Monolithic Tissue Interface for Low-Bias Pulse Oximetry
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Solution Overview
Problem
Pulse oximeters exhibit disparate bias in blood oxygen saturation measurements for individuals with darker skin due to higher melanin levels, leading to overestimated readings and potential misinformed clinical decisions.
Innovation Solution
A photoplethysmography device with a monolithic tissue interface made from a single material, featuring a first region that transmits light effectively and a second region that attenuates stray light, reducing bias while maintaining user comfort and lowering manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional tissue interface is used, then manufacturing is simpler, but measurement precision deteriorates due to stray light interference in highly pigmented skin
Solution Approach 1:
The tissue interface is divided into multiple regions with different optical properties: a first region with higher light transmission for the direct light path and a second region with lower light transmission for attenuating stray light. This segmentation allows the device to differentiate between useful light signals and interfering stray light, improving measurement precision without requiring complex external components.
Solution Approach 2:
Different regions of the tissue interface are assigned different optical transmission characteristics tailored to their specific functions. The first region (covering light source/detector) has high transmission to maximize signal strength, while the second region (surrounding area) has low transmission to minimize stray light interference. This local differentiation resolves the contradiction by optimizing each region's properties for its specific role.
2Measurement precision
If multiple components are used in the tissue interface, then light transmission control improves, but manufacturing complexity increases
Solution Approach 1:
Multiple functional regions (first region for light transmission and second region for stray light attenuation) are merged into a single monolithic tissue interface component. This integration maintains the complex optical functionality needed for stray light attenuation while simplifying manufacturing by eliminating the need to assemble multiple separate components, thus resolving the contradiction between precision and ease of manufacture.
3Ease of manufacture
If a monolithic tissue interface is used, then manufacturing complexity reduces, but light transmission control capability decreases
Solution Approach 1:
The monolithic tissue interface incorporates local quality variations through its multi-region structure, where each region has optimized optical properties for its specific function. This allows the single component to maintain sophisticated light transmission control capability while benefiting from simplified manufacturing, resolving the contradiction between ease of manufacture and light path control precision.
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
The device improves accuracy and reduces bias in blood oxygen saturation measurements by effectively attenuating stray light from highly pigmented skin layers, enhancing user comfort and reducing manufacturing complexity.
Implementation Method 1
a light source configured to emit light signals at one or more wavelengths into tissue of the subject
Implementation Method 2
a light detector configured to detect light after travelling from the light source through the tissue of the subject to the light detector along a light path and generate one or more detection signals based on the detected light
Implementation Method 3
a first tissue interface region covering the light source and/or the light detector along the light path and adapted to transmit light at the one or more wavelengths
Implementation Method 4
a second tissue interface region at least partially surrounding the first tissue interface region and adapted to provide relatively less light transmission (i.e., attenuate light and/or have relatively less transmission compared to the direct or line-of-sight light path from the light source to the light detector through the tissue of the subject) at the one or more wavelengths
Data Source
Figure 1~2
Figure 3
AI summary
The present invention relates to a photoplethysmography device (10) for acquiring a biosignal of a subject (2), in particular for blood oxygen saturation measurement, the device comprising: a light source (31) configured to emit light signals at one or more wavelengths into tissue of the subject (2); a light detector (32) configured to detect light after travelling from the light source (31) through the tissue of the subject (2) to the light detector (32) along a light path (33) and generate one or more detection signals based on the detected light; wherein the device comprises a tissue interface (40, 50) comprising a first tissue interface region (41, 51) covering the light source (31) and/or the light detector (32) along the light path (33) and adapted to transmit light at the one or more wavelengths, and a second tissue interface region (42, 52) at least partially surrounding the first tissue interface region (41, 51) and adapted to provide relatively less transmission at the one or more wavelengths, wherein the tissue interface (40, 50) comprising the first tissue interface region (41, 51) and the second tissue interface region (42, 52) is a monolithic component are made from the same one single material. The present invention further relates to a corresponding tissue interface (40, 50) and system (1) for determining vital sign information of a subject (2).