 2) decreased accuracy due to frequent motion of hands, [ 5 ] 3) possible interference with daily activities and 4) unreliable readings during low perfusion of hands (when blood flow is insufficient due to, for example, a medical condition, exposure to severe cold or mechanical pressure). [ 2 ] In addition, the functional parts of smartwatches (including the optoelectrical and electronics subsystems) and similar devices are still bulky, typically with a thickness of over 10 mm.…”
Pulse oximetry is widely used in medical settings and in everyday life for the estimation of peripheral blood oxygen saturation (SpO2). However, SpO2 response measured on the peripheral parts of the body (such as fingers and wrists) has a time lag compared to measuring on the forehead. In addition, current devices are centimeter‐thick, making seamless integration with the body difficult, and hindering continuous monitoring. Here a design, fabrication, and evaluation of a SpO2 and heart rate sensor based on flexible hybrid electronics (FHE) is presented. The marriage of flexible electronics with high‐performance commercially available integrated circuit (IC) chips makes advanced sensing, data processing, and wireless data transmission functionalities possible on a thin (1.6 mm) and flexible form that can be attached to various parts of the body. Differently from most devices using FHE, here a cost‐efficient and mass‐production compatible multilayer screen‐printing process for making the interconnection circuitry is described in detail, including topographic analysis. By optimizing the printing steps, interconnecting lines vertically traversing up to five printed layers over several tens of micrometers can be fabricated, increasing the spatial density. The device reliably detects hypoxemia, and when applied on the forehead, changes in SpO2 appear >10 s earlier compared to a finger‐based medical‐grade device.
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