Current pulse oximetry has been facing inevitable challenges of skin tones, low perfusion, and motion artefacts due to the limitations of Lambert-Beer’s law based photoplethysmography (PPG). This becomes a hurdle to achieve clinical standard practice when using a wearable device. Opto-physiological monitoring (OPM) is the exploration outcome of utilizing Radiative Transfer Theorem (RTT) to generate high-definition models to interact light with various types of tissues. A multi-wavelength opto-electronic patch sensor (mOEPS) based on these OPM models, has been developed to overcome those limitations of PPG devices. The mOEPS has multi-spectral illuminations associated with a specific sensing configuration and bespoke electronics with real-time embedded AI signal processing platform. to work out heart rate (HR), blood oxygen saturation (SpO2%), perfusion index (PI), and respiration rate (RR). One physical intensity protocol with five subjects aligned with Monk Skin Tone (MST) scale has been carried out in a controlled chamber to validate the mOEPS functionalities where the sensor was attached on the back of wrist and chest of the subjects. The unprocessed signals captured by OPM sensor clearly reveal multi-spectral pulsatile waveforms for subjects with all skin types. The comparison of HR, RR, SpO2 gathering with the references from the comparators is executed to show the performance differences between mOEPS and these patient monitor and wearable devices. The outcomes demonstrate that the mOEPS enables physiological monitoring for all types of skin tones in real-time and at any time either in clinical sets or personal/home care at routine physical states compared to present PPG technology.
Real-time physiological monitoring faces inevitable challenges arising from physical activity accompanying body motion and contact pressure variations, disturbing photoplethysmography (PPG) based monitoring. Opto-physiological modelling (OPM) underpins the radiative transfer theorem (RTT) to reveal the essence of light trans-illumination beyond the standard Beer-Lambert law driving PPG technologies. The principles of OPM have been well established through a new multiwavelength optoelectronic patch sensor (mOEPS) that overcomes drawbacks of present PPG sensors caused by gravity, imbalance, skin tone, thermoregulation, and contact force. A protocol engaging six healthy subjects has been implemented to obtain high-quality pulsatile signals using mOEPS system, and corresponding perfusion indices were computed. Comparative results with two selected clinical grade pulse oximetry probes are presented. The outcomes demonstrate the capability of the mOEPS system to provide real-time and any time physiological monitoring across different variations of skin types (I – VI, Fitzpatrick scale). Upcoming mOEPS validation work against gold-standards will be performed to validate a prospective wearable system for clinical grade monitoring and assessment over continuous physiological statuses.
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)).
In this study, the Carelight multi-wavelength opto-electronic patch sensor (OEPS) was adopted to assess the effectiveness of a new approach for estimating the systolic blood pressure (SBP) through the changes in the morphology of the OEPS signal. Specifically, the SBP was estimated by changing the pressure exerted on an inflatable cuff placed around the left upper arm. Pressure acquisitions were performed both with gold standard (i.e. electronic sphygmomanometer), and Carelight sensor (experimental procedure), on subjects from a multiethnic cohort (aged 28 ± 7). The OEPS sensor was applied together with a manual inflatable cuff, going slightly above the level of the SBP with increases of +10mmHg and subsequently deflated by 10mmHg until reaching full deflation. The OEPS signals were captured using four wavelength illumination sources (i.e., green 525 nm, orange 595 nm, red 650 nm and IR 870 nm) on three different measuring sites, namely forefinger, radial artery and wrist. The implemented algorithm provides information on the instant when the SBP was reached and the signal is lost since the vessel is completely blocked. Similarly, it detected the signal resumption when the external pressure dropped below the SBP. The findings demonstrated a good correlation between the variation of the pressure and the corresponding OEPS signal with the most accurate result achieved in the fingertip among all wavelengths, with a temporal identification error of 8.07 %. Further studies will improve the clinical relevance on a cohort of patients diagnosed with hyper- or hypotension, in order to develop a wearable blood-pressure device.
