Volume catheter parallel conductance varies between end-systole and end-diastole

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Electrical Impedance Tomography

Background:

• Accurate cardiac blood volume measurement is crucial for diagnosing heart conditions.
• Existing methods often oversimplify myocardial tissue properties (resistive or capacitive).
• This simplification leads to inaccuracies in instantaneous cardiac output estimations.

Purpose of the Study:

• To propose and validate a new method for measuring cardiac electrical properties using admittance.
• To investigate the frequency-dependent and beat-cycle variations of myocardial electrical properties.
• To develop an improved technique for calculating instantaneous myocardial contribution to measured signals.

Main Methods:

• Measured left ventricular admittance (magnitude and phase angle) in murine models.
• Utilized numerical finite-element models based on MRI data.
• Performed in vivo admittance measurements in the murine left ventricle.

Main Results:

• Cardiac admittance is measurable and increases with frequency.
• Myocardial contribution to admittance varies significantly between end-systole and end-diastole.
• The proposed admittance method provides a more accurate assessment than previous conductance-based approaches.

Conclusions:

• Myocardial tissue exhibits both substantial resistive and capacitive properties, necessitating admittance measurements.
• The beat-cycle variation in myocardial contribution challenges previous assumptions.
• A novel, non-invasive method for determining instantaneous myocardial contribution is proposed.