66,028 research outputs found
DistancePPG: Robust non-contact vital signs monitoring using a camera
Vital signs such as pulse rate and breathing rate are currently measured
using contact probes. But, non-contact methods for measuring vital signs are
desirable both in hospital settings (e.g. in NICU) and for ubiquitous in-situ
health tracking (e.g. on mobile phone and computers with webcams). Recently,
camera-based non-contact vital sign monitoring have been shown to be feasible.
However, camera-based vital sign monitoring is challenging for people with
darker skin tone, under low lighting conditions, and/or during movement of an
individual in front of the camera. In this paper, we propose distancePPG, a new
camera-based vital sign estimation algorithm which addresses these challenges.
DistancePPG proposes a new method of combining skin-color change signals from
different tracked regions of the face using a weighted average, where the
weights depend on the blood perfusion and incident light intensity in the
region, to improve the signal-to-noise ratio (SNR) of camera-based estimate.
One of our key contributions is a new automatic method for determining the
weights based only on the video recording of the subject. The gains in SNR of
camera-based PPG estimated using distancePPG translate into reduction of the
error in vital sign estimation, and thus expand the scope of camera-based vital
sign monitoring to potentially challenging scenarios. Further, a dataset will
be released, comprising of synchronized video recordings of face and pulse
oximeter based ground truth recordings from the earlobe for people with
different skin tones, under different lighting conditions and for various
motion scenarios.Comment: 24 pages, 11 figure
Visual onset expands subjective time
We report a distortion of subjective time perception in which the duration of a first interval is perceived to be longer than the succeeding interval of the same duration. The amount of time expansion depends on the onset type defining the first interval. When a stimulus appears abruptly, its duration is perceived to be longer than when it appears following a stationary array. The difference in the processing time for the stimulus onset and motion onset, measured as reaction times, agrees with the difference in time expansion. Our results suggest that initial transient responses for a visual onset serve as a temporal marker for time estimation, and a systematic change in the processing time for onsets affects perceived time
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Systems and methods for physiological signal enhancement and biometric extraction using non-invasive optical sensors
A system and method for signal processing to remove unwanted noise components including: (i) wavelength-independent motion artifacts such as tissue, bone and skin effects, and (ii) wavelength-dependent motion artifact/noise components such as venous blood pulsation and movement due to various sources including muscle pump, respiratory pump and physical perturbation. Disclosed are methods, analytics, and their uses for reliable perfusion monitoring, arterial oxygen saturation monitoring, heart rate monitoring during daily activities and in hospital settings and for extraction of physiological parameters such as respiration information, hemodynamic parameters, venous capacity, and fluid responsiveness. The system and methods disclosed are extendable to include monitoring platforms for perfusion, hypoxia, arrhythmia detection, airway obstruction detection and sleep disorders including apnea.Board of Regents, University of Texas Syste
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A review of machine learning techniques in photoplethysmography for the non-invasive cuff-less measurement of blood pressure
Hypertension or high blood pressure is a leading cause of death throughout the world and a critical factor for increasing the risk of serious diseases, including cardiovascular diseases such as stroke and heart failure. Blood pressure is a primary vital sign that must be monitored regularly for the early detection, prevention and treatment of cardiovascular diseases. Traditional blood pressure measurement techniques are either invasive or cuff-based, which are impractical, intermittent, and uncomfortable for patients. Over the past few decades, several indirect approaches using photoplethysmogram (PPG) have been investigated, namely, pulse transit time, pulse wave velocity, pulse arrival time and pulse wave analysis, in an effort to utilise PPG for estimating blood pressure. Recent advancements in signal processing techniques, including machine learning and artificial intelligence, have also opened up exciting new horizons for PPG-based cuff less and continuous monitoring of blood pressure. Such a device will have a significant and transformative impact in monitoring patientsâ vital signs, especially those at risk of cardiovascular disease. This paper provides a comprehensive review for non-invasive cuff-less blood pressure estimation using the PPG approach along with their challenges and limitations
Timing jitter of passively mode-locked semiconductor lasers subject to optical feedback; a semi-analytic approach
We propose a semi-analytical method of calculating the timing fluctuations in
mode-locked semiconductor lasers and apply it to study the effect of delayed
coherent optical feedback on pulse timing jitter in these lasers. The proposed
method greatly reduces computation times and therefore allows for the
investigation of the dependence of timing fluctuations over greater parameter
domains. We show that resonant feedback leads to a reduction in the timing
jitter and that a frequency-pulling region forms about the main resonances,
within which a timing jitter reduction is observed. The width of these
frequency-pulling regions increases linearly with short feedback delay times.
We derive an analytic expression for the timing jitter, which predicts a
monotonous decrease in the timing jitter for resonant feedback of increasing
delay lengths, when timing jitter effects are fully separated from amplitude
jitter effects. For long feedback cavities the decrease in timing jitter scales
approximately as with the increase of the feedback delay time
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Methods and systems for extracting venous pulsation and respiratory information from photoplethysmographs
A system and method for separating a venous component and an arterial component from a red signal and an infrared signal of a PPG sensor is provided. The method uses the second order statistics of venous and arterial signals to separate the venous andarterial signals. After reliable separation of the venous and thearterial component signals,the component signals can be used for different purposes. In a preferred embodiment, the respiratory signal, pattern, and rate are extracted from the separated venous component and a reliable ?ratio of ratios? is extracted for SpO, using only the arterial component of the PPG signals. The disclosed embodiments enable real-time continuous monitoring of respiration pattern/rate and site-independentarterial oxygen saturation.Board of Regents, University of Texas Syste
Probing motion of fast radio burst sources by timing strongly lensed repeaters
Given the possible repetitive nature of fast radio bursts (FRBs), their
cosmological origin, and their high occurrence, detection of strongly lensed
sources due to intervening galaxy lenses is possible with forthcoming radio
surveys. We show that if multiple images of a repeating source are resolved
with VLBI, using a method independent of lens modeling, accurate timing could
reveal non-uniform motion, either physical or apparent, of the emission spot.
This can probe the physical nature of FRBs and their surrounding environments,
constraining scenarios including orbital motion around a stellar companion if
FRBs require a compact star in a special system, and jet-medium interactions
for which the location of the emission spot may randomly vary. The high timing
precision possible for FRBs () compared to the typical time
delays between images in galaxy lensing () enables the
measurement of tiny fractional changes in the delays (), and
hence the detection of time-delay variations induced by relative motions
between the source, the lens, and the Earth. We show that uniform cosmic
peculiar velocities only cause the delay time to drift linearly, and that the
effect from the Earth's orbital motion can be accurately subtracted, thus
enabling a search for non-trivial source motion. For a timing accuracy of ms and a repetition rate (of detected bursts) per day of a
single FRB source, non-uniform displacement AU of the
emission spot perpendicular to the line of sight is detectable if repetitions
are seen over a period of hundreds of days.Comment: 21 pages, 6 figures, 1 table. New version accepted to ApJ with
abstract revised, typo corrected, and references adde
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