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).
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.
This study presents an effective engineering approach for human vital signs monitoring as increasingly
demanded by personal healthcare. The aim of this work is to study how to capture critical physiological
parameters efficiently through a well-constructed electronic system and a robust multi-channel opto-electronic
patch sensor (OEPS), together with a wireless communication. A unique design comprising multi-wavelength
illumination sources and a rapid response photo sensor with a 3-axis accelerometer enables to recover pulsatile
features, compensate motion and increase signal-to-noise ratio. An approved protocol with designated tests was
implemented at Loughborough University a UK leader in sport and exercise assessment. The results of sport
physiological effects were extracted from the datasets of physical movements, i.e. sitting, standing, waking,
running and cycling. t-test, Bland-Altman and correlation analysis were applied to evaluate the performance of
the OEPS system against Acti-Graph and Mio-Alpha.There was no difference in heart rate measured using
OEPS and both Acti-Graph and Mio-Alpha (both p<0.05). Strong correlations were observed between HR
measured from the OEPS and both the Acti-graph and Mio-Alpha (r = 0.96, p<0.001). Bland-Altman analysis
for the Acti-Graph and OEPS found the bias 0.85 bpm, the standard deviation 9.20 bpm, and the limits of
agreement (LOA) -17.18 bpm to +18.88 bpm for lower and upper limits of agreement respectively, for the Mio-Alpha and OEPS the bias is 1.63 bpm, standard deviation SD8.62 bpm, lower and upper limits of agreement, -
15.27 bpm and +18.58 bpm respectively. The OEPS demonstrates a real time, robust and remote monitoring of
cardiovascular function.
Spontaneous expression is associated with physiological states, i.e., heart rate, respiration, oxygen saturation (SpO2%),
and heart rate variability (HRV). There have yet not sufficient efforts to explore correlation of physiological change and
spontaneous expression. This study aims to study how spontaneous expression is associated with physiological changes
with an approved protocol or through the videos provided from Denver Intensity of Spontaneous Facial Action Database.
Not like a posed expression, motion artefact in spontaneous expression is one of evitable challenges to be overcome in
the study. To obtain a physiological signs from a region of interest (ROI), a new engineering approach is being
developed with an artefact-reduction method consolidated 3D active appearance model (AAM) based track, affine
transformation based alignment with opto-physiological mode based imaging photoplethysmography. Also, a statistical
association spaces is being used to interpret correlation of spontaneous expressions and physiological states including
their probability densities by means of Gaussian Mixture Model. The present work is revealing a new avenue of study
associations of spontaneous expressions and physiological states with its prospect of applications on physiological and
psychological assessment.
The demand for rapid screening technologies, to be used outside of a traditional healthcare setting, has been vastly expanding. This is requiring a new engineering platform for faster and cost effective techniques to be easily adopted through forward-thinking manufacturing procedures, i.e., advanced miniaturisation and heterogeneous integration of high performance microfluidics based point-of-care testing (POCT) systems. Although there has been a considerable amount of research into POCT systems, there exist tremendous challenges and bottlenecks in the design and manufacturing in order to reach a clinical acceptability of sensitivity and selectivity, as well as smart microsystems for healthcare. The project aims to research how to enable scalable production of such complex systems through 1) advanced miniaturisation of a physical layout and opto-electronic component allocation through an optimal design; and 2) heterogeneous integration of multiplexed fluorescence detection (MFD) for in vitro POCT. Verification is being arranged through experimental testing with a series of dilutions of commonly used fluorescence dye, i.e. Cy5. Iterative procedures will be engaged until satisfaction of the detection limit, of Cy5 dye, 1.209x10-10 M. The research creates a new avenue of rapid screening POCT manufacturing solutions with a particular view on high performance and multifunctional detection systems not only in POCT, but also life sciences and environmental applications.
