Wearable PTT Blood Pressure Monitoring With Image-Based Recalibration
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Solution Overview
Problem
Existing blood pressure monitoring methods, such as sphygmomanometers and PWV measurement, are bulky and interfere with daily activities, and require frequent recalibration due to drifting correlations over time.
Innovation Solution
A wearable device using photoplethysmographic sensors and near-infrared imaging to measure pulse transit time (PTT) and adjust calibration based on artery images to derive blood pressure (BP), incorporating structured light tomography and machine-learning classifiers for continuous monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If photoplethysmographic sensors and near-infrared imaging are used to measure pulse transit time and derive blood pressure, then continuous blood pressure monitoring is achieved without interference with daily activities, but the correlation between pulse wave velocity and blood pressure drifts over time requiring frequent recalibration
Solution Approach 1:
The system performs preliminary calibration to establish the initial correlation between pulse wave velocity and blood pressure, then uses periodic image-based recalibration to maintain accuracy over time. The near-infrared imaging capability is prepared in advance to capture artery images when needed for recalibration.
Solution Approach 2:
The system uses feedback from near-infrared artery images to detect mechanical changes in the artery over time. These image-based measurements provide feedback that triggers recalibration of the PTT-BP conversion, ensuring the system adapts to physiological changes while maintaining continuous monitoring capability.
2Measurement precision
If frequent recalibration is performed to maintain accurate blood pressure readings from pulse wave velocity, then measurement precision is improved, but device complexity and user burden increase
Solution Approach 1:
The system performs self-calibration using its own near-infrared imaging capability. The artery images captured by the integrated camera are processed to detect mechanical changes, and the system automatically adjusts the PTT-BP conversion parameters without requiring external calibration equipment or user intervention.
Solution Approach 2:
The near-infrared imaging system serves multiple functions: it captures artery images for recalibration, monitors artery mechanical properties over time, and provides the data needed for adaptive calibration. This multi-functionality reduces the need for separate calibration mechanisms.
3Ease of operation
If a wearable device is designed to be small and non-invasive for continuous monitoring, then ease of operation and patient compliance improve, but the ability to accurately measure pulse transit time and correlate it with blood pressure becomes more difficult
Solution Approach 1:
The system combines multiple measurement functions into a single wearable device: photoplethysmographic sensors for pulse detection, near-infrared imaging for artery visualization, and processing algorithms for PTT calculation. This integration maintains wearability while achieving accurate measurements through complementary techniques.
Solution Approach 2:
The near-infrared artery images serve as an intermediary measurement that bridges the gap between simple PTT measurement and accurate blood pressure correlation. The images provide additional information about artery mechanical properties that mediates the relationship between pulse wave velocity and blood pressure, improving accuracy without compromising wearability.
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
Provides stable, continuous blood pressure monitoring without interference, adapting to mechanical changes in arteries over time, ensuring accurate BP readings through periodic image-based recalibration.
Implementation Method 1
measuring the Pulse Wave Velocity (PWV) of blood flowing through the body's arteries... The PWV is the speed of the pressure pulse that emanates from the heart
Implementation Method 2
obtain a first and a second artery image at a first time and a second time, respectively... using a readjustment procedure to enter both first and second artery images into a trained classifier to determine adjustments
Data Source
AI summary
A device has a first and second PPD sensor configured for placement over an artery; a camera between the first and second PPD sensors; and a processor having memory with firmware for determining pulse transit time (PTT) between the PPD sensors, and determines blood pressure (BP) therefrom using a calibrated conversion from PTT to BP. The firmware also obtains initial and subsequent images of the artery, extracts features, and adjusts calibrated conversion from PTT to BP based upon features extracted from the initial and subsequent images of the artery. In embodiments the processor enhances the initial and subsequent images of the artery using a structured light tomographic enhancement process. A method uses first and second PPD sensors placed over an artery to determine pulse transit time; obtains initial and subsequent images of the artery with a camera; and uses features extracted from the initial and subsequent images of the artery to adjust a calibrated conversion from PTT to BP.