Computation of aortic flow from pressure in humans using a nonlinear, three-element model

Area of Science:

• Biomedical Engineering
• Cardiovascular Physiology
• Medical Device Technology

Background:

• Accurate measurement of cardiac output is crucial for patient management, especially in critical care.
• Existing methods for cardiac output monitoring can be invasive or intermittent.
• Non-invasive methods are needed to continuously assess hemodynamic status.

Purpose of the Study:

• To compute aortic flow pulsations from arterial pressure using a nonlinear, time-varying three-element model.
• To evaluate the accuracy of this model-derived flow for estimating cardiac output.
• To assess the potential for continuous cardiac output monitoring.

Main Methods:

• Simulated a three-element model of aortic input impedance, incorporating aortic characteristic impedance, arterial compliance, and systemic vascular resistance.
• Derived model parameters from published age-dependent aortic pressure-area relationships.
• Compared model-derived mean flow from radial arterial pressure with thermodilution cardiac output measurements in surgical patients.

Main Results:

• Initial comparison showed a pooled mean difference of +7% and SD of 22% between model flow and thermodilution cardiac output.
• After single-patient calibration, the model accurately tracked quantitative changes in cardiac output.
• Calibrated model demonstrated a mean deviation of +2% and SD of 8% from thermodilution measurements.

Conclusions:

• The developed model can accurately compute aortic flow pulsations from arterial pressure.
• The method, after calibration, provides a reliable means for monitoring cardiac output.
• This approach offers a promising tool for continuous, non-invasive cardiac output monitoring in clinical practice.