The demand of non-invasive ocular screening is rapidly growing due to an increase of age related eye diseases
worldwide. An indeed in-depth understanding of optical properties is required to elucidate nature of retinal tissue. The
research aims to investigate an effective biomedical engineering approach to allow process region of interests (ROIs) in
eyes to reveal physiological status. A dynamic opto-physiological model (DOPM) representing retinal microvascular
circulation underlying a diffusion approximation to solve radiative transport theorem (RTT) has being developed to
interpret patho-physiological phenomena. DOPM is being applied in imaging photoplethysmography (iPPG) to extract
PPG signals from a series of 2D matrix images to access blood perfusion and oxygen saturation distributions. A variation
of microvascular circulation could be mapped for an effectively diagnostic screening. The work presents mathematical
modelling based ten layers of ocular tissue tested with four set of controlled parameters demontrated detection ratio
between normal tissue damage or abnormal tissue and significant change of AC signal amplitude in these tissues. The
result shows signicant change of AC signal amplitude in abnormal tissue. The preliminary results show extractable PPG
signals from eye fundus video; experimented at five ROIs: whole fundus, optical disk, main vein vessel, lesion area and
affected area. The outcome shows optical disk region gave a better performance compared to whole fundus region and
main vein vessel. The robustness, miniaturization and artefact reduction capability of DOPM to discriminate oxygenation
levels in retina could offer a new insight to access retinal patho-physiological status.
Non-contact imaging photoplethysmography (PPG) is a recent development in the field of physiological data acquisition, currently undergoing a large amount of research to characterize and define the range of its capabilities. Contact-based PPG techniques have been broadly used in clinical scenarios for a number of years to obtain direct information about the degree of oxygen saturation for patients. With the advent of imaging techniques, there is strong potential to enable access to additional information such as multi-dimensional blood perfusion and saturation mapping. The further development of effective opto-physiological monitoring techniques is dependent upon novel modelling techniques coupled with improved sensor design and effective signal processing methodologies. The biometric signal and imaging processing platform (bSIPP) provides a comprehensive set of features for extraction and analysis of recorded iPPG data, enabling direct comparison with other biomedical diagnostic tools such as ECG and EEG. Additionally, utilizing information about the nature of tissue structure has enabled the generation of an engineering model describing the behaviour of light during its travel through the biological tissue. This enables the estimation of the relative oxygen saturation and blood perfusion in different layers of the tissue to be calculated, which has the potential to be a useful diagnostic tool.
This study presents a non-invasive and wearable optical technique to continuously monitor vital human signs as required
for personal healthcare in today’s increasing ageing population. The study has researched an effective way to capture
human critical physiological parameters, i.e., oxygen saturation (SaO2%), heart rate, respiration rate, body temperature,
heart rate variability by a closely coupled wearable opto-electronic patch sensor (OEPS) together with real-time and
secure wireless communication functionalities. The work presents the first step of this research; an automatic noise
cancellation method using a 3-axes MEMS accelerometer to recover signals corrupted by body movement which is one
of the biggest sources of motion artefacts. The effects of these motion artefacts have been reduced by an enhanced
electronic design and development of self-cancellation of noise and stability of the sensor. The signals from the
acceleration and the opto-electronic sensor are highly correlated thus leading to the desired pulse waveform with rich
bioinformatics signals to be retrieved with reduced motion artefacts. The preliminary results from the bench tests and the
laboratory setup demonstrate that the goal of the high performance wearable opto-electronics is viable and feasible.
Noncontact imaging photoplethysmography (PPG) can provide physiological assessment at various anatomical locations with no discomfort to the patient. However, most previous imaging PPG (iPPG) systems have been limited by a low sample frequency, which restricts their use clinically, for instance, in the assessment of pulse rate variability (PRV). In the present study, plethysmographic signals are remotely captured via an iPPG system at a rate of 200 fps. The physiological parameters (i.e., heart and respiration rate and PRV) derived from the iPPG datasets yield statistically comparable results to those acquired using a contact PPG sensor, the gold standard. More importantly, we present evidence that the negative influence of initial low sample frequency could be compensated via interpolation to improve the time domain resolution. We thereby provide further strong support for the low-cost webcam-based iPPG technique and, importantly, open up a new avenue for effective noncontact assessment of multiple physiological parameters, with potential applications in the evaluation of cardiac autonomic activity and remote sensing of vital physiological signs.
