Cardiac output by impedance cardiography: two alternative methodologies compared with thermodilution

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Medical Instrumentation

Background:

• The Kubicek stroke volume equation is crucial for cardiac output measurement using impedance cardiography.
• A key parameter in this equation is dZ/dt(max), representing the maximum rate of change in impedance.
• Accurate quantification of dZ/dt(max) is essential for reliable cardiac output estimations.

Purpose of the Study:

• To compare two methods of quantifying dZ/dt(max) within the Kubicek stroke volume equation.
• To evaluate the accuracy of impedance cardiography-derived cardiac output against thermodilution.
• To determine the optimal method for dZ/dt(max) quantification for relative cardiac output changes.

Main Methods:

• The study used six anesthetized dogs.
• Cardiac output was measured simultaneously using impedance cardiography and thermodilution.
• Two methods for quantifying dZ/dt(max) were compared: relative to dZ/dt = 0 baseline (impedance-A) and relative to the dZ/dt B-point (impedance-B).
• Cardiac output was systematically altered using isoproterenol, phenylephrine, and nitroprusside.

Main Results:

• Impedance-A cardiac output changes were statistically identical to thermodilution measurements across all drug conditions.
• The impedance-B method showed similarity to thermodilution in only two of the three drug conditions.
• Correlations between impedance cardiography and thermodilution were generally higher for the impedance-A method.

Conclusions:

• Quantifying dZ/dt(max) relative to the dZ/dt = 0 baseline is supported for use in the Kubicek stroke volume equation.
• The impedance-A method offers a more reliable approach for measuring relative changes in cardiac output compared to the impedance-B method.
• These findings have implications for improving the accuracy of non-invasive cardiac output monitoring.