Blood Pressure Calibration with Fitting-Function Derivatives
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Solution Overview
Problem
Existing wearable BP measurement technologies face challenges in achieving user-friendly and accurate calibration due to the dependence of pulse transmission on factors other than blood pressure alone, such as artery elasticity and diameter, requiring a wide range of BP values for optimal calibration.
Innovation Solution
A device and method that utilizes a pressure input to obtain cuff pressure values and sensor inputs for heartbeat signals during inflation and deflation, computing pulse-related values and fitting functions to derive calibration parameters, focusing on the derivative of these values at a reference BP point to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration uses a wide range of BP values to account for varying artery elasticity and diameter, then measurement precision improves, but ease of operation deteriorates
Solution Approach 1:
The system performs preliminary calibration actions by automatically determining calibration parameters from sensor signals obtained during a single cuff inflation/deflation cycle. The processing unit extracts pulse-related values (PAT or PTT) and cuff pressure values, then computes calibration parameters before actual BP measurement begins, eliminating the need for users to perform multiple calibration maneuvers.
Solution Approach 2:
The calibration process is fully automated and self-executing. The processing unit autonomously determines calibration parameters by analyzing the relationship between pulse-related values and cuff pressure values from the sensor signals, without requiring user intervention or manual input. The system serves itself by automatically adapting to individual user characteristics.
2Measurement precision
If calibration requires multiple BP reference measurements over a wide BP range, then measurement precision improves, but loss of time increases
Solution Approach 1:
The system performs all necessary calibration computations as a preliminary action during a single cuff inflation/deflation cycle. The processing unit determines calibration parameters by analyzing pulse-related values and cuff pressure values obtained during this one-time measurement, completing calibration before actual continuous BP monitoring begins.
Solution Approach 2:
The system uses partial action by obtaining sensor signals during only one cuff inflation/deflation cycle rather than requiring multiple cycles or extended calibration periods. This partial measurement is sufficient to determine accurate calibration parameters for continuous BP monitoring.
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 reliable and user-friendly calibration of BP measurements by accounting for varying BP ranges and dynamic filling effects, enhancing the accuracy of non-invasive BP estimation.
Implementation Method 1
They bear the promise of easier and more comfortable usage and the possibility to measure continuously. Typically, these solutions use a PPG (Photoplethysmography) sensor, generally comprising a pair of (one or more) LEDs and (one or more) photodiodes, that measures the light reflection by the underlying tissue or transmission through the underlying tissue, including one or more pulsing arteries.
Implementation Method 2
Insights on physiological effects during cuff inflation and/or deflation resulted in optimized methods and procedures used for computing the one or more calibration parameters. The reliably calibrated blood pressure surrogates enable accurate non-invasive estimation tracking/monitoring of blood pressure
Implementation Method 3
Both the pulse's morphology and the time the pulse takes to transit the arteries depend on BP, and both can be used to estimate the BP. For obtaining the transit time, a second PPG sensor, most often located elsewhere, or an ECG (Electrocardiogram) sensor is used, such that a (transit) path exists between the two pulses.
Data Source
Figure 1
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Figure 3A~3B
AI summary
The present invention relates to device, system and method for calibrating a blood pressure, BP, measurement function. The device comprises a pressure input (51) configured to obtain time-dependent cuff pressure values during inflation and/or deflation of a cuff (11) of a pressure-delivery system (10) attached to a subject's body part; a sensor input (52) configured to obtain a first time-dependent sensor signal and a second time-dependent sensor signal, both related to the subject's heartbeat and measured during the inflation and/or deflation of the cuff; and a processing unit (53) configured to calibrate the blood pressure measurement function based on a reference BP value, a computed pulse-related value and a computed derivative value of the derivative of the fitting function at the reference BP value.