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.
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.
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.
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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