Remote PPG Signal Weighting for Motion-Robust Vital Sign Extraction
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Solution Overview
Problem
Existing vital sign measurement technologies, particularly remote photoplethysmography (rPPG), suffer from insufficient robustness against subject motion, leading to distorted signals that challenge accurate extraction of vital signs like heart rate and blood oxygen saturation.
Innovation Solution
A device and method that utilize spectral decomposition of detection signals to determine the relevance of spectral components based on their energy, amplitude, or relative strength, and apply weighted suppression or attenuation to improve signal quality, followed by vital sign extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If remote PPG devices are used for unobtrusive measurements, then ease of operation is improved, but measurement precision deteriorates due to lower signal-to-noise ratio
Solution Approach 1:
The detection signal is segmented into multiple spectral components through spectral decomposition (e.g., Fourier transform, wavelet transform). Each spectral component corresponds to different frequency ranges, allowing separation of physiological signals (heart rate, respiration) from motion artifacts and illumination changes. This segmentation enables selective processing of relevant frequency bands while filtering out noise.
Solution Approach 2:
The patent applies weighting factors to different spectral components based on their relevance to vital signs. By dynamically adjusting the weight of each spectral component (parameter change), the system enhances the contribution of physiologically relevant frequencies while suppressing frequencies dominated by motion or illumination variations. This parameter adjustment optimizes the signal-to-noise ratio for remote PPG measurements.
2Measurement precision
If spectral decomposition and weighting is applied to improve measurement precision, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system performs preliminary spectral decomposition of the detection signal before vital sign extraction. By pre-processing the signal into spectral components and identifying relevant frequency bands in advance, the system simplifies subsequent vital sign extraction. This preliminary action organizes the complex signal structure, making it easier to isolate physiological parameters from noise.
Solution Approach 2:
The patent employs adaptive weighting of spectral components based on signal characteristics. The system continuously analyzes the spectral content and adjusts weighting factors in real-time to optimize signal quality. This feedback mechanism allows the system to adapt to varying motion conditions and illumination levels, maintaining high measurement precision without requiring manual intervention or complex manual tuning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the accuracy and robustness of vital sign measurements by effectively suppressing motion-induced distortions, particularly in challenging environments with severe motion or varying illumination.
Implementation Method 1
a decomposition unit for performing a spectral decomposition of the at least two detection signals to obtain two or more spectral components of the detection signals
Implementation Method 2
Plethysmography generally refers to the measurement of volume changes of an organ or a body part and in particular to the detection of volume changes due to a cardio-vascular pulse wave traveling through the body of a subject with every heartbeat
Implementation Method 3
Photoplethysmography (PPG) is an optical measurement technique that evaluates a time-variant change of light reflectance or transmission of an area or volume of interest. PPG is based on the principle that blood absorbs light more than surrounding tissue, so variations in blood volume with every heart beat affect transmission or reflectance correspondingly
Implementation Method 4
By evaluating the transmittance and/or reflectivity at different wavelengths (typically red and infrared), the blood oxygen saturation can be determined
Implementation Method 5
By evaluating the transmittance and/or reflectivity at different wavelengths (typically red and infrared), the blood oxygen saturation can be determined
Data Source
AI summary
In an approach to obtaining vital signs of a subject, a subject monitoring device obtains at least two detection signals acquired from a subject that are related to a physiological property of the subject and allows extraction of a vital sign of the subject. The subject monitoring device performs a spectral decomposition of the at least two detection signals to obtain two or more spectral components of the detection signals and determines a weight per spectral component based on an estimate of the relevance. The subject monitoring device determines a weight value by determining at least one of a variance of the spectral component and a standard deviation of the spectral component and determines whether at least one of the variance and the standard deviation exceed a predetermined limit. Responsive to determining that at least one of the variance and the standard deviation do not exceed the predetermined limit, the subject monitoring device setts the weight to a weight value of 1 and extracts the weighted vital sign of the subject.