Dual-Altitude Optical Blood Pressure Sensing Without a Cuff
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Solution Overview
Problem
Conventional portable electronic devices, such as smartphones and wearable fitness trackers, are unable to accurately measure blood pressure due to limitations in existing cuff-based and photoplethysmography (PPG) methods, which rely on specialized equipment, manual operation, and are prone to noise and location-dependent signal variations.
Innovation Solution
A dual-altitude-based approach using a portable electronic device with an illumination subsystem and optical detection subsystem to measure blood pressure by projecting light through a body part and detecting changes in illumination at different altitudes relative to the heart, applying a linear fit and calibration factors to derive accurate systolic and diastolic blood pressure measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional photoplethysmography (PPG) methods are used for blood pressure measurement, then portability is improved, but measurement precision deteriorates due to noise and location-dependent signal variations
Solution Approach 1:
The patent transitions from single-altitude PPG measurements to dual-altitude measurements by adding a vertical dimension (altitude difference between measurement site and heart). This dimensional change enables the system to account for gravitational effects on blood pressure and eliminates location-dependent signal variations, thereby improving measurement precision while maintaining portability
Solution Approach 2:
The patent changes the measurement parameter from single-point PPG signal to dual-altitude PPG signals with known altitude difference. By introducing altitude as a controlled parameter and using the altitude difference (Δh) in the blood pressure calculation formula, the system achieves accurate blood pressure measurement without requiring bulky equipment
2Measurement precision
If cuff-based methods are used for blood pressure measurement, then measurement precision is improved, but device complexity and ease of operation worsen due to specialized equipment and manual operation
Solution Approach 1:
The patent replaces the mechanical cuff-based measurement system with an optical PPG-based system. Instead of using inflatable cuffs and manual auscultation, the invention uses light projection through body tissue and photodetector signal processing, eliminating bulky mechanical equipment and manual operation requirements while achieving accurate blood pressure measurement through the dual-altitude approach
3Ease of operation
If single-altitude PPG measurements are used, then ease of operation is improved, but measurement precision deteriorates due to unaccounted gravitational effects
Solution Approach 1:
The patent adds the altitude dimension to the PPG measurement system by performing measurements at two different altitudes with a known vertical separation. This dimensional enhancement allows the system to capture gravitational effects on blood pressure and eliminates location-dependent signal variations, thereby improving measurement precision while maintaining operational simplicity
Solution Approach 2:
The patent introduces altitude difference (Δh) as an intermediary parameter that mediates between the PPG signals and blood pressure calculation. By using the known altitude difference between measurement sites and the heart in the calculation formula, the system accurately compensates for gravitational effects without complicating the measurement process
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, non-invasive blood pressure measurement using consumer-grade optical detection techniques, eliminating the need for bulky equipment and manual operation, and accounting for gravitational effects on blood flow.
Implementation Method 1
Illumination is projected through a body part and received by photodetectors on the other side of the body part. The transient changes in blood volume result in corresponding transient changes in the amount of illumination that is absorbed by the body part versus the amount that passes through to the photodetectors
Implementation Method 2
Except for the effective altitude difference between the first and second positions, factors affecting blood pressure measurement are controlled so that any difference between the first and second detection output signals primarily results from different gravitational effects on the blood flow in the different relative positions
Data Source
AI summary
Techniques are described for non-invasive, dual-altitude-based measurement of blood pressure of a user using a portable electronic device having a sensor head. Illumination is projected into a body part and received by photodetectors. A changing amount of illumination received by the photodetectors changes corresponds to a changing amount of blood volume in elastic circulatory system pathways in the body part. Measurements of the received illumination are obtained at multiple altitudes relative to the user's heart. A linear fit is applied to the multiple measurements based on at least a predetermined slope-calibration factor to obtain a slope-corrected mean blood pressure measurement (BPM). Some embodiments use similar techniques to further measure pulse-to-mean (PTM) at multiple altitudes. The PTM measurements are used to simulate a systolic and/or diastolic BPM.