Imaging photoplethysmography (PPG) is able to capture useful physiological data remotely from a wide range of anatomical locations. Recent imaging PPG studies have concentrated on two broad research directions involving either high-performance cameras and or webcam-based systems. However, little has been reported about the difference between these two techniques, particularly in terms of their performance under illumination with ambient light. We explore these two imaging PPG approaches through the simultaneous measurement of the cardiac pulse acquired from the face of 10 male subjects and the spectral characteristics of ambient light. Measurements are made before and after a period of cycling exercise. The physiological pulse waves extracted from both imaging PPG systems using the smoothed pseudo-Wigner-Ville distribution yield functional characteristics comparable to those acquired using gold standard contact PPG sensors. The influence of ambient light intensity on the physiological information is considered, where results reveal an independent relationship between the ambient light intensity and the normalized plethysmographic signals. This provides further support for imaging PPG as a means for practical noncontact physiological assessment with clear applications in several domains, including telemedicine and homecare.
In light of its capacity for remote physiological assessment over a wide range of anatomical locations, imaging
photoplethysmography has become an attractive research area in biomedical and clinical community. Amongst recent
iPPG studies, two separate research directions have been revealed, i.e., scientific camera based imaging PPG (iPPG) and
webcam based imaging PPG (wPPG). Little is known about the difference between these two techniques. To address this
issue, a dual-channel imaging PPG system (iPPG and wPPG) using ambient light as the illumination source has been
introduced in this study. The performance of the two imaging PPG techniques was evaluated through the measurement of
cardiac pulse acquired from the face of 10 male subjects before and after 10 min of cycling exercise. A time-frequency
representation method was used to visualize the time-dependent behaviour of the heart rate. In comparison to the gold
standard contact PPG, both imaging PPG techniques exhibit comparable functional characteristics in the context of
cardiac pulse assessment. Moreover, the synchronized ambient light intensity recordings in the present study can provide
additional information for appraising the performance of the imaging PPG systems. This feasibility study thereby leads
to a new route for non-contact monitoring of vital signs, with clear applications in triage and homecare.
With the advance of computer and photonics technology, imaging photoplethysmography [(PPG), iPPG] can provide comfortable and comprehensive assessment over a wide range of anatomical locations. However, motion artifact is a major drawback in current iPPG systems, particularly in the context of clinical assessment. To overcome this issue, a new artifact-reduction method consisting of planar motion compensation and blind source separation is introduced in this study. The performance of the iPPG system was evaluated through the measurement of cardiac pulse in the hand from 12 subjects before and after 5 min of cycling exercise. Also, a 12-min continuous recording protocol consisting of repeated exercises was taken from a single volunteer. The physiological parameters (i.e., heart rate, respiration rate), derived from the images captured by the iPPG system, exhibit functional characteristics comparable to conventional contact PPG sensors. Continuous recordings from the iPPG system reveal that heart and respiration rates can be successfully tracked with the artifact reduction method even in high-intensity physical exercise situations. The outcome from this study thereby leads to a new avenue for noncontact sensing of vital signs and remote physiological assessment, with clear applications in triage and sports training.
