The preliminary investigation of imaging photoplethysmographic system

A preliminary CCD camera-based imaging photoplethysmographic (PPG) system is described to detect the blood perfusion in tissue. Attention of imaging photoplethysmography (PPG) is drawn to the potential applications in visualised blood perfusion. The introduction of the fast digital camera inspires the development of imaging PPG which allows the ideally contactless monitoring with larger field of view and different depth of tissue by applying multi-wavelength LEDs. The CCD camera-based spectral imaging PPG system in both transmission mode and reflection mode is constructed to validate the feasibility of this technique. The PPG signal can be derived in both transmission mode and reflection mode, which is obviously different from multi-wavelength LEDs or monitoring at various regions of tissue. The investigation for the system functionality leads to the further development of imaging PPG system and the engineering model for 3-D visualised blood perfusion of tissue

Validation of a Monte Carlo platform for the optical modelling of pulse oximetry

A custom Monte Carlo (MC) platform has been established to generate opto-physiological models of mechanisms in pulse oximetry. The current research is an exploration of the process of empirically validating such a platform. With the growing availability and accuracy of tissue optical properties in literatures, MC simulation of light-tissue interaction is providing increasingly valuable information for optical bio-monitoring research. However, the extent of the validity of results from such simulations depends heavily on its agreement with empirical data. The use of images captured from a CMOS camera for the construction of intensity distributions of light transmitted through the human finger has been investigated to compare with corresponding distributions produced in the MC simulations

Recovery of heart rate variability after treadmill exercise analyzed by lagged Poincaré plot and spectral characteristics

© 2017 International Federation for Medical and Biological Engineering The aim of this study was to analyze the recovery of heart rate variability (HRV) after treadmill exercise and to investigate the autonomic nervous system response after exercise. Frequency domain indices, i.e., LF(ms 2 ), HF(ms 2 ), LF(n.u.), HF(n.u.) and LF/HF, and lagged Poincaré plot width (SD1 m ) and length (SD2 m ) were introduced for comparison between the baseline period (Pre-E) before treadmill running and two periods after treadmill running (Post-E1 and Post-E2). The correlations between lagged Poincaré plot indices and frequency domain indices were applied to reveal the long-range correlation between linear and nonlinear indices during the recovery of HRV. The results suggested entirely attenuated autonomic nervous activity to the heart following the treadmill exercise. After the treadmill running, the sympathetic nerves achieved dominance and the parasympathetic activity was suppressed, which lasted for more than 4 min. The correlation coefficients between lagged Poincaré plot indices and spectral power indices could separate not only Pre-E and two sessions after the treadmill running, but also the two sessions in recovery periods, i.e., Post-E1 and Post-E2. Lagged Poincaré plot as an innovative nonlinear method showed a better performance over linear frequency domain analysis and conventional nonlinear Poincaré plot

Frame registration for motion compensation in imaging photoplethysmography

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Imaging photoplethysmography (iPPG) is an emerging technology used to assess microcirculation and cardiovascular signs by collecting backscattered light from illuminated tissue using optical imaging sensors. An engineering approach is used to evaluate whether a silicone cast of a human palm might be effectively utilized to predict the results of image registration schemes for motion compensation prior to their application on live human tissue. This allows us to establish a performance baseline for each of the algorithms and to isolate performance and noise fluctuations due to the induced motion from the temporally changing physiological signs. A multi-stage evaluation model is developed to qualitatively assess the influence of the region of interest (ROI), system resolution and distance, reference frame selection, and signal normalization on extracted iPPG waveforms from live tissue. We conclude that the application of image registration is able to deliver up to 75% signal-to-noise (SNR) improvement (4.75 to 8.34) over an uncompensated iPPG signal by employing an intensity-based algorithm with a moving reference frame

Opto-physiological modeling applied to photoplethysmographic cardiovascular assessment

This paper presents opto-physiological (OP) modeling and its application in cardiovascular assessment techniques based on photoplethysmography (PPG). Existing contact point measurement techniques, i.e., pulse oximetry probes, are compared with the next generation noncontact and imaging implementations, i.e., non-contact reflection and camera-based PPG. The further development of effective physiological monitoring techniques relies on novel approaches to OP modeling that can better inform the design and development of sensing hardware and applicable signal processing procedures. With the help of finite-element optical simulation, fundamental research into OP modeling of photoplethysmography is being exploited towards the development of engineering solutions for practical biomedical systems. This paper reviews a body of research comprising two OP models that have led to significant progress in the design of transmission mode pulse oximetry probes, and approaches to 3D blood perfusion mapping for the interpretation of cardiovascular performance

A preliminary attempt to understand compatibility of photoplethysmographic pulse rate variability with electrocardiogramic heart rate variability

We investigated the difference between heart rate variability (HRV) derived from electrocardiogramic (ECG) signals and pulse rate variability (PRV) derived from photoplethysmographic (PPG) signals. Ten-minute recordings of finger and ear photoplethysmogram (PPG) and Lead I electrocardiogram (ECG) were collected in fourteen healthy subjects. In this study, analyses accounting for time and frequency domain, agreement, correlation coefficient and geometrical distribution were utilized to process the ear pulse rate variability (ePRV) and finger pulse rate variability (fPRV). The agreement analysis showed high degree of agreement (Bland-Altman ratio < 0.1) between ePRV or fPRV of PPG and HRV of ECG for all the parameters except the normal-to-normal (NN) range with a moderate agreement (0.1 < Bland-Altman ratio < 0.2). Highly significant (p < 0.001) correlations (0.97 < r <1) were found between HRV and ePRV or fPRV parameters except in the NN range, where the r values were 0.92 and 0.85, respectively. Also, the experimental results indicated that the frequency-domain parameters appeared inadequate in statistical analysis. Both fPRV and ePRV were acceptable surrogates for time-domain HRV study, especially when the ECG recording was unavailable and inconvenient. Photolethysmography could offer a simple and robust means to fulfill the requirements of rhythmical pulsation assessment

