PPG Signal Derivative Skew Metric for Stroke Volume
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Solution Overview
Problem
Existing methods for determining stroke volume, such as pulse contour analysis, face limitations in accuracy, especially under conditions of high or low blood pressure and heart abnormalities, making them unreliable for continuous and non-invasive monitoring.
Innovation Solution
A system and method that calculates the first derivative of photoplethysmogram (PPG) signals to determine a skew metric, which is indicative of pulse wave morphology, allowing for the estimation of stroke volume through a skew-determining module and analysis module, using coefficients and constants derived from historical data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse contour analysis is used to estimate stroke volume, then a less invasive method is provided, but the estimate becomes unreliable under certain circumstances (very high or low blood pressure, heart abnormalities)
Solution Approach 1:
The patent transforms the PPG signal from time-domain to frequency-domain by calculating the first derivative, which changes the parameter representation of the pulse wave. This transformation allows extraction of morphological features (skew metric) that remain reliable across different blood pressure conditions and heart abnormalities, resolving the contradiction between ease of operation and reliability
Solution Approach 2:
The patent replaces traditional mechanical/physical measurement methods (invasive catheters, Doppler probes) with optical-based PPG signal processing. By substituting the measurement mechanism with optical detection and mathematical transformation, the system achieves both non-invasiveness and reliability through derivative-based morphological analysis
2Ease of operation
If traditional PPG analysis methods are used, then the system is simple to operate, but the measurement precision deteriorates under varying blood pressure and heart conditions
Solution Approach 1:
The patent performs preliminary signal processing by calculating the first derivative of the PPG signal before analyzing pulse wave morphology. This preliminary action transforms the raw signal into a derivative waveform that enhances morphological features, allowing subsequent skew metric calculation to achieve high measurement precision while maintaining operational simplicity
Solution Approach 2:
The patent transitions from analyzing the PPG signal in the time-domain to analyzing its first derivative, effectively moving to another dimension of signal representation. This dimensional change reveals morphological characteristics (skewness) that are more precisely correlated with stroke volume across varying physiological conditions
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 quick, reliable, and continuous non-invasive monitoring of stroke volume, improving measurement quality by analyzing changes in the skew metric over time, and facilitating the calculation of cardiac output and other cardiac parameters.
Implementation Method 1
photoplethysmogram (PPG) signals of the individual... PPG signals may correspond to pulse waves detected from blood flow of the individual
Data Source
AI summary
A system for determining stroke volume of an individual. The system includes a skew-determining module that is configured to calculate a first derivative of photoplethysmogram (PPG) signals of the individual. The first derivative forms a derivative waveform. The skew-determining module is configured to determine a skew metric of the first derivative, wherein the skew metric is indicative of a morphology of at least one pulse wave detected from blood flow of the individual in the derivative waveform. The system also includes an analysis module that is configured to determine a stroke volume of the individual. The stroke volume is a function of the skew metric of the first derivative.