Systolic Phase Interval Determination Using QT Interval Constraints
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Solution Overview
Problem
Existing methods for determining the end of the systolic phase in arterial pressure curves are prone to errors due to difficulties in detecting the dicrotic notch, especially in over-damped signals, and struggle to adapt to changes in the blood circulation system, leading to inaccuracies in calculating stroke volume.
Innovation Solution
A method that uses the QT interval from the heart's electrical cycle, restricted to measured points where the time difference between the end and start of the systolic phase is less than the QT interval, and employs a factor between 0.25 and 0.8 to estimate the end of the systolic phase, along with fitting parabolic and exponential functions to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the dicrotic notch is used to determine the end of the systolic phase, then the measurement is based on a clear physiological marker, but the detection becomes unreliable in over-damped signals and prone to false identifications
Solution Approach 1:
The patent introduces an intermediary computational model (three-element windkessel model) that mediates between the raw pressure signal and the physiological parameters. This model translates the pressure curve into stroke volume and other parameters without requiring direct detection of the dicrotic notch, thereby eliminating the reliability issues associated with notch detection in over-damped signals
Solution Approach 2:
The patent replaces the mechanical/visual detection method of identifying the dicrotic notch with a mathematical/computational approach using pulse contour analysis. Instead of relying on the physical presence of a detectable notch in the pressure waveform, the system uses empirical relationships and mathematical models to determine systolic phase parameters, substituting a fragile mechanical detection with a robust computational system
2Device complexity
If purely empirical methods are used to calculate stroke volume without identifying the systolic phase, then the calculation is simpler, but the method cannot respond to parameter changes in the blood circulation system
Solution Approach 1:
The patent implements a dynamic system where the pulse contour analysis continuously adapts to changing blood circulation parameters. The three-element model parameters (compliance, impedance, resistance) are updated based on the evolving pressure waveform characteristics, allowing the system to respond dynamically to physiological changes while maintaining a relatively simple computational framework
Solution Approach 2:
The patent utilizes parameter changes in the pressure waveform (amplitude, shape, timing) to detect and respond to changes in blood circulation. By monitoring how the pressure curve evolves over time and comparing it against the mathematical model, the system can detect physiological changes without requiring complex additional sensors or procedures
Data Source
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AI summary
The invention relates to a method and an apparatus for determining the systolic phase interval (SP) of an arterial pressure curve with a starting point (t0) of the systolic phase interval (SP) and an end point (tN) of the systolic phase interval (SP) wherein a QT interval is defined as the start of the Q wave and the end of the T wave in the hearts electrical cycle and wherein the determination of the end point (tN) of the systolic phase interval (SP) is restricted to the measured points of arterial pressure which fulfill the condition that the difference in time between the end point (tN) to be determined of the systolic phase interval (SP) and the starting point (t0) of the systolic phase interval (SP) is smaller than the QT interval.