Impedance cardiography using the Sramek-Bernstein method: accuracy and variability at rest and during exercise

Area of Science:

• Cardiology
• Biomedical Engineering
• Physiology

Background:

• Impedance cardiography (ICG) is a non-invasive technique for assessing cardiac function.
• Established methods for measuring stroke volume and systolic time intervals are often invasive or complex.
• A validated, simple, and inexpensive method for cardiac output measurement is needed.

Purpose of the Study:

• To evaluate the accuracy and reliability of Sramek and Bernstein's impedance cardiography method.
• To compare ICG measurements of stroke volume and systolic time intervals with established reference techniques.
• To assess the utility of ICG in healthy volunteers, critically ill patients, and patients with coronary heart disease.

Main Methods:

• Comparison of ICG measurements with mechanophonocardiography, thermodilution, and dye dilution techniques.
• Assessment of pre-ejection period (PEP), ventricular ejection time (VET), and their ratio (PEP/VET).
• Correlation of ICG-derived parameters with angiographic left ventricular ejection fraction in coronary heart disease patients.

Main Results:

• No significant bias and narrow limits of agreement for PEP, VET, and PEP/VET ratio in healthy volunteers compared to mechanophonocardiography.
• Moderate agreement for stroke volume measurements in critically ill patients (vs. thermodilution) and healthy volunteers (vs. dye dilution).
• Accurate detection of drug-induced stroke volume changes and correlation of ICG parameters with left ventricular ejection fraction (r = -0.81 to 0.65).

Conclusions:

• Impedance cardiography provides reproducible semi-quantitative measurements of cardiac performance and blood flow.
• The method demonstrates good agreement with established techniques in various patient populations.
• ICG is a valuable tool for pharmacodynamic measurements when invasive methods are not suitable.