Pulse Oximetry Using Dual Optical Paths to Correct Tissue Scattering
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Solution Overview
Problem
Existing pulse oximetry methods provide inaccurate SpO2 readings due to variations in LED light spectrum, inconsistent source-detector distance, tissue light scatter, irregular blood flow, and differences in light absorption based on skin tone, especially in patients with erratic pulses.
Innovation Solution
A pulse oximeter system with dual transmissive and reflective light emitters and detectors, oriented to minimize tissue scatter effects, and a processor to calculate SpO2 using both signals, adjusting for variations in LED wavelengths and skin tone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AC/DC method is used to calculate SpO2, then the measurement process is simple, but measurement precision deteriorates due to tissue scatter and LED variations
Solution Approach 1:
The patent segments the measurement process into multiple wavelength measurements (at least three wavelengths including red and infrared) and separates transmissive and reflective signal detection. This segmentation allows independent analysis and compensation of different tissue optical properties, improving SpO2 accuracy by accounting for tissue scatter effects that a single wavelength measurement cannot resolve.
Solution Approach 2:
The patent changes the measurement parameters by using multiple wavelengths instead of a single wavelength ratio method. By measuring absorption at multiple wavelengths and analyzing the differential absorption characteristics, the system can mathematically separate hemoglobin absorption from tissue scatter effects, thereby improving measurement precision while managing complexity through algorithmic processing.
2Measurement precision
If LED light spectrum variations are not compensated, then device manufacturing is simpler, but measurement precision deteriorates
Solution Approach 1:
The patent measures the actual light spectrum emitted by each LED at multiple wavelengths and uses these measured parameters in the calculation algorithm. By incorporating actual LED spectral characteristics into the multi-wavelength analysis, the system compensates for LED variations without requiring tight manufacturing tolerances, thus maintaining ease of manufacture while improving measurement precision.
Solution Approach 2:
The patent implements a feedback mechanism where the measured light absorption at multiple wavelengths is used to continuously adjust and refine the SpO2 calculation. The system uses the actual measured spectral data from each LED to feedback-correct for LED variations, allowing the measurement algorithm to adapt to each specific LED's characteristics rather than relying on idealized reference values.
3Measurement precision
If source-detector distance is not controlled, then device design is simpler, but measurement precision deteriorates due to distance variations
Solution Approach 1:
The patent transitions from a single-dimensional transmissive measurement to a multi-dimensional approach by incorporating both transmissive and reflective detection geometries with multiple wavelengths. This dimensional expansion allows the system to use geometric relationships and multiple measurement paths to infer and compensate for distance variations, improving measurement consistency without requiring rigid mechanical alignment.
Solution Approach 2:
The patent creates a universal measurement algorithm that works across different source-detector configurations by using multi-wavelength absorption analysis. The algorithm is designed to be configuration-agnostic, extracting SpO2 information from the spectral characteristics rather than relying on fixed geometric relationships, thus improving measurement precision while reducing alignment complexity.
4Measurement precision
If tissue scatter effects are not accounted for, then measurement process is simpler, but measurement precision deteriorates especially in diverse skin tones
Solution Approach 1:
The patent segments the total light absorption into separate components by measuring at multiple wavelengths. By analyzing the differential absorption patterns across wavelengths, the system can mathematically separate hemoglobin absorption (which varies with oxygen saturation) from tissue scatter absorption (which is relatively wavelength-independent), thereby improving SpO2 accuracy across diverse skin tones while managing signal processing complexity through structured analysis.
Solution Approach 2:
The patent changes the measurement approach from single-wavelength ratio to multi-wavelength spectral analysis. This parameter change enables the extraction of tissue scatter characteristics from the spectral data, allowing the algorithm to compensate for scatter effects that vary with skin tone. The increased measurement dimensions provide enough information to solve for both hemoglobin concentration and tissue scatter properties simultaneously.
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
Provides accurate SpO2 measurements across a wide range of skin tones and irregular patient pulses by compensating for LED variations and tissue scatter, enhancing measurement precision.
Implementation Method 1
a plurality of light emitters comprising a first transmissive light emitter adapted to emit light at a first wavelength and a second transmissive light emitter adapted to emit light at a second wavelength
Implementation Method 2
a transmissive detector adapted to detect light at the first and second wavelength, convert light detected at the first wavelength into a first transmissive signal and to convert light detected at the second wavelength into a second transmissive signal
Implementation Method 3
Hb and HbO2 absorb different wavelengths. Hb has a higher absorption at 660 nm and HbO2 has a higher absorption at 940 nm
Implementation Method 4
it assumes that light scatter by tissue is negligible. When a patient's tissue is subjected to intense light, it can absorb or reflect incident light
Data Source
AI summary
A pulse oximeter and method of calculating blood oxygen saturation that enables increased accuracy when signal levels and/or quality are low, as well as across a range of skin tones. Increased accuracy is enabled by detecting red and IR LED signals using both transmissive and reflective light detectors. In addition, several criteria are used to evaluate whether the detected transmissive or reflective signal provides a more accurate blood oxygen saturation value.