Light-to-Frequency Conversion for Blood Pressure Measurement
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Solution Overview
Problem
Non-invasive blood pressure measurement systems using PPG signals face challenges with noise interference, affecting the accuracy of continuous blood pressure monitoring, while invasive methods are painful and disruptive.
Innovation Solution
A digital control system for a blood pressure measurement system that employs a light-to-frequency conversion (LFC) device to convert light signals into alternating frequency signals, reducing noise susceptibility and allowing for continuous, accurate measurement of blood pressure using a pressure cuff with a computing device controlling the cuff pressure based on measured light intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a PPG system with light detector is used for non-invasive blood pressure measurement, then the measurement is non-invasive and continuous, but the light signal is susceptible to noise interference reducing accuracy
Solution Approach 1:
The patent replaces the conventional light-to-voltage conversion system with a light-to-frequency conversion system. The light detector output is converted to a frequency signal through a modulator, which is then processed by a frequency-to-voltage converter. This substitution of the signal conversion mechanism reduces noise susceptibility and improves measurement accuracy while maintaining non-invasive operation.
Solution Approach 2:
The patent changes the parameter domain of the detected signal from voltage/amplitude to frequency. By converting the light intensity variations into frequency modulations and then into voltage signals through a frequency-to-voltage converter, the system achieves better noise rejection and signal fidelity, resolving the contradiction between non-invasive measurement and signal accuracy.
2Measurement precision
If invasive intra-arterial catheter is used for blood pressure measurement, then high frequency transmission and accuracy are achieved, but the device is painful and disruptive to the patient
Solution Approach 1:
The patent replaces the invasive mechanical catheter system with a non-invasive optical system that uses light-to-frequency conversion. This substitution eliminates the need for arterial puncture and catheter insertion, removing patient discomfort while maintaining high signal fidelity through frequency-based signal processing that rejects noise effectively.
Solution Approach 2:
The patent introduces a frequency signal as an intermediary between the optical detection and electrical processing stages. This frequency intermediary allows the system to achieve high-fidelity signal transmission similar to invasive methods while using non-invasive optical detection, thus eliminating patient discomfort without sacrificing measurement precision.
3Device complexity
If conventional light-to-voltage conversion is used in PPG system, then the system structure is simple, but noise interference reduces measurement accuracy
Solution Approach 1:
The patent substitutes the simple but noise-susceptible light-to-voltage conversion with a light-to-frequency-to-voltage conversion system. Although this adds a frequency modulation and frequency-to-voltage conversion stage, the overall system complexity remains manageable while achieving significant improvement in noise rejection and measurement precision.
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
The system achieves enhanced accuracy and reliability in continuous non-invasive arterial pressure measurement, reducing noise interference and eliminating the need for expensive electronic components, thus providing a more effective and cost-efficient method for calculating parameters like stroke volume and cardiac output.
Implementation Method 1
a light detector for measuring a photo-plethysmographic (PPG) signal
Implementation Method 2
employes a light-to-frequency conversion (LFC) device to convert light signals into alternating frequency signals
Implementation Method 3
The NBP applies pressure to the arteries, causing them to constrict and limit blood flow
Data Source
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AI summary
A system and method of digital control for a blood pressure measurement system is provided. According to at least one embodiment, a photo-plethysmographic (PPG) system produces a frequency signal that corresponds to the measured light in the PPG system. Such light may be indicitive of blood volume in a vein or artery. The frequency signal may be used to control one or more pressure valves of the system in order to measure blood pressure and hold the frequency signal constant.