Conductance based Pressure Volume systems utilize Baan's equation to calculate ventricular volume from measured conductance.
- alpha = volume correction factor
- rho = resistivity of blood
- L = length of ventricle
- G = conductance
- Gp = parallel conductance
It is well understood that conductance based Ventricular Pressure-Volume systems underestimate volumes inside the ventricle. This is especially true in larger animal models. Assuming that p and Gp have been properly measured and applied during the resistivity and saline calibration process, this would cause an effect on the total volume measured, lowering measured volumes in large animals approximately 20% on average.
Alpha can be derived by any independent measure of Stroke Volume or Cardiac Output. Alpha is calculated as:
Alpha = SVmeas/SVind (or Alpha = COmeas/COind)
Where SVmeas = Stroke Volume measured from the conductance system
SVind = Independent measure of stroke volume (e.g. Echocardiograph, Aortic Flow Probe)
Note: Alpha should be less than 1 when derived from an independent measure.