A comparative study of physiological monitoring with a wearable opto-electronic patch sensor (OEPS) for motion reduction

This paper presents a comparative study in physiological monitoring between a wearable opto-electronic patch sensor (OEPS) comprising a three-axis Microelectromechanical systems (MEMs) accelerometer (3MA) and commercial devices. The study aims to effectively capture critical physiological parameters, for instance, oxygen saturation, heart rate, respiration rate and heart rate variability, as extracted from the pulsatile waveforms captured by OEPS against motion artefacts when using the commercial probe. The protocol involved 16 healthy subjects and was designed to test the features of OEPS, with emphasis on the effective reduction of motion artefacts through the utilization of a 3MA as a movement reference. The results show significant agreement between the heart rates from the reference measurements and the recovered signals. Significance of standard deviation and error of mean yield values of 2.27 and 0.65 beats per minute, respectively; and a high correlation (0.97) between the results of the commercial sensor and OEPS. T, Wilcoxon and Bland-Altman with 95% limit of agreement tests were also applied in the comparison of heart rates extracted from these sensors, yielding a mean difference (MD: 0.08). The outcome of the present work incites the prospects of OEPS on physiological monitoring during physical activities

An applicable approach for extracting human heart rate and oxygen saturation during physical movements using a multi-wavelength illumination optoelectronic sensor system

© 2018 SPIE. The ability to gather physiological parameters such as heart rate (HR) and oxygen saturation (SpO2%) during physical movement allows to continuously monitor personal health status without disrupt their normal daily activities. Photoplethysmography (PPG) based pulse oximetry and similar principle devices are unable to extract the HR and SpO2% reliably during physical movement due to interference in the signals that arise from motion artefacts (MAs). In this research, a flexible reflectance multi-wavelength optoelectronic patch sensor (OEPS) has been developed to overcome the susceptibility of conventional pulse oximetry readings to MAs. The OEPS incorporates light embittered diodes as illumination sources with four different wavelengths, e.g. green, orange, red, and infrared unlike the conventional pulse oximetry devices that normally measure the skin absorption of only two wavelengths (red and infrared). The additional green and orange wavelengths were found to be distinguish to the absorption of deoxyhemoglobin (RHb) and oxyhemoglobin (HbO2). The reliability of extracting physiological parameters from the green and orange wavelengths is due to absorbed near to the surface of the skin, thereby shortening the optical path and so effectively reducing the influence of physical movements. To compensate of MAs, a three-axis accelerometer was used as a reference with help of adaptive filter to reduce MAs. The experiments were performed using 15 healthy subjects aged 20 to 30. The primary results show that there are no significant difference of heart rate and oxygen saturation measurements between commercial devices and OEPS Green (r=0.992), Orange(r=0.984), Red(r=0.952) and IR(r=0.97) and SpO2% (r = 0.982, p = 0.894)

A multiplexed electronic architecture for opto-electronic patch sensor to effectively monitor heart rate and oxygen saturation

To effectively capture human vital signs, a multi-wavelength optoelectronic patch sensor (MOEPS), together with a schematic architecture of electronics, was developed to overcome the drawbacks of present photoplethysmographic (PPG) sensors. To obtain a better performance of in vivo physiological measurement, the optimal illuminations, i.e., light emitting diodes (LEDs) in the MOEPS, whose wavelength is automatically adjusted to each specific subject, were selected to capture better PPG signals. A multiplexed electronic architecture has been well established to properly drive the MOEPS and effectively capture pulsatile waveforms at rest. The protocol was designed to investigate its performance with the participation of 11 healthy subjects aged between 18 and 30. The signals obtained from green (525nm) and orange (595nm) illuminations were used to extract heart rate (HR) and oxygen saturation (SpO2%). These results were compared with data, simultaneously acquired, from a commercial ECG and a pulse oximeter. Considering the difficulty for current devices to attain the SpO2%, a new computing method, to obtain the value of SpO2%, is proposed depended on the green and orange wavelength illuminations. The values of SpO2% between the MOEPS and the commercial Pulse Oximeter devics showed that the results were in good agreement. The values of HR showed close correlation between commercial devices and the MOEPS (HR: r1=0.994(Green); r2=0.992(Orange); r3=0.975(Red); r4=0.990(IR))

Noncontact blood perfusion mapping in clinical applications

© 2016 SPIE.Non-contact imaging photoplethysmography (iPPG) to detect pulsatile blood microcirculation in tissue has been selected as a successor to low spatial resolution and slow scanning blood perfusion techniques currently employed by clinicians. The proposed iPPG system employs a novel illumination source constructed of multiple high power LEDs with narrow spectral emission, which are temporally modulated and synchronised with a high performance sCMOS sensor. To ensure spectrum stability and prevent thermal wavelength drift due to junction temperature variations, each LED features a custom-designed thermal management system to effectively dissipate generated heat and auto-adjust current flow. The use of a multi-wavelength approach has resulted in simultaneous microvascular perfusion monitoring at various tissue depths, which is an added benefit for specific clinical applications. A synchronous detection algorithm to extract weak photoplethysmographic pulse-waveforms demonstrated robustness and high efficiency when applied to even small regions of 5 mm2. The experimental results showed evidences that the proposed system could achieve noticeable accuracy in blood perfusion monitoring by creating complex amplitude and phase maps for the tissue under examination