A study of blood perfusion mapping was performed with a remote opto-physiological imaging (OPI) system coupling a
sensitive CMOS camera and a custom-built resonant cavity light emitting diode (RCLED) ringlight. The setup is suitable
for the remote assessment of blood perfusion in tissue over a wide range of anatomical locations. The purpose of this
study is to evaluate the reliability and stability of the OPI system when measuring a cardiovascular variable of clinical
interest, in this case, heart rate. To this end, the non-contact and contact photoplethysmographic (PPG) signals obtained
from the OPI system and conventional PPG sensor were recorded simultaneously from each of 12 subjects before and
after 5-min of cycling exercise. The time-frequency representation (TFR) method was used to visualize the time-dependent
behavior of the signal frequency. The physiological parameters derived from the images captured by the OPI
system exhibit comparable functional characteristics to those taken from conventional contact PPG pulse waveform
measurements in both the time and frequency domains. Finally and more importantly, a previously developed opto-physiological
model was employed to provide a 3-D representation of blood perfusion in human tissue which could
provide a new insight into clinical assessment and diagnosis of circulatory pathology in various tissue segments.
Non-contact reflection photoplethysmography (NRPPG) is being developed to trace pulse features for comparison with
contact photoplethysmography (CPPG). Simultaneous recordings of CPPG and NRPPG signals from 22 healthy subjects
were studied. The power spectrum of PPG signals were analysed and compared between NRPPG and CPPG. The
recurrence plot (RP) was used as a graphical tool to visualize the time dependent behaviour of the dynamics of the pulse
signals. The agreement between NRPPG and CPPG for physiological monitoring, i.e. HRV parameters, was determined
by means of the Bland-Altman plot and Pearson's correlation coefficient. The results indicated that NRPPG could be
used for the assessment of cardio-physiological signals.
A CMOS camera-based imaging photoplethysmography (PPG) system has been previously demonstrated for the
contactless measurement of skin blood perfusion over a wide tissue area. An improved system with a more sensitive
CCD camera and a multi-wavelength RCLED ring light source was developed to measure blood perfusion from the
human face. The signals acquired by the PPG imaging system were compared to signals captured concurrently from a
conventional PPG finger probe. Experimental results from eight subjects demonstrate that the camera-based PPG
imaging technique is able to measure pulse rate and blood perfusion.
This paper presents a camera-based imaging photoplethysmographic (PPG) system in the remote detection of PPG signals, which can contribute to construct a 3-D blood pulsation mapping for the assessment of skin blood microcirculation at various vascular depths. Spot measurement and contact sensor have been currently addressed as the primary limitations in the utilization of conventional PPG system. The introduction of the fast digital camera inspires the
development of the imaging PPG system to allow ideally non-contact monitoring from a larger field of view and different tissue depths by applying multi-wavelength illumination sources. In the present research, the imaging PPG system has the capability of capturing the PPG waveform at dual wavelengths simultaneously: 660 and 880nm. A
selected region of tissue is remotely illuminated by a ring illumination source (RIS) with dual-wavelength resonant cavity light emitting diodes (RCLEDs), and the backscattered photons are captured by a 10-bit CMOS camera at a speed of 21 frames/second for each wavelength. The waveforms from the imaging system exhibit comparable functionality characters with those from the conventional contact PPG sensor in both time domain and frequency domain. The mean amplitude of PPG pulsatile component is extracted from the PPG waveforms for the mapping of blood pulsation in a 3-D format. These results strongly demonstrate the capability of the imaging PPG system in displaying the waveform and the potential in 3-D mapping of blood microcirculation by a non-contact means.
We investigated a custom Monte Carlo (MC) platform in the generation of opto-physiological models of motion artefact
and perfusion in pulse oximetry. 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. Motion-induced artefact and loss of signal quality during low perfusion are currently the primary limitations in
pulse oximetry. While most attempts to circumvent these issues have focused on signal post-processing techniques, we
propose the development of improved opto-physiological models to include the characterisation of motion artefact and
low perfusion. In this stage of the research, a custom MC platform is being developed for its use in determining the
effects of perfusion, haemodynamics and tissue-probe optical coupling on transillumination at different positions of the
human finger. The results of MC simulations indicate a useful and predictable output from the platform.
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