Optical Blood Pressure Characterization via Limb Compression
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Solution Overview
Problem
Existing methods for characterizing blood pressure using pressure sensors and compression armbands rely on empirical laws, which can be disputed, and optical techniques, like Photo-Plethysmography, face challenges such as sensitivity to positioning and noise in pulsatile component measurements.
Innovation Solution
An optical method involving a light source and photodetector on a limb, with compression phases to measure low-frequency components of light intensity, filtered to extract blood pressure information, allowing for estimation of systolic, average, and diastolic blood pressures based on stabilization and slope changes during inflation and deflation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensors and compression cuffs are used to measure blood pressure, then blood pressure can be characterized by measuring pressure oscillations, but the method relies on empirical laws that can be contested and reduces measurement reliability
Solution Approach 1:
The patent replaces the mechanical pressure sensor system with an optical measurement system. Instead of using a pressure sensor coupled to a compression cuff that measures pressure oscillations based on empirical laws, the invention uses a photodetector to measure optical properties of blood vessels during limb compression. This substitution eliminates reliance on contested empirical laws and provides a more reliable physiological measurement approach.
Solution Approach 2:
The invention changes the measurement parameter from pressure oscillation amplitude to optical intensity variations detected by a photodetector. By measuring how optical properties of blood vessels change during compression phases (inflation and deflation), the system determines systolic and diastolic pressures based on physiological responses rather than empirical pressure oscillation relationships.
2Ease of manufacture
If optical techniques like Photoplethysmography are used to detect blood volume changes, then the method offers low cost and ease of integration, but the measurements are sensitive to positioning and noise
Solution Approach 1:
The patent applies periodic compression to the limb through controlled inflation and deflation phases. This periodic mechanical stimulus creates consistent, repeatable physiological responses in the blood vessels that are captured by the photodetector. The regular compression cycles help distinguish true physiological signals from random noise and positioning artifacts, improving measurement robustness while maintaining the simplicity of optical detection.
Solution Approach 2:
The system uses feedback from the photodetector measurements to determine when characteristic physiological events occur during compression (such as when arterial flow is occluded or when venous return changes). This feedback mechanism allows the system to dynamically identify measurement points based on actual physiological responses rather than fixed timing, reducing sensitivity to positioning variations and noise.
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 method provides a reliable and accurate characterization of blood pressure using simple optical components, integrated into wearable devices, reducing reliance on empirical laws and improving measurement robustness.
Implementation Method 1
a light source, arranged to emit light towards the limb; a photodetector, the photodetector being arranged to detect an intensity of light emitted by the light source and having propagated in the limb
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3A~3B
AI summary
A method for characterizing a user's blood pressure, comprising: - a) placing an optical device (1) on a limb (2), the optical device comprising: • a light source (10), arranged to emit light towards the limb; • a photodetector (20) facing the limb; - b) compression of the individual's limb, the compression time comprising an increasing phase, during which the applied pressure increases, and a decreasing phase, during which the applied pressure decreases; - c) during the compression time, illumination of the limb by the light source and measurement of an intensity detected by the photodetector to obtain a time function; - d) low-pass filtering of the time function; - e) characterization of the individual's blood pressure.