Pulse Oximeter Offset Correction for Low Pulsatility Accuracy
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Solution Overview
Problem
Current pulse oximeters tend to overestimate oxygen saturation under low pulsatility conditions, leading to potential misclassification of normal subjects as hypoxemic, as the calculated SpO2 values are higher than actual arterial oxygen saturation (SaO2) when pulse wave signals have low amplitudes.
Innovation Solution
The proposed solution involves a pulse oximeter configuration that includes multiple light emitters and detectors to acquire light attenuation variations at different wavelengths, with offsets calculated to correct for the bias in SpO2 values, specifically using a first offset (k1) to adjust the light attenuation variations, thereby improving the accuracy of non-invasive SpO2 measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse oximeter measures SpO2 using conventional methods, then non-invasive measurement is achieved, but measurement precision deteriorates under low pulsatility conditions causing overestimation
Solution Approach 1:
The patent applies preliminary action by pre-calculating offset values (k1, k2) during a calibration phase with normal pulsatility, then applying these offsets during low pulsatility measurements. The offset k1 compensates for the fundamental bias in low pulsatility conditions, while k2 provides additional correction based on the ratio of light attenuation variations. This pre-computed correction approach allows accurate SpO2 measurement under low pulsatility without requiring real-time complex calculations.
2Device complexity
If conventional SpO2 calculation is used, then calculation simplicity is maintained, but reliability deteriorates when pulse wave amplitude is low
Solution Approach 1:
The patent changes the calculation parameters by introducing offset values (k1, k2) that are added to the light attenuation variations. The modified calculation becomes: SpO2 = f(ΔA1 + k1, ΔA2 + k2) where ΔA1 and ΔA2 are the light attenuation variations at different wavelengths. This parameter modification maintains the overall structure of the calculation while improving reliability under low amplitude conditions through the compensatory offsets.
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 configuration reduces the bias in SpO2 calculations, especially in regions with low pulse wave amplitudes, enhancing the accuracy of non-invasive oxygen saturation measurements by aligning them closer to invasive SaO2 values, thereby preventing false hypoxemia indications.
Implementation Method 1
the living tissue of the subject is irradiated with light beams at a plurality of wavelengths
Implementation Method 2
light beams at a plurality of wavelengths which have different ratios of the blood light absorbances depending on the blood light absorber concentration
Implementation Method 3
The intensities of the light beams at the wavelengths transmitted through or reflected from the living tissue are detected
Data Source
Figure 1
Figure 2(A)~2(B)
Figure 3
AI summary
A pulse photometer includes: a first variation acquirer acquiring a first variation corresponding to a light attenuation variation of a first light beam due to pulsation of blood in a subject, based on a first intensity signal corresponding to an intensity of the first light beam that is transmitted through or reflected from a body of the subject, and that has a first wavelength; a second variation acquirer acquiring a second variation; and a concentration calculator calculating a blood light absorber concentration, based on the first and second variations, the second variation containing a first offset which is based on an inverse of the light attenuation variation of the first light beam.