PPG Sensor Motion Artifact Reduction via Intermediary Signal
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Solution Overview
Problem
Photoplethysmography (PPG) signals are susceptible to motion artifacts, which hinder their use in activities like daily living, cardiopulmonary exercise testing, and cardiopulmonary resuscitation, leading to inaccurate pulse rate variability and oxygen saturation measurements.
Innovation Solution
A sensor device with integrated motion sensing capabilities, using accelerometers, gyroscopes, or barometric pressure sensors, processes motion reference signals to estimate and subtract motion artifacts from PPG signals, maintaining compatibility with existing pulse oximetry systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If algorithmic filtering and rejection of entire time spans is used to circumvent motion artifacts, then motion artifacts are reduced, but response time is delayed and measurement accuracy is compromised
Solution Approach 1:
The patent introduces an accelerometer as an intermediary device that measures motion independently of the PPG signal. This motion reference signal serves as a mediator that enables artifact removal through adaptive filtering without requiring rejection of entire time spans, thus maintaining both signal quality and response time.
Solution Approach 2:
The patent extracts the motion artifact component from the PPG signal by using the accelerometer-derived motion reference signal. Through adaptive filtering, the motion-related components are separated and removed, allowing the underlying physiological signal to be recovered without discarding entire time spans.
2Reliability
If algorithmic filtering is applied to reduce motion artifacts, then signal quality improves, but measurement accuracy deteriorates due to inaccuracies
Solution Approach 1:
The accelerometer acts as an intermediary that provides an independent motion reference signal. This allows for more precise artifact removal through adaptive filtering, as the filtering process is guided by actual motion measurements rather than attempting to identify and reject entire time spans, thereby preserving measurement accuracy.
Solution Approach 2:
The patent employs adaptive filtering that dynamically adjusts based on the motion reference signal. This dynamic approach allows the filter to adapt to varying motion conditions in real-time, improving both signal quality and measurement accuracy compared to static filtering methods that require rejection of entire time spans.
3Reliability
If a motion reference signal is integrated into the sensor device, then artifact reduction capability is improved, but device complexity increases
Solution Approach 1:
The patent integrates a motion sensor (accelerometer) into the sensor device, enabling it to perform both PPG measurement and motion reference signal acquisition. This multi-functionality allows the device to reduce motion artifacts while maintaining a relatively simple overall structure, as the same device housing contains both sensing capabilities.
Solution Approach 2:
The patent combines the PPG sensor and motion sensor into a single integrated sensor device. By merging these functions into one device rather than using separate devices, the overall system complexity is reduced while still providing artifact reduction capability through the integrated motion reference signal.
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
This approach enhances the quality and applicability of PPG signals by effectively reducing motion artifacts, allowing for accurate pulse rate and oxygen saturation measurements without adding complexity to the clinical workflow or requiring additional sensors.
Implementation Method 1
a PPG sensor for providing a photoplethysmography, PPG, signals modulated on a first set of one or more carrier signals
Implementation Method 2
a motion sensor for providing a motion reference signal representing motion of the body part, at which the sensor device is arranged
Data Source
AI summary
The present invention relates to a sensor device and method for obtaining physiological information of a subject. The sensor device comprises a PPG sensor (20), a motion sensor (30) and a device (10) for obtaining physiological information of the subject. The device comprises a processing unit (13) for generating an output signal carrying physiological information by (i) modulating the motion reference signal on a carrier signal of the first set of carrier signals or on a second carrier signal orthogonal to the first set of carrier signals to obtain a modulated signal and combining the modulated signal with the modulated PPG signals to obtain the output signal or (ii) demodulating the modulated PPG signals, performing artifact-reduction on the demodulated PPG signals using the motion reference signal to obtain artifact-reduced PPG signals and modulating the artifact-reduced PPG signals on the first set of carrier signals to obtain the output signal.