Cuffless Blood Pressure Estimation With Dual-Pressure Optical Sensors
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Solution Overview
Problem
Existing non-invasive blood pressure measurement devices using the 'volume-clamp' method are cumbersome, technically complex, and require frequent adjustments due to the non-linear relationship between pressure and volume curves, leading to inaccurate readings.
Innovation Solution
A non-occlusive method using two optical sensors under different pressures, with a compliance model updated per cardiac cycle, to accurately calculate systolic, diastolic, and pulse pressures by measuring relative blood volume changes and applying a calibration parameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the volume-clamp method is used for continuous blood pressure recording, then continuous monitoring capability is achieved, but the device becomes technically complex and requires frequent adjustment
Solution Approach 1:
The device is segmented into two independent optical sensing channels, each with its own photodetector and processing path. This segmentation allows the system to avoid the complex servo mechanisms of traditional volume-clamp methods while achieving continuous monitoring through differential measurement of blood volume changes at two different pressures
Solution Approach 2:
The system uses the physiological pulsations themselves to drive the measurement process. By detecting natural blood volume changes during cardiac cycles at two different pressures, the device eliminates the need for external servo control systems, achieving continuous monitoring through self-service physiological signals
2Ease of manufacture
If the relationship between pressure and volume curves is assumed to be linear or exponential, then calculation is simplified, but measurement precision deteriorates due to non-linear physiological variations
Solution Approach 1:
The system dynamically changes the operating parameters by measuring at two different fixed pressures simultaneously. This allows the device to capture the non-linear pressure-volume relationship across different operating points, improving accuracy without requiring complex real-time curve fitting or adaptive algorithms
Solution Approach 2:
Instead of attempting to model the entire non-linear pressure-volume curve, the system uses partial measurements at two specific pressure levels. This partial action approach provides sufficient information to accurately determine blood pressure while maintaining calculation simplicity
3Device complexity
If a single optical sensor is used for blood pressure measurement, then device structure is simplified, but measurement precision is insufficient due to the non-linear pressure-volume relationship
Solution Approach 1:
The system adds a pressure dimension by implementing two optical sensors operating at different pressure levels. This dimensional expansion transforms the measurement from a single-point observation to a multi-point sampling approach, enabling accurate blood pressure determination while maintaining relatively simple device structure
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 accurate, continuous, and non-invasive blood pressure monitoring with reduced complexity and cost, achieving high precision in estimating blood pressures with minimal device adjustments.
Implementation Method 1
The LED of the optical sensor emits light that is absorbed and scattered in the artery or microvascular bed of tissue and fraction of photons are detected by photodiode
Implementation Method 2
The optical sensor consists of a light emitting diode and a photodiode that are placed next to each other at determined distance
Implementation Method 3
Both optical sensors are equipped with force transducer that measures the pressure that is applied by the optical sensor to the artery or microvascular bed of tissue
Implementation Method 4
The photodiode signals from the optical sensors are connected to transimpedance amplifiers that convert the photocurrents of the photodiodes to the voltage signals
Data Source
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AI summary
The invention describes a measurement method for the continuous non-invasive determination of blood pressure using two blood volume sensors, which are under two different applied pressures. The non-linear function, which is updated for each cardiac cycle, is used to model the relationship between blood pressure and relative blood volume change. The model depends on relative blood volume changes and applied external pressures to the sensors. The derived model needs one point blood pressure calibration. The blood volume sensor can be optical sensor, such as photoplethysmographic sensor, however, any transducer, which converts blood volume or relative blood volume to electrical signal, is applicable. As one possible application, the method can be used for the blood pressure determination at one finger. However, the method is not limited with the blood volume measurement sites (e.g. radial artery etc.).