Technique & Measurements

Admittance

The pressure-volume loop technique uses inserted catheter. Cardiac volumes are derived from electrical signals measured by intracardiac electrodes located on catheter. Pressure and volume are plotted in an XY graph to study cardiac cycles and retrieve hemodynamic parameters such as ejection fraction, cardiac output, pressure and volume derivation or stroke volume for instance.

The pressure and volume signals are used to compute PV loops curves, when connected to IOX2 software through a usbACQ interface.

The Transonic Scisense “Advantage” system measures ventricular volume either using the traditional conductance method or using the admittance method. The latter discriminates blood and muscle contributions to the conductance signal.

Indeed, the capacitive properties of the cardiac muscle, in opposition to the purely resistive blood, cause a phase shift between the excitation signal and the measured signal. The admittance technique uses this phase shift to quantify and remove muscle contribution from the measured conductance signal, in real time.

This provides a great advantage over classical conductance volumetry which treats parallel conductance as a constant, rather than a dynamic variable which changes throughout the cardiac cycle.

The ADV500 system employs an equation developed by Dr. Chia-Ling Wei to convert conductance to volume instead of the traditional Baan’s equation. Wei’s equation corrects for the nonhomogeneous nature of the Catheter’s electrical field distribution, by assuming a non-linear relationship between conductance and volume, gamma (γ), thus improving accuracy over a wider volume range.

Outcomes
  • End systolic and end diastolic pressures and volumes
  • Max and min pressure derivation dp/dt
  • Cardiac output, stroke volume, ejection fraction and heart rate etc.
References

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