Pulse contour cardiac output estimation using waveform shape parameters
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Solution Overview
Problem
Current methods for estimating cardiac output (CO) are either invasive, inaccurate, or reliant on calibration, which can lead to errors in measurement due to the complexity of cardiovascular parameters and the need for precise compliance calculations.
Innovation Solution
A pulse contour method and system that uses a non-impulsive input flow waveform, with parameters determined from peripheral resistance and shape-characterizing values in the current pressure waveform, to estimate cardiovascular parameters like CO, reducing reliance on calibration and improving accuracy by incorporating more information from the pressure waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If invasive flow-measuring devices are used to determine cardiac output, then measurement accuracy is improved, but patient safety and ease of operation deteriorate due to catheterization risks
Solution Approach 1:
The patent replaces invasive mechanical flow-measuring devices with a non-invasive pulse contour analysis method that uses blood pressure waveform characteristics to estimate cardiac output, thereby eliminating catheterization risks while maintaining measurement capability
Solution Approach 2:
The patent uses blood pressure waveform analysis as an intermediary method to indirectly determine cardiac output without direct flow measurement, avoiding the need for invasive catheter-based flow sensors while still providing accurate CO estimation
2Ease of operation
If traditional pulse contour method with Windkessel model is used, then non-invasive measurement is achieved, but measurement accuracy deteriorates due to reliance on calibration and assumptions
Solution Approach 1:
The patent extracts and utilizes additional waveform characteristics (area under the curve, rising slope, dicrotic notch timing) from the blood pressure waveform to improve measurement accuracy without requiring invasive procedures or complex calibration protocols
Solution Approach 2:
The patent inverts the traditional approach by using multiple waveform characteristics to directly calculate cardiac output and stroke volume without relying on calibration against invasive measurements, thereby improving accuracy while maintaining non-invasive operation
3Measurement precision
If calibration-based methods are used to improve accuracy, then measurement precision is improved, but device complexity and sensitivity to calibration errors increase
Solution Approach 1:
The patent enables the system to self-calibrate using intrinsic waveform characteristics from the blood pressure measurement itself, eliminating the need for external calibration procedures and reducing sensitivity to calibration errors while maintaining high measurement accuracy
Data Source
AI summary
A cardiovascular parameter such as cardiac output is estimated from a current pressure waveform data set without needing to directly measure blood flow or arterial compliance. The general shape of an input flow waveform over one beat-to-beat cycle is assumed (or computed), and then the parameters of a flow-to-pressure model, if not pre-determined, are determined using system identification techniques. In one embodiment, the parameters thus determined are used to estimate a current peripheral resistance, which is used not only to compute an estimate of the cardiovascular parameter, but also to adjust the shape of the input flow waveform assumed during at least one subsequent beat-to-beat cycle. Another embodiment does not require computation of the peripheral resistance and still another embodiment computes a flow estimate from an optimized identification of the parameters defining the assumed input flow waveform.