Pulse Oximeter Optical Filtering for Pigmentation-Insensitive Readings
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Solution Overview
Problem
Conventional LED-based pulse oximeters provide falsely elevated arterial oxygen saturation readings in patients with high melanin levels due to the broadband nature of red LEDs, causing a spectral shift that misinterprets the absorption characteristics of melanin, particularly affecting darkly pigmented individuals.
Innovation Solution
A photoplethysmographic sensor design incorporating a first light source with a narrow spectral bandwidth, an optical filter to constrain the output light to a specific bandpass, and a second light source in the near-infrared range, along with an optical filter to attenuate unwanted wavelengths, ensuring accurate measurements by minimizing spectral shifts caused by melanin absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If broadband red LEDs are used to illuminate tissue, then the optical signal intensity is strong, but the spectral bandwidth is too wide causing falsely elevated oxygen saturation readings in patients with high melanin levels
Solution Approach 1:
The patent changes the spectral parameter of the light source by using a laser with a narrow spectral bandwidth (less than 30 nm at 5% of peak intensity) instead of a broadband LED. This parameter change eliminates the spectral shift problem caused by melanin absorption while maintaining sufficient light intensity for accurate photoplethysmographic measurements
Solution Approach 2:
The patent introduces an optical filter as an intermediary component between the light source and the tissue. The filter has a passband less than 30 nm and attenuates light at wavelengths outside the passband by at least 85%, thereby mediating the interaction between the broadband light source and the tissue to achieve narrow spectral bandwidth without sacrificing illumination intensity
2Measurement precision
If the spectral bandwidth of the red light source is reduced to minimize melanin absorption effects, then measurement accuracy improves, but the optical signal intensity decreases
Solution Approach 1:
The optical filter acts as an intermediary that enables the system to achieve narrow spectral bandwidth (less than 30 nm passband) while maintaining high illumination intensity. The filter is positioned to receive light from the laser and transmit only the desired narrow bandwidth to the tissue, ensuring both measurement accuracy and sufficient signal intensity
Solution Approach 2:
The patent employs a composite optical system combining a laser light source with specific optical filtering materials. The laser provides intense narrow-bandwidth light, and the optical filter (with passband less than 30 nm and at least 85% attenuation outside passband) refines the spectral characteristics, creating a composite system that achieves both high intensity and narrow bandwidth
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 sensor provides more accurate oxygen saturation readings by reducing spectral shifts induced by melanin, thereby improving diagnostic accuracy for patients with varying skin pigmentation.
Implementation Method 1
the optical filter adapted to attenuate light incident on the optical filter at wavelengths outside the passband by at least 85%
Implementation Method 2
a photodetector configured to detect light from the first and second light sources and to convert the detected light signal into an electronic signal
Implementation Method 3
a first light source adapted to emit light with a spectral bandwidth greater than 30 nm at 5% of peak intensity and a peak intensity in the wavelength range of 620 nm to 770 nm
Data Source
AI summary
A photoplethysmographic sensor has a first light source, a second light source, an optical filter positioned within the path of the light emitted by the first light source and adapted to pass light within the spectral bandwidth of the first light source, an output aperture positioned to allow light passing through the optical filter and light emitted by the second light source to pass through, and a photodetector configured to detect light from the first and second light sources and to convert the detected light signal into an electronic signal. The first light source, the optical filter, and the output aperture configured to prevent light output by the first light source from passing through the output aperture without first passing through the optical filter.