Wrist PPG Detector Placement Using Multi-Distance Light Sensing
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Solution Overview
Problem
Pulse oximetry on the wrist is challenging due to low capillary density and the presence of arteries and veins, which cause noise and inaccurate measurements, especially with normal everyday movements.
Innovation Solution
A wearable device with a plethysmograph module that uses multiple light emitters and detectors at different radial distances to estimate attenuation parameters, correct physiological parameter bias, and determine detector positioning for accurate measurements, incorporating a gyroscope and accelerometer to manage motion noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motion-tolerant processing is used for wrist-based pulse oximetry, then measurement reliability improves, but measurement precision deteriorates due to low capillary density and weak signals
Solution Approach 1:
The patent divides the measurement system into multiple independent light emitters and detectors positioned at different radial distances from the wrist tissue. This segmentation allows the system to collect multiple light signals that can be processed to extract accurate physiological information even in the presence of motion artifacts and low capillary density
Solution Approach 2:
The patent transitions from traditional single-point measurement to multi-dimensional measurement by positioning detectors at different radial distances from the light emitters. This spatial dimensionality allows the system to capture light signals that have traveled through different tissue paths, enabling more robust measurement that is less susceptible to motion interference
2Measurement precision
If multiple light emitters and detectors at different radial distances are used, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent designs the wearable device with multiple light emitters and detectors that serve multiple functions simultaneously. The same hardware components are used for both motion detection and physiological parameter measurement, eliminating the need for separate dedicated sensors and reducing overall device complexity
Solution Approach 2:
The patent combines motion sensing capabilities and physiological measurement capabilities into a single integrated system. The light emitters and detectors serve dual purposes: detecting motion artifacts and measuring physiological parameters like oxygen saturation, thereby simplifying the device architecture
3Measurement precision
If attenuation parameter correction is applied, then measurement precision improves, but computational requirements and processing time increase
Solution Approach 1:
The patent performs attenuation parameter estimation and correction in advance during the signal processing pipeline, before final physiological parameter calculation. By pre-computing the attenuation corrections based on light intensity measurements at different radial distances, the system reduces the computational burden during real-time measurement
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
Enables accurate and consistent measurement of physiological parameters like SpO2 and heart rate on the wrist by compensating for capillary density and motion artifacts, improving measurement accuracy and consistency.
Implementation Method 1
an emitter for emitting light and a detector for collecting light after the light interacts with a tissue of a wearer
Data Source
AI summary
A non-invasive physiological sensor system implemented as a smart watch or other wearable device includes an emitter for emitting light and a detector for collecting light after the light interacts with a tissue of a wearer. The system can measure light intensity at one or more radial distances to estimate attenuation parameter values that can be used to correct physiological parameter bias across subjects. In addition or alternatively, the system can determine whether a detector is positioned sufficiently proximate to an obstructing tissue (for example, an artery or vein) so as to cause inaccurate measurements by the detector.