Adaptive Cardiac Output Calibration for Bandwidth and Accuracy
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Solution Overview
Problem
Existing cardiac output measurement techniques, such as APCO algorithms using peripheral pressure signals, lack accuracy compared to CCO or ICO algorithms that directly measure central blood flow, while APCO algorithms provide higher bandwidth and are less averaged.
Innovation Solution
A hemodynamic monitor that adaptively calibrates APCO measurements using CCO or ICO measurements to enhance accuracy, employing a time-varying linear scaling and offset calculated via least mean-square error, with weighting based on measurement precision and a forgetting factor to update calibration parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If APCO algorithms using peripheral pressure signals are used to measure cardiac output, then bandwidth is improved and measurements can follow rapid changes, but measurement accuracy deteriorates compared to central blood flow measurement
Solution Approach 1:
The patent divides the measurement system into two independent measurement paths: one using peripheral pressure signals (APCO) for high bandwidth and another using central aortic flow signals for high accuracy. Each path processes data independently before combining results, allowing optimization of each path for its specific strength without compromise
Solution Approach 2:
The patent merges the outputs of two different measurement algorithms (APCO and central aortic flow) into a single calibrated measurement. The high bandwidth APCO measurements are combined with the high accuracy central flow measurements through adaptive calibration to produce a unified cardiac output measurement that achieves both speed and precision
2Measurement precision
If CCO or ICO algorithms directly measuring central blood flow are used, then measurement accuracy is improved, but bandwidth is reduced and measurements are more averaged
Solution Approach 1:
The patent segments the measurement functions by assigning different roles to different algorithms: central aortic flow measurement handles accuracy-critical moments while APCO handles continuous high-speed monitoring. This segmentation allows each algorithm to operate in its optimal performance regime
Solution Approach 2:
The patent implements dynamic calibration where the system adaptively adjusts calibration parameters in real-time based on the correlation between APCO and central aortic flow measurements. This dynamic adjustment allows the system to maintain high accuracy while preserving the high bandwidth of APCO measurements
3Measurement precision
If adaptive calibration using time-varying linear scaling is applied to APCO measurements, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements feedback-based adaptive calibration where the system continuously monitors the correlation between APCO measurements and reference central aortic flow measurements. The calibration parameters are automatically adjusted based on this feedback loop, improving accuracy while keeping the complexity manageable through automated control
Solution Approach 2:
The patent changes the calibration parameters (scaling factor and offset) dynamically over time based on measured physiological conditions and correlation between measurement methods. This parameter adaptation allows the system to maintain high accuracy across varying physiological states without requiring complex hardware modifications
Data Source
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Figure 3A~3B
AI summary
A hemodynamic monitor implements an adaptive method that optimally estimates scaling and offset calibration parameters by using a computationally efficient, iterative online method to minimize the mean square error between a high bandwidth arterial pressure cardiac output (APCO) measurement generated by a first physiological sensor affixed to a patient and a relatively low bandwidth continuous cardiac output (CCO) measurement generated by a second physiological sensor also affixed to the patient. When calibration parameters are used to adjust an APCO measurement, the combined APCO/CCO estimate provided by the hemodynamic monitor has accuracy comparable to a CCO measurement, but also tracks cardiac output dynamical variations that are outside of the CCO algorithm bandwidth.