Pulse Oximetry Signal Selection for Tissue Scattering and Skin Tone
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Solution Overview
Problem
Existing pulse oximetry methods face inaccuracies due to variations in LED light spectrum, inconsistent detector-to-light source distance, tissue light scatter, irregular patient pulse, and differences in light absorption based on skin tone, leading to unreliable SpO2 readings, especially in erratic or irregular pulses.
Innovation Solution
A pulse oximeter system using a combination of transmissive and reflective light emitters and detectors, along with a processor to evaluate multiple criteria, selects the most accurate signal based on transmissive or reflective measurements to compensate for scattering and skin tone variations, ensuring precise SpO2 calculations.
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 the SpO2 readings are inaccurate due to tissue light scatter and skin tone variations
Solution Approach 1:
The patent segments the measurement process into multiple evaluation criteria (transmissive criteria, reflective criteria, error criteria) that are assessed independently. The processor evaluates each criterion separately and selects the most appropriate measurement path, breaking down the complex problem of accurate SpO2 measurement into manageable decision steps that improve accuracy without overwhelming complexity
Solution Approach 2:
The patent changes the measurement parameters by switching between transmissive and reflective measurement modes based on evaluated criteria. Instead of using a fixed measurement method, the system dynamically adjusts the measurement parameters (measurement mode selection) based on tissue characteristics and signal quality, thereby improving SpO2 accuracy across different skin tones and pulse conditions
2Illumination intensity
If transmissive measurement is used, then the signal strength is strong, but the measurement is affected by tissue light scatter and skin tone differences
Solution Approach 1:
The patent implements feedback by continuously evaluating measurement criteria and using that information to select the appropriate measurement mode. The system monitors signal characteristics and tissue response, then feeds this information back into the measurement selection process, switching between transmissive and reflective modes based on real-time assessments of signal quality and tissue properties
Solution Approach 2:
The measurement system transitions from a static, fixed-method approach to a dynamic, adaptive approach. The system can switch between transmissive and reflective measurement modes dynamically based on evaluated criteria, allowing it to optimize for signal strength when transmissive measurement is appropriate while compensating for tissue scatter and skin tone variations through mode selection
3Measurement precision
If LED light spectrum variations are not compensated, then the device manufacturing is simple, but the SpO2 measurements are inaccurate across different wavelengths
Solution Approach 1:
The patent applies preliminary action by pre-establishing multiple evaluation criteria (transmissive criteria, reflective criteria, error criteria) that account for LED spectrum variations. These criteria are prepared in advance and include compensations for wavelength variations, allowing the system to automatically select the most appropriate measurement path without real-time complex calculations
Solution Approach 2:
The patent adds another dimension to the measurement approach by introducing multiple measurement modes (transmissive and reflective) and multiple evaluation criteria. Instead of relying solely on wavelength-based measurements that are sensitive to LED variations, the system evaluates multiple dimensions (signal strength, error criteria, measurement mode suitability) to compensate for spectrum variations and improve measurement consistency
4Measurement precision
If the distance between light source and detector varies due to patient motion, then the device portability is high, but the SpO2 readings become unreliable
Solution Approach 1:
The patent applies dynamics by making the measurement system adaptive to patient motion. Instead of relying on a fixed geometric relationship between light source and detector, the system dynamically evaluates measurement criteria and switches between transmissive and reflective modes based on real-time signal quality assessments, thereby maintaining reliability despite distance variations caused by patient movement
Solution Approach 2:
The system changes measurement parameters (measurement mode, evaluation criteria) in response to patient motion. When motion causes distance variations that affect transmissive measurement quality, the system can switch to reflective mode or adjust evaluation thresholds, thereby maintaining SpO2 reading reliability despite changes in the light source-detector distance
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 system provides more accurate SpO2 measurements across varying skin tones and irregular patient pulses by minimizing the effects of light scattering and skin tone differences, enhancing measurement reliability.
Implementation Method 1
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
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
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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.