Dual-Pressure Optical Sensing for Cuff-Less Beat-to-Beat Blood Pressure
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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, which varies with physiological conditions.
Innovation Solution
A non-occlusive method using two optical sensors under different pressures, with a compliance model updated for each 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
1Reliability
If the volume-clamp method is used for continuous blood pressure recording, then continuous blood pressure measurement is achieved, but the device becomes technically complex and requires a servo system
Solution Approach 1:
The patent divides the measurement function into two independent optical sensors operating at different fixed pressure levels, eliminating the need for a single complex servo-controlled sensor. Each sensor independently measures blood volume at its respective pressure, and the system processes both signals to derive blood pressure without requiring active servo control of a single sensor.
Solution Approach 2:
The invention changes the operating parameter from a single dynamically controlled pressure (requiring servo system) to two fixed pressure levels. By measuring blood volume at two different static pressure points simultaneously, the system determines blood pressure through signal processing rather than active servo control, thereby reducing device complexity while maintaining continuous measurement capability.
2Reliability
If the volume-clamp method is used, then continuous blood pressure recording is possible, but frequent adjustment of the operating point is required
Solution Approach 1:
The system performs preliminary measurement at two different fixed pressure levels to establish the relationship between blood volume and pressure. By pre-determining this relationship through dual-pressure measurement, the system eliminates the need for frequent operating point adjustments, as the two fixed pressure points provide sufficient information to continuously calculate blood pressure without manual intervention.
Solution Approach 2:
The patent uses feedback from two independently measured blood volume signals at different pressures to continuously calculate and update blood pressure values. This dual-signal feedback mechanism allows the system to maintain accurate continuous blood pressure recording without requiring manual adjustment of operating points, as the system automatically processes both signals to determine the current blood pressure state.
3Device complexity
If a single optical sensor is used, then the device structure is simple, but accurate continuous blood pressure measurement cannot be achieved
Solution Approach 1:
The patent applies local quality by placing two optical sensors at different fixed pressure levels (different local conditions) to measure blood volume. Each sensor operates at its specific pressure level, and the combination of these localized measurements provides the information needed to accurately determine blood pressure, achieving measurement precision that a single sensor cannot provide.
Solution Approach 2:
The invention adds another dimension to the measurement by introducing a second pressure level. Instead of using a single sensor measuring one parameter, the system uses two sensors measuring blood volume at two different pressure dimensions. This dimensional expansion provides sufficient data to calculate blood pressure accurately without requiring a single complex multi-functional sensor.
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 without the need for servo systems, reducing complexity and cost, and maintaining accuracy over time.
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. The detected pulsatile light intensity changes are related to the relative blood volume changes in the artery or microvascular bed of tissue.
Data Source
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.).