Tapped Laser Monitoring in Photoplethysmography for Mode Hopping Detection
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Solution Overview
Problem
Existing photoplethysmographic devices using LEDs face challenges with spectral alteration due to tissue pigments, leading to inaccurate measurements, while laser-based devices struggle with laser failures, mode hopping, and signal-to-noise ratio degradation, making it difficult to maintain accurate readings, especially on thicker tissues or with nail polish.
Innovation Solution
Incorporating a tapped laser system with a secondary optical path for monitoring light intensity and stability, allowing the photoplethysmographic monitor to detect laser failures, mode hopping, and adjust operating conditions to maintain stable light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser-based light sources are used in photoplethysmographic devices, then spectral resolution and measurement accuracy are improved, but device complexity and reliability concerns increase due to laser failures and mode hopping
Solution Approach 1:
The patent implements a tapped light path that continuously monitors laser output characteristics before the main light path interacts with tissue. This preliminary monitoring detects mode hopping and laser failures early, allowing the system to compensate or alert before measurements are compromised.
Solution Approach 2:
The system uses a photodetector in the tapped light path to provide real-time feedback about laser performance. This feedback loop enables the monitor to detect changes in laser characteristics and adjust or flag measurements accordingly, maintaining reliability despite using high-performance lasers.
2Device complexity
If LED light sources are used in photoplethysmographic devices, then device simplicity and cost are improved, but measurement accuracy deteriorates due to spectral alteration by tissue pigments
Solution Approach 1:
The patent transitions from broadband LED light sources to narrow-band laser light sources, fundamentally changing the spectral parameter of the illumination. This parameter change eliminates the spectral broadening issue that causes inaccuracies with LEDs, particularly in tissues with melanin or nail polish.
3Ease of manufacture
If broadband LED light is used, then ease of manufacture and cost are improved, but spectral content stability deteriorates when light passes through pigmented tissue
Solution Approach 1:
The invention changes the spectral parameter from broadband (LED) to narrowband (laser), which fundamentally alters how the light interacts with pigmented tissue. The narrow spectral width of lasers remains stable when passing through melanin or nail polish, unlike broadband LED light whose spectral content is significantly altered.
4Measurement precision
If laser light is used for photoplethysmographic measurement, then spectral resolution is improved, but signal-to-noise ratio may deteriorate due to mode hopping and laser failures
Solution Approach 1:
The tapped light path continuously monitors laser performance before the main measurement path is affected. By detecting mode hopping and instability in advance, the system can prevent noisy measurements from being taken, preserving signal-to-noise ratio.
Solution Approach 2:
The photodetector in the tapped path provides real-time feedback on laser stability. This feedback mechanism allows the system to identify and exclude measurements taken during mode hopping events, maintaining high signal-to-noise ratio despite using lasers.
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
Enables accurate photoplethysmographic measurements by detecting and correcting laser issues, ensuring consistent signal quality and reducing measurement errors, particularly on tissues with high melanin content or nail polish.
Implementation Method 1
the emitters including at least one laser and at least one of the at least one lasers is a tapped laser configured to emit light through a primary optical path from the emitter to a sensor
Implementation Method 2
a photodetector coupled to the monitor and positioned to receive light tapped from the tapped laser prior to the point where the light exits the sensor. The photodetector generates an electrical signal indicative of the intensity of the amplitude of the light tapped from the tapped laser
Implementation Method 3
In later pulse oximeters the broadband tungsten light source was replaced with two light emitting diodes (LEDs)... The spectral content of LEDs, while centered at the required wavelengths, is spectrally very broad, typically about 100 nm. This spectral content can be altered when passing through tissue including by non-arterial pigments, such as fingernail polish or melanin.
Implementation Method 4
The monitor processes the electrical signal to determine a condition of the tapped laser and determines if the tapped laser is damaged and/or if one or more operating conditions of the tapped laser needs to be altered
Data Source
AI summary
A photoplethysmographic device includes a photoplethysmographic monitor, two or more emitters coupled to and controlled by the monitor, the emitters including at least one laser and at least one of the at least one lasers is a tapped laser configured to emit light through a primary optical path from the emitter to a sensor, and a photodetector coupled to the monitor and positioned to receive light tapped from the tapped laser prior to the point where the light exits the sensor, the photodetector generating an electrical signal indicative of the intensity of the amplitude of the light tapped from the tapped laser. The monitor processing the electrical signal to determine the condition of the tapped laser, whereby the monitor determines if the tapped laser is damaged and/or if one or more operating conditions of the tapped laser need to be altered.