Blood Pressure Estimation via Ballistocardiogram and Photoplethysmogram
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Solution Overview
Problem
Current vital sign monitoring in hospitals is limited by the intermittency of conventional measurement devices, which hinders early detection of patient deterioration, especially in low-equipped settings or at night, due to the lack of continuous and accurate blood pressure measurement.
Innovation Solution
A method using load cell ballistocardiogram and photoplethysmogram signals, combined with a deep learning model that includes a contractive and expansive path, to estimate blood pressure by calculating the inverse of pulse transit time and accounting for individual calibration and posture, providing continuous and accurate BP monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional monitoring devices are used to measure vital signs, then measurement accuracy is maintained, but measurement frequency is limited to intermittent (2-3 times per day)
Solution Approach 1:
The patent replaces conventional mechanical blood pressure measurement devices (cuff-based oscillometric or auscultatory methods) with a photoplethysmogram (PPG) based optical system. The PPG sensor uses light absorption changes in blood to detect pulse waveforms continuously, eliminating the need for mechanical cuffs and enabling uninterrupted blood pressure monitoring while maintaining clinical accuracy through pulse transit time analysis.
Solution Approach 2:
The patent implements continuous blood pressure monitoring by continuously采集ing PPG signals from the patient's finger or earlobe. The system processes pulse waveforms in real-time to calculate pulse transit time and derive blood pressure values continuously, rather than intermittently. This allows constant surveillance of blood pressure trends, enabling early detection of deterioration and immediate clinical intervention.
2Reliability
If conventional blood pressure monitoring is implemented, then measurement reliability is ensured, but device complexity and cost increase
Solution Approach 1:
The patent makes the PPG sensor serve multiple functions: it simultaneously measures pulse rate, pulse transit time, and blood pressure. The same optical sensor that detects oxygen saturation can be used to extract pulse waveforms for blood pressure calculation, eliminating the need for separate dedicated blood pressure measurement devices and reducing overall system complexity.
Solution Approach 2:
The patent introduces pulse transit time as an intermediary parameter that links the easily measurable PPG signal to blood pressure. By measuring the time delay between the ECG R-wave (heart electrical activity) and the PPG pulse arrival, the system derives blood pressure information indirectly through this intermediate temporal measurement, avoiding the need for complex direct pressure sensing.
3Ease of operation
If pulse arrival time is used for blood pressure estimation, then measurement convenience is improved, but measurement precision decreases due to inclusion of pre-ejection period
Solution Approach 1:
The patent extracts and removes the pre-ejection period component from the pulse arrival time measurement. By using pulse transit time (time from aortic valve opening to pulse arrival) instead of pulse arrival time (time from ECG R-wave to pulse arrival), the system excludes the variable PEP interval that is influenced by ventricular contractility and autonomic tone, isolating only the pressure-dependent pulse wave propagation component for accurate blood pressure estimation.
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 approach enables continuous and accurate blood pressure estimation, improving patient outcomes by enhancing early warning systems and reducing the need for frequent calibration, while being robust to postural variability.
Implementation Method 1
collecting a signal of each of a plurality of load cells supporting the person to determine a ballistocardiogram
Implementation Method 2
collecting a signal from a photoplethysmogram signal from an appendage of the person
Data Source
AI summary
Algorithms for continuous BP monitoring using the load cell ballistocardiogram and the finger/toe photoplethysmogram (PPG) signals. This disclosure includes two different approaches; (1) a conventional pulse transit time-based model and (2) a U-Net-based model to predict BP from ballistocardiogram and PPG signals. In pulse transit time-based models, the pulse transit time was acquired through signal processing and linear regression was performed on its inverse to estimate BP. In the U-Net-based model, the source signals (ballistocardiogram and PPG) were translated to BP waveforms from which the BP values were estimated